Photochemistry (Specialist Periodical Reports) (Vol 13)

Photochemistry Volume 13 A Specialist Periodical Report Photochemistry Volume 13 A Review of the Literature publish...

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Photochemistry Volume 13

A Specialist Periodical Report

Photochemistry Volume 13

A Review of the Literature published between July 1980 and June 1981

Senior Reporter D. Bryce-Smith, Department of Chemistry, University of Reading Reporters

N. S. Allen, Manchester Polytechnic A. Cox, University of Warwick J. D.Coyle, The Open University R. B. Cundall, University of Salford G . Hancock, The University of Oxford W. M. Horspool, University of Dundee J. M. Kelly. Trinity College, University of Dublin C. Long. Trinity College. University of Dublin L. M. Peter, University of Southampton S. T. Reid, The University of Kent A. J. Roberts, The Royal Institution, London M. Wyn-Jones, Allen Clark Research Centre, Towcester

The Royal Society of Chemistry Burlington House, London, WIV OBN

ISBN 0-85 186- 1 15-6 ISSN 0556-3860

Copyright @ 1983 The Royal Society of Chemistry All Rights Reserved N o part of this book may be reproduced or transmitted in any form or by any means-graphic, electronic, including photocopying, recording, taping, or information storage and retrieval systems-without written permission from The Royal Society of Chemistry

Organic formulae composed by Wright’s Symbolset method

Typeset and printed by John Wright & Sons (Printing) Ltd. at The Stonebridge Press, Bristol.

Contents Introduction and Review of the Year By D. Bryce Smith

Part I

xv

Physical Aspects of Photochemistry

Chapter 1 Developments in Instrumentation and Techniques By A. J. Roberts 1 Introduction 2 Plasma Sources

3

3 3

3 Laser Sources Molecular Gas Infrared Lasers Solid-state Lasers Dye Lasers Picosecond Pulsed Dye Lasers Laser Dyes Visible and U.V.Gas Lasers Frequency Conversion Techniques

4 4 5 7 8 9 10 11

4 Detection and Monitoring of Laser Radiation Monochromators and Detectors

12

5 Spectroscopic Techniques U.v.-Visible Absorption Spectroscopy Intracavity Laser Absorption Spectroscopy Infrared Spectroscopy Tunable Diode Laser Spectroscopy Fourier Transform Infrared Spectroscopy Remote Atmosphere Monitoring Optical and Infrared Double-resonance Spectroscopy Photoacoustic Spectroscopy Multiphoton Excitation Raman Spectroscopy Emission Spectroscopy Chemiluminescence

16 16 17 18 18 19

20

6 Transient Absorption Spectroscopy Nanosecond Flash Photolysis Measurements Picosecond Transient Absorption Measurements

29 30 31

13

21 21

23 24

25 29

vi

Contents

7 Transient Emission Spectroscopy

32

8 Chemical Techniques

36

Chapter 2 Photophysical Processes in Condensed Phases By R. B. Cundall and M. Wyn-Jones

39

1 Introduction

39

2 Singlet-state Processes Quenching Processes Energy Transfer Micellar Systems Macromolecule Systems Biologically Related Systems

39 75 80 82 85 87

3 Triplet-state Processes Biological Aspects Esr., Microwave, and Related Studies

92 102 103

4 Physical Aspects of some Photochemical Studies Photolysis and Related Reactions Photo-oxidation Photoisomerization Photochromism Chemiluminescence and Bioluminescence

105 105 111 113 114 115

Chapter 3 Gas-phase Photoprocesses By G. Hancock

117

1 Aliphatic Hydrocarbon Molecules, Ions, and Radicals

117

2 Aromatic Hydrocarbons

119

3 Organic Compounds Containing Oxygen

120

4 Sulphur-containing Compounds

125

5 Nitrogen-containing Compounds

127

6 Halogen-containing Compounds

131

7 Atom Reactions

136

8 Infrared Photochemistry

139

vii

Contents 9 Photochemistry of Atmospherically Important Species H Atoms, H,, and H, 0 Atoms, 02,0,, and HO, N Atoms, N,,land NO,

10 Miscellaneous

149 153 155 158 162

Part I/ Photochemistry of fnorganic and Organometallic Chemistry Chapter 1 The Photochemistry of Transition-metal Complexes By A. Cox

171

1 Introduction

171

2 Titanium

171

3 Vanadium

171

4 Chromium

172

5 Molydenum and Tungsten

176

6 Manganese

177

1 Iron

177

8 Ruthenium

178

9 Osmium

184

10 Cobalt

184

11 Rhodium

186

12 Iridium

188

13 Nickel

188

14 Palladium and Platinum

189

15 Copper

190

...

Contents

Vlll

16 Lanthanides

191

17 Uranium

193

18 Actinides

195

Chapter 2 The Photochemistry of Transition-metal Organometallic Compounds, Carbonyls, and Lowoxidation-state Compounds By J. M. Kelly and C. Long

196

1 General

196

2 Titanium and Zirconium

196

3 Vanadium and Niobium

197

4 Chromium, Molybdenum, and Tungsten

198

5 Manganese and Rhenium

20 1

6 Iron, Ruthenium, and Osmium

203

7 Cobalt and Rhodium

207

8 Nickel, Palladium, and Platinum

209

9 Copper and Silver

210

10 Mercury

210

11 Lanthanides and Actinides

210

Chapter 3 Photochemistry of Compounds of the Main Group Elements By J. M. Kelly and C. l o n g

21 1

1 Group 3 Elements

21 1

2 Silicon and Germanium

212

3 Tin and Lead

216

ix

Contents 4 Nitrogen and Phosphorus

217

5 Oxygen, Sulphur, and Selenium

218

6 Other Elements

219

Part Ill Organic Aspects of Photochemistry Chapter 1 Photolysis of Carbonyl Compounds By W. M. Horspool

223

1 Introduction

223

2 Norrish Type I Reactions

224

3 Norrish Type I1 Reactions

230

4 Oxetan Formation

234

5 Fragmentations and Miscellaneous Reactions

236

Chapter 2 Enone Cycloadditions and Rearrangements: Photoreactions of Cyclohexadienones an'd Quinones By W. M. Horspool

24 1

1 Cycloaddition Reactions Intramolecular Intermolecular

24 1 24 1 245

2 Enone Rearrangements

255

3 Photoreactions of Thymines etc.

268

4 Photochemistry of Dienones Cross-conjugated Dieones

274 275

5 1,2-, 1,3-, and 1,rl-Diketones

278

6 Quinones

290

Contents

X

Chapter 3 Photochemistry of Olefins, Acetylenes, and Related Compounds By W. M. Horspool

297

1 Reactions of Alkenes Addition Reactions Hydrogen Migrations and Abstractions Fission Processes cis-trans Isomerization

297 297 299 300 300

2 Reactions involving Cyclopropane Rings

302

3 Diene Isomerization

314

4 Reactions of Trienes and Higher Polyenes

319

5 [2 + 2]Intramolecular Additions

322

6 Dimerization, Intermolecular Cycloaddition, and Reactions of Acetylenes

325

7 Miscellaneous Reactions

328

Chapter 4 Photochemistry of Aromatic Compounds By J. 0.Coyle

333

1 Introduction

333

2 Isomerization Reactions

333

3 Addition Reactions

339

4 Substitution Reactions

353

5 Intramolecular Cyclization Reactions

369

6 Dimerization Reactions

386

7 Lateral-Nuclear Rearrangements

389

Chapter 5 Photo-reduction and -oxidation By A. Cox 1 Reduction of Carbonyl Group

394

394

xi

Contents

2 Reduction of Nitrogen-containing Compounds

396

3 Miscellaneous Reductions

398

4 Singlet Oxygen

400

5 Oxidation of Aliphatic Compounds

402

6 Oxidation of Aromatics

41 1

7 Oxidation of Nitrogen-containing Compounds

416

8 Miscellaneous Oxidations

419

Chapter 6 Photoreactions of Compounds Heteroatoms other than Oxygen By S. T. Reid

containing 422

1 Nitrogen-containing Compounds Rearrangements Addition Miscellaneous Reactions

422 422

2 Sulphur-containing Compounds

457

3 Compounds Containing Other Heteroatoms

463

Chapter 7 Photoelimination By S. T. Reid

444 454

469

1 Introduction

469

2 Elimination of Nitrogen from Azo-compounds

469

3 Elimination of Nitrogen from Diazo-compounds

477

4 Elimination of Nitrogen from Azides

484

5 Photodecomposition of Other Compounds having N-N Bonds

489

6 Photoelimination of Carbon Dioxide

49 1

xii

Contents

7 Fragmentation in Organosulphur Compounds

492

8 Miscellaneous Decomposition and Elimination Reactions

495

Part lV Polymer Photochemistry

50 1

By N. S. Allen 1 Introduction

50 1

2 Photopolymerization Photoinitiated Addition Polymerization Photografting Photocrosslinking

50 1 502 513 514

3 Optical and Luminescence Properties

519

4 Photodegredation and Photo-oxidation Processes Poly olefins Poly(viny1 halides) Polystyrenes Poly acrylics Polyamides Poly(2,6-dimethyl- 1,4-phenylene oxide) (PPO) Polyurethanes Rubbers Natural Polymers Miscellaneous Polymers

529 529 53 1 534 536 537 538 538 539 54 1 54 1

5 Photosensitized Degredation Photosensitive Polymers Photoactive Additives

544 544 546

6 Photostabilization

546

7 Photochemistry of Dyed and Pigmented Polymers

55 1

8 Appendix: Review of Patent Literature Photopolymerizable Systems Review Tables

554 554 555

...

Contents

Xlll

Part V Photochemical Aspects of Solar Energy Conversion

569

By L. M. Peter 1 Introduction

569

2 Biological Systems

57 1

3 Homogeneous and Microheterogeneous Photochemical Systems

573

4 Photogalvanic Cells

579

5 Photoelectrolysis with Semiconductor Electrodes

582

6 Liquid-junction Solar Cells Cadmium Chalcogenides Gallium Arsenide Gallium Phosphide Indium Phosphide Layer-type Dichalcogenides Silicon Other Semiconductors Photosensitization

586 586 587 587 588 589 594 595 595

7 Advances in Theory and Techniques of Semiconductor Electrochemistry

595

8 Organic Solid-state Systems

598

Author Index

600

Introduction and Review of the Year For this, and probably also for subsequent Volumes, the separate treatment of purely theoretical and spectroscopic aspects is being discontinued. This step has been taken partly to keep the length, and thence the price, to a reasonable level and partly because of organizational difficulties. Readers will however find many of these aspects incorporated within the more ‘physical’ sections of this Report. We are pleased to welcome Dr. A. J. Roberts who has contributed a section on Instrumentation and Techniques covering the period July 1980-July 1981, inclusive. Many references to spectroscopic techniques are included. Despite the development of lasers, synchrotron sources, etc., most photochemists still employ conventional mercury or xenon discharge lamps for photochemical (as distinct from photophysical) studies: nevertheless the use of lasers often leads to different chemistry (see Letokhov, Turro, inter afia).Gough and Sullivan have developed a controlled temperature-gradient U.V. lamp. The high intensity and sharp emission lines pro.vide the possibility of particularly valuable applications in atomic absorption spectroscopy. Laser sources continue to be actively developed, often with great ingenuity, and now dominate spectral calibration applications in the physical and infrared regions; but plasma sources still prove attractive for the vacuum ultraviolet. Synchrotron radiation, being completely tunable, is finding increasing applications, notably in biochemical and biophysical research (see e.g. Castellani and Quercia). Fork, Green, and Shank have obtained dye laser pulses of 90 fs, the shortest yet reported, by the interaction of two oppositely directed pulses in a saturable absorber within a ring system. In laser absorption spectroscopy, major increases in sensitivity have been obtained by use of the intracavity absorption techniques now under active development by several groups. Nordal and Kanstad have derived absorption spectra by photothermal radiometry (PTR), a technique whereby the absorption of amplitude-modulated light causes pulsating surface temperatures and hence a pulsed thermal reradiation. Applications of this technique to biological materials such as blood and leaves have been demonstrated. The use of microprocessors in absorption and emission spectroscopy can provide major improvements in the signal-to-noise ratio (Hannah and Coates; Edgell, Schmidlin, and Balk; Saito et af.,Christmann et al., inter afia). Wren’s observation that many commonly used materials for optical components in vacuum U.V. spectrometers exhibit strong luminescencewhen irradiated at short wavelengths should be noted by workers in the field of V.U.V. fluorescence. Arbeloa has developed an improved and simplified method for quantum yield measurements. The use of 9,lO-diphenylanthracene as a singlet counter has been questioned: 9,lO-dibromoanthracene seems to be preferable (Adam et al.). xv

xvi

Introduction and Review of the Year

Room-temperature phosphorescence (RTP) techniques in which the sample is adsorbed onto an inert solid support are proving valuable in the analysis of traces of polynuclear aromatic compounds (Parker et al.; Vo-dinh et al.). Useful techniques are being developed for the hitherto troublesome resolution of ncomponent fluorescence decays (Weber and Jameson; Slifkin and Darby). The successful use of a pulsed laser in conjuction with conductivity measurements to study the photochemistry of [Cr(en),13 + represents an interesting new approach which probably has wider potential applications (Waltz et al.). Boule et al. report that the practical yields in some photoreactions can be usefully increased by employing a poor solvent for the reactants: this gives the advantages of high dilution without the normal associated disadvantages. In the field of techniques, one of the more unusual reports during the year is a new photochemical method for the analytical determination of carbon in organic compounds involving the formation of carbon dioxide by Ce(SO&sensitized photo-oxidation (Ivanov and Atanov). Brauchle et al. have described a new technique termed ‘holographic photochemistry’, and have used it to study Habstraction by benzophenone in a polymer host. The theoretical understanding of radiationless transitions has been extended in an important paper by Sarai and Kakitani. Among numerous studies on intermolecular energy-transfer mechanism in fluid media, attention is particularly drawn to the very detailed classical treatment by Balzani et al., and Dewey and Hammes’ study of systems having donors and acceptors on surfaces. This latter is relevant to membrane biochemistry. Zemel and Hoffman have used zinc- and magnesium-substituted haemoglobins to make the first detailed study of longrange Forster-type energy transfer in which both the separation and orientation of the donor and acceptor are accurately known. Zimmerman et al. have described energy transfer between chromophores at the termini of rod-like linked bicyclo[2,2,2]octane units. There is considerable continuing interest in the possible role of charge transfer in fluorescence quenching phenomena. Watkins has concluded that oxygen-quenching of fluorescence of aromatic hydrocarbons in methyl cyanide does not involve charge transfer to give radical ions even though such a process is energetically favourable in principle. The process appears to be that conventionally assumed, namely

+ 02(?Zg-) T , + 02(?Eg-) T , + 02(3Zg-) So + 0 2 ( l A g ) .

S,

-+

-+

It does however appear that oxygen-quenching of porphyrins and metalloporphyrins does at least partly proceed via charge transfer (Cox, Whitten, and Gianotti). Prutz and Maier have reported the following energy-pooling reaction of singlet oxygen. ‘Ag + ‘Ag-+ ‘Zg+ + 3CgTheir emission lifetime of ca. 35ps for the ‘C,+ state does however seem surprisingly long. In this connection it is interesting to note that singlet oxygen generated by photochemical dye-sensitization does not react with simple acetylenes, but does react with these in the presence of dicyanoanthracene: thus diphenylacetylene gives benzil (Berenjian et al.; Mattes and Farid). The reaction is

Introduction and Review of the Year xvii thought to involve O2 ; but an alternative possibility would involve addition of singlet oxygen to a charge-transfer complex of dicyanoanthracene with the acetylene. Myers and Birge have derived a simple expression for the effect of solvent polarizability on the oscillator strength of a solute. Various improved procedures (including the use of microcomputer-aided systems) for determining luminescence quantum yields have been described in addition to the development by Arbeloa already mentioned (see Kirkbright; Cahen; Ritter; Christman; Knorr; and Weber, inter alia.). There is increased interest in the effects of pressure on luminescence phenomena (Drickamer; Paladini and Weber; Sonnenschein; inter a h ) . In some systems the effects are similar to those of increasing solvent polarity. Pressure can certainly shift the relative positions of energy levels relative to each other. Fischer continues his deeply probing studies on the photophysics and photochemistry of 1,2-diarylethyIenes,and has reported interesting effects of excitation wavelength on the flourescence quantum yield. Becker et al. have reported some strong effects of solvent viscosity in these systems. Lewis and Holman report what appears to be the first example of divergent reactions from two almost isoenergetic excited singlet states ('La and 'Lb)in the photoaddition of 1-cyanonaphthalene to 1,2-dimethylcyclopentene.This is of course the photochemical equivalent of dual fluorescence. Murai et al. have made the first observation of a quintet-state triplet-triplet radical pair (cf: Huber and Schwoerer). van der Waals complexes of rare gases continue to attract considerable interest. For example, the complexes of argon and krypton with pentacene (P) have been studied by a supersonic expansion technique (Amirav, Even, and Jortner). It appears that two isomers of each complex may exist. The shorter life-times of PKr, than PAr, species are attributed to the promotion of S, + T, crossing by the 'external heavy-atom effect'. Coherent anti-Stokes Raman scattering (CARS) provides a promising method for examining vibrationally excited intermediates formed in isomerization reactions of polyatomic molecules. The technique may permit kinetic spectroscopy of single vibrational levels during fast reactions (Luther and Wieters). Much remains to be understood about the photochemical behaviour of formaldehyde and related species despite further work published this year. For example, the question of the possible formation of the isomeric hydroxycarbene (CHOH) remains unresolved. The following tautomeric equilibrium between singlet a-oxocarbenes (1) formed by photolysis of the corresponding adiazoketones (2, R = Me, Et, Pr') has been reported by Tomioka et al. Ph I pm has been fabricated from a commercially available Si avalanche photodiode.' 5 2 A risetime of 200 ps was reported. An edge-incident Si photodiode was shown to have a similar temporal response, 53 and in addition, as a phototransistor it responded to CW radiation with current gain. An n+-InP/n-GaInAsP/n-InP/p+-InPstructure was found to operate out to 1.25 pm with a risetime -c1 6 0 ~ s .A' ~p-type ~ In,~,,Ga,~,,As was shown to be suitable for the region 1.0-1.7 pm.'" The response was 70ps (FWHM) with a 45 ps rise and decay time. A strontium barium niobate pyroelectric detector for ps laser pulses in the wavelength regions ~ 4 0 nm 0 and 7 pm-I mm was investigated using an 'upconversion' technique in which birefringence in a CS, Kerr cell, induced by a pulse from a CO, laser, allowed light from an argon ion laser to be detected using a ps streak camera.' 5 6 The time response, linearity, and other properties of germanium, silicon, and vacuum photodiodes were investigated using ps pulses from a Ramantuned mode-locked Nd-YAG laser. 5 7 Single-photon avalanche diodes (SPADS) have been utilized to monitor 15Ops (FWHM) laser pulses, although it would seem that the response of the SPAD should be significantly faster than this. Several mounting schemes have been investigated for thin-film photoconductors. 5 9 Risetimes approaching 25 ps (detector limited) were obtained. Non-linear autocorrelation techniques still remain the only viable method for monitoring laser pulses with true picosecond resolution. Several rapid scanning schemes for a Michelson interferometer have been proposed, allowing autocorrelation measurements in real time, thus greatly assisting the alignment of synchronously pumped dye laser systems. Length variation was achieved using (a) a rotating slab of quartz,16* (6) a rotating two mirror system,16' or (c) a mirror fixed to a loudspeaker cone. 162 The interpretation of autocorrelation measurements has been discussed by McDonald et aLg2with the conclusion that the true pulse width may be up to 2 x longer than previously assumed. The profile of ps ruby laser pulses has been detected using two-photon absorption. 163

'

Monochromators and Detectors.-A basic review of spectrometer types and design, suitable perhaps as undergraduate tutorial material, has been pubIs'

"*

H. Gruter, ./. Appl. Phys., 1980, 51, 5204. J . M . Harris. W. T. Barnes, T. L. Gustafson. T. H . Burshaw, and F. E. Lytle, Rev. Sci. Instrum.. 1980, 51, 988.

15' Isti

Is'

161

Iti3

C. W. Chen and T. K. Gustafson, Appl. Phys. Lett., 1980, 37, 1014. V. Diadiuk, S. H. Groves, and C. E. Hurwitz, Appl. Phys. h i t . , 1980, 37, 807. J . Degani. R. F. Leheny, R. E. Nahomy, M. A. Pollack, J. P. Heritage, and J. C. Dewinter, Appl. Phys. Lett., 1981, 38,27. E. J. McLekan and S. C. Stotlar, Opt. Spectrosc., 1981, 15, 55. P. Valat, G . Ripoche, M. Nail, and J. P. Gex, Opt. Commun., 1981, 36, 378. S. Cova, A. Longoni, and A. Andreoni, Rev. Sci. Instrum., 1981, 52, 408. P. R. Smith, D. H. Austin, and A. M. Johsnon, Rev. Sci. Instrum., 1981.52, 138. S. N. Ketkar, J. W. Keto. and C. H. Holder, Rev. Sci. Instrum., 1981, 52, 405. Z. A. Yasa and N. A. Amer, Opt. Commim., 1981, 36, 406. K. L. Sala, G . A. Kenney-Wallace, and G . E. Hall, I E E E J . Quantum. Electron., 1980, 16, 990. W. Blau and A. Penzkofer, Opt. Commun., 1981, 36, 419.

14

Photochemistry

lished.164A spectrometer designed to monitor the spectral output from CO, lasers has been described. 165a Fifty pyroelectric detectors were positioned for the various P and R lines and a substantial increase in sensitivity over conventional methods was reported. Unwanted reflections and coma were eliminated in a mid-resolution infrared spectrometer by placing the entrance and exit slits above and below the grating. 1 6 5 b Several systems for automation of spectrometers have been discussed. A computer-controlled Echelle monochromator allowed wavelength increments of 0.01 nm. A wavelength-scan and lamp-intensity control scheme for the popular Bausch and Lomb high-intensity monochromator has been described.' 67 The accurate synchronization of monochromator wavelength-scan and chart-recorder speed,168and the possibility of rapid scanning allowing spectra to be displayed in real time on an oscilloscope,169 has also been discussed. Details have been provided for the modification of a commercially available mirror mount (Oriel model 1450) for use as a stepper-motor controlled grating mount.170 A method for the alignment of Ebert-Fastie monochromators, by observing the Fresnel diffraction pattern from a He-Ne laser has been described.17' A deuterium lamp with MgF windows has been employed for the calibration of a vacuum-u.v. monochromator over the region 115-340 nm.' 7 2 A 5 m Echelle vacuum-u.v. monochromator was found to display diffraction-limited resolution in the U.V. and visible spectral regions, falling to 54% of the diffraction limit at 120nm. The temporal broadening of a 10ps laser pulse on passing through a monochromator system has been investigated using a streak-camera-video readout device.174Periodic errors in the dispersion of a scanning U.V. monochromator (McPherson model 225-1 m vacuum-u.v.), amounting to kO.01 nm with a period of 2.5 nm, have been reported. 175 A mechanically (rather than holographically) prepared concave grating was utilized in a high-efficiency aberation-corrected monochromator. 76 Highfrequency plane holographic gratings, however, were found to be preferable for vacuum-u.v. applications in the wavelength range 120-450 nm. 177 The efficiency of gratings for wavelength selection in dye lasers has been found to be improved by dielectric coating. 78 The generation of surface gratings with periods less than 100nm, by doubling the spatial frequency, has been demonstrated.17' Some other recent optical developments of possible interest include MgF, multiplate resonant 16*' 165 166

167 168

169

170 171 172

173 175

176 177

E. F. Young, O p t . Spectra, 1980, 14, 44. ( a ) J. G . Edwards, R. Jefferies, and J. D. Ridgen, J . Phys. E., 1981, 14, 731; ( b ) R. LeDoucen, V. Menoux, M. Larvor, and C. Haeuster, Appl. Opt., 1980, 19, 31 10. D. L. Anderson, A . R. Forster, and M. L. Parsons, Anal. Chem., 1981, 53, 771. D. C. Look and J. W. Farmer, Rev. Sci. Instrunt., 1980, 51, 968. S.Mil'shtein and D. Mordowicz, J . Phys. E., 1981, 14, 682. R. Angus, O p t . Spectra, 1980, 14, 49. T. W. Carman, P. E. Dyer, and P. Monk, J . Phys. E.. 1980. 13, 718. C. Julien and C. Hirlmann, J . Phys. E., 1980, 13, 923. D. H. Nettleton and R. C. Preston, Appl. Opt., 1981, 20, 1274. H. Nubbermeyer and B. Wende, Appl. Phys., 1980,23, 259. N . H. Schiller and R. R. Alfano, O p t . Commun., 1981, 35, 451. R. DeSerio, Appl. Opt., 1981, 20, 1781. T. Harada and T. Kita, Appl. Opt., 1980, 19, 3987. A . J. Caruso, G . H. Mount, and B. E. Woodgate, Appl. Opt., 1981, 20, 1764. D. Mayster, J. P. Laude, P. Gascoin, D. Lepere. and J. P. Priou, Appl. Opr., 1981, 19, 3099. L. F. Johnson and K. A. Ingersol, Appl. Phys. Lett., 1981. 38, 532.

Developments in Instrumentation and Techniques

15

reflectors for the vacuum-u.v.,180a high-performance thin liquid film MacNeille prism polarizer for the u.v.4.r. regions,'81 and a 6-sided prism designed to transmit a particular wavelength without spatial deviation. Several precautions for safe operation of photomultiplier tubes have been discussed. 183 After-pulsing in photomultipliers due to helium poisoning was examined for the RCA 4522 tube. 84 In applications in which exposure to helium cannot be avoided, purging with nitrogen may be desirable. The effect of after-pulsing on photon-correlation experiments has been discussed. 8 5 With careful calibration procedures the problems may be largely overcome. A wider dynamic range for light intensity measurements using photomultiplier tubes has been obtained by simultaneously monitoring and controlling the anode current and dynode voltages. 86 An application involving the simultaneous measurement of absorption and circular dichroism spectra was proposed. An inexpensive pulse amplifier4iscriminator suitable for photon counting detection systems operating at high repetition rates and avoiding pulse pile-up effects has been reported. 18' Pulse repetition rates up to 250 MHz were possible with 10 ns pulse pair resolution. The various methods for the detection of infrared radiation have been reviewed. For broad-band detection with moderate sensitivity, thermal devices were recommended. However, for increased sensitivity photon detectors should be employed. PbS,Se, -, and Pb,Sn, -,Se photodiodes have been shown to have high quantum efficiencies over the range 1-10 pm.18gA p+-nGe avalanche photodiode has been found to provide a low noise, low dark current detector for the region 1.3-1.55 pm.19' The performance of a Gao~4,1n,~,3Asphotodiode has been evaluated and shown to be a most sensitive detector in the 1-1.7pm range."' The response of metal-oxide-metal diodes for the detection of i.r. and visible radiation was found to be temperature dependent. l g 2 Suggestions for improving the response of such systems are given. The noise from a Ge: Cu photoconductive detector in an i.r. absorption spectrometer was found to be reduced with the use of a grating cooled to 90 K. 1 9 3 The construction of a Ge detector for low light intensities in the wavelength range 1-1.6pm has been reported by McLaren and Wayne.lg4 Fast amplifiers for low background Ge :Hg detector^"^ and a photovoltaic indium antimonide detector in the 3.5-4.2 pm range' 9 6 have been described. The acousto-optic interaction with a thermally

'

'

"' Is'

lS7 lS8

I9O

W. R. Hunter, M. H. R. Hutchinson. and M. R. 0. Jones, Appl. Opt., 1981, 20, 770. J. A. Dobrowolski and A. Waldorf, Appl. Opr., 1981. 20. I 1 1. M. V. R. K. Murtly and R. P. Shukla, Opt. Eng., 1980, 19. 621. C. Tassell, Opt. Laser Terhnol., 1980, 12. 271. D. F. Bartlett. A. L. Duncan, and J. R. Elliot, Rev. Sci. Instrum., 1981, 52, 265. H . C. Burstyn, Rev. Sci. hutrum.. 1980. 51, 1431. H. Hayashi, H. Tdchibana, and A. Walda, Rev. Sri. Instrum., 1980, 51. 1501. R. A. Borders, J. W. Birks, and J. A. Borders, Anal. Chem., 1980. 52. 1273. P. N. J. Dennis, SOC.Photo-opt. Instrum. Eng.. 1980. 234, 27. R. B, Schoolar, J. D. Jensen, G. M. Black. S. Foti, and A. C. Bouley, Infrared Pliys.. 1980, 20, 271. S . Kagawa, T. Kdneda. T. Mikawa. Y. Banaba, Y. Toydma, and 0.Mikami. Appl. Phys. Lett.. 1981. 38.429.

19'

T. P. Pearsill. IEEE J . Quantum. Electron.. 1980, 16. 709.

"' M. I, Kostenko, V. I. Stroganov, and A. I. Kondratyev, Opt. Commun.. 1981, 36. 140. 193 194 19' 196

0. Bernard, C. Deloupy. and M. Palpacuer, J . Phys. E . . 1981, 14, 299. I. A. McLdren and R. P. Wayne, J . Phoiochem., 1981, 16, 9. J. D. McDonald. Rev. Sci. Instrum.. 1980. 51, 1270. J. Altmann, S. Kohler. and W. Lahmann. J . Phys. E., 1980, 13. 1275.

16

Photochemistry

induced grating in an optical waveguide has been employed to measure the 1 ms pulse from a CO, Iaser.19' CsTe solar blind tubes, semi-transparent bi-alkali diodes, and bi-alkali image intensifiers have been compared as detectors for the vacuum-u.v. region.I9* The optogalvanic effect has been utilized to enable the detection of relatively low intensities of resonance light by the measurement of ionization currents in high concentrations of atomic vapours. 199The system has been specifically designed for the 253.7nm Hg line, and the high resolution and good tolerance to stray light characteristics suggest it may offer a useful detector for atomic absorption spectroscopy. 5 Spectroscopic Techniques

review of currently available U.v.-Visible Absorption Spectroscopy.-A u.v.-visible spectrophotometers and accessories has been compiled by Tayler,'" Several sample cells have been reported allowing absorption spectra to be recorded under non-ambient sample conditions. A high-temperature cell, designed for a Cary model 15 spectrophotometer, has been employed in an investigation of the octahedral-tetrahedral equilibrium in aqueous solutions of cobalt(I1) compounds. 201 A cell for a double-beam instrument (Beckman Acta M-VII) enabled studies of aqueous systems with temperatures up to 325 "C at maximum pressures of 12 MPa.202Sample pressure and temperature variation was also possible in a study of volatile uranyl complexes in the gas phase using a home-built spectroph~tometer.~~~ Synchroton radiation has been employed as a spectral source for a study of the absorption of HCN and DCN in the wavelength range 80-120nm.204 A vacuum-u.v. spectrophotometer for absorptions in the region 105-200 nm has been described.20s Solid-, liquid-, and gas-phase samples could be analysed at temperatures from -200 to 100°C and at pressures between 0 and 150 atmospheres. The absorption spectrum of trans-di-imide in the vacuum-u.v. has been measured.206First-derivative U.V.spectroscopy has been employed in the analysis of Watts nickel plating solutions for trace amounts of ~accharin.~" Impurity levels of 0.1 p.p.m. have been recorded. A wavelength modulated derivative spectrophotometer with a multi-pass absorption cell has been developed for the automatic analysis of atmospheric Traces of SO2, NO, and NOz were detected with limits of 15, 13, and 8 p.p.b., respectively. A double-beam single-detector absorption spectrometer has been Independence I"

"* 20'' '('I '()'

'('.' '(" '()'

I"-

'('' I"

T. D. Black a n d V. A. Komotskii. Appl. P/i,r.s.Left.. 1981. 38, 113. G. H. C. Freeman, Soc. Photo-opt. Itistrutii. Dig.. 1980, 234, 84. R. Stephens. Cm. J. Client.. 1980, 58, 1621. C. Tayler. L f h . E4irip. Dig., 1981. 19, Feb.. 65. T. W . Swaddle a n d L. Fabes, Cuti. J . Clienr., 1980. 58, 1418. N. J. Susak. D. A. Crerar, T. C. Forseman, and J. L. Haas. Rev. Sci. Itisrrutii., 1981. 52. 429. A. Ekstroin. H. J . Hurst. C . H. Randall, and H . Loch, J . Ph!,s. C l m i . , 2980, 84, 2626. T. Nalapa. T. Kondow. Y. Ozaki. and K. Kuchitsu. Cl~cvii.P/~I..F.. 1981. 57. 45. P. Laporte. J. L. Subtil. M. Bon, and H. Damany, A p p l . Opr.. 1981. 20. 2133. P. S. Neudorful. R. A. Black, a n d A . E. Douglas, Can. J . Clrmi., 1981. 59. 506. G . L. Fin and J . D. Pollack. Atid. Chetii., 1980, 52. 1589. T. I m n i and K . Nahaniur;i. J. P/ij.s. E.. 1981. 14. 105. S.-Y.Shaw and J . T. Lue, ./. P/i,rs. E.. 1980. 13, 845.


17 from spectral distributions of the source was achieved using an electronic automatic gain control. The system performed well when used for derivative spectroscopy. For the comparison of two absorption spectra, the method of weighted least-squares fitting, with a two-parameter model, has been utilized and improved Using the procedures described, effects due to stray light and flicker may be eliminated. Problems, owing to deviations from Beer's law, encountered when the excitation-source bandwidth is greater than that of the absorber may be overcome with the use of a fluorescence cell placed after the sample permitting selective monitoring of the absorption at the centre of the source line.211Using a flashlamppumped dye laser for the source, rovibronic transitions in H 2 C 0were observed by this method. The absorption spectrum of Cs vapour at 0.1 Torr has been measured by observing the perturbations of the electromagnetic impedence owing to absorption of light.2l 2 The absorption of amptitude-modulated light causes pulsating surface temperatures in a sample and, hence, a pulsed thermal reradiation. By monitoring the variation of radiant emission with the wavelength of the incident light, the absorption spectrum may be derived. Such photothermal radiometry (PTR) has been performed on such various substances as Nd,O, powder, blood, and a leaf.213 Intracavity Laser Absorption Spectroscopy.-Considerable signal enhancement may be expected when using intracavity absorption methods. A CW dye laser was employed for the intracavity measurement of broad-band absorbing species in aqueous solutions.214Enhancements of 6 x 10' were obtained for absorbances in the range 5 x 10-5-10-3. Spectra for H,O and I, were recorded in a CW dye laser intracavity spectrometer in which several tuning mechanisms, cavity lengths, and pumping powers were investigated.2 The sensitivity enhancement was found to be independent of cavity length and pumping power, but to increase with the bandwidth of the tuning element. A CW dye laser was also employed to measure HCl ( 5 4 ) and ( 7 4 ) overtone vibration-rotation bands.216 An intracavity absorption spectrometer has been described using a broad-band uncoded LiF-F, +.colour centre laser, pumped using a pulsed excimer laser, suitable for the range 880-970 nrn3.,l7High sensitivity has been reported for intracavity absorption spectroscopy of dimethyl-sym-tetrazine and I,, which were rotationally and vibrationally cooled in a supersonic molecular beam.218A delay in the onset of lasing following pumping, because of the increased loss, is resultant upon the inclusion of an absorbing species in the cavity. The measurement of this delay, rather than the optical loss, has been shown to be capable of resolving absorbances of 1 0 - 3 . 2 ' 9

'

'lo 'I'

2'2

K. L. Ratzlaff, Atiul. Cheni.. 1980. 52. 1415. P. W. Fairchild, N . L. Garland, W. E. Howard, and E. K. C. Lee, J . Cheni. P1i.w.. 1980.73, 3046. C. Stanciulescu, R. C . Bobulescu, A. Surmeian, D. Popescu, I. Popescu. and C. B. Collins, Appl. P/IJ*.s. LcJt/.,1980. 37, 888.

'I3

*I5 'Ib

'"

' I K

'Iy

P. E. Nordal and S. 0. Kanstad, Appf. Phys. Lett.. 1981, 38,486. J. S. Shirk, T. D. Harris, and J. W. Mitchel. Anal. Client., 1980. 52, 1701. S. J . Harris and A. M . Weiner. J . Chern. PiiFs.. 1981. 74. 3673. K. V . Reddy, J . Mot. Spectrosc.. 1980, 82. 127. V. M . Bacv. H . Schroder, and P. E. Toschak, Opt. Coniniun., 1981, 36, 57. W. R. Lambert. P. M . Felker, and A. H. Zewail, J . Chent. Plijs., 1981. 74. 4732. J . M . Rainsey and W. B. Whitten. A t i d . Client.. 1980, 52, 2192.

18 Photochemistry Infrared Spectroscopy.-A review of commercially available i.r. spectrometers has been published.220A 3 m vacuum grating instrument with digital data recording has provided resolution of 0.025 cm - I : computerized deconvolution of spectra improved this to 0.010cm-1.221Similar resolution was reported for a 5 m focal length littrow vacuum grating spectrometer when used for the 2v, band of 13CH, at 1.67 pm.222Line positions were determined with a precision of +0.002cmThe application of microprocessors to infrared spectroscopy has been discussed by Hannah and C o a t e ~ A. ~computer-controlled ~~ instrument has been constructed and found to offer substantial improvement in signal-to-noise.224 A 1 m multipass cell for i.r. spectroscopy, utilizing two parallel concave mirrors, has allowed path lengths up to 150m to be achieved.225For a study of collisioninduced simultaneous transitions in binary gas mixtures, a 2m sample cell has been constructed that allows pressure variation up to 1500 bar.226A cell has been designed for pressures up to 10Kbar and temperature variation over the range 10-300K.227 A Pfund-type cell has been constructed for i.r. spectroscopy with sample temperatures of 1300 K,228and a dual purpose cell, for i.r. absorption and electrical conductivity measurements, allowing temperatures to be achieved in the range 293-773 K, has been employed in a study of adsorbed gases on solids.229A reaction cell has been designed to enable i.r. spectroscopy of heterogeneously catalysed gas-phase reactions at elevated temperatures under reaction conditions. ’O Second-derivative i.r. spectroscopy has enabled the separation of sharp peaks from broad structureless Spectra of trace C 0 2 are used as illustrations. A useful bibliography of published data for i.r. spectroscopy has been provided by Oliver and M a r ~ d e n . ~The , ~ problem of searching an i.r. reference library using a computer has also been ~onsidered.~,’

’.

Tunable Diode Laser Spectroscopy.-During the past few years, tunable diode lasers have emerged as an important spectral source for infrared spectroscopy. A review of this field, dating back to 1976 has been published.234 A dual beam tunable diode laser spectrometer for mid-i.r. measurements has been described.235 Successive sweeping of the current-modulated laser permitted signal averaging and hence a good signal-to-noise ratio. Similar improvements were obtained by a scanning mechanism in which the laser output was modulated and the current

221

222

223 224

225

226

”’

”*

229

230

232 233 234

235

‘Ranging into the Infrared’, Lab. Equip. Dig., 1981, 18. Dec., 78. D. B. Braund, A. R.H. Cole, J. A. Cugley, F. R. Honey. R. E. Pulfrey. and G. D. Reece, Appl. O p t . , 1980, 19, 2146. K. Fox, G. W. Halsey, and D. E. Jennings, J. Mol. Spectrosc., 1980, 83, 213. R. W. Hannah and J. P. Coates, Eur. Spectrosc. N e w , 1980, 32, 30. W. F. Edgell, E. Schmidlin, and M.W. Balk, Appl. Spectrosc., 1980, 34, 420. J. Altmann, R. Baumgart, and C. Weitkamp, Appl. Opt., 1981. 20, 995. C. Brodbeck, J.-P. Bouanich, P. Figuiere, and H. Szwarc, J. Chem. Phys., 1981.74, 77. F. D. Medina, Infrared Phys., 1980, 20. 297. W. S. Dalton and H. Sakai, Appl. Opt., 1980, 19, 2145. P. T. Walsh, S. J. Gentry, A. Jones, and T. A. Jones, J . Phys. E., 1981. 14, 309. P. C. M. vanwoerkom, P. Blok, H. J. vanveenendaal, and R. L. de Groot, Appl. Opt., 1980,19,2547. M. R. Whitbeck, Appl. Spectrosc., 1981, 35, 93. R. W. A. Oliver and B. Marsden, Eur. Spectrosc. News, 1980, 33, 33. R. H. Shaps and J. F. Sprouse, Eur. Spectrosc. News, 1980, 32, 39. R. S. Eng, J. F. Butler, and K. J. Linden, O p t . Eng., 1980, 19, 945. D. E. Jennings, Appl. Opt., 1980, 19, 2695.


19

advanced during the dark time.236A computer-controlled spectrometer for the range 2.2-3.3 pm was constructed using a CW colour centre laser.237 Tunable diode laser spectroscopy has been employed in order to observe the Zeeman effect in the i.r. absorption of molecules with no electromagnetic moment, due to differences between the excited- and ground-state g - f a ~ t o r s . ~Doppler~' limited resolution was obtained for I3CH3I and 12CH2DIin the region 820866cm-' with a resolution of 0 . 0 0 0 6 ~ r n - ' 240 . ~ ~In ~ ~addition, the relative abundance of 1291 with respect to I2'I was found to be 0.032, comparing well with mass spectroscopic data. Doppler-limited resolution was also reported for ['H,]-ethylene in the 2174-2227 cm- region.241Other systems that have been investigated include NH, (931-954cmMoF, ( v 3 Q branch, 7407 5 0 ~ m - ' ) , ~H2"C0 ~~ and H213C0 (band centres 1746.009cm-' and 1707.981cm- l , the radicals C35Cl, C37C1,245and CF,246 and HNO, (430 transitions in the region 1690--1727~m-').~~~ The i.r. spectrum of ,'O14N was investigated over the sample temperature range 800-1050 0C.248 Eight ozone absorption lines around 1068.7cm-' were resolved using a Pb salt diode laser and heterodyne frequency measurements after mixing the laser output with that from a C 0 2 laser.249A long optical path absorption cell was used in a study of the v , transition in UF, at 16 pm.250A tunable far-i.r. optically pumped laser was used to measure the absorption of water vapour between 8 and 1 0 4 ~ m - l The . ~ ~ absorption ~ of SO2 was monitored at 20 lines from a DF laser.252

Fourier Transform Infrared Spectroscopy.-New Fourier transform (FT) spectrometers recently described in the literature include a double-beam optically compensated spectrometer suitable for weak i.r. absorptions (0.5-1%) 2 5 3 and a system based upon a refractively scanned interferometer, in which the optical path length variation is achieved by translating a wedge of refractive material across one of the arms.254Such a design should permit lower construction costs and improved ruggedness. A FT i.r. spectrometer designed around a polarizing Michelson interferometer has been shown to offer several advantages over 236 "'l

238 239 240

241 242 243 244

245 246 247

24g 249

250

2s1 252 253 2s4

J. N.-P. Sun, M. L. Olsen, D. L. Grieble, and P. R. Griffiths, Appl. Opt., 1980, 19, 2762. G. Litfin, C. R. Pollock, J. V. V. Kasper, R. F. Curl, and F. K. Tittle, IEEE J. Quantum. Electron., 1980,16, 1154. V. G. Koloshinikov, Y. A. Kuritsyn, I. Pak, N. I. Ulitskiy, B. M. Kharlamov, A. D. Britov, I. I. Zasavitsky, and A. P. Shotov, Opt. Commun., 1980, 35, 213. P. P.Das, V. M. Devi, and K. N. Rao, J. Mol. Spectrosc., 1981, 86, 202. M. Wahlen and G. Tucker, Opt. Commun., 1981, 36, 39. N. Ohashi, K. Kawaguchi, and E. Hirota, J. Mol. Spectrosc., 1981, 85, 427. G. Baldachini, S. Marchetti, and V. Montelatici, J. Mol. Spectrosc., 1981, 86, 115. J. C. Cummings, J. Mol. Specrrosc., 1980, 83, 417. D. M. Sweger and R. L. Sams, J. Mol. Spectrosc., 1981, 87, 18. C. Yamada, K. Nagai, and E. Hirota, J. Mol. Spectrosc., 1981,85, 416. K. Kavaguchi, C. Yamada, Y.Hamadd, and E. Hirota, J. Mol. Spectrosc., 1981, 86, 136. A. G. Maki and J. S. Wells, J. Mol. Spectrosc., 1980, 82, 427. A. G. Maki and F. J. Lovas, J. Mol. Spectrosc., 1981, 85, 368. M. Lyszyk, J. C. Depannemaecker, J. G. Bantegnie, F. Herlemont, J. Lemaire, and Y . Riant, Opt. Cornmun., 1981, 37, 53. K. C. Kim and W. B. Person, J . Chem. Phys., 1981, 74, 171. 0. A. Simpson, R. A. Bohlander, J. J. Gallagher, and S. Perkowitz, J. Phys. Chem., 1980, 84, 1753. J. Altmann and P. Pokrowsky, Appl. Opt., 1980, 19, 3449. S.C. Shen, T.Welker, J. Kuhl, and L. Genzel, Infrared Phys.. 1980, 20, 277. W. M. Doyle, B. C. McIntosh, and W. L. Clarke, Appl. Specfrosc., 1980, 34, 599.

20

Photochemistry

conventional systems for dual beam Fourier transform, circular dichroism, and reflectance ellipsometric i.r. s p e c t r o ~ c o p y . For ~ ~ this application suitable i.r. grid polarizers for the range 5&700 cm- have been described, along with several suggestions for improving the performance of polarizing interferometers. 2 5 6 The technique of rapid scanning FT time-resolved infrared spectroscopy has been discussed with particular emphasis on the practical aspects and care required for such m e a s ~ r e m e n t s . ~ ~ ’ Improvements in the detection limits of FT i.r. spectroscopy are possible with the application of least-squares spectral regression techniques. 2 5 With base-line fitting and use of all the information available from a reference spectrum, trace gas levels may be detected even if the individual spectral features lie below the noise level. Target factor analysis has been applied in order to determine the number and identity of components in a series of related multicomponent mixtures.259FT i.r. spectroscopy has been employed in order to identify HOCH,OCHO as an intermediate in the gas-phase reaction of 0,and C2H4.260A long path (180 m) cell was used to detect glycoaldehyde, at the p.p.m. level, among products in the photolysis of C,H4, NO, and R O N 0 (R = aryl group).261 A method for continuously monitoring the total gaseous effluent from a heterogeneously catalysed reaction, using mid4.r. FT spectroscopy, has been described.262 Products may be identified and analysed semi-quantitatively and changes in the reactor performance diagnosed. FT i.r. spectroscopy has been used to determine the solvent-induced frequency of the FT i.r. shifts for the C-H stretching bands of n - ~ c t a n e . Measurement ~~, spectra for HCl and DCl over the range 2 8 4 0 - 8 4 5 0 ~ m - ’ , and ~ ~ ~for HI and DI over the range 3000-10 380 cmallowed accurate prediction of the TC1 and TI spectra. For D2160,the high resolution (5 x 10-3cm-1) available using FT i.r. spectroscopy enabled an extended and more precise set of rotational levels to be derived for the vibrational states (000), (020), (loo), and (O01).266Rotational constants and vibrational term values were evaluated for 13CS2 from FT i.r. measurements between 250-430 cm- with 0.01 cm- res01ution.~~’1988 lines were observed for ozone recorded using a FT i.r. spectrometer with a solar source. 268 Remote Atmospheric Monitoring.-Several techniques for remote atmospheric monitoring of pollutants, trace gases, etc. by LIDAR (Light Detection And Ranging) have become popular over recent years. Of these, DIAL (Differential Absorption Lidar) spectroscopy would seem to be of most interest to the 25s

25h 257 258 259

’”

260

’” “’ 264

’” 267

268

M. J. Dignam and M. D . Baker, App/. Specfrosc., 1981.35. 187. W. A. Challener, P. L. Richards, S. C. Zilio, and H. L. Garvin, Infrared Phys., 1980, 20, 215. A. A. Garrison, R. A . Crocombe. G. Mamantov, and J. A. deHaseth. Appl. Specfrosc., 1980,34,398. D. M. Haaland and R. G . Easterlang, Appl. Specfrosc., 1980, 34, 539. M. McCue and E. R. Malinowski, Anal. Chim. Arfa. 1981, 133, 125. H. Niki, P. D. Maker, C. M. Savage, and L. P. Breitenbach, J . Phys. Chem., 1981, 85, 1025. H. Niki, P. D . Maker, C. M. Savage, and L. P. Breitenbach. Chem. Phys. Lett.. 1981, 80, 499. D . D. Saperstein, Anal. Chem., 1980, 52, 1565. D. G . Cameron. S. C. Hsi, J. Umemura, and H. H . Mantsch, Can. J . Chem., 1981, 59. 1357. G. Guelachvili, P. Niay, and P. Bernage. J . Mol. Spectrosr., 1981, 85, 271. G . Guelachvili, P. Niay, and P. Bernage, J . Mol. Spectrosc., 1981, 85, 253. N . Papineau. J.-M. Flaud, and C. Camy-Peyret, J . Mu/. Specfrosc.. 1981, 87. 219. J . Kauppinen and K. Jolma, J. Mol. Specfrosc.. 1981, 85, 314. A . Barbe, C. Secroun. P. Jouve, A. Goldman, and D. G. Murray, J. Mu/. Spectrosr., 1981,86, 287.

Developments in Instrumentation and T e c hiques

21

photochemist. The advantages of using two lasers for DIAL, with one tuned to a known absorption line of the molecule of interest and the other serving as a reference, have been discussed.269In the same report, the effects of atmospheric turbulence were considered. DIAL instruments have been constructed using two simultaneously pulsed C 0 2 lasers (for sensing of ozone at 9 . 5 ~ m ) , ~and ~ ’ two Nd-YAG-pumped dye lasers (for the monitoring of water v a p o ~ r ) A . ~single ~~ CO, laser, operated at two wavelengths using an angle-modulated diffraction grating, was suggested to be an ideal source for DIAL.272A single XeCl laser was used to determine vertical ozone distributions in the stratosphere from 15 to 25 km.273Descriptions of a mobile g r ~ u n d - b a s e d , ~and ’ ~ an orbiting 2 7 5 DIAL system have been reported. The possibilities for remote sensing of H 2 0 and methane (from natural gas spills) by laser Raman and atmospheric alkali atoms, OH, NO, and NO, by fluorescence LIDAR 2 7 7 have also been examined and reviewed. Optical and Infrared Double-resonance Spectroscopy.-Sub-Doppler optical spectroscopy of BaO has been performed using two CW dye lasers.278A crossed-beam i.r.-u.v. double-resonance spectrometer has been described for observing electronic hot-band spectra of molecules vibrationally excited by a C 0 2 laser.279 Vibrational relaxation from NO (v = 1) has been studied by exciting at 5.3pm using a C 0 2 laser and then monitoring the resonance U.V.fluorescence induced using a discharge lamp.280An i.r.-u.v. double-resonance technique has revealed vibrational energy redistribution times in HFB of 30-100 ns.281Two 30ps pulses from 2 tunable C 0 2 lasers were used in a pump-probe ps double resonance study of SF6.282A deep-hole burning feature was observed at the pump wavelength. An apparatus has been described for the investigation of isomerization reactions using C0,-laser-induced fluorescence and i.r. doubleresonance absorption spectroscopy.283 Photoacoustic Spectroscopy.-Photoacoustic spectroscopy (PAS) and its applications have been recently reviewed.284A single-beam i.r. PAS spectrometer has been constructed for the range 800--4000cm- using a broad-band carbon rod spectral source in preference to a laser.285A double-beam in-time PAS instrument has been described,286in which a single microphone was used to monitor both the 269 ’’O

’’I

”’ 273 274 275

’” ’” 279

’” 283

’” 284 286

D. K. Killinger and N. Menyuk. Appl. PAYS. Lett.. 1981, 38. 968. R. W. Stewart and J. L. Bufton. Opt. Eng.. 1980. 19. 503. E. V. Browell. A. F. Carter. and T.D. Wilkerson. Opt. Eng.. 1981, 20, 85. M. Hamza, T. Kobayasi, and H. Inaba. Opt. Quantum. Electron., 1981, 13, 187. 0. Uchino, M. Maeda, T. Shibata, M. Hirono, and M. Fujiwara, Appl. Opr., 1980, 19, 4175. J. G. Hawley, Laser Focus, 1981, Mar., 60. V. J. Abreu, Opt. Eng.. 1980, 19, 489. D. A. Leonard. Opt. Eng., 1981, 20, 91. T. J. McIlrath, Opt. Eng.. 1980, 19, 495. R . A . Gotscho, P. S. Weiss, and R. W. Field. J . Mol. Spectrosc., 1980, 82. 283. M. B. Robin and N. A. Kuebler. Chem. PIijs. Lett., 1981, 80, 512. J . Kosanetzky, U. List. W. Urban, H. Vormann, and E. H. Fink, Chem. Phys.. 1980. 50, 361. S. Speiser and E. Grunwald, Chem. PIiys. Lett., 1980. 73, 438. R. C. Sharp, E. Yablonovitch, and N. Bloembergen. J . Chem. Phys., 1981, 74, 5357. I. Glatt and A. Yogev, Chem. Phps. Lett., 1981, 77. 228. G . F. Kirkbright, and S. L. Castleden, C h m . Br., 1980. 16. 661. M. J. D. Low and G . A. Parodi, Injrared Phys., 1980. 20, 333. M.F. Cox. G . N. Coleman, and T. W. McCreary. Anal. CIieni., 1980, 52, 1421.

22 Photochemistry reference and sample signals, which were 180" out of phase. Real-time compensation for intensity source vibrations were possible by this method. A highperformance photoacoustic cell has been used over the temperature range 9 0 320 K.287The frequency dependence of the photoacoustic signal was investigated using carbon black for a reference. The instrument was applied to investigations of the photocycle in a bacteriorhodopsin system, and to excitonic levels in semiconductors.288A cell for PAS for samples on t.1.c. plates has also been described.289Q Several carbon black samples were examined for suitability as reference standards for PAS.289bNorbit A decolourizing carbon was found to be most satisfactory. However, the problems associated with using carbon black for a reference has led to abandonment of the method and, instead, calibration of the spectrometer by a direct measurement of the emission spectrum of the excitation source has been used.290 The absorption spectrum 291 and quantum yields of fluorescence2 9 2 - 293 of solutions with high optical densities have been determined using PAS. An improvement in the responsivity of PAS to trace gas absorptions was obtained with a Helmholtz resonator attached to the sample cell.294Low C 0 2 levels were monitored by PAS using a 1mW diode laser and exciting into the 4.803 pm line.295 Photoacoustic detection with C 0 2 laser excitation permitted the detection of several hydrazines and oxidation products at the p.p,b. A theoretical and experimental study has compared methods for detecting low absorption in liquid nitrogen by either PAS or a photorefractive technique.297 PAS has been found to be an ideal technique for the study of surfaces and adsorbed species. In studies of optically thin samples, pulsed laser excitation has 299 The degree of been shown to enable sensitivities of to be obtained.298* chemical modification of silica gel surfaces has been monitored by PAS.300A linear relationship between the photoacoustic signal and the amount of carbon or nitrogen adsorbed on the surface was found. PAS has also been used to study the photoinduced transient formed when eosine Y was adsorbed onto ZnO p~wder,'~'and the thin oxide layers (S

61 but in the phenol molecule it is slower with a delay of about 12 ps. Two-photon processes are probably involved in hydrated electron formation. Nanosecond and picosecond photochemical kinetics of quinoid fluorescence produced by excitation of the enol form salicylideaniline have been investigated in various environments. ' 2o An excited-state tautomeric proton transfer occurs within 5 ps at temperatures above 4 K in both protic and aprotic solvents. Ford et al. l 2 have measured fluorescence lifetimes for the 450 nm excitation of methyl and phenyl salicylate in various solvents. Quenching studies on the short wavelength fluorescence band at 340 nm point to the existence of three distinct ground-state conformers. Lopez-Delgado and Lazare 2 2 have also studied methyl salicylate in the gas, liquid, and solution phases. They conclude that the dual fluorescence arises from two conformers (or rotamers) in the ground state. The blue fluorescence arises from excitation of the more abundant conformer, and the U.V. fluorescence arises from the other. Emission and intersystem crossing of aniline in various solvents have been measured using tris(dibenzy1methano)europium as a ~ c e p t 0 r . lThe ~ ~ results are listed in Tables 10-12.

'

Table 10 Egect of various solvents on aniline emission parameters Aiiilitic

TctllI / > C ~ U -

cottcviitrrrtic~ti 3g1-1

3gl-I 3g1-1 3z1-l

8 8 8 8 8

10-5M 10-5M 10-5M x 10-5M

x x x

x 1 0 - 5

Solrent

Cyclohexane Ethanol MP EPA Cyclohexane Ethanol MP EPA ~ EPA

A,, (nm) 265-310 265-300 265-290 265-290 265-295 275-295 275-300 290 290

tiire

20 C 20 c 77 K 77 K 20 C 20 c 77 K 77 K 77 K

hFmix

bmax

(nm) 315 339 330 340 315 339 330 340 340

(nm)

420 420

420 420 420

@F

0.08 0.10 0.08 0.10 0.17 0.10 0.17 0.10 0.10

@P

0.074 0.76

0.65 0.85 0.50

A hsorption

Solrcw t

Cyclohexane Diethyl ether Benzene Dioxan Tetrahydrofuran Butanol Propanol Ethanol Methanol Water " I"

Dielectric c*onstcrrtI

2.023 4.335 2.284 2.209 7.39 17.8 20. I 24.3 33.62 80.37

'-ma,

'.ma x

(nm) 287.5 289 289 290 290.5 286 285.5 284 282 280

t:

1760 1920 1800 2260 1840 1480 1440 1480 1430 1300

(nm) 315 33 1 327 339 335 340 340 340 340 342

E i i q g y of' Mhrind

''Illax

(cm-I) 31746 30211 30581 29498 29850 29411 29411 29411 29411 29239

@F

0.17 0.13 0.14 0.13 0.12 0.11 0.10 0.10 0.09 0.12

P. F. Barbara. R. M. Rentzepis. and L. E. Brus. J. A i i i . Cliiw. Soc.. 1980. 102. 2786. D. Ford. P. J. Thistlewaite. and G. J . Woolfe. Cliiwi. f h ! x Lctt., 1980, 69, 246. R. Lopez-Delgado and S. Lazare. J. f/i.r.s. C l i m . . 1981. 85. 763. G. Perichet. R. Chapelan, and B. Pouyet. J. f l i o t o d i i w i . , 1980, 13, 67.

(cm - I ) 32 937 32 255 -

31 992 31 923 32 062 32 062 32 062 32 132 -

Aniline solution in MP (77 K ) Aniline solution in cyclohexane (20"C ) Aniline solution in EPA (77K) Aniline solution in ethanol (20 "C)

-

0.85

-

3.9

2.7

2.7

0.10

0.10

~ d n s ) Qp 3.9 0.65

0.17

0.17

@F

-

5.4

-

4.2

T~/(S)

0.90

-

0.75

-

QlC

0.83

3.7 x 107

-

0.17

lo7

3.7 x

-

-

lo7

4.3 x

0.18

kp"/(S - I )

kFC/(s-') 4.3 x 107

0.81

.r,"/(ms) -

-

1.0 x

-

5.1 x

k,"/(s-

1)

3.3 x lo8

-

1.9 x lo8

-

k,,%(s-

Table 12 Calculated rate constants,for fluorescence (kF),intersystem crossing (kIC),and phosphorescence (kp).for vurious aniline solutions

Photophysical Processes in Condensed Phases 63 Picosecond spectroscopy has been used to study diffusion-limited processes in pdimethylaminobenzaldehyde (8)’ 24 and the related species (9), which exhibit dual or multiple fluorescences.

’’

Me,

,Me N

Me,

N

,CH,-CH,-CH,,

N

,Me

Ground-state aggregation, solvent-assisted relaxation, and excimer formation are responsible for long-wavelength fluorescence bands. Roy et al. 26 have studied the time-resolved emission from benzil and naphthil in semi-solid glasses to show that the relaxed excited triplet shows a growth followed by decay. This shows a geometrical relaxation occurs in the excited states. The fluorescence of relaxed and unrelaxed states of benzil.’” The unrelaxed emission exhibits a mirror image with absorption and blue shift in hydroxylic solvents. The fluorescence properties of ophthaldehyde derivatives of iodinated amino-acids have been studied by Miller and Thakrar. 1 2 * The photochemical aspects of carbonyl photochemistry remain important subjects of research. Wagner and Thomas’29 have used CIDNP to elucidate Irradiation of benzophenone radical formation from z,a,a-trifluoroacetophenone. and its derivatives in the presence of molecules with abstractable hydrogen atoms can give rise to intensely fluorescent compounds. This effect may interfere with the observation of nanosecond-domain kinetics. Quantum yields and kinetic isotope effects in nanosecond flash studies of the reduction of benzophenone by aliphatic amines have been measured by Inbar et Rate constant data are given in Tables I3 and 14. Winnik and Maharaj 32 have studied the reaction of benzophenone with n-alkanes through hexane to hexatriacontane EA is 3.9f0.2kcal for all chain lengths.I3’ The effects of substituents on the benzophenone on these reactions have also been examined.133 The reactions of phenylacetophenone when used as polymerization initiator have been reviewed by Merlin and Fouassier. 34 Harris and Selinger 35* 36 have, in two papers, studied the proton-induced fluorescence quenching of 1- and 2-naphthol. The respective rate constants for

’ ’

2*

125

12’

I”) I3O

13’ 13’

13’

I34 13’

E. Heumann, A h . Mol. Rcl~rsolioiiPro(*cwc~s.1979, 15, 297. S. Dlhne. W. Freyer. K . Teuchner. J . Dobkowski. and Z . R . Grabowski, J .

O i r i i k . . 1980. 22, 37. D. S. Roy, K . Bhattacharyya. S. C. Berd. and M. Chowdhury. Clicin. fliys. Lelt., 1980, 69, 134. K. Bhattacharyya, D . Roy. and M. Chowdhury. J . Lirriiin., 1980. 22. 95. J . M. Miller and H. Thakrar. Aritrl. Cliiiii. Actcr. 1981. 124. 221. P. J . Wagner and M. J . Thomas. J . Ant. Chmi. So(,.. 1980, 102, 4173. A. Lamire. A. Mar, U. Maharaj. D. C . Dong, S.-T. Cheung, and M. A. Winnick. J . Plii)/ocliorii.. 1980, 14. 265. S. Inbar. H. Linschitz. and S. G . Cohen, J . Am. Climi. Soc.. 1981. 103. 1048. M . A. Winnick and U. Maharaj. M~ic.r.oiiinl.c.irlc.s,1979. 12, 902. U . Maharaj, M . A, Winnick. B. Dors. and H . J. Schlfer. Mcrc.i.oc.o/(~cirl(~.s. 1979. 12, 905. A. Merlin and J.-P. Fouassier. J . Cliiwi. Pliys., 1981. 78. 267. C. M . Harris and B. K . Selinger. J . Pli,r.s. Clicni., 1980, 84. 1366. C . M . Harris and B. K . Selinger. J . P/il..v. Clicvii.. 1980. 84. 891.

64

Plto tochemistry

Table 13 Pulsed-her photolysis of 0.004M henzoplienone-~i~~nor systems

Cotiipountl

Solvenr C6H6

0.002-0.02

C6H6

0.002-0.02

CHJN

0.001--0.01

C6H6

0.0014.0 I

CH,CN

0.0014.01 0.0001-0.005 0.00014.005 0.000 06-0.003 0.00005--0.0006

'bH6 C6H6 C6H6 C6H6

C,H6:CH3CN (3:2)

ki,/(M - s- I ) 9.0 x 10'. 7.5 x 10' 6.4 x 107,7.0 x lo7 1 . 1 x lo8 2.3 x lo8,2.5 x lo8 3.0 x lo8 3.3 x lo8 3.4 x 109 3.0 x lo9,2.3 x lo9 4.5 x 109 8.9 x lo9

Table 14 Pulsed-her pltotolysis of0.004 M henzophenone-primary umine sj'stems. Effects of N-D and a-C-D Atiiine

k,,/(M - s - I ) 3.6 x 107 6.4 x lo7 3.0 x 1 0 7 5.6 x 107

Concentrution (M) 0.01-0.08 0.014.08 0.01 4 . 0 5 0.01 4 . 0 5 0.01-0.06 0.0 1-O.06 0.0 1 4 . 0 6

1.7 x

lo8 lo8 lo8 lo8

2.4 x 1.86 x 1.80 x 2.25 x lo8 2.31 x lo8

0.014.06

k,,/k,

1.8 I .9

I .4 1.2 1.3

"In benzene saturated with D20. 'In benzene saturated with H 2 0

quenching of ROH* and RO-* by Haq+ are 1.7 f 0.5 x 1 0 9 s - ' M - ' and 2.8 f 0.5 x 1 0 ' o s - l M - ' for I-naphthol, and 2.4 & 0.3 x I O 7 s - ' M - I and 6 f 1 x l O9 s - ' M - ' for 2-naphthol. The neglect of these effects has led to errors in the rate constants for protonation and deprotonation. The effect of nitrile geometry (linear or bent) on the singlet-state properties of benzonitrile and p-dimethylaminobenzonitrile has been investigated by INDO/S calculations. 1 3 ' A previously low-lying hidden state is the bent form. Solvent viscosity has a marked effect on the fluorescence yield of p-N,N-dialkylaminobenzylidenemalononitrile.3 8 The yield is increased by decreasing molecular rotation of surrounding molecules and so the molecule can be used as probe of microenvironments. Two papers have appeared on the photoionization of N,N,N',N'-tetramethyl-pphenylenediamine (TMPD) in various solvents. 39* Em ission and absorption spectra of some substituted 4-hydroxypyridines as well as pK and pK* values have

'

'

I-'-

I.' I.'

I"'

F. D. Lewis and B. Holnian. 111. J. P/rj..v. Chcrn., 1980. 84. 2326. K . Y . Law. < ' / / C W / . P//l.s. LcJtt..1980. 75. 545. K. Sioiiios. G . Kourouklis. L. G . Christophorou. and J . G . Carter. R d i w . P h j x Chwr.. 1980. 15. 313. K . Lee and S. Lipsky. R(/t/itr/.f/r,r\. ~ ' / r w r . . 19x0. 15. 305.

Pliotopliysicd Processes in Condensed Pliases 65 been r e ~ 0 r t e d . I ~This ' paper discusses the relevance of tautomerism to DNA structure. The fluorescence spectra of 4-cyanobiphenyl and 4 ' 4 kyl- or 4 ' 4 koxysubstituted liquid crystals have been examined as a function of solvent polarity and solute concentration. 142 The fluorescence originates from the planar ' L astate polarized along the long axis of the molecule. A red shift in fluorescence with increasing solvent polarity is due to orientation relaxation. Excimers which have not been reported to form in the first excited ' L astate of biphenyl are observed in concentrated solutions of cyanobiphenyl derivatives. Pande et at. 43 have studied the red-edge effect in excited-state reactions of 2-naphthylamine. The effect appears due to the participation of some non-promoting out-of-plane modes which slow proton transfer in the excited state. Picosecond and nanosecond pulse methods have been used to measure the timeresolved absorption spectra of 9-nitroanthracene, 9-benzoyl- 10-nitroanthracene, and 9-cyano- 10-nitroanthracene. 144 The long build-up time for triplet-triplet absorptions (72-86 ps) suggests that these do not represent the lifetimes of the singlet states but are the rates of internal conversion within the triplet manifold and that indirect intersystem crossing S,(n,n*) -+ T,(n,n*)+ T,(n,x*) is the most important process for populating T,. The fluorescence quantum yields of pyrene- 1-carboxaldehyde in water and methanol are 0.98 and 0.07,14' an effect attributed to solvent effects on x,n* and n,n* states. Cycloaddition reactions of 1-naphthonitrile to 1,2-dimethylcyclopentene are attributed to both ' L a and ' L , states.146It is pointed out that although dual fluorescence is known, this is the first example of divergent reaction from two nearly isoenergetic singlet states. An analysis of the U.V. spectra of some acyl pyridines, 4 7 including a theoretical examination of the molecular geometry, and excited states of bipyrimidine compounds'48 have also been made. Phototautomerism and the fluorescence of the cation of 4-aminopyrazole[3,4-dJpyrimidine, an analogue of adenine, has been published by Wierzchowski et al. 149 Intramolecular heteroexcimer formation in p-(CH,),NC6H4(CH2),(9-anthryl) and P - ( C H , ) ~ N C ~ H ~ ( C H1-pyrenyl) ~),( in hexane and propan-2-01 have been investigated by picosecond time-resolved fluorescence measurements.I 5 0 Two types of heteroexcimer (loose and sandwich) are postulated. The scheqe put forward is: A * m D %loose heteroexcimer e sandwich heteroexcimer. INDO/S calculations on excited states of aza-analogues of stilbene show the lowest excited states to be n,n*, the n,n* states being slightly higher. Extensive experimental studies on the reactivity, fluorescence, and photoisomerization as a function of substitution 5 2 and

'

'

''

D . Sen and C. H. J . Wells, SpiJi,troi,/iiiii.Acrrr. Purr A . 1980, 36, 563.

'" C. David and D. Baeyens-Volant. M o l . CrIw. Liq. CrIxr., 1980. 59. 181. 'L' U. Pande. N . B. Joshi. aiid D. D. Pont. Clicvrt. P/IJ.s.Lcrr.. 1980. 72. 209. '" K . Hmaiioue. S. Hirayama. T . Nakayama, and H. Teranishi. J . P/iI:s. C/icin., 1980. 84, 2074. IJ5 IJh

''-

'" 151

'sI

J . Oton and A. U. Acuna. J . P/ioloihiw.. 1980. 14. 341. F. D. Lewis aiid B. Holman, 111. J . P1i.r.s. C/iivii.. 1980. 84, 2328. W. Pietrzycki. P. Tomasili. and A. Sucharda-Sobczyk. J . M o l . Slriiiv.. 1981. 73. 49. J . Siihnel. U. Kenipka. and K . Gustav. J . M o l . Srrir1.r.. 1981. 76. 213. J . Wierzchowski. M. Szczesniak. and D . Shugar. Z . N~itrrrfimch.1980, 35. 878. M. Migita. T. Okada. N . Mataga. N . Nakushima. K . Yoshihara, Y. Sakata. and S. Misumi. C h c ~ i . P/i.rs. L c / [ . . 1980. 72, 229. 6. Orlaiidi. G. Poggi. and G . Marconi, J . Clicrii. SOL. .. FrrrcitkiJ. Trms. 2. 1980. 76. 598. G. Bartocci. U . Mazzucato. F. Masetti. and G. Galiazzo, J . PhI:c.. Chcwi.. 1980, 84, 847.

66

Pho tocliernistrey

protonation I s 3 have been made by another group. The asymmetric photochemistry occuring under the influence of circularly polarized light has been studied by Horman er a/. 54 Keto-enolization in 2-( l'-hydroxy-2'-naphthyl)benzothiazolehas been studied by laser flash photolysis.Is5 The photochemical properties of the group of compounds loosely described as dyes continues because of the interests in laser technology as well as textiles, photography, etc. The light stability and photodegradation of dyes has been the subject of a recent review.'56 The low energy of n,n* absorption spectra of anthraquinones has been analysed by Kuboyama.157The spectra of the lowest 'n,n* and 'n,n* states of phenazine and acridine have been studied in a biphenyl matrix at 2 K . I 5 * Electronic origins and vibrational analyses can be made in the biphenyl matrix, which allows clear separation of differently polarized spectra. Fluorescence spectroscopy provides evidence for hydrogen bonding of catecholamines, resorcinolamines, and related compounds with phosphate and other anionic species in water.159 Siegmund and Bendig'" have measured the absorption and fluorescence spectra of acridine, N-methylacridine, and N-phenylacridine at 298 K in 35 solvents. The polarity of the excited states and intersystem crossing efficiency are related to solvent properties. Absorption and fluorescence spectra, fluorescence lifetimes, and fluorescence quantum yields for 5,l O-dimethyl5,IO-dihydrophenazine (1 0), 9,14-dimethy1-9,14-dihydrodibenzo[a,c]phenazine ( I l), 9,14-dimethy1-9,14-dihydrophenanthro[4,5-abc]phenazine (1 2), and 6,13-dihydrodibenzo[b,i1phenazine (1 3) have been measured in benzene at room temperature.I6' The spectra are shown in Figure 12 and fluorescence data in Table 15. The long natural radiative lifetimes and large separation between Me I

Me 1

I Me (10)

Ifr3

I" 15'

'" Is' 'sI I6O "'

G . Bartocci. G. Favaro. and G. G. Aloisi. J . Phoroc./irrii.. 1980. 13, 165. M. Htiriiiann. D. Ufermann. M. P. Schneider. and H. Rau. J . P / i o / o c / w i . , 1981. 15, 259. A. Graness. H. Hartman. and J. Kleinschmiett. Z . Plijx Clicwi. ( L ~ i p z i g )1980. . 261, 946. R . S. Sinclsir. Photochriii. Photohid.. 1980. 31. 627. A. Kuboyarna, Birll. CIieni. Sot.. Jpii,. 1979. 52. 329. D. L. Harva and D. S. McClure. C/tcw. Phjx., 1981. 56, 167. J . de Vente, P. J. M. Bruyn, and J. Zaagsma, J . Pharm. Pharmacol., 1981, 33, 290. M. Siegmund and J. Bendig. Z. Narurforsch., Teil A , 1980, 35, 1076. G. 9. Schuster, S. P. Schmidt. and B. G . Dixon. J . P / ~ j xC'hiwi.. . 1980, 84. 1841.

67

Photophysicul Processes in Condensed Phuses

A (nm)

Figure 12 Absorption (A) und jluorescent'e (F) spectru of 5,1O-chnetli~l-5,IO-diIiyclrophencrzine (a), 9.14-ciiniethyl-9.14-ciil~~~tlro~liben;o[cc,c.17l1ena~ine (b), 9,14-dimetli~I-9,14dihydrophenanthro[4,5-abclphenazine (c), and 6,13-dimethy1-6,13-dihydrodibenzo[b,4 plrenazine (d) in benzene ut 24 T. Tlir ortiinutr sccili~scrpply to the uhsorpiion spectru: niusittiirni ,f[uoressCence intensities cwe arbitrury (Reproduced by permission from 1. Phj*s. Cliem., 1980,84,1841).

Table 15 Culculuted und esperimentul opticul transitions of' ( 10) und ( 13) (C2,,) Wuvelengt h /( nm ) Ctilc.

Ohs."

419 385 342 300 288 346 322 312 278 245

397

(

- 296 370) 337

(-315) 266 248

Oscill~itor strength Cuk.. Ohs. 0.95 0.15

0 0 0 0.17 0 0.22 0.0I 0.16 0.83

0.37 0.22 0.07 0.67

In benzene solution at 24 C. hother work. Experimental values were determined in 3-methylpentane at 77 K

"

absorption and emission maxima suggest that the first transition is symmetry forbidden for ( lo)-( 12). The photophysical behaviour of (1 3) is different, so state ordering must be changed in this compound. Excited-state absorption spectra of p-phenylene-bis(5-phenyl-2-oxazole) (POPOP) in dioxan have been obtained over the spectral range 310-760nm. In

Plio t ochniiis t q* 68 the gas phase and in solution S , - S , and not S , + S , absorption is the most probable cause of fluorescence quenching in dye laser operation. Jaraudias has studied the effect of solvent on the relaxation processes of 3,3’-diethyloxadicarbocyanine iodide (DODCI). Solvent viscosity and specific interactions, depending o n the nature of the solvent, are involved in the excited-state relaxation. Picosecond fluorescence measurements have been made on acridine by Shapiro and Winn. 64 The fluorescence lifetime depends upon the excitation and emission wavelengths in some solvents: see Table 16. The lifetime is a sensitive function of temperature and medium. The results are complex but differences of hydrogen bonding with the solvents are important. The \’&& v’ = I vibrational relaxation of sjw-tetrazine in n-hexane has been shown to occur within 8ps although weakly coupled.’65 Harriman and Mills have confirmed that the triplet state of anthraquinone-2,6-disodium sulphonate reacts with water to produce a photosolvate. Anomalous S , + So fluorescence and T2 + So phosphorescence have been found in the triphenyl methane derivatives (14)-(20): 16’ the results are shown in Table 17. The gap between the S2 and S , levels is large, 14000cm-’. The coordination of a lanthanide ion quenches in several cases the S , + Sofluorescence, but the S , + So emission is not significantly affected. The time-resolved fluorescence spectrum of Quinacrine Mustard at pH 4.6 shows three exponential components whose amplitudes depend on both excitation This behaviour is tentatively assigned to the and observation wavelenghts. formation of three protonated species of the excited molecule. The merocyanine dye ( 1 -methyl-4-hydroxystyryl)pyridiniumbetaine (21) shows in rigid ethanol an excitation wavelength-dependent fluorescence. 69 This is interpreted as arising from differentsolute-solvent orientations. In fluid solutions at room temperature there is rapid orientational and translational relaxation of the solvent cage. Three species of 3-hydroxycoumarin can be characterized by their absorption spectra. 7 0 The neutral molecule and cation are fluorescent, whereas the anion is not. First excited singlet state pK, values were calculated using the Forster-Weller equation but the values obtained by fluorimetry, Table 18, are in complete agreement with the ground-state data indicating a rapid excited-state deactivation prior to protolytic equilibration. A very thorough study of the solvent acid acidity dependence of the absorption and fluorescence of the plant estrogen coumestrol(22), has been made by Wolfbeis and Schaffner. ” In aqueous solution, five different species (dianion + dication) can be involved. Other related compounds have also been examined. The yellowgreen luminescence from quercetin and 3-hydroxyflavone at room temperature has

’

’

G. Marowsky and H. Schomburg, J. Pltotochiwt.. 1980, 14, I . J. Jaraudias. J . P/totochm?..1980, 13, 3 5 . S. L. Shapiro and K. R. Winn. J . Cliwt. Plijx. 1980, 73. 5958. Ihi P. F. Barbara. L. E. Brus, a n d P. M. Rentzepis. Cltcvit. Pliys. Lett., 1980, 69, 447. Ihh A. Harriman a n d A . Mills, Pltotochmi. Pltorohiol., 1981, 33. 619. lh7 A. Jarowski and J. Rzeszotarska, J. Ltrriiin.. 1980. 21. 409. IhH A . Andreoni. R. Cubeddu. S. de Silvestri, and P. Laporte. Opt. Cotiirni~ti.. 1980, 33, 277. IhY K . A. AI-Hassan and M . A. El-Bayoumi. Clttvit. P1i.v.v. Lc//.. 1980. 76, 121. ”() 0.S . Wolfbeis, Z . Phys. Chem. (Frankfurt am Main), 1981, 125, 15. I 0. S. Woltbeis and K. Schatfner. Pltotocltiwt. Photohiol.. 1980, 32, 143. lh2 lh3

Menthanol Methanol Ethanol Ethanol Isopropanol Butanol Decanol Ethylene glycol Glycerol Water Carbon tetrachloride Hexane Benzene Acetonitrile

Solvent

Escitntion iiuvelengrli/(nm) 355 396 355 396 355 355 355 355 355 355 355 355 355 355

328 f 50ps 346 f 50ps 339 f 50ps 539 f 50ps 723 f 50ps 1 1.6 ns 60 f 15ps 46 f lops 53 f lops 46 f lops

-

371 f 50ps 21 ns 350 f 50ps

T, 450 nm

-

> 580nm

407 f 50ps 904 k 80ps 375 _+ 50ps 817 & 80ps 346 f Sops 396 f 50ps 325 & 50ps 1.87ns+ Ions 1.92 ns +long tail 28.4 ns

T

Table 16 Dependence 0f:fiuorescence lifetime of ucriiiine upon severul purunwters T.

2.02 ns I .49 ns

5 ns

(450nm 77 K)

-

77 ps

33 ps

-

-

-

I23 ps

-

200: 1 ns 250 ps

Tripkt rim.

jiirtii.

50

+_

6; 38ps

10 13; 27 & 3; 30ns

3.2 ns

0.8 ns: 0.9 ns 350 ps; 0.8 ns; 0.7 ns 0.9 ns 0.9 ns (ri-propanol)

Privioiis rtiiis.vion

9 7~

k

2

5

Y \

2

2.

Photochemistry

70

HOOC OH (14)

Me

H03s0 0 HOOC

OH

(19)

Me

Me

Me

Me

c'fY1

HO,S

\

Me

(21)

been shown by Sengupta and Kasha 7 2 to arise from a tautomer produced by proton transfer in the excited state. At 77K in 2-methylbutane glass, where tautomerization cannot occur, a normal U.V. fluorescence corresponding to the U.V.absorption is observed. 4-Phenylumbelliferone (4-PU), is a model for several natural compounds, which fluoresce from a species formed in acidic solution by an P. K. Sengupta and M.Kasha, Chem. Phys. Lett.,

1979,68, 382.

‘

(cm-’) 18900 19 200 17100 I7 150 I8 700 I8 700 17600

1’

1700 800 55000 9500 I 00 I 00 28000

c

A hsorpt ioti

--*

s,

(cm-I) 20 850 23 300 23 800 22 700 22 000 22 000 21 500

s, +

Fiuorescmw r s, so (ns) (cm-’) 6.5 6.3 16950 1 16500 3.2 I7 400 6.4 10.0 6.4 I6 500

5.7

I 1.7

r (ns) -+

T, so 23 200 23 800 23200 22 800 23 800 23 500 23800 22300 22300 21 700 21500 22500 22500 21800

21 I50 20800 20500 19750 21300 20800 21000

19500 18700 16000 19750 21300 20800 13700

95 1540 230 210 340 290 280

13400 I3 300 I5 200 I6 450 12 900 I2 900 I6 400

Energy

5

p

Table 17 Musiniu qf uhorption spectru in the visible (and corresponding molar ubsorptivities E) , .fluorescence, und phosphorescence sspc’c-tru,Iifitinws qf S , -, So und S, -+ S,,fluorescence and T2 + So phosphorescence, undS2 + S , energy gups estimuted,from 2 the absorption spectru ,for compounds ( 14)-(20) s

Plio t ochsmis t rjv 72 Table 18 Ground und first excited singlet stute dissociution constunts of 3hjdro.yycoumarin at 22 "C 0-0 \Imaxabs

Species

Anion Neutral molecule Cation

pKa(So) 7.16 f 0.04 -3.9

0.2

mitisition

\~m,xf'u

(cm- ') (cm- I ) (24 165) (27349) (estimatedy 32616 26247 29431

(cm- ') 30534

29455

23529

PKa(S,1 PKa(S1) by F&sfer,fluoriWr//rr-cri/c. merrictill~ 2.6 7.2 2.5

- 3.9

26492

"Assuiiiing the same Stoke's shift as for the cation

adiabatic photoreaction of the excited state [Scheme 2, path (b)]."3 This could be enrichment a tautomer or more likely a quinoid keten phototautomer: provides evidence for the latter. Path (a) is preferred in slightly acidic solution. anion(S,)

A

4-PU(S,) (b) phototautomer (exciplex)

I -

1

photochemical ring-opening

517nm flu

anion(S,)

111;

/enw

4-PU(S0) 4Ruorescence

keten tautomer

(?)

Scheme 2

Lumichrome [7,8-dimethylalloxazine, (23)], a flavin tautomer, has two fluorescence emissions with maxima at 440 and 540 nm in pyridine-dioxan mixtures.' 7 4 Nanosecond time-resolved fluorescence shows fast growth of the latter due to proton transfer from N-1 of the excited lumichrome (23*) to N-10 during the lifetime of lumichrome singlet, and emission occurs from the excited flavinic chromophore (24*). Quinizarin and daunorubicin (an anti-cancer drug) have been studied to obtain information on transition-moment direction. 7 5 Quinizarin has been examined in

(23) I-' I''

(24)

0. S. Wolfbeis. E. Lippert mid H. Schwarz. Bcr. Bwi.scvigc~.v. P/i.~x.Chcrii.. 1980. 84. I 1 IS J . D. Choi. R. D. Fugate. and P.-S. Song. J . A m . C/ICW.SOL. 1980, 102, 5293. R. N . Ci~pps;111dM . Viilit. P h ~ ~ f ~ ~Photohid.. c h ~ i . 1981. 33. 673.

..

Pliotoplysical Processes in Condensed Phmes

73 Shopolski and EPA matrices. The first four electronic transitions are assigned and fluorescence is due to the ' B , (nn*) -, ' A transition. Since the n + n* transitions are higher in energy, intersystem crossing is inefficient, as observed. The natural pigment, 2-amino-4-pteridinone, has been the subject of an intense photophysical investigation and the photosensitizing properties have also been studied. 7 6 Picosecond fluorescence kinetics and polarization anisotropy measurements have been obtained from anthrocyanin pigments and in vivo samples.'77 Evidence of quenching and non-random orientational order in in vivo systems has been indicated. Fleming and co-workers have examined the birefringence and dichroism of dye solutions during picosecond pulse excitation. Rotational reorientation times for oxazine-725, cresyl violet, rhodamine B, and DODCI measured were 144 f 10, 223 & 12, and 153 & 8ps, respectively. The rotational motion of small chromophores has been measured by a combination of steadystate polarization and single-photon lifetime measurements, in which there is simultaneous delection of two polarization directions. 7 9 Nemet et ul. ''O have measured a fluorescence decay time of 4.1 & 0.1 ns for rhodamine 6G. The same dye has been the subject of two papers dealing with its properties as a laser dYe*'". 1 8 2 Karstens and Kobs ' 8 3 have compared rhodamine B (25) and rhodamine 101 (26) as fluorescence quantum yield reference substances. For rhodamine 101 the quantum yield was 1.0 at all the temperatures investigated. This was not true for rhodamine B, and at room temperature OF d 0.5. A number of luminescence quantum counters based on organic dyes in polymer matrices have been described. 184 Poly(viny1 alcohol) films are suitable for water-soluble dyes, and poly(viny1pyrrolidone) is compatible with dyes soluble in organic solvents. The photoionization of 9-anilino- I -naphthalenesulphonate (ANS) is shown to occur through a biphotonic process. '" An intermediate charge-transfer complex

'

' ''

i

'$7

C , Ch.'I h'tdt. M. Aubailly. A. Motnzikolf. M. Bazin. and R . Santus. P l r o ~ o i h ~Pliotohiol.. r~~. 1981, 33, '

641.

F. Pellegruno. P. Sekuler. and R. R. Alfaro. P l i ~ t ~ ~ l i cPlrotohioplrjx., ~ti. 1981. 2, 15. D. Waldeck. A . J. Cross, jun.. D. B. McDonald. and G . R . Fleming, J . Chcw. P/ij*s..1981.74, 3381. R. W. Wijnnendts van Resandt and L. De. Maeyer. C'lrcw. Phjx Lotr.. 1981, 78. 249. "" N . Nemet. K. Szues. M. Hilbert. and L. Kozina. Ac./ir P/rI..s. C/IP/JI.. 1979. 25. 103. P. R. Hanimond. lEEE J . Qiwrituiir Elviwoii.. 1980. 1 I . I 157. In' P. R. Haintnond and R . Nelson, lEEE J . Qirtrririrrii E/li1'/~O/7.. 1980, 1 I , 1161. l n 3 T. Karstens and K. Kobs. J . P l i j x C ~ J I J 1980. ~ . . 84. 1871. In' K . Maiidal. T. D. L. Pearson. and J. N . Demas. Ant//. Chivir.. 1980. 52. 2184. I n s H. Nakaniura. J . Tonakii. N . Nakashimii. and K . Yoshihara. Clrcwi. P/rj*.s.Lit//.. 1981. 77, 419. I--

IiH

I-'

74 Pl~otoc.liPniisri.!. involving the solvent is reported. The pressure dependence of excited-state proton transfer equilibria has been examined in several substituted naphthalene dyes, in particular 1-dimethylamino-naphthalene-5-sulphonic acid (DANS). 8 6 High pressure has been used in the luminescence of intramolecular charge transfer compounds by Rollinson and D r i ~ k a m e r . To ' ~ ~a large extent the increase of pressure alters luminescence in a way similar to an increase of solvent polarity. The technique is obviously a powerful one for elucidating systems where n,n* and n,n* states can be involved as well as proton transfer and solvent cage effects. Pollis and Drickamer188 have made high-pressure luminescence measurements on metalloporphyrins in polymeric media. This very interesting paper shows how pressure can be used to control the relative rates along the various paths available since pressure shifts energy levels with respect to one another. The energy-level diagram for Cu-octaethylporphyrin in Figure 13 illustrates this. An investigation of Group 3A phthalocyanines using laser photophysics has been made by Brannon and Magde. ' 8 9 Fluorescence yield and lifetime and triplet yields have been measured at room temperature. LOW PRESSURE

HIGH PRESSURE

Absorption spectra and decay kinetics of electron adducts of proflavin and acridine yellow in aqueous solution have been studied and the rates of transfer to different electron acceptors measured. '90 Electron injection from xanthene dyes and tetraphenylporphines into ZnO and TiO, has been shown to compete with fluorescence. ' 'I Picosecond spectroscopy has been used to determine excited-state absorption spectra and decay mechanisms in photostabilizers. ' 9 2 Fluorescence I"'

InIxx

"" 1"'' '"I

I"'

C . J . M;istritllpelo i i d H.W . Otfen. J . Sdliiio/i C ' h ~ i . 1980. . 9. 325. A. M. Rolliiisoii and H . G . Drickamer. J . C'licwi. P/I.IT..1980. 73. 5981. T . G. Politis and H . G . Drickamer. J . C ' / i w i . f / i j x . , 1981. 74. 263. J . H . Briinnoii iund D. Magde. J . Am. C ' h ~ ~ iSoc.. ~ i . 1980. 102. 62. M. T. Neiiadovic. 0. 1. Micic. and M . M. Kosanic. R d i i i [ . fli,r.y. C/icwi., 1981. 17, 159. M. Miitsumura. K . Mitsuda. N . Yoshizawa. mid H . Tsubomura. Bull. Clirrti. Soc. Jpz.. 1981. 54. 692. A. L. Huston, C. D. Merritt, G . W. Scott, and A. Gupta, Proc. 2nd Int. Conf. on Picosecond

Phenomena, ed. R. Hochstrasser. W. Kaiser, and C. V. Shank, Springer-Verlag, Berlin, Heidelberg, and New York, 1980, p. 232.

Photopi1j i c d Psoc~c~ssc~s iiI Cor I ~icwse~l Pit iisc.v 9

s

75

has been used to determine constants between riboflavin and a series of phenothiazines. 1 9 3 Cline Love and Upton 19' propose that measured and natural fluorescence lifetimes can be used for the selective determination of drugs and metabolites. Quenching Processes.-Complexes formed between excited states and ground states are now recognized to be very widespread in all aspects of photochemistry. Consequently they are the subject of numerous papers. Large rates of quenching by different states of fluorescent solvent excited state liquid cis-decalin and cyclohexane as observed by pulse radiolysis are caused by large reaction radii.195Values of 14, 13, and I5 A are found for the quenching of the excited state is cis-decalin by CCI,, in cyclohexane by CCI, and 0,. respectively. Aliphatic aldehydes undergo self-quenching ( k 2: 1O9 M - ' s - ') from the singlet state leading to a dimeric a-ketol. l g 6 Quenching of fluorescence by dienes has a rate constant of about the same value ( e u . 4 x lo9 M - ' s - ') giving rise to the formation of oxetans. Watkins '91 has concluded that, although energetically favourable, quenching of the fluorescence or aromatic hydrocarbons by oxygen in acetonitrile does not produce radical ions. The experiments support earlier views that 0, quenching involves reactions ( I ) and (2). Deuteriation has

little effect on the rate of oxygen quenching. By contrast, quenching of porphyrin and metalloporphyrin excited states by oxygen in protic and aprotic solvents has been shown by spin-traps to form both superoxide and singlet oxygen.198The

quenching of the fluorescence of naphthylalkyl halides (27) and (28) by haiogen group is dependent on the length of the chain and nature of the halogeno-group (see Table 19).'99 Triplet yields are dependent upon the orientation of the halogenogroup with respect to the aromatic nucleus. Ramakrishnan and his colleagues have studied the interaction of excited anthracene and carbon tetrachloride, 2oo fluorescence quenching of anthracene by acrylonitrile, 201 and solvent effects on the I43 IYS IYS

1Yh

1Y7

14H I4Y

200

E. Martin. F. R. Mowgon. and A. PdrdO. Aiiril. @rim. Rivrl. Sou. Esp. Fi.s. Quirii.. 1980. 76. 77. L. J. Cline Love and L. M . Upron. A d . Clrirrr. ,4c.fr,. 1980. 118. 325. L. H. Luthjens. H . D . F. Codee. H . C. de Leng. and A. Huinmel. CIrcvrr. P / I , I ~Lc.tr.. . 1981. 79. 444. J . Kossanyi. G . Daccord. S. Sabbah. B. Furth. P. Chaquin. J . C. Andre. and M . Buchy. N o m . J . Chiiii.. 1980. 4. 337. A. R . Watkins. C/rwi. Phyv. Lc,rr.. 1979. 65. 380. G. S. Cox. D. G . Whitten. and C. Gianotti. Clrc~rir.P/I.I.S.Lcvr.. 1979. 67. 51 I . R. S. Davidson. R. Bonneau. J . Jousott-Dubien. and K . R . Trethwey. C/r[wi.P h ~ xLcrr.. 1980. 74. 318. N . Se1var:ijan. M . M . Panicker. S. Vaidyanathitn. and V . Rumakrishnan. Iiiclicrri J . Clrcwi.. 1979. 18.

23. 20I

N . Selvarajan and V . Riimakrishnan. Irrrliciri J. CIrewi. See,.. Scc.r. A. 1979. IS. 340.

I -methylnaphthaleiie (27). I? = I . x = c1 (27). I ? = 2. x = c1 (27). I? = 3. x = CI (27). I I = 2. X = Br (27).I 1 = 2. x = I 2-met hy I n ;ip ht hale ne (28). I 1 = 2. x = CI (28). I I = 2. X = Br (28). I? = 2. x = I

0.044 0.10 0.20 0.06 0.55 0.30 0.03 0.06 0.18 O the decay becomes triple exponential with the appearance of a long component whose contribution to the total emission intensity increases rapidly with increasing pH at the expense of the other two emissions (Tables 22-24). The authors do not consider the mechanisms or states giving rise to the emission. The widely held view has been that 'Laand ' L , states, uncoupled to each other, but coupled to the ground state, are involved, although Rayner and Szabo 322 have recently suggested an alternative mechanism involving the coexistence of different rotational conformers in the ground state. Another possibility is the existence of different ionic species. Gudgin et al. criticize the work of

'

Table 22

Tryptophan fluorescence lifetimes and relative emission intensities in aqueous solution in function of p H : citric acid-sodium phosphate bufler. ien 280nm; emission through 350nm cut-offfilter, T = 20°C

-

Citric acid

'I9 320 321

322

PH

T l / W

I1

2.55 3.0 3.5 4.0 4.5 5.0 5.5 6.0 6.8

2.33 k 0.15 2.57f0.13 2.65 f 0.12 2.76 f 0.1 2.87 f 0.1 2.95 0.1 2.98 & 0.1 3.07 k 0.1 3.16 f 0.1

0.89 0.92 0.94 0.93 0.93 0.94 0.93 0.94 0.93

r2/(ns) 0.38 f 0.15

0.44fO.15 0.49 & 0.15 0.45 f 0.15 0.50 f 0.15 0.52 f 0.15 0.40 f 0.15 0.55 f 0.15 0.59 f 0.15

12

( M x 102)

0.11 0.08 0.06 0.07 0.07 0.06 0.07 0.06 0.07

8.86 7.95 6.97 6.15 5.46 4.85 4.30 3.68 2.27

R. Klein, I. Tatischeff, M. Bazin, and R. Santus, J . PIiys. CIicrn.. 1981, 85, 670. E. Gudgin, R. Lopez-Delgado, and W.R. Ware, Con. J . Chem., 1981,59, 1037.

D. M. Rayner and A. G.Szabo. Cum J . Clieni., 1978,56, 743. A. G.Szabo and D.M.Rayner, J . Ant. Clicni. Sor., 1980, 102, 554.

Pho t ocheniist rj

88 Table 23

-

H' 3.5 2.0 1.6 I .45 I .28 1.21 1.1 1 .o 0.84

7.0 7.5 8.0 8.5 9.0 9.5 10.0 10.5

2.5 3.5 5.25 6.2 7.9

x x x x x

=2

'51

(MIL) 3.2 x 10-4

PH

Table 24

9

Trj*ptoipIiun,f[uosewence lifetimes und relutive eniission intensities in HCl-wuter solutions us u .function of' pH. jLeX 280 nm; eniission through 305 nm cut-off,filter, T = 20 PC

lo-'

lo-' lo-'

lo-' 0. I45

(ns) 3.2 f 0.1 1.70 k 0.1 1.20 f 0.15 1.05 f 0.15 0.80 f 0.15 0.75 f 0.2 0.51 f 0.2 0.49 f 0.2 0.34 f 0.25

(ns) 0.52 f 0.15 0.43 & 0.15 0.40 f 0.15 0.37 f 0.20 0.31 f 0.25 0.13 f 0.4 -

1, 0.94 0.80 0.65 0.70 0.80 0.85

1 .oo 1 .oo

-

1.00

1'

0.06 0.20 0.35 0.30 0.20 0.15 -

-

Tryptophun fluorescence lifetime vulues and relutive emission intensities 280 nm; in sodium tetruborute bufjer solutions us a.functionof pH. E., eniission through 305 nm cut-off.filter, T = 20 "C

3.19 3.08 3.16 3.20 3.15 3.16 3.15 3.1 1

f 0.1 f 0.1 k 0.1 f 0.1 rf: 0.1 f 0.1 0.2 f 0.4

0.94 0.9 1 0.855 0.735 0.495 0.255 0.10 0.03

"Because of the increasing activity of

0.60 f 0.15 0.55 f 0.15 0.55 f 0.15 0.50 f 0.20 0.47 & 0.30 (0.5 f 0.5)" (0.5 f 0.5)" (0.5 f 0.5)" T ~ .the

0.06 0.05 0.045 0.035 0.025 -0.015 240 nm) photolysis of thiirane results in intersystem crossing to the lowest excited triplet state with a quantum yield of about 0.86.385 It is reported that r,x-dinaphthylalkanes form triplet excimers instantaneously with excitation by laser Investigations of the temporal characteristics and chain-length dependence of this triplet excimer suggest that the precursor is a ground state van der Waals force bound dimer. Enhanced phosphorescence is shown in intramolecular exciplex systems [carbazole(CH,),-(terephthalic acid methyl ester)] owing to electron transfer that causes fluorescence quenching of the carbazole residue.387 Wilson and H a l ~ e r report n ~ ~ on ~ exciplex formation between a triplet alkanone and alkylbenzene, and thus reaffirm the role of exciplexes in the quenching of triplet carbonyl compounds by olefimc and aromatic hydrocarbons. The effect of the heavy-atom substituents, bromine and iodine, on the electrondonor aniline in the electron-transfer reaction with thiopyronine triplet has been investigated by flash spectroscopy in solvents of different viscosity and polarity.389 Triplet quenching and radical yields are presented in Table 30. The results are analysed in terms of decay constants of an intermediate triplet exciplex. The influence of an external heavy-atom effect on the phosphorescence spectra of quinoxaline and 2,3-dichloroquinoxaline has also been reported.390The influence of chloride ion on the decay rate of Methylene Blue triplet in 0.01 M acid in the

Table 30 Triplet quenching parameters of tkiopyronine with N,N-dimethylated unilines ( D M A ) p - Br-D M A

DMA

k,U

Solvent Acetonit rile Water (50% acetonitrile) "Quenching constant ( IO9M-'s-I ). quenching

383

8.2

2.3

@,"

1 .o 0.93

k,"

orb

8.0 2.5

0.88 0.13

Radical yield per triplet under conditions of complete triplet

R. J. Hurtubise, Trrlcrrttci. 1981, 28. 145.

R. S. Ddvidson, D. Goodwin, and P. F. de Violet. Cltcwi. P1ij.s. Lett.. 1981. 73, 471. "' E. M. Lown. K . S. Sidhu. A. W. Jackson. A. Jodham. M. Green. and 0.P. Stransz. J . PIiys. Clicwi., 1981.85, 1089.

"' D. Webster, J.

F. Baugher. B. T. Lim, and E. C. Lim.. C/iem. P l i w Lett., 1981, 77, 294. Y. Hatano, M . Yamamoto, and Y . Nishijima, CIreni. P/r.r.y. Lett.. 1981, 77, 299. "' T. Wilson and A. M . Halpern. J . Ant. Client. Soc.. 1981. 103. 2412. 389 G. Winter and U . Seiner, Bey. Bunsenges Pltjx. Clieni.. 1980. 84, 1203. 390 S. Yamauchi, H. Saigusa. and T. Azumi. J . C/iiwt. Pli.~*s.,1981, 74. 5335. 387

98

Photochemistry

presence of ferrous ions has been investigated by means of laser flash photol y ~ i sChloride . ~ ~ ~ ions weakly accelerate decay of 3MBH2+in aqueous solution in the absence of Fe". Quenching of 3MBH2+ by Fe" is more strongly catalysed by Cl- in both water and SOv/v% aqueous CH3CN. A possible role of chloride is as a bridging species in quenching via electron transfer between 3MBH2+and Fe" is examined. Further reports of the quenching of triplet Methylene Blue by complexes of cobalt(I1) have also been presented and the results discussed in terms of a reversible electron-transfer Rate constants for the energy-transfer quenching of the lowest excited triplet states of anthracene, acridine, and naphthalene by Cr"' have been presented.393Low k, values were obtained and are attributed to low values of the pre-exponential factor of the energy transfer rate constants. A detailed analysis has been presented by Zemel and Hoffman394of the longrange (Foster-type) triplet-to-triplet energy transfer between the photoexcited triplet states of the zinc and magnesium protoporphyrin IX chromophores of Znand Mg-substituted haemoglobin. This difficult observation was made on fluid media and at ambient temperature by monitoring the time dependence of triplet-triplet absorption. This work represents the first detailed study of a longrange energy-transfer process, where both distances between the acceptor and donor and their orientations are accurately known. Further evidence of Forster-type energy-transfer effects has been obtained for several excited triplet-state donors and several ground-state doublet nitroxyl radicals.395Critical transfer distances of the order of 12-20 8,were measured and were on good agreement with calculated values. Several papers have been presented on various spectroscopic energy transfer studies involving triplet ketones. Wilson and Halpern have presented a detailed kinetic study of sensitized 9,lO-dibromoanthracene (DBA) fluorescence produced by energy transfer from triplet ketones involving a ~ e t o p h e n o n and e ~ ~acetone397 ~ as donor. The results indicate that DBA is a sensitive probe for triplet ketones. Quenching results have also been presented for acetone phosphorescence by a series of aryl alkyl ketones possessing lower triplet energies than acetone.398 Quenching constants for phenyl alkyl ketones are considerably lower than for a diffusion-controlled process (k, = lo8-lo9 M - s- l), whereas those for quenchers with high electronaffinity are close to diffusion-controlled rates (k, = 10" M - ' s - l ) . Quenching of the benzophenone triplet and its derivatives with electron-attracting substituents by aryl ketones bearing electron-releasing substituents reveal a dependence of the quenching rate parameter on the structure of the two interacting partners.399 Excitation-resonance energy-transfer 39' 392 393 394 395

396 397

398 399

T. L. Osif and N . N. Lichtin, Pltotochmt. Pltotohiol.. 1980. 31. 403. T. Ohno and N. N. Lichtin. J . P h p . C'hent., 1980, 84. 3019. V. Balzami, M. T. Indelli, M. Maestri, D. Sandrini. and F. Scandola. J . Pltys. CIieni.. 1980,84, 852. H. Zemel and B. M. Hoffman, J . Am. CItent. Soc.. 1981, 103. 1192. N. N. Quan and A. V. Guzzo. J . P/t,~s.CIient.. 1981. 85, 140. T. Wilson and A. M. Halpern, J . A m . Clieni. Soc.. 1980. 102, 7272. T. Wilson and A. M. Halpern. J . Ant. Client. Soc.. 1980. 102. 7279. M. F. Mirbach. V. Ramamurthy. M . J. Mirbach. N. J. Turro. and P. J. Wagner. Noicv. J . Chint.. 1980, 4, 47 I . G. Favaro and F. Masetti. J . Pltotochem., 1981. 15. 241.

Photophysical Processes in Condensed Phases 99 efficiencies in n-hexane from 3(n, n*) and 3(n,n*) states of seven aromatic ketones to dienes have been mea~ured.~"The results indicate that excitation energy migration within the benzoyl sensitizer is sufficiently rapid to make state differences of little importance during excitation-resonance energy transfer. Experiments show that in the photoreduction of acetophenone by 1-phenylethanol, half of the ketone triplets are quenched by reaction with the OH bond rather than the conventionally accepted reaction with the a-C-H bond.401 The quantum yield for the photoreduction in benzene was 0.59 and 0.50 in acetonitrile. Laser flash photolysis techniques have been used in energy-transfer studies of aromatic hydrocarbons and ketones to di-t-butyl peroxide.402Rate constants for triplet quenching in benzene at 25°C are 7.9 x lo6, 3.4 x lo6, and 7.ox 1 0 4 ~ 4 s - for p-methoxypropiophenone, benzophenone, and benz[a]anthracene, respectively. The kinetics of triplet quenching are shown in Table 31. Aromatic ketones, made water soluble by ionic substituents, have also been employed in the photosensitized cis-trans isomerization in the maleicfumaric acid system.403The photostationary state cis : trans ratio was dependent on the triplet energy of the sensitizer and the pH of the medium.

Table 31 Kinetics of triplet quenching by di-t-butyl peroxide. TT

Sensit t e r Propiophenone p-Methox ypropiophenone Benzophenone Benzophenone Phenanthrene Phenanthrene Naphthalene Benzil Fluorenone Benz[a]anthracene Anthracene "Units of M-'s-'. at 25°C.

Solvent benzene benzene benzene acetonit rile benzene acetonitrile benzene benzene benzene benzene benzene

k,"

9.6 7.9 3.4 3.7 1.8 3.0 1.1 2.8 2.4 7.0 9.7

(perox)b

x x x

lo6 lo6

x x x x x x

lo6 lo6 lo6 lo6

lo6

lo4 105

x 104 x lo4

11'

23 60

0.57 0.72

98

0.85

150 3000 680 2200 1500

0.62

nanoseconds, in neat peroxide. 'Efficiency to t-butoxy radical generation neglecting any differences in cage recombination between direct and sensitized photodecompositions

The triplet-triplet energy transfer from aromatic hydrocarbons to trans- and cis-stilbene has been investigated by applying the Ulstrup and Jortner quantum mechanical description of electron-transfer This analysis accounts well for the experimental results, the main features of the energy-transfer process being determined by the (low-frequency) twisting mode and the (high-frequency) stretching C=C mode of donor and acceptor molecules. Further work, using flash kinetic spectroscopy, has been reported on the rate constants for triplet-energy transfer from indeno[2,l-O]indene to a ~ u l e n e . Energy ~ ~ ' transfer was studied as a 'O0 *O' *02

Oo3 40' '05

R. B. Abakerli and V. G. Toscano. J . Pliotochiwi.. 1981. 15, 229. P. J. Wagner and A. E. Puchalski, J . Am. Clteni. Soc., 1980, 102, 7138. J. C. Scaiano and G. G. Wubbels, J . Am. C'limt. Soc.. 1981, 103, 640. A. Gupta, R. Mukhtar. and S . Seltzer. J . Pliss. Cltc~iii.,1980. 84. 2356. G. Orlandi. S. Monti. F. Barigelletti. and V. Balzani. Clicin. Pliys., 1980. 52, 313. J. Saltiel, P. T. Shannon. 0. C . Zafiriou. and A. K . Uriotte, J . An?. Chcm. Soc.. 1980. 102. 6799.

100

Photochemistry

function of both temperature and solvent and the results critically assessed in terms of the Debye equation for diffusion controlled process. Scaiano406reports on the temperature dependence of the quenching of seven aromatic hydrocarbon triplets by tetramethylpiperidine N-oxide. The results indicate that the change in rate constants in the triplet energy range I .28-2.90 eV is largely caused by entropic factors. Sciano407 has also examined solvent effects in the photochemistry of xanthone. Both the lifetime and the rate constants for the interaction of xanthone triplets with hydrogen donors are dependent on solvent. The change is attributed to the effect of hydrogen bonding in bringing about an inversion of n, n* and n,n* triplet states. Effects on xanthone triplet lifetime and rate constant are shown in Tables 32 and 33. Table 32 Kinetic parameters .for triplet decay in severul solvents ~~/(ns)a 8300 I 7 200 1300 71 700 22 60 370 270

Sol vent Acetonit rileb Water-acetonitrile' Methanol Benzene Carbon tetrachloride Cyclohexane n-Heptane 2-Propanol CI,C (0.05 M-propan-2-01)

k s Q / ( M - ' s-')" 4.5 x lo8 4.2 x 107 2.1 x lo8 4.3 x lo8 9 x lo8 d 4 x 109= 2.5 x 10' 7.5 x lo8

"At 22 C ; typical errors in k,, are IS',,. According to the manufacturer's specifications. the sample used contained 0.04",, water. A 1 : 1 mixture in volume. Not measured. Error could be as large as 3 0(,

Table 33 Rate constants ,for the interaction qf xanthone triplets \+ith severul hydrogen donors Suhstrcite Bu,SnH Pr'OH Pr'OH Pr'OH n-Heptane Cyclohexane Cyclohexane Cyclohexane

Medicr C1,C Cl,C I : I. CI,C-Pr'OH Pr'OH n-heptane CI,C methanol cyclohexane

-

"At 22 C. 'Typical errors are 10--15",, approximate figures (preceded by )

k,/(M-' 1.5 x 109 1.1 x lo8 4.1 x 105 2.2 x 105 2.5 x lo6 7.7 x lo6 -2 x 105 -5.4 x lo6 s - ' ) u v b

for most values and about 30:',, for those indicated as

Watkins408 has also reported on the solvent effects on the quenching of aromatic hydrocarbons by tetramethylpiperidone N-oxide. N o correlation of quenching efficiency with the charge-transfer properties of the aromatic hydrocarbon free-radical collision complex was found. Other work by Watkins409 has been concerned with the quenching of aromatic hydrocarbons by stable carbon free radicals. The results are summarized in Table 34. The author proposes that J . C. Scdiano. C'h~nr./'hj..\. Lett.. 1981. 79. 44 I . J. C. Scaiano. J . Ant. C/rcm. Sol .. 1980. 102. 7747. JOR A. R. Watkins. C h o n . f l t r s . Lc~rr..1980. 70. 262. "' A. R. Watkins. Cltcwt. PIIVJ.Lcrr.. 1980. 75. 230. 'Oh do-

Photopiiysical Processes in Condensed Phases 101 Table 34 Bimolecular rate contants k , .for quenching of aromatic hydrocarbon triplet states by bis-biphenylene ally1free radicals in methylcyclohexane A roniutic

hydrocurbon Biphenyl Fluorene Tri phenylene Phenanthrene Naphthalene Coronene Fluoranthene Pyrene 1,2-Benzanth racene I , 12-Benzperylene Ant hracene Perylene An thanthrene Tetracene

Triplet energy (ev) 3.01 2.98 2.90 2.69 2.63 2.41 2.30 2.10 2.05 2.01 1.82 1.56 I .45 1.28

k,/(109

~ - 1 s - 1 )

(1)

(11)

9.3 11.4 7.3 11.3 2.6 1.31 3.4 3.0 3.2 2.6 2.8 2.0 1.92

4.7

(111) 5.7

-

-

6.1 7.3 7.4 8.2

5.1 5.3 0.63

-

-

4.3 3.6 3.6 4.5 2.8 2.8

1.58 3.9 1.88 1.62 0.46 3.7 3.2

the mechanism leading to quenching is based on an exchange interaction between the free radicals and the triplet state. The triplet-triplet annihilation of Nmethylcarbazole (NMC) leads to primary population of upper excited singlet states which is detected by delayed fluorescence. In toluene, energy transfer from the upper excited states of NMC to toluene is The effects of ring substitution and the effect of aromatic quenchers on the photoreduction by toluene of r,r,a-trifluoroacetophenonehave been pre~ented.~' The results are interpreted in terms of differing reactivities of the nn* and n,n* triplets. The quenching of the monoprotonated lowest state of Methylene Blue, 3MBH2+by the ground state of the dye MB+ has been investigated by laser flash p h o t o l y ~ i s . ~Rate ' ~ constants for quenching were found to be of the order 1 x 1O8MP1s- in water, aqueous acetonitrile, and aqueous ethanol. Electrontransfer reactions between triplet Methylene Blue and ferrocenes in acetonitrile have also been reported.413Rate constants and radical yields are presented and the results explained in terms of a heavy-atom-induced intersystem crossing in the triplet exciplex. The photophysical properties of the lowest triplet state of Nmethylthioacridone (NMTN) have been examined, including the effect of oxygen quenching of the thione triplet.414 The quenching of triplet excitons on poly(N-vinylcarbazole) by biacetyl has also been examined and delayed fluorescence (20-50 ns) observed indicating some exciton mobility occurs even after triplet-triplet annihilation has become in~ignificant.~'An exciton-trapping model is used to describe the results. Further

'

'

'

*I"

'I'

8 . Nickel and G. Roden. Cliaii. P l i j - . ~ .1980, , 53. 243. P. J . Wagner and H . M . H. Lam. J . Ant. Cliivii. Soc.. 1980. 102. 4167. P. V. Kamat and N . N . Lichtin, J . P l i ~ x Cliiwi.. . 1981, 85. 814. S. Tamura. K . Kikuchi. H . Kokubin, and A. Weller. P1iy.v. Cliiwi.. 1980, 121. 165. A. Safarzadeh-Amiri. D. A. Condirston. R. E. Verrall. and R . P. Steer, Cliciii. Pltys. Let/.. 1981, 77,

415

S. E. Webber and P. Arots-Avotins. J . Clicwi. Pl1y.v.. 1980. 72. 3773,

*I'

'I2 *I3

99.

102

Pliotocliemisrrv

papers of interest concern the quenching of phenanthrene triplets by conjugated dienes in anionic m i ~ e l l e s quenching ,~~~ of benzophenone by o l e f i n ~ , ~tripletenergy transfer from the disodium salt of naphthalene disulphonic acid to the acridinium ion,418 and from aromatic hydrocarbons to trans- and cisa~obenzene.~” An interesting paper by Turro and Aikawa4” reports the first observation of delayed fluorescence and phosphorescence of 1-chloronaphthalene (CI-N)in conventional anionic and cationic micelles. The authors give experimental evidence of prompt fluorescence, phosphorescence, delayed fluorescence, and delayed excimer fluorescence. The delayed fluorescence is shown to arise predominantly from triplet-triplet annihilation within a single micelle.

’’

Biological Aspects.-The lowest excited triplet states of all-trans-p-carotene produced by pulse radiolysis has been studied by time-resolved resonance Raman spectro~copy.”~’ Six transient Raman bands at 965, 1009, 1125, 1188, 1236, and 1496cm-’ were observed and assigned to the triplet state of /?-carotene. The authors conclude that the molecule may be substantially twisted, presumably at the 15,15’ band in the triplet state. Further work has also been carried out by the same workers on the triplet state of a l l - t r a n ~ - r e t i n a l .The ~ ~ ~results indicate increased n-electron delocalization in the triplet state and propose that the relaxed excited triplet-state exists in either all-trans or 9-cis conformation. Das and B e ~ k e r have “ ~ ~ also employed pulse radiolysis and laser flash photolysis to study several photophysical properties of the triplet states of the series of polyenals (29)-(33) related to retinal (31) as homologues (Table 35). Results are presented

‘lh

*I7 ‘I’

‘” ‘” ‘” *” ‘13

J . C . Selwyn and J . C . Scaiano, Crrri. J . Chmi., 1981. 59, 663. A. Mar and M. A. Winnick. Clwii. PIij-s. LPII.,1981, 77, 73. Y. Nishida, K. Kikuchi, and H. Kokubun, J . Pliotochern., 1980, 13, 75. S. Monti, E. Gardini. P. Bortolus. and E. Amouyal, Clieni. Pliys. Li.tt., 1981, 77, 115. N . J. Turro and M . Aikawa, J . Ant. Client. Soc.. 1980, 102, 4866. N . H. Jensen. R. Wilbrandt, P. B. Pagsberg, A. H. Sillesen, and K . B. Hausen, J . Ani. Cliem. Sol.., 1980, 102, 7441. R. Wilbrandt and N . H. Jensen. J . Ant. Ckern. Soc.. 1981, 103. 1036. P. K . Das and R. S. Becker, J . Ant. Clieni. Soc.. 1979. 101, 6348.

Photopliysicul Processes in Condensed Phases 103 Table 35 Triplet-state photopliysicalproperties of polyenals in various solvents Tripfet-triplet absorption All-transpolyenal (29)

(30)

(31)

(32)

(33) fl

Sol W i l t Hexane Methanol Cyclohexane Benzene Ace toni t rile Methanol Hexane Benzene Acetonit rile Methanol Cyclohexane Benzene Acetoni trile Methanol Cyclohexane Methanol

Band ma.\(nmfl) 385 400 410 430 440 440 445 460 470 460 470 490 490 475 500 510

E-winction coefi at band maxb*C

(M-'cm-' x 3.85 (3.4)' 6.3 6.3 (7. I)' 5.1 (6.1)' 5.1 (5.7)' 7.8 6.7 (6.2)' 5.9 (6.7)' (3.38)E 12. I (I 1.9)' (11.2)' (14.9)' 20. I 13.6

f 5 nm. & IS",. 'Obtained from calculations.

Triplet state decay constant

(ccs-')d 10

5.3 0.16 0.1 1

0.094 0.092 0.11 0.1 1 0.083 0.062 0. I4 0.12 0.084 0.097 0.14 0.12

4r,b 0.42 -0.45 0.66 0.72 0.51 0.4 1 0.4-0.7 0.58 0.16 0.08 0.54 -0.038 -0.095 -0.033 0.018 GO.01

1074

on the effects of various solvents (nonpolar, polar, and hydrogen bonding) on the photophysical behaviour of two longer and two shorter homologues of retinals, and are discussed in relation to possible state orders and intersystem crossing. The dependence of quantum yields on wavelength have been reported for the rhodopsin system at 77K.424 These measurements provide an insight into the primary photochemistry and photoisomerization of retinal in cattle and sea squid rhodopsin. It is shown that a photoequilibrium can be established between rhodopsin, bathorhodopsin, and isorhodopsin according to Scheme 4. rhodopsin (1 1 -cis)

bathorhodopsin (all-trans)

\Ivvvr

m . um

isorhodopsin (94s)

Scheme 4

The naphthalene-sensitized formation of triplet-excited chlorophyll a (chl a) and all-trans B-carotene has been investigated by pulse radioly~is.~~' Rate constants for transfer of triplet energy from naphthalene to chl a and all-trans pcarotene in benzene at 25°C are 3.6 f 0.6 x 109M-'s-' and 10.7 f 1.2 x lo9 M - ' s - ', respectively. Rate constants for triplet-triplet annihilation are 1.4 f 0.3 x 109M-'s- forchl uand 3.6 & 0.4 x 109M-'s-' for all-trans /3-carotene.

'

E.s.r., Microwave, and Related Studies.-E.s.r. studies of phosphorescent triplet states of 2,2'-bipyridyl, 3,3'-, 4,4'-, 5,5'-, and 6,6'-dimethyl-2,2'-bipyridyls and 2,2'-

424

'I5

T. Suzuki and R . H. Callender, Biopltys. J . . 1981. 34,261. N. H. Jensen. R. Wilbrandt. and P. B. Pagsberg, Pitorochem. Pliotobiol., 1980. 32. 719.

104

Pliotoc.hc~tiiistr?.

biquinolyl have been carried out in ethanol glasses.426E.s.r. spectra of both the Eand 2-conformers were observed in poly(viny1 alcohol) films and their assignment examined by changing the direction of applied magnetic field. The conformations of the phosphorescent triplet states of molecules were confirmed to be all E in ethanol glasses. Huber and Schwoerer 4 2 7 describe e.s.r. experiments which show the existence of quintet states ( S = 2) after U.V. irradiation at 4.5 K in perdeuteriated p-toluenesubstituted diacetylene. Nine e.s.r. transitions per quintet were detected and were attributed to bicarbenes of short oligomers. E.s.r. has also been applied to the study of photochemical reactions of fluoro-substituted ketones with amines, tetraphenylborates, and o r g a n o m e t a l ~ . ~ ~ ~ Time-resolved e.s.r. is shown to be a useful technique in the direct observation of k -+k ' scattering in a one-dimensional triplet exciton system, 1,2,4,5-tetrachlor ~ b e n z e n e . "This ~ ~ technique appears to be well suited to the determination of time constants involved in the scattering process. Two papers have been presented on the photochemistry of 5-methylphenazinium salts in aqueous solution."30*4 3 Fluorescence, optical flash photolysis, and electron paramagnetic resonance (e.p.r.) techniques have been used to elucidate various aspects of product formation and quantum yield. Two products have been identified, namely the 5-methyl- 10-hydrophenazinium cation radical cation (PyH +) (MPH ?) and the pyocyanine (I-hydroxy-5-methyl-phenozinium) in a stoicheiometric ratio of 2 : 1. The quantum yield of formation of (MPH ?) was found to be 0.29 & 0.03 at pH 7.0 and 1.1 f 0.1 at pH 3.0. The triplet state of MP' ( T , )has also been detected by triplet-triplet absorption and is found to have a lifetime of 0.5 ns. Flash photolysis and e.p.r. have also been used to study a geminate triplet radical pair obtained from hydrogen abstraction by excited triplet acetone from propan-2-01."~~The authors demonstrate that the geminate pairs contribute most of the polarization in photochemically-induced dynamic electron polarization (CIDEP) as compared with free random-phase pairs. An e.p.r. optical study has been made on randomly oriented triplets of magnesium tetraphenylporphyrin (MgTPP) and zinc tetraphenylporphyrin in solvents ethanol, toluene, and t~luene-pyridine."~~ A strong temperature dependence was observed over the narrow range 100-180 K, and these observations are interpreted in terms of an equilibrium process between two or three photoexcited triplet forms. Hutchinson and Kemple 434 report e.p.r. and ENDOR spectroscopic measurements for the lowest triplet state of ['H ,]biphenyl molecules in [2H ,,]biphenyl singlet crystals at 1.9 K. Information pertaining to the relative orientations of these triplet-state molecules are given. Further papers of interest relate to the dynamic behaviour of transient e.p.r. signals following

-

'''

J . Higuchi. M . Yagi, T. Inaki. M. Bunden. K . Tanigaki. and T. Ito, Bid/. Clicw. Soc. J p . , 1980. 53, 890. R. Huber and M . Schwoerer, Cliiwi. f/i,r.s. Lcvt., 1980, 72. 10. K . S. Chen. T. Foster and J . K . S. Wan, Cciri. J . Cli~ni..1980, 58, 591. 'lY A. J . Van Strient. J. F. C. Van Kooten, and J . Schmidt. Client. P/~.I:T. Lett.. 1980. 76, 7 . *'" V. S. F. Chew and J . R. Bolton. J . fli.r.9. Clrm.. 1980, 84. 1903. V. S. F. Chew, J . R. Bolton, R. G . Brown, and G . Porter, J . fhys. Clrcvii.. 1980. 84, 1900. *32 K . Wong. T. M. Chen. and J. R. Bolton. J . fhys. Clicwi., 1981. 85, 12. *'.' S. A. Scherz and H . Levanon. J . Plivs. Clicrtt.. 1980, 84, 324. "* C. A. Hutchinson and M. D. Kemple. J . C ~ B I Ifh!:v.. I. 1981, 74. 192.

*"

"'

105 laser excitation of molecular triplet states in single crystals of 9,9-[ 'H,][2H,]fluorene.S3s A time resolution of 15 ns is demonstrated. Also an e.p.r.. study of triplet states of porphyrins, chlorophyll u, and the covalently linked dimer of Zn pyrochlorophyllide u, in a liquid crystal, has been The nearest-neighbour excited-state exchange matrix elements in dimers of 1,2,4,5-tetrachIorobenzene(TCB) have been independently obtained using highresolution phosphorescent - microwave double resonance (p.m.d.r.) and 0.d.m.r. technique^."^' The authors conclude that the matrix element for energy transfer in the triplet state of TCB is not the same for dimer and exciton states. Schutz and co-workers 438. 439 report on the use of 0.d.m.r. experiments at zerofield monitoring the delayed fluorescence (DF) and phosphorescence signals. The lowest triplet state in anthracene single crystals has been investigated and the following zero-field splitting (ZFS) parameters obtained D , = 0.06 967, E , = 00793, D, = 0.0694, and E , = 0.00808. Further investigations have been made on the metastable triplet excitons in 1 : 1 CT crystal anthracenetetracyanobenzene. Exciton ZFS values of D = 2019.5 and E = -248 MHz were obtained. Both the radiative and non-radiative properties of the lowest triplet state T , of a series of pyrene derivatives have also been determined by 0.d.m.r. techniques. 440 The assignment of the orbital symmetry of the phosphorescent triplet state of N,N,N',N'-tetramethyl-p-phenylenediamine(TMPD) has been studied by microwave-induced delayed phosphorescence (M IDP) and the assignment of B,, for the orbital symmetry established.441 Kinoshita, Iwasaki and Nishi442 have provided an interesting review of the molecular spectroscopy of the triplet state through optical detection of 0.d.m.r. The authors provide an interesting account of triplet-singlet excitation spectroscopy together with a compliation of the data available on ZFS parameters and decay rates. Steiner 443 provides a theoretical treatise of the effect of magnetic field on the sublevels of a triplet exciplex and shows how this modulates the radical dissociation yield of the exciplex. Triplet-triplet energy transfer in the system quinoxalene in ethanol studied by 0.d.m.r. reveals that such energy transfer takes place at concentrations above 2 x lo-, M dm-3.444 Photc)pli!.sic~trlProc~esse~s it1 Cotidevisctl Phtrsus

4 Physical Aspects of Some Photochemical Studies

Photolysis and Related Reactions.-The phosphorescent decays of the triplet-state sublevels in ketones has been investigated by generation through photolysis of J35

436 437

*" 43y ,

440

'*I

'" 443

"'

R. Furrer and M. C. Thurnaver, Cliivii. fliys. Lett., 1981. 79. 28. V. Crebel and H . Levanon. Clicwi. P1i.1-s.LiJtt., 1980, 72, 218. W. G. Breiland, T. E. Altman, and J. S. Voris, Clicwi. Pliys. Lptt.. 1979, 67,30. J. U.Von Schutz. F. Guckel. W. Steudle. and H . C. Wolf. Clicwi. f l i j - s . . 1980. 53. 365. J. U . Von Schutz. W . Stendle. H. C. Wolf, P. Reineker. and U . Schinid, Clicni. P1iy.v. Lctt., 1981. 79. I . C. Brauchle. H . Kabza, and J. Voitlander. Cliem. f l i j x . 1981. 55. 137. K. Matsui. H. Morita. N . Nishi, M . Kinoshita, and S. Nagakura, J . Cliiwi. Pli.~*.v..1980. 73, 5514. M. Kinoshita. N. Iwdsaki, and N. Nishi, Appl. Spctrosc. Rev.. 1981. 17, I . U. Steiner. Ber. Bittis~vigi~s Pl1.1-s.Clicwi., I98 I , 85, 228. A. Inoue. N. Nishi. M. Kinoshita. and N . Ebara. J . Cltmi. Soc.. Jpn.. 1980. 53. 2466.

106

Photochemistry

substituted 1 , 2 - d i o ~ e t a n s . ~ The ~ ' results indicate that the only source of triplet ketones in the dioxetan photolysis is through intersystem crossing from the excited singlet state of the ketone. No evidence was given for a metastable intermediate form of dioxetan. Laser flash photolysis has also been employed in the study of the excited singlet state of benzene, toluene, p-xylene, polystyrene, and poly(xm e t h y l ~ t y r e n e )Some . ~ ~ ~ of the physical properties of these compounds are given in Table 36. Flash photolysis has been used to elucidate the photochromic

Table 36 Physical properties

of

the singlet states First-order decuy constant ( 1 0 7 s- 1 ) 3.2 3.2 2.9 2.9 5.0 4.2

A hsorp t ion muximu (nm)

Cotnpound Benzene

620 480 640 630 530 520

Toluene p-Xylene Polystyrene Poly-methylst st yrene

Assignment

'El,, c ' E l , , +'El,c 'El,, c lElu t 'El, t

B,,(monomer) ' B , , (excimer) B,, (monomer) ' B t u (monomer) 'B1,(excimer) ' B , , (excimer)

behaviour of triphenylformazan 447 and on the study of electron-transfer reactions from phenolate ions to various carbonyl triplets.448 Rate constants for electron transfer are in the range 2 x lo9 to 1 x 1 0 l 0 M - ' s - The quantum yields of primary photoproducts (phenoxy-radicals and radical anions of carbonyl compounds) are essentially unity. Laser flash photolysis of more substituted azobenzenes has shown the existence of a triplet state whose behaviour is viscosity dependent.449It is suggested that this transient species be assigned to the lowest (71, n*) triplet state of the trans-4-nitroazobenzenes (34 a-g) investigated (Table 37). The temperature dependence of the photochemistry of o-methylacetophenone

R

(34)

R a; NO, b; CN c; NO, d; NO, e; Br 445

446 44 7

448

449

R'

RZ

R3

R4

Br Br CI H H

NHCOMe NHCOMe NHCOMe NHCOMe H

(HOCH,CH,)N(CH,CH,CN) (HOCH,CH,)N(CH,CH,CN) (HOCHzCH2)N(CH,CH,CN) (HOCH,CH,)N(CH,CH,CN) NMe,

OMe OMe OMe OMe H

D. C. Doetschman, J. L. Fish, P. Lechtken, and D. Negus. Clietit. f/?w.,1980, 51, 89. S. Tagdwa and W. Schnakel. Climi. Plij-s. Lett., 1980, 75, 120. U . W. Grummit and H . Langbein. J . fltotoclien~.,1981. 15, 329. P. K. Dds and S. N. Blattocharyya. J . f l i w . Client.. 1981, 85, 1391. H . Corner, H . Gruen. and D. Schulte-Frohlinde. J . fhys. Clieni.. 1980,84. 3031.

17 9 4.7 5

2.9 2.2 0.6 0.60 0.55 0.35

o-Terphenyl-diphenyl ether ( I : 1) 1 -Phenylethanol Diphenyl-diphenyl ether ( 1 : 3) GT

Propan-2-01 1.3-Dibromobenzene MTHF Benzene Methanol Acetonitrile PMMA DNBT GT DNBT GT DNBT GT PMMA PMMA Toluene Toluene

17 5 17 5 17 5

17

q, CP

DNBT

Solvent

j.,,,

(nm) 353 530 694 530 530 530 353 530 694 530 530 530 530 530 530 530 530 530 530 530 530 530 530 530 530 530

--

680 (740) 400, 685 400, 685 (780) 400, 690 (770) 400, 695 (780) 700 700 660 690 780 750

h h h

(nm) 400, 695 (760) 400, 700 (750) 710 (760) 400, 695 (780) 400, 700 (780) 420. 700 (800) 700 400. 695 (770) 710 700-800 390, 700 (780) 700-800

R,," 107

4.4 7 3.6 5 28

2 12

3.8 4.0 10 8 12 9 8 27 8 10

s-I

kObS

.o

8

10

d 0.005

0.01

0.2 0.15 0.03

1

0.05 0.2 0.0 1 c 0.005 < 0.005 c0.005

0.05

0. I 0.1 0.07

0.3

OD

Absorption maxima, decay rate constants, and yield of the transient of substituted trans-azobenzenes in various solvents at room temperature

lues in parenthesis refer to weak absorption maximum o r a shoulder. No discernable absorption between 700 and 800 nm

P

ound

37

.4

-.

. I :

. I :

n ,

.-

n

108 Photochemistry has been examined by laser flash p h o t o l y s i ~Data . ~ ~ ~are presented on the decay of the biradical generated in the photoenolization of o-methylacetophenone. A temperature study of the triplet state of iodonaphthalene and iodobiphenyl indicates that an intramolecular energy relocation process is inhibited as the temperature is lowered from 20 "C with a resulting increase in triplet lifetime.451 The activation energies for this process in toluene are given as 5.9, 4.8, and 3.4 kcal mol for 1-iodonaphthalene, 2-iodonapththalene and, 4-iodobiphenyl, respectively. Both laser flash photolysis and flash photolysis have been used to elucidate the transient species produced from solutions of a series of hydra zone^."^^ These compounds were synthesized from substituted 1,3-diones coupled to substituted aromatic amines. These compounds exists as the two distinct stereoisomers (35a) and (35b), for which the transient characteristics are summarized in Table 38.

Brauer and co-workers report on the photolysis of endoperoxide (PO) of heterocoerdianthrone (HCD = dibenzo[q]perylene-8,1 t j - d i ~ n e ) . ~4'5~4 . Two photoreactions were observed, vk, irreversible decomposition of PO with a quantum yield Qdec = 0.006, probably from T,(n,n*), and secondly a photoreversible cleavage of PO into HCD and 0, from the S,(n,n*) state with a maximum quantum yield of 0.26. The disodium salt of 9,l O-anthracenediproprionic acid (ADPA) has been used as a singlet-oxygen monitor.455 ADPA is bleached to an endoperoxide on reaction with singlet oxygen and the change in absorbance followed by time-resolved laser photolysis experiments. The rate constant for ADPA bleaching in 'H,O is given as 8.2 = lo7 M - s- and is the bimolecular rate constant for quenching of singlet oxygen by ADPA. The behaviour of the scintillation emission from 2,5-diphenyloxazole in liquid cyclohexane has been investigated by use of a picosecond ( - lops) electron The subsequent emission was detected by streak camera and attributable to the fluorescence from excited 2,5-diphenyloxazole. Energy transfer was observed from excited cyclohexane molecules to 2,5-diphenyloxazole with a rate constant of 4 x 10" M - ' s - ' . The lifetime of the excited singlet state of cyclohexane was 300ps. Further photolysis studies have been made on liquid oxepan with particular emphasis being placed on the dependence on ring Scaiano. Clictn. P/i,~*s. Lctt.. 1980. 73, 3 19. '" J.F. C.Grieser J. K. Thomas, J. Clwii. P/I,I*s.,1980. 73, 21 15. '" J . McVie. Aand Mitchell. R. S. Sinclair. and T. G. Truscott. J . Clion. Soc.. P d i n Trtms. -7, '" R. Schmidt.. D. W. Dreus. and H. D. Brauer, J . Am. Clieni. So c.. 1980, 102, 2791. "('

"' W. Dreus. R. Schmidt. and H. D. Brauer. Climi. P h j x . L ~ t t .1980, . 70, 84. '" 9. A. Lindip. M. A. J. Rodgers. and A. P. Schaap. J. Am. Cliwii. Soc.. 1980. 102. 5590. J5h

4s7

Y. Katsumura, S. Tagawa, and Y. Tabata. J . Pli1.s. Clic~n.,1980. 84. 833. H. P. Schuchmann and C. Von Sonntag. J. Photochcni., 1980. 13. 347.

1980. 286.

Me Me Me Me Me Me Me Ph

Me Me Me Ph Ph Ph p-N02C,H4 Ph

Sliort-lived trunsients In hesane In ethanol R a e of decuy Rate of cieccy 10-5k/(s-') imax/(nm) 1 0 - ~ k / ( s - ' ) i,,,/(nm) 460 0.10 452 4.4 455 0.10 470 4.4 470 0.08 480 2.8 455 0.12 455 1.4 0.12 * 455 445 0.14 470 17.3 0.14 470 27.7 460 462 0.15 468 10.0

Transient characteristics in hesane and ethanol solution

Isomer (35a) is rapidly converted into (35b) in a polar solvent

(35) (35) (35) (35) (35) (35) (35) (35)

Table 38

42 1 42 I 425 425

I .4 I .4 0.4 0.4

1.7 2.2 5.8

450 420

*

436

110 Pliot o d i mi istrj Transient species with lifetimes of several nanoseconds have been observed in the laser photolysis of en one^.'^^ These transient species have been identified as orthogonol or twisted triplet states, the angle of twisting varying with the rigidity of the molecule. Bonneau discusses the nature of the reactive triplet state involved in the photochemistry of some enones. Photolysis of [2,2]paracyclophane in glassy solvents at 77 K produces a species with two benzyl radicals linked by an ethylene bridge.459 From studies of excitation spectra and emission lifetime a broad band was observed, which is attributed to intramolecular excimer fluorescence of this radical pair. Photolysis experiments have elucidated the mechanism for the efficient production of phenyl benzoate, the geminate product, from direct and sensitized irradiations of dibenzoyl peroxide in solution.460Photolysis has also been used to obtain rate constants for addition ( k , ) of benzothiazole-2-thiyl radical to vinyl monomers.46' Rate constants of 6.3 x I O5 to 2.5 x 1 O8 M - ' s- ' were obtained for reactions with vinyl acetate and styrene monomers. The effect of concentration, temperature, and solvent on the photodegradation of benzothiazolinospiropyrans using flash photolysis has been presented.462transCyclo-octene is shown to be the major product in the photolysis of cis-cyclo-octene ~ ~ ~ on with a quantum yield of 0.34.463Hamanoue and c o - w o r k e r ~report intersystem crossing and lowest triplet states of 4-chromanone, chromone, and flavone and of some nitroanthracene derivative^.'^^ For the latter long build-up times for triplet-triplet absorption were observed (72-86 psec) and represent the effect of the rates of internal conversion (T,, Tl). Indirect intersystem crossing to higher levels of the triplet manifold is most important in these systems. Intermolecular hydrogen abstraction by benzophenone in a poly(methy1 methacrylate) host has been studied by an argon laser using a new technique of holographic p h o t ~ c h e m i s t r y ,which ~ ~ ~ involves the absorption of two laser photons. A benzophenone triplet state abstracts a hydrogen atom from the host to produce a ketyl radical. Subsequent reaction with the host produces a long-lived intermediate. Hydrogen abstraction occurs only from the higher nn* triplet state. Further investigations have been reported on the extinction coefficients for the triplet-triplet absorption of benzophenone and naphthalene in benzene solution and of anthracene in benzene, ethanol, and cyclohexane solution.467 Rate constants for several processes involved in the photochemistry of a series of substituted benzophenones have been obtained by laser spectroscopy.468 The results are discussed in relation to photoinduced vinyl polymerization. The effect of oxygen on the photocyclization of N-methyldiphenylamine to Nmethylcarbazole in n-hexane, water, and aqueous surfactants has been studied by +

45q

"" I '" 46

463

"' '6S

'" '" 46 i

R. Bonneau, J. A m . Clicwi. Sol.., 1980. 102, 3816. S. Ishikawa, J . Nakamura, and S. Nagakura, Birll. Clieni. Soc. Jpn., 1980, 53, 2476. A . Kitamurd. H. Sakuragi, M. Yoshida, and K. Tokumaru. Bull. Clicni. Soc. Jpii.. 1980, 53. 1393. 0. Ito. K. Nagami, and M. Matsuda, J. P1i.w. Cli~wi..1981. 85, 1365. D. Gaude. R. Gautron. R. Ouglielmetti, and J. C . Dully. Bull. Soc. Cliifn. R., 1981, 11. 14. H . P. Schuchmann and C . Von Sonntag. J. Plioioc~l~cwi.. 1981. 15, 159. K. Hamanoue, T. Nakayama, T. Miyake, and H. Teranishi. Clien~.Lett., 1981, 39. K. Hamanove. S. Hirayama. T. Nakayama, and H. Teranishi. Client. b i t . , 1980. 407. C. Brauchle. D. M. Burland, and G. C. Bjorklund. J. P h ~ xClicvn., 1981, 85, 123. R. H. Compton, K. T. V. Grattan. and T. Morrow. J. Plioioclilwi., 1980. 14. 61. A. Merlin, D.-J. Lougnot, and J.-P. Fouassier. Polwii. Bull., 1980. 2 , 847.

PIIo t ophj *.Y icul Proc~c~ssc~s ii I Cot 1ticvised PI1c~.sc~.s 111 steady-state and flash photolysis The reaction sequence in micelles involves the same intermediate steps as in homogeneous solutions. The biinolecular dehydrogenation of the intermediate dihydro-N-methylcarbazoleby oxygen is enhanced in aqueous and micellar solutions, whereas the quenching rate of triplet intermediates by oxygen is not affected. Laser photolysis has also been used to study the photoinduced electron transfer from zinc tetraphenylporphyrin to acceptors solubilized either in the lipid interior or aqueous bulk of anionic oilcorrelation has been established in-water m i c r ~ e m u l s i o n s .A~ ~quantitative ~ between isotopic enrichment parameters and photochemical efficiencies of dibenzyl ketone in micellar s ~ l u t i o n . " ~The ' radical anions and cations of 1,6diphenylhexatriene (DPH) have been produced and characterized in both homogeneous and micellar solutions by pulse radiolysis and laser flash p h o t o l y ~ i s . ~ ~ ~ Both radical ions show intense ( c z lo5 M - ' cm-') absorption peaks at 600650nm. Electron transfer in micelles and vesicles and from the radical anion of biphenyl to carotene and DPH and from the radical anions of these to inorganic acceptors has also been studied. Reaction kinetics of ligand binding to myoglobin (M b), haemoglobin (Hb), horseradish peroxidase (HRP), and microperoxidase- 1 1 (MP-I 1 ) down to a temperature of -90 "C in supercooled mixed solvents, using dye laser and flash photolysis, have been reported.473 The photodissociation kinetics were characteristic of a case geminate transient diffusion-controlled reaction. Photo-oxidation.-Turro and c o - w o r k e r ~ 'report ~ ~ the rate constants for quenching of singlet molecular oxygen ( '0,) by several strained molecules. The authors also discuss a non-photochemical method for determination of quenching constants of singlet oxygen involving thermolysis of 1,4-ditnethylnaphthalene-1,4endoperoxide. Laser flash photolysis has been used to determine the bimolecular rate constants for the reaction between 0, ( 'A,) and several lipid-soluble and water-soluble substrate^."^^ 1,3-diphenylisobenzofuranand 9,lO-anthracene dipropionic acid disodium salt were used as singlet oxygen monitors. Prutz and Maier 4 7 6 report on the time dependence of various fluorescence bands from 0, ('Zg+).O2 ('Z,') was produced by an energy-pooling reaction from O 2 (*A,) (equation 5). 'C,-

'A,

+

'A,

-

-

'Z,+

+ 3zg-

-

fluoresces at 765 nm in liquid 0, with a fluorescence lifetime of 35 p, which is much longer than the lifetime 5 of the 'Xg+state which is about 8ps. Further experimental work is necessary to explain on the long emission lifetime now attributed to the 'Zg+ state in the liquid phase. Khan477 further reports on the first observation of emission corresponding to both the 'Ag N . Roessler and T. Wolff. Pliotoclt~ni.Pltotohiol.. 1980. 31, 547. M.-P. Pileni. Clirvtt. PIt,rs. Let/.. 1980. 75. 540. B. Kraeutler and N. J. Turro. C/ti.nt. P1i.r.s. Lr>ti.. 1980, 70, 266. 472 M. Almgren and J . K . Thomas. Pltotoclier~t.Pltotohiol.. 1980. 31. 329. 473 B. Hasinoft. J . PIijx. CItrw.. 1981, 85, 526. "' B. N . J . Turro. M . F. Chow. S. Kaufer. and M. Jacobs, Tim~rltcclrortLcti.. 1981. 22. 3. 475 B. A. Lindig and M . A . J. Rodgers. Pltotoc*hi~rtt.Photohid.. 1981. 33, 627. 47h R. Protz and M. Maier. J . Cltrw. Plt~s..1980. 73. 5464. A. U. Khan. Cltc~rti.P/i,~:v.Lrtt.. 1980. 72. 112.

470 471

'"

112

Photochemistry

= 0) -P 'Xg-(v'' = 0) and the 'An (v' = 0) -, 'Zg- (v" = 1) transitions of molecular oxygen in liquid solutions at room temperature. These observations were made possible by the use of a specially built highly sensitive near-i.r. spectrophotometer. An example of such emission is shown for the classic H,O,-OCI - chemiluminescence reaction in which singlet oxygen was first detected as a chemical intermediate (Figure 18). Of further interest are papers

(1,'

I

lo00

B

I

B

I

1200 1400 WAVELENGTH nm

e

I

0

Figure 18 Cliemilirniinescen~espectrum of H,O,-OCI - reuction at room remperuture. (a) lnstrunientul background rind (b) eniission ut 1.27 pm and 1.58 pm (Reproduced by permission from Clteni. f l z j s . Lett.. 1980, 72, 112).

relating to the ene reaction between singlet oxygen and 01efins.~'~ The potential usefulness of photosensitized oxygenations of olefins has been realized for some time and some examples are given in Scheme 5. Various spectroscopic techniques have been applied to unravel the nature of the reactive intermediate present in these reactions. The authors summarize the various theories put forward to explain these reactions and concentrate on data available for the ene reaction.478 Photoreduction and photo-oxidation reactions of porphyrin compounds have been further i n ~ e s t i g a t e d ; ~also ~ ' the photoperoxidation of unsaturated organic molecules.480*48 It is shown that photoperoxidation of 1,3-diphenyIisobenzofuran (DPBF) in benzene is accompanied by molecular oxygen consumption on a 1 : 1 stoicheiometric basis consistent with the formation of the endoperoxide as a L. M . Stephenson, M. J. Grdina, and M . Orfanopoulos, Acc. Chem. Res., 1980. 13, 419. Y . Hare1 and J. Manassen, Pliotochiwi. Pliolohiol.. 1980, 31. 457. '"" B. Stevens and K . L. Marsh, J . Charii. RPS.,1980, 290. ''I B. Stevens, J . A. Ors, and C . N . Christy, J . PI1.r.s. Clicwi.. 1981. 85, 210.

478

Photophysicul Processes in Condensed Phases

113

'

1

Me/fMe OOH

Scheme 5

-

primary product. Triplet DPBF reacts with the endoperoxide with a rate constant of 10' M - ' s - ' to form unidentified secondary products.

Photoisomerization.-Birge and H ~ b b a r d analyse ~ ~ * the molecular dynamics of cis-trans isomerization in the visual pigment rhodopsin using INDO-CISD molecular orbital theory and semiempirical molecular dynamic theory. The analysis predicts that the excited-state species is trapped during isomerization in an activated complex that has a lifetime of - 0 . 5 ~ s . This activated species oscillates between two components which preferentially decay to form isomerized product (bathorhodopsin) or unisomerized 1 1-cis-chromophore (rhodopsin) within 1.9-2.3 ps. The authors further conclude that the chromophore in bathorhodopsin has a distorted all-trans-geometry and is the most realistic model for the first intermediate in the bleaching cycle of rhodopsin. In the photoisomerization of 13-desmethylretinal it is shown that the hitherto unseen 13-cis-isomer is also present to an extent of 7% in addition to the 7-cis-, 9cis-, and 1 1- c i ~ - i s o m e r s The . ~ ~ ~photoisomerization processes of polyenes have been investigated using a theoretical approach and results of calculations for the potential energy surfaces with particular references to radiationless transitions presented.484 The monoanion of bromothymol blue shows reversible spectral changes in organic solvents, which are attributed to photoinduced rotational isomerizat i ~ n Transient . ~ ~ ~ species involved in direct photoisomerization of transthioindigo have been investigated using picosecond spectroscopy.486 The longlived transient absorption band at 600nm is shown to be formed on a picosecond time scale. Such ultrafast formation is inconsistent with the earlier assignment of this band to triplet-triplet absorption. A photoisomerization quantum yield for thioindigo of nearly unity has been observed at temperatures of around 180 K.487 A detailed analysis indicates that an isomerization via the singlet as well as via the triplet state is possible. 482

484

485 486 487

R. R. Birge and L. M. Hubbard, J . Am. Cltem. Soc.. 1980. 102, 2195. W. Gartner, H . Hopf. W. E. Hull, D. Oesterhelt, D. Scheutzow. and P. Towner, Tetrcrltedron Left., 1980, 21. 347. I. Ohrnire and K . Morokuma, J . Cliem. Plijs., 1980, 73, 1908. U. W. Grummit, A h . Mol. Rekcmition Processes, 1980, 18, 181. S. A. Krysanov and M. V. Alfirnov. Client. PItys. Lett., 1980, 76. 221. R. Memming and K. Kobs, Ber. Bunsenges PIiJs. Client., 1981. 85, 238.

114

Photochemistry

Photochromism.-Heller and co-workers have described various photochromic properties of heterocyclic In their first report the authors present the rearrangement reactions of (E)-r-3-furylethylidene(isopropylidene) succinic anhydride (36). It is shown that compound (36) undergoes conrotatory and thermal disrotatory ring-closure to give red 7,7a-dihydro-4,7,7-trimethylbenzo[b]furan-5,6-dicarboxylic anhydride (37) in near quantitative yield. The

&o

&i0

Me /

Me Me

(36)

(37)

reverse process occurs on exposure to white light. Analogous electrocyclic reactions of the pale yellow (E)-r-2,5-dimethyl-3-furylethylidenesuccinic anhydrides, which photocyclize on exposure to ultraviolet light, give thermally-stable deep red (37).The reverse process is shown on exposure to white light (Scheme 6).

R' = H, R2 = Me b; R' = Me, R 2 = Et c; R' = R2 = Me a;

Scheme 6 488

489 490

H . G. Heller, J . Chmi. Soc.. Prrkin Trcrns. 1, 198 I . 198. P. J . Dords, H . G . Heller, P. J . Strydom, and J. Whittall, J . Clrc~m.Soc.. Perkin Trrms. I, 1981, 202. H . G. Heller and J. R . Langan, J . C/itw. Sw., Pcrkin Trcms. 2. 1981, 341.

Photoplipic*uI Processes in Condensed Phusi~s

115

Further uses of the anhydride as a chemical actinometer are discussed. Acyclic azines having higher condensed aromatic and heterocyclic substituents are shown to be photochromic and show both thermal and photochemical isomerization with 492 Seventeen different substituted azines were investigated large spectra shifts.491* and were found to vary with respect to their reaction mechanism. The azines can therefore be divided into four reaction groups depending on the substituents. The differing behaviour can be rationalized if a photochemically induced E-2 isomerization about a C=N bond is involved. The sensitized as well as unsensitized photochemical E-Z and Z-E isomerization of benzophenone-9anthraldehyde azine have been investigated and the S , state of the E isomer is shown to be reactive. Sensitization of the triplet state does not induce the reaction. Chemiluminescence and Bioluminescence.-The chemiluminescent properties of several imino- 1,2-dioxetans, prepared by photosensitized oxygenation of ketenimines at - 78 "C, reveal that their decomposition to the corresponding ketones and isocyanates proceeds viu a biradical mechanism.493 Chemiluminescence is shown to be a convenient monitor of the lipid peroxidation reactions.494 Chemiluminescence is indeed induced or enhanced by conditions that normally increase lipid peroxidation or that create a peroxidative stress. The synthesis of fluorescein hydrazide and the study of the chemiluminescence accompanying its oxidation in protic as well as aprotic solvents has recently been Of further interest is the synthesis of anthracene derivatives bearing a -COCHgroup and measurement of their direct chemiluminescence on air oxidation in alkaline The chemiluminescence is explained in terms of a chemically-initiated electron-exchange luminescence mechanism. Direct chemiluminescence has been found from the air oxidation of 3-acyl-9methyl~arbazole.~~' The chemiluminescence of dioxetanone has been investigated theoretically and the results provide insight into the structure, reactivity, and properties of peroxides.498 The electrogenerated chemiluminescence (ECI) of five 1-amino-3-anthryl-9propane derivatives has been studied in t e t r a h ~ d r o f u r a n .Emission ~~~ from intramolecular exciplexes in ECI spectra and weak emission from the locally excited anthracene moiety were observed. The influence of triplet state interaction in ECI emission is discussed. The cheiniluminescent decomposition of three SIperoxy-lactones gives C O , and the corresponding ketone in high yield.500 The chemiluminescent species produced has been investigated in some detail by measurements of lifetime, energy-transfer activation parameters, and photochemical reactions. *"

K . Appenroth, M. Reichenbacher, and R. Paetzold, J . Plrotoclicwi.. 1980, 14. 39. K. Appenroth, M. Reichenbacher, and R. Paetzold. J . Plrotoc*lierii.. 1980, 14. 51. Y. Ito. H. Yokoyd, K . Kyono, S . Yamamurd, Y . Yamada. and T. Matsuura, J . Chiwi. So(..,Chcm. Coinrnuri., 1980, 807. ")' A. Boveris. E. Cadenas. and B. Chance, Fed. Proc.. 1981, 40. 195. '95 J. Nokokavouras, J. Zois, G. Vassilopoulos. and A. Perry, J . Piidit. C ~ P I ?1981. ~ . . 323. 21. 'y6 T. Hiramatsu. T. Harada, and T. Yamafi, Bull. Clicwi. Soc. Jprt.. 1981. 54, 985. 4y7 I. Kamiya and T. Sugimoto. BtrN. Cltc~ni.Soc. Jpn., 1981. 54. 25. *" S. P. Schmidt. M . A. Vincent, C. E. Dykstra, and G. B. Schuster, J . Ant. Cherii. So(,..1981. 103, 1292. *99 R. Ziebig, H. J . Hamann, W. Jugelt, and F. Pragst, J . Luniin., 1980, 21, 353. 500 N. J. Turro and M.-F. Chow, J . Ani. Clicmi. Soc., 1980, 102, 5058.

*"

Pho t oc*lwiristq* The quenching of peroxidized luminol chemiluminescence by reduced pyridine nucleotides has been r e p ~ r t e d . ~ ' 'Neither superoxide nor hydroxyl radical scavengers were found to quench the chemiluminescence of luminol in the presence of horseradish peroxidase and H 2 0 2 . Both chemi- and bio-luminescence of firefly luciferin have been investigated and a dioxetanone mechanism proposed for the light-producing pathway.'02 The relation between structure and triboluminescence has been investigated in two polymorphic systems, viz, hexaphenylcarbodisphosphorane and anthranilic acid.jo3Only one phase is triboluminescent. A correlation between triboluminescence and unit cell symmetry groups is given. The detection and possible applications of lyoluminescence are described in an interesting paper by Ettinger c't a/. I t is shown that lyoluminescence can be used to measure the radical scavenging activity of chemical compounds, particularly those with potential for use as radioprotective agents. 116

'''' '("

'O.'

504

J . K . Wong and M . L. Salin. Plrotoi~licwi.Pliotohiol.. 1981. 33. 737. E. H . White. M . G . Steinmetz. J . D. Miano. P. D. Wildes. and R . Morland, J . h i . C/i~wi. Soc.. 1980. 102. 3199. G. E. Hordis. W. C. Kaska. B.-P. Chandra. and J . I. Zink. J . ,4111.Clicwi. Soc., 1981. 103, 1074. K. V. Ettinger, J. R. Mallard, C. I. Anunuso, E. D. V. Filho, C. Regen, and S. Srirath, Nucl. h s t . Mct,~. .. 1980. 175. 136.

3 Gas- phase Photoprocesses BY

G. HANCOCK

1 Aliphatic Hydrocarbon Molecules, Ions, and Radicals Fluorescence spectroscopy of the ovalene molecule, C3,H 14, seeded in a supersonic beam of rare gas atoms, has been used to unravel the dynamical behaviour of the first (S,)and second (S,) excited singlet states.' The S, t So transition shows a sparse, well resolved vibrational structure, with S , lifetimes indicating that its decay is almost wholly radiative. In contrast, the fluorescence decay times following S2 t So excitation are some 200 times larger than those expected from measurements of the oscillator strength of this transition, and this has been interpreted in terms of S2 - S , interstate mixing, with the number of states in the S , background manifold coupling with the S2electronic origin (only 1800 cm higher in energy than the S, origin) as -3 x lo5 for this huge isolated molecule. Supersonic expansion of another polycyclic hydrocarbon, pentacene (C2,H 36) in Ar and Kr has, in contrast been used to study the properties of van der Waals complexes formed between pentacene (P) and rare gas (R) species., PAr, and PKr, complexes each show a pair of features in the vibrationless fluorescence excitation spectrum separated by 4 and 7cm- respectively, thought to arise from two separate isomers of each PR, complex. Spectral shifts between the isolated P molecule electronic origin and the vibrationless excitation of PR, do not obey simple additivity rules as a function of n, in contrast to the behaviour seen in complexes formed between iodine and rare gases, I,R,,. As expected, lifetimes of excited PKr, species are considerably shorter than those of PAr,, a nice illustration of the 'external heavy-atom effect' promoting S , --+ T , intersystem crossing (and hence reducing the fluorescence lifetime) in the decay kinetics of an isolated molecule. Infrared irradiation of van der Waals complexes containing ethylene has been used to measure absorption linewidths and hence predissociation rates of the vibrationally excited specie^.^ Predissociation lifetimes were found to be in the range 0.3 ps for large ethylene clusters, to 0.9 ps for C,H4*C,F4, corresponding to between 9 and 26 vibrational periods before dissociation. Coherent anti-Stokes Raman scattering, CARS, appears to be a promising spectroscopic method of investigating vibrationally excited intermediates formed in isomerization reactions of large polyatomic molecule^.^ The S, state of cycloheptatriene and its 7-methyl derivative, formed by absorption at 266 nm,

',

' A. Amirav. U. Even. and J. Jortner. J. Chem. Phys.. 1981, 74. 3745. Amirdv, U. Even, and J. Jortner, J. Pliys. Chem.. 1981, 85, 309. ' A. M. P. Casassa, D. S. Bomse. and K. C. Janda. J. Chem. Phys.. 1981, 74, 5044. K.Luther and W. Wieters, J. Chem. Phys.. 1980, 73, 4131.

117

118

Plio t oclieniistr!,

rapidly undergo internal conversion (IC) to So species with high vibrational energies: before these transient molecules isomerize into aromatic products (e.g. cycloheptatriene into toluene) their CARS spectra can be observed. The authors suggest that as this technique can be used on the ps time scale, kinetic spectroscopy of single vibrational levels during fast reactions should prove p ~ s s i b l e . ~ End-product analyses have been used to investigate the far-u.v. photolyses of several aliphatic hydrocarbons. Elimination of CH, is the predominant process in the photolysis of 1 ,1 -dimethylcyclopropane at both 147 and I24 nm (primary quantum yields of 0.34 and 0.39, respectively): nine additional reaction channels were identified. Tetramethylethylene (TME) photolysed at various wavelengths between 185-229nm shows products that can be divided into two groups, according to whether the quantum yield falls or rises with increasing total pressure.6 The former group is thought to originate from loss of either H or CH,, with the resultant vinylic (CH,),&H, or allylic (CH,), e&H,&, fragments either decomposing further, or being stabilized by collision. The latter group, a set of isomers of the parent compound, is believed to result from a collisionally induced pre-isomerization mechanism ( 1) competing with collisionless removal TME*

M

A*

A

processes (fluorescence or IC). CH, formation is the most important radical process in the far-u.v. photolysis of but-I-yne ' and b ~ t - 2 - y n e . ~ The decay mechanisms of cations of several unsaturated hydrocarbons have been investigated by coincidence techniques (photoelectron-photon and photoelectron-ion l o * I ) and by laser-induced fluorescence. I' Radiative and nonradiative contributions to the rate constants for removal of the first excited states of the cations of diacetylene and several substituted derivatives l o * l 2 have been evaluated, with radiative decay apparent in some of these species containing up to 0.4 eV internal energy, even though competing fragmentation channels can also be detected.12 For the buta-1,3-diene cation (C4H6+), the dependence of the unimolecular decomposition rate constant upon internal energy of the parent ion has been determined.' Rate constants for reaction of the CH radical with a number of atomic l 3 and molecular collision partners have been reported, with multiple-photon dissociation of suitable precursor molecules using either infrared or ultraviolet l 4 laser radiation used as the pulsed photolysis source, and laser-induced fluorescence near 431 nm employed as a sensitive time-resolved detection method. A similar technique has been used to measure removal rates of a"A, CH, and CD, with

'

'

J. B. Binkewicz, M. Kaplan, and R . D . Doepker. Crm. J. Client., 1981, 59. 537.

' G . J . Collin, H . Deslauriers. and A. Wieckowski. J . fliys. Client.. 1981, 85, 944. '

"

' lo

" l2 13

l4

H . Deslauriers, J . Deschenes. and G. J . Collin. C m . J. Clicwi., 1980, 58. 2100. J. DeschOnes. H. Deslauriers. and G . J . Collin, Cm. J . Clieni.. 1980. 58. 2108. J. P. Maier and F. Thommen. J . Clieni. Plgx., 1980. 73, 5617. J . Dannacher. J . P. Stadelmann. and J . Vogt, J . Client. Pliys.. 1981. 74, 2094. J . Dannacher, J. P. Flamme. J. P. Stadelmann, and J. Vogt, Cliem. Pl1.m.. 1980, 51. 189. J . P. Maier and L. Misev, CIieni. Pliys., 1980. 51, 311. I . Messing, T. Carrington. S. V. Filseth. and C. M. Sadowski, Cliem. PIiys. k i t . , 1980, 74, 56; I. Messing. S. V. Filseth, C. M. Sadowski. and T. Carrington. J. Clieni. P l i p . . 1981, 74. 3874. J . E. Butler, J . W. Fleming, L. P. Goss, and M. C. Lin. Clieni. Pliys., 1981. 56, 355.

119 various reactive and non-reactive collision partners. Absolute rate constants were measured to be an order of magnitude larger than those previously accepted, although relative values were in agreement with earlier results. The singlet-triplet separation in methylene retains its fascination, with the latest calculated value of 10.5kcal mol- agreeing with other theoretical treatments and values obtained from various photochemical and photodissociation studies. The recurrent problem is the considerably higher value (19.5 kcal mol- I ) found from photodetachment measurements on CH,-. and a careful reconsideration of the experimental data has revealed no reason to change this to the more popular smaller value. There is agreement upon at least one aspect concerning CH,, that any relativistic contribution to the calculated singlet-triplet energy separation is a negligible one. Gus-phase Plz(~tol?r.oc’c.~sc..s

’

2 Aromatic Hydrocarbons A two-laser photoionization method has been used to measure the collision-free

lifetime of benzene triplets produced in a molecular beam.” Excitation of the 6, level of S , benzene at 259 nm is followed by rapid ( 80 ns) ISC to vibrationally excited TI, and the decay of this (by ISC to S o * ) can be followed by monitoring C6H6+ions formed by 193-nm photoionization as a function of time following the initial S , excitation. The triplet states, possessing 1.1 eV of vibrational energy, were found to decay with a lifetime of 470 ns. Measurements of triplet decay for benzene, C6D6, and various alkylbenzenes by sensitized phosphorescence of biacetyl have highlighted differences between the short lifetimes seen in the gas phase and long lifetimes in low-temperature matrices, and the different decay paths in these media have been discussed.” Vibrational relaxation within S, benzene has been measured by observations of the changes in the fluorescence spectrum brought about by added collision partners.21Pulsed laser excitation of benzene at 248nm leading to production of molecular clusters via what are believed to be single-photon absorption processes has been reported,22 and emission from electronically excited CN has been seen following irradiation of toluene-NO mixtures at 266 nm, apparently resulting from chemical reaction involving fragments produced by multiple-photon dissociation. 2 3 A series of n-alkylbenzenes, cooled by supersonic expansion and excited to what are initially well localized ring distortion vibrations within the first excited singlet states, show fluorescence spectral behaviour that is dependent upon the alkyl chain length.24 For the first three members of the series (toluene to n-propylbenzene) resonance fluorescence from the initially pumped mode in S , was observed, but for

-

I’

19

’*

22 23 24

M . N . R. Ashfold. M. A. Fullstone. G . Hancock. and G . W. Ketley. Client. Pliys., 1981, 55, 245. P. Saxe, H. F. Schaefer. 111, and N. C. Handy, J . Pliys. Climi., 1981, 85, 745. P. C . Engelking. R. R. Corderman. J . J . Wendoloski, G . B. Ellison, S. V. O’Neil, and W. C. Lineberger, J . Cliem. Phys., 1981. 74, 5460. E. R. Davidson, D. Feller, and P. Phillips, C l i ~ n t Pliys. . L f r r . . 1980, 76, 416; C. P. Wood and N. C. Pyper. Mol. Pliys.. 1980. 41, 149. M. A. Duncan, T. G . Dietz. M. G. Liverman. and R. E. Smalley, J . Pliys. Cliem., 1981, 85, 7. K . W. Holtzclaw and M. D. Schuh, Chm. Pliys.. 1981, 56. 219. L. M. Logan, 1. Buduls, A. E. W. Knight, and 1. G. Ross. J . Cliem. Pliys., 1980, 72, 5667. N . Nakashima, H. Inoue, M . Sumitmi. and K . Yoshihara. J . Cliem. Pliys.. 1980. 73, 4693. J. B. Lurie and M. A. El-Sdyed, J . P l i . ~ Cliem.. . 1980, 84. 3348. J. B. Hopkins, D. E. Powers, and R. E. Smalley, J. Cliem. Pliys., 1980. 73, 683.

120 Photochemistry longer alkyl chains the fluorescence showed no resonant features, indicating that intramolecular vibrational relaxation (IVR) was essentially complete. Rates of these IVR processes were estimated to be on the sub-nanosecond time scale. Similar processes in isolated naphthalene molecules, excited to levels of S , containing up to 4000 cm- of vibrational energy, were again found to take place on a time scale much faster than f l ~ o r e s c e n c e . ~ ~ Laser flash photolysis has been used to prepare vibrationally excited Solevels of azulene, viu rapid IC from the initially populated S , state.26 Decay of infrared emission in the 3.3pmC-H stretch region was used to monitor rates of vibrational energy removal from So,and a stepladder model used to calculate the average amount of energy transferred per gas kinetic collision. The surprising result was that azulene - azulene collisions transfer 3500cm-’ of energy, a large amount in comparison with that normally expected for gas-phase collisional processes. Observations of laser-induced fluorescence of several polycyclic aromatic hydrocarbons in atmospheric pressure flames at 1200-1 500 K have been reported,,’ with spectra not differing greatly from those obtained at lower temperatures, indicating little net change in vibration on excitation of these molecules. 3 Organic Compounds Containing Oxygen Although many experimental and theoretical investigations have been carried out on formaldehyde, the dynamics of the behaviour of the first excited singlet state are still not completely understood. A recent review has highlighted several aspects of this topic, in particular the problems of the fast ‘collisionless’ non-radiative decay of S , , and the time lag observed at higher pressures for the appearance of products.28 The authors report that no experiment has yet demonstrated conclusively that S , dissociates at the zero-pressure limit, although theory suggests that it does, as the molecule is not large enough to undergo non-radiative nondissociative S , decay. A significant experimental point is made, that surprisingly low pressures are required for collision-free conditions to apply.28 Under these low-pressure conditions (0.1-1 mTorr) single rotational level lifetimes have been measured in the 4’ states of S , H 2 C 0 and D,CO. In H,CO, the lifetimes vary between 20 ns-3.1 ps, whereas in D 2 C 0 they cluster around 6.2 ps, thought to be close to the pure radiative lifetime. Higher vibrational levels of S , D,CO, 43,and 2143 show shorter lifetimes, which again fluctuate with rotational quantum number. A collisionless sequential decay mechanism (2) is invoked to explain the S1

-So

H,(DJ

+ CO

(2)

results, in which the last step may, for low vibrational levels of S , , involve tunnelling through a barrier to dissociation. Coupling between S , and So cannot be satisfactorily explained in terms of a smooth continuum of So states, as

25 26

” 28

S. M. Beck, J. B. Hopkins, D. E. Powers, and R. E. Smalley, J . Chem. Phys., 1981, 74,42. G . P. Smith and J. R. Barker, Chem. Pliys. Lett., 1981. 78, 253. D. S. Coe and J. 1. Steinfeld, Cliem. PIiys. Left.. 1980, 76, 485. W. M. Gelbart, M. L. Elert. and D. F. Heller, G e m . Rev., 1980, 80, 403.

Gas-phase Photoprocesses

121

electric 2 9 and magnetic 30 field effects can change the fluorescence 2 9 9 30 and photodissociation 30 rates appreciably. Thus the continuum of So levels is thought to possess local structure, at least near the S , origin:,' clearly Stark shifting at higher vibrational levels would be of interest in providing further details of this. Collisional relaxation of formaldehyde following single rotational level excitation has been reported by several groups. Curvature of the Stern-Volmer plots at pressures between and lo3 Torr for electronic quenching of both H 2 C 0 and D,CO, and the increase in quenching rate by Ar, C o t , and CH,F on deuteriation are factors that appear to have no simple quantitative e ~ p l a n a t i o n .An ~~ important clue would be identification of the elusive intermediate state between S , and the dissociation products populated by collisions: is it So, T,, or possibly HCOH? Calculations show that similar barriers exist for formaldehyde dissociation to H, + CO, and for isomerization to the HCOH intermediate; however for HFCO, the fluorohydroxycarbene species has a much higher energy barrier for its formation than does the dissociation step to H F + C 0 . 3 2Unfortunately the U.V. spectrum of fluoroformaldehyde only sets in above 1 10 kcal mol- higher than barriers to either process, and thus there exists no simple means of excitation of HFCO to energies between the two barriers in order to probe the importance of the isomerized form of the molecule in the dissociation dynamics. Following excitation of 4l S , H,CO, rotational and vibrational relaxation by collisions to levels of different lifetimes to that initially pumped make a major contribution to the observed curvature of the Stern-Volmer plots.31 For the corresponding vibrational level in S , D,CO, rotational relaxation by self collision appears to be , ~ ~is still somewhat slower than the very rapid 4' -, 4O vibrational ~ e l a x a t i o nyet five times faster than gas kinetic.33*34 Collision-induced rotational state changes of A J = & 1 are observed to p r e d ~ m i n a t eevidence ,~~ for a long-range dipole-type mechanism controlling the interaction. Finally, the lifetime of the electronically excited cation of deuteroformaldehyde, D,CO+(A2B,) has been measured, and the rate-determining step in the fragmentation of this ion to give DCO+ is thought to be IC to the electronic ground state.3s Low-pressure studies in glyoxal have shown that the S1state has a significant dissociation decay channel at the zero-pressure limit.36 Fluorescence intensity following CW Ar' laser irradiation at 454.4 nm shows a gradual decline with time with a rate constant that is independent of glyoxal pressure in the range 0.483.2mTorr, and that increases linearly with laser power. The primary quantum yield of dissociation is estimated to be 20.1. 3 6 Collision-induced S , + T, ISC in glyoxal has been studied in the presence of various added gases, with the relative magnitudes of the collision cross-sections found to be dependent upon the value of the intermolecular well depth between S1 glyoxal and the collision partner.,' Such

',

30

31

32

33 34

35 36 3'

J. C. Weisshaar and C. B. Moore, J . Chem. Phys., 1980.72, 5415. N. I. Sorokin, V. I. Makarov. N. L. Lavrik, Y. M. Gusev, G . I. Skubnevskaya, N. M. Bazhin, and Y. N. Molin, Chem. Phys. Left., 1981, 78, 8. J. C. Weisshaar, D. J . Bamford, E. Specht, and C. B. Moore, J. Chem. Phvs., 1981, 74, 226. K. Morokuma, S. Kato, and K. Hirao, J . Chem. Phys., 1980, 72, 6800. P. W. Fairchild and E. K. C. Lee, J . Pliys. Chem., 1980, 84, 3346. B. J. Orr, J. G. Haub. G. F. Nutt, J. L. Steward, and 0. Vozzo, Chem. Pli-vs. Left., 1981, 78, 621. R. Bombach, J. Ddnndcher, J. P. Stadelmann, and J. Vogt, Chem. Phys. Left., 1981,77, 399. G . W. Loge, C . S. Parmenter, and B. F. Rordorf. Chem. Phys. Left., 1980, 74, 309. C. S. Parmenter and M. Sedver, Cliem. Phys., 1980. 53. 333.

122

Photochemistry

behaviour has now been observed in several sets of rapid gas-phase quenching processes (for example in the removal rates of ;‘A CH, by non-reactive collision partners lS) and provides evidence for the long-range attractive part of the intermolecular potential dominating the collision process. Low-energy collisions at a translational temperature of 0.5-0.1 K between He and S , glyoxal expanded in a supersonic jet appear to be some 20-30 times more efficient at causing ISC than those at room t e m p e r a t ~ r e Furthermore, .~~ there appears to be essentially no dependence of the ISC rate upon the initially prepared rovibronic state of S , g l y o ~ a l which, , ~ ~ for rotational states, is consistent with theoretical prediction^.^' No distinct propensity rules for changes in K appear to apply in collisions transferring rotational energy in S , glyoxal with ground-state species or with CO;40 other studies on this molecule include a discussion of the retention of polarization in collision-free fluorescence excited by a polarized source, and its effect on measurements of relative rotational state populations via the Honl-London factor^,^' and further observation of the magnetic quenching of fluorescence in both glyoxal 4 2 and m e t h y l g l y ~ x a l . ~ ~ Quantum beats observed in biacetyl following pulsed irradiation in a molecular beam have been analysed to obtain the density of vibrationally hot triplet states interacting with the initially pumped singlet levels,44 and the effects of collisions and magnetic fields on such quantum beats have been studied, yielding the first direct measurements of cross-sections for dephasing collision^.^^ The kinetics of quenching of 3 A , biacetyl have been studied for several collision partners.46*47 Negative temperature-dependences for quenching by O 2 and NO are cited as evidence for the formation of collision complexes, whereas, for acetaldehyde, the magnitudes of the Arrhenius parameters are similar to those expected for freeradical H-atom abstraction reactions, possibly implying that triplet biacetyl acts as a biradical in the gas phase.47 ISC in biacetyl from T I -, S , , the reverse of that normally observed, has been seen in an experiment in which CO, laser radiation was used to pump triplet molecules (produced near the T , origin by initial excitation to S , , followed by ISC and vibrational relaxation) by multiple-photon absorption to S,.48 Figure 1 shows the effect of the i.r. pulse on the phosphorescence and fluorescence signals from biacetyl: the phosphorescence is seen to be rapidly and irreversibly quenched, and simultaneously a strong S , fluorescence signal is observed. Since the triplet-singlet energy separation in biacetyl is 2100cm- the generation of the fluorescence signal sets a lower limit of two CO, laser photons absorbed per triplet molecule excited.48 A similar reduction in the

,

’,

39 40

41

42 43 44

45 46

47 48

C. Jouvet and B. Soep, J . Chem. Phys.. 1980,73,4127. F . A. Novak and S. A. Rice, J . Cliem. Phys., 1980, 73, 858. H. M . Tenbrink, J . Langelaar, and R. P. M . Rettschnick, Cliem. Phys. Lett., 1980, 75, 115. G. W. Loge and C. S. Parmenter, J . Chem. Phys., 1981, 74, 29. C. Michel and C. Tric, Chem. Phys., 1980, 50, 341. K . Hashimoto, S. Nagakura, J . Nakamura, and S. Iwata, Cliem.Pliys. Lett., 1980, 74, 228. J . Chaiken, M. Gurnick, and J. D. McDonald, J . Chem. Phj-s., 1981, 74, 106, 117. W . Henke, H. L. Selzle, T. R. Hays, S. H . Lin, and E. W. Schlag, Chem. Plivs. Lett.. 1981, 77, 448. C. O’Concheanainn and H. W. Sidebottom, J. Photochem., 1980, 13, 175; M. B. Foley and H. Sidebottom. ;bid.. 1981, 15, 59. C. O’Concheanainn, M. B. Foley. and H . W. Sidebottom, J . Photochem., 1981, 15, 185. J . Y . Tsao, J . G . Black, E. Yablonovitch, and I . Burak, J . Cliem. Pli.vs., 1980, 73, 2076.

123

Gas-phase Pho topro cesses

I

2

6

4

8

10

crs

Figure 1 The efSect of i.r. radiation on the phosphorescence (upper trace, a) and.fltlorescence (lower trace, b) signals,from biacetyl. Time zero corresponds to optical excitation at 405 nm from a dye laser pulse, and the time of introduction of the 9.6 pm CO, laser pulse is indicated by the arrow

phosphorescence quantum yield caused by i.r. multiple-photon absorption by propynal triplets has been reported.49 The zero-pressure decay rates of H C S - C H O and HC&-CDO triplet states have been measured to be 3.1 x lo3 and 1.7 x lO3sd1, respe~tively.~~ Subtracting the contribution from radiative decay (0.71 x lo3s-' in each case) yields the T , --+ So ISC rates, and these show that the substitution of an 49

H . Stafast, J . Opitz, and J . R. Huber, Chem. PIiys., 1981, 56. 63. U. Briihlmann. P. Russegger, and J. R. Huber. Cliem. Pliys. Lerr., 1980, 75. 179.

I24 Pho t oc‘hemist iyq aldehydic hydrogen by deuterium reduces the ISC rate by a factor of 2.4. Calculations using either the v l 0 or v4 vibrations of propynal So as the dominant accepting mode for ISC [vl0 is the CH(D) aldehyde wag, v4* the C L O stretch] are able to reproduce this deuteriation effect.50 Multiple-photon ionization of acetaldehyde, and end-product analysis of the single-photon photolysis of CCI3CHOS2 have been reported. Emission between 250-450 nm in the ’ A , - X’E transition in the methoxy-radical C H 3 0 occurs in the reaction of metastable rare-gas atoms with CH,0H,53 and laser-induced fluorescence of single vibrational levels of the vinyloxy-species CH,=CHO has been detected.54 The collisional relaxation of vibrationally excited C F 3 0 - ions, formed in an ICR cavity, has been studied by using i.r. multiple-photon dissociation of these species by process (3) as a time-resolved method for their d e t e ~ t i o nAs . ~ ~the ease of the CF,O-

11/11’

---+

F-

+ CF,O

(3)

multiple-photon dissociation step (and hence the yield of F-) depends upon the internal energy content of the parent C F 3 0 - , the fraction of ions decomposed by the laser decreases as the vibrationally excited ions relax, thus yielding information upon rates of these de-excitation proce~ses.~’ An elegant experiment that measures directly the unimolecular decomposition rate of process (4)has been r e p ~ r t e d . ’Tetramethyldioxetan ~ is excited in the near-

i.r. to high overtones of the C-H stretching vibrations, u = 4 and 5, corresponding to internal energies of 32 and 39 kcal mol- respectively, and exceeding the energy barrier to dissociation, some 27 kcal mol - Part of the decomposition pathway yields electronically excited acetone, and observations of time-resolved fluorescence from this enables rates of unimolecular decay of state-selected tetramethyldioxetan to be found: these are 0.12 x lo6 and 3.4 x 106s-’ for u = 4 and 5, re~pectively.’~ Measurements of phosphorescence intensities in gas-phase benzaldehyde have shown that S, -, T , ISC dominates over S , + So IC at low to moderate vibrational energy content of the initially prepared S, state, whereas IC becomes important at higher energie~.~’ Deuteriation of ring hydrogens changes both ISC and IC rates dramatically, but these are only moderately affected by deuteriation of the aldehydic hydrogen, and the possible identities of the vibrational modes which couple the electronic states to yield this unexpected behaviour have been suggested.” Studies of intramolecular redistribution of excess energy within T ,

’,

“ 52

s3

’‘ 55

” 57

G. J . Fisanick, T. S. Eichelberger, B. A. Heath. a n d M . B. Robin, J. Cheni. PhFs., 1980, 72, 5571. T. Ohta and I. Mizoguchi, Int. J. Chm. Kitzc.r.. 1980, 12, 717. M. Sutoh, N. Washida, H. Akimoto, M. Nakamura. and M. Okuda, J. Clieni. Phys., 1980, 73, 591. G. Inoue and H.Akimoto, J. C/iwi. Ph1.s.. 1981. 74, 425. J. M. Jasinski and J. 1. Brauman. J . Clicw. fl1y.s.. 1980, 73. 6191. B. D. Cannon and F. F. Crim, J. C / m i . P/~ys..1980, 73. 3013. Y. Hirata and E. C. Lim, J. Cllcwi. P / I ~ S1980. .. 72, 5505.

125


states of aryl alkyl ketones have shown that energy flow between carbonyl and ring vibrations is significantly slower for molecules wi!h bulky alkyl groups.58 Deuteriation of ring hydrogens decreases the T , + So ISC rate by a factor of four, a far smaller effect that the three orders of magnitude difference caused by a similar deuteriation in ben~aldehyde.~'An alternative interpretation of the behaviour of vibrationally excited triplet states TI* formed following excitation of acetophenone has been suggested,59 the dissociation step ( 5 ) instead of the conventionally assumed ISC process (6).58 The emission behaviour of 1,4-

C6H,COCH3(Tl*)

-

C,H,eO + e H 3 C6H5COCH3 (so)

(5)

(4)

naphthoquinone and its 2-methyl derivative,60 and the 'dual fluorescence' caused by the two possible forms of intramolecular hydrogen-bonded rotamers of methyl salicylate 6 1 have been investigated.

4 Sulphur-containing Compounds Thiiran, C,H,S, when irradiated at wavelengths > 240 nm, undergoes ISC to T , with high efficiency (a = 0.86).62The triplet state has a long radiative lifetime and is resistant to collisional de-excitation, and can undergo reversible addition to alkenes, inducing their geometrical isomerism without energy transfer and subsequent quenching of the triplet state. Process (7) is believed to take place in the

observed cis-trans isomerism of butene. Product analyses of the U.V. photolyses of tri- and tetra-methylene sulphoxide 6 3 - 64 have been used to model their dissociation pathways. In trimethylene ~ u l p h o x i d e ,the ~ ~ cyclopropane product appears to be formed with a non-random distribution of internal energy, and this has been used to suggest that the SO fragment is formed in the metastable 'A state, reaction (8). Collision-induced electronic quenching of S , thioformaldehyde n

L'

s\. +

'* 59 6o 61

62

63 64

hv

-A

+

SO('A)

Y. Hirdta and E. C. Lim, J . Cltetn. Pliys., 1980, 73, 3804. A. R. Rennert and C. Steel, Clteni. Phys. Lett., 1981, 78, 36. T. Itoh and H. Bdba, Cltem. fhys.. 1980. 51, 179. A. U. Acuna. J. Catalan. and F. Toribio. J. PItys. Cheni.,1981. 85, 241; R. Lopez-Delgardo and S. Lazare, ibid., 1981, 85, 763. E. M. Lown. K. S. Sidhu, A. W. Jackson. A. Jodhan, M.Green, and 0. P. Strausz. J . P1ty.v. Client., 1981, 85, 1089. F. H. Dorer and K. E. Salomon, J . PIiys. Client., 1980, 84, 3024. F. H.Dorer and K. E. Salomon, J. P l i w Clieni., 1980, 84. 1302.

126

Pho t ockcmistry H,CS is seen to dominate over vibrational and rotational relaxation, as the fluorescence spectra of S , show that the species retain their memory of the initially excited rovibronic levels at relatively high pressure^.^^ Fluorescence excitation of jet-cooled thiophosgene, Cl,CS, has been reported.66 Vibrational and rotational energy disposal in the CS(A l7) fragment of the monochromatic V.U.V.dissociation of CS, shows that a high proportion (1530%) of the available energy is found in product vibration, with most or all energetically possible vibrational levels populated.67 Electronic quenching of CS (A'n,v' = 0-5) by CS2 and Xe shows rates which are intensive to v', and too fast to allow collisional rotational and vibrational redistribution, although these relaxation processes do occur for other gases.68Quenching of CS(A l7, u' = 0) by 0 atoms shows a distinct rotational state d e p e n d e n ~ e with , ~ ~ levels which are perturbed by nearby triplet states being selectively removed. A model for quenching via the formation of a collision complex, followed by reaction or ISC, is invoked to explain the observations. Photolysis of CS, at 193nm yields S('D), which has been observed directly by time-resolved resonance fluorescence, and rate constants for quenching of the excited S atom with CS,, OCS, and CH, have been m e a s ~ r e d . 'The ~ primary quantum yield of S( ' D ) was estimated as % I5%, considerably lower than that previously reported by less direct photofragment spectroscopy studies '' at the same wavelength. The co-product of 193nm photolysis, C S ( X ' C + ) , has also been observed.72 In the 193-nm photolysis of H,S, around 20 000 cm - of energy is available for partitioning within the ground-state fragments, yet the SH radical is found to have only -320cm-' internal energy.73 A model for recoil of the departing H atom along the original H-SH bond direction can be used to explain the data: the recoil will be orthogonal to the remaining S-H vibrational mode and this is unlikely to couple effectively to it, and considerations of angular-momentum conservation preclude high rotational-state population in SH. The laser-induced fluorescence technique has been used to study the B3Cu-X3C,- transition in S,, revealing details of the perturbing Bn3nustate,74 and the 2 'A'--f2A'' transition in HSO, with the latter radical formed by reaction of discharged O2 with H,S.75 Fluorescence quantum yields and lifetimes of various sulphur-containing ions have been measured,76 and V.U.V.photoionization efficiencies reported for formation of CS2+ from the parent CS2.77

'

'

" 66

67

68 69 70

7'

72 73 74 75

'' 77

D . J . Clouthier, C. M. L. Kerr. and D. A. Ramsay, Ciicni. PIiys., 1981, 56. 73. R. Vasudev, Y. Hirata. E. C. Lim, and W. M. McClain. Clieni. Phys. Lett., 1980, 76. 249. M. N . R. Ashfold, A. M. Quinton. and J. P. Simons. J . Ciieni. Sot.. Fnrcitkny Trcins. 2, 1980,76, 905. M. N. R. Ashfold, A. M. Quinton, and J. P. Simons, J . Clieni. Sot..Fcircickciy Trcins. 2, 1980, 76, 915. A. J . Hynes and J . H. Brophy, Ciieni. Pliys. Lett., 1980. 75. 52. M. C. Addison, R. J. Donovan. and C. Fotakis. Ciieni. PIiys. Lett., 1980, 74. 58. S. C. Yang, A. Freedman. M. Kawasaki, and R. Bersohn, J . Cliem. Pliys.. 1980, 72, 4058. J . E. Butler, W. S. Drozdoski. and J. R. McDonald. Ciieni. P I i w . . 1980, 50. 413. W. G . Hawkins and P. L. Houston, J . Cheni. Phys., 1980, 73, 297. D. A. Peterson and L. A. Schlie, J . Chem. Phys., 1980, 73, 1551; C. R. Quick, jun. and R. E. Weston, jun., ibid., 1981, 74, 4951. M . Kawasaki, K . Kasatani, and H. Sato. Clicwi. PIiys. Lett., 1980, 75, 128. J . P. Maier and F. Thommen, Clieni. Phys., 1980, 51, 319. Y . Ono, S. H. Linn. H. F. Prest, M. E. Cress. and C. Y. Ng. J . Ciiem. fiiys., 1980, 73. 2523.

127

Gus-phuse Pho toprocesses

5 Nitrogen-containing Compounds Emission accompanying excitation of Hg-NH mixtures with XeI exciplex radiation (253.2nm) has been studied in the Hg pressure range 1-40 Torr.” At low pressures ( < 1 Torr), the familiar U.V.emission of the HgNH, complex at 342nm is seen, whereas at higher Hg concentrations this is replaced by a strong green emission band near 500 nm. Lifetime measurements on this band eliminate Hg3* as the emitter, and its identity is suggested as Hg,NH,*: potential gain on this system does not appear promising as the carrier absorbs throughout the green emission band. Multiple-photon ionization of expansion-cooled NH, has been carried out, with 2- and 3-photon absorption features being identified, and the state confirmed.” Similar studies on previously reported position of the pyrroles 8o and on trimethylenediamine have been reported, with ‘two colour’ excitation demonstrating the usefulness of the technique in elucidating pathways for the resonantly enhanced MPI processes.8’ One-*,, 8 3 and t ~ o - p h o t o nexcitation ~~ of trialkylamines has been observed. For trimethylamine, S1 appears to radiate following excitation at wavelengths where both S , and S2 are populated ”* 8 3 and the fluorescence shows a dual exponential decay at pressure low enough to ensure that collisional relaxation is not of imp~rtance.’~ Relaxation of two different vibronic distributions in S , , one formed directly by excitation, and the other by rapid IC from S,, is invoked to explain this behaviour, with these isoenergetic levels having different fluorescence lifetime^.'^ Rapid quenching of S , trimethylamine by 0, and NO has been interpreted as due to complex formation between the colliding species.’’ Product analyses of the 193 nm photolysis of methylamine show that the major decomposition route involves formation of HCN.86 Single vibrational levels of the ‘ B , state of aniline, formed by excitation within a He-aniline molecular beam, have been shown to relax in low-energy collisions with the He diluent at rates which are markedly dependent upon the identity of the vibrational mode excited.” Intramolecular vibrational energy transfer within the ‘ B , state induced by collision with H,O and CH,F is also mode specific,*’ and rates for these processes are of the same order for these two collision partners and considerably faster than for energy transfer caused by Ar. Within p-alkylanilines, collisionless intramolecular vibrational relaxation from the initially excited NH, inversion mode to the alkyl chain modes appears to be complete within 1 n ~ , ’ ~

e’

’’

’’ A. Mandl and H. A. Hyman, J. Clrem. Phys.. 1981, 74, 3167. 79

’’ 83 84

’’ 86

” 89

J. H. Glownia, S. J. Riley, S. D. Colson, and G. C. Nieman, J. Cliem. Phys., 1980, 72, 5998; J. H. Glownia, S. J. Riley, S. D. Colson, and G. C. Nieman, ibid,, 1980, 73, 4296. C. D. Cooper, A. D. Williamson. J. C. Miller, and R. N. Compton, J. Chem. Phvs., 1980, 73, 1527. K. R. Newton, D. A. Lichtin, and R. B. Bernstein, J. Pliys. Cliem., 1981, 85, 15. Y.Matsumi and K. Obi, Chem. Phys., 1980, 49. 87. C. G. Cureton, D. V. OConnor. and D. Phillips, Clteni. Pliys. Left., 1980, 73, 231. K. Kasatani. M. Kawaskak, H. Sato, Y. Murasawa. K. Obi, and 1. Tanaka, J . Chem. Phys., 1981,74, 3164. K. Obi and Y. Matsumi, Cliem. f l i y s . , 1980. 49, 95. N. Nishi. H.Shinohara, and I. Hanazaki. Clretii. PI7y.s. Lerf.. 1980. 73. 473. J. Tusa, M. Sulkes, and S. A. Rice, J. Clrcm. f I 7 . 1 x . 1980. 73, 5897. M. Vandersall, D. A. Chernoff. and S. A. Rice, J . Cliem. Phys., 1981, 74, 4888. D. E. Powers, J. B. Hopkins, and R. E. Smalley, J. Chcni. Phys., 1980, 72, 5721.

128

Photochemistry

with little vibronic isolation being provided by the benzene ring between these two functional groups. Continuous irradiation of pentafluoropyridine (1) in the near-u.v. forms a product identified as the Dewar isomer (2), which was found to revert to (1) in a period of 5 days." Two short-lived transients, with half lives of 22 and 3 ms were detected by flash photolysis, and assigned to the two fulvene isomers, (3) and (4). Pyrazine excited in its 'B,,(nz*) t ' A , transition shows a marked variation of

-

mF F

F

FfJF

F

F

&F

F&F F

F

F

fluorescence quantum yield over the limited wavelength range of a vibrational absorption band c o n t ~ u r , ~apparently ' due to ISC rates being enhanced with increasing rotational quantum number. A K2 dependence of the non-radiative rate fits the data.92 Rates of collision-induced vibrational energy transfer within 'B,, pyrazine have been measured, with both energy defect considerations and propensity rules being found necessary to explain their observed magnitudes.', Lifetime measurements of various vibrational levels of 'B,(nn*)pyrimidine show that the v 1 totally symmetric ring stretch is the predominant accepting mode for the biexponential fluorescence decay rates observed being explained by mixing of nn* and nn* low-lying states. 9 5 Phosphorescence from pyrimidine has been reported for the first time.96 Photofragment vapour (@ = spectroscopy of sym-tetrazine at 266nm ('B2, t 'A,) shows that one HCN molecule formed [reaction (9)] receives considerable translational excitation, yet C2N,H2 ('B,,)

-

2HCN

+ N,

(9)

the second is translationally co0L9' This suggests stepwise rather than concerted HCN elimination, with the recoil direction (estimated from the angular distribution of photofragments) determined by the parent molecular geometry. Interestingly, photolysis at 532 nm ('B,, + ' A , ) yields exactly the same photodissociation dynamics as at 266nm, implying that a two-photon absorption step is necessary 90

" " 93 '4

" '6

''

E. Ratajczak, B. Sztuba, and D. Price, J . Pliotochem.. 1980, 13, 233. H . Baba, M . Fujita, and K. Uchida, Clirm. P l i j x Left., 1980, 73, 425. G. ter Horst, D. W. Pratt. and J. Kommandeur, J . Chem. Phys., 1981,74, 3616. D. B. McDonald and S. A. Rice, J . Clieni. Pliys., 1981, 74, 4907. A. K. Jameson and E. C. Lim, Chem. Pliys. Leff., 1981, 79, 326. W. A. Wassam and E. C. Lim, Clieni. Pliys., 1980, 48, 299. T. Takemura, K. Uchida, M. Fujita, Y. Shindo, N . Suzuki. and H. Babd. Cliem. Phys. Lett., 1980,73. 12. J . H . Glownia and S. J. Riley, Clieni. Plijx Lett., 1980, 71. 429.

Gas-phase Photoprocesses 129 for decomposition in the visible, and that the truly isolated B,, state of tetrazine is photochemically stable.” For dimethyltetrazine, fluorescence quantum yield measurements have shown that although decomposition is observed following visible excitation, it does not take place directly from the ‘B,, state, and that an intermediate (and unidentified) state is involved.98aFurther low-pressure studies on these systems will clearly be stimulated by these observations. The wavelength dependence of the quantum yield of I(2P,) formation in the photodissociation of ICN has been measured in the region 240-280 nm.98bFigure 2 shows the ICN absorption spectrum in this region (the A continuum), together

’

100

80 W

--

I

’

-

60-

;L’

B

5

C .c a8 L

g

40

1

A’

ii

-

‘0

/. ’‘o-l a\

1

! \

-

O,

/ 20-

- ,ooor I O3.5

\. \.

\ ; \=\

/

/

-

’ ’

.@A\.

/./ ,-‘

c

.g

‘Pi’ I

/

‘ 0

1

-\ ‘ 0

I 37

I

I

39

1

-I

41

-

-0

I

I

43

I 45

with the contribution to this from dissociation to form I(’P+) [the product of E~~~ and the I(’p+) quantum yield], and the difference between these two curves, with the last of these giving the contribution from dissociation to ground-state I atoms (2P3,2).As can be seen from the Figure, at least three electronic states are responsible for the A continuum absorption in ICN. Vibrational and rotational energy disposal in the CN(A211iand BZZ+)products of v.u.v. photodissociation of ClCN, BrCN, and ICN has been determined from observations of fragment 98

99

(a)M . Paczkowski, R. Pierce, A. B. Smith, and R. M. Hochstrasser, Chem. Ph-vs. Lett., 1980, 72, 5; (6) W. M. Pitts and A. P. Baronavski, hid.. 1980, 71, 395. M. N.R. Ashfold, A. S. Georgiou, A . M . Quinton, and J. P. Simons, J. Chem. Sor.. Faraday Trans.2, 198 1, 77, 259.

130

Photochemistry

fluore~cence,~~ The nature of the cyanogen halide excited state (either directly dissociative, formed by an intravalence electronic transition, or predissociative, formed via a Rydberg transition) influences these energy distributions, and qualitatively the Franck-Condon description of the dissociation process explains the data.99Cross-sections for CN production in the 105-155 nm dissociation of HCN have been measured,loOand several calculations have been carried out of energy disposal following dissociation of bent and linear triatomic molecules, with specific application to those fragmenting to give CN. lo' Photolysisof cyanogen has been used to produce CN(A211i) and to observe the B2C+ t A211 transition by laser-induced fluorescence. O 2 Vibrational and rotational distributions in N0(217) formed in the visible photodissociation of CF,NO have been measured.l o 3 The NO production rate is equal to the rate of decay of excited CF,NO molecules (the fluorescence lifetimes of which have been recently determined lo4) showing that although predissociation of the initially populated CF,NO(A) state results in the photofragments, no long-lived intermediate state is involved: 95% of the NO product is formed in u = 0, and vibrationally excited state populations do not fit a linear surprisal plot, possibly indicating the existence of more than one predissociation mechanism. Vacuum-u.v. photolysis of CF2CIN0, leading to formation of electronically excited NO and CF, radicals, has been reported."' The near-u.v. photolysis of methyl nitrite yields methoxy radicals [equation (lo)] with a quantum yield of unity.lo6 Reaction rate constants of CH,O with 0, CH,ONO

+ hv

-

CH,O

+ NO

(to yield formaldehyde+ HO, lo6) and NO (forming HNO, detected by laserinduced fluorescence lo') have been measured. Vacuum-u.v. photolysis of CH,ONO yields NO in the A 2 Z + , C 2 n , and D 2 Z + states (albeit with low quantum yields lo'), and the distributions of energy within the vibrational levels of NO (A'C') produced by photolysis of this l o g and other nitrites ' l o have been discussed in terms of statistical models of energy partitioning. Dimethylnitrosoamine, excited to S , by absorption at 363.5nm, dissociates with unit quantum yield to form NO, and vibrational excitation in the product has been detected by i.r. emission.l 1 U.V. photolysis of HN, at wavelengths around 290nm yields metastable NH (a'A), and observations of the rate of removal of this species (by laser-induced fluorescence) have resulted in a rate constant for reaction (1 1) of NH(a'A) loo

lo3 lo4 lo'

Io6 lo'

lo' lo9

'lo

+ HN,

A

NH2(A2Al)+ N,

(11)

L. C. Lee, J . Chem. Phys., 1980, 72, 6414. M. D. Morse and K. F. Freed, Chem. Phys. Lett., 1980, 74, 49; M. D. Morse and K. F. Freed, J . Chem. Phys., 1981, 74, 4395; K. Takatsuka and M. S. Gordon, ibid., 1981, 74, 5718, 5724. C. Conley, J. B. Halpern, J. Wood, C. Vaughn, and W. M . Jackson, Chem. Phys. Lett., 1980,73,224. M. P. Roellig, P. L. Houston, M. Assher, and Y. Haas, J . Chem. Phys., 1980, 73, 5081. K. G. Spears and L. D. Hoffland, J . Chem. Pl7y.s.. 1981,74. 4765. C. A. F. Johnson and H. J. Wright, J . Chem. SOC., Faraday Trans. 2, 1980,76, 1409. R. A. Cox, R. G. Derwent, S. V. Kearsey, L. Batt, and K. G . Patrick, J . Phorochem.. 1980. 13, 149. N. Sanders, J. E. Butler, L. R. Pdsternack, and J . R. McDonald, Chem. Phys., 1980, 48, 203. F. Lahrnani. C. Lardeux, M. Ldvollke, and D . Solgadi, J. Chem. Phys., 1980, 73, 1187. F. Lahrnani, C. Lardeux, and D. Solgadi, J . Chem. Phys., 1980,73, 4433. F. Lahmdni, C. Lardeux, and D . Solgddi, J . Photochem., 1981, 15, 37. G. Geiger, H. Stafast, U. Bruhlmann, and J. R. Huber. Chem. Phys. Left., 1981, 79; 521.


131

1.8 x 10-'ocm3 molecule-'s-' l 2 Absolute cross-sections for the absorption of HNO,, and quantum yields for the formation of OH('C) in the wavelength region 110-190 nm have been reported,'13 the excess energy in the OH* fragment appearing mainly in rotation with an approximately Boltzmann distribution, in sharp contrast with that for dissociation of H,O and H,O, at the same wavelength. Laser-induced fluorescence of the J1At'-z1A' transition in the HNO radical has been comprehensively studied, with the predissociation mechanism evaluated from the observed S (but not K' or u') dependence of the fluorescence quantum Finally in this Section , the fluorescence excitation spectrum of phthalocyanine in a supersonic-free jet has been analysed, with vibrational structure in this large molecule resolved for the first time,"' and studies of exciplex formation l 6 and quenching behaviour ' of 9,lO-dicyanoanthracene have been reported.

'

6 Halogen-containing Compounds In the 248 nm photolysis of methyl iodide, i.r. fluorescence from the CH, fragment has shown that this is formed with vibrational excitation in the out-of-plane bending mode, but that higher frequency C-H stretching modes are not A calculation for this dissociation process using an assumed populated. potential energy surface for the excited CHJ state implies that the vibrational distribution in the CH, 'umbrella mode' peaks at u = 2, and the results are seen to fit recent photofragment spectroscopy measurements of the total fragment internal energies in CH,I photolysis.119Quantum yields for the production of I(,P+) from CH,I and CH,I, have been measured at 248 and 308nm: at the former wavelength, i.r. emission from the CH,I product in CH,I, photolysis was seen, peaking near the C-H stretching and CH, bending vibrations, but present at all other i.r. wavelengths, indicating that the fragment is produced with excitation into a high density of internal states, nearing the vibrational quasicontinuum.' l 8 I, elimination does not appear to be of importance in the near-u.v. photolysis of CH,I,,120 although some emission from excited I, (3nau) is seen in photolysis at V.U.V. wavelengths.12' From studies of the 147nm photolyses of CH,CHCl,, and CH,ClCH,Cl evidence is presented for the elimination of 2 C1 atoms, either simultaneously, or by C1,* formation and subsequent decomposition. Photolyses of HCC1, in the u.v.',, and of vibrationally excited cations of fully halogenated methanes by i.r. radiation 124 have been studied, and the spectral 'I2 'I3

'I4 'I5 'I6

'I7 'I8

'I9 12' 122

L. G. Piper, R. H. Krech, and R. L. Taylor, J . Chem. f l i p . , 1980, 73, 79. H.Okabe, J. Chem. fIiys., 1980, 72, 6642. R. N. Dixon, K. B. Jones, M. Noble, and S. Carter, Mol. fliys., 1981, 42, 455. P. S. H. Fitch, C. A. Hayndm, and D. H. Levy, J . Chem. fliys., 1980, 73, 1064.

S . Hirayama and D. Phillips, J. fhys. Chem., 1981, 85, 643. S. Hirayama, Chem. fliys. Lett., 1981, 79, 174. S. L. Baughcum and S. R. Leone, J. Chem. fhys., 1980, 72, 6531. M. Shapiro and R . Bersohn, J. Chem. fhys., 1980, 73, 3811. G. Schmitt and F. J. Comes, J. fhotochem., 1980, 14, 107. H. Okabe, M. Kawasaki. and Y. Tanaka, J. Cliem. fhys., 1980, 73, 6162. T. Yano, K. H. Jung, and E. Tschuikow-Roux, J. fliys. Cliem., 1980, 84, 2146; T. Yano and E. Tschuikow-Roux, ibid, p. 3372. S . Hautecloque, J. fhofochem., 1980, 14, 157. M.J. Coggiola. P. C. Cosby, and J. R. Peterson, J. Chem. fliys., 1980, 72, 6507.

132

Photochemistry

dependences of I('P*) and ( , P 3 , 2 ) formation in the photolyses of various perfluoroalkyl iodides have been reported.' 2 5 Intramolecular redistribution in S , p-difluorobenzene 'has been studied directly by observations of the fluorescence spectra in the presence of increasing concentrations of an efficient electronic quenching gas (in this case, 0,). 2 6 Under these conditions, emission is observed only from molecules that radiate during the interval between absorption and quenching, which, at high pressures of added gas (up to 30 kTorr), can be reduced to the ps time scale. Redistribution of vibrational energy is seen to take place with a rate constant of 10' s- 1 . 1 2 6 Spectroscopic and kinetic studies of several triatomic halogenated carbene radicals have been reported in the past year, with detection of these in their ground electronic states by laser-induced fluorescence a common experimental technique. X'A' C H F has been formed by infrared multiple-photon dissociation of CF,HCI, with the laser excitation spectrum of the J ' A " - f ' A ' transition recorded, and radiative lifetimes of four vibronic states measured to lie in the range 1.92.5 p.'2 7 Emission has been seen from HCF and DCF produced electronically excited in methane-F, flames. '2 8 Reaction rates of ground-state CFCl and CCl, radicals with various scavengers ' 29, 30 have been reported, with the radicals generated either by U.V.photodissociation of a suitable halogenated hydrocarbon,'29 or, in the case of CFCl, by chemical reaction between oxygen atoms and CF,CFCI:'30 laser-induced fluorescence was used in both cases to monitor the radical concentrations. For the CFCl + NO reaction (the only one common to both studies for which a removal rate was quantitatively determined), rate constants differing by almost an order of magnitude have been reported, 1 x 10- l 4 and 1.4 x 10- l 5 cm3molecule- s- (refs. 129 and 130, respectively). The radiative lifetime of the A state of CFBr has been measured as 1 150 & 50 ns,' and U.V.emission from the corresponding state of CF, seen in reactions of metastable He atoms with CF,CI,.' 32 The dissociation of several alkali halides in the near U.V.has been studied by three different groups using the technique of photofragment spectroscopy.' 3 3 - 3 5 Contributions to the absorption spectrum from parallel and perpendicular transitions (corresponding, at least for the heavier halides, to upper electronic states with quantum numbers fi = 0 or 1) can be determined from the anisotropy of the dissociation yield with respect to the polarization of the laser beam, and this has been accomplished for KI and NaI (300-337nm),'33 KBr and NaBr (265310nm),'33 Na, K, Rb, and Cs iodides at 347.1 nm,134 and the corresponding chlorides at 266 nm. 35 Dissociation energies for several of these molecules have been reported.' 3 3 * ' 35 Photodissociation of HgBr, at 193nm yields excited HgBr

'

-

'

'

'

'

'

125

Iz6

I29

V. S . Ivanov, A. S. Kozlov, A. M . Pravilov. and E. P. Smirnov, Kvantovayo Electron., 1980,7, 993. R. A. Coveleskie, D . A. Dolson. and C. S. Parmenter, J . Chem. Phys., 1980, 72, 5774. M . N. R. Ashfold, F. Castano, G. Hancock, and G. W. Ketley, Cltem. Pltys. Lett.. 1980, 73, 421. R. I. Patel, G . W. Stewart, K. Casleton, J. L. Cole, and J. R. Lombardi, Cliem. Phys., 1980,52,461. J. J . Tiee, F. B. Wampler, and W. W. Rice, Clrem. Pltys. Lett., 1980, 73, 519. H. Meunier, J. R. Purdy, and B. A. Thrush, J. Clirm.Soc., F(imday Trans. 2 , 1980, 76, 1304. J. R. Purdy and B. A. Thrush, Chem. Phys. Lett., 1980.73. 228. T. Ishiguro, Y. Hamada, and M. Tsuboi, Bull. Chern. Soc. Jpn., 1981, 54, 367. N. J. A. van Veen, M. S. de Vries, J. D. Sokol, T. Bailer, and A. E. de Vries, Cliem. Pliys., 1981,56,81. W. R. Anderson, B. M . Wilson. R. C. Ormerod, and T. L. Rose. J . Cltem. Phvs., 1981, 74, 3295. T. M. R. Su and S. J . Riley, J . Cliem. Phys., 1980, 72, 6632.

*'' 135

Gus-pkusse Photoprocesses

133

(B'C') with almost unit quantum yield, 136 and the nascent vibrational distributions of both HgI and HgBr from photolyses of the corresponding dihalides at this wavelength have been determined. 3 7 The distributions were separable into relative contributions from processes forming ground-( 2P3,2)and excited-(,Pt) state halogen atoms, X: production of X( P312) was accompanied by vibrational population inversion in HgX(B), and X('P,) by a Boltzmann-like HgX(B) state distribution. Quenching of the vibrational levels of HgBr(X) with He has been shown to be an efficient process, and thus the HgBr (B + X ) laser can extract energy efficiently if He is present to remove the terminating laser level by vibrational relaxation. '38 Another publication describing laser action on this transition has appeared. 39 Photofragment spectroscopy of thallium halides has helped characterization of the upper electronic states involved in the U.V.absorption spectra.14' For TIBr, photolysis at I93 nm produced population inversions in neutral TI transitions, and photon efficiency) has been r e ~ 0 r t e d . l ~Two-photon ' lasing (with 2 x absorption of KrF radiation at 248 nm by InCl and InBr yields excited states of In,142and similar processes take place in the 193nm photolysis of SnI,, SbI,, Ge14,'43 PbI,, and PbBr,.'44 One- 145 and two-photon 146 absorption processes in UF, have been studied in some detail, with the quenching behaviour of the fluorescent state(s) produced being, not surprisingly, somewhat complex. This year's group of publications upon the rare-gas halides includes a careful study of the ordering of the B and C states in XeCI, XeBr, and KrCl by observation of the temperature dependences of the C + A and B + A emission^.'^^" For KrCI, the alphabetic ordering of the states is confirmed, whereas the B state is found to lie above the C for the xenon halides.147uThe value of E,--E, for XeC1,'47u -130 & 35cm-' differs considerably from that estimated from XeCl fluorescence measurements carried out at room temperature, 5.4 &- 25cm- 1.1476 The determination of the correct ordering of these states is of some importance, not only for overall modelling of the rare-gas halide laser systems, but also because if the C state lies sufficiently below the B, then lasing on the C -+ A transition becomes possible, as has been shown in the successful operation of the XeF (C + A ) laser at 470 nm. Measurements of the polarization of fluorescence from XeF(B) produced by 193nm photolysis of XeF, has been

'

136

13' ''13

140

14' 14' 144

lo5

'46

14'

B. E. Wilcomb, R. Burnham. and N. Djeu, Client. Pliys. Lett., 1980, 75. 239. J. A. McGarvey. jun., N. H. Cheung, A. C. Erlandson, and T . A. Cool, J. Client. Pliys.. 1981, 74. 5133. H. Helvajian and C. Wittig, Appl. Pliys. Lett., 1981, 38, 731. R. T. Brown and W. L. Nighan. Appl. PIiys. Lett., 1980. 37. 1057. M. S. de Vries, N. J. A. van Veen, T. Baller, and A. E. de Vries. Client. Pliys. Lett., 1980, 75, 27; N. J. A. van Veen. M. S . de Vries, T. Baller, and A. E. de Vries, Cliem. Pliys., 1981, 55. 371. P. Burkhard. W. Liithy. and T. Gerber. Opt. Commun., 1980, 34, 451. T. A. Cool and J. B. Koffend. J. Clieni. Pliys.. 1981, 74. 2287. H. Hemmati and G. J. Collins. IEEE J. Quantum Electron., 1980, 16, 1014. H. Hemmati and G. J. Collins. IEEE J . Quantum Electron.. 1980. 16, 594. E. Borsella, F. Catoni, and G. Freddi, J. Cliem. Pliys., 1980.73, 316; W. W. Rice, R. C. Oldenborg, P. J. Wantuck. J. J. Tiee. and F. B. Wampler. ibid., p. 3560; K. C. Kim, M. Reisfeld, and D. Seitz, ibid.,p. 5605. E. R. Bernstein and P. M . Kennedy, J. Cliem. Pliys., 1981, 74, 2143. (a)J. Tellinghuisen and M.R. McKeever. Client. Pliys. Lett., 1980, 72, 94; ( h ) J . Bokor and C . K. Rhodes, J. Client. Pliys., 1980. 73, 2626.

134

Photochemistr~*

used to suggest the symmetry of the parent molecule's dissociative state Collisional depolarization and electronic quenching rates for the XeF(B) state were determined in this and formation and quenching processes involved in the XeCI(B) state have also been investigated.'49 Lasing has been seen from the Kr,F exciplex at 430nm,'50 and emission spectra have been recorded from various mixed rare-gas halide trimers (e.g. KrXeCI). ' ' Vibrational relaxation of I, (311,,+)in very low-energy collisions with He and Ne in a seeded molecular beam is found to be an extremely efficient process, with cross-sections at least as large as hard-sphere collision values.'s2 Models incorporating orbiting or rotational resonances of the colliding pair are found to fit the data, and it is suggested that this mechanism will be quite a common one for relaxation process at low energies. 5 2 Excitation and dispersed fluorescence spectra of several van der Waals molecules containing I, have been reported. 1 5 3 - 1 5 5 For I ,Ar,Heb complexes, additivity rules predict the shift of the absorption band from that of free I, to be of the form Aa + Bb, where A and B are constants (in contrast to the behaviour described earlier in this Report for pentacene complexes2). An increase in the number of rare-gas atoms in the complex resulted in a more than proportional increase in the number of vibrational quanta per rare-gas atom required for dissociation.' 53 Evidence for anisotropy in the intermolecular potential between I, and H, has been found from similar studies on the 12-H2 complex, with different absorption spectra seen for ortho- and para-H,, and different product-state distributions observed when orthoand para-H, complexes predissociate.' 5 5 For o-H,--I,, the relatively high van der Waals stretching frequency (100cm- ') couples well with the I, vibrational frequency (128 cm- ' in the B state), and hence makes vibrational predissociation rapid, an 18 ps lifetime being obtained from bandwidth measurements. The influence of rotations upon the vibrational predissociation rate of the HeI, complex has been explored theoretically.' 5 6 30% Conversion of 193 nm photons to 342 nm laser output in molecular iodine has been found in irradiated I,-SF, mixtures. " Relatively high pressures of buffer gas, to induce collisional energy transfer from the initially populated D state to the lasing 3112e levels, is the key to achieving high efficiencies.'s7 Recombination of I atoms formed by photolysis at 694.3 nm at relatively high pressures (up to l00atm.) of various buffer gases has been used to test models of the cage effect, and to determine second-order rate constants for atomic recombination. 5 8 Photofragment spectroscopy of the products of multiple-photon ionization has

'

'

'

'41 149

Is' Is'

153

is4

Is'

Is6 Is'

Is'

G . W. Loge and J. R. Wiesenfeld, Client. Pliys. Left., 1981, 78. 32.

T. G . Finn, R. S. F. Chang. L. J . Palumbo. and L. F. Champagne, Appl. Phys. L e f t . , 1980,36, 789. F. K . Tittel, M . Smayling. W. L. Wilson, and G. Marowsky. Appl. Pliys. Lerf.. 1980, 37, 862. H . C. Brashears, D. W. Setser, and Y. C. Yu, J . Climt. P/I.I~.Y.. 1981. 74. 10. M. Sulkes, J. Tusa. and S. A. Rice, J . Chm7. Phys., 1980, 72, 5733. K. E. Johnson, W. Sharfin. and D. H . Levy, J . CIi~ni.PIiys., 1981, 74. 163. K. E. Johnson and D. H . Levy, J . CIwrn. Pliys., 1981. 74. 1506. J . E. Kenny, T. D. Russell, and D. H . Levy, J . Clwm. Pliys.. 1980, 73, 3607. J. E. Beswick and G . Delgardo-Barrio, J . C h m . Phys., 1980. 73, 3653. M . J. Shaw, C. B. Edwards, F. O'Neill, C. Fotakis, and R . J. Donovan, Appl. Phys. Lett., 1980.37. 346. J. M . Zellweger and H . van den Bergh. J . Cliem. Pltys., 1980.72, 5405.

135

Gus-phuse Plwropr.oc*esses

been achieved, with positive and negative ions and neutral products observed in the high-intensity irradiation of I, in a molecular beam. l s 9 Extensive studies of the kinetic behaviour of the B3lIo,,+states of Br, and C1, have been reported.16'- 1 6 5 For Br,, rates of electronic quenching and internal energy transfer within the B state have been measured for several collision partners, 6o with the role of collision-induced predissociation responsible for removat of Br,* molecules discussed in detail.'60 The absence of fluctuations in the experimentally observed fluorescence lifetimes of predissociating states as a function of vibrational quantum number can be explained if the repulsive parts of the potential curves of the bound and predissociating states are approximately parallel, and an analytical interpretation of the predissociation behaviour under this assumption has been presented.16' Radiative lifetimes of the B states of Br, and C1, are 12.4 162 and 305 164* 165 ps, respectively, and the dependence of predissociation rates upon rotational quantum number in these states has been explored and shown to be consistent with a heterogenous predissociation mechanism involving the B state and one or more 'n(1u)states.'63*1 6 5 Discharge pumping of mixtures of NF,, CF,l, and rare gases gives rise to laser action between 480--490nm on the E -+ A(311) transition in IF.'66 Franck-Condon pumping of the B state of IF (formed in the I, + F, reaction) with a broad-band laser source at 500 nm results in red-shifted stimulated emission between 650-720 nm.' 67 Photofragment spectroscopy of ICl and IBr ,has provided Landau-Zener parameters for avoided crossings within the excited states of these molecules, and, in ICl, resolution of transitions originating from different vibrational levels of the electronic ground state has provided some information on the repulsive part of the 311potential curve.168Radiative lifetimes have been measured 169 and a and collisional relaxation rates of BrF(B 3110+) detailed report on the dependence of the isotopically selective addition of ICl(A311) to acetylene on buffer gas pressure and excitation wavelength has appeared. 70 Relaxation of the ,P, states of I and Br 1 7 2 in collisions with H, has been studied by optoacoustic spectroscopy 7 1 and by i.r. emission techniques,' 7 2 respectively. The optoacoustic method allows determination of whether translational energy is absorbed or released in the collision process, and with H, it is found that absorption occurs, i.e. there is net translational cooling. The formation

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'"

159

'6l 16' 16'

164 165

'" '61

17' 17'

'

M. S. de Vries, N. J. A. van Veen, T. Baller. and A. E. de Vries, Client. PIiys., 1981. 56. 157. M . A. A. Clyne, M. C. Heaven, and S. J. Davis, J . Clieni. Soc., Furadciy Trans. 2, 1980, 76, 961. M. S. Child, J . PIiys. B . . 1980. 13, 2557. M. A. A. Clyne. M. C. Heaven, and E. Martinez. J . Clieni. Soc., Furaday Truns. 2, 1980, 76, 405. R. Luypaert. G . de Vlieger, and J. van Craen, J . Clieni. f l i p . , 1980, 72, 6283. M. A. A. Clyne and E. Martinez, J . Cliem. Soc., Fnrnduy Trcins. 2, 1980,76, 1275. M. A. A. Clyne and E. Martinez, J . Clieni. SOC..Faraduy Trans. 2, 1980,76, 1561. R. J. de Young, Appl. Pliys. Lett., 1980,37,690; M . L. Dlabal. S. B. Hutchinson, J. G. Eden, and J. T. Verdeyen, ibid.. p. 873. S. J. Davis and L. Hanko, Appl. P1ty.v. LRtt., 1980. 37, 692. M. S. de Vries. N. J. A. van Veen. M . Hutchinson, and A. E. de Vries. Client. Pltjs., 1980. 51, 159. M. A. A. Clyne and J. P. Liddy. J . Climi. Soc.. Furaduy Truns. 2, 1980, 76, 1569. M . Stuke and E. E. Marinero. Bcr. Birrisenges. Pliys. Clieni., 1980, 84. 657. T. F. Hunter and K. S. Kristjansson, Cliem. PIiys. L ~ t t . 1980, , 75. 456. D. J. Nesbitt and S. R. Leone, J . Climi. P1ij.s.. 1980. 73, 6182.

136

Photochemistry

of H,(v = 2) by the slightly endothermic process (12) is thought to be responsible. ' 7 1 An efficient near resonant E- Venergy transfer also takes place in the

0) ---+ I(,P3/,) + H,(u = 2), A E = 119cm-' (12) Br('P+)-H, system, and measurements of the rates of quenching of Br(,P+) with H, need to take the formation of the equilibrium process (13) into a ~ c 0 u n t . l ~ ~ I('P,)

+ H,(v

=

+

Br(2P,) + H2(u = 0) Br(,P,/,) H,(u = 1) (13) When this is done, a rate constant for the forward process of 6.3 x 10- cm3 molecule- s- is obtained, and discrepancies in the previously reported values are probably due to neglect of the reverse processes taking place.172 For the corresponding ,P, state in atomic fluorine, diode laser measurements of the absorption cross-section of the ,P, t 'P3/, transition at 404 cm - ' yields a radiative lifetime of 660 s for the upper spin-orbit state.' 7 3

'

7 Atom Reactions Associative ionization of Na atoms [equation (14)] takes place in the presence of laser radiation tuned to either member of the sodium D line doublet Na(3s)

+ Na(3s) + 2hv1 Na(3p) + Na(3p)

-

Na(3p)

----+

Na'

Na,'

+ Na(3p) +e

]

(14)

(*P+,3/2 +- 'S,).' 74 However, at moderately high laser powers, when the 3p t 3s transition is saturated, a further photon is seen to be absorbed from the field. A true laser-induced ionization process (15) forming N a + is thought to be 2Na(3s)

+ 2hv1 + hv,

+ Na + e

(1 5 )

responsible for this, with resonant photon absorption hv, by both colliding partners followed by absorption of another photon hv, during the course of the collision. Enhancement of N a + formation was also observed when v2 was tuned off resonance with the 3p t 3s transition. 74 The ion-exchange process (1 6 ) has

H+

+ Na

--+

H(n = 2)

+ Na+

(16)

also been found to be enhanced when Na is in the 3p state, and this has been studied as a function of relative kinetic energy of the colliding pair.175Measurements of E-V exchange between Na(3p) and CO show the final distribution of vibrational levels in CO is near Poisson, peaking at u = 2, and is insensitive to effects of temperature. 76 The results are consistent with a curve-crossing mechanism, involving the formation of a N a +CO- ionic complex. Flames of H,-0,-N, containing Na can lead to chemical reaction between excited Na states (2P+,3,2)and H,O or H2.177 Measurements of Na atom concentrations via laserinduced fluorescence of the 3p-3s transition can thus be affected by substantial chemical removal of the 3p atom population, and this needs to be taken into

'

173 174

17' 17' '77

A. C. Stanton and C. E. Kolb, J . Cliem. P1i.w.. 1980, 72, 6637. J. Weiner and P. Polak-Dingels, J . Cliem. Pliys.. 1981, 74, 508. V. S. Kushawaha, C. E. Burkhardt, and J. J. Leventhal, Phys. Rev. Lett., 1980, 45, 686. D. S. Y. Hsu and M . C. Lin, J . Cliem. Phys., 1980, 73, 2188. C . H . Muller, 111, K. Schofield, and M . Steinberg, J . Cliem. Pliys., 1980, 72, 6620.


137

account, particularly when saturated absorption of laser radiation is used as a quantitative probe of atom concentrations.' 7 7 Studies on the higher members of the alkali family include measurements of rates of quenching of the spin-orbit states of several atomic levels of Rb 7 8 - ' and Cs, 'O with, in the case of 5,P +, 3,2 Rb, the temperature dependence of the cross-section in collisions with CH, and its deuteriated derivatives indicating that quenching takes place via an E-R energytransfer process. 7 8 Quenching of Mg(3s3p3PJ)by H, is found to increase sharply with temperature Inefficient E to V, R energy transfer is thought to take in the range 612-841 K. place in competition with chemical reaction to form MgH, with the activation energy for the latter process being equal to the reaction endothermicity. Theoretical studies of this process indicate that side attack of Mg* on the H-H bond is favoured. 8 2 Electronic energy redistribution in collisions between two excited Mg atoms ( 3 P J )has been studied, with consideration given to its effect upon limiting the energy-storage capabilities of possible Group I1 excimer lasers at relatively high excited-atom densities.183 Electronic energy partitioning in chemical reactions of Mg* and Ca* ( 3 P )with F, and C1, has been measured (with the results not in accord with those expected on adiabatic correlation arguments),' 84 and rates of quenching of the Ca* ( 3 P ) state by Ca, Mg, and inert gases have been determined by a phase-shift method. 8 5 The near resonant spin-forbidden energy-transfer process (17) is found to be efficient, with the 3 P , state

'

'

'

'"

'

'

Ca(4s5p'P1)

+ Ar

---+

Ca(4s5p3P,,,,,)

+ Ar

preferentially populated with a state-specific rate constant of 5.2 x 10- l 1 cm3 molecule-' s - '.lg6 Rates for similar processes involving4s4p 'P and P states of Ca and Sr have also been measured. l g 7 Chemiluminescence in the reactions of metastable ('D) Ca with 0, 18' and of Ca and Sr with HCl has and Sr 192 been observed, ground-state reactions of Mg with FOz 190 and Ba with hydrogen halides have been reported, and the Hanle effect has been used to measure the lifetime of the 5d6p 3D, state of Ba (10.2 ns). 193 Spin-forbidden quenching of Cd (5S5p1P1) to the metastable 'Po, l , z levels occurs with high efficiency for many collision partners, despite the existence of several energetically available chemical or additional energy-transfer processes. 194

'''

184

190

19* 193 194

R. A. Phaneuf and L. Krduse, Can. J . Phys.. 1980, S8, 1047. M. Glodz, J. B. Atkinson, and L. Krause, Can. J. Chem., 1981, 59, 548. P. Munster and J. Marek, J . Phys. El., 1981, 14, 1009. W. H. Breckenridge and W. L. Nikolai, J . Chem. Phys., 1980, 73, 2763. N. Adams, W. H . Breckenridge, and J. Simons, Chem. Phys.. 1981,56, 327. W. H. Breckenridge, W. L. Nikolai, and J . Stewart, J . Chem. Phys.. 1981, 74, 2073. A. Kowalski and M. Menzinger. Chem. Phys. Lett., 1981, 78, 461. R. J. Malins and D. J. Benard, Chem. Phys. Lett., 1980, 74, 321. W. H. Pence and S. R. Leone, J . Chem. Pliys.. 1981,74, 5707. J. J. Wright and L. C. Balling, J . Chem. Phys., 1980, 73, 1617. J. A. Irvin and P. J. Dagdigian, J . Chem. Phys., 1980, 73, 176. U. Brinkmann, V. H. Schmidt, and H. Telle, Chem. Phys. Lett., 1980, 73, 530. R. D. Coombe and R. K. Home, J . Pliys. Chern., 1980,84, 2085. A. Gupta, D. S. Perry, and R. N. Zare, J . Chem. Phys.. 1980,72,6237; A. Siege1 and A. Schultz, ibid., p. 6227. A. Gupta. D. S. Perry, and R. N. Zare, J. Chem. Phys., 1980, 72, 6250. G. Brink, A. Glassman, and R. Gupta, Opt. Commun., 1980,33, 17. W. H. Breckenridge and 0. K. Malmin, J . Chem. Phys., 1981,74, 3307.

138

Photochemistry Chemical reaction does take place with H2,1g5 producing CdH ( v = 0) in rotational states well represented by a Boltzmann distribution at a temperature of 5200 K. Rate constants for quenching of Cd(3P0,,)lg6 and lifetime measurements of several excited Cd states have been reported. Spin conservation is not seen to be a major constraint in the quenching of Zn (43P1) by ground-state Ca, with states with approximateelectronic energy exchange creating Ca (4lP,) and (53s1) ly equal probability. 198 Quenching rates of Hg(3P,) with several simple gases have been measured from deconvolution of the P, fluorescence decay curves, lg9 and a conventional photochemical separation scheme of Hg isotopes, in which iHg(3P,), excited in an isotopically selective fashion by 253.7 nm radiation from a iHg lamp, reacts with hydrogen halides, has been revitalized, with the authors pointing out a timely reminder to all those who carry out laser isotope separations that experiments of a similar nature were being successfully carried out almost fifty years ago.200 Fluorescence from electronically excited fragments formed in collisions of rotor accelerated beams of metastable rare-gas atoms with Br, and BrCN has been measured and used to probe the mechanisms of the processes involved. Polarization of fluorescence from KBr (B) and Br,*, produced in the Kr(3P,,o) + Br, system shows that rotational alignment perpendicular to the relative velocity vectors of the colliding partners is retained in both inelastic and reactive scattering processes.2o' No such polarization is observed in the fluorescence of CN(B2Z+) formed in reaction (18), and this can be explained by a two-stage harpooning Xe(3P2,0)+ BrCN

Xe('So)

+ CN(B2C+) + Br

(18)

mechanism, in which an excited (Xe+CN-)* intermediate is formed.,', More conventional studies have measured vibrational and rotational distributions in electronically excited CN formed in the reaction of BrCN with metastable Ar (3P0,,).,03 Calculations of the potential curves of ArH have been carried out, with estimates made of curve-crossing parameters for the states involved in the rapid quenching process of metastable Ar( P) with H atoms.204 Penning ionization predominates in the quenching of Ne and Ar (3P0,2)by Hg, whereas for Kr(3P,), excitation transfer to metastable Hg(3P,) is the major step. All processes take place with very large c r o s s - s e ~ t i o n s .Penning ~~~ ionization is also observed in collisions between metastable He(23s) and Ne(3Po,,) with CS 206 and CS2.207 Reactions of Xe(3P,) with various Br- and I-containing species, leading to 195

196

'91

19' 199

'O0 '01

'O' '03 *04 '05 '06 '07

W. H. Breckenridge and D. Oba, Chem. Phys. f u t t . , 1980,72,455. H.Umemoto, T. Kyogoku, S. Tsunashima, and S. Sato, Chem. Phys., 1980,52, 481. B. Cheron, J. Jarosz, and P. Vervisch, J . Phys. B., 1980, 13, 2413; M. Chantepie, J. L. Cojan, J. Landais, and B. Laniepce, J . Phys. Lett., 1980,41, L433; H. Kerkhoff, M.Schmidt, U. Teppner, and P. Zimmermann. J . P h p . B.. 1980, 13, 3969. R. D.Coombe, F. J. Wodarczyk, and R. K. Home, J. Chem. Phys.. 1981, 74, 1044. T. Hikida, M. Santoku, and Y. Mori, Rev. Sri. Instrum., 1980,51, 1063. C. R. Webster and R. N. Zare, J . Phys. Chem., 1981, 85, 1302. R. J. Hennessy and J. P. Simons, Chem. Phys. Lett., 1980. 75. 43. R.J . Hennessy, Y. Ono, and J. P. Simons, Chem. Pliys. Lett., 1980,75,47. A. J. Yencha, Y. Ozaki, T. Kondow. and K. Kuchitsu, Chem. Phys., 1980,51, 343. R. L. Vance and G . A. Gallup, J . Chem. Phys., 1980,73. 894. D.J. Wren and D. W. Setser, J. Chem. Ph.vs., 1981, 74,2331. H. Obase, M. Tsuji, and Y. Nishimura, Chem. Phys., 1981,57, 89. A. J. Yencha and T. Wu, Chem. Ph.vs., 1980,49, 127.

Gas-phase Photoprocesses 139 emission from Band C state XeBr and XeI, have been studied, with rate constants, electronic branching ratios, and vibrational energy distributions reported;208 kinetic parameters for quenching of several excited Kr states have been measured,209 and collisions between Ar(4s3P,,,) and Fe(CO), have been shown to lead to emission from electronically excited Fe atoms.210 Chemiluminescence from CaX species (X = halogen) arises from the reaction of copper with X, molecules. For Cu + F,, ground-state copper atoms (,S)react to produce A, B, and C states of CuF, with an inversion of population of the C state relative to the B state observed,211whereas metastable Cu atoms ('0)are responsible for chemiluminescent reactions with the other halogem2l 2 Emission is seen in reactions of the ground-state Group IIIa atoms from GaF and InF (311) with F2,,13 with population inversions formed in the vibrational levels of these excited states; the products of ground-state reactions of Y,'14 SC,''~,2 1 5 and Yb216 atoms with various molecular species have been studied by and laser-induced fluorescence 2 1 4 * * techniques. chemiluminescence 14. Laser excitation of atomic levels in S ~ I , ~ Zr,"' '' Dy,219and U 2 2 0 has been carried out, with lifetime measurements,2 quenching rates,217and chargeexchange reactions 2 1 of the excited species reported.

'

"9

8 Infrared Photochemistry The majority of past publications on infrared photochemistry have made use of observations upon the yields of products of multiple-photon dissociation (MPD) to infer details of the multiple-photon absorption (MPA) processes taking place. The appeal of such experiments is that they are relatively straightforward, at least by end-product analysis techniques, although sophistication in the methods inevitably (and very successfully) has crept in: molecular-beam photofragment spectroscopy and laser-induced fluorescence detection of photofragments are examples of this. In many aspects, MPA experiments are harder, as interesting effects tend to take place at low average numbers of i.r. photons absorbed per molecule, and these are difficult to measure by standard calorimetric techniques. However, significant progress is now being made, with optoacoustic methods of detection of energy deposition, and, particularly, with spectroscopic 'pump and probe' techniques to monitor the time-resolved behaviour of specific sets of internal energy levels of molecules excited by MPA. Sulphur hexafluoride still commands considerable attention. Single-photon excitation of v 3 = 1 has been studied in high-resolution diode-infrared laser '09

*Io 'I' '13

'I4 '15

'" 'I9 O''

K. Tdmagake, D . W. Setser, and J . H. Kolts, J . Ciiem. Piiys., 1981, 74, 4286. R. S. F. Chang, H. Horiguchi, and D. W. Setser, J . Ciiem. Piiys., 1980, 73, 778. J. Kobovitch and J. Krenos, J . Ciipm. Piips., 1981. 74, 2662. R. W. Schwenz and J. M. Parson, J . Ciiem. Piiys., 1980, 73, 259. R. W. Schwenz and J . M. Parson, Cliem. Pliys. Lett., 1980, 71, 525. R. W. Schwenz, L. C. Geiger, and J. M. Parson, J . Chem. Ph.vs.. 1981.74, 1736. H. C. Brayman, D. R. Fischell, and T. A. Cool, J . Chem. Phys., 1980,73, 4247, 4260. J. L. Gole and S. A. Pace, J . Chem. Piiys., 1980, 73, 836. R. Dirscherl and H. U. Lee, J . Chem. Phys., 1980. 73, 3831. J. A. Gelbwachs, R. S. Nesbitt, and R. P. Frueholz, Chem. Pliys. Lett., 1981, 77. 222. P. Hannaford and R. M. Lowe, J . Phys. B, 1980, 14, L5. B. Burghardt, R. Harzer, G. Meisel, and S. Penselin, Opt. Cummun.. 1980. 33, 169. P. Benetti, M . Broglia, and P. Zampetti, Opt. Commun.. 1981, 36,218.

140

Pho t oc&m ist rj’ double-resonance experiments, with the observed line shapes able to be reproduced theoretically.221N o evidence of intramolecular coupling at this low level of excitation is seen. At higher intensities, double-resonance experiments using very short (30ps) i.r. pulses show evidence of deep and narrow spectral hole burning at the pump wavelength at energies corresponding to 4-5 photons absorbed per molecule, in contrast to previous ns time scale experiments, for which a broad bleaching had been found to occur to high and low wavelengths of the pump line.222The existence of this saturation effect seems to point to a bottleneck in the absorption process due to discrete vibrational states at these levels of excitation: raising the pump fluence decreases the hole burning, as molecules are pumped into the quasicontinuum where saturation effects became insignificant. Furthermore, an extraordinarily fast collisional process repopulating the absorbing level was observed taking place with a rate constant of 1.5 x 10-8cm3m01ecule-1s-1. This emphasises the need for use of very low pressures and short pulse lengths in order to probe truly collision-free absorption processes in SF,, and accounts for the behaviour previously observed at similar pressures with only ns time Quantitative optoacoustic spectroscopy measurements of MPA processes are generally limited to pressures 2 0. I Torr, and thus for collision-free conditions to apply during the pumping process, the pulse length needs to be SlOOns for collisions with gas kinetic cross-sections, and considerably shorter than this if processes as rapid as those described above for SF, apply. At lower pressures, 10-3-10Torr, MPA in SF, has been measured by using a pyroelectric detector offset from the path of a CO, laser beam in a static sample of gas, and acting as a bolometer for the detection of vibrationally excited molecules impinging upon its 2 2 4 MPA cross-sections can be quantitatively estimated by this novel surface.223* technique: it is found that at low pressures ( < 10-2Torr) and low fluences ( < 10- J cmP2,where little MPD takes place), laser intensity (W cm-2) plays the essential role in the absorption process, whereas in the presence of collisions at higher pressures the fluence is the dominant parameter.224Pressure and fluence effects upon the MPA of C O , laser radiation in CF312 2 5 and of H F laser radiation by molecules containing OH groups 226 have been measured in a higher pressure regime by optoacoustic spectroscopy. Double-resonance experiments involving i.r. pumping followed by visible or U.V.laser probing of the vibrationally excited species have been reported by several groups. Laser-induced fluorescence of thiophosgene following MPA of CO, radiation at intensities > 3 MWcm-2 has shown that the vibrational populations of u = 0 4 , 6 , and 8 of the v4 mode are depleted or not populated under collisionfree conditions when the initially pumped mode is 2v4, and only at lower laser intensities are population increases in these levels observed.227It appears that all

”’ 222

223 224

*”

2’6

227

C. Reiser. J. I . Steinfeld. and H . W. Galbraith, J . C I i ~ n iPhys., . 1981, 74, 2189. R. C. Sharp, E. Yablonovitch, and N . Bloembergen, J . Cliem. Pliys., 1981, 74, 5357. R. V. Ambartzumian, L. M . Dorozhkin, G. N. Maliarov, A . A. Puretzky, and B. A. Chayanov, Appl. Phys., 1980, 22, 409. R . V. Ambartzumian, G . N. Makarov. and A . A . Puretzky, Opt. Contntun.. 1980. 34. 81. J. M . Weulersse and R. Genier, Appl. PliJs., 1981, 24, 363. R. D. McAlpine, D. K . Evans, and F. K. McClusky, J . Chm. Phys., 1980, 73, 1153. D. M. Brenner, J . Clic~ni.fliys.. 1981, 74, 2293.

Gus-phase Pltotoprowsses 141 rotational levels are able to interact with the laser field at the intensities used and no bottlenecking of vibrational populations occurs in this molecule, in contrast to the behaviour of propynal 2 2 8 studied under similar conditions. Clearly the extent of pumping of the low levels of these small molecules will depend crucially upon their spectroscopic features, as well as on the laser intensities employed. Depletion of fluorescence from the A ' A , state of thiophosgene has been seen following excitation of state selected vibronic levels by MPA to predissociating levels 2 2 9 (a similar experiment to that reported earlier for biacetyl and propynal 49). No obvious dependence of the fluorescence depletion upon the total vibrational energy of the initially produced ' A , state was observed: it is suggested that this method could be employed for quantitative measurements of absorption crosssections of vibrationally excited molecules in electronically excited states.229 Cross-sections for absorption of 193nm radiation in SF, are found to be considerably enhanced following i.r. MPA;230time-resolved observations of hotband absorption following MPA in C6F, 2 3 1 and CF31232 have been used to measure rates of collisional redistribution of vibrational energy. MPA of two different laser wavelengths in CCI, appears to have markedly different effects near the dissociation threshold.233 CO, laser excitation at 980cm-' interacts initially with the v 1 + v 2 + v4 combination mode, and at the threshold for dissociation ( 120J cm - ,), approximately 28 photons are measured to be absorbed per molecule. Radiation from an ammonia laser at 794cm- is initially absorbed by the v 3 fundamental in CCI,. The threshold for dissociation is considerably lower, 1.2 Jcm-2, and at this point 60 photons are absorbed, i.e. far more energy is required at this wavelength to dissociate the molecule. The authors appear to put the view that as the combination mode contains the C - C I stretch, v l , this contributes more efficiently to dissociation than does the pure v 3 2 3 3 . Bond selectivity arguments of this kind have been advanced before, but it has been shown that alternative plausible explanations can just as easily explain the experimental observations:234 developments in this case are eagerly awaited. Irradiation of C2H,CI at non-CO, laser wavelengths, in this case around 3.3 pm, shows resonances in the MPD yield at wavelengths corresponding to peaks in the fundamental and overtone absorption At this relatively high photon energy, it is shown that for many rotational states the quasicontinuum is reached after absorption of only two photons: absorbed energy increases almost linearly with fluence with no bottlenecking, in contrast to the behaviour observed at 10 pm, and a simple rate equation treatment of absorption in the quasicontinuum is shown 22a

229

230 23' 232 233

234

235

D. M. Brenner, K. Brezinsky. and P. M. Curtis, Ciiem. P i i n . Leii.. 1980. 72. 202. D. M. Brenner. J . Pliys. Cliem.. 1980, 84. 3341. J. J. Tiee, F . B. Wampler, and W. W. Rice, Clirwi. Pli,w. Lcti.. 1980. 76. 230. S. Speiser and E. Grunwald, Client. PIiw. Lei(.. 1980. 73. 438. Y. A. Kudriavtsev and V. S. Letokhov, Clieni. Pliys., 1980. 50, 353. B. I. Vasilev. N. A. Vishnyakov. V. T. Galochkin, A. Z. Grasyuk. A. P. Dyadkin, A. K. Zhugalkin. V. A. Kovalevskii, V. N. Kosinov, A. N. Oraevskii, A. N. Sukhanov, and N. F. Starodubtsev, Sov. Pliys. JETP Letr.. 1980. 30. 25. M. N. R. Ashfold and G . Hancock. "Infrared Multiple Photon Excitation and Dissociation; Reaction Kinetics and Radical Formation", in 'Gas Kinetics and Energy Transfer', ed. P. G . Ashmore and R. J. Donovan (Specialist Periodical Reports). The Royal Society of Chemistry, London, 1981, Vol. 4, p. 73. H.L. Dai, A. H.Kung, and C. B. Moore, J . Client. Plijs.. 1980, 73, 6124.

142

Photochemistry

to be valid also for the discrete levels in this molecule.235 Narrow peaks in the MPA spectrum of ethylene (taken with a high-pressure continuously tunable CO, laser) have been observed within the relatively low intensity range 40-600 kW ern-,, and ascribed to stepwise multiple-photon absorption resonances. 36 Laser-induced fluorescence detection of radical fragments formed by i.r. M P D is now an established technique, and its ability in determining quantum states of such species has been exploited in measurements of their internal energy distribution^.,^^ The CN fragment, formed in the M P D of C,H,CN has been studied in some detail, with particular emphasis upon the effect of the intensity of the CO, laser pulse upon the rotational energy distribution in the X2C’ (u” = 0) ground When molecules are excited during the laser pulse to levels above the dissociation limit, unimolecular decomposition can compete with further photon absorption, and, as the rate of the latter process depends upon the laser intensity, higher intensity pulses will access a higher range of internal states in the dissociating species, and hence provide more energy for distribution in the internal states of the fragments. Figure 3 illustrates experimental evidence for this.237Time-resolved measurements of the C N (X2C’,u” = 0) rotational state distribution show that fragments produced during the high-intensity peak of a CO, laser pulse are hotter than those formed late in time by the low-intensity tail despite the fact that for the latter species dissociation arises from absorption at a considerably higher laser fluence.2 3 7 Similar conclusions have been reached in experiments using single and multimode pulses of the same fluence: CN fragments have more internal energy for the higher intensity multimode p ~ l s e s39. ~All distributions are well represented by Boltzmann temperatures, as can be seen from the data in Figure 3. Intensity effects have also been reported for the partitioning of energy in the (O,O,O) and (0,1,0) vibrational levels of ‘CH, produced in the MPD of acetic anhydride and acetic acid, with again Boltzmann distributions observed by laser-induced fluorescence in the rotational states of the radical fragments.240 When two or more competing dissociation pathways occur for molecules excited by MPA, as the relative rates of dissociation from the two transition states will, in general, change with increasing energy, laser intensity will in a similar way affect the relative product yields. Such an effect has been seen for the competing pathways eliminating H F and HCl in the M P D of CH,=CClF.241 However in the MPD of C,F,H, competition between channels eliminating H F and breaking the C-C bond is found to be invariant with laser fluence (and hence intensity) and this has been interpreted in terms of a simple ‘threshold fluence’ model appropriate for the focused beam geometries employed.242Competing channels in the M P D of cyclobutanone have been characterized,243* 244 and an attempt made to explain 236 237

239 240 24’

242 243 244

1. N . Knyazev, N. P. Kuzmina, V. S. Letokhov, V. V. Lobko, and A. A. Sakisyan, Appl. Opt.#1980, 22, 429. M . N. R. Ashfold, G . Hancock, and M . L. Hardaker, J . Phofochcm., 1980, 14, 85. C. M. Miller and R. N. Zare, Chem. Phys. L c f f . , 1980. 71, 376. A. M. Renlund, H . Reisler, and C. Wittig, Cliem. Phys. LRff., 1981, 78, 40. A. J. Grimley and J. C. Stephenson, J . CIiem. Pliys., 1981, 74, 447. W. A. Jalenak and N . S. Nogar, J . PIiys. Clicm.. 1980, 84, 2993. P. A. Hackett, C. Willis, M . Drouin, and E. Weinberg, J . Phys. Chem., 1980, 84, 1873. S. Koda, Y. Ohnuma, T. Ohkawii, and S. Tsuchinya, Bull. Cliem. SOC.Jpn., 1980, 53, 3447. V. Starov, N. Selamoglu, and C. Steel, J . Phys. Cliem.. 1981, 85, 320.

+

c c

6

0

L

250

N"(N"t 1)

500

750

I

1000

Figure 3 Rotational distributions of CN(X'C+, v" = 0)produced in the i.r. MPD of lOmTorr C,H,CN. On the left are$uorescence excitation spectra taken at times of 160 ns (upper trace) and 3 ps (lower trace)from the peak of the C 0 2laser pulse. The pulse shape, with these times indicated by arrows, is illustrated to the upper right of the Figure. The plots of ln{Z/(N" + 1)) against N"(N" + 1) to the upper right of each excitation spectrum represent the populations of the (X'C', v" = 0) state rotational levelsplotted in such a way that a straight line would indicate a Boltzmann distribution. As can be seen from the Figure, the rotational distributions can be well represented by Boltzmann temperatures, but with very different values, 970 K and 435 K for the 160 ns and 3 ps observations, respectively. TheJEuenceswere 18 J cm-2 at 16011s and 55 J cm-' at 3 ps

C

5-

.+

2

1

-2

+

Photochemistry the discordant results presently in the literature for the variation of relative product yields with precursor pressure. 244 The effects of magnetic 2 4 s and electric 246 fields have been found to increase the M P D yields of CF2HCI.The effects are most pronounced at low values of the laser fluence (and hence for the pulses of constant temporal shapes used, of the laser intensity) and is illustrated for the electric field in Figure 4.246Breakdown of the

144

R

Fluence (Jcm-* 1 Figure 4 The ratio R of the fraction of CF,HCl dissociated by i.r. MPD per laser pulse in the irradiated volume with and without the electric jield, as a function of the laser ,fluenee (J cm- 2). The electricfield strength was 4.2 kV cm- and the CF,HCI pressure 300 mTorr

’,

angular momentum selection rules caused by the field is believed to cause the effective density of states to increase at low values of the total absorbed i.r. energy, and this removes the effect of a low-energy bottleneck limiting the absorption efficiency.246At higher fluences this bottleneck is eliminated by the increased laser intensity,246 and hence an increase in the field has a smaller (and eventually negligible) effect on the MPD yield. MPD of n-butyl vinyl ether at 9.6 and 10.6pm produce different sets of dissociation products; for example, acetylene is found at 9.6pm, yet not at the longer ~ a v e l e n g t h . ~The ~ ’ authors point out however that this does not necessarily justify the assumption of a bond- or mode-selective dissociation process, since acetylene may be formed by wavelength-dependent dissociation of a product of the MPD of the parent molecule.247 245 246 25’

R. Duperrex and H . van den Bergh, J . CIiem. Phj-s., 1980,73, 585. P. Gozel and H. van den Bergh, J . Chem. Phys., 1981, 74, 1724. H . Hofmann, W. Klopffer. G . Schafer, and J . Gloor, Ckem. P/iys., 1981, 56. 337.


145

1.r. emission has been seen from the vibrationally excited CO, product of MPD of vinylacetic and pyruvic from hydrogen halides formed by chemical reaction of Cl, with H atoms produced in the MPD of various hydrocarbon^,^^' and of HBr with F and C1 atoms formed in the MPD of CF,C1.250 Infrared fluorescence from C,F,Cl following MPA shows emission from both discrete levels and the quasicontinuum, with efficient intramolecular vibrational redistribution out of the pumped mode evident after absorption of only 2-3 photons.251Emission in the i.r. has been seen following MPA in N,F,,252 and has been used to study the interconversion of perfluorocyclobutene to perfluorobutadiene isomers following MPA.25 Further isomerization reactions induced by CO, lasers have been reported.254 Comprehensive studies have been carried out on the MPD of hexafluoroacetone as a function of laser fluence, frequency and substrate pressure,255 and the influence of collisional effects on the formation of CF, in the MPD of CF2CFC12 5 6 and CF,HCl 2 5 7 has been experimentally measured and theoretically modelled. Fluence dependences of the H F laser-induced decomposition of 2,2,2trifluor~ethanol,’~~ and the 9.4pm CO, laser MPD of C,F,Cl 2 5 9 have been reported, and triethylphosphite joins the increasing list of molecules dissociated by CO, laser radiation.260 Several instances of visible emission accompanying collisionless MPA have now been described in the literature, and recently some of the examples have now been studied in detail. In OsO, the emitting species is believed to be the parent molecule in an (unidentified) electronically excited state 2 6 1 formed by intramolecular vibrational to electronic energy transfer (‘inverse electronic relaxation’, IER). Identification of the emitter in these cases is no easy task: however a method has been recently described 262 that allows distinction to be made unambiguously between emission from parent molecules and from fragments formed by MPD, and this has been applied to the luminescence accompanying MPA in CrO,Cl,. A molecular beam of the parent molecule is crossed with a pulsed CO, laser beam, and the angular dependence of the emitting species with respect to the original beam direction is detected in a time-resolved fashion. If the emission is solely from excited parent molecules then the angular distribution should lie along the original

248

249 251

252

253 254

255

256

J. L. Buechele, E. Weitz, and F. D. Lewis, Chem. Phys. Lett.. 1981, 77, 280. C. R. Quick, A . B. Horwitz, R. E. Weston, and G. W. Flynn, Chem. Ph-ys. Lett., 1980, 72, 352. A. B. Horwitz, J. M. Preses. R. E. Weston, and G. W. Flynn, J . Chem. Phys., 1981, 74, 5008. J. W. Hudgens and J. D. McDonald, J . Chem. Phys., 1981, 74, 1510. C. Kleinermanns and H. Gg. Wagner, Z . Phys. Chem., 1980, 119, 159. I. Glatt and A. Yogev. Chem. Phys. L e r r . , 1981, 77, 228. A. Ben-Shad and Y. Haas, J . Chem. Phys.. 1980, 73, 5107; D. Garcia and E. Grunwald, J . Am. Chem. Soc., 1980, 102, 6407. P. A. Hackett, M. Gauthier, W. S. Nip, and C. Willis, J . Phys. Chem., 1081, 85, 1147; P. A. Hackett, V. Malatesta, W, S. Nip. C. Willis, and P. B. Corkum, J. Phys. Chem., 1981, 75, 1152. J. Stone, E. Thiele, M. F. Goodman, J. C. Stephenson, and D . S . King, J . Chem. Phys., 1980, 73, 2259.

257 258 259

260 261 262

A. C. Baldwin and H. van den Bergh, J . Chem. Phys., 1981, 74, 1012. D. Anderson, R. D. McAlpine, D . K. Evans, and H. M. Adams, Chem. Phys. Let[., 1981,79, 337. K. Nagai and M. Katayama, Jpn. J. Appl. Phys., 1980, 19, 1235. C. N . Merrow and N . S. Nogar, Chem. Ph-vs. Lett., 1981, 79, 69. A. A. Makarov, G. N. Makarov, A. A. Puretzky, and V. V. Tyakht, Appl. Phys., 1980 23, 391. T. A. Watson, M. Mangir, C. Wittig, and M. R. Levy, J . Phys. Chem., 1981, 85, 154.

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Photochemistry

molecular beam axis. In fact in CrO,Cl, considerable off-axis emission occurs, which can only be attributed to luminescencefrom fragments presumably formed in their ground electronic state that subsequently absorb CO, laser radiation and then undergo IER: parent electronic excitation is a minor channel.262 More conventional bulb studies of the emission accompanying MPA of CrO2C1,, while demonstrating the collisionless nature of the IER process, were unable to determine the identity of the emitting species.263 Differences and similarities in the behaviour of reactions induced thermally and by CO, laser radiation at relatively high pressures have been described in several cases. Decomposition of CH,CF,Cl with a CW laser source takes place with a rate constant equal to the thermal value at 200 Torr, but vibrational and translational degrees of freedom appear not to be completely equilibrated at lower pressures.264 In the irradiation of perdeutero-acetone, a classical thermal mechanism does not explain the results, but what is believed to happen is that decomposition of the parent molecule takes place near the laser focus, a rapid temperature rise results from the recombination of CD, radicals, and the subsequent chemistry is largely the thermal decomposition of C,D, at temperatures approaching 1900 K.265Laser heating of N,H,-H2S mixtures,266of pure NH, (leading to NH 311and NH, under collisional conditions emission) 267 and of HN,-DN,-HCl mixtures have been reported, with, in the last of these, the temperature of the reacting mixture being monitored by time-resolved i.r. spectral photography (TRISP) of the internal state distribution of the HCl ‘thermometer’.268CW irradiation of lowpressure C2H, is reported to produce triplet-state molecules,269and excitation of SF, near the nozzle of a supersonic expansion molecular beam leads to the production of translationally cool but internally excited SF, molecules.270 Sensitized decomposition of C0C1,,271 UF6,272and tetralin (ClOHl2)2 7 3 by CO, lasers has been carried out, with, in the case of tetralin, different products being found from those produced in pyrolysis experiment^,,'^ and this has been attributed to the laser-induced process reducing heterogeneous decomposition effects. The photodissociation rate of the cyanobenzenecation at 568 nm is found to be significantly increased in the presence of CW CO, laser radiation.,’, Without the laser present, the dissociation is via a sequential two-step mechanism (19), and the

263 264

’” 265

267

I. Burak and J. Y. Tsao, Chem. Phys. Lett., 1981,77, 536. R. N. Zitter, D. F. Koster, A. Cantoni, and A. Ringwelski, Chem. Phys., 1981, 57, 1 1 . W. Braun and J. R. McNesby, J . Phys. Chem., 1980. 84, 2521. S. F. Bureiko, A. P. Burtsev, N. S. Golubev, I. L. Danilov, and Y . M. Ladvishchenko, High Energy Chem., 1980, 14, 282. I. Hanazaki, K. Kasantani, and K. Kuwata, Cheni. Phys. Lett., 1980, 75, 123. P. Avouris, D. S. Bethune, J. R. Lankard, J. A, Ors, and P. P. Sorokin, J . Chem. Pliys., 1981, 74, 2304.

’O

X. de Hemptinne and D. de Keuster, J . Chem. fhys.. 1980, 73, 3170. D. R. Coulter, F. R. Brabiner, L. M. Casson, G. W. Flynn, and R. B. Bernstein, J . Chem. Phys., 1980,

2’1

73, 281. C. Riley and L. MacLean, J . Am. Chem. SOC.,1980, 102, 5108.

269

272 273

274

R. S. Karve, S. K. Sarkar, K. V. S. Rama Rao, and J. P. Mittal, Chem. Phys. Lett., 1981, 78, 273. M. R. Berman, P. B. Comita, C. B. Moore, and R. G . Bergman, J . Am. Chem. Soc., 1980,102,5692. C. A . Wight and J . L. Beauchamp, Chem. Ph-vs. Lett., 1981, 77, 30.


147

enhancement is believed to be due to vibrationally excited ground-state molecules, produced by IC from the (C6H5CN+)*species, absorbing CO, laser photons and undergoing MPD. The wavelength dependence of this effect exhibits a pronounced peak at 970cm- and is believed to probe the molecule within its quasicontinuum of states. A similar increase in the 610nm photodissociation rate of the iodobenzene cation with CO, laser radiation has been seen, but with little i.r. wavelength selectivity.275The ion molecule reaction (20) is markedly affected by

',

+

(CH,OH)H '(OH,) + CH30H CW CO, laser irradiati~n.,'~The rate constant for the forward reaction is increased by a factor of > 1000 to 2.6 x 10- cm3molecule- s - under conditions in which each (CH,OH),H+ species absorbs an average of - 4 photons from the laser. The CW laser-induced MPD of (CH,),Cl+ and its deuteriated derivatives 2 7 7 and of CF31+278 have been reported, and saturation effects in the pulsed MPD of CH,OHF- 2 7 9 have been investigated. Steady-state rate coefficients for unimolecular decomposition can be extracted from measurements of the fluence dependence of the MPD yield, providing that laser intensity effects are unimportant in the MPA process.280Application of the Pauli master equation and the energy-grained master equation to MPD have been presented, and the effects of unimolecular decomposition rates 2 8 3 and laser pulse shapes284on the dissociation yields and energy distributions in the products have been considered theoretically. Models for the MPA process involving a single active absorbing oscillator coupled to a heat bath,28s and two non-linearly coupled oscillators interacting with the laser field 286 have been presented. Calculations have been made of the dependence of the fraction of SF, molecules excited below the dissociation limit on the laser fluen~e,,~'and of the role of transfer of angular momentum in the MPA process,288 and further theoretical papers have described a Bloch equztion derivation of rate expressions for MPA,289and the effect of mixing ground-state quantum levels in the presence of the laser field, enabling a large number of rotational states to be pumped at moderate laser inten~ities.~~' 275

276

277 278 279

280

"'

283

284

286

287 288

289

290

R. C. Dunbar, J. D . Hays, J . P. Honovich, and N . B. Lee, J . Am. Chem. Soc., 1980, 102, 3950. D. S. Bomse and J. L. Beauchamp, J . Am. Chem. Soc., 1980, 102, 3967. D . S . Bomse and J . L. Beauchamp, Chem. Phys. Lett., 1981, 77, 25. L. R . Thorne and J . L. Beauchamp, J , Chem. Phys.. 1981.74, 5100. R. N. Rosenfeld, J. M. Jasinski, and J. I. Brauman, Chem. Phvs. h i t . . 1980, 71, 400. M . Quack, P. Humbert, and H. van den Bergh, J . Chem. Phys., 1980,73, 247. J. Troe, J . Chem. Phvs., 1980, 73, 3205. A. C. Baldwin and J. R. Barker, J . Chem. Phys., 1981, 74, 3813, 3823: W. D. Lawrance, A. E. W. Knight, R. G. Gilbert, and K. D. King, Cheni. Phys.. 1981, 56, 343. E. Thiele, J. Stone, and M. F. Goodman, Chem. Phys. h i t . , 1980. 76, 579; J . C. Stephenson, S. E. Bialkowski, D. S . King, E. Thiele, J. Stone, and M. F. Goodman, J . Chem. Phys., 1981, 74, 3905; E. Zamir and R. D . Levine, Chern. Phys., 1980, 52, 253. E. Thiele, M. F. Goodman, and J. Stone, Chem. Phys. Lett.. 1980, 72, 34. P. G . Harper, I. Mackie, and S. D. Smith, Opt. Commun.. 1980,32,41 I ; J. J . Chou and E. R. Grant, J . Chem. Phys.. 1981, 14. 384. R. Ramaswamy, P. Siders, and R. A. Marcus. J . Chem. P h j x , 1981, 74. 4418. D. Poppe, J . Chem. Phys., 1981, 74, 5326. D. Poppe, Chem. Phys. Lett., 1980, 75, 264. H. Friedmann and V. Ahiman, Opt. Commun.. 1980, 33, 163. M. V. Kuzmin, Opt. Commun., 1980, 33, 26.

148

Photochemistry

Most experiments carried out to date in isotope separation using pulsed infrared lasers have been restricted to relatively low pressures, 1 Torr, in order to reduce 100 ns pulse width. For collision-induced isotopic scrambling during the economic separation of deuterium, higher pressures are needed in order to reduce reactor size and gas pumping costs, and thus lower pulse lengths are needed. Pulses of 2 ns duration have been used in the MPD of several deuteriated fluorocarbons at pressures up to 1 atmosphere, and these studies have shown that both difluoromethane and tritluoromethane are photochemically satisfactory as starting materials for large scale deuterium isotope separation by MPD.291Tritium separation from CTF, has been considered, with i.r. absorption spectra of the parent molecule Isotopically selective MPD of the 'UO,(hexafluoroacetylacetonate),.tetrahydrofuran complex in a molecular beam is found to increase in efficiency at lower temperatures, and the factors governing isotopic selectivity in large molecules of this kind have been discussed.293 Carbon-isotope separation schemes involving pulsed and CW C 0 2 lasers have received considerable attention. In the MPD of 'CF,I, scavenging of 'CF, by HI improves the dissociation yield by preventing rapid recombination of the radicals with I Improvements in isotopic selectivity by a factor of 20 are seen by increasing the temperature in the MPD of 'CF2C12at specific wavelengths to the blue of the 927 cm- vs fundamental;295temperature- (and wavelength-) dependent MPA rates competing with collisional scrambling processes are invoked to explain the results.295 Pulsed CO, irradiation of C,F,CI 2 9 6 and CF,Br 297 leads to isotopically selective MPD, and CW pumping of 'CH,F and its subsequent reactions with Br atoms has been seen to retain isotopic selectivity even when states above u = 1 are populated.298 Single visible photon absorption of high overtones of CH stretching frequencies in 'CH,NC leads to isotopically selective i s ~ m e r i z a t i o nCW , ~ ~ CO, ~ laser dissociation of ethylene clusters is suggested as a potential method for isotope separation,300and a review has appeared of recent work on laser isotope separation at the Los Alamos fa~ility.~"Several isotope enrichment processes involving BCI, have been described, with scavenging of dissociation fragments or of vibrationally excited parent molecules by reaction with 0 , , , 0 2 H2S,303and N(CH,), ,04 reported. Isotopically selective MPD of

--

"I

292

293 294 295

296 297 298

299

'01 '02

'03

'04

J . B. Marling, 1. P. Herman, and S. J. Thomas, J . Cliem. Pli~s.,1980, 72, 5603. I. P. Herman and J . B. Marling, J . Pltys. Chem., 1981, 85, 493. J . A . Horsley, D. M . Cox, R. B. Hall, A. Kaldor, E. T. Maas, jun., E. B. Priestley, and G. M. Kramer, J . Chem. Phys., 1980, 73, 3660. C. N . Plum and P. L. Houston, Appf. Phys.. 1981. 24. 143. J . S. J. Chou and E. R. Grant, J . Client. Pliys., 1981, 74, 5679. E. Borsella. R. Fantoni. A . Giardini-Guidoni, and G . Sanna, Chem, Phjx Lett., 1980, 72. 25. M. Neve de Mevergnies and P. del Marmol. J . Cheni. Pliys., 1980, 73, 301 I . D. S. Y. Hsu and T. J. Manuccia, Cliem. Pliys. Lctt., 1980, 75, 16. K. V. Reddy and M. J . Berry, Clieni. Phys. Lett., 1980, 12, 29. M. P. Casassa, D. S. Bomse, J . L. Beauchamp, and K. C. Janda, J . Cliem. Phys., 1980, 72, 6805. R. J . Jensen, J. A. Sullivan, and F. T. Finch, Sep. Sci. Technol., 1980, 15, 509. Y . Ishikawa, 0. Kurihara, R. Nakane, and S. Arai, Cliem. Phys., 1980, 52, 143; H. Kojima, T . Fukumi, K . Fukui, and K. Naito, J . P h j x Cliem., 1980, 84, 2528. K. Takeuchi, 0. Kurihara, and R. Nakane, Chem. Phys., 1981, 54, 383. G. A. Kapralova, L. E. Makharinskii, E. M. Trofimova, and A. M . Chaikin, Sov. Phys. JETP Lett., 1980. 31, 504.


149

another B-containing compound, 2-chlorovinyldichlorodiborane,has been carried Measurements of the rates of removal of small free radicals, produced by pulsed i.r. MPD and detected by laser-induced fluorescence, have been carried out by several research groups, and the results of recent experiments have been reviewed.234The C, radical in its ground X'Z; and low-lying first excited a 3 n , state has been investigated in detail by this method.306*,07 Oxygen is found to cause equilibration between the two states at a rate that is faster than overall removal by reaction,306 and for many other species, both reactive and collision-induced ISC rates have been quantitatively determined.," C2(a31J,) removal rates have also been measured by using U.V.MPD (by means of an excimer laser) as a photolysis source,3o8and the rate constant for recombination of CF, radicals formed in their ground electronic state by i.r. MPD, has been measured by a mass spectrometric technique. ,09 Finally in this Section on infrared photochemistry, the i.r. laser-induced reaction of SF, with a Si surface has been described.310Pulsed CO, laser radiation in the absence of SF, causes momentary heating of a Si target, but no Si removal: in the presence of a few Torr of SF,, etching of the Si is observed. The mechanism for the process is yet to be established, but it appears that both the reactions of excited species produced by the laser, and the effect of the laser radiation at the gas-surface interface are of importance., l o 9 Photochemistry of Atmospherically Important Species An estimate of the global burden of CHF2C1 (Freon 21) has been made from measurements of its atmospheric concentration. The result indicates that the total amount released from anthropogenic sources has been underestimated by almost a factor of 2. In clean background tropospheric air its concentration is virtually immeasurably small (0.1-2.5 p.p.t.v.), and it seems that a potential route for its production by reaction of CFCI, (Freon 11) on tropospheric aerosols is not of importance., l 2 The interpretation of CFCI, and CCI, measurements at Harwell has been debated with regard to the proximity of the site to local sources of these species.313Concentrations of C10 have been measured for the first time by a landbased experiment, by monitoring the J = 11/2 + J = 9/2 emission line.314The C10 column density was lower than that found from balloon flights, and a greater vertical gradient was obtained than that predicted from theoretical models. '05 '06 '07

309

'I0 'I1

"' "*

R. J. Jensen, J. K. Hayes, C. L. Cluff, and J. M. Thorne. IEEE J. Quantum Electron., 1980.16, 1352. M. S. Mangir, H. Reisler, and C. Wittig, J. Chem. Phys., 1980, 73, 829. H. Reisler, M. S. Mangir, and C. Wittig, J. Cheni. Phys.. 1980. 73, 2280. L. Pasternack, A. P. Baronavski, and J. R. McDonald, J. Chem. Phys., 1980,73,3508; L. Pasternack, W. M. Pitts and J. R. McDonald. Client. Phys., 1981, 57. 19. R. I. Martinez, R. E. Huie, J. T. Herron, and W. Braun, J. Phys. Chem., 1980, 84, 2344. T. J. Chuang, J. Chem. Phys., 1980, 72, 6303. R. A. Rasmussen, M. A. K. Khalil, S. A. Penkett, and N. J. D. Prosser, Geophys. Res. Lett.. 1980.7. 809. S . A. Penkett, N. J. D. Prosser, R. A. Rasmussen, and M. A. K. Khalil. Nature (London), 1980,286, 793. D. M. Cunnold, F. N. Alyed, and R. G. Prinn, Atmos. Environ., 1980. 14, 617; S. A. Penkett, K. A. Brice, R. G. Derwent, and A. E. J. Eggleton, ibid., p. 618. A. Parrish, R. L. de Zafra, P. M. Solomon, J. W.Barrett, and E. R.Carlson, Science. 1981,211,1158.

I50

Pho t o c h w is t r j * HCI 3 15 - 3 1 6 and H F 3 1 6 mixing ratios in the stratosphere, and total atmospheric CI and Br concentrations have been reported.317Further measurements have been made of NO,318* 3 1 9 NO 2, 319* 320 N 0 321 0 atoms,322H2C0,323 and alkanes324 in various regions of the atmosphere, and the results of a field sampling program of a wide range of tropospheric gases and aerosols have been published.325 Photolysis of ozone within the Hartley continuum does not appear to produce O ( ' D ) with unit quantum yield: @O('D) has been measured as 0.85 0.02 at 248 nm 3 2 6 and 0.88 0.02 at 266nm 3 2 7 from experiments monitoring O ( 3 P )by The U.V.absorption time-resolved absorption 326 and resonance spectrum of 0, 3 2 8 and its photolysis rate to produce O( 'D)329 both show changes when the parent molecule is vibrationally excited. At wavelengths above 310 nm 'Ag)],vibrational excitation [the energy threshold for production of O(' D)+ 02( increases the cross-section for O(' D)production by two orders of magnitude, and this effect was found to diminish as the energy of the dissociating photon was increased.329At shorter wavelengths ( 1 70-240 nm) the production of O('S) from 0, photolysis has an upper limit of O.l(%, and so any contribution from this excited state in, for example, the atmospheric OH production rate is thought to be insignificant . 3 3 0 The effects of low concentrations of sulphur dioxide upon the rates of 0, and N O formation in irradiated mixtures of NO, and air have been investigated, in an effort to determine the reasons for formation of increased tropospheric concentrations of 0, near the plumes of power plants emitting N o such effects were observed for SO, concentrations up to 10 p.p.m.; when the experiments were repeated with added CI, however an increase in the O3 concentration was observed, and a chain-reaction mechanism involving formation of the ClOO species has been suggested to explain the observations.331 Further twodimensional modelling calculations of 0,depletion rates have been described.332 The importance of establishing the fraction F of the removal rate of O(' D)by N,O 2

'I5

317 'IH

31y

"'

9

K . V. Chance. J . C. Brasunas, and W . A. Traub, Gmp/i,rs. Res. Lett.. 1980. 7. 704: P. Marche. A. Barbe. C. Secroun. J . Corr. and P. Jouve. G1wphy.v. Ros. L ~ t t .1980, , 7. 869. H. Libuijs, G. L. Vail. G. Tremblay. and D. J . W . Kendall, Gcop/i.rs. Res. Lett.. 1980, 7, 205. W. W. Berg. P. J. Crutzen. F. E. Grahek, S. N. Gitlin. and W. A. Sedlacek. Gcwppliys. Res. Lett., 1980, 7. 937. N . lwagami and T. Ogawa. P h c i Spircv Sci., 1980, 28. 867. H . K . Roscoe. J . R. Drummond, and R. J . Jarnot. Proc. R. Sot. London. SLT. A . 1981, 375, 507. B. B. McMahon and E. L. Simmons. Nutiiri> (Lonilon). 1980.287,710: J . P. Naudet, P. Rigaud. and D. Huguenin. Gwp/i,rs. Ros. Lett.. 1980, 7. 70 I . P. S. Connell. R. A. Perry. and C. J . Howard, GiwpIgx. RPS.Lett.. 1980. 7, 1093. W . E. Sharp. Gcopli.rs. Rcs. Lcw.. 1980. 7. 485. V. Neitzert and W. Seiler. Gaoph,r.s. Rev. Lett., 1981, 8, 79.

"' "' R . Eichrnann. G . Ketseridis, G. Schebeske, R . Jaenicke, J . Hahn. P. Warneck, and C. Junge. Atnios. 1980. 14, 695. '" DEni*iron.. . D. Davis. J . GwpIijx. RPS..1980. 85, 7285.

S. T. Amimoto, A. P. Force, J . R. Wiesenfeld, and R. H . Young, J . Clicni. Pliys.. 1980, 73. 1244. J. C . Brock and R . T. Watson. CIi~vii.P h ~ x Lctt.. . 1980, 71. 371. 3 2 n 1. C. McDade and W . D . McGrath. C l i m . Ph,rs. Lett., 1980, 72. 432; I . C. McDade and W . D. McGrath, C h m . PIiys. Lett.. 1980, 73, 413. "' P. F. Zittel and D. D. Little, J . Cliem. PIij:v.. 1980. 72. 5900. 3 3 0 L. C. Lee, G. Black, R. L. Sharpless. and T. G . Slanger. J . C h ~ n i Plijx.. . 1980. 73. 256. 3 3 ' J. S. Wallace. G. S. Springer, and D . H . Stedman. .4tnio.s. Emiron. 1980, 14, 1147. 3 3 2 J. A. Pyle and R. G . Derwent. Ncrturt I Lonilon). 1980. 286,373; C. Miller, J . M. Steed, D . L. Filkin, and J . P. Jesson. N(itiirc (Lontlori). 1980. 288, 461. 32h

"'

151 G ~ ~ v -(isc p h PI]0 tO ~oCC~SSCS S leading to formation of 2 N 0 molecules upon the 0, depletion rate by halocarbon release has been stressed in a recent publication:333a 1% variation in the NO production rate via this mechanism is expected to result in a 0.43Xchange in the 0, depletion. Measurements of F at different temperatures and total pressures have been carried out.,,, The involvement of excited 0, species (produced in an unspecified state by 0 + O2 recombination) in formation processes of N 2 0 in the atmosphere has been p r ~ p o s e d34, ~the wavelength dependences of 0, absorption coefficientshave been measured,335and the rate for the 0, +CH, reaction has been determined. 3 3 6 Photolysis of 0, in the Hartley bands leads to 02('A,) production, with 60% formed vibrationally excited,,,' and under atmospheric conditions quenching is found to be a rapid process. Rates of formation of O,('A,) by this mechanism in the upper atmosphere of Venus have been calculated and compared with those determined by observations of the O,( 'Ag) emission at 1.27 pm: for the values to agree, the previously accepted ozone concentrations would have to be revised upwards by a factor of In the terrestrial atmosphere, the photolysis of 160180 at wavelengths between 170-205 nm could be an important source of odd oxygen in the high stratosphere and mesosphere, as solar radiation not absorbed by discrete I6O, features may penetrate these regions and photolyse the minor isotopic constituent (present as 4 ' : ~of naturally occurring 0,).339 Laser-induced fluorescence measurements of atmospheric OH have been carried out now for several years, and shown to be capable of detecting extremely low concentrations of the radical. It has been pointed out however that interference from laser-generated OH could affect the results considerably: 340 the wavelength used for OH excitation, 282nm, generates O('D) from 0,photolysis, and this reacts with H,O to form OH in the troposphere in a time ( - I ns) which is shorter than the laser pulse width. Calculations and experimental assessments of the importance of this effect have been described.340*3 4 1 The reaction of OH with CS, has been shown to be too slow to act as either a substantial sink for CS,, or a source for OCS in the troposphere,342 and the OH+OCS reaction, the rate constant of which is < 8.8 x 10-'5cm3 molecule- s- ' at room temperature is a similarly minor degradation path for OCS.3 4 3 The role of reaction (21) in atmospheric chemistry is now well recognized, and general agreement upon the value of its rate constant, of critical importance for modelling calculations of the stratospheric ozone balance, now appears to be H02+N0 333 334

335 336 33i

338 33y

"' 3J2

343

-

OH + N O ,

(21)

L. Lam, D. R. Hastie, B. A . Ridley, and H. 1. Schiff. J . Pltoroclient., 1981, 15, 119. S. S. Prasad, Natirw (London). 1981, 289, 386. J. J . DeLuisi. Gropltys. Res. Lett., 1980, 7. 1102. N . Washida. H. Akimoto. and M . Okuda, J . Chrm. Pli,v.s., 1980, 73, 1673. 0. Klais, A . H . Laufer. and M . J . Kurylo, J . Client. Pli,w.. 1980, 73, 2696. J. P. Parisot and G . Moreels, f c u r ~ v1980. , 42. 46. R. J . Cicerone and J. L. McCrumb, Gcwp/i,w.Rcs. Lett.. 1980. 7 , 251. G . Ortgies. K. 11. Gericke, and F. J . Comes, Gcopltj:~.Res. Lctt., 1980, 7, 905. D. D. Davis, M . 0. Rodgers, S. D. Fischer, and K . Asai, Gcwp/i.w. Res. Lett., 1981, 8, 69; D. D. Davis. M. 0. Rodgers. S. D. Fischer. and W . S. Heaps. GcopliJx Res. Lert., 1981. 8. 73. P.H . Wine, R. C . Shah, and R. Ravishankara. J . fliys. Clicnt.. 1980, 84, 2499; R. S. Iyer and F. S. Rowland, Gcophjx Rcs. LPII. 1980, 7. 197. A. V. Ravishankara, N . M . Kreutter, R. C . Shah. and P. H. Wine. Gcopltjx Rcs. Lett., 1980.7, 861.

Photochenzistry reached amongst several sets of investigators. Measurements of both forward and reverse rates of (21) have now fixed the previously uncertain heat of formation of HO, as AH,' (298) = 2.5 & 0.6 kcal mol- ', and this has established the thermochemistry of other reactions involving HO, of potential importance in the atm~sphere.~"" The forward rate constant for reaction (21) has been shown to be independent of pressure in the region 2-1 7 rnbar.,"' The catalytic cycle reactions (22) and (23) removes odd oxygen in the stratosphere, and is of particular

152

HO,

+ 0,

+

-

OH

+ 20,

+

OH 0, HO2 0, (23) importance at altitudes below 25km, as it does not involve oxygen atoms (in contrast to similar cycles involving nitrogen oxides or chlorine species). The rate constant for reaction (22) has now been measured directly for the first time over the temperature range 245--365 K,346and extrapolation of the Arrhenius plot to 220 K yields a value five times larger than that previously assumed for atmospheric modelling calculations. Further quantitative studies of reactions of atmospheric importance include measurements of the temperature dependences of process (24)347and of the recombination rate of methylperoxy radicals with NO,,348and

CI

+ HOCl

-

HCI

+ C10

(24)

an estimation of an upper limit for the reaction between C10 and H2C0,349not fast enought to be an appreciable sink for C10 radicals. The photolysis rate of atmospheric NO, has been measured, and its dependences upon parameters such as the solar zenith angle and the amount of cloud cover have been evaluated.350The photochemistry of small molecules containing sulphur, and its implications for the atmospheric S cycle have been discussed,351 as has the role of stratospheric 'reactive nitrogen' as a source for species such as NO and HNO, in the unpolluted t r ~ p o s p h e r e . ~Ammonia '~ concentrations have been calculated in the atmospheres of both Earth 3 5 3 and Saturn;354the far-u.v. photolysis of mixtures of NH, with methane results in the formation of amines and nitriles, and the relevance of these results to the evolution of primitive atmospheres has been discussed. Ions of the form HfX,(H20)m,where X has mass 41, have been detected in the stratosphere, and recent laboratory experiments on clustering equilibria for these species suggest that X is acetonitrile, CH,CN.356The stratospheric chemistry of J44

'" "-

'" '" "'

''' "' 353

355 35h

C. J . Howard. J . Am. Ciiwi. Soc., 1980, 102, 6937. W. Hack, A. W. Preuss, F. Temps, H . Gg. Wagner. and K . Hoyermann. I t i t . J . Chcrii. Kinet.. 1980. 12, 851. M. S. Zahniser and C. J. Howard, J . Ciicwi. P/i?*s., 1980. 73, 1620. J. L. Cook. C. A . Ennis. T. J . Leck. and J. W. Birks, J . Chcni. P l i ~ s . ,1981, 74, 545. A . R. Ravishankara. F. L. Eisele, and P. H . Wine, J . Chnii. PIIJs., 1980, 73, 3743. G. Pulet, G. Le Bras, and J. Combourieu, G c o p h ~ sRcs. . Lrt1., 1980, 7. 413. F. C. Bahe. U . Schurath. a n d K . H. Becker. Atnios. Etzviron.. 1980, 14, 71 I . N . D. Sze and M . K . W . KO,Atnios. Environ.. 1980, 14, 1223. H . Levy, J . D. Mahlman, and W. J. Moxim. Gcwph~x.Rcs. Li>tt., 1980, 7,441. J . S. Levine, T . R. Augustsson, and J . M. Hoell, Gcoph~*s.Res. Let[., 1980, 7. 317. S. K . Atreya, W. R. Kuhn, and T. M . Donahue. G e o p l i ~ ~Rrs. s . L P I I . .1980. 7, 474. A . Bossard and G. Toupance, Klitiire (Lonilon). 1980, 288, 243. H. Bohriiiger and F. Arnold. Ntrlurc lLonrlon), 1981, 290, 321.

153 metal atoms (formed by aircraft emission or meteoroid ablation) has been described,357 and measurements of intensities of Na(D) lines in the upper atmosphere have led to the suggestion of the mechanism for formation of the excited species being reaction ( 2 5 ) , with NaO formed from Na + 03.358a Gas-phase Photoprocesses

NaO

+0

----+

Na('P)

+ 0,

(25)

Reaction (26) is believed to be the major source of O('D) above 150 km in the daytime thermosphere, and the influence of this previously unconsidered reaction N(,D)

+ 0,

-

NO

+ O('D)

(26)

on the O('D) 630 nm emission rate has been calculated.358bThe auroral chemistry of N('D), formed by dissociative excitation of N, by fast electrons,359 and of N,O, formed in the reaction of N,(A3C,+) with 0, 360 has been reported. H Atoms, H,, and H,.-Reactions of ground-state H atoms with the following molecules and radicals have been reported: HBr,361HN3,362C2H4,363i-C4H8,364 T,,365 CF3Br,366 dimethyl s ~ l p h i d e ,368 ~ ~ dimethyl ~. ether,368 NF2,369- 3 7 1 03,372 - 3 7 5 and various fluorine- and bromine-containing compounds.376 Hotatom studies of the H + CH3C1 reaction have determined the apparent energy threshold for the process as 47 14kJmoi-',377 and D atom reactions include measurements of the internal energy distribution in OD formed from D + and of the rates and kinetic isotope effects in the D + Cl, and Br, systems.379Reaction (27) is believed to produce NF(a'A) highly selectively, with a

-

H + NF, NF(a'A) + H F (27) quantum yield of 20.9,369-371 and subsequent reactions of this with H atoms, process (28) is again selective in populating the N('0) state.369The radiative lifetimes of metastable NF(a'A) is estimated to be H

+ NF(a'A)

----+

N('0)

+ HF

(28)

The contribution of the reaction channel (29) to the removal rate of 0, by H atoms has been estimated by several ~ ~ r k e rHigh ~ yields . ~ ~of O ~ ( 3-P )have ~ ~ ~ H 357 358

359 360

+ 0,

-

HO,

+ O(3P)

E. Murad, W. Swider, and S. W. Benson. Ncrturv (London), 1981, 289, 273. D. R. Bates and P. C. Ojha, Ntrrure (London), 1980,286,790; ( b ) D. G. Torr, P. G. Richards, and M. R . Torr, Geophjx Res. Lett., 1980, 7, 410. J . C. Gerard and 0. E. Harang, J . Gropliys. Res., 1980, 85, 1757. E. C. Zipf, NCrtiwv (London), 1980.287. 523; E. C. Zipfand S. S. Prasad, Nature (London), 1980,287, (N)

'" J.525.L. Jourdain, G. Le Bras, and J. Combourieu. Clreni. P/I.Y.S.Lett., 1981, 78, 483. 362

365 366

368 369 370

37' 372

(29)

0. Kajimoto, T. Kawajira, and T. Fueno, Cheni. Ph)*s. Lett., 1980, 76, 315. K. Sugawara, K. Okazaki, and S. Sato, CIimi. P l i j x Lett., 1981, 78, 259. C . E. Canosa, R. M. Marshall, and A. Sheppard, Int. J . Cliem. Kinet., 1981, 13, 295. G . H . Kwei and V. W . S. Lo, J . Chem. PI1y.s.. 1980, 72, 6265. D. M. Silver and N . de Haas, J . Cheni. Phys.. 1981, 74, 1745. M . M . Ekwenchi, A. Jodhan, and 0. P. Strausz, Int. J . Chsm. Kinet., 1980, 12, 431. J. H . Lee, R . C. Machen, D. F. Nava, and L. J. Stief, J . CIieni. Phys., 1981, 74, 2839. C. T. Cheah and M . A. A. Clyne, J . CIieni. So(,.,Frrrrrdq* Trrrns. 2, 1980, 76, 1543. R . J. Malins and D. W. Setser, J . Phj-s. Clrem., 1981, 85, 1342. C. T. Cheah and M. A. A. Clyne, J . P/rotoc/ieni., 1981, 15, 21. A. P. Force and J. R . Wiesenfeld, J . Cliem. Phj-s., 1981, 74, 1718.

154

Ptiotochemistrj*

been detected by time-resolved atomic absorption spectroscopy 3 7 2 and by laser paramagnetic resonance 3 7 3 in this reaction system. Failure to observe HO, radicals however has led to an estimate of 5 2 % of the H + 0, reaction leading to their formation, and the participation of vibrationally excited OH * (formed by H + 0,) reacting with either H atoms or 0,, process (30) is suggested as the Time-resolved observations indicate that if O(,P) is produced source for O(3P).373 by reaction (30) then its rate constant would need to be increased by an order of

OH* +03

-

OH

+ 0, + O(3P)

(30)

magnitude over the presently accepted value for the de-excitation of OH* by 0,.372 Further measurements upon the role of OH* in this system are promised. 3 7 2 The effects of isotopic substitution 3 8 0 * 3 8 1 and of internal and kinetic on the calculated cross-section for the H + H, reaction on an accurate potential energy surface have been described. At a given translational energy, vibrational energy in H, increases the reaction rate, whereas rotational energy has the opposite effect near the threshold for reaction.383 Classical trajectory studies of the H + 0, reaction have reproduced values of the experimental rate constant over a wide temperature range,384and the temperature dependence of the effect of third-body stabilization of the excited HO, species formed in this system have been similarly calculated.385Approximate theories of thermal rate constants have been used to estimate that for the H + F, reaction, with comparisons made of this value with that calculated quantally for colinear collisions on an accurate potential energy surface. Agreement between variational transition-state theory and the quanta1 results is found to be within 5% over a wide temperature range.386 Theoretical investigations of reactions of H atoms with HC0,388and C2H4 3 8 9 have also been described. Frequency tripling of KrF laser output in Xe results in radiation near 83nm, tunable over a region of 0.5 nm, and this has been used to measure absorption line profiles in the B”lX,+ +-- XIZg+ system in H,, and the corresponding B” t X 373

374 375 376

377 37H

379

3x0 381

382

383 384 38s

386

387

’*’

389

B. J. Finlayson-Pitts, T. E. Kleindienst, M . J. Ezell, and D. W. Toomey, J . Cliem. Ph!*s., 1981, 74, 4533. N. Washida, H. Akimoto, and M . Okuda, J. CIILWI. P/tj..c., 1980, 72, 5781. B. J. Finlayson-Pitts and T. E. Kleindienst, J. Clietni. P / i j 3 . , 1981, 74, 5643. R. J. Malins and D. W. Setser, J . Ckem. P l i j x . , 1980, 73. 5666. P. L. Gould, G. A. Oldershaw, and A. Smith, Cheni. f / i y . s . Left., 1980, 76, 319. E. J. Murphy, J . H. Brophy. G . S. Arnold, W. L. Dimpfl, and J . L. Kinsey, J . Chem. Pliys., 1981, 74. 324. S. Jaffe and M. A. A. Clyne, J . Chem. So(,.,Frrrcidqv Trrms. 2. 1981, 77, 531. H. R. Mayne, J . Clieni. PIiys.. 1980, 73, 217; B. C. Garrett, D. G . Truhlar, R. S. Grev, and R. B. Walker, ibid., p. 235. J. C. Sun, B. H. Choi, R. T. Poe, and K . T. Tang, J . Cheni. Phys., 1980, 73, 6095. C. D. Barg, H. R. Mayne, and J . P. Toennies, J. Chrm. Pl1j.s.. 1981, 74. 1017. M. Baer, H . R. Mayne, V. Khare, and D. J. Kouri. Clwm. Phys. Lett., 1980, 72, 269. J. A. Miller, J . Clieni. Pli?v., 1981, 74, 5120. R. J. Blint, J . Cliern. PhJx., 1980. 73, 765. H. C. Garrett, D. G . Truhlar, R. S. Crev, A. W. Magnuson, and J. N. L. Connor, J . C‘/lcn?.Phj-s.. 1980, 73, 1721. B. C. Garrett. D. G. Truhlar, and R. S. Grev, J . Pliys. Chetn., 1980, 84, 1749. S. C. Farantos and J . N . Murrell, Mol. Ph?.s., 1980, 40, 883. W. L. Hase, D. M. Ludlow, R. J . Wolf, and T. Schlick, J . Phys. Chem. 1981, 85. 958.

Gas-phase Pliotoprocvsses

155

transition in HD.390Predissociation takes place viu crossing to the repulsive limits of the B"C,* state above its dissociation limit, and an analysis of the B t X linewidths and asymmetries has shown that the rate of this process depends significantly upon the Franck-Condon factors for the B"--B' interaction.390 Spectroscopic constants for the i.r. 2Al'-2E' transitions in H, and D, near 3600cm-' have been measured, and these states have been found to be the upper levels of the 602.5 and 710nm bands previously observed for these triatomic radicals.391

0 Atoms, 02,0,,and H0,-Rate constants for bimolecular reactions of groundstate 0 atoms with the following substrates have been measured: H2,392HCN,393 CH30H,394i ~ o b u t a n e , ~CF,HC1,396 ~' f l ~ o r e t h y l e n e s OH,398 , ~ ~ ~ CH3,399propane,400OCS,401CH,SSCH3,402and SO,.403In the 0 + H, reaction, measurements at 298 K have provided further evidence for curvature at the low temperature end of the Arrhenius plot, and the influence of vibrationally excited H, on this reaction has been carefully considered.392 Calculations on the 0 + H, reaction 405 with the properties of various potential energy surfaces have been reported,404* for the reaction evaluated.405Hydrogen abstraction in the 0 + C H 3 0 H reaction takes place from the methyl group,394whereas for 0 + isobutane, the H attached to the tertiary carbon atom is preferentially removed.395The rate constant for the latter process, 1.0 x 10- l 3 cm3 molecule- s- l , is in agreement with that predicted from a sum rule of the rates of attack on individual H atoms.395The dynamics of the 0 + C,F,,406 C2F,I,407 and C3F,1408 reactions have been studied by molecular beam scattering; OH product distributions have been measured 409 and calculated 410 for various 0 + alkane reactions. CO vibrational distributions have been determined in the 0 + HC=CCH,X reactions (X = C1, Br),411the temperature dependence of the third-body recombination of 0 + 0, has been

390

M. Rothschild, H. Egger, R. T. Hawkins, H. Pummer. and C. K. Rhodes, Chcm. P h j x . Lctr., 1980,

72, 404. G. Herzberg, H . Lew, J. J. Sloan. and J. K . G . Watson, C m . J . PItys., 1981, 59, 428. 3q2 G . C. Light and J. H. Matsumoto. Int. J . C/tcwi. KincJt.. 1980. 12. 451. 393 P. Roth, R. Lohr. and H. D. Hermanns, B w . Bunscwgc>s.Plty.s. C'/tc.nt.. 1980, 84, 835. 394 H. H. Grotheer and Th. Just, Cltcwi. P h ~ sL. P I I . .198 I . 78, 71. 395 N. Washida and K. D. Bayes. J . P h j ~ Chcwt., . 1980, 84, 1309. 396 V. I. Egorov, S. M. Temchin, N. 1. Gorbdn, and V. P. Balakhin, Kinat. Critril.. 1979, 20, 850. 397 K. Sugawara, K. Okazaki, and S. Sato, Bull. Cltcwt. Sot. J p n . , 1981. 54. 358. 398 R.S. Lewis and R. T. Watson, J . PIIJS.C / t m . *1980, 84, 3495. 399 N. Washida, J . CAem. Phys., 1980, 73. 1665. 4oo S. P. Jewell, K. A. Holbrook, and G . A. Oldershaw, f n t . J. Cheni. Kinct.. 1981, 13, 69. jol J . S. Robertshaw and I. W . M. Smith, Int. J . Client. Kinat., 1980, 12, 729. 402 J . H. Lee and I. N. Tang, J . Chem. Phys., 1980, 72, 5718. jo3 M. Slack and A. Grillo, J . Cheni. Pltys., 1980, 73. 987. 404 D. C. Clary and J . N. L. Connor, M o f . Phys.. 1980, 41, 689. jo5 A. F. Wagner, G . C. Schatz. and J . M. Bowman, J . Clieni. Pltys., 1981,74,4960; G . C. Schatz, A. F . Wagner. S. P. Walch. and J . M. Bowman, J . Cltctn. P h ~ * s .1981, . 74, 4984. 406 P. A . Gorry, R. J. Browett, J. H. Hobson, and R. Grice, M o l . P l i j x . 1980, 40, 1325. jo7 R. J. Browett, J. H. Hobson, P. A . Gorry. C. V. Nowikow. and R. Grice, Mol. Pltys., 1980,40. 1315. 408 R.J. Browett, J. H. Hobson, and R. Grice, Mol. Phys., 1981, 42, 425. P. Andresen and A. C. Luntz, J . C/tm, P/tys., 1980, 72, 5842. 410 A. C. Luntz and P. Andresen. J . Clicni. P/IJ*s.,1980. 72, 5851. jl' G. T. Fujimoto, M. E. Umstead. and M. C. Lin, Cheni. P h ~ : s . .1980. 51. 399. 391

156

Photoc.hc~iiistr.?,

further investigated.412and a theoretical study of the 0 + acetylene reaction has been r e p ~ r t e d . " ' ~ Energy distributions in the OH(X2ni) products of the O ( ' D ) reaction with H,0,414-417H2,418HCL4I9 NH3,420and saturated hydrocarbons 4 2 1 have been measured by laser-induced fluorescence 4 1 s - - 4 2 and resonance absorption technique~.~ In' ~the O ( ' D ) + H,O reaction [equations (31) and (32)], bimodal O('D)

+ H20

-

20H H2

+

(31) 0 2

(32)

rotational state distributions in OH ( u = 0) have been observed, corresponding to rotational temperatures of 400 and 1900 K,"14 500 and 2500 K,41s and 360 and 4200 K "' in three separate experiments. The origin of the colder fragments has been ascribed both to direct reaction 4 1 4 * 41 and to partial rapid rotational relaxation of the hot species formed."16 Isotopic labelling of the oxygen atom in H 2 0 has demonstrated that the vibrational energy in the new OH bond is significantly greater than that in the old, and this has been interpreted in terms of H-atom abstraction (or stripping) dynamics rather than 0-atom insertion into the bond.416 OH formation [equation (31)] appears to be the major water 0-H channel in this reaction, with process (32) accounting for 510% of the overall O ( ' D ) removal rate at 298 K."17 Bimodal rotational distributions in the OH product of the O ( ' D ) + alkane reactions have been interpreted as due to contributions from insertion (leading to a broad distribution of high rotational states) and abstraction (leading to population of a few rotational states only).42' Insertion dominates for small hydrocarbons (CH, and C2H6), whereas for C,H, these results are consistent and C(CH3), abstraction is of greater imp~rtance:"~' with recent crossed molecular beam studies of the O ( ' D ) + CH, reaction, in which mainly CH,O + H products were Rates of collisional removal of O(' 0 ) with atmospheric gases 4 2 3 and halogenated methanes 4 2 4 have been measured, with in the latter case observations of the O ( 3 P )product allowing estimations of the contributions from quenching and chemical reaction to be determined. The rapid near resonant equilibration process (33) is thought to be responsible 02(lAg)

for pumping I('P,,,)

+

1(2p3,2)

in the 0,-iodine

0 2 ( 3 2 g - ) + I(2p1j2) (33) energy-transfer laser. Production of

'" 0. Klais. P. C. Anderson, and M . J. Kurylo. hi/.J. CI76~77.K k p / . , 1980, 12. 469. B. Harding, J . Phj.s. C/?Cm..1981, 85, 10. "' L. K. H . Gericke and F. Comes, Chiwi. P/rj..s. Lctt., 1980. 74, 63. 'I3

'I5

M . 0. Rodgers, K . Asai. and D. D. Davis. Cllc~7.P/II.s. f>c>tt.,1981, 78. 246. J. E. Butler. L. D. Talley. G. K. Smirh. and M . C . Lin, J . C/~cnl.P h j ~ . 1981. . 74, 4501. R. Zellner, G. Wagner, and B. Hiinme. J . PIrJx. Ch~w7..1980. 84, 3196. 'Ix G. K. Smith and J. E. Butler. .I. CIww. Phj-.s.. 1980. 73. 2243. 'Iq A . C . Luntz. J . C ' l i c ~ r v . Plijx., 1980. 73, 5393. "" D. Sanders. J. E. Butler. and J . R . McDonald, J . C ~ C WPhI..v., I. 1980, 73, 5381. '" AN .. C. Luntz, J . Clroii. PIrjx., 1980. 73, 1143. Casavecchia, R. J . Buss, S. J . Sibener. and Y . T. Lee. J . C ' h ~ n i .P h j ~ . 1980, . 73, 6351. "' P. P. H . Wine and A . R. Ravishankara. Chon. P h j . ~ Lc.rt., . 1981, 77, 103. "' A. P. Force and J. Wiesenfeld, J . P/IJ..c.Chrn7.. 1981. 85. 782. 41 7

GUS -phU.W Ph o t O

--

157 ground-state iodine atoms has been assigned to process (34), with O,('c,+) being ~ 0VI'CSSIJS

+

O,('C,+) I, 0 2 ( 3 z ~+ /2~1 ( )2 p 3 ; 2 ) (34) formed either by the energy pooling reaction of two O,( 'Ae) molecules, or by the energy-transfer process (35). However, measurements of the rate of de-excitation of 02(1A(8)

+ r(2p3/2)

02(1cg+)

+

r(2p3/2)

(35)

O,('C,+) by I, have suggested that process (34) is of minor importance, and that an alternative source of iodine atoms in this system must be identified.425 The temperature dependences of process (35) and of the 02('Ag) energy-pooling reaction have been determined;426 'dimol' emission resulting from collisions between two O,( 'A,) molecules has also been i n v e ~ t i g a t e d . ~Vibrational ~' relaxation rates of O2(lAe, v = 1) have been measured at high temperatures in a shock sensitized ernision from SeO, Se,, and SeS produced in the b'C+ states by near-resonant energy exchange with O2(lAs)appears to hold promise for the production of electronic population inversions in these systems,429and a search for O,( 'A,) by photoionization mass spectrometry in the products of the reactions of 0, H, and NO with ozone has failed to detect it in significant concentration^.^^^ Quenching rates of the b'Xg+ 4 3 1 and A%:,' 432 states of O2 have been reported. Photofragment spectroscopy of 0 3 + between 457.9-752.5 nm has determined energy partitioning in the 0' and 0, photofragments formed from ground and vibrationally excited (in the v 1 symmetric stretching mode) parent rn01ecules.~~~ 4 3 5 states of O,+ has been studied. Predissociation of the b4X,- 434 and f4ng Reactions of ground-state OH radicals with H2,436 H,02,437 HCH0,438 NH3,439C0,440 HN03,442and various hydrocarbons 4 3 6 * 443 and their J25

J26

"' 'lfl

"' 431 432

J33 J3J

J35

436 J37

438

439

"O

441

D. F. Muller, R. H. Young, P. L. Houston, a n d J. R. Wiesenfeld, Appl. f / i j * . s . Lerr., 1981, 38, 404. R. F. Heidner, C. E. Gardner. T. M. El-Sayed. G. I. Segal, and J. V. V. Kasper, J. C / W J IPhj*s.. . 1981, 74, 5618. P. M . Borrell, P. Borrell. and K . R. Grant, J. Chcv~7.Soc.. Ftrrrrtkrj. Trtr17.s. 2. 1980. 76, 1442; G . A. Fisk and G. N . Hays. CIiwi. Pl7j.s. Lctt., 198 I . 79. 33 I . P. M. Borrell, P. Borrell. and K . R. Grant, J. C/wrt7.Sot,.. Fwrrticry Truris. 2 , 1980, 76, 923. R. Winter. I. Barnes, E. H. Fink. J. Wildt. and F. Zabel. C/itv~i. P h ~ : s .Lrtt.. 1980. 73, 297. N. Washida, H. Akimoto, a n d M . Okuda, Bull. c/?C'/?7. Sol.. J p . , 1980, 53. 3496. R . G. Aviles. D. F. Muller, and P. L. Houston, A p p / . P h ~ . s Lctr.. . 1980. 37, 358. R. D. Kenner and E. A. Ogryzlo, Int. J . Chci~7.K i n c f . , 1980, 12, 501. J. T. Moseley, J. B. Ozenne, and P. C. Cosby, J . Chcvii. P h j x . 1981. 74. 337. M. Carre, M . Druetta, M. L. Gaillard, H . H . Bukow. M . Horani, A. L. Roche, and M. Velghe, Mol. Ph.rs., 1980. 40, 1453; J. C. Hansen. M . M . Graff. J. T. Moseley. and P. C . Cosby, J. C ~ U Jfhj*s.. I. 1981. 74, 2195. H. Helm, P. C. Cosby. and D. L. Huestis. J . C h ~ 7fhys., . 1980. 73, 2629. F. P. Tully and A. R. Ravishankara, J. PIiJs. C h ~ n i .1980. , 84, 3126. U. C. Sridharan, B. Reimann, and F. Kaufman. J. Chmt. fhjx., 1980. 73, 1286; L. F. Keyser. J. P h ~ s . Chcm., 1980, 84. 1659. B. M.Morrison. jun., and J . Heicklen. J. f h o r o c l i m . . 1980. 13. 189; L. J. Stief, D. F. Nava. W. A . Payne, and J. V. Michael, J. Chcr~i.Phj:s.. 1980. 73, 2254. J. A. Silver and C. E. Kolb, C/wm f h j - s . Lett.. 1980,75, 191; K . J. Niemitz. H. Gg. Wagner. and R. Zellner, Z. PI7j.s. C/iuJ7., 1981, 124, 155. C . M. Stevens. L. Kaplan, R. Gorse, S. Durkee. M . Compton. S. Cohen. and K . Bielling, Irzt. J . Cheni. Kinrt., 1980, 12, 935. L. G . Anderson, J. f l 1 j . s . C l i m . . 1980, 84, 2 152. H . H . Nelson, W. J. Marinelli, and H . S. Johnston, Chern. Phjx. Lett., 1981. 78. 495. G. Paraskevopoulos and W. S. Nip, Ctnr. J . CIJPIJI.. 1980, 58, 2146; G . K . Farquharson and R. H. Smith. Airst. J. C / J W ~1980.33. ., 1425; J . V. Michael. D. F. Nava. R.P. Borkowski, W. A. Payne, and L. J. Stief. J . C/icv~i.f h j . s . , 1980. 73, 6108.

I58 Photochemistry halogenated derivatives 444 have been studied. Two recent determinations of the rate constants of process (36) ds a function of temperature in the region OH

+ H,O,

-

HO,

+ H20

(36)

245-460 K are in substantial agreement,',' but find values of k , , a factor of 2 higher at 298 K and factors of 3-5 higher at temperatures corresponding to 1030 km altitude than those previously accepted. The effect of these new values upon atmospheric modelling calculations is liable to be ~ o n s i d e r a b l e . Trajectory ~~ calculations upon the OH + H, surface have been carried out, with the effect of vibrational energy on product-state distribution and reaction enhancements evaluated.445The use of laser-induced fluorescence of the A-X transition in OH to monitor flame temperatures has been predissociation linewidths in the A 2 C + states have been calculated 447 and lifetimes of the B and C states of the radical measured.448 The first three-dimensional quantum mechanical calculations of triatomic photodissociation has been performed on H 2 0 , with calculated extinction coemcients in the region 130-1 35 nm agreeing well with experimentally observed features.449 Mechanistic 4 5 0 and kinetic 4 5 1 details of the reactions of HO, with itself 4 5 1 and with OH radicals 4 5 1 have been reported. 4503

N Atoms, N,, and NO,.-Resonance fluorescence methods have been used to study the reactions of ground-state N atoms (4S) with several molecular collision 4 5 3 The question whether N atoms react with unsaturated hydrocarpartners.452* bons has been raised. Removal rates of N(4S) by C,H4 have been seen to increase with N, pressure in time-resolved experiments, and the reaction is presumed to be third order;452at a total pressure of 3 Torr the calculated removal rate is however over two orders of magnitude larger than that estimated from flow-discharge and the discrepancy between these results, both using direct methods of N(4S) observation, remains unexplained. Energy partitioning in the NO product of the slow N(4S) + 0, reaction has been studied, with absolute values of the rate constants into vibrational levels u = 2-7 determined.454A minimum energy path calculation has been made for this reaction on quartet and doublet surfaces, with comparisons of experimental activation energies with theoretical barrier heights showing that reaction on the doublet appears to predominate.455The excitation rates of ground-state N atoms in collisions with Ar metastables have been determined,456and both quenching and reactions of

'" D. 445

44h JAi

448 449

45 I

452 453 454

455

'"

L. Singleton. G. Paraskevopoulos, and R . S. Irwin, J. Phys. Cliem., 1980, 84, 2339; G. Paraskevopoulos, D. L. Singleton, and R. S. Irwin, ihid., 1981, 85, 561. G. C . Schatz and H. Elgersma. Climr. Pli.v.7. Leif., 1980, 73, 21: G. C. Schatz, J . Clienr. P/r?9s.,1981, 74. 1133. c'. Chan and J . W. Daily, Appl. Opr., 1980, 19, 1963. M . L. Sink. A . D. Bandrauk, and R. Lefebvre, J . Cliem. P l i ? ~ .1980, , 73. 4451. T. Bergeman, P. Erman, and M. Larsson, Cliem. Pli?*s., 1980, 54, 55. E. Segev and M. Shapiro. J . Cli~wr.P h ~ s . .1980, 73, 2001. H . Niki, P. D. Maker, C . M. Savage, and L. P. Breitenbach, Clicwr. Pliys. krr.,1980, 73, 43. C. J. Hochanadel, T. J . Sworski. and P. J. Ogren. J . Pliys. Clrcm., 1980, 84, 3274. D. Husain and N. K . H. Slater, J . Clim. Soc., Frrrrirkij* Trrins. 2, 1980, 76, 606. J . V. Michael, Ciiem. Phys. Lcfi.. 1980, 76, 129. A. Rahbee and J . J . Gibson, J . CIiem. PA?..s.. 1981, 74, 5142. G. Das and P. A. Benioff, Cliem. P1iy.s. I,ctt.. 1980, 75, 519. L. G. Piper, M. A. A. Clyne, and P. B. Monkhouse, C l i ~ mPliys., . 1980. 51, 107.

Gas-phase Photoprocesses 159 ~ ~ e.s.r. ~ , ~detection ~ ~ of excited N atoms ( 2 D and ’ P ) have been s t ~ d i e d , with N(’D) being utilized for the first time in kinetic experiments.458 Measurements of the removal rates of N2(A3Z:,+)by various small molecules have been r e p ~ r t e d . ~ Modelling ~ ~ - ~ ~ lof the HgX(X = Br, C1) lasers requires knowledge of such rate constants, as the addition of N, to the mercury halide laser system is found to increase the efficiency and output energy by an order of magnitude, and the potential mechanism for this is dissociative excitation with HgX2.459 The energy-pooling reaction of reactions of N2(A3Zu+) 2N,(A3&,+) molecules has been shown to generate the near-i.r. Herman band system of nitrogen, yet the states linked by this transition have yet to be assigned.461The fluorescence decay behaviour of the N2(B31’I,)462 and (C3n,)463 states have been studied, and the mechanism for vibrational relaxation within the A2n,state of N 2 + has been shown to involve collision-induced transitions into and out of high vibrational levels of the X 2 Z , + ground state.464 Fine details of the effect of internal states of NO upon the cross-section for its reaction with 0, are starting to emerge.465.466 No dependence of the chemiluminescence yield of the NO2* product upon the electronic fine structure states of NO (21’1, and 2113,2) is 466 but an increase in rotational energy increases the cross-section appreciably: the development of molecular beam electric field focusing techniques is such that J and m, state-selected beams of NO are now able to be used in reactive studies.466Theoretical studies of the effects of vibrational energy in this reaction show no mode-specific enhancement of the cross-section for various model potential energy surfaces, although the presence of energy is more effective in overall vibration than in t r a n ~ l a t i o n . ~Lifetimes ~’ of the A , B, and D states of NO have been measured.468 In the multiple-photon ionization of rotationally cooled NO seeded in a molecular beam of He, high laser powers have been seen to produce appreciable line broadening Figure 5 shows the MPI spectra at high and low intensities in the beam, together with a high intensity spectrum from a room-temperature ‘bulb’ sample, both sets of spectra showing features due to the two-photon A 2 Z + t X211,(0, 0) transition, with the A state then ionized by further absorption. Rotational cooling is evident in the beam, and the broadening effect is seen to be absent in the ‘bulb’ sample of NO. An explanation offered for this is that in the presence of the laser field, low-energy NO-He collisions (similar to those 457 458 459

460

46’ 462

463 464 465

466 467 468 469

M. P. Iannozzi and F. Kaufman, J . Cliem. Pliys.. 1980, 73, 4701; K. Sugawara, Y. Ishikawa, and S. Sato, Bull. Chem. SOC.Jpn., 1980, 53, 3159. B. Fell, I. V. Rivas, and D. L. McFadden, J . Pliys. Chem., 1981, 85, 224. T. D. Dreiling and D. W. Setser. Chem. Pltys. Lett., 1980, 74, 21 1 . W. G. Clark and D. W. Setser. J . Pliys. Cliem., 1980, 84, 2225; L. G. Piper, G. E. Caledonia, and J. P. Kennedly. J . Cliem. Phys., 1981, 74, 2888. I. Nadler, D. W. Setser, and S. Rosenwaks, Cliem. Phys. Lett., 1980, 72, 536. N. Sadeghi and D. W. Setser, Cliem. PIiys. Lett.. 1981, 77, 304. E. I. Asinovskii, L. M. Vasilyak, and Y. M. Tokunov, High Temp., 1979, 17, 719. D. H. Katdyatna, T. A. Miller, and V. E. Bondybey, J . Chem. Phys., 1980, 72, 5469. S. L. Anderson, P. R. Brooks, J. D. Fite, and 0. V. Nguyen, J . Chem. P h p . , 1980, 72, 6521. D. van den Ende and S. Stolte, Chem. Pliys. Lett., 1980, 76, 13. S. Chapman, J . CIiem. Phys., 1981, 74, 1001. T. Hikida, S. Yagi, and Y. Mori, Cliem. Phys., 1980. 52, 399. (a) R. E. Demaray, C. Otis, K. Aron, and P. Johnson, J . Chem. Phys., 1980,72, 5772; (b) C. E. Otis and P. M. Johnson, Chem. Phys. Lett., 1981,83, 73.

160

Plz o tochemist rq’

I

4 52.2

I

I

I

452.4 Laser wavelength/ nm

Figure 5 ( a ) Multiple-photon ionizution spectruni qf’tlieNO A’C’ t X2111(0,0)hund at lou~ Iuser intensitl?in N tnolechr henm q f ” 0 seeded in He. This is (I two-photon resonance in N ,four-photon ionizution process ut this h e r wvelength. Onlj. three lines, representing AN = 0, I , and 2 trimsitions ure seen, indicating that the rotutional temperature in the heam is less thun I K . (b) Scan of the suine spec.trril region US (a) except NI higher loser power, showing broadening. (c) Room-temperature spectrum of pure NO in the same region with the same intensity as (b)showing laser resolution limited linewidths

reported earlier in beams of glyoxa13*and aniline87 in He) cause crossings between the potential energy curves of a real excited state and a two-photon ‘dressed’ state produced by the laser field. Subsequent experiments however have shown that AC Stark broadening rather than laser-enhanced collisions are responsible for this effect,469band its absence in the higher-pressure experiments [Figure 5(c)] is yet to be explained. Fluorescence spectroscopy of NO, has been used to determine the onset of predissociation in the and to measure the absolute cross-section for emission following monochromatic excitation at 532 nm,47 and the temperature dependences of both the NO, fluorescence spectral distribution and its collisional ”(’

C. H . Chen. D . W. Clark. M . G . Payne, and S. D. Kramer, Opt. C o m r n ~ t .1980, . 32, 391 C. S. Dulcey. T. J . McGee. and T. J. McIlrath. C h m . PItjx. Lcrt.. 1980. 76. 80.

161

Gus-phuse Photoprocesses

quenching behaviour have been measured.472 The dynamics of the photodissociation of NO, at 337 nm have been investigated by measurements of the energy distribution in the NO fragment using laser-induced fluore~cence.~'Figure 6 shows rotation-vibration population distributions for both for spin-orbit states of NO, with a strong vibrational population inversion apparent, and with rotational energies appearing non-statistical, with some evidence of a bimodal rotational of laser-induced fluorescence from photofragments d i s t r i b ~ t i o n .Detection ~~~ such as NO in this fashion can be a useful method for measurements of low concentrations of non-fluorescing molecular species.474 Electronically excited NO, (produced by absorption of Ar' radiation) abstracts tertiary H atoms directly from isobutane, with t-nitrobutane formed as the major product by subsequent reaction of the t-butyl radicals.475 Internal Energy Distribution "%IS

i

0,015

NO,+ hv -NOW

A,,,=

* n)+O(3p)

337.1 nm 0

0

I

0 0 0

I

0

Internal energy/cm-'

Figure 6 Population distribution of the NO-fragments (is a,function of the internal energy of their specific rotation-vibration states, produced by photodissociution of NO, ut 337.1 nm. Open circles denote the 2111, ground electronic state,jlled circles the 2n3,2 state

The photochemistry of the nitrate radical, NO,, needs to be incorporated into realistic models of the chemistry of the stratosphere: NO, arises mainly from the reaction of NO, with 0,, and its photolysis products can take part via reactions (37) and (38) in the photochemical cycles upon which the balance of stratospheric

NO,

+ hv

-

+ 0,

(37)

NO, + O

(38)

NO

ozone depends. Accurate measurements of the absorption cross-section are a first requirement, and a value of 1.21 x 10-'7cm2 at 294K at the absorption maximum, 663nm, has been derived from an experiment in which known

"'

D. G. Keil, V. M . Donnelly. and F. Kaufman. J . Clwni. P h ~ : s . .1980, 73. 1514. M . Geilhaupt, K . Meicr, and K . H. Welge, J . C/imi. Ph,vs., 1981, 74. 218. "' HM.. Zacharias, 0. Rodgers. K . Asai, and D. D. Davis, Appl. U p . , 1980. 19. 3597. M. E. Urnstead. J. W. Fleming. and M. C. Lin, IEEE J. Q w t i i u t ? i E k t r o t i . . 1980, 16. 1227.

162 Photochemistry concentrations of NO, were quantitatively converted into N 0 3 . 4 7 6Processes (37) and (38) have photochemical thresholds at wavelengths of 8 pm and 580nm, respectively,476 and their relative rates by solar photolysis over the wavelength region 470-700 nm favour process (38) by a factor of 10 over (37), the quantum yield of 0 atoms being close to unity at wavelengths below 580nm.477In the photodissociation of N,O at vacuum-u.v. wavelengths, excited-state NO (B21T) and N, (B311) products have been observed, and their quantum yields and mechanisms of formation investigated.478

-

SO, and COX.-Collision-induced rotational relaxation within the 2' A , excitedstate manifold of SO, has been studied.479,480 Excitation of single rovibronic levels of the 2 state near 304.3nm yields single exponential decays, in contrast with previous reports of double exponential decay behaviour when broader band excitation sources were used. Interference from the underlying continuous ' B , state appears to be the cause of the latter behaviour, and narrow band excitation can remove this problem.479Total removal rates of the selected levels by SO, have cross-sections of 500 state-to-state rotational energy transfer crosssections of 50 A' are observed, with dipole-like propensity rules (AKa = 1) occuring from these collision processes.48o Near-u.v. emission from SO, has been seen following infrared multiple-photon absorption by the ground-state molecule, with subsequent 'inverse electronic relaxation', possibly assisted by collisions, populating the $ A , and BIB, emitting states.481 Excitation of CO in the A'n(v' = 13) t-X'C+(v" = 0) transition has been accomplished using tunable V.U.V.radiation at 123 nm produced by frequency tripling the output of a dye laser in Kr gas. The production of the excited state was detected by its subsequent ionization to form CO+ at 266 nm.482Lifetimes of the d3A state of CO have been measured by a delayed coincidence A method of calculating bound-free Franck-Condon factors has been applied to the photodissociation of C02;484reactions of ground-state C,O (Z3C-) with NO, O,, and isobutene have been studied using time-resolved laser-induced fluorescence to monitor the radical concentration^.^^^

- -

*

10 Miscellaneous Rotational relaxation within the first excited states (A'C,') of Li, 486 and Na, 4 8 7 has been studied with several collision partners. For Li,, a strong asymmetry in the ratios of cross-sections for upward and downward AJ changes is observed,486 in contrast to the Na, work, in which little dependence of this kind is seen.487 A

'" D. N. Mitchell, R. P. Wayne, P. J. Allen, R. P. Harrison, and R. J . Twin, J . Chiwt. Soc., Formk/!Tucrns. 2 , 1980. 76, 785. 47'

F. Magnotta and H. S. Johnston. Geoplij-s. Rc~s.Lett., 1980, 7, 769. 478 I. P. Vinogradov and V. V. Firsov, Higli Eticrgj. Clietn., 1980, 14. 16. 479 D. L. Holtennann, E. K . C. Lee. and R. Nanes, Cl7en7. Plys. Lctt., 1980. 75, 91. D. L. Holtermann, E. K . C. Lee, and R. Nanes, Clrrwi. Pl7j.s. L c r r . . 1980. 75, 249. G. L. Wolk. R. E. Weston, jun., and G. W. Flynn, J . Chc~rti.Phj-s., 1980, 73, 1649. 482 H. Zacharias, H . Rottke, and K . H. Welge, Opt. Comrnun., 1980, 35. 185. W. C . Paske. J . R. Twist, A. W. Garrett, and D. E. Golden, J . Cliem. Pliys., 1980, 72, 6134. 4H4 K . C. Kulander and J. C. Light, J . Cliuti. P/7j-x., 1980, 73, 4337. V. M . Donnelly, W. M . Pitts, and J . R. McDonald. Clw77. Phys., 1980, 49, 289. 4 X h Ch. Ottinger and M . Schroder, J . PAjx. B , 1980, 13. 4163. '" T. A. Brunner, N. Smith. A. W. Karp. and D. E. Pritchard. J . C h m ~Phrs., . 1981. 74. 3324.

'"

Gas-phase Photoprocesses 163 simple exponential energy-gap dependence of the cross-section is found to be inadequate in explaining the data in both m o l e c ~ l e s4,8 ~7 and ~ ~ ~empirical scaling laws have been reported, which fit a large range of experimental results extremely For the C'll and D ' n states of NaK, energy transfer from single rotational levels has been studied using polarized laser fluorescence, and crosssections have been measured for transfer of orientation as well as population;488 the former is believed to be a valuable indication of anisotropy in the intermolecular potentials. Collisional effects determining the internal energy distributions in ground-state Na, expanded in a low-pressure free jet of sodium vapour have been determined.489 A Boltzmann distribution is observed at the nozzle exit, yet deviations from this occur downstream, indicating that relaxation processes away from the nozzle are of importance. Dissociation and predissociation of alkali-metal dimers in one-490-492 and two-photon 493 absorption processes have been investigated experimentally 490, 49 493 and t h e ~ r e t i c a l l y .The ~ ~ ~fluorescence from Na('P,) atoms formed in the dissociation of Na, via excitation of the B'n, c X'&+ transitions is found to be polarized,490 and its magnitude and direction (with respect to the electric vector of the laser beam) are in accord with earlier theoretical predictions of this effect. Predissociation products from the C and D states of Rb2491and from the states reached by two-photon absorption in Csz 493 have been identified. Emission in the d3n1-a3C+494 and D'rI-a3Z+ 495 bands of NaK has been analysed spectroscopically, and comparisons have been made between observed and calculated emission bands of LiCa 496 (produced in the reaction between Ca atoms and electronically excited lithium dimers). Bound-free transitions in alkalimetal dimers have been i n v e ~ t i g a t e d , ~and ~ ' dispersed laser-excited fluorescence used to obtain rotational and vibrational constants for the ground states of the monohydrides and deuterides of sodium and potassium.498 Rotational relaxation studies have been carried out on BaO radicals in the A 'Z+ with scaling laws again developed for the rates of rotational redistribution brought about by collisions with Ar and CO,, and simultaneous measurements of line-shapes in the C'C+ t A ' C + transition have allowed the centre of mass scattering angle distribution, brought about by velocity changing collisions, to be characterized. Collisions with CO, cause significantly smaller angle scattering than do those with Ar, although for both species scattering is predominantly forward in the centre of mass frame. Small changes in rotational quantum number J result in small centre-of-mass deflection angles and larger 3 '

488

489

490 491

492

493 494

495 496

497 4y8 499

J . McCormack and A. J. McCaffery, Cliem. Phys., 1980, 51. 405. F. Aerts and H . Hulsman, Chem. Phys. Lett.. 1980, 72,237. E. W . Rothe, U. Krduse, and R. Duren, Chem. Phys. Lett., 1980, 72, 100. E. J. Breford and F. Engelke, Cliem. Pliys. Lett., 1980, 75, 132. T.Uzer and A. Dalgarno, Chem. Pliys.. 1980, 51, 271.

C. B. Collins, J. A. Anderson, D. Popescu. and I. Popescu, J . Cliem. Plips., 1981, 74, 1053, 1067. H . Kato and C. Noda, J . Chem. Pliys., 1980. 73,4940. C. L. Chi0 and H . Chang, Cheni. P l i j ~ Left., . 1980, 73, 167. D.K. Neumann. D. J. Benard, and H . H. Michels, Chem. Pltys. Lett., 1980, 73, 343. J. Tellinghuisen, G. Pichler, W. L. Snow, M. E. Hillard, and R. J. Exton, Chem. Pliys., 1980,s. 3 13; D. D. Konowalow and P. S. Julienne, J . Chem. Phys., 1980, 72, 5815. M. Giroud and 0. Nedelec, J . Cliem. P l y . , 1980, 73,4151. R. A. Gottscho, R . W. Field, R . Bacis, and S. J. Silvers, J . Cliem. Pliys., 1980, 73, 599.

Pho t o c h i v I~is trj*

164

changes in J result in large deflections, implying that these distinct processes are controlled by the long- and short-range parts, respectively, of the intermolecular potential.499 The radiative lifetime of the C'C' state BaO has been measured as 10.5 1 n ~ ; ~ ' 'similar measurements on the A2n states of BO, and BO 5 0 1 have been reported. The 147 nm photolysis of Si,H, has been carried out by classical photochemical technique^."^ Three primary processes are suggested, all of which result in the formation of H atoms, and of which reaction (39) has the largest quantum yield 5 0 1 3 5 0 2

Si,H,

+ hv

-----+

SiH,

+ SiH, + H

(39)

(@ = 0.61). The U.V. photolysis of PH, has been reinvestigated, with the

formation of P,H4 (from PH, recombination) in the subsequent chemical reactions emphasized, particularly with respect to its role in the photochemistry of the atmosphere of Jupiter.504 Laser-induced fluorescence studies of PbS have produced lifetimes for the A , a, and B state^;''^ linewidth measurements on the C10, J2A2t f 2 B , transition have been used to study the predissociation mechanism as a function of spin and rotational angular momentum, and vibrational quantum numbers. 506 Laser transitions operating with the ' S state of Se as the upper level are currently of interest, as the possibility of storing considerable amounts of energy in this optically metastable state implies that high-power pulsed output on the ' S - ' D , and ' S - , P , transitions at 776.8 and 488.7nm will result. Photolysis of OCSe at 172nm forms Se('S) with a quantum yield of 0.63.507 Substantial quantities of free electrons are formed [by photoionization of Se('S)] and these quench the ' S state extremely rapidly (at a rate constant of 1.2 x l0-'cm3 molecule- s-');~'' this undesirable effect can be controlled by addition of SF6,507q which itself undergoes an efficient electron-attachment process. Laser output on both transitions corresponding to 0.3 photons per OCSe molecule in the irradiated volume has been achieved.508 At 193nm, the Se('S) quantum yield is lower (0.25) 5 0 9 but this wavelength may be a more suitable one for OCSe photolysis, as the ArF laser is more efficient than the Xe,* 172nm source, and photoionization of Se('S) is not possible at 193 nm. Substantial formation of one of the lower lasing levels t 3 P 1 )is found (a = 0.25) but this can be rapidly removed by quenching collisions with CO or C0,.509 Lifetime and quenching behaviour of SeO, excited at 288.8 nm has been reported."' The spectroscopic and kinetic behaviour of rare-gas excimer states have been studied in some detail. Rapid quenching of He,(a3C,+) by several collision

'*

500 50 I

503 504

5"5

'07

'')' 50y

'lo

Y. C. Hsu. B. Hegemann, and J . G. Pruett, J . C'heni. P / i . ~ x 1980, . 72, 6437. M . A. A. Clyne and M. C . Heaven, Client. Phj-s., 1980, 51, 299. S. McIntosh. R. A. Beaudet, and D. A. Dows, Ckem. P/ij.s. Lett., 1981, 78, 271. G. G. A . Perkins and F. W. Lampe, J . A m . Cliiwt. Soc.. 1980, 102, 3764. J. P. Ferris and R. Benson, J . An?. CAiwi. Soc., 1981, 103, 1922. 9. Burtin, M . Carleer, R. Cocin, C . Dreze. and T. Ndikumana, J . PIiys. B . 1980, 13, 3783. S. Michielsen, A. J. Merer. S. A. Rice. F. A. Novak. K . F. Freed, and Y . Hamada, J . Chm7. PIij~s., 198I , 74, 3089. W. M. Trott, J . K . Rice, and J. R. Woodworth, J . Chem. Pliys., 1981, 74, 518. H . T. Powell and 9. R. Schleicher, J . Chetn. Phj-s.. 1980, 73, 5059. M . J . Shaw, M. C . Gower, and S. Rolt, Cliiwt. PIiys. Lett., 1980. 73, 478. A . W. Miziolek. Climi. Phys. Lett., 1980, 74, 32.

Gus-pliuse Ph o t cipr oc ~ ~ s s e . s

165

partners has been quantitatively o b ~ e r v e d ,*~high excited Rydberg states (11 < 25) of He, have been found by absorption from the CI state and detected by collisional or autoionization processes,512and the kinetics of removal of the He2(d3X:,') state by He have been studied.513Neon,"4 k r y p t ~ n , " ~ and " xenon 5 1 5 b dimers have received spectroscopic 4- 5 1 5 h and kinetic 5 u attention. Exciplexes of MgXe j 1 and CdHg 5 1 7 have been investigated with the aim of determining their potential as candidates for lasing action: neither appears promising owing to the large excitation energies needed to produce the Mg* excited-state precursor^,^ and to absorption of potential lasing wavelengths by the upper ( a )CdHg state,5l 7 respectively. Green emission produced in the pulsed excitation of Hg-N, mixtures at 253.7 nm has been ascribed to the Hg3* species, and its spectroscopy and kinetic behaviour have been investigated experimentally. Considerable research effort is presently directed towards the photodissociation of metal carbonyls, partially because population inversions and laser action has been achieved upon the atomic metal vapours formed. The mechanisms of the fragmentation processes are naturally of interest. For Fe(CO),, irradiation at 248 nm produces Fe(CO),, Fe(CO),, and Fe(CO), from single-photon absorption at fractional yields of 0.55,0.35, and 0. 1 , 5 1 9 and it is thought that at this and other wavelength^,^^' sequential loss of CO from highly internally excited fragments formed results in the observed products. The intensity and spectral distribution of Fe* fluorescence produced by multiplephoton absorption of 248 nm radiation in Fe(CO), is highly dependent upon conditions of excitation, and could explain the varying results obtained in different laboratories.521The detection of metal atoms by multiple-photon ionization following their production by multiple-photon dissociation of volatile precursor molecules is now a common technique, and has been reported for the Fe,522Cr,523W,523and Mn 5 2 4 carbonyls, f e r r ~ c e n e ,5~2 5~ ~ . and n i ~ k e l o c e n e . ~Plasma ,~ formation has been seen in the C 0 2 laser irradiation of Fe, Ni, and Cr c a r b o n y l ~ . ' ~ ~ The effect of non-resonant laser fields upon the cross-section for simple chemical reactions ('laser-assisted collisions') is currently of theoretical interest,527- 5 3 0 and 511

512

'I3 '14 515

516 'I7

'I9 ''O

'" '" '" '" 523

52b

''' 529

530

S. Takao, M. Kogoma. T. Oka, M. Imamura. and S. Arai, J . Cli~~nt. P l i j x . . 1980, 73, 148. R. Panock, R. R. Freeman, R. H. Storz, and T. A. Miller, Cltem. Pltj*.s. Lett., 1980, 74, 203. J. W. Parker, L. W. Anderson, W. A. Fitzsimmons, and C. C. Lin, J. Client. Pltjs., 1980, 73, 6179. Y. Tanaka and W. C. Walker, J . Clieni. Pli.rs., 1981, 74, 2760. ((1) Y. Salamero. A. Birot, H. Brunet, H. Dijols, J. Galy, P. Millet. and J. P. Montagne, J. Clieni. P I y . , 1981,74,288; ( b )0. Dutuit, M. C. Castex, J. Le Calvt, and M. Lavollee, ibid., 1980,73. 3107. L. Schumann, D. Wildman, and A. Gallagher, J. Clteni. Phj*s., 1980, 72. 6081. M. W. McGeoch, J. Clteni. Pl~ys.,1980, 73, 2534. A. B. Callear and D. R. Kendall, Cltem. Pltys., 1981, 57, 65. G . Nathanson, B. Gitlin, A. M. Rosan, and J. T. Yardley, J. Ciiem. Phys.. 1981, 74, 361. J. T. Yardley. B. Gitlin, G. Nathanson. and A. M. Rosan, J. Cliem. Pltj,s., 1981. 74, 370. J. Krasinski, S. H. Bauer, and K. L. Kompd, Opt. Contniun., 1980, 35, 363. P. C. Engelking, Clteni. Pl1y.s. Lett.. 1980, 74, 207. D. P. Gerrity, L. J. Rothberg, and V. Vaida. Clieni. Plijx Lett., 1980, 74, 1. L. J. Rothberg. D. P. Gerrity, and V. Vaida, J . Cltem. P l t j x , 1981, 74, 2218. S. Leutwyler, U. Even, and J. Jortner, Cliem. Pltys. Lett., 1980, 74, 1 I . Y. Langsam and A. M . Ronn, Cheni. Ph?~s.,1981, 54, 277. I. H. Zimmerman. T. F. George. J. R. Stallcop. and B. C. F. M. Laskowski, Clieni. Pliys.. 1980, 49, 59. J. Weiner, J. Chenr. Pltys., 1980, 72, 5731. A. E. Ore1 and W. H. Miller, J . Cltem. Phys., 1980, 73, 241. M. Crance and S. Stenholm. J . Pl1j.s. B . 1980. 13. 1563.

166

Photochemistry

calculations upon the predicted enhancements for several systems have appeared, for example Br + H 2 , 5 2 7Hg + C12,528and H + LiF.529Clear experimental evidence for such processes is difficult to obtain, but this does seem to have been achieved for reaction (40).531The channel to form electronically excited HgBr K

+ HgBr,

-

KBr

+ HgBr

(40)

(B2C') becomes energetically feasible if energy corresponding to a photon of wavelength < 606 nm is added to the system. In the presence of 595 nm laser light, emission attributed to the HgBr(B) state is seen, despite the fact that neither reagents nor products absorb at this wavelength, and the cross-section for this process is estimated to be -10-'7cm2 at a laser intensity of ~ M W C ~ ~ ~ Experiments of this kind may provide direct details of the properties of the transition state for a chemical reaction: an alternative approach is to observe the effects of 'pressure broadening' of a spectroscopic transition in an atom or molecule formed by chemical reaction as it is in the vicinity of its co-product. For reaction (41) such an effect has been observed.532D-line emission from Na(2P)

F

+ Na,

-

FNaNa* ------+ I

I

h(a)

NaF I

+ Na(32P)

(41)

I

-

Figure 7 Spectral distribution of the radiation in the wings of the sodium D lines (589.0 and 589.6nm) recorded a1 a total D line intensity IN=*of'(2.4 0.2) x 106countss-'. Each lo point on the wing represents -3QQcounts repeated once or twice: error bars give iieviution. Intensities Icere corrected fbr instrument sensitivity

-

53'

P. Hering, P. R. Brooks, R. F. Curl,jun., R. S. Judson, and R. S. Lowe, Phys. Rev. Lett., 1980, 44, 687.

532

P. Arrowsmith. F. E. Bartoszek, S. H. P. Bly, T. Carrington, P. E. Charters, and J. C. Polanyi, J . Clwni. Plij*s., 1980, 73, 5895.

Gus-phuse Photoprocesses 167 formed is seen to be considerably broadened, the wings of the emission profile extending asymmetrically to several tens of nm on either side of the pure atomic transitions, as can be seen from the data of Figure 7. In principle this provides information upon the relative position of the emitting FNaNa* and the lower FNaNa states on the potential energy surfaces connecting reagents and products.532 Laser-induced predissociation in the presence of a surface magnetic field,533and dissociation dynamics in the presence of an intense laser field 5 3 4 have been treated theoretically. The dynamics of unimolecular decomposition and its relation to statistical theories of energy partitioning in fragments have been investigated. 5 3 5 The effect of reagent vibrational energy on the addition reactions between hydrogen halides and unsaturated hydrocarbons has been calculated: HX vibration is found to enhance the reaction probability, but not to an extent that suggests full utilization of the energy in overcoming the activation barrier.536 A threedimensional quantum treatment of vibrational predissociation in van der Waals molecules has been de~cribed,’~’theories have been proposed to explain intramolecular vibrational energy transfer in statistical 5 3 8 , 5 3 9 and intermediate 5 3 8 case molecules, and a review of laser-induced photoionization has appeared.540

533 534 535

53h 537 538

539 540

D. K. Bhdttacharyya, K . S. Lam, and T. S. George, J . Chem. Phys., 1980, 73, 1999. J. Weiner, Chem. Pliys. Lett., 1980, 75, 241; A. D. Bandrauk and M. L. Sink, J . Client. Phys.. 1981, 74, 1110. B. A. Waite and W. H. Miller, J. Ciiem. Phys., 1980, 73, 3713; ibid., 1981, 74, 3910. E. Zamir, Y. Haas, and R. D. Levine, J . Chem. Phys., 1980, 73, 2680. J. A. Beswick and A. ReqUend, J. Chem. PhJs., 1980,73, 4347. K. F. Freed and A. Nitzan, J . Ciiem. Phys.. 1980, 73, 4765. S. Mukamel and R. E. Smalley, J . Chem. Phys., 1980, 73, 4156. V. S. Antonov and V. S. Letokhov, Appl. Pliys.. 1981, 24, 89.

Part 11 PHOTOCHEMISTRY OF INORGANIC AND ORGANOMETALLIC COMPOUNDS

1 The Photochemistry of Transition-metal Complexes BY A. COX

1 Introduction Topics, which have formed the subjects of reviews this year, include the luminescence kinetics of metal complexes in solution, photochemical rearrangements of co-ordination compounds,2 photochromic complexes of heavy metals with diphenylthiocarbazone derivative^,^ the photochemistry of actinide^,^ actinide separation processes,' and light-induced electron-transfer reactions in solution and organized assemblies.6 A discussion has also appeared on assigning excited states in inorganic photochemistry.'

2 Titanium

Hydrogen has been reported to be formed together with Ti'" compounds on irradiation of aqueous-EtOH solutions of Ti'" at wavelengths greater than 3 10nm. In C,D,OH, equimolar amounts of H, and D, were produced.' Ti'" compounds also arise on photoreduction of Ti(OR),, R = alkyl, in the presence of a r n i n e ~ . ~ 3 Vanadium Following excitation of the CT bands at 313 nm, quantum yields of photoreduction and fluorescence have been obtained for the V" alcoholates of MeOH, EtOH, and PrOH. Absorption, emission, and excitation spectra of the V"' alcoholates are presented and the photochemical reaction mechanism and emission processes of V"' alcoholates are discussed.l o Low-temperature experiments have shown" the existence of radical transients in the formation of V" by photolysis of aqueous VCl, in alcoholic solvents. These transients are the products of one-electron oxidation of the alcoholic ligand in the V"-HOR complex. The

' ' * lo

T. J. Kemp, Prog. React. Kinet., 1980, 10, 301. F. Scandola, Org. Chem., 1980, 42, 549. A. Fabrycy and J. Soroka, Wiad. Chem., 1980,34,47. L. M. Toth, J. T. Bell, and H. A. Friedman, ACS Symp. Ser., 1980, 117, 253. G. L. Depoorter and C. K. Rofer-Depoorter. ACS Symp. Ser., 1980, 117, 267. D. G. Whitten, P. J. DeLaive, T. K. Foreman, J. A. Mercer-Smith, R. H. Schmehl, and C. Gianotti, Sol. Energy: Chem. Convers. Storage,[Symp.], ed.,R. R. Hautala, B. R. King, and C. Kutal, Humana Press Inc., Clifton, N.J, 1978, p. 117. A. W. Adamson, Gov. Rep. Announce. Index (U.S.), 1981,81, 61. I. A. Potapov, M. B. Rozenkevich, and Yu.A. Sakharovskii, Koord. Khim., 1981,7, 229. I. Kijima, Jpn. Kokai Tokkyo Koho. 1980,80, 139 392. Y. Doi and M. Tsutsui, Fundam. Res. Homogeneous Catal., 1979, 3, 859. B. V. Koryakin and T. S. Dzhabiev, Izv. Akud. Nuuk SSSR, Ser. Khim., 1980, 1769.

171

172 Photochemistry oxalato-vanadium(Ir1) complex, V(C204)2- is reported to sensitize the decomposition of oxalic acid in aqueous solution at 254nm, giving C 0 2 and CO as products. Following CT excitation, V" and the oxalate radical are produced and the latter decomposes to the formic acid radical, which is then reduced by V" to CO. A study l 3 of the mechanism of phototransformations of co-ordination compounds of vanadium in alcohol solutions has shown the existence of a stepwise redox process involving reduction of the metal atom and oxidation of solvent molecules. Trichloro-oxovanadium undergoes a similar phototransformation in alcoholic media,', and at low temperature a V"' compound is stabilized. Photolysis of VO(OR),, R = Me, Et, Pri, Pr, Bu, and amyl, brings about reduction only to the V"' level. l 5 This observation contrasts with the behaviour of chlorine-containing complexes and is a result of the greater tendency of the alkoxides to associate. Following photoreduction, the products derived from the alkoxides are more easily reoxidized by 0, than those containing C1. The effect of alcohol additives on the photoreduction of Vv ions and the liberation of hydrogen from aqueous solution has been examined,16 and found to decrease in the order Pr'OH > EtOH > PrOH > MeOH > Bu'OH. Irradiation of ethanolic solutions of acetylacetonate complexes of vanadium of the type VO(acac),OEt brings about two-electron reduction of the Vv ion.'' At shorter wavelengths (Airr = 254nm), ligand substitution occurs in CCl, to give VO(acac),Cl. This undergoes further photoreduction by visible light to VO(acac),. 4 Chromium

Measurements have been made of the room-temperature luminescence quantum yields of various Cr"' ammine and ethylenediamine complexes in water. l 8 Most emission was phosphorescence, but some fluorinated complexes emitted delayed fluorescence.The range of quantum yields was accounted for in terms of processes degrading the 2E state. Radiationless decay rates for the 4T2g + 4A2gtransition have been obtained for several Cr"' compounds in different glassy hosts and these have revealed a discrepancy in the 4T2g behaviour between crystals and glasses.l 9 It is suggested that this has its origin in the Cr"' site symmetry. The solid-state emission lifetimes of deuteriated and undeuteriated [Cr(NH3),I3 and [Cr(en),13 have been used as a probe to study the back intersystem-crossing deactivation pathway for these compounds.20 General agreement is found between the evidence presented and recent suggestions concerning a direct photochemical role for the 2 E state. Measurements of the temperature dependence of the +

+

'

l2

'' l4

l5 l6 l7

l9

2o 21

A. Matsumoto, H. Kumafuji, and J. Shiokawa, Inorg. Chim. Acta, 1980, 42, 149. A. I. Kryukov, S. Ya. Kuchmii, A. V. Korzhak, Z . A. Tkachenko, and V. A. Il'yushenok, Tezisy Dokl. Ukr. Resp. Konf. Fiz. Khim., 12th, 1977, p. 218. A. V. Korzhak and S. Ya. Kuchmii, Tezisy Dokl. Resp. Konf. Molodykh Uch. Khim., 2nd, 1977, p. 31. S. Ya. Kuchmii and A. I. Kryukov, Ukr. Khim. Zh.. 1980, 46, 1052. I. S. Shchegoleva, S. Ya. Kuchmii, T. I. Serdyukova, and A. I. Kryukov, Tezisy Dokl. Ukr. Resp. Konf. Fiz. Khim., 12th, 1977, p. 226. S. Ya. Kuchmii, A. M . Turchaninov, and A. I. Kryukov, Ukr. Khim. Zh., 1980,46,806. A. D . Kirk and G. B. Porter, J . Phys. Chem., 1980, 84, 887. L. J. Andrews, A. Lempicki, and B. C. McCollurn, Chem. Phys. Lett., 1980, 74, 404. N. A. P. Kane-Maguire, G. M. Clonts, and R. C. Kerr, Inorg. Chim. Acta, 1980, 44, L157. R. Fukuda, R. T. Walters, H. Macke, and A. W. Adamson, J . Phys. Chem., 1979, 83, 2097.

173 The Photochemistry of Transition-metal Complexes luminescence lifetimes of Cr"' complexes have been made in various media.22 These have enabled an expression to be developed for the rate constant of the luminescence decay. The activation energy of the temperature-dependent nonradiative term was found to be strongly solvent-dependent and this has lead to a chemical mechanism being suggested for deactivation of the 2E,state rather than simply accounting for it in terms of back intersystem-crossing. In another study, luminescence, time-resolved luminescence, and decay-time measurements over the range 4-100 K have enabled the exchange interaction parameters in several trinuclear Cr"' complexes of the type fCr,O(RCOO),(H,O),]X .nH,O (R = Me or Et) to be determined.23 Pulsed laser conductivities have been used 24 to study the photobehaviour of [Cr(en),13'. The method depends on measuring conductivity changes associated with reaction (1) following laser excitation. This is a new [Cr(en),(en)(H,0)I3+

+ H+

___+

[Cr(en),(enH)(H,O)l4+

(1)

approach and may be generally helpful in avoiding complications with excitedstate absorption. In a series of Cr'"-alkylamine complexes with CrN, skeletons, a correlation has been shown to exist between the radiationless transition rate and the number of active hydrogens attached to the donor atoms.25 The authors also report an expression that predicts the dependence of the non-radiative rates from the vibrational degeneracy and the displacement of the maximum frequency modes. A new formalism, namely bond indexes, Z(ML) has been developed which explains photolabilization and photosubstitution reactions of some hexacoordinated complexes of transition metals such as Cr, Co, and Rh. These bond indexes have been applied to ground and excited states, and the rule established that the leaving ligand is the one characterized by the smallest value of the bond index I*(ML). In the complex trans-[Cr(en),NCSF]+, thiocyanate photoaquation is quenched in parallel with the emission, and (en) photoaquation is quenched in a wavelength-dependent manner. " The differential quenching suggests participation by two quartet ~ t a t e s , ~and E 4B,together with some doublet participation, and accords with theoretical predictions as well as with known behaviour in other systems. The quantum yield of photoracemization of [Cr(en),I3+ has been found to be independent of pH. Although some of the data obtained suggest that the twist mechanism of photoracemization might be preferred, it has not proved possible to discriminate definitively between this and the bond-rupture mechanism.28 In aqueous HC1 solutions, irradiation of [Cr(en)J3 or [Cr(NH,Me),13 is reported to lead to substitution of one ligand by water.*' Photoaquation also occurs in

',,

+

22

23 24 25 26

2'

29

+

S. R. Allsopp, A. Cox, T. J. Kemp, W. J. Reed, S. Sostero, and 0.Traverso, J . Chem. SOC..Faraday Trans. I , 1980, 76, 162. M. Morita and Y. Kato, In?. J . Quantum Chem.. 1980,18, 625. W. L. Waltz, R. T. Walters, R. J. Woods, and J. Lilie, Inorg. Chim. Acta. 1980, 45, L153. K. Kuehn, F. Wasgestian, and H. Kupka, J . Phys. Chem., 1981, 85, 665. L. G. Vanquickenborne and A. Ceulemans, Inorg. Chem., 1981, 20, 110. A. D. Kirk, L. A. Frederick, and S. G. Glover, J. Am. Chem. SOC.,1980, 102, 7120. M. C. Cimolino, N. J. Shipley, and R. G. Linck, Inorg. Chem., 1980, 19, 3291. Yu. N. Shevchenko, V. A. Krasnova, A. A. Svezhentsova, V. V. Sachok, and A. I. Kryukov, Zh. Neorg. Khim., 1980, 25, 1834.

174

Photochemistry

NaClO,-HClO, solutions. By contrast, however, photolysis of [Cr(en),]' in aqueous HCl-KCl results in formation of cis-[Cr(en),Cl,]+. Irradiation of trans-[Cr(en),FiJ in aqueous solution gives [Cr(en)(enH)(H20)F2l3+, plus an isomer of [Cr(en)(enH)(H,0)F,l3 and cis-[Cr(en),F(H,0)J2+, of which the first is the dominant product.30 Thus, although the net stereochemistry of the starting material is retained, there is still some stereochemical inversion. These results appear to be in conflict with those of other workers.31 The products obtained from the photoaquation of trans-[Cr(NH,),F,I2 are consistent with the edge-displacement model and also with recent suggestions invoking a dissociative symmetry-restrictedphotoprocess.32 Results obtained in a similar investigation of the cis-isomer are consistent with only the symmetryrestricted photoreaction. A study has been made 3 3 of the ligand-fieldphotolysis of [Cr(tren)F,]+ in acidic solution, and release of F- is found to occur with a quantum yield of 0.21. the same aquofluoro isomer is formed in this process as is generated in the acid- or base-catalysed thermal reaction, and it is concluded that the photochemistry of this complex does not fit the current theoretical models of LF photochemistry of d3 centres. Under the stimulus of interest in the photoactive excited state of a Crnr C,, complex, the ligand-field photochemistry of [Cr(NH,),(CN)12 + has been examined in acidic solution.34 Aquation of NH, occurred and CN- was released thermally. Adamson's rules and other theoretical models were found to be helpful in interpreting these observations, and the product distribution suggests that equatorial photoaquation takes place with partial stereochemical change. The role of the doublet state in the photochemistry of Reinecke's ion, trans-[Cr(NH,),(NCS),] - ,continues to stimulate interest. It has now been tentatively suggested35 for Reinecke's ion itself, and indeed for Cr"' ammine complexes generally, that the doublet state disappears by chemical reaction rather than by intersystem crossing to the first quartet thexi state. The photochemistry of trans-Cr(tfa), has been studied in non-aqueous solvents by both continuous and flash experiment^.^^ For Airr >, 366 nm the dominant process is trans --+ cis isomerization, whereas at iirr = 254nm both isomerization and redox decomposition occur, being markedly solvent dependent. The existence of the photoredox process suggests at least a qualitative similarity between the photochemistry of this complex and that of other first-row transitionmetal b-diketonate complexes. Photoinduced bridge-cleavage has been reported for the rhodo complex [Cr(NH,),0HCr(NH3)5]C15 in acid solution at 254nm. A model is suggested in which all of the photoreactions arise from the CT state or the third quartet state, L,. The quantum yields of photolysis of [Cr(NH,),I3' in 1 0 ~ aqueous NaOH at 77 K and 365 or 436 nm have been observed to decrease with continued irradiation.,* However, warming the solution briefly to the devitrification temperature, restores the quantum yields to their original value. It is +

+

+

+

,

30 31

32 33 34

35

36

37 38

S. C. Pyke and R. G. Linck, Inorg. Chem., 1980, 19, 2468. M. F. Manfrin, D. Sandrini, A. Juris, and M. T. Gandolfi, Inorg. Chem., 1978, 17, 90. A. D. Kirk and L. A. Frederick, Inorg. Chern., 1981, 20, 60. M. J. Saliby, P. S. Sheridan, and S. K. Madan, Inorg. Chem., 1980, 19, 1291. P. Riccieri and E. Zinato, Inorg. Chem., 1980, 19, 3279. A. W. Adamson and A. R. Gutierrez, J. Phys. Chem., 1980,84, 2492. C. Kutal, D. B. Yang, and G. Ferraudi, Inorg. Chem., 1980, 19, 2907. R. R. Ruminski and W. F. Coleman, Inorg. Chem., 1980, 19,2185. A. Kh. Vorob'ev and V. S. Gurman, Kinet. Katal., 1979, 20, 1439.

The Photochemistry of Transition-metal Complexes

175

believed that this is because some ions which absorb light do not undergo a photochemical reaction because of their particular environment. There is still widespread interest in the photochemistry of [Cr(bipy),13 + and related complexes. The ' E and 4T, electronic excited states of this complex have been studied by Raman scattering in aqueous solution.39Similarities were noted between the 2E and ground-state spectra, but differences between the intensities and shifts of corresponding vibrational Raman bands of 4T2 and 4A, [Cr(bipy),13+ are more pronounced. The 4T2 -+ ' E intersystem-crossing rates have been determined using photoaquation quantum yield data for the two complexes [CrL313+,(L = bipy and 1,lO-phen) and both were found to be approximately unity.40 This result is in agreement with that obtained by KaneMaguire and Langford 41 from oxygen-quenching studies of the photoracemization of optically active [ C r ( ~ h e n )+. ~ ]The ~ values of for [Cr(bipy),13+ in H,O and D 2 0have been determined as 1.O and 0.23 with no change being noticed in the lifetime of the emitting state.42These results are taken to imply a change in the efficiency of the intersystem crossing from 4Tz,and is thought to arise from the rigidity of the phen ligands, which reduces the distortion of the 4T, state. Formation of thermally equilibrated Cr"' excited state and formation of Cr" have now been shown to be competitive processes that occur following irradiation of polypyridyl complexes of Cr" in alcoholic media.43The Cr' complexes arise as a result of oxidation of the solvent by the upper excited state and this kind of solvent-dependent photoredox process has now been found in various coordination complexes. Evidence has also appeared for the existence of a Cr" intermediate in the photolysis of [Cr(bipy),13 in DMF.44 An autocatalytic reaction is implicated in which a Cr"-bipy complex acts as the chain carrier. Luminescencequantum yields and a wavelength dependence have been reported 45 for the photohydrolysis of [Cr(bipy)J3+ over the wavelength range 488.0610.0nm. At about 590nm a crossover appears to exist at which disc decreases. The rate of ISC must, therefore, be fast enough to compete with relaxation within the quartet manifold, and at long wavelength the quartets mainly relax to ground state. Oxidation of [Cr(bipy)3]2' by Sz082- and T13+has been found 46 to lead to the generation of an excited state of [ C ~ ( b i p y ) ~ ]which ~ + , luminesces between 700-750 nm, and which forms with pseudo-first-order kinetics. Oxidations using H,O, did not lead to any chemiluminescence. Chromic acid esters have been photolysed in aqueous solutions of potassium chromate in 40% alcohol (MeOH, EtOH, 2-PrOH) in the presence of aquoamine cobalt(m) and the reaction appears to involve formation of CrVin the first step.47 It is also reported 48 that CrVoccurs as a short-lived species in the photoreduction of Crvl in the liquid phase; in rigid glasses it has been detected by e.s.r. However, +

39 40 4*

42 43 44 4s O6

47 48

M. Asano, J. A. Koningstein, and D. Nicollin, J . Chem. Phys., 1980, 73, 688. N. Serpone, M. A. Jamieson, and M. Z. Hoffman, J. Chem. SOC.,Chem. Commun., 1980, 1006. N. A. P. Mane-Maguire and C. H. Langford, tnorg. Chem., 1976, 15,464. R. Sriram, M. Z. Hoffman, and N. Serpone, J . Am. Chem. SOC.,1981, 103,997. G. J. Ferraudi and J. F. Endicott, Inorg. Chim. Acta, 1979, 37, 219. G. B. Porter and J. van Houten, tnorg. Chem., 1980, 19, 2903. R. L. P. Sasseville and C. H. Langford, tnorg. Chem.. 1980, 19, 2850. F. Bolletta, A. Rossi, and V. Balzani, tnorg. Chim. Acta, 1981, 53, L23. H. Hennig, P. Scheibler, R. Wagener, and D. Rehorek, fnorg. Chim. Acta. 1980, 44, L231. P. Rusev, M. Mitewa, P. Bonchev, and A. Malinovski, Dokl. Bolg. Akad. Nauk, 1980, 33, 519.

176 Photochemistry irradiation of [CrO,Cl]-[HPy] +-DMF induces a two-electron-transfer process with generation of Cr" as a transient. In the Crv'-oxalic acid-DMF-MeCN system, the photoreactions were found 49 to be solvent dependent: CrVwas again produced and Cr" and Cr"' were intermediates. A red luminescence of low quantum efficiency has been detected from chromate in some specific host lattices. Complexes of CrVand Cr"' are produced 5 1 in the photoprocess leading to the hardening of chromated poly(viny1 alcohol). Methods have also been reported for the determination of chromium by a luminescence methods2 and by a photochemical titration procedure.53 For other reports on chromium see references 65, 78, and 98. 5 Molybdenum and Tungsten It is reported that the Mo" cluster ion [MO,C~,,]~-is phosphorescent in solution at room temperature with a lifetime Br > I and to be independent of the wavelength of the exciting radiati~n."~ Increases in dipole moment also bring about increases in the amount of cis-isomer. In the particular case of the irradiation of trans[Pd(PPr,)Cl,] in MeNO,, the cis-configurationof the product has been established by X-ray analysis.173 The transformation appears to occur by an intramolecular mechanism involving a tetrahedral intermediate, which can collapse to a squareplanar form. Examination of the temperature-dependence of the luminescence of single crystals of the chain compound BaPd(CN),a4H2O has revealed the presence of two component^.'^^ One is short-lived (1011s) and is centred at -26 x l0,cm-l and one is long-lived (2ms at 5K) and is centred at 19 x lo3cm-'. A smaller spin-orbit coupling is more evident in Pd compounds than in Pt compounds, and this causes differences of lifetimes and emission energies between the two metals. An investigation of the photoisomerization of the Pt" complexes, cis- and trans(Et,P),PtPhCl, in MeCN has shown 176 that the cis-trans and trans-cis conversions occur by different mechanisms. The former appears to proceed by an intramolecular twisting in a low-lying LF state and the latter by a dissociative pathway from a CT state. The platinum complex (8) has been reported to display a

'',

-

169

170 17'

173 174 175

17'

A. Vogler and H. Kunkely, Angew. Chem. fnt. Ed. Engl.. 1980, 19, 221. R. Henning, W. Schlamann, and H. Kisch, Angew. Chem., Int. Ed. Engl., 1980, 19, 645. S.I. Mah, Hanguk Swnyu Konghakhoe Chi, 1979, 16, 215. M. Cusamano, G. Guglielmo, V. Ricevuto, S. Sostero, 0. Traverso, and T. J. Kemp, J. Chem. SOC., Dalton Trans., 1981, 302. N. W. Alcock, T. J. Kemp, F. L. Wimmer, and 0. Traverso, Inorg. Chim. Acra, 1980, 44,L245. N. W. Alcock, T. J. Kemp, and F. L. Wimmer, J. Chem. SOC.,Dalton Trans., 1981, 635. W. D. Ellenson, A. K.Viswanath, and H.H. Patterson, Inorg. Chem., 1981, 20, 780. L. L. Costanzo, S. Giuffrida, and R. Romeo, Znorg. Chim. Acta, 1980, 38, 31.

Photochemistry

190

hv S

s

CI

(8) S = Me,SO, MeCN

(9)

novel photochromic process.177 This consists of displacement of solvent on irradiation, and solvolysis of the product (9) in the dark in which the terminal aldehyde group reacts with a solvent molecule. A 5-co-ordinate intermediate is most probably involved in the thermal solvolysis and possibly also in the photosubstitution. 15 Copper Reviews have appeared of the photochemistry of copper complexes,17' the luminescence properties of copper(1) compounds,' 79 and of the mutual influence of ligands in co-ordination complexes.''O, The first emission and emission-quenching studies of bis(2,g-dimethyl-1,lOphenanthroline)copper(r) in fluid solution have been described,182 and at room temperature in CH2C12 the lifetime and quantum yield were found to be 54 & 10ns and 2 x respectively. Donor solvents such as MeOH, EtOH, and CH,CN tend to quench the emission, possibly by interaction with the metal centre. Luminescence spectra and decay times of emission have been measured 1 8 3 down to liquid helium temperatures for the complex [Cu(PPh,),(phen)]+ . The decay time at low temperatures suggests the involvement of a triplet level of the CT state and the radiative processes have to be described in terms of at least a threelevel system. A monoclinic form of the Cu' iodide pyridine complex has been prepared 84 but unlike the cubane tetrameric modification, this isomer does not show luminescence thermochromism. The photochemistry of copper@)chloride has been examined at 3 13 nm and 77 K in ethanol and HCl solutjon and has shown transient radical complex formation between Cu' and CH3CHOH. Photolysis of.DMF solutionsof [CuC1412- is reported 186 to lead to formation of the radical,CH,(CH,)NCHO, (10) and the Cu'-(lO) complex. At higher concentrations of [CuCl4l2-, photooxidation of (10) by excited [CuC1,J2- predominates. The photochemistry of the 177 178 179 180 181

182 I83 184 185

186

W. G. Rohly and K. B. Mertes, J . Am. Chem. SOC.,1980, 102, 7939. G. Ferraudi and S. Muralidharan, Coord. Chem. Rev., 1981,36, 45. H. D. Hardt and A. Pierre, Ann. Univ. Sarav., Math.-Naturwiss. Fak., 1980, 15, 7. J. Gazo, Proc. Conf. Coord. Chem., 8th, 1980, p. 99. J. Sykora, J. Sima, D. Valigura, E. Horvath, and J. Gazo, Proc. Conf. Coord. Chem., 8th, 1980, p. 393. M. W. Blaskie and D. R. McMillin, horg. Chem., 1980, 19, 3519. G. Blasse and D. R. McMillin, Chem. Phys. Left., 1980, 70, 1. E. Eitel, D. Oelkrug, W. Hiller, and J. Straehle, 2.Naturforsch., Teil B, 1980, 35, 1247. V. F. Plyusnin, N. M. Bazhin, and 0. B. Kiseleva, Zh. Fiz. Khim., 1980, 54, 672. V. F. Plyusnin, N. M. Bazhin, and 0. M. Usov, Koord. Khim., 1980, 6, 856.


191

halocuprates has also been investigated 8 7 in connection with photochemical solar energy conversion. In particular, a study of their photo-oxidation in acidic media has included such topics as the nature of the optical transition and also of the photolysis intermediates, medium effects, and an evaluation of the efficiency of CTTS transitions. The intermediate produced in the flash photolysis of copper(I1) oxalato complexes in deaerated aqueous solution has been identified 18* as CuCO,. This species, which is also generated by pulse radiolysis of the Cu'I-oxalate-formate system, decays by first-order kinetics. A dependence of the rate constant on pH and on the concentrations of Cu" and oxalate ions is established and this is interpreted in terms of competing reactions of CuCO, [equations (7) and (8)]. CuCO,

+ 2H+

cuco, + CU"

-

Cu"

+ HC0,H

(7)

2cu'

+ co,

(8)

The copper(m) tetraglycinate complex [Cu(H- ,Gly,)] - is reported ls9 to be photodecomposed to triglycinamideand tetraglycine (Gly,). Product distributions vary with pH, and in neutral solution room light is found to cause substantial reaction. Another Cu"' complex Cu(H-,Aib,) in which the ligand is the tripeptide of cc-aminoisobutyric acid is known to undergo a similar photocatalysed decarboxylation, and an analogous decarboxylation leading to Gly is proposed in the case of the photolysis of [Cu(H-,Gly,)]-. Rate constants have been determined I g l for the photochemical bleaching of the thionine cation in salts such as Q5[Cu8LSH].1 1.5H20 (Q = Cu, Mn, or Mo containing Cu' and Cu"'; H,L = maleonitriledithiol; and Q,[Mo,L,O,(OH),] - 7.6H20, H,L' = toluene3,4-dithiol. The results show that incorporation of the thionine cation into the complexes increases its photoreactivity.

,,

16 Lanthanides A discussion has appeared of the mechanism of sensitization of Tb" luminescence by Ce"' in CaF,. As part of a search for reversible, photoinduced, oneelectron-transfer reactions of the type shown in equation (9), which can in hv

Ce3+(aq) + A"+(aq)7 Ce" A

+ A("-')+(aq)

(9)

principle generate a photogalvanic current, the photoinduced electron-transfer between Ce"aq and Cu"aq ions has been investigated Ig3 by ps flash photolysis. The primary photochemical step appears to be bimolecular collision of the lowest energy 4d -+ 5fexcited state of Ce"' with Cu" leading to CeIV and Cu' as the la'

"' la9

190 191

D. D. Davis, R. K. Thamburaj, K. L. Stevenson, and C. R. Davis, Energy Res. Abstr., 1980,5, Abstr. No. 330. S. Das and G. R. A. Johnson, J. Chem. Soc.. Faraday Trans. 1. 1980, 76, 1779. J. S. Rybka, J. L. Kurtz, T. A. Neubecker, and D. W. Margerum, Inorg. Chem., 1980, 19, 2791. S. T. Kirksey, T. A. Neubecker, and D. W. Margerum, J . Am. Chem. SOC.,1979, 101, 1631. M. Kaneko, H. Araki, and A. Yamada, Polym. Prepr., Am. Chem. SOC.,Div. Polym. Chem., 1979,20, 1053.

192

193

M. S. Orlov, E. A. Pudovik, A. L. Stolov, and V. D. Shcherbakov, Paramagnitn. Rezonans, fKazan), 1978, 81. R. P. Asbury, G. S. Hammond, P. H.P. Lee, and A. T. Poulos, Inorg. Chem., 1980, 19, 3461.

192

Photochemistry

photoproducts. A method of determining organic carbon has been reported 194 using chemical and photochemical oxidation of the organic material with Ce(SO,), as sensitizer. In this procedure CO, is liberated and is determined coulometrically. Eu" ions are photo-oxidized in aqueous solutions of HC1 at room temperature by a mechanism that involves transfer of an electron from the excited ion to a proton or other acceptor.lg5 At Airr = 250 or 365nm, the reaction efficiency is increased with the acidity of the soluiion; Eu"' ions were observed to have an inhibiting effect. In frozen solutions of hydrohalic acids at 77K the photooxidation occurs by a similar r n e c h a n i ~ m , 'and ~ ~ under these conditions the rate constant measured for luminescence quenching was found to be in good agreement with the theoretical value.lg7 Ed' complexes of crown ethers and polyethylene glycols luminesce with an intense blue emission, which in the case of 15-crown-5 is over 600 times as strong as that of methanolic EuCl,. This enhancement is attributed to a reduced internal quenching rate. 19' A time-resolved study of the emission from Na3Eu(C4H,05), .2NaC10,. 6H20-europiumdiglycolatehas shown lg9 that following excitation to the 5D2(E) state, the emission from ' D o exhibits a fast and a slow build-up. This is interpreted in terms of two independent decay modes for 5D,.The luminescence of the complex formed between Eu"' and 2-propionylindan-1,3-dione has been studied 2oo at pH 4.0-4.5 and this forms the basis of a luminescence method for the determination of europium. Fluorescence measurements have been made 2o on Dy"', Er"', Eu'", and Sm"' salts of methacrylic acid-methyl methacrylate copolymer, and copolymers of acrylic acid with styrene, 1-vinylnaphthalene, and 1-vinylanthracene.In the case of Eu"', the results suggest the formation of ionic aggregates. The fluorescence intensity decreases in the order methacrylate > styrene > naphthalene > anthracene suggesting that the aromatic groups successfully compete with the exciting radiation and that there is negligible energy transfer from aromatic groups to the Eu"' ions. The coordination and solvation of Ed1' and Tb"' ions have been investigated 202 using fluorescence quenching and other techniques in anhydrous CH,CN (CD,CN) and DMF. In MeCN, Eu(NO,), is not dissociated whereas in DMF both ionic and coordinated NO, - are present. Similar results are obtained for Tb"'. Complexes of the form Ln(N0,)3(4-bipy),.4H,0 Ln = Eu, Tb, Lu, and LnC1,(4bipy),.6H20, Ln = Eu, Tb, Lu, or Y have been prepared 203 and all are found to be luminescent in the solid state. Similarly the fluorescence spectra of [EuL(NO,),]. H 2 0 and [EuL,](ClO,), -2H,O, L = 2,2"2""erpyridine-1,1',1''trioxide, have also been reported. 204 CPL (circularly polarized luminescence) 194

195 196 19'

19* 199

*O0 201 *02 203 '04

T. N. Ivanov and A. N. Atanov, Zh. Anal. Khim, 1980,35, 588. V. V. Korolev, N. M. Bazhin, and S. F. Chentsov, Khim. Vys. Energ., 1980, 14,542. V. V. Korolev, N. M. Bazhin, and S. F. Chentsov, Zh. Fiz. Khim., 1981,55, 138. V. V. Korolev, N. M. Bazhin, and S. F. Chentsov, Zh. Fiz. Khim., 1981,55, 144. G.Adachi, K. Tomokiyo, K. Sorita, and J. Shiokawa, J . Chem. Soc., Chem. Commun., 1980,914. D.S.Roy, K. Bhattacharyya, A. K. Gupta, and M. Chowdhury, Chem. Phys. Lett., 1981,77,422. S.V. Bel'tyukova, N. S. Poluektov, T. B. Kravchenko, and L. I. Kononenko, Zh. Anal. Khim., 1980, 35, 1103. E. Banks, Y. Okamoto, and Y. Ueba, J . Appl. Polym. Sci., 1980,25, 359. J. C. G. Buenzli, J. R. Yersin, and M. Vuckovic, Rare Earths Mod. Sci. Technol., 1980,2, 133. D.M.Czakis-Sulikowska and J. Radwanska-Daczekalska, Pol. J . Chem., 1979,53,2439. A. Musumeci, R. P. Bonomo, and A. Seminara, Inorg. Chim. Acta. 1980,45,L169.


193 measurements have been made 2 0 5 of the ternary complexes formed between pyridine-2,6-dicarboxylic acid (DPA), Tb"', and some amino-acids (AA). In Tb(DPA),(AA), a weak unipositive CPL was observed when the amino-acid was co-ordinated in a unidentate manner. For bidentate co-ordination, a doublesigned CPL was observed, and in the region pH8-10 this was also the case for most amino-acids. The fluorescence properties of several europium and samarium P-diketonates have been measured and assignments of the transitions made. 206 Rare-earth element hexafluoroacetylacetonates with amino-acids have also been reported to The luminescence of the heptafluoroheptane-2,4-dionecomplexes of Sm, Eu, and Tb has been measured 208 in dilute ethanol at pH 8 and 610nm; mixed-ligand complexes with 1,lO-phenanthrolineexhibited an enhanced luminescence. Photolysis of the Tb"' chelate of 2,2,6,6-tetramethylheptane-3,5-dionehas been examined 209 at 3 1 1 nm in various alcohols, and loss of one P-diketone ligand found to be the primary photochemical step. A linear correlation was demonstrated between the quantum yield of dissociation of the complex and the formation constant of the complex-alcohol adduct. 17 Uranium A review of the photochemistry of uranium compounds has appeared.210 In a paper discussing ground- and excited-state interaction between aquauranyl(v1) and nitrate ion, the structure and thermodynamic formation functions of photoexcited (UO,NO,)+ are shown to differ from those in the ground state.211 Exchange of the nitrato-ligand in excited (U02N03)+occurs faster than U022-Idecays, and the rate of deactivation, quantum yield, and radiative probability are higher than those of *UOZ2+.The luminescence of U 0 2 2 +in aqueous acidic NO3- and C10,- has been investigated in terms of acidity, temperature, selfquenching, and H-donor concentration. 'I2 Complex processes in which *[UO2HI2' and *[U2O4HI4+are formed adiabatically appear to be involved, and more than one mechanism may be necessary to explain the results. Another study of the luminescence lifetime of U 0 2 2 + ,reports 213 it to be strongly temperaturedependent at room temperature, but largely independent of temperature at 77 K. Both effects are sensitive to [2H]-substitution in such solvents as water, mildly acidic water, concentrated aqueous LiCl, and methanol. The low-temperature deactivation mechanism was concluded to be a physical process. The Ag +-induced quenching of U 0 2 2+ luminescence has been investigated l4 and analysed in terms of outer- and inner-sphere models. A mechanism is suggested in which electron transfer leads to formation of an excited-state inner-sphere complex of significant 205

206 207 208

209 210

212 '13 214

H. G. Brittain, J . Am. Chem. SOC.,1980, 102, 3693. H. G. Huang, K. Hiraki, and Y. Nishikawa, Nippon Kagaku Kaishi, 1981, 66. V. E. Karasev, N. I. Steblevskaya, and R. N. Shchelokov, Koord. Khim., 1981, 7 , 147. L. I. Konenko, T. B. Kravchenko, S. V. Bel-tyukova, V. E. Kuz'min, and E. S. Suprinovich, Ukr. Khim. Zh.. 1980, 46, 427. H. G. Brittain, J. Phys. Chem.. 1980,84, 840. R. T. Paine and M. S. Kite, ACS Symp. Ser., 1980, 131. M. D. Marcantonatos, M. Deschaux, and F. Celardin, Chem. Phys. Lett., 1980,69, 144. M. D. Marcantonatos, J. Chem. SOC.,Faraday Trans. 1, 1980, 76, 1093. A. Cox, T. J. Kemp, W. J. Reed, and 0. Traverso, J . Chem. SOC.,Faraday Trans. 1, 1980,76, 804. M. D . Marcantonatos and M. Deschaux, Chem. Phys. Left.,1980, 76, 359.

194

Photochemistry

binding energy. The first direct demonstration of electron transfer to the photoexcited uranyl ion in a reversible system appears to have been made.215 *U022+is quenched by [Ru(bipy),]'+ to give [Ru(bipy),13+ and conversely, . [Ru(bipy),13+ is observed to be the *[Ru(bipy),]'+ is quenched by U 0 2 2 + Again product showing that UO," is an electron acceptor in both its excited and ground state. Values have been determined 2 1 6 for the luminescence quenching of uranyl ions by inorganic ions such as Co2+,Pb2+,Cu2+,Ce3+,Hg22+,Tl', Ag', Mn2+,CNS-, C1-, Br-, I-, and NO2- in aqueous solution at pH2.3 and room temperature. The values suggest that quenching occurs by intermolecular electrontransfer. In the cases of Cu2+,Co2+,Mn2+, and NO,'-, however, quenching by an energy-transfer mechanism is also possible. A mechanism (Scheme 3) has been

Scheme 3

proposed * 1 7 for the UOZ2+-or Fe2'-catalysed photo-oxidations of olefins for which the term 'long-range electron-transfer mechanism' has been suggested. It involves interligand electron-transfer from the electron-donating ligand (HO- or C1-) to O2 through the metal ion and olefin molecule, and is similar to the pathway already suggested * for the TiC1,-catalysed photoreactions of ketones with methanol. Support for this comes from the establishment of a correlation between reactivities and product ratios with half-wave reduction potentials of the polyhalogenated compounds. The results of a study219 of the photolysis of the uranyl-malonic acid-bimalonate system suggest that the primary photosensitive species is a (1 : 1) uranyl bimalonate complex, which forms as a precipitate. Kinetic and other evidence supports the mechanism shown in equations (1 O H 1 3), where Ma1 = malonate. UOZ2++ HMal-

UO,(HMal)+

UO,(HMal)+

(10)

, 2 UO,*(HMal)+

(1 1)

hv

dark

UVb,*(HMal)+ UVO2+

+ &,CO,H

UVO2++ &,CO,H

+ CO,

Uv'022+ + CH,CO,-

(12) (13)

Several interesting photoreductions of the excited uranyl ion have appeared. Irradiation of U 0 2 2 + in MeCN or PrCN solution using wavelengths above 400nm brings about reduction by a first-order process, which is in competition with physical quenching pathways.220 No ground-state complex seems to be involved, and the reduction proceeds by an a-H-abstraction from the nitrile '16 217 2'8

219

220

T. Rosenfeld-Gruenwaldand J. Rabani, J. Phys. Chem., 1980,84, 2981. G. I. Romanovskaya, V. I. Pogonin, and A. K. Chibisov, Zh. Prikl. Spektrosk., 1980, 33, 850. E. Murayama, A. Kohda, and T. Sato, J . Chem. Sac., Perkin Trans. 1, 1980, 947. T. Sato, S. Yoshiie, T. Imamura, K. Hasegawa, M. Miyahara, S. Yamamura, and 0.Iro, Bull. Chem. SOC.Jpn., 1977, 50, 2714. A. G. Brits, R. Van Eldik, and J. A. Van den Berg, Inorg. Chim. Acta, 1980, 39, 47. A. S. Brar, R. Chander, and S. S. Sandhu, Indian J . Chem., Sect. A , 1979, 17, 554.

195


molecule. Photoreduction of U 0 2 2 +is also reported 2 2 2 to occur on irradiation of solutions containing either Ph,P or Ph,Bi and gives UIV and Ph,PO or Ph,BiO, respectively. An exciplex seems to be formed in both reactions followed by oxygen-atom transfer. The structure of tetra(glycinato)uranium(Iv) dihydrate, a photoreduction product of U022fin the presence of glycollic acid, has been determined by X-ray cry~tallography.~~~ A study of the luminescence of uranates and of energy-transfer processes involving these compounds has been reported 224 and the excitation spectra of the luminescence of the uranate group has been described for various U-doped corn pound^.^^^ The decay of UF, fluorescence following 375 nm excitation has been reviewed,226and UF, also undergoes 227 decomposition following irradiation with a TEA-CO, laser in the presence of SF,. 221v

18 Actinides The photochemistry of the Np'", NpV,and Np"' ions has been investigated 228 in HNO, solutions at 254 and 300 nm. All oxidation states were converted to Np". In the presence of urea and mild reducing agents, the quantum efficiencies were found to vary widely and to be a function of pH, wavelength, and reaction conditions. The Np"' ion will undergo 2 2 9 photo-oxidation to Np"'" in aerated solution and in A decrease in the rate of this transformation was the presence of K2S208. observed with increasing concentrations of LiOH or an addition of NO,-. 47

221

222

223 224 225

226 227 228

229

A. S. Brar, A. S. Sarpal, and S. S. Sandhu, Indian J. Chem.. Sect. A , 1980, 19, 413. A. S. Brar, A. S. Sarpal, and S. S. Sandhu, Indian J. Chem., Sect. A , 1980, 19, 902. N. W. Alcock, T. J. Kemp, S. Sostero, and 0. Traverso, J . Chem. SOC.,Dalton Trans., 1980, 1182. D. M. Krol, INIS Atomidex, 1980, 11, Abstr. No., 550026. K. C. Bleijenberg, J. Chem. Phys.. 1980, 73, 617. R. Cubeddu, Quad. Ric. Sci., 1980, 105, 27. R. S . Kame, S. K. Sarkar, K. V. S. Rao, and J. P. Mittal, Chem. Phys. Lett., 1981, 78, 273. L. M. Toth and H. A. Friedman, Radiochim. Acta, 1980,27, 173. V. P. Shilov, E. S. Stepanova, and N. N. Krot, Radiokhimiya, 1980, 22, 5 3 .

2 The Photochemistry of Transition-metal Organometallic Compounds, Carbonyls, and Low-oxidation-state Compounds BY J. M. KELLY AND C. LONG

1 General The photoactivation of organometallic catalysts and the infrared laser photochemistry in low-temperature matrices have been the subject of recent reviews.

,

2 Titanium and Zirconium Previous studies (especially using deuterium-labelled compounds and solvents) have revealed that photo-excitation of dialkyltitanocenes Cp2MR2leads to several products including RH formed by hydrogen-atom abstraction from the cyclopentadienyl ring. A recent investigation of CIDNP observed during irradiation of Cp,MMe, (M = Ti or Zr) in solution both in the presence and absence of trapping agents such as oxygen, thiophenol, and nitroxides provides much useful information on the nature of the initial steps in this type of r e a ~ t i o n .It~ was observed, for example, that during irradiation of Cp,TiMe, or (MeCp),TiMe, in oxygen-free solution there were no changes in the n.m.r. spectrum of the sample. However, if traces of oxygen were present, enhanced absorption of the metalbound methyl group of the starting material, a very small emission signal from ethane, and a small enhancement for methane were detected. On the basis of Kaptein’s rules it was shown that (i) a singlet excited state was responsible for the observed reaction, (ii) the recombination [equation (l)] is highly efficient, and (iii) methane is formed from caged radicals whereas ethane is produced from escaped methyl radicals. In the presence of methanol, the n.m.r. signal of the metal-bound methyl of the product Cp,TiMeOMe is seen in emission, consistent with the reaction of methanol with the caged radical pair rather than with the escaped products [equation (2)]. Cp,TiMe, Cp,TiMe

+ Me’ + MeOD

hv

~

-4

---+

-

Cp,TiMe

+ Me’

Cp,TiMe(MeOD)

------+ Cp,TiMeOMe

+ Me’

+ MeD

(2)

M . S. Wrighton, J. L. Graff, C. L. Reichel, and R. D. Sanner, Ann. NY Accid. Sci.,1980, 333, 188. M. Poliakoff and J. J. Turner, in ‘Chemical and Biochemical Applications of Lasers’, ed. C. B. Moore, Vol. 5, p. 175. P. W. N. M. Leeuwen, H. Van der Heijden, C. F. Roobeek. and J. H. G. Frijns, J . Orgrinomet. Chem.. 1981, 209, 169.

196

The Photochemistrj~qf Transition-metal Organonietallic Cornpounds

197

Photoinduced insertion of ethylene into the M-Me bond is observed for Cp,ZrMe, [equation (3)], but not for c ~ , T i M e , . ~Upon irradiation Cp,TiR, Cp,ZrMe,

+ C,H,

I1 1s

Cp,ZrPr"Me

(3)

(R = Me, Bz, or Ph) are converted into catalysts for the hydrogenation of olefins, the reaction being truly photocatalytic for Cp,TiMe, and Cp,TiBz, and photoassisted for c ~ , T i P h , . In ~ each case the initiating step has been identified as homolysis of the Ti-C bond, and the Ti"' species was monitored by e.s.r. Either styrene or methyl methacrylate can be caused to polymerize by irradiating (Bu'CH2),Ti in their presence. The molecular-weight distribution in both cases is bimodal suggesting that both the (Bu'CH,),Ti and the neopentyl radical may initiate the polymerization.

A mixture of q4-diene zironocene complexes (1) and (2) is formed on photolysis of Cp,ZrPh, with 1,3-dienes at - 30 oC.6It was further observed that the sym-cisform could be completely transformed into the sym-transform by irradiation. Although photosubstitution of Cp,Ti(CO), by PF, proceeds readily, that of its analogue (C,Me,),Ti(CO), does not occur under similar conditions.' 3 Vanadium and Niobium Photocleavage of the M-Me bond is observed for Cp,VMe, Cp,NbMe,, and Cp,VMe,.' The first two complexes yield only methane as the organic product, whereas about 36% ethane is formed from Cp,VMe,. Labelling experiments reveal that the ethane is formed by both inter- and intra-molecular processes, whereas the hydrogen abstracted in the production of methane can come from a methyl group, the Cp-ring, or the solvent.' Cp,V,(CO),, which may be considered to contain a V-V bond, was prepared by photolysis of CpV(CO), in t.h.f.9 Photocleavage of this bond is not observed: photosubstitution of carbon monoxide (e.g. by phosphines) occurs instead. The photochemical formation of CpV(NO),CO by irradiation of CpV(CO), and [Co(NO),Br], has been described." Photolysis of CpNb(CO), in hexane solution gives the unusual cluster Cp,Nb,(C0)7,", whereas in t.h.f. the useful reagent 4

5 6

7 8

9 10 11

E. Samuel, J. Organomet, Chem., 1980, 198, C65. J. C. W. Chien, J.-C. Wu, and M. D. Rausch, J. Am. Chem. SOC.,1981, 103, 1180. G. Erker, J. Wicher, K. Engel, F. Rosenfeldt, W. Dietrich, and C. Krueger, J . Am. Cliem. Soc., 1980, 102,6344. D. J. Sikora. M. D. Rausch, R. D. Rogers, and J. L. Atwood, J . A m . Chem. Soc., 1981, 103, 982. D. F. Foust, M. D. Rausch, and E. Samuel, J. Organomel. Chem.. 1980, 193, 209. L. N. Lewis and K. G. Caulton, fnorg. Chem., 1980, 19, 1840. F. Nlumann and D. Rehder, J. Orgunornet. Chem., 1981, 204, 411. W. A. Herrmann, M. L. Ziegler, K. Weidenhammer. and H. Biersack, Angew. Chem. Int. Ed. Engl., 1979, 18, 960.

12

W. A. Herrmann, H. Biersack, M. L. Ziegler, K. Weidenhammer. R. Siegel, and D. Rehder, J . Am. Cliem. SOC.. 1981, 103, 1692.

198

Photochemistry

CpNb(CO),(t.h.f.) is formed: this has been employed to yield I3CO and phosphine derivatives, ' and sulphur-bridged binuclear complexes. ' [V(CO) (m.t .h.f.)] - and cis-[V(CO),(m. t .h. f.)2]- have been characterized in low-temperature solvent glasses following photodissociation of [v(Co),] - in the presence of methyltetrahydrofuran (m.t.h.f.)." Compound (3) is formed by irradiation of [v(co),]- and 3-chlorocyclohex- 1-ene.

,

4 Chromium, Molybdenum, and Tungsten The photochemistry of the Group VI hexacarbonyls in low-temperature solvent glasses continues to attract attention.". 1 7 - l 9 The infrared spectra of M(CO), (hydrocarbon) in methylcyclohexane ' and methylcyclohexane-isopentane l 5 glasses, as well as the spectra of M(CO),(arene).I7 M(CO),(H,0),'8 and M(CO),L (L = m.t.h.f., Me,CO, MeCHO, and MeOH) have been recorded. U.V. irradiation of M(CO), in hydrocarbon glasses for extended periods gives M(CO), and M(CO), as well as M(CO),.' 8, l 9 Irradiation at longer wavelengths causes partial reversal of M(CO), to M(CO), and of M(CO), to M(CO),. C0,laser-induced decomposition of metal carbonyls including Cr(CO), has been studied. 2o (q2-L)M(CO), and (q2-L),M(CO), (M = Mo or W) (L = methyl acrylate or dimethyl acrylate) are formed by irradiation of M(CO), in the presence of the ligand.2' Irradiation of Mo(CO), with 3,4-dimethylphosphole or l-phenylphosphole gives the dimer complexes (4)and (5) as well as the expected Mo(CO), derivatives. 22

(4)R l3

l4 l6 I' l9 'O 21

22

=

Me, P h , or But

(5)

W. A. Herrmann and H. Biersack, J. Organomet. Chem., 1980, 191, 397. W. A. Herrmann, H. Biersack, M. L. Ziegler, and B. Balbach, J. Organornet. Chern., 1981, 206, C33. J. D. Black, M. J. Boylan, P. S. Braterman, and A. Fullarton, J. Chem. Soc., Dalton Trans., 1980, 1651. U. Franke and E. Weiss, J. Organornet. Chern., 1980, 193, 329. D. R. Tyler and D. P. Petrylak, J. Organomet. Chem., 1981, 212, 389. M. J. Boylan, J. D. Black, and P. S. Braterman, J . Chem. Soc., Dalton Trans., 1980, 1646. J. D. Black and P. S. Braterman, Inorg. Chim. Acta, 1980, 44,L181. Y. Langsam and A. M. Ronn, Chem. Phys., 1981, 54, 277. F. W. Grevels, M. Lindemann, R. Benn, R. Goddard, and C. Krueger, Z. Naturforsch., Teil 5 , 1980, 35, 1298. C. C. Santin, J. Fischer, F. Mathey, and A. Mitschler, J. Am. Chem. Sac., 1980, 102, 5809.

The Photochemistry of Transition-metal Organometullic Compounds 199 The nature of the intermediate species formed on photolysis of mixtures of M(CO), and CCl,, (a useful initiating system for olefin metathesis 23 and acetylene polymerization 24) have been further investigated using spin-trapping reagents.25 It is known from the work of Wrighton et that for W(CO), L complexes the luminescence properties in solvent glasses at 77K and the photochemical behaviour in fluid solution at room temperature are determined by the relative energies of the LF and MLCT excited states. In that work it was shown that when the LF state is lowest the complex undergoes CO-photosubstitution efficiently and exhibits short-lived emission (- 1 ps) in EPA glasses at 77 K, whereas when the CT state is lowest photosubstitution is much less efficient' and the observed lifetime much longer ( 15-30 ps). It has now been reported that relatively weak emission = 640nm; z = 360ns) even in may be observed from W(C0),(4-CNpy) (A, fluid solution and this has allowed a comparison of the photochemical and emission properties of this complex." It undergoes relatively inefficient (a = 0.021 at 25 "C) CO-photosubstitution with an apparent activation energy of 32 kJ mol- '. Both the emission and the photoreaction may be quenched by anthracene and the same Stern-Volmer constant is found in both cases, indicating that the same state (i.e. the MLCT species) is involved in both processes. However, another attractive explanation is that the photoreaction takes place from the LF state reached by thermal activation from the lowest but non-reactive MLCT state. Recent studies with other M(CO),L complexes 2 8 - 3 2 reveal that there are substantial differences between their photochemical and photophysical properties in low-temperature matrices, solvent glasses, and fluid solution, which is due, at least in part, to the temperature dependence of the non-radiative processes. W(CO)5L (L = py, 3-Br-py, and piperidine) all show two emission bands (at about 420 and 530 nm, respectively) in argon or methane matrices at 12 K, whereas + ' A , phosphorescence) is only the lowest-energy emission (assigned as the recorded in solvent glasses at 77K.28 The higher energy band is assigned to ' E + 'A, fluorescence, and it is assumed that the observation of the fluorescence is due to the markedly reduced rate of internal conversion at 12 K. The phosphine complexes W(CO),PMe, and W(CO),PCl, show only weak fluorescence and no phosphorescence in 12K matrices, possibly because the triplet state is not appreciably p ~ p u l a t e d . ~The ' photochemical behaviour of Cr(CO),PMe, and Cr(CO),PCl, in argon matrices differs strikingly, CO-loss being predominant for the former and PC1,-expulsion for the latter.29 These results have been explained by the existence of two photoactive excited states, whose relative position is dependent on the ability of the unique ligand to undergo x-backbonding with the

-

23 24

" " 28

F. Garnier and P. Krausz, J . Mol. Catal., 1980,8,91. T. Masuda, Y. Kuwane, K. Yamamoto, and T. Higashimura, Polym. BUN. (Berlin), 1980,2 , 823. R. G.Gasanov and R. Kh. Freidlina, Dokl. Akad. Nauk SSSR, 1980,254, 113. M.S.Wrighton, H. B. Abrahamson, and D . L. Morse, J . Am. Chem. SOC.,1976,%, 4105. A. J. Lees and A. W. Adamson, J . Am. Chem. Soc., 1980, 102,6874. G.Boxhoorn, A. Oskam, E. P. Gibson, R. Narayanaswamy, and A. J. Rest, fnorg. Chem., 1981,20,

783. 30

G.Boxhoorn, G . C. Schoemaker, D. J. Stufiens, and A. Oskam, fnorg. Chim. Acta, 42, 241. G.Boxhoorn, G. C. Schoemaker, D. J. Stufkens, A. Oskam, A. J. Rest, and D. J . Darensbourg, fnorg.

31

Chem., 1980, 19,3455. G.Boxhoorn, G. C. Schoemaker, D. J. Stufkens, and A. Oskam, Inorg. Chim. Acta, 1981,53,L121.

29

'' G . Boxhoorn, D. J. Stufkens, and A. Oskam, J. Mol. Strurt., 1980,60,321.

200

Photochemistry

metal. The sensitivity of the photochemistry of M(CO),L in argon or methane matrices to irradiation wavelength has been exemplified by studies with M(CO),(pip) (M = Cr, Mo, or W) 30 and Cr(CO),(pyrida~ine).~'The latter case is particularly interesting as it appears to suggest that MLCT states can be photoreactive even when thermal activation is unlikely. The photochemical behaviour of Cr(CO),NMe, has been found to depend on the temperature of the xenon matrix.32 MCD studies of M(CO),EPh, (M = Cr or W; E = P, As, or Sb) 3 3 and M(CO), (alkylamine) 34 confirm that the lowest-energy spin-allowed band arises from a ' E t ' A , transition. Photoexcitation of W(CO), CPh, appears to yield diphenylcarbene as this has been trapped by diethyl f ~ m a r a t e . ~In ' the absence of trapping agents Ph,C=CPh, is formed, probably by reaction of the carbene with W(CO),CPh,. A full report has been published on the resonance Raman spectra of M(CO), (di-imine) (M = Cr, Mo, or W), and their relevance to the photosubstitution reactions of the complexes has been discussed.36 It was observed that the complexes are only photoactive if v, (COcis) shows resonance enhancement of Raman intensity. This enhancement is a result of the CT transition causing delocalization of the negative charge over the cis-carbonyls and hence reduction of n-backbonding with the metal and weakening of the M - C O bond. A useful polymer-bound catalyst has been prepared by photolysis of Cr(CO),(norbornadiene) in the presence of polystyrene-containing pendant PPh, groups. 3 7 Photodecarbonylation of (arene)Cr(CO), derivatives has been employed in the preparation of (phenanthrene)(Cr(CO), bound to phosphinated p ~ l y s t y r e n e ,in ~ ~the synthesis of the structurally unusual (C6Et6)Cr(CO),PPh,,,' and in the formation of the cluster (~6-PhMe)CrCo,(yS-C,Me,),(CO)4.40 In the presence of 6,6-dimethylfulvene, photolysis of (arene)Cr(CO), leads to both carbon monoxide and arene elimination and the consequent formation of (6).41

The principal reaction induced by photoexcitation of CpM(CO),Et (M = Mo ~ or W) is olefin elimination with the consequent formation of C P M ( C O ) , H . ~In the presence of PMe,, the product is CpM(CO)(PMe,),M(CO),Cp. The nitrene complex (7) is formed in low yield by irradiation of CpMo(CO),Me in the 33 34

35 3h

37 38 3y

" 42

A. F. Schreiner, S. Amer, W. M . Duncan, and R. M. Dahlgren, J . Phys. Chem., 1980, 84, 2688. A. F. Schreiner, S. Amer, W. M. Duncan, G. Ober, R. M . Ddhlgren, and J. Zink, J . Am. Chem. SOC., 1980, 102, 687 1 . B. H . Edwards and M. D. Rdusch, J . Orgunomel. Chem., 1981, 210, 91. R. W. Balk, T. Snoeck, D . J. Stufkens, and A . Oskam, Inorg. Chem., 1980, 19, 3015. H . B. Gray and C. C. Frazier, US P, 4228035, 1980 (Chem. Ahsfr., 1981, 94, 37 128). D. Tatarsky, D. H. Kohn, and M . Cais, J . Polym. Sci., Polym. Chem. Ed., 1980, 18, 1387. G. Hunter. D . J. Iverson, K. Mislow, and J. F. Blount, J. Am. Chem. Soc., 1980, 102, 5942. L. M. Cirjak, J . 3 . Huang, Z.-H. Zhu, and L. F. Dahl, J . Am. Chem. Soc., 1980, 102, 6623. F. Edelmann, D. Wormsbaecher, and U. Behrens, Chem. Ber., 1980, 113, 3120. H. G. Alt and M. E. Eichner, J . Orgunomer. Chem.. 1981, 212, 397.

The Pli o tochemis t ry of Transition-metal Organome tallic Compounds

20 1

presence of BzN,.,~ Photo-induced 1,2-methyl migration to yield CpM(CO),Me (M = Mo or W) has been observed for CpM(CO),PbMe,, whereas with the corresponding triethylplumbane derivative the product is [CpM(C0)3]2PbEt,.44 The photochemistry of Cp,Cr,(CO), and ($-C,Me,),Cr,(CO),, which contain Cr-Cr triple bonds, has been in~estigated.~’ The observed photoreaction is expulsion of carbon monoxide and not cleavage of the C d r bond. The increasing quantum yield for CO-dissociation at shorter wavelengths indicates that an upper excited state is involved. Irradiation of Cp,Mo,(CO),(EtC&Et) in the presence of hydrogen and EtCECEt yields (8).46 Oxidation of the 17-electron species CPW(CO)~generated by photolysis of [CpW(CO)3]2has been

(8)

The spectroscopic properties and photochemistry of Cr( 1-norbornyl), have been studied.48 The primary process is loss of a norbornyl radical following the homolytic cleavage of the metal-alkyl bond, although the identity of the final chromium-containing product is still uncertain. The photoactive state appears to be a LMCT species as quantum yields in the U.V. are quite high (@366 = 0.036), whereas visible light excitation of the LF states is inefficient in inducing the reaction ( @ 5 5 0 = 2-3 x lo-,).

5 Managanese and Rhenium The photocleavage of Mn,(CO),, or Re,(CO),, has been carried out in the presence of ferricenium ions, substituted ferricenium ions, and other mild oxidants.47 Relative rates for the oxidation of the initial photoproduct M(CO), compared with the rate of chlorine abstraction from CCI, have been obtained. Products identified following photolysis of Mn,(CO),, or Re,(CO),, in the presence of 3,5-di-t-butyl-1,Zbenzoquinone (DBQ) are Mn(DBQ), 49 and Re(CO),(DBQ).’O Initial formation of Mn(CO), is also implicated in the photochemical synthesis of [Mn(CO),EPh], (E = Se or S) from Mn,(CO),, and from Ph,E, 5 1 and of the polynuclear complex { Rh,L,[Mn(CO),],)(PF,), Mn,(CO),, and Rh,L4PF, (L = 2,4-dimethyl-2,5-di-i~ocyanohexane).~~ 43 44 45 46 47

48 49

R. Korswagen and M. L. Ziegler, Z. Naturforsch., Teil B, 1980, 35, 1196. K. H.Pannell and R. N. Kapoor, J. Organomet. Chem., 1981, 214, 47. J. L. Robbins and M. S. Wrighton, Inorg. Chem., 1981, 20, 1133. S. Slater and E. L. Muetterties, Inorg. Chem., 1981, 20, 946. A. F. Hepp and M. S. Wrighton, J. Am. Chem. SOC.,1981, 103, 1258. H. B. Abrahamson and E. Dennis, J. Organomet. Chem.. 1980, 201, C19. M. W. Lynch, D. N. Hendrickson, B. J. Fitzgerald, and C. G. Yierpont, J. Am. Chem. SOC., 1981,103, 3961.

50 51

52

K. A. M. Creber and J. K. S . Wan, J . Am. Chem. SOC.,1981, 103, 2101. P. Jaitner, J. Organomet. Chem., 1981, 210, 353. D. A. Bohling, T. P. Gill, and K. R.Mann, fnorg. Chem., 1981, 20, 194.

202

Photochemistry

The primary photoproduct of U.V.photolysis of Mn(CO),X and Mn(CO),R ( X = C1, Br, or I;,, R = Me or MeCO 54) in argon or methane matrices at 12 K is the trigonal bipyramidal complex [Mn(CO),X or Mn(CO),R] in which the unique ligand occupies an equatorial position. The u.v.-induced photoreaction of Mn(CO),Me as in equation (4) may be reversed using longer wavelength Mn(CO),Me

-

Mn(CO),Me

+ CO

(4)

radiation. However an analogous reverse reaction is not observed with Mn(CO),COMe. Instead it was noted that this species rearranges to Mn(CO),Me, thereby offering some support for the theory that in solution the decarbonylation of Mn(CO),COMe to Mn(CO),Me may proceed by a dissociative mechanism. Examination of the chemical, electrochemical, and spectroscopic behaviour of R,EM(CO),L (R = Ph or Me, E = Ge or Sn, M = Mn or Re, L = phen or bpy) reveals that the lowest state is one in which an electron has been transferred from the HOMO, which has sigma E-M bonding character to the LUMO which is mainly localized on L.55The rhenium complexes emit in fluid solution at room temperature, and the luminescence may be quenched by both electron acceptors and electron donors, as in reactions ( 5 ) and (6). No net photochemistry is observed

+Q Ph,Sn-Re(CO),(phen)* + Q

Ph,Sn-Re(CO),(phen)*

-

[Ph,Sn-Re(CO),(phen)l+ [Ph,Sn-Re(CO),(phen)l-

+ Q+ Q'

(5)

(6)

for reductive quenching (6),whereas the cation formed by oxidative quenching ( 5 ) decomposes to give [Re(CO),(phen)]+ and Ph,Sn, as predicted from cyclic voltammetry experiments. MLCT state offac-[XRe(CO),L,] (X = C1, L = 4-PhCOpy; X = I, L = 4MeCOpy) is quenched by NEt, via an electron-transfer mechanism. Photolysis eventually leads to reduction of the co-ordinated ketone to the corresponding alcohol and oxidation of NEt, to Et,NH and MeCHO. As the irradiated alcohol slowly exchanges with free ketone in solution this photoreaction can be exploited to effect the reduction of ketones to alcohols using visible light. Data from resonance Raman experiments confirm that the lowest-energy absorption bands of various Re(CO),(di-imine)X complexes are MLCT in ~ h a r a c t e r . ~ ' The infrared spectra of the decarbonylation photoproducts of CpMn(CO),, (MeCp)Mn(CO),, and CpMn(CO),(CS) in low-temperature solvent glasses have been recorded.58 In general the rate of photolysis of these starting materials is less than that for M(CO), suggesting that rapid CO-recombination may be occurring. In alcohol glasses two CpMn(CO),(ROH) species, probably rotamers, have been observed. The preparation of MnCo, clusters by the photoreaction of CpMn(CO), and (C,Me,),Co,(CO), has been de~cribed.~'Photolysis of CpMn(CO),CPh, liberates the carbene CPh,, and the organic products obtained

''

53

''

'' 56 57

5N

T. M . McHugh, A. J. Rest, and D. J. Taylor, J . Chem. Soc., Dulfon Trans., 1980, 1803. T. M . McHugh and A. J. Rest, J . Chem. Soc., Dalton Trans., 1980, 2323. J . C. Luong, R. A. Faltynek, and M . S. Wrighton. J . Am. Cliern. SOC.,1980, 102, 7892. S. M . Fredericks and M. S. Wrighton, J . Am. Chem. Soc., 1980, 102, 6166. R . W. Balk, D. J. Stufkens, and A. Oskam, J . Cliem. SOC.,Dalton Trans., 1981, 5 , 1124. J. D. Black, M. J. Boylan, and P. S. Braterman, J . Chem. Soc., Dalron Trans., 1981, 673.

203

The Pliotocliemistry of Transition-metal Orgunometallic Compounds

in hexane solution include hydrogen-abstraction products Ph,CH, and Ph,CHCHPh,, and its dimer Ph2C=CPh2.35 Both the emission lifetime and quantum yield of D,Re,(CO), are greater than those of H4Re,(C0),2 owing to the decreased rate of non-radiative decay in the lowest triplet state of the deuteriated complex.59 A similar but somewhat larger effect is noted for [H6Re4(C0)12]2- and [D6Re4(CO)12 ] 2 - , the increased magnitude of the effect being possibly attributable to the H atoms in [H,Re,(CO), 2]2being edge-bridging, whereas those in H,Re,(CO) are face-bridging. Dihydrogen is eliminated upon U.V.irradiation of ReH 3(Ph2PCH2CH2PPh2)2, and the resulting reactive fragment ReH(Ph,PCH,CH,PPh,), has been trapped by N,, CO, C2H4, or C2H2.60If the irradiation is carried out in C6D6 solution, deuterium is exchanged between solvent and the complex presumably via the rapid insertion and elimination reactions (7) and (8). In ReH,(PMe,Ph),, efficient

,,

,

ReH( Ph ,PCH ,CH PPh,)

, + C6D,

-

ReH D(C D5)( Ph,PCH ,CH 2PPh,)

ReHD(C,D 5)( Ph ,PCH ,CH ,CH ,PPh,), ReD(Ph,PCH,CH,PPh,), ____+

,

(7)

+ C,D,H

(8)

photo-induced exchange between the metal-hydride protons and those of benzene or the phenyl group of the phosphine ligand occurs.61 However in this case the primary photoprocess is expulsion of a phosphine ligand and not elimination of dihydrogen. In the absence of excess phosphine, the products are H,Re,(PMe,Ph), or H,Re(PMe,Ph),. 6 Iron, Ruthenium, and Osmium

Photo-oxidation of ferrocene by CC1, in solution can normally only be effected by U.V.irradiation. However it has been observed that the reaction may be carried out with visible light in cetyltrimethylammonium chloride micelles, albeit with low quantum yield.62 It is suggested that the main effect of micellization may be an increase in the oxidation potential of ferrocene or alternatively that a CTTS state of ferrocene is involved under these conditions. The ring substitution of ruthenocene by irradiation in 1 : 1 (v/v) solutions of ethanol with CCl,, CHCl,, or CH2C12proceeds by a mechanism similar to that previously found for f e r r ~ c e n e . ~ , Other reports consider the synthesis of ferrocenyl thioesters 64 and the photooxidation of f e r r ~ c e n e . ~ ' Visible (A > 400nm) excitation of [CpFe(p-xylene)]+PF,- in the presence of a suitable ligand L, e.g. isonitriles, phosphines, or CO, leads to expulsion of the pxylene and formation of [CpFeL3]+.66In acidic aqueous solution the product is Fe2 . +

59

6o 61 62

63 64 65

66

J . L. Graff and M. S. Wrighton, J . A m . Chem. Soc., 1981, 103, 2225. M . G. Bradley, D. A. Roberts, and G. L. Geoffroy, J. Am. Chem. Soc., 1981, 103, 379. M. A. Green, J. C. Huffman, and K. G. Caulton, J . Am. Chem. Soc., 1981, 103, 695. D. M. PdpSUn, J. K. Thomas, and J. A. Labinger, J . Organomel. Chem., 1981, 208, C36. A. Sugimori, M. Matsui, T. Akiyama, and M . Kajitdni, Bull. Chem. Soc. Jpn., 1980, 53, 3263. C. Gotzmer, US P, 4219490, 1980 (Chem. Abstr., 1980, 93, 239659). M . Yokota and T. Sato, Kokagaku Toronkai Koen Yoshishu, 1979, 192; Chem. Abstr., 1980,93,25561. T. P. Gill and K. R. Mann, Inorg. Chem., 1980, 19, 3007.

204

Photochemistry

Two transients have been observed following flash photolysis of Cp,Fe,(C0),.67 From a study of their spectra, kinetics, and reactivity towards CO, phosphines, or CCI,, they have been assigned as CpFe(CO), and Cp,Fe,(CO), This finding should help to reconcile the uncertainties of the primary photoprocesses of Cp,Fe,(CO), discussed in last year’s Report. Photolysis of Cp,Fe,(CO), in the presence of 2-3-diazanorbornene (dnb) yields Cp,Fe,(CO),(q’-dnb) and Cp,Fe,(CO)2(q2-dnb).68 Carbene complexes (9) are formed by photolysis of a mixture of Cp,Fe,(CO), and N,CHCO,R (R = Et or

(9)

(10)

Recent reports on the photochemistry of CpFe(CO),-derivatives include the observation of CpFe(CO),Me following irradiation of CpFe(CO),PbMe,,” the formation of the orthometallated derivative (10) and the elimination of Ph,MeSiH upon irradiation of CpFe(CO),SiMePh, and P(OPh),,’ the photodecarbonylation of CpFe(CO),(trans-COCH=CHR) (R = Me or Ph) to give the corre~ the observation sponding alkenyl complex C p F e ( C 0 ) , ( t r a n ~ - C H 4 H R ) , ’and of CpFe(C0) (m.t.h.f.)I upon photolysis of CpFe(CO),I in methyltetrahydrof ~ r a n . ’ ~The photoelimination of ethylene from CpFe(CO),Et, giving CpFe(CO),H, has been monitored in low-temperature matrices. 7 3 In the same report it is also shown that the initial photoprocess in the conversion of (1 1) into

(13)

(14)

(15)

( 1 2) is CO-expulsion, with the methyl migration from the cyclopentadiene ring to

the metal occurring either when the matrix is allowed to warm or when it is further ”

”

‘’ ’()

”

’’ ’.’

J. V. Caspar and T. J . Meyer, J . Am. Chem. SOL-.,1980, 102, 7794. R . Battaglia, P. Mastropasqua, and H . Kisch, Z . Noturforsck., Teil B, 1980, 35, 401. W. A. Herrman, J . Plank, I. Bernal, and M. Creswick, 2. Nnrurfbrsciz., Teil B, 1980, 35, 680. K. H . Pannell, J. Orgnnomet. Ciiern., 1980, 198, 37. G. Cerveau, G . Chauviere, E. Colomer, and R. J. P. Corriu, J . Orgnnomet. Chem., 1981, 210, 343. S. Quinn and A. Shaver, Inorg. Ciiini. Acta, 1980, 38, 243. W.Gerhartz, G. Ellerhorst. P. Dahler, and P. Eilbracht, Liebigs Ann. Chem., 1980, 1296.

The Photochemistry of' Transit ion-me tul 0rgctnometullic Compounds

205

irradiated.73With (13) the final product is (14), the reaction probably proceeding riu ( 1 5 ) , which however did not build up in appreciable concentration probably because of its high photosensitivity. The yields of Fe(CO), (n = 1-4) produced by laser excitation of Fe(CO), in the gas phase at ;1. = 352 nm, 248 nm, or 193 nm have been measured by trapping the species with PF3.74* 7 5 The striking conclusion is that the lower carbonyls are formed in high yields [e.g. at 248 nm the quantum yields for Fe(CO), and Fe(CO), are 0.55 and 0.35, whereas that for Fe(CO), is only 0.101 even though the decomposition is induced by single-photon absorption. It is not clear whether these species are produced directly from the excited state [e.g. equation (9)] or by Fe(CO),* Fe(CO),* Fe(CO),+ Fe(CO),+

-

+ 3CO Fe(CO),t + CO Fe(CO),t + CO Fe(CO), + CO

Fe(CO),

(9) (10) (1 1) (12)

stepwise decomposition of the vibrationally excited fragments (steps 10-12), although the latter process seems more likely. These observations could have important consequences for the photochemistry of Fe(CO), in condensed phases, although it is likely that in solution cage recombination and removal of excess vibrational energy by the solvent will greatly reduce the yield of the lower carbonyls. Other papers describe the production of excited iron atoms from multiphoton U.V.excitation of Fe(CO), or sensitized with excited argon atoms,77and the multiphoton C0,-laser induced excitation of Fe(CO),.,' E.s.r studies on u.v.-irradiated pentane solutions of Fe(CO), under 30 atm. of hydrogen reveal the presence of HFe,(CO),, which is also produced if H,Fe,(CO), is ph~tolysed.'~ The same species as well as [(CH,CHCH,)Fe(CO),]' is also formed if Fe(CO), is irradiated in the presence of cyclopropane. More data on the highly reactive catalytic species responsible for the Fe(CO),photocatalysed isomerization of pent-1-ene have been obtained both by laser and flash photolysis methods,79 and by Fourier Transform i.r. spectroscopy.*' Very high quantum yields (>>I)and high turnover rates are found. As an induction period for the process is observed it appears that the active catalyst is not formed from Fe(CO), by a one-photon process and the sequence (13) was suggested WCO),

hv

+ Fe(CO),(pentene)

hv

Fe(CO),(pentene) (13)

earlier. Other authors have suggested that the active catalysts are CO-bridged dimeric iron species on the basis of their studies with Fe(CO),(PF,), --n (n = 0-5) as photocatalysts for pentene isomerization. They observed a gradual decrease in activity as II decreased from 5 to 1, and a sudden fall to zero activity for Fe(PF,),. 74

G . Nathanson, B. Gitlin, A. M. Rosan, and J. T. Yardley, J. Chem. Phys.. 1981, 74, 361.

'' J . T. Yardley, B. Gitlin. G . Nathanson, and A. M. Rosan, J . Chem. Phys., 1981, 74, 370. l6

J . Krasinski, S. H. Bauer, and K . L. Kompa, Opt, Commun., 1980, 35, 363.

'' J. Kobovitch and J. Krenos, J . Clrem. Phys., 1981, 74, 2662, 78

79

*'* O

P. J. Krusic, J. Am. Chem. SOC.,1981, 103, 2131. J. C. Mitchener and M . S. Wrighton, J . Am. Chem. SOC..1981. 103, 975. D. B. Chase and F. J. Weigert, J . Am. Clzem. Soc., 1981, 103, 977. G. L. Swartz and R. J. Clark, Inorg. Chem.. 1980, 19, 3191.

206

Photochemistry

Pentene isomerization and hydrosilylation have also been induced by irradiation of phosphinated polystyrene-bound Fe(CO), complexes.82 The photochemistry of Fe(CO), with dienes or olefins in polytetrafluoroethylene has been 84 1.r. evidence for (diene)Fe(CO),, (diene),FeCO, and for (ethylene)Fe(CO), is presented, and it has been found that the stability of these complexes towards air oxidation is much higher in the polymer matrix than in solution. Hydrosilylation of butadiene may be induced by photolysis of the diene with R,SiH (R = Me, Ph, or Et) and Fe(C0),.85 With Me,SiH the observed products are trans- 1-butenyl-, trans-2-butenyl-, and cis-2-butenyl-trialkylsilanes.The reaction appears to proceed‘through (1 6), which may be independently synthesized by irradiation of (butadiene)(FeCO), and R,SiH.

(H,C=CH)3SiCH=CH,

I

‘‘7 I \

I (19)

Recent synthetic applications of the photochemical reactions of Fe(CO), are the formation of (17) from (18),86 and of (19) from di~henylketen.~’ Fe(CO), and presumably dihydrogen are formed upon U.V.irradiation of H,Fe(CO), in argon matrices.88Upon exposure to Nernst glower radiation the reverse process [oxidative addition of hydrogen to Fe(CO),] takes place. Oxidative addition in low-temperature matrices has also been observed upon irradiation (1 < 360nm) of Fe atoms in methane, the species MeFeH being identified by its i.r . spectrum. Photoexpulsion of the axial CO group is observed for Fe(CO),NMe, or Fe(CO),py in rare-gas matrices, the effect being reversed by warming the matrix or by i.r. p h o t o l y ~ i s .The ~ ~ photodissociation spectrum of Fe(CO),- (to give Fe(CO), -) has been measured in an ion cyclotron resonance s p e c t r ~ m e t e r . ~ ~ 82

83 84

85

86

’’ ’* 89 90

R. D . Sanner, R. G. Austin, M.S. Wrighton, W. D. Honnick, and C. U. Pittman, jun,, Adv. Chem. Ser., 1980, 184, 13. M . A. De Paoli, S. M. De Oliveira, and F. Galembeck, J . Orgunomet. Chem., 1981, 193, 105. M. A. De Paoli, J . Macromof. Sci.,Chem., 1981, 16, 1359. I. Fischler and F.-W. Grevels, J . Orgunomet. Chem., 1981, 204, 181. A. S. Batsanov, Yu. T. Struchkov, G . V. Nurtdinova, A. A. Pogrebnyak, L. V. Rybin, V. P. Yur’ev, and M . I. Rybinskaya, J . Organomet. Chem., 1981, 212, 211. W. A. Herrmann, J. Gimeno, J. Weichmann, M. L. Ziegler, and B. Balbach, J . Orgunomet. Chem., 198 1, 213, C26. R. L. Sweany, J . Am. Chem. Soc., 1981, 103, 2410. W. E. Billups, M. M . Konarski, R. H. Hauge, and J. L. Margrave, J . Am. Chem. Soc., 1980,102,7393. C . M . Rynard and J. I. Brauman, fnorg. Chem., 1980, 19, 3544.

207 In CO-saturated acetonitrile solution, [Fe(CO), 1]2- appears to be quite photo~table.~’ However in the presence of triphenylphosphine, Fe(CO),(PPh,), and [Fe(CO),]’ - are formed. These findings, and the observed photodecomposition [equation (14)] in alkaline aqueous solution, may be rationalized by The Photochemistry of Transition-metal Organometallic Compounds

[Fe,(CO), J 2 -

+ 4H20

[F%(CO)1 11

I11’

[Fe(CO),]’-

k

hv

+ 2Fe(OH), + 2H2 + 7CO

+ [Fe3(C0),,]2-

-

+ CO

(14) (15)

assuming that the initial photoreaction is CO-extrusion [equation (15)] and not cluster fragmentation. New cluster compounds have been formed by the irradiation of mixtures of Fe(CO), or (q4-cyclobutadiene)Fe(CO), and (q5C5Me5)2C02(C0)2,40 and of Fe(CO), or Ru,(CO),, and H , O S , ( C O ) ~ ~Photo.~~ lysis of mixtures of (20) and Sn2Me, or Co,(CO), yield (21) and (22).93 Me I

Me-Sn Se-

x ,/

,(CO)Fe-

Se

(20)

\

Fe(CO),

se/

‘se

LxJ (OC),Fe-Fe (21)

(CO),

co (COh (22)

7 Cobalt and Rhodium

The photochemistry of Co(CO),(NO) has been studied both in the gas phase and in solution.94 Reaction with gaseous HCl produces N 2 0 [equation (Mi)].This Co(CO),NO

hv

HCI

CoCl,

+ N 2 0 + H,O + CO

(16)

suggests that the excited state has a bent ‘ N 4 - l i k e ’ M-N-0 unit rather than a linear ‘N-0’-like’ M-N-0 unit. In the latter case the product might be expected to be NOC1. In solution it was noted that the quantum yield for substitution with phosphines, arsines, or pyridine was strongly dependent on the type of entering ligand, suggesting associative attack by the ligand on the ‘bent’ excited state species. The i.r. bands of the species obtained on photolysis of HCo(CO), in argon matrices, previously assigned to HCO(CO),,~~ are now considered to be characteristic of c0(co)4.96This is expected to arise from photohomolysis of the Co-H bond in HCo(CO),, and the presence of H’ and Co(CO), has also been verified by e.s.r. measurements. A study of the reaction conditions for conversion of Co,(CO), to C O , ( C O ) , notes ~ that the reaction may be photoassisted although the quantum yield is ” 92 93 94

’*

96

”

D. R. Tyler and H. B. Gray, J . Am. Chem. SOC.,1981, 103, 1683. E. W. Burkhardt and G . L. Geoffroy, J. Organomet. Chem., 1980, 198, 179. D. Seyferth and R. S. Henderson, J . Organomet. Chem., 1981, 204, 333. W. Evans and J. 1. Zink, J . Am. Chem. SOC..1981, 103, 2635. P. Werner, B. S. Ault, and M. J. Orchin, J . Orgunomet. Chem., 1978, 162, 189. R. L. Sweany, inorg. Chem., 1980, 19, 3512. M. F. Mirbach, A. Saw, A. M. Krings, and M. J. Mirbach, J . Organomet. Chem., 1981, 205, 229.

Photochemistry

208

In solution CO-dissociation is the main photoreaction upon U.V. excitation of Co(CO),SiR, (R = Me or Ph).98The co-ordinatively unsaturated Co(CO),SiR, produced may be trapped by P(OPh), or by pentene, and it may also reversibly oxidatively add R,SiH [e.g.equation ( I 7)]. R,SiCo(CO), is a photocatalyst for the isomerization or hydrosilylation of pent- I-ene. Co(CO),SiPh,

+ Et,SiH

Co(CO),(SiPh,)(SiEt,)(H)

.------

Co(CO),SiEt,

+ SiPh,H

(17)

Wilkinson's compound CIRh(PPh,), has been found to be a useful photocatalyst for the hydrosilylation of olefins in the presence of oxygen.99The primary photoprocess is phosphine expulsion, which generates the suspected catalytically active species ClRh(PPh,),. Hydrogen evolution has been observed upon photolysis of HRh(PPr',), in aqueous phosphoric acid. l o o More information on the properties and photoreactions of the isocyanidebridged complexes [Rh2b4I2' [b = CN(CH,),NC] have been published.lO'- l o 4 Polarized single-crystal studies and time-resolved resoname Raman spectra reveal that the 3 A 2 uexcited state has a much stronger Rh-Rh bond than the ground state. The ,A2" state may be quenched by azulene and other low-energy quenchers, allowing its ET to be estimated as about 164 kJmol- ' . I o 3 The excited state may also undergo electron transfer, and the species formed, either from oxidative quenching (e.g. with methylviologen) or by reductive quenching (e.g. with amines) have been characterized by flash photolysis. The photoproduction of hydrogen by reaction of [Rh2b4I2+has been shown to proceed in two steps, namely a thermal reaction (1 8) and a photoinduced process (19) of the tetranuclear complex. O4 2[Rh2b4I2+ + 2HC1 [Rh4b,C1,]4+

+ 2HC1

""

[Rh4b,C1J4+

+ H,

2[Rh2b4Cl2I2+ + H,

(18)

(19)

Compound (23) undergoes photo-elimination of nitrogen and the formation of product (24).lo' The reaction proceeds via an intramolecular pathway, possible by insertion of an initially formed co-ordinated nitrene into the ortho-CH bond of the neighbouring group. The photochemistry of surfactant alkylcobaloximes in sodium lauryl sulphate (SLS) or cetyltrimethylammonium bromide (CTAB) micelles has been described. l o 6 The quantum yield for anaerobic photohomolysis of the Co-C bond was found to be three times larger in saturated micelles compared with those containing only 1 or 2 cobaloximes. This effect is possibly caused by a co-operative 99 '()"

I"'

'(''

I 05 'Oh

C . L. Reichel and M. S. Wrighton, fnorg. Chem., 1980, 19, 3858. R. A. Faltynek, fnorg. Chem., 1981. 20, 1357. R. F. Jones and D. J . Cole-Hamilton, J . Chem. Soc., Chem. Commun., 1981, 58. S . F. Rice and H . B. Gray, J . Am. Chem. Soc.., 1981, 103, 1593. R. F. Dallinger, V. M. Miskowski, H. B. Gray, and W. H . Woodruff, J . Am. Chem. Sor., 1981, 103, 159.5. S. J . Milder, R. A. Goldbeck, D. S. Kliger, and H. B. Gray, J . Am. Ckem. Soc., 1980, 102, 6761. I. S. Sigat K . R. Mann, and H . B. Gray, J . Am. Chem. SOC.,1980, 102, 7252. M . E. Gross and W. C. Trogler, J . Orgrmomet. Cliem., 1981, 209, 407. D. A. Lerner, F. Ricchiero, and C . Giannotti, J . Phys. Cliem., 1980, 84, 3007.

The Photochemistry of Transition-metal Organometallic Compounds

209

(24)

(23)

effect owing to the organization of the cobaloximes in the micelle. Other work on models for B,, includes the photochemistry of alkyl derivatives of cholestanocobaloximes,l o 7 and of dehydrocorrins.lo*

8 Nickel, Palladium, and Platinum Excitation of the charge transfer (5d-n&,,) state of cis- or trans[PtC1,(C,H4)(4Mepy)] by 254 nm radiation causes ethylene expulsion and the resultant formation of the dimer [PtC12(4Mepy)],. O9 The cis-trans isomerization reactions that occur with modest quantum efficiencies (0.07 for cis + trans; 0.01 for trans -,cis) have been ascribed to reactions of d-d excited states. The photoisomerisation of trans-[PdCl,(PR,),] (R = Et, Pr", or Bu") proceeds predominantly by an intramolecular process with only a few per cent involving The trans -, cis isomerization of intermolecular phosphine exchange. Pd(CNMe),(SCN), has been reported to take place upon irradiation into C?' bands.", Irradiation of q3-allylpalladiumcomplexes results in the formation of 1,5-dienes [e.g. (25) from (26)], products presumably of the coupling of ally1 radicals.' The '"3

(25)

(26)

p h oto-induced oxidative addition of CH,Cl, to (Ph3P),PtC2H4, giving cis- and trans-[(Ph3P),PtCl(CH ,el)] and cis-[PtCl,(PPh,),], is quenched by radical traps.' l 4 Ultraviolet irradiation of acidic solutions of M(PEt,), (M = Pd or Pt) results in the formation of [M(PEt3)3(H20)]2'and hydrogen.'" The dissociation of Ni(CO), by multiphoton i.r. laser excitation 2o or sensitized by excited argon atoms 1 1 5 has been described. lo'

'08 lo9 ''O

''I

'I3

'I5

M. Fountoulakis and J. Retey, Chem. Ber., 1980, 113, 650. Y. Murakami, Y. Aoyama, and K. Tokunaga, J. Am. Chem. SOL'.,1980, 102, 6736. R. Rumin and P. Courtot, J. Organomet. Chem., 1980, 193, 407. N. W. Alcock, T. J. Kemp, F. L. Wimmer, and 0. Traverso, Inorg. Chim. Acta, 1980, 44, L245. N. W. Alcock, T. J. Kemp, and F. L. Wimmer, J. Chem. Soc., Dalton Trans., 1981, 635. L. L. Costanzo, S. Giuffrida, G. Condorelli, A. Giuffiida, and G. Guglielmo, Congr. Naz. Chim. Inorg., [Atti], 13th, 1980, 206 (Chem. Abstr., 1981, 94,217457). J. Muzart and J. P. Pete, J. Chem. SOL'., Chem. Commun., 1980, 257. 0. J . Scherer and H. Jungmann, J. Organomet. Cliem., 1981, 208, 153. J. S. Winn, Faraclny Svmp. Chem. SOC.,1980, 14, 102.

210

Photochemistry 9 Copper and Silver

A review of the photochemical properties of copper complexes includes a survey of the photocatalysed reactions of copper-olefin complexes. l6 The addition of acetonitrile to norbornene may be induced by irradiation in the presence of silver ions. The reaction appears to involve excitation of a LMCT excited state of the norbornene-silver complexes and the formation of norbornene radical cations. The detection of CuH and CuMe in methane matrices at 12 K following the 320nm photolysis of copper atoms has led to the proposal that optically excited copper atoms insert into the C-H bond of methane. l 1 The HCuMe species thus produced undergoes secondary photolysis to give CuH and methyl radicals and also CuMe and hydrogen atoms. The photoproperties of silver atoms in matrices have been studied in detail. l 9

'

'

'

10 Mercury

The photo-induced substitution reactions of alkenylmercury compounds appear to proceed by a free-radical chain mechanism [e.g.reactions (20)]. 120 Photolysis of Bu'CH=CHHgCl

+ SPh'

Bu"CHCH(SPh)HgCI

-----+ B u ' C H d H S P h

+ HgCl

(20)

1-alkenylmercury halides in the presence of sulphinate ions provides a useful route to a,B-unsaturated sulphones. 2 1 The effect on the triplet state kinetics of binding MeHg' to tryptophan or benzimidazole has been monitored using 0.d.m.r. and polarized phosphorescence excitation measurements. * **

'

11 Lanthanides and Actinides Irradiation of t.h.f. solutions of Cp,UR (R = Me or Bun) gives CpJU t.h.f., although elevated temperatures ( e . g . 60 "C) are required for efficient reaction.',, Homolytic cleavage of the U-R bond is presumed to be the first step. Photoinduced cleavage of the Yb-Me bond allows the conversion of [(MeCp),YbMej, into (MeCp),Yb.' 24

'Ih

'" '"

l9 ''I 12'

"'

G . Ferraudi and S. Muralidharan, Coord. Cliem. Rev.,1981, 36, 45. J. W. Bruno, T. J. Marks, and F. D. Lewis, J . Am. Chem. Soc., 1981, 103, 3608. G. A. Ozin, D. F. Mcintosh, S. A, Mitchell, and J . Garcia Prieto, J . Am. Clrem. Sot,., 1981, 103, 1574. S . A . Mitchell, J. Farrell, G . A. Kenney-Wallace, and G. A. Ozin, J. Am. Chem. Soc., 1980, 102, 7702. G . A. Russell and J. Hershberger, J . Am. Chem. Soc., 1980, 102, 7603. J. Hershberger and G . A. Russell, Synthesis, 1980, 475. R . R. Anderson and A. H. Maki, J . Am. Chem. Soc., 1980, 102, 163. E. Klahne, C. Giannotti, H . Marquet-Ellis, G. Folcher, and R. D. Fischer, J . Orgcinomet. Cliem., 1980, 201, 399. H A . Zinnen, J. J . Pluth, and W. J . Evans, J . Ckem. Soc., Chem. Commun., 1980, 810.

3 Photochemistry of Compounds of the Main Group Elements BY J. M. KELLY AND C. LONG

1 Group 3 Elements A detailed quantum yield study of the photocyclization of anilinodimesitylboranes [ e g . (l)] in the presence of iodine has been published.' When the iodine concentration is less than lop3M, the major product is (2), whereas at high iodine concentrations (3) predominates. It is proposed that the initial step in the formation of (2) is an electron transfer to iodine from the excited state of ( I ) , and that the cation so produced then cyclizes and subsequently loses a methyl group. At higher concentrations the iodine appears to act as a heavy-atom quencher of the excited state of (1) which produces the cation. and iodine also seems to promote the methyl group migration required for the formation of (3).

H\

H

\

4

N -3 I

There have been several recent papers on i.r. laser-induced decomposition of boron trichloride in the presence of other substances, e.g. phosgene2 and hydrogen sulphide. 3, At 15 K in argon matrices, gallium and indium atoms undergo photochemical insertion into water. Dimers also photoreact giving bridged species, which may then undergo a further photodecomposition (equations 1 and 2).

' '

M . E. Glogowski and J. L. R. Williams, J . Orgrmomef. Cltem., 1980, 195, 123. C. Riley and L. Maclean, J . A m . Chem. Soc., 1980, 102, 5108. K . Takeuchi, 0. Kurihara, and R. Nakane. Cltem. Phys.. 1981,54, 383. K. Takeuchi, 0. Kurihard, and R . Nakane, J . Chem. Eng. Jpn., 1980, 13, 246. R. Hauge, J. W. Kauffman, and J . L. Margrave, J . Ant. Clrem. Soc., 1980. 102, 6005.

21 1

212

Piio toc'iieniis t ry

The luminescence of TI' in lithium chloride6 and in potassium iodide' has been further studied.

2 Silicon and Germanium Several primary photoprocesses have been identified for MeSiH, excited by 147 nm radiation in the gas phase. Of these the processes represented in equations (3)-(5) have quantum yields greater than 0.2.8

11\%

MeSiH, MeSiH, MeSiH,

/I

v

Me

+ H + SiH,

(3)

+ H,

(4)

MeSiH

I1 \!

-----+ CH,SiH,

+ H,

(5)

For polysilanes in 2,3-dimethylbutane solution, photolysis induces a net disproportionation (e.g. Si,H, and Si,H,, from If acetone is present then isopropoxysilanes [e.g. Me,CHOSiH(SiH,), from SI,H8] are formed. ' The insertion of CCI into the Si-H bond of silanes has been studied.' Upon photoexcitation, either in the gas phase or as liquid, SiMe, undergoes mainly two primary photoprocesses (6) and (7) (@ = 0.55 and 0.22, respectively).' The Me,SiCH,, so formed, may react further by dimerization to give the 1, 1,3,3-tetramethyl-1,3-disiIacyclobutane (4a). However in the gas phase the

,

(4)a; R = Me b:R=H

majority of the silaolefin species are intercepted by radicals, and this accounts for the lower yield of (4a) in the gas phase compared with that found in the liquidphase photolysis reaction, where cage recombination of the radicals produced in reaction (6) may occur. SiMe, SiMe,

I?\'

-----+ SiMe, I1 \!

+ Me

Me,SiCH,

+ CH,

(6) (7)

' M . U . Belyi, S. E. Zelenskii. B. A . Okhrimenko, and V. P. Yashchuk, Ukr. Fiz. Zh. (Russ.Ed.). 1981, 102. ' 26, D. J . Simkin, J . P. Martin, M . Authier-Martin, K. Oyama-Gannon, P. Fabeni, G . P. Pazzi, and A. ' lo I ' 12

Ranfagni. P h j s . Rev. B, 1981, 23, 1999. P. A. Longeway and F. W . Lampe. . I Pliotoc,lieni., . 1980, 14. 31 I . F. Feher and I. Fischer, Z . Anorg. Allg. CAem., 1980, 466, 23. F. Feher. I. Fischer, a n d D. Skrodzki, Z . Anorg. A&. Ciimi., 1980, 466, 29. F. C. James, H. K. J . Choi, 0. P. Strausz, a n d T. N. Bell, Chem. PIi.vs. L e i f . , 1979, 68,131. E. Bastian. P. Potzinger, A. Ritter, H . P. Schuchmann, C . Von Sonntag, and G . Weddle, Bcr. Bunscngcs. P h ~ . s Chcm., . 1980, 84, 56.

Plio t oc~henzisty*of' Conzpmds qf

'

tl i p

Mairi Groi11, Eliw ien ts

21 3

SiMe,, may be conveniently generated by photolysis of cyclo-Si,Me, ,, and this method has been used in the study of its insertion into Si-H bonds (e.g. in Me,SiH),13* l 4 S i - 0 bonds (e.g. Me,Si0Et),I3 and into HCI.l4 I n lowtemperature matrices it has been shown that SiMe, may be converted by visible light (A = 450nm) into MeHSi=CH2.l5 Annealing the photolysed matrix yields (4b). In Several workers have studied the photochemistry of silacyclobutanes. E, < 210nm) excitation of 1,l-dimethylsilacyclothe gas phase, U.V.(185nm butane causes elimination of ethylene and the formation of Me,Si = CH,.', This silaolefin, when formed, has an internal energy which is probably in excess of the Si-C 7r-bond energy, and it may be that its reactivity is different from that of Me,Si=CH, generated thermally or in solution. In particular it is possible that its isomerization to Me,HSicH occurs and this might be an explanation for the substantial amounts of polymer that accompany the ethylene and 1,1,3,3tetramethyl- 1,3-disilacycIobutane as products. Mass spectrometric measurements show that the products from octamethyl- 1,2-disilacyclobutane are mainly 2,3dimethylbut-2-ene and hexamethylsilacyclopropane. ' The primary photoprocess is probably that shown in equation (8).

-=

-

I

Me,CCMe,SiMe,SiMe,

Me,C----CMe,

+ Me,Si=SiMe,

(8)

The products of photolysis of substituted silacyclobutanes in methanol solution are either those derived from initial formation of the silaolefin [e.g.equation (9)] or by cleavage of the Si-C bond [e.g. equation ( 10)].18 A similar sensitivity to the nature of the substituent is observed with 1,3-disilacyclobutanes, where it is 1,3-disilacyclobutane undergoes observed that l,l93,3-tetramethy1-2,4-diphenylphotocleavage of a Si-C bond, whereas 1,1,3,3-tetraphenyl-1,3-disilacyclobutane is stable.

-

Ph,SiCH,CH,CHPh

Bu',SiCH,CH,CHPh

hv

h 1' MeOH

Ph,Si(OMe)Me

+ PhCH = CH,

Bu',Si(OMe)CH,CH,CH,Ph

(9) (10)

An examination of the photoproducts formed from Me,SiSiMePhSiMe, and dienes reveals that the initial reactive species formed on photodecomposition of the trisilane are ( 5 ) and MePhSi:.I9 The adduct formed from (5) and 2,3dimethylbuta-l,3-diene, which was earlier" thought to be (6) is now assigned the more reasonable structure (7). The silylene MePhSi: reacts with the diene to give the alkenylsilacyclopropane (8). This species builds up to a substantial concentration if a low-pressure mercury lamp is used, whereas if a high-pressure mercury lamp is employed, (8) photoisomerizes to (9) and (10). l3

l4 I'

l9

2o

T. Y. Gu and W. P. Weber, J . Orgcmomcf. Client.. 1980. 195, 29. 1. M . T. Davidson and N. A. Ostah, J . Orgnnomct. Cliem., 1981, 206, 149. T. J . Drahnak, J. Michl, and R. West, J . Am. Chem. Soc., 1981, 103, 1845. H . C. Low and P. John, J . Orgcmomet. Cliem., 1980, 201, 363. I . M . T. Davidson, N. A. Ostah, D. Seyferth, and D. P. Duncan, J . Orgcmomet. Chem., 1980, 187,297. P. Jutzi and P. Langer, J . Organamet. Clteni., 1980, 202, 401. M. Ishikawa, K . Nakagawa, R. Enokida, and M. Kumada, J . Orgcmonier. Chem., 1980, 201, 151. M . Ishikawa, F. Ohi, and M . Kumada, J . Orgunomet. Cheni., 1975. 86, C23.

214

Photochemistry

In low-temperature matrices (1 1) undergoes a photoreversible di-.n-methane photorearrangement to give (1 2).2' Tetramethylsilene, which could be formed by photoelimination from (1 l), is not observed at low temperatures but is produced in cyclohexane solution at room temperature where it has been trapped by dienes.21

Ye x

SiMel I Si (Me)- C H

Ph SiMe,

SiMe,

Me,Si-Si-CH

Me

Me

Ph

Me

Me

Me

g

F M e Me-Si-H

/ \

X

Me

I

/ \

Ph (9)

Ph

Me

An interesting series of photochemical interconversions of unsaturated silane derivatives starting from the alkynyldisilane (1 3) has been described (Scheme 1).22

Me3Si

I

I

/SiMe3 c-c

\

\ /

Si

/ \

Ph Ph

hi*

Me,Si

\

C=C= SiPh2 Me3SiC~CSiPh2SiMe35 / (13) Me Si .~

,

Me3Si

SiMe,

\ /

Me Si\ ,C=C=C Me,Si

C

/ \

SiPh,

\Si/

hi,, heat

Ph,

Me3Si

Me3Si-C

I

\c-c

SiMe, I /C-SiMe,

I. I Ph, Si-SiPh,

Scheme 1

Unlike most silacyclopropenes the mesityl-substituted compounds (1 4), which are formed by irradiation of the alkynyldisilanes (1 5 ) are remarkably stable towards oxygen and moisture and therefore particularly suitable for photochemical 21

22

J. D. Rich, T. J. Drahnak, R. West, and J. Michl., J . Urganomet. Chern., 1981, 212, C1. M, Ishikawa, D . Kovar, T. Fuchikami, K. Nishimura, M . Kumada, T. Higuchi, and S. Miyamoto, J . Am. Chem. SOL-.,1981, 103, 2324.

21 5

Photochemistry of Compounds of the Main Group Elements

studies.’, With (14a) (R = Ph) extrusion of the silylene is the only observed reaction, whereas with (14b) (R = SiMe,) photoisomerization to the alkyne (15b) and formation of a silapropadiene are also found.

R

SiMe,

\

RC =C f i Si Me,

/

(14) a; R = Ph

b; R

=

(15) a; R = Ph b; R = SiMe,

SiMe,

The cis-trans-photoisomerization of Me,SiCR = CRSiMe, (R = SiMe,Ph)24 and the reaction of singlet oxygen with 1,l-dimethyl-1-silacyclopent-3-enezshave been described. A short review in Japanese of the photochemistry of organosilicon compounds including acylsilanes has been published.26 Sensitization and quenching experiments show that the triplet state of acetyltrimethylsilane is involved in reaction (ll).” Furthermore, as the lifetime of the triplet state (z 13ns) does not vary

-

MeCOSiMe,

+ Pr’OH

-----+

MeCH(OPr’)OSiMe,

(1 1)

with the concentration of propan-2-01, it is clear that the excited state decomposes to give some other species, probably MecOSiMe,, which then reacts with the alcohol. By contrast it has been demonstrated that reaction of the acetylsilane with dimethyl fumarate proceeds by direct attack of either the singlet or the triplet state of MeCOSiMe, on the electron-acceptor olefin.28A possible mechanism is given in Scheme 2. Photolysis of 1,l -dimethyl-1-sila-2-cyclopenianonein t-butylalcohol gives the cyclic acetal product expected from a siloxycarbene intermediate.” 0

II MeCSiMe,

+

h I’

C0,Me

Me SiMe,

M e OSiMe3 V C 0 , M e -+ M e , S i O d c o z M e ‘C0,Me 23 24

25 26

” 29

Me

‘CO2Me

Scheme 2 M. Ishikawa, K. Nishimura, H . Sugisawa, and M. Kumada, J . Orgunornet. Cliem., 1980, 194, 147. H. Sakurai, H. Tsbita, M. Kird, and Y. Nakadaira, Angew. Chem., 1980,92, 632. A. Laporterie, J. Dubac, and P. Mazerolles, J. Orgmomet. Chem.. 1980, 202, C89. H. Sakurdi, Y. Ndkadaira, and H. Tobita, Kngaku N o Ryoiki, 1979, 33, 879. R. A. Bourque, P. D. Davis, and J. C. Dalton, J . Am. Clzem. Soc.. 1981, 103, 697. J. C. Dalton and R. A. Bourque, J . Am. Chem. Soc., 1981, 103, 699. A. Hassner and J. A. Soderquist, Tetrcrhedron Lett., 1980, 21, 429.

216

Photochemistry

However the germanium analogue (16) forms Me,HGe(CH,),CO,Bu‘ apparently by initial photochemical cleavage of the Ge-acyl bond and subsequent formation of the ketene Me,Ge(CH,),CH=C==O.

Other publications consider the photochemical reactions of Hg(SiMe,), with f l u o r o - ~ l e f i n s ,the ~ ~ photo-induced reaction of Me,SiCI, -,(n = 1-3) with S0,C12,31the e.s.r. properties of photochemically produced substituted triarylsilyl radicals,32 and a comparison of the phosphorescence spectra of SiPh,, GePh,, SnPh,, and PbPh,.,,

3 Tin and Lead From e.s.r. and l19Sn CIDNP measurements it is clear that photolysis of Me,SnSnR,SnMe, (R = Me or Et) leads to both Sn-Sn and Sn-C bond cleavage [equations (12) and ( 13)].,“ The polarization and enhancement factors observed for the CIDNP signals agree with those calculated for the triplet state of the tristannane as the precursor for both reactions Me,SnSnR,SnMe, Me,SnSnR,SnMe,

I1 11

----+

Me,Sn

+ SnR,SnMe,

hv -----+ (Me,Sn),SnR

+R

(12) (13)

Irradiation of (17) causes elimination of SnMe,, and the consequent production of (18).35The stannylene produced extracts a tellurium atom from (17) to yield (1 9). Laser flash photolysis of di-t-butylperoxide solutions of Bu,SnH produces Bu,Sn, which rather surprisingly absorbs strongly in the visible.36 The photoreactions of Et,SnCH,CH=CH, and thiols have been described.,’

30 31

32 33 34

3s 36

”

A. K . Datta, R. Fields, and R. N . Haszeldine, J. Cliem. Res. ( S ) , 1980, 1, 2. N. N. Voronkov, S. A. Bolshakova, V. P. Baryshok, A. I. Albanov, and B. Z. Shternberg, Dokl. Aknd. Ncruk SSSR, 198I, 256, 90. H. Sakurai, H. Umino, and H. Sugiyama, J. Am. Chem. Soc., 1980, 102, 6837. H. Mie and T. Azumi, Koen Yoshishu-Bunshi Kozo Sogo Toronkai, 1979, 384. C. Grugel, M . Lehnig, W. P. Neumann, and J. Sauer, Tetrnhedron Lett., 1980, 21, 273. B. Mathiasch, J. Orgunomet. Cliem., 1980, 194, 37. J. C. Scaiano, J. Am. Cliem. Soc., 1980, 102, 5399. M. G. Voronkov, V. I. Rakhlin, S. Kh. Khangazheev. R. G. Mirskov, and A. I. Albanov, Zh. Ohshch. Kliim., 1980, 50, 1771.


21 7 Photoassisted lead tetra-acetate oxidation of alcohols38 and laser-induced fluorescence of gaseous lead ~ u l p h i d e ,have ~ been the subject of recent reports. 4 Nitrogen and Phosphorus

-

Conductometric methods have been used to follow the reactions of the transient species formed by flash photolysis (A 200nm) of nitrate ions in aqueous ~ o l u t i o n . ~The ' initial excited state produced was shown to decay by two routes either to give HOONO or to give a lower energy excited state. Other reactions observed, and also those described previously by other workers, are summarized in Figure 1. A study of the photolysis of HN, induced by 290 nm dye-laser pulses has been reported.41The isomerization of N,F, in the presence of fluorine and oxygen has been initiated p h o t ~ c h e m i c a l l y . ~ ~

NO,*

-

(200) N03*-(300)+OH

I

0

4-l + NO2 =@N,O4--

H2O 10-3s

hu

Figure 1 Kinetic pathways in the photolysis of nitrate ions in aqueous solutions (Reproduced by permission from Z . Phys. Chem., 1980, 123, 1). 38

39 'O 4'

42

M. Lj. Mihailovic, V. Andrejevic. and A. V. Teodorovic, Glas. Hem. Drus. Beogrcicl, 1980, 45, 327. B. Burtin, M. Carleer, R. Colin, C. Dreze, and T. Ndikumana. J . Phy. B., 1980, 13, 3783. I. Wagner, H . Strehlow, and G. Busse, Z . Pliys. Client. (Wieshaden), 1980, 123, 1. L. G. Piper, R . H . Krech, and R. L. Taylor, J . Chem. Phys., 1980, 73, 791. A. A. Kibkalo and V. I . Vedeneev, Kinet. Katal., 1980, 21, 850.

Photochemistry

218

U.V. photolysis of phosphine gives diphosphine as the initial product = 1.78).43 Although a detailed analysis of the reacLion course was hampered by the accumulation of red phosphorus as the reaction proceeded, it is clear that reactions (14)--(16) are important processes. The photochemical decomposition of PPh, has been monitored by 31P n.m.r.44 The reaction proceeds via the triplet state and evidence was also found for the production of benzyne from the phenyl radical produced in the initial photoreaction.

(aPzH4 = 0.80 : @ - p H 3

PH, H

+ PH,

I1v

PH,

+H

(14)

PH,

+ H,

(1 5 )

5 Oxygen, Sulphur, and Selenium Rate constants for the reaction of hydrogen, methane,45 or ammonia 46 with hydroxyl radicals generated by flash photolysis of water in the gas phase have been determined. The photoreactions of SO, in argon, nitrogen, or oxygen matrices at 12 K have been studied."' Only in oxygen matrices are photoproducts (SO,) observed and it was demonstrated that the dimer (SO,),, but not monomeric SO,, was reactive. In the gas-phase photochemistry of both CH2(CH2),S04*and CH2(CH,),S049 the primary photoprocess appears to be rupture of a C-S bond to give a diradical that subsequently ejects SO. A very detailed laser-molecular beam study of the multi-i.r.-photon dissociation of SF, has been reported." The translational energy distribution and the dissociation lifetime of the excited SF, have been studied as a function of the laser intensity and energy influence, and it has been demonstrated that the dissociation of the excited SF, (to SF, and F) is in good agreement with the predictions of RRKM theory. The photo-induced cyclizations of the selenol esters (20) and (21) to give (22) and (23), respectively, have been described. Photolysis of benzyl phenyl selenide (24a) or of the phenyl ribosyl derivative (24b) yield the corresponding diselenides (25).52The photoreduction of acetophenone by H2Se has been in~estigated.~,

- -

43 44

" 46

'' 48

"

s2

s3

J. P. Ferris and R. Benson, J . Ani. Clwm. Soc., 1981, 103, 1922. Y. A. Levin, E. I. Gol'dfarb, and E. I . Vorkunova, Zh. Ubshdi. Kiiim., 1980, 50. 1981. F. P. Tully and A. R. Ravishankara, J . Plija. Clwmi., 1980, 84, 3126. K. J. Niemitz, H . G . Wagner, and R. Zellner, 2.Phys. Client. (Wiesbrrden), 1981, 124, 155. J. R. Sodeau and E. K. C. Lee, J. PlIj*s. Ciieni., 1980, 84, 3358. F. H. Dorer and K. E. Salomon, J. Phys. Cliem., 1980, 84, 3024. F. H . Dorer and K. E. Salomon, J . Plijs. Client., 1980. 84, 1302. P. A. Schulz, A. S. Sudboe, E. R. Grant, Y . R. Shen, and Y. T. Lee, J . Chem. Plijs., 1980, 72, 4985. K. Beelitz. K. Prdefcke, and S. Gronowitz, J. Organonlet. Chem.. 1980. 194, 167. J.-L. Fourrey. G. Henry, and P. Jouin, Tetraliedron Lett., 1980, 21. 455. N. Kambe, K. Kondo, and N. Sonoda, Clreni. Lefr., 1980, 1629.


& S e 0o M e

0

(20)

AcOH2C =

Me

(22)

(24) a; R = CH2C,H5

b; R

219

9

Se -Sd (25)

AcO OAc

6 Other Elements The quantum yield for the photodissociation of iodine and the rate of recombination of the iodine atoms so produced have been determined in alkane solvents at pressures up to 3 kbar.54The higher pressure causes an increase in the viscosity ( q ) of the solvent, and it was shown that the quantum yield (i.e. the fraction of iodine atoms escaping from the solvent cage) depends on q - ’. The photoinduced reaction of fluorine and methane in low-temperature matrices yields a hydrogen-bonded species MeF...HF. A study of the effect of infrared radiation on the interaction of XeF, and silicon surfaces56 and a report on excited states of xenon produced by vacuum-u.v. irradiation” have been published.

J. Schroeder, J. Troe, and U. Unterberg, J. Phys. Chem., 1980, 84, 3072. ’’ KG.. Luther, L. Johnson and I. Andrews, J. Ant. Chenr. Soc., 1980, 102, 5737. T. J. Chuang, J . C h m . Plivs., 1981, 74, 1461. ’’ G. Di Stefano, M. Lenzi, A. Margani. and C. N . Xuan, J. Clwni. Pli>ts., 1981, 74, 1552 ” 56

Part I11 ORGANfC ASPECTS OF PHOTOCHEMISTRY

1 Photolysis of Carbonyl Compounds BY W. M. HORSPOOL

1 Introduction The decline of interest over past years in the photochemistry of simple carbonyl compounds now seems to have reached a deficiency state. The number of research groups actively studying in this area appears to be diminishing very quickly, and the quantity of really important advances has decreased dramatically. Much of the remaining interest has switched from the synthetic aspects of carbonyl photochemistry to more physical studies involving energy transfer and excited-state lifetime measurements. Typical of this area of study is the account by Zimmerman and his co-workers of the details of their studies of energy transfer in rod-like molecules (e.g., 1,2). A detailed study of the photochemical reaction of

(1)

4

R 2= 1-naphthyl R' = Me, R2 R' = C6H4, R2 = I-naphthyl R' = Me, R2 = 2-naphthyl. R' = C,H,,, R2 = 2-naphthyl

R2

(2) R' = Me, R2 = 1-naphthyl R' = Ph, R2 = I-naphthyl

excited acetophenone in the presence of l-phenylethanol has shown that half of the ketone triplets are quenched by the OH bond rather than by reaction with a C-H bond.2 Earlier work by Wagner and Schott also focused attention on the interpretation of the results of ketone photolysis in alcohol solution. Wagner and his co-workers have also studied charge-transfer quenching of triplet trifluroroacetone. The CIDNP effects in this system were also reported.' Albini has reviewed the useful synthetic reactions achieved by energy-transfer I

*

H. E. Zimmerman, T. D. Goldman, T. K. Hirzel, and S. P. Schmidt, J . Org. Chem., 1980, 45,3933. P. J. Wagner and A. E. Puchalski, J . Am. Chem. SOC., 1980, 102, 7138. P. J. Wagner and H. N. Schott, J . Am. Chem. Soc., 1969, 91, 5383. P. J. Wagner and H. M. H. Lam, J. Am. Chem. SOC., 1980, 102,4167. P. J. Wagner and M. J. Thomas, J. Am. Chem. Suc., 1980, 102,4173. A. Albini, Synthesis, 1981, 249.

223

224

Photochemistry

and electron-transfer photosensitization, and Warrener review.

' has published

a short

2 Norrish Type I Reactions

Turro and Mattay * have studied the photochemistry of 1,2-diphenyl-2,2dimethylpropan-1-one (3) in micellar solution. The products formed from this reaction are the olefin (4,23%) and benzaldehyde (5,23%). Trace amounts of other products (Scheme 1) were detected. The reaction appears to be dominated by the P h q P h Me Me

+

+

PhCHO ( 5 ) 23%

Me i PhC=CH, (4) 23%

+

PhCH(CH,), trace

+

PhC(CH,),C(CH,),Ph trace

(3)

Scheme 1

Norrish Type I reaction leading to radicals (PheO and PhMe,C*) from which the products are formed. Another study in micellar solution has examined the photochemical decomposition of 1,3-diphenylpropan-2-0ne(6).' P

h y Ph 0 (6)

Turro and Kraeutler l o have reviewed the state of the art of magnetic field and magnetic isotope effects in the study of organic reactions. A study of the photochemical behaviour of phenyladamantyl ketone (7) in benzene has shown that the reactions are dominated by fission processes (a Norrish Type I reaction) to yield the products shown in Scheme 2." When the irradiation is carried out in hexadecyltrimethylammonium chloride (HDTCI) solution, adamantane (AdH) is the main product. There is a poor mass balance in this experiment which is thought to be due to interaction of the PhCO radical with the miceller medium. When Cu2 is used as a radical trap a different distribution of products is observed (Scheme 2, third entry). +

0 PhAAd

Ad = I-adamantyl

(7) (7)

(7)

A PhCHO C A

-L HDTCI

75% 7%

+

PhCOPh 6%

-

+

AdH

+

I-PhAd

+

33%

35%

Ad-Ad 3%

60"L

-

-

AdOH 3%

+

PhCOCOPh 3% AdCI 33%

+

PhCO,H 45%

Scheme 2

' lo

l1

R. W. Warrener, Chem. Aust., 1980, 47, 163 (Chem. Abstr., 1980, 93, 149009). N. J. Turro and J. Mattay, Tetrahedron Lett., 1980, 1799. H. Hayashi, Y.Sakaguchi, and S . Nagakura, Chem. Lett., 1980,1149 (Chem.Abstr., 1981,94, 102414). N. J. Turro and B. Kraeutler, Acc. Chem. Res., 1980, 13, 369. N. J. Turro and C.-H. Tung, Tetrahedron Lett., 1980, 4321.

225

Photolysis of Curbonyl Compounds

Irradiation of acetoxystyrene (8) in hexane solution affords acetophenone (one of the products of a-fission: presumably the other product, acetaldehyde is also present) and the diketone (9) (formed by what is formally a [1,3]-acetyl migration) as the primary photoproducts. Continued irradiation of the reaction mixture brings about cleavage of this diketone (9) into radical pairs (10, 11) which can either reform starting material [from radical pair (lo)] or produce acetophenone as well as yielding isopropenyl benzoate (12) and benzoic acid [from radical pair (1 l)].

A study of the wavelength and temperature dependence of the photochemistry of the cyclobutanone (13) has been reported. The reactions normally encountered in the photochemistry of such species are a-cleavage leading to decarbonylation, cycloelimination yielding olefins and ketenes, ring expansion to a carbene intermediate, and recyclization to the starting material (Scheme 3). The present

deca rbonylation

b, +

4

cis

+ CH,CO,R + 7+ CH,CH,CO,R

cycloelimination

ring expansion

OR and trans

Scheme 3

work has shown that reformation of the starting material does not arise to a significant extent. The stereospecificity of the cycloelimination and ring-expansion paths is high at 25 "Cand 3 13 nm. Decarbonylation of the trans-isomer (13) is also stereospecific but only moderate stereospecificity is shown for the decarbonylation of the cis-isomer (1 3). Such high stereospecificity is indicative of the involvement of the singlet state but there is obviously leakage from S , to T , in the case of the cis-compound with the resultant loss of stereospecificity. Decrease in the wavelength from 313 + 254nm brings about only a small change in the reaction H . Garcia, R. Martinez-Utrilla, and M. A. Miranda, Tetrahedron Left., 1980, 3925. N . J. Turro, D. Bauer, V. Ramamurthy, and F. Warren, Tetrahedron Lett., 1981, 611.

226

Photochemistry

pattern. With change in temperature from 25 to -78 "Cthe yield of the cyclization product (reformed starting material) is enhanced at the expense of the cycloelimination and decarbonylation. Stereospecificity of the reactions does not appear to be greatly effected by such temperature change apart from a slight decrease in the stereospecificity of the decarbonylation process. Interest in the ring-expansion process for its synthetic potential has also been reported. Photolysis of the ketones (14a-c) in methanol afforded the ring-expanded acetals (1 5 a - c ) via the now wellexemplified route of ring expansion to a carbene intermediate (e.g., 16) which l 5 In competition with this subsequently is trapped by solvent (methan~l).'~? reaction is the cleavage of the four-membered ring (in 1 4 a - c and 17) to yield the olefin products (18 and 19, respectively). When the ring-opening process was applied to the ketones (14b, d, e) by irradiation in aqueous tetrahydrofuran high yields of the lactols (20) were obtained without the competition of ring opening to olefins. It is clear that in this instance the change of solvent has a profound effect on the outcome of the photochemical reaction.

c;: 0

R2

(14)

R'

Te

9

:

CAR]

0

R2

R2

' 0

Q 0 ,..I1

R'

0

(1 5 ) (16) (17) a; R' = CHSMe=CHSMe, R 2 = OH b; R' = CH=CHCHOHC5H11, R2 = OH c; R' = CH=CHCH(OSiMe,Bu') C,H,;, R2 = OSiMe2But d; R' = R2 = H e; R' = Bun, R 2 = OH

$OH

R' (18)

(19)

R' (20)

Population of the triplet nz* state of the esters (21) results in the conversion to the unsaturated aldehydes (22) by an a-fission process.'6*17 The reaction is sometimes complicated by the intervention of Norrish Type I1 reactivity dependent on the length of the alkyl substituent. The singlet state of the compounds is unreactive. 1-Menthone (23) is photochemically active and yields, on prolonged irradiation, the acid (24) following Norrish Type I fission and disproportionation of the R. F. Newton, D. P. Reynolds, N . M. Crossland, D. R. Kelly, and S. M. Roberts, J . Chem. Soc., Perkin Trans. I , 1980, 1583. For reviews see D. R. Morton and N. J. Turro, Adv. Photochem., 1974, 9, 197; P. Yates and R. D. Loutfy, Arc. Chem. Res., 1975, 8, 209. J. Kossanyi, I. Kawenoki, B. Furth, and V. Meyer, J . Photochem., 1980,12,305 (Chem. Abstr., 1980, 93, 167 207).

See also J. Kossanyi, J. Perales, A. Laachach, I. Kawenoki, and J. P. Morizur, Synthesis, 1979, 279.

Photolysis of Carbonyl Compounds

227

0

0

QR (21) n = I or 2

R

@C02&

C0,Et =

H , Me, Et, Pr, Pr’CH,

(22)

resultant biradical.’ Other products, (25) and (26), are also formed and arise from the decarbonylation and the Norrish Type I1 cyclization of (23). The other two products (27) and (28) encountered presumably arise by secondary processes. The ester (29) is the only volatile photoproduct obtained from the irradiation of the

(23)

(24)

(25)

(26)

(27)

(28)

ketone (30a) in methanol.” An analogous path (that of a-fission) is followed by the ketone (31), which yields the ester (32) on irradiation under similar conditions. The reason for the apparent preferred fission of bond ‘a’ in the ketones (30a and

R’

(29)

(30) a; R’ = RZ = Me b; R 1 = Me, R2 = H c;,R’ = R2 = Me

(31)

3 1) is not instantly obvious and the authors l 9 investigated the influence of methyl substitution upon the photochemical reaction of (30). When a single methyl substituent is included in ketone (30b) products (33) and (34) are obtained from the two possible paths of a-fission leading to the biradicals (35) and (36) (Scheme 4). However, when two substituents were incorporated as in (30c) the compound was only very slowly reactive and failed to yield identifiable products. The influence of methyl substitution can be overwhelming, as with the bicyclic ketone (37), which yields only products (38) and (39) derived from Norrish Type I fission towards the more stable biradical (40).’ Norrish Type I reactivity can also lead to photoepimerization as has been reported for the conversion of (41) into (42).20 The photoconversion of the silane (43) into the acetal(44) in propan-2-01 can be sensitized and quenched.’l A kinetic study has shown that the triplet lifetime of l9 2o

R. K.Baslas, Int. Congr. Essent. Oils,(Pap.), 7th. 1977, 7 , 484. R. K. Murray, jun. and T. M. Ford, J . Am. Chem. Soc., 1980, 102, 3194. I. Kitagawa, T. Kamigauchi, K. Yonetani, and M. Yoshihdra, Chem. Pharm. Bull., 1980, 28, 2403 (Chem. Absrr., 1981, 94, 84324). R. A. Bourque, P. D. Davis, and J. C. Dalton, J . Am. Chem. Soc., 1981, 103, 697.

GOB

228

Photochemistry

(30b)

--+

4

(35)

(34)

(36)

i Me

(33)

Scheme 4

the silane (43) is not affected by changing the concentration of the alcohol. Thus the mechanism for the formation of the acetal involves the excitation of the silane to its triplet state followed by transformation into the carbene (45). This carbene is then trapped by the solvent. Such a mechanism is in agreement with that proposed earlier by Brook et ~ 1Photoaddition . ~ ~ of the silane (43) to dimethyl fumarate gives the trans-cyclopropane (46).23No evidence was found for the presence of the

doAc ***

...Me

JoA=

Me

OMe (42)

(41)

0 II Me-C -SiMe3 (43)

OPri I Me-C-OSiMeJ

I

H

Me-E-OSiMe3 (45)

(44) 22

23

A. G . Brook and J. M . J. Duff, J . Am. Chem. Soc., 1967, 89, 454;Can. J . Chem., 1973, 51, 2869. J. C . Dalton and R. A. Bourque, J. Am. Chem. Soc., 1981, 103,699.


229 0. .,CO2Me

C0,Me MeflCO,Me OSiMe,

C0,Me MeflCO,Me OSiMe,

Me-iJC02Me SiMe

Me-74C0,Me OSiMe (49)

cis-product (47); but this is formed along with the trans-adduct (46) in a ratio of 2 : 3 from the photoaddition of the silane (43) to dimethyl maleate. From a careful study of the reaction the authors23 suggest that the formation of the product involves the addition of the excited triplet or singlet state of the silane (43) to give a short-lived biradical(48), which rearranges to the 1,3-biradica1(49),prior to ring closing to the cyclopropane. No evidence was collected for the intermediacy of the carbene (45) in this reaction. The phosphonates (50) are photochemically reactive and lead to products dependent upon the nature of the substituents.24 Irradiation of the phosphonate (50a) yields the product (51a) as a result of a photoreaction analogous to a Norrish Type I process. An analogous product (51b) is also encountered in the photolysis of phosphonate (50b). In this instance however other products (52b) and (53b) are produced as a result of Norrish Type I1 reactivity and fission of the resultant biradical. Norrish Type I1 fission dominates the photoreactions of (5Oc) and (50d) yielding the monoester (52c, d) and the olefin (53c, d). Fission of the C-P bond to afford the radical (54) and products derived from it is the result of irradiation of the phosphine (55).25 0 II CI,CP(OR)2 (50) a; R = Me

b; R = Bu' c; R = Pr" d; R = Et

p

(OR 1

0

j

(51) a; R = Me

b; R = Bu'

II I

C1JCP-OH

OR (52) b;

R = Bu'

c; R d; R

(54)

= Pr" = Et

RifR2 (53) b: R1 = R2 = Me c; R' = Me, R2 = H d; R' = R2 = H

(55)

The formation of chromones (56) from the photolysis of acetates (57) is brought about by a free-radical path involving the fission of a C-0 bond to yield the radical intermediate (58).26 24 25

N. Suzuki, T. Kawai, S. Inoue, N. Sano, and Y. Izawa, Bull. Chem. Soc. Jpn., 1980, 53, 1421. M. Dankowski, K. Praefcke, J.-S. Lee and S. C. Nyburg, Phosphorus Sulphur, 1980.8, 359 (Chem. Abstr., 1981, 94, 29797). H. Garcia, R. Martinez-Utrilla, and M. A. Miranda, Tetrahedron Lett., 1981, 1749.

Photochemistry

230

"Ac (57)

(56)

R' R'

= =

R2 = H; R'

(58)

H, R2 = OMe, Cl,lor Me; M e 0 or OH, R2 = H; R' = R2 = Me =

3 Norrish Type I1 Reactions Wagner 2 7 has reviewed the photochemistry of simple carbonyl compounds and the rearrangements involving 1,4-biradicals produced by, for example, Norrish Type I1 behaviour of ketones. A study of the photochemistry of alkanals in dilute solution and in the presence of H-donors or olefins has been reported by Encina et a1.28The behaviour towards unsaturated compounds appears to be related to the difference in the ionization potentials and electron affinities. Kossanyi et al.29have reported their studies into the quenching of aldehyde singlet states by dienes. The influence of naphthalene on the photoreaction of 4-methylpentan-2-one in solution has been e~aluated.~' A detailed study of the photoelimination reactions of the racemic trifluoroacetates (59,60) has been reported by Gano and Chien.3' A kinetic analysis

(59)

of the reaction was carried out to evaluate the contribution of the triplet and the singlet processes to the overall formation of the products (61), (62), and (63) (Table 1). The alternative fate, i.e. other than elimination of the 1,4-biradical formed by a Norrish Type I1 process, is the formation of cyclobutanols. Such is the outcome of the irradiation of the gibberellin derivative (64a) which yields the cyclobutanol (65). Treatment of this derivative with a tritium or deuterium donor affords the labelled derivative (64b).32 Azetidinols (66) are formed on irradiation of the ketones (67) in ethereal solution. The azetidinols (66) arise by way of the Norrish 27

28

29

30 31

32

P. J. Wagner, Org. Chem., 1980, 42, 381. M. V. Encina, E. A. Lissi, and F. A. Olea, J . Photochem., 1980, 14, 233 (Chem. Abstr., 1981, 94, 102431). J. Kossanyi, G. Daccord, S. Sabbdh, B. Furth, P. Chaquin, J. C. Andre, and M. Bouchy, N o w . J . Chim., 1980, 4, 337 (Chem. Abstr., 1981, 94, 29792). W. Augustyniak, J . Photochem., 1980, 12, 99 (Chem. Abstr., 1980,93, 167 238). J. E. Gano and D. H.-T. Chien, J . Am. Chem. Soc., 1980, 102, 3182. M. Lischewski and G . Adam, Br. Pat. Appl., 2022077 (Chem. Abstr., 1980, 93, 132654).

P ho t olysis of Carbony 1 Compounds

23 1

Table 1 Stereospecificity of product formation from triuoroacetates (59) and (60) 3 1 Ester

Product

(59)

(62) (61) (63) (61) + (62) (63)

(60)

Regioselectivity Singlet Triplet 6.6 7.38 7.38 6.6 4.32 3.5 4.39 3.5

+

Stereospecificity Singlet Triplet

0.88

0.56

0.74

0.02

Type I1 process via intermediate (68).33 Minor products are also produced in the reaction by cleavage of the biradical (68). An analogous cyclization is also reported for the ketones (69) yielding the products (70).34

(64) a; R b:R

(66)

= =

H DorT

(67) Ar' = ArZ = Ph

Arl Ar' Ar' Ar' Ar' Ar'

= = =

= = =

(68)

MeOC,H,, ArZ = C,H, C,H5CbH4, Arz =C,H, C,H,, ArZ = CIC,H, C6H5, Arz = MeOC,H, C,H,, Ar2 = MeC,H, 2-naphthy1, Ar2 = C,H,

0H

d-"

Me

N

Ph (69) R = 2-fury1, benzo[b]furan-2-y1, 2-thienyl, pyrrol-2-yl, 1 -methylpyrrol-2-yl, 2, 4-dimethylthiazol-5-y1, or 3-pyridyl

Ph

A laser flash study of the behaviour of o-methylacetophenone has been reported in a study of the hydrogen-abstraction process leading to the quinomethide intermediate.35The ketones (7 1) also undergo photochemical conversion into a quinomethide intermediate, which cyclizes to the cyclobutenols (72) with reasonable efficiency. It is interesting that, although these ketones (71) undergo complete conversion on prolonged irradiation, the conversion of ketone (7 1, X = COC,H,Pr3'-2,4,6) yields a mixture of the cyclobutenol (72, 33

34

35

K . L. Allworth, A. A. El-Hamamy, M. M . Hesabi, and J. Hill, J . Cliem. Soc., Perkin Trans. I, 1980, 1671. M. M. Hesabi, J. Hill, and A. A. El-Hamarny, J . Chem. Soc., Perkin Trims. I , 1980, 2371. J. C . Scaiano, Chem. PIiys. Lett., 1980, 73, 319.

Photochemistry

232

(71) (72) X = OMe, Me, Bu', H, C8O2H,CO,Me, CF,, or CN

X = COC,H,Pr,'-2,4,6) and the starting material. This arises as a result of photoconversion of the cyclobutenol into starting material. The formation of cyclobutenols (72) was quenched using 2,5-dimethylhexa-2,4-dieneand the triplet lifetime thereby calculated. It was readily demonstrated that a Hammett plot of log zH/zx against otwas linear and gave a negative value for p. It was concluded that there is a strong effect exercised on the reaction by the presence of the bulky ortho-sub~tituents.~~ Quinkert and his co-workers 37 have reported a photochemical route to the synthesis of (_+)-oestrone(73). The reaction involves photoexcitation of the keto-olefin (74), which is transformed into the o-quinomethide (75) and then undergoes intramolecular addition to afford (76). Subsequent chemical transformation yields the product (73). The extension of this process to the synthesis of (+)-oestrone was also reported.38

HO

w \

Irradiation of the furanone derivative (77a) affords the two products (78) and (79) shown in Scheme 5.39 When the oxygen function at C-2 is not methylated (77b), irradiation yields the products (80, 81) (Scheme 6). In this case a different rearrangement mechanism is permitted as a result of the relative ease of opening of the furanone ring. The route to product (80) is thought to involve a Norrish Type I1 process of the carbonyl group with the proximate methoxy function. Subsequent rearrangement via the spiro intermediate (82) ultimately provides the product (80). In the first example (Scheme 5 ) the formation of (78) also involves 36 37

38 39

Y. Ito, Y. Umehard, Y . Yamada, and T. Matsuura, J . Chem. SOC., Chem. Commun., 1980, 1160. G. Quinkert, W.-D. Weber, U. Schwartz, and G. Durner, Angew. Chem.,hi.Ed. Engl., 1980,19, 1027. G.Quinkert, U. Schwartz, H. Stark, W.-D.Weber, H. Baier, F.Adam, and G. Durner, Angen. Chem. Int. Ed. Engl., 1980, 19, 1029. J. H. van der Westhuizen, D. Ferreira, and D . G. Roux, J . Chem. SOC.,Perkin Trans. I , 1980, 1540.


233 _ ,,r. _ *~M

M & -yM m eJJe

c\ o

W

O

M

e

\

Me0

HOCH, (774

(78)

t

OMe

Me (79)

Scheme 5

M

e

o

\

w

o

M

e &

OH

I

OH 0

OMe

Me M e 0 Ho

Scheme 6

the spiro intermediate but the presence of a 2-alkoxy group prevents further rearrangement.

The Norrish Type I1 reaction, while commonly following a path that yields a 1,6biradical, can sometimes yield 1,5-or higher biradicals. A 1,5-biradical path is the key to the cyclization involved in an approach to the synthesis of dodecahedrane and its derivatives reported by Paquette and his co-~orkers.~' The photocyclization of the aldehyde (83) yields, after oxidation, the ketone (84). Further 40

L. A. Paquette, D. W. Balogh, and J. F. Blount, J . Am. Chem. SOC.,1981, 103,228.

234

Photochemistry

irradiation of this material yields the alcohol (85) via an analogous 1,5-biradical intermediate. Higher biradical species are discussed in a review by Breslow 41 of his work in the area of biomimetic control of chemical stereoselectivity.

Me

Me

(83)

(84)

(85)

4 Oxetan Formation

The gas-phase irradiation of hexafluoroacetone and 1,2-dichlorofluoroethylene (mixture of 2 and E isomers) gives the two oxetans (86) and (87) in a ratio of 55 : 45.42

F 3FC T \ H CI c1

F 3H C T i CI C1 F

(87)

(86)

Photoaddition of benzophenone to the methylene ketone derivatives (88) yields . ~ ~ biradical (90) the oxetan derivatives (89a) in 28 and 26% yield, r e ~ p e c t i v e l yThe is presumed to be the intermediate in the formation of these compounds. The authors 43 suggest that there are two competing pathways for reaction within this biradical, one leading to the oxetans (89), and another by rearrangement through Z

0

0

Me

Mi (88) R = H or Me

(89) a; Z . = 0; R b; R = H; Z

Ph Ph H or Me H , OH

= =

(90)

TPh2

I

,o

MC

(92) Z = HOor H 41

42

''

(93)

R. Breslow, Acc. Chem. Res., 1980, 13, 170. M . G. Barlow, B. Coles, and R. N. Haszeldine, J . Fluorine Chem., 1980, 15, 381. M . Nitta, T. Kuroki, and H. Sugiyama, J . Chem. Soc., Chem. Commun., 1980, 378.


235

(91) to yield adducts of the type (92). This route manifests itself in the photoreaction of the ene-ol (93) to yield the oxetan (89b) and the rearranged adduct (92). Another account of the photoaddition of benzophenone to norbornadiene has been reported.44 The products encountered (94,95,96a) seem to differ little from earlier reports 4 5 of this addition. The same products are formed from benzophenone and quadricyclane. The addition of (97) to norbornadiene yields the adducts (98, 62%) and (96b, 38%).

(95)

o=c/C0,Me

(96) a; R b; R

4 0

= =

Ph C0,Me

C0,Me

\

C0,Me

C0,Me

(97)

(98)

A detailed study of the photoaddition of trans-dicyanoethylene to the ketones (99-101) has been published.46 The results indicate that the cycloaddition is

b; R'-R2

N :@

C;

= CH,-CH, = Me

R 1 = R2

(102)

stereospecific, yielding in each case two oxetans (102), the result of em-attack on the carbonyl group. Minor products are also obtained where the oxetan is produced by endo-attack. The quantum yield measurements appear to indicate 44

45

46

K. Shima, M. Ikenoue, and K . Kamei, Kokagaku Toronkai Koen Yoshishu, 1979, 162 (Chem. Abstr., 1980, 93, 7263). T. Kubota, K. Shima, and H. Sakurai, Chem. Lett., 1972, 343; A. A. Gorman and R. B. Leyland, Tetrahedron Lett., 1972, 5345; A. G . Barwise, A. A. Gorman, R. B. Leyland, C. T. Parekh, and P. G. Smith, Tetrahedron, 1980, 36, 397. N. J. Turro and G . L. Farrington, J . Am. Chem. Soc., 1980, 102, 6056.

236

Photochemistry

that the cycloaddition from the em-face is enhanced by increasing steric hindrance: the relative quantum yield for the formation of oxetans from ketone (99) is 3.4 times higher than that for ketone (100). Reasonable yields of the adducts (103) are obtained when acetone is irradiated Compounds of in the presence of 2,3-dihydro- and 2-methyl-2,3-dihydro-furan. this structure can also be obtained by the photocyclization of the vinyloxy ketones (104a) and (104b),. which yields the adducts (105a) and (105b), re~pectively.~’ Intramolecular cycloaddition is also encountered in the photoreactions of the cyclic alkanones (106).48However the reaction favours the formation of the crossed adduct (107) in all the cases studied. The accompanying products are the alternative oxetan (108) and the products from Norrish Type I fission.

M Me e Rr (103) a; R b; R

n H = Me

=

R (104) a; R = H

(105) a; R = H

b; R

b; R

R (106) n

=

n =

1-3, R = H 2,R = MeorH

=

Me

R

=

Me

R

(107)

5 Fragmentations and Miscellaneous Reactions The diene (109) is formed when the keto-diene (110) is irradiated in various solvents using 1 = 254nm.49 The Diels-Alder activity of the diene (109) was

investigated. A detailed study of the photochemical gas-phase decarbonylation of bicyclic ketones (111, 112) has been reported (Scheme 7).50 The photodecarbonylation of the sugar derivatives (1 13, 1 14) yields the products (1 15, 1 16) shown in Scheme 8.’l Irradiation (A < 220 nm) of the saturated esters (1 17, 1 18, and 1 19) and acids results in two p h o t o p r o c e s s e ~ The . ~ ~ ester ( I 17) undergoes elimination of acetic

‘’ 49

’’ 50

s2

H. A. J. Carless and D. J. Haywood, J. Chem. Soc., Chem. Commun., 1980, 1067. J. Kossanyi, P. Jost, B. Furth, G. Daccord, and P. Chaquin, J. Chem. Res. (S), 1980, 368. L. Schwager and P. Vogel, Helv. Chim. Acta, 1980, 63, 1176. P. S . Mariano, E. Bay, D. G. Watson, T. Rose, and C. Bracken, J . Org. Chem., 1980, 45, 1753. K. Heyns, H.-R. Neste, and J. Thiem, Chem. Ber., 1981, 114, 891. G. Wolff and G. Ourisson, Tetrahedron Lett., 1981, 1441.

Photolysis of Carbonj4 Compounds

H

237

H

Me

Me

Me

Me

Scheme 7

(113)

R' = Me = R2 R * = Ph. R2 = H

(1 14)

Scheme 8

acid, presumably via a process akin to the Norrish Type I1 reaction, yielding the olefin (120). The same olefin (120) is obtained from the irradiation of the ester (121) presumably by a similar mechanism. Similar elimination reactions are encountered for the bile acids (1 18) and (1 19) (Scheme 9). A detailed analysis of the photosolvolysis of the chiral acetate (122) has been carried The products formed from the reaction are shown in Scheme 10 for the two solvents used. The results indicate that there is partitioning of the excited state between an allowed I ,3-sigmatropic shift of the benzyl group on the acetate system and the involvement of heterolytic and homolytic pathways. An electron-transfer mechanism is used to explain the formation of products (123-125) (Scheme 11) resulting from the photolysis of ester (126).54 The products are formally obtained by the loss of an acetyl group (C-0 bond fission) and hydrogen abstraction by the resultant ally1 radical. 53 54

D. A. Jaeger and G. H . Angelos, Tetrahedron LRtt., 1981, 803. K. Tsujimoto, Y. Kamiyama, Y. Furukawa, and M . Ohashi, Kokagaku Toronkai Koen Yoshishu, 1979, 208 (Chern. Abstr., 1980, 93, 70 529).

(1 19)

Scheme 9 Ar

Ar / I 1’

M e t H IR

\

OCOCH, (1 22)

Ar

I

1

MeC-H

f

I

I R

OR a ; R = H b i r r = Me

+

MeC-H

Ar

Ar = 3,5-diMeOC,H,

a ; R = H b; R = Me

CF,CH,OH

Ar

I

+

Me-C-H

I

I I

Me-C-H

R

OCH2CF3

R = H or Me Scheme 10

&OAC

R&Me Me

-t

R& Me

+

Me ( 126)

(123; 779

(124; 14:i)

(125; 3%)

R = 2-naphthyl

Scheme 11

The photolysis of the ether (127) in n-heptane yields free radicals in a first-order reaction.55The lactone (128) and the 3-tetrahydropyrone (129) are formed when the compound (1 30) is subjected to solution-phase irradiation.s6 55

56

V. Cermak, P. Vetesnik, and P. Pecen, Chern. Prum., 1979, 29, 642 (Chern. Abstr., 1980.92, 197550). C. Bernasconi, L. Cottier, G. Descotes, M. F. Grenier, and F. Metras, J . Heterocycl. Chern., 1980, 17, 45.

Phot olysis of Carbony1 Compounds

(127)

(1 28)

239

( 130)

( 129)

From the results (Scheme 12) obtained from the irradiation of the halocyclohexanones (1 3 I), the authors suggest that both free-radical and ionic paths are operative. They have further shown that sensitized reaction leads to radical products derived from the reaction of an nn* triplet state, whereas the singlet state leads to the ionic product^.^'

’’

(131) X

X X

X

=

C1, R = H

= C1, R = Me = Br,R = H = I, R = H

28% 16% 90% 70% Scheme 12

59%

13% 26% 10% 30%

58% -

A study of a series of bis-sulphenylated keto compounds has revealed a remarkable solvent effect.58Thus irradiation of, for example, (1 32) in acetonitrile yields ( 1 33, 43%) as the major product accompanied by two minor products (134, 25%) and (135,23%). But in benzene the products (1 34,63%) and (1 35,4973 were produced with no evidence for the formation of the cyclized material (1 33). Several examples of the reaction are cited. The photodegradation of some sulphonamides (e.g., 136) has been studied.59

(132)

(133)

(134)

(135)

The epoxycholestanone (1 37) undergoes conversion into the isomer ( 1 38) when irradiated at 254 nm.60 The irradiation of mixtures of 1,2-diarylketones and benzhydrylamine has been reported.61 The products encountered in this reaction are thought to arise from free radicals produced by hydrogen abstraction from the amine by the excited carbonyl compound. Caronna et ~ 1have . reported ~ ~ the formation of the adduct 5’ 58 59

P. C. Purohit and H. R. Sonawane, Tetruhcdron, 1981, 37. 873. T. Sasaki, K. Hayakawa, and S. Nishida, Tetrahedron Left., 1980. 3903. B. Weiss, H. Durr, and H. J. Haas, Angeir, Chem., I n / . Ed. Engl., 1980, 19, 648. P. Morand and S. A. Samad, Bangladesh J. Sci. Inn. Res., 1979, 14, 265 (Chem. Abstr.. 1980, 92, 181 481).

61

62

K. N. Mehrotra and G. P. Pandey, Bull. Chem. Soc. Jpn., 1980, 53, 1081. T. Caronna, S. Morrocchi, and B. M. Vittimberga, J. Heterocjd. Chent., 1980. 17. 399.

Plzot ochemistry

240

R' /

R3 (136) R L = H , R 2 = Ph, R3

R' R'

R1

= = =

R'

=

Me

PhCO, R 2 = Ph. R 3 = M e H , R 2 = 2-thiazolyl. R 3 = N H ,

'H '8H o

&HI7

HO

=

R 2 = Ph, R3 = M e H , R 2 = PhCO, R3 = M e

6

,,,

0

( 137)

( 138)

(1 39) from the irradiation of 2-pyridinecarbonitrile with benzophenone in non-

acidic solution. When the irradiation is carried out in acidic propan-2-ol-H20 the adduct (1 39) is accompanied by the reduced cyclized material (140). Ph

( 139)

ph

( 140)

Cycloaddition occurs when the silacyclobutenes (141) are irradiated in the presence of aldehydes and ketones.63 The preferred reaction mechanism for the process involves photoexcitation of the carbonyl compound followed by attack of the carbonyl oxygen at silicon. This yields two biradical intermediates (142) and (143) that lead to the two isolated products (144) and (145) (Scheme 13).

I R; ( 144) Scheme 13 b3

R. Okazaki, K.-T. Kang, and N. Inamoto, Tetruhedron Lett., 1981, 235.

3

L

Enone Cycloadditions a nd Rearrangement s: Photoreactions of Cyclohexadienones and Quinones BY W. M. HORSPOOL

1 Cycloaddition Reactions Intramolecular.-A full account of the synthetic approaches' using intramolecular cycloaddition of enones (1) eventually to yield the hirsutane skeleton (2, Scheme 1) has supplemented the material originally published in note form.2

Intramolecular cycloaddition can often provide an easy synthetic entry to novel strained compounds. Thus the photocycloaddition of the butenolides (3) yields the adducts shown in the Scheme 2. Irradiation of the enone (4)at 330 nm affords the 0

total yield 62"/,; ratio m 3 : l

Scheme 2

'

J. S. H. Kueh, M. Mellor, and G. Pattenden, J . Chem. SOC..Perkin Trans. I , 1981, 1052. J. S. H. Kueh, M. Mellor, and G. Pattenden, J. Chem. Soc., Chem. Commun., 1978, 5 . W. R. Baker, P. D. Senter, and R. M. Coates, J. Chem. SOC.,Chem. Commun., 1980, 1011.

24 1

242

Photochemistry

tricyclic product (5) in good yield (67%).4 Subsequent thermal reactions transformed this compound into (6), a derivative of tricyclo[4,2,0,0 1, 4]octane.

(5)

(4)

(6)

The photocyclization of the enone (7) to yield (8) has been used as an approach to the synthesis of the spiro(4,5)decane system.’ The tetracyclic product (9a) is obtained from the photo-induced intramolecular cyclization of the pyridone (10a)6, Increase in the chain length involving (lob) resulted in the formation of

(7)

(8)

the head-to-head adduct (1 la). However with an intermediate chain length (1Oc) the irradiation afforded the two adducts (9b) and (1 1b) in a ratio of 7 : 1. When intermolecular cycloadditions were effected between (12) and a range of olefins (1 3), the addition took place in a head-to-tail fashion affording (14)?

(9) a; n = 1 b;n=2

(10) a; n = 1 b;n=3 c;n=2

RCH =CH

H (12)

0

(13) R = OAC, CN, CO,Me, or CH

a:

(11) a; n = 3 b;n=2

K.

H (14)

The cage compounds (1 5) are produced from the enones (1 6) by irradiation in benzene solution.’ The identity of the products from the reactions was established

’ a

S. Wolff and W. C. Agosta, J. Chem. Soc., Chem. Commun., 1981, 118. W. Oppolzer, L. Gorrichon, and T. G. C. Bird, Helv. Chim. Acta, 1981, 64, 186. C. Kanoeka, T. Naito, H . Fujii, K. Shiba, M . Ito, and M. Somei, Kokagaku Toronkai Koen Yoshishu, 1979, 108 (Chem. Abstr., 1980, 93, 70805). C. Kaneoka, T. Naito, and M. Somei, J. Chem. SOC.,Chem. Commun., 1979, 804. G. Gowda and T. B. H. McMurry, J . Chem. SOC.,Perkin Trans. 1, 1980, 1516.

243

Enone Cycloadditions and Rearrangements

by spectroscopic and chemical means. The current interest in cage compounds is prompted by energy conservation i.e., the ability to trap energy in a strained molecule from which it can be recovered at a later stage. The cage compound (1 7) is formed on irradiation of the cyclopentadienone dimer (18).9 Fuchs l o has also R2 .R'

3: Me

(16)

(15) a; R' = H , R2 = Me

b; R'

=

Me U

(17) R

=

2-fury1 or 2-thienyl

Me, R2 = H

(18b) R'

(1 8a)

= R2 =

R 3 = H ; R'

=

R2 = H, R 3 = Ph; = R2 = Me, R 3 = Ph

R' = Me, R2 = H, R3 = Ph; R'

reported on the photochemical transformations of cyclopentadienone dimers (18b). Hamada et a!.' 1* l 2 have reported the synthesis of the cage compounds (19a) by the irradiation of the adducts (19b) using Pyrex-filtered light as the actinic source. The conversion could be carried out with wavelengths up to 360nm. For longer wavelengths, up to 390nm, the adducts (20) were useful and could be readily converted into the cage compounds (21). The X-ray structure determination of the cycloadduct (22) formed by photochemical ring-closure of (23) has been reported.

'

R'

lo

l2

l3

Y. Yamashita and M. Masumura, Heterocycles, 1980, 14, 29. B. Fuchs, Isr. J. Chem., 1980, 20, 203 (Chem. Abstr., 1981, 94, 46633). T. Hamada, H. Iijima, T. Yamamoto, N . Numao, K. Hirao, and 0.Yonemitsu, J . Chem. Soc., Chem. Commun., 1980, 696. T. Hamada, H. Iijima, T. Yamamoto, N . Numao, and 0. Yonemitsu, Kokaguku Toronkai Koen Yoshishu, 1979, 2 (Chem. Abstr., 1980,93, 70445). H. D. Becker, B. W. Skelton, and A. H. White, J . Chem. SOC.,Perkin Trans. 2, 1981, 442.

Pho tockemistry

244

(20)

R'

= -Me*,R 2 = p-MeOC,H,

(21)

PhH,C M e Ph \

H , C Me

4,Ph 0 Me (22)

(23)

The unstable cycloadducts (24) and (25) are obtained from the photolysis of the enone ethers (26).14 A similar approach has been reported by Barker and Pattenden in their study of the photocyclization of enol acetates. Thus the intramolecular photocycloaddition affords the adducts (27) from the mixture of enol acetates derived from (28). An analogous regioselective cycloaddition is encountered in the irradiation of the enol acetates derived from (29) to afford the adduct (30).

(25)

R

=

Me or 6u'

(27) a; R3 = M e , R 2 = H (62%) (28) R' = H or Me (29) R = H or Me b; R 3 = H,R2 = Me (16%)

(30)

The norbornene derivatives (3 la, b) gradually disappear on irradiation without the formation of oxetan derivatives, the result of intramolecular cycloaddition. l4

Is l6

W. Oppolzer and S. C. f)urford, Helv. Chin?.Acta, 1980, 63. A. J. Barker and G. Pattenden, Tetrahedron Lett.. 1980, 3513. R. R. Sauers and D. C. Lynch, J . Org. Chem., 1980, 45, 1286.

Enone Cycloudditions und Rearrungements

245

c

0" 'kH2 (31) a; R b; R

= SCH2Ph

(32)

NEt, C; R = ON d; R = C1 e;R=H =

R = OH d; R = CI

C;

(33)

Th derivative (3 lc), however, undergoes a clea photoreaction to afford the oxetan (32c). The chloroketone (3 Id) affords, on irradiation, many products among which are the oxetan (32d) and the dechlorinated compound (31e). The homolysis of (31d) to the radical (33) is a facile process and occurs in competition with cyclization to the oxetan.16 Intermolecular.-The control of regiospecificity in photocycloadditions remains a much sought after goal. de Mayo and Syndes l 7 have found that some control can be exercised on the reaction when the cycloadditions are carried out in micellar potassium dodecanoate (KDC). The ratios of products are sufficiently different (Table 1) from those obtained in non-polar solvents to merit further study of this

Table 1 Products from the cycloaddition of olefins (34) to 3-butylcyclopentenone' Medium KDC Diethyl ether Cyclohexane KDC Acetonitrile Methanol Cyclohexane KDC Methanol Diethyl ether KDC Methanol Diethyl ether

R'

=

Olejin (34) Bu", R 2 = H

R'

=

hexyl, R2 = H

R'

=

Bu", R2 = OAC

R'

= pentyl,

R2 = OAc

Products (%) (35) (36) 78 22 57 43 51 49 88 12 63 37 62 38 53 47 70 30 0 100 0 100 70 30 0 100 0 1 00

effect. The authors believe that the regioselectivity observed is a micellar effect and not a function of the solvent polarity. The regiospecific photoaddition of the P. de Mayo and L. K. Sydnes, J . Chem. Sac., Chem. Commun., 1980, 994.

246

Photochemistry

cyclopentenone (37) to the olefins (38,39) affords the [2 + 2ladducts (40,41) shown in Scheme 3.18 When the acetylene (42) and the olefin (43) are used as the substrate for the addition, two [2+2]adducts are formed in both cases, one from head-tohead addition and the other from the head-to-tail mode (Scheme 4).The additions

&

SiMe, + MeM 'e (38)

(37)

A

&le

+

Me (40) 0

&Me ratio 5.4: 1

+ (39) R'--R2 = (CH,), R ' = OAc; R 2 = Me

(41)

Scheme 3

SiMe3

+ H,C=CHMe (43)

--+

*Me (20%)

H

'*H

(47%)

H (33%)

Scheme 4

are sometimes complicated by the formation of additional products, as shown in Scheme 3. Furthermore, care has to be taken to select the correct wavelength for the irradiation to avoid secondary photolysis of the adducts, e.g., the conversion of (40) and (44) by a Norrish Type I process. The addition of olefins to the uracil

derivative (45) was also studied (Scheme 5). In these experiments the influence of the trimethylsilyl group was seen in that only one addition mode was observed in each case." C . Shih, E. L. Fritzen, and J. S. Swenton, J . Org. Chem., 1980, 45, 4462.


247

0

H (45)

R 1 = R 2 = Me RI-R~

=

(CH,),

R 1= H, R2 = Me

90% 85% 87% ex0 : endo 15:85

Scheme 5

nn* Excitation (350 nm) of the enones (46a-d) in the presence of the cyclobutene (47) affords good yields (75-80%) of the cycloadducts ( 4 8 a 4 ) . 1 9 The use of enones (46e, f) gave lower yields (4&50%) of the corresponding adducts (48e, f), whereas enone (46g) gave only a trace of a photoproduct. This enone (46g) is apparently noted for its abnormal behaviour.20*2 1 The formation of (*)-adduct (48d) (73%) was also reported from the photoaddition of the olefin (47) to (-)piperitone (46d) using Corex-filtered light at 0 0C.22After desilylation and cleavage of the resultant diol the 1,Cdione (49) is obtained. A full account,23,24 originally reported in note of the photoaddition of 1-methylcyclobutene (50) at low temperature (- 78 "C)to piperitone (46d) as a route to the synthesis of shyobunone (51) and isocalmendiol (52) has been published. Blechert 26 has published a short review dealing with the photochemical synthesis of natural products.

R1QR3 R2 0 (46) a; n = 1, R' = R3 = H, RZ = Me a O SOSiMe3 iMe3 b; n = 1, R' = R2 = Me, R 3 = H c; n = 2, R' = Me, R2 = R 3 = H (47) d; n = 2, R' = Me, R2 = H, R 3 = Pr' e; n = 1 , R' = Me, R2 = R3 = H f; n = 2, R' = R2 = Me, R 3 = H g; n = 2, R' = R 3 = H, R2 = Me

(48)

?! Me

l9 2o 21

23 24 25

26

M. Van Audenhove, D. De Keukeleire, and M. Vanderwalle, Tetrahedron Lett., 1980, 1979. E. J. Corey, J. D. Bass, R. Le Mahieu, and R. B. Mitrd, J . Am. Chem. Soc., 1964, 87, 5570. E. P. Serebryakov, S. D. Kulomzina, and A. K. Margaryan, Tetrahedron, 1979, 35, 77. J. R. Williams and T. J . Caggiano, Synthesis, 1980, 1024. J. R. Williams and J . F. Callahan, J. Org. Chem., 1980, 45, 4479. J. R. Williams and J. F. Callahan, J . Org. Chem., 1980, 45, 4475. J. R. Williams and J . F. Callahan, J . Chem. SOC.,Chem. Commun., 1979, 404, 405. S. Blechert, Nachr. Chem. Tech. Lab., 1980, 28, 883 (Chem. Abstr.. 1981, 94, 64641).

248

Photochemistry

A high yield of the cycloadduct (53) is obtained from the direct irradiation of a hexane solution of tetramethylethylene and the enone (54).2 Controlled hydride

reduction and ring opening affords the keto aldehyde (55) which undergoes basecatalysed cyclization to yield the cyclohexenone derivative (56). Several examples

(54)

(53)

(56)

(55)

of this process are reported. Of importance in this reaction is the apparent regioselectivity observed when unsymmetrical olefins are employed (Scheme 6). The cycloaddition of enones to olefins is a reaction of great synthetic utility. Duc et ~ 1 have . extended ~ ~ the synthetic value in their report of the BF,-etheratecatalysed ring opening of the enone-allene adducts (e.g., 57 and 58). This chemical treatment of the adducts is a convenient method for the introduction of an isopropenyl group into unsaturated ketones (e.g., 59 and 60, respectively).

ratio 1.1.6

0

0 Scheme 6

Earlier work by Wiesner 2 9 proposed a set of empirical rules to account for the outcome of cycloaddition reactions to enones. Wiesner et a/. have now examined the photoaddition of allene to the sterically hindered system (61).30This work has

(57)

''

'' 29

''

(59)

(58)

S. W. Baldwin and J. M. Wilkinson, J . Am. Chem. Soc., 1980, 102, 3634. D. K. M. Duc, M . Fetizon, I . Hanna, and S. Lazare, Synrhesis, 1981, 139. K. Wiesner, Tetrahedron, 1975, 31, 1655. J. F. Blount, G. D. Gray, K. S. Atwal, T. Y . R. Tsai, and K. Wiesner, Tetrahedron Lett., 1980, 4413.


249

R' = 0, R2 = H2, R3 = b; R' = H,, R2 = 0, R3 = C8H17

(61) a;

(62)

aimed at answering the criticism of de Mayo and L o ~ t f y , ~who ' had implied that stereochemical control of the cycloaddition might depend exclusively upon steric factors. The cycloaddition to enone (61a) yielding the adduct (62) on the a-fxe is in line with Wiesner's predictions. This product was accompanied by the byproduct (63) formed by the route outlined in Scheme 7. Enone (61a) is sterically

I

H2%

HC

CH2 Scheme 7

hindered on the a-face as is enone (61b) but in addition to this, if the empirical rules are operative, then a-addition should also be inhibited. Indeed when the enone (61b) was irradiated in the presence of allene no adduct was obtained under conditions where (61a) yielded an adduct. On prolonged irradiation a trace of an adduct was obtained. The photoaddition of allene to the enone (64) yields the [2 + 21-adduct (65) in 78% yield. 32 0

H$

C0,Me (64) 31

32

(65)

R. 0. Loutfy and P. de Mayo, J . Am. Chem. Soc., 1977, 99, 3559. R. B. Kelly, M. L. Harley, and S. J. Alward, Can. J . Chem.. 1980, 58, 755.

250

Photochemistry

The single adduct (67a) is obtained by photoaddition of 1,l -dimethoxyethylene to the ester (66a). Adducts (67b) and (68) were also obtained by the photoaddition of the same olefin to the enone (66b). The molecules obtained by this process were chemically elaborated to yield compounds with the proto-illudane skeleton (69).33

Me Me& Me

HA

Me0 (67) a; R = C 0 2 M e , 67% b; R = Me, 19%

(66) a; R = C 0 2 M e b; R = Me

M eO (68) 5%

The cyclopentenones (70) do not undergo cycloaddition reactions with cyclohexene.34 The only reaction encountered in the irradiation of these molecules is the facile isomerization by a 1,3-alkyl shift to (71).35 In contrast with this, irradiation of cyclopentenone (72a) in the presence of ethylene yields (73a). The cyclopentenone (72b) yields (73b) with cyclohexene. It is clear from these results that there is some structural phenomenon within the molecules which make some, the (4,3,2)-propellanes prone to rearrange, while others, the (3,3,3)-propellanes, undergo cycloaddition.

(70)

R' = RZ = H; R' R' = R2 = Me

=

(72) a; R' = R2 = Me b; R' = Rz = H 33 34

35

R'

Me, R2 = H; (71)

(73) a; R' = R 2 = Me, R 3 = H b; R' = R 2 = H, R3-R3 = (CH,),

H. Takeshita, I. Kouno, H . Iwabuchi, and D. Nomura, Buff. Chem. SOC. Jpn., 1980, 53, 3641. R. L. Cargill, N. P. Peet, D. M . Pond, W. A. Bundy. and A. B. Sears, J . Org. Chem.. 1980,45, 3999. See later in this chapter for further examples of 1,3-alkyi migrations.

Enone Cycloadditions and Rearrangements 25 1 Two modes for the photoaddition of acetylene to the cholestenone (74) have been reported.36 Thus [2 21-cycloaddition yields the adducts (75) and (76) whereas an ene-type addition yields the ethylidene derivative (77).

+

@ ogl

0 '

;/

/

.

o@ Me

I

H (77)

(76)

(75)

(74)

The acetone-sensitized photoaddition of ethylene to the imidazolinone (78) yields the adduct (79).37Other adducts can also be obtained by the use of different I

Ac

Ac

olefins of imidazolinones. Photoaddition of olefins (e.g.,2-methylbut-2-ene)to the dienone (80a) results in the formation of the conventional adduct (81). When the thioketone (80b) is employed the reaction affords the adduct (82) where cyclization involving the sulphur has taken place.38 The adducts (83) are formed by the photoaddition of electron-rich olefins (CH,=CMe,, CH,=CHOAc, CH,=CHOMe) to the pyridone (84) in acetone. 39 When electron-deficient olefins (CH,==CHCO,Me, CH,==CHCN) were employed the photoaddition yielded the adducts (85). It seems reasonable that the formation of the adducts arises from the triplet state df the pyridone populated by acetone-sensitization. Evidence to this effect comes from the formation of the photo-pyridone (86) when irradiation is carried out in alcohol, ether, or dichloromethane. 39 Regioselective addition of 2methylpropene to the quinolones (87) affording the adducts (88a, b) is achieved when the photolysis is carried out in MeOH-Et3N. Similar addition was achieved

"$. Me

C Y R

MeM

/N Me (80) a; X = 0, R = H, Me, or Ph b; X = S, R = H 36 37

j9

d

Y /N R

\ N II

Me

Me (81)

(82)

E. P. Serebryakov, I:v. Akad. Nauk SSSR, Ser. Khim., 1979, 2313 (Chem. Abstr., 1980,92, 147037). K.-H. Scholz, J. Hinz, H.-G. Heine, and W. Hartmdnn, Chem. Ber., 1981, 114, 248. Y. Kanaoka, M. Hasebe. and E. Sato, Fukusokan Kagaku Toronkai Koen Yoshishu, 12rh, 1979, 156 (Chem. Abstr., 1980, 93, 71 679). H. Fujii, K. Shibd, and C. Kaneko, J . Chem. SOC.,Chem. Commun.. 1980, 537.

Photochemistry

252

using acrylonitrile and 1-acetoxyethylene affording (88c) and (88d), respectively. Ring opening to (89) was readily achieved using NaHCO, in boiling methanol.40 R' RZ

H

H

(83) a; R' = R2 = Me b; R' = CH,OAc, RZ = H c; R' = OMe, R2 = H

(84)

H

(85) a; R = C02Me b;R=CN

(86)

Cerfontain and van Noort 4 1 have reported a photosynthesis of 4-0x0-alkanoic acids and esters (90). The reaction is achieved by the benzophenone-sensitized addition of aldehydes (91) to a$-unsaturated esters (92). The yields obtained from

(87) a; R = H b;R=Me

H (88) a; R' = H, R2 = R3 = Me b; R 1 = R2 = R 3 = Me c; R2 = CN, R3 = H, R' = H or Me d; R2 = OAc, R 3 = H, R' = H or Me

RI-C-H-H II 0

3

~2

4

~

(90)

0

R'CHO (91)~ R' =~ Me, 5Pr", or Ph

(89)

R3 R4

X

R2 COOR5 (92) R2 = R3 = R4 = H, R5 = Me R2 = R4 = H, R3 = R5 = Me R2 = R3 = Me, R4 = H, R5 = Et

the process are varied ranging from 7 to 8 1%. This technique has also been used in the formation of the adduct (93) by acetone-induced addition of formamide to the ester (94).42 Irradiation of dimethyl acetylenedicarboxylate in the presence of propylene oxide yields the adducts (95,96).43 The products are the results of hydrogen abstraction by the excited acetylene followed by radical combination reactions. The reaction can be both quenched and triplet sensitized (benzophenone) suggesting the involvement of a triplet state. The yields on the whole are only moderate. Cyclohexene oxide behaves in a like manner and yields the two products (97).43 The dimerization of the enone (98a) in micellar and liquid-crystal systems gave dimers of both the cis- and the trans-enone. The presence of a long chain 40 41

42

43

T. Naito, and C. Kaneko, Chem. Phurm. BUN., 1980, 28, 3150 (Chern Abstr., 1981, 94, 139591). H . Cerfontain and P. C. M. van Noort, Synthesis, 1980, 490. A. Rosenthal and J. Chow, J. Curbohydr., Nucleosides, Nucleotides, 1980, 7 , 77 (Chem. Abstr., 1980, 93, 168537). H. Hasegawa, H. Saito, and K. Tsuchitani, Waseda Daigaku Rikogaku Kenkysusho Nokoku, 1979, 16 (Chern. Abstr.. 1980, 92, 214564).


253

H O OH (93)

(94)

(94) (4.3%)

R2 (95) a; R' = C02Me, R2 = H (27.1%) b; R' = H, R2 = C02Me (3.4%) Me0,C

R' R2

(97) a; R' = CO,Me, R2 = H (7.5%) b; R' = H, R2 = C0,Me (7.5%)

substituent on the benzene ring (98b) facilitated the dimerization of the cisThe solid-state dimerization of the cinnamic acid (99) yields the head-to-head dimer (100). When this process is carried out in the presence of hydrocarbons as a dispersant the dimer obtained contains incorporated solvent.45.46 A study of a series of crystalline compounds based on benzylidenecyclopentanone (101) has provided a basis for the assessment of topotactic and topochemical phot~reactivity.~'The topochemical photodimerization of the

R (98) a; R = H b; R = CH,(CH,),O

compound (101, Ar = Ph) has been determined.48 The crystal structure of the ester (102) has been determined and the solid-state photoreactivity of the molecule has been rationalized in terms of the molecular packing in the crystal. The main product from this photoreaction is the dimer (103).49 44

M. Nakamura and T. Sato, Kokagaku Toronkai Koen Yoshishu, 1979, 186 (Chem. Absfr., 1980, 92,

45

F. Nakanishi, M . Hiriakawa, and H . Nakanishi, Isr. J . Chem., 1979, 18, 295 (Chem. Abstr., 1980,93,

46

F. Nakanishi, S. Yamada, and H. Nakanishi, J . Chem. SOC.,Chem. Commun., 1977, 247. W. Jones, H. Nakanishi, C. R.Theocharis, and J. M. Thomas, J . Chem. SOC., Chem. Commun., 1980,

214 557). 94 473). 47

610. 48

49

H. Nakanishi, W. Jones, J. M. Thomas, M. B. Hursthouse, and M. Motevalli, J. Chem. SOC.,Chem. Commun., 1980, 61 1. L. Kutschabsky, G . Reck, E. Hohne, B. Voigt, and G . Adam, Tetrahedron, 1980, 36, 3421.

Ph o t oclzemist r y

254

(103)

The sensitized irradiation (acetophenone) of the coumarin (104) yields two dimers which have been identified as (105) and (106).50All four possible dimers (107, 108) are obtained from the irradiation of the thio-chromone (109) in aromatic solvents. In contrast the sulphone (1 10) is u n r e a c t i ~ e . ~ '

M e 0W

0W 0 O

O

M Me e

%

Me

(107) a; R b; R

= a-H

a-H

(108) a; R b; R

= a-H = P-H

0

J0 st

A. Z . Abyshev, Khim. Prir. Soedin., 1980, 165 (Chem. Ahstr., 1980, 93, 150082). I. W. J. Still and T. S . Leong, Tetrahedron Lett.. 1981, 1183.

Enone Cycloadditions and Rearrangements 255 2 Enone Rearrangements Agosta and Wolff 5 2 have studied the influence of substituents upon the mode of cyclization of the enones (1 1 1). The irradiation of enones (1 1la+) follows the path dictated by Srinivasan's rule of five 53 yielding the biradical (1 12) which subsequently yields the products shown in Scheme 8. Enone ( l l l b ) had to be

( 1 1 1 ) a; R' = R 2 = R3 = R4 = H b; R ' = R 2 = H, R 3 = R4 = Me

(1 12)

bc)

c; R 1 = R 2 = Me, R 3 = R4 = H

6Me 0

Scheme 8

0-

Me

0

(1 13)

p"'

0 (1 1 Id)

_____)

+k

co \

0 QM'-

(-p Me

OMe (1 14)

Scheme 9

irradiated in refluxing xylene to achieve cyclization. With enone (1 1 Id) the rate of cyclization in the 1,5-sense is diminished somewhat, and cyclization follows both the 1,6-pathway to yield (1 13, 27%) and the 1,5-path to yield (1 14, 4373, as in Scheme 9. The results are compared with earlier studies related to the cyclization of 5-hexenyl radicakS4 A full account of the photochemical behaviour of citral (1 15) at elevated temperatures has been p ~ b l i s h e d , ~supplementing ' the original note.56At 80 "C irradiation results in the formation of aldehyde (1 16) and (1 17) as well as other products (118-120). These products are not formed at 30°C. The 52 53

54

55 56

W. C. Agosta and S. Wolff, J. Org. Chem., 1980, 45, 3139. R.Srinivasan, Abstracts, 156th National Meeting of the American Chemical Society, San Francisco, April 1968, 89. A. L. J. Beckwith, 1. A. Blair, and G. Phillipon, Tetrahedron Lett., 1974, 2257. S. Wolff, F. Barany, and W. C. Agosta, J. Am. Chem. SOC., 1980, 102, 2378. F. Barany, S. Wolff, and W. C. Agosta, J. Am. Chem. SOC.,1978, 100, 1946.

256 Photochemistry temperature effect is thought to be a manifestation of the control exercised upon the biradical intermediates (121) and (122), the former being dominant at higher temperatures (Scheme 10). Other workers have observed similar effects.5 7

I

(1 16)

Scheme 10

Detailed studies of the &-trans and trans-cis isomerization of chalcone 5 8 and some of its derivatives and analogues (123) 5 9 have been reported. Perkins and his co-workers 6o have reported an irradiative method of reducing enone systems such as chalcone to the corresponding saturated compounds. The cis-trans isomerization o f chalcone has been studied in CC1, solution.61

(123) R2 = H, NO,; R' = MeO, Me, H, Br, or NO,

A solvent dependence has been reported for the photocyclization of the chalcones ( 124).62Efficient cyclization takes place yielding the flavanones (125) 57 58

59

6o 62

M. Yoshioka, K. Ishii, and H. R. Wolf, Helv. Chim. Acra, 1980,63, 571. V. G . Mitina, M. Reinhardt, and W. F. Lavrushin, Zh. Obshch. Khim., 1980,550,134 (Chern. Abstr., 1980,92, 197 665). M.Reinhardt, V. G . Mitina, N. S. Pivneko, and V. F. Lavrushin, Zh. Obshch. Khim., 1980,550,2770 (Chem. Abstr., 1981,94,120601). M.J. Perkins, B. V. Smith, and E. S. Turner, J . Ciiem. SOC.,Chem. Commun., 1980,977. M . Nowakowska and J. Kowal, Bull. Acad. Pol. Sci., 1979,27,409(Chem. Abstr., 1980,92,180344). R. Matsushima and I. Hirao, Bull. Chem. Soc. Jpn., 1980,53, 518.

Enone Cycluadditiuns and Rearrangements

257

when irradiation (A > 365 nm) is carried out in ethyl acetate or dioxan. However low efficiency of cyclization is experienced when benzene, chloroform, ether, acetonitrile, or ethanol is employed. An explanation for this observation is awaited. The photochemical ring-opening of a series of flavanones ( I 26) in benzene to yield the chalcones (127) has been reported.63

R

eR .

/

\

R

/

0

0 ( 124)

/ \

W

wR (125)

R' \

f\ l

R2 0

R

R,

\

\

OH 0

( 1 26)

'

R3

(127)

R 1 = R 2 = R 3 = R4 = H; R 1 = R2 = R3 = H, R4 = OMe or OCOMe; R' = OMe or OCOMe,. R2= R3 = R4 = H

trans-cis Isomerization of (1 28) occurs upon irradiation. Subsequent irradiation converts the cis-isomer into the coumarin (129), a process thought to involve a triplet

Me

do

aM

A study of the photochemical behaviour of the enone epoxide (130) has been published.6s Several compounds (Scheme 11) are formed upon irrlidiation (2 > 347 nm) in pentane. When the reaction is carried out in methanol these products are accompanied by the methanol addition product (131) which is proposed as good evidence for the intermediacy of the ylide (132), and the cyclopropane (133). Compounds (1 34) and (135), related to epoxy-enone (1 30), are also photoreactive and studies of these have been reported.66-68

64 65 66 6'

68

R. Matsushima, T. Kishimoto, M. Suzuki, M. Morioka, and H. Mizuno, Bull. Chem. SOC.Jpn., 1980, 53, 2938. I. R. Bellobono, D. E. Paglia, B. Marcandalli, and M. T. Cataldi, Ga::. Chim. Ital., 1979, 109, 697 (Chem. Abstr., 1980, 93, 203 633). K. Murato, H. R. Wolf, and 0. Jeger, Helv. Chim. Acta, 1980, 63, 2212. N . Nakamura, W. B. Schweizer, B. Frei, H. R. Wolf, and 0.Jeger, Helv. Chim. Acta, 1980,63, 2230. A. P. Alder, H. R. Wolf, and 0. Jeger, Helv. Chim. Acta, 1980, 63, 1833. K. Murato, B. Frei, W. B. Schweizer, H. R. Wolf, and 0. Jeger, Helv. Chim. Acta, 1980, 63, 1856.

258

Photochemistry

p*y-Jy+Q+&-J H

AC

Scheme 11

The oxiran system in (136) undergoes bond cleavage on excitation (m*) and yields the furan derivative (137) as the major product (13%). Several other minor products were also isolated and identified.69 The irradiation of the enone (1 38) has been r e p ~ r t e d . ~ '

(135) a; R = H2 b; R = CH,

(1 36)

0

(137)

(138)

Further work has been carried out on the photoconversion of enones (e.g., 139) into the cyclic ethers (140) and the enone (141). The conversion may be carried out using either i= 254 or A > 347nm.7' The results of a detailed study of the photochemical behaviour of the ionone (142) and its conversion into the pyran (143) has been published.72

(139) 69

( 140)

(141)

K . Tsutsumi and H. R. Wolf, Helv. Ckim. Acra, 1980, 63, 2370.

O '

Murato, H. R. Wolf, and 0. Jeger, Helv. Chim.Acta. 1981, 64, 215. '' K. Ishii, H . R . Wolf, and 0. Jeger, Helv. Cliim. Arta, 1980, 63, 1520. '' K. H . Cerfontain, J. A. J. Geenevasen, and P. C. M. van Noort, J. Chem. Soc., Perkin Trans. 2, 1980, 1057.

259

Enone Cycloadditions and Rearrangements M

F

o

M

b Me

Me

O

y

y

t

x

EtO NHC0,Bu'

Me

(142)

(143)

(1 45)

(144)

The pyrrolinone (144) undergoes photochemical ring contraction in Bu'OH to yield ultimately the cyclopropyl carbamate ( 145).73Formally this is a reaction akin to the Norrish Type I process in ketones in that initial fission of a C-C bond results in a biradical which recombines to yield a ring-contracted isocyanate. The irradiation of the thioisoxazolinones (146) in methanol results in the extrusion of CO, and the formation of products (147).74 The products are thought to be

(146) R

=

Me R SPh, S-P-naphthyl, SCH,CH=CH,, SCH,CH,OH, SCH,CH,OAc Me I

M e q o M e

R ( 147)

. I

A.

. Me

. SR'

(1 48)

Me\

N=r 9

0

Me R (149) R = H, C1, or OPh

formed by the intermediacy of a sulphur-stabilized carbene (e.g., 148) which is trapped by solvent and the resultant imine hydrolized by water. The presence of the sulphur is critical for the success of the reaction since the compounds (149) appear to be inert under the same conditions. Cossy and Pete 7 5 have reported the conversion of the (alky1amino)cyclohexenone (150) into the cyclized derivatives (1 5 1 and 152, Scheme 12) by irradiation in diethyl ether. The reaction superficially

Scheme 12

appears similar to a Norrish Type I1 process, but irradiation in MeOD only leads to incorporation of D at C-3 of the cyclohexenone. Thus the exact mechanism of the process is unknown although the possibility of an electron-transfer process cannot be excluded. The use of sulphonated derivatives (153) affords different The behaviour of the compounds (153) is seen to be dependent upon 73

'* l5 76

G . C. Crockett and T. H . Koch, Org. Synth., 1980, 59, 132 (Clzern. Ahstr., 1980, 93, 149837) T. Sasaki, K. Hayakawa, and S. Nishida, J . Chem. Soc., Client. Contrnun., 1980, 1054. J. Cossy and J. P. Pete, Tetrahedron Lett., 1980. 2947. J. C. Amould, J. Cossy. and J. P. Pete, Terrahetiron, 1980, 36, 1585.

260

Photochemistry

Table 2 Products from irrcrdiution of uminoenones (153) in ethanol76 (154) 30 50 40

Me Ph ally1 Pr' Pr' Pr' Pr' Pr'

-

-

__ -

Products PA) (155) (156) 25 10 35 15 30 40 -

20 40 35

the nature of the substituent on the nitrogen atom (Table 2). Pete and Portella 7 7 have studied the photoconversion of arene sulphonates into alcohols in various solvents.

R

The direct or sensitized irradiation (1, > 330nm) of the enone (157) in solution affords the [2 + 21 cycloadduct (158).78 When the irradiation is carried out using the same wavelength but with the compound in the crystalline phase the main product (75%) obtained in (159) formed by a hydrogen-abstraction path. Some of the [2 + 2ladduct (158, 25%) is also obtained. The change in the reaction from solution to crystal phase is the result of (1 57) being the preferred conformation in the crystal, a prediction which was verified by an X-ray structure. Scheffer 7 9 has reviewed the influence of crystal lattice control on the outcome of such photochemical reactions.

&;

Me

Me

Me

Me

\OH

Me

0 (157)

HO

Me OH ( 1 58)

Me (1 59)

The enone (160) undergoes a Norrish Type I fragmentation in methanol to afford the product (161).80The product is formed from the intermediate biradical (162) by fission of the 5.10-bond to give a trappable ketene. Irradiation of the -_l

'' ''

J . P. Pete and C. Portella. Bull. Soc. Chim. Fr., 1980, 275. Z . Q. J i m g .I.R. ScheKer. A. S. Secco. and J . Trotter, 7etrcrlrc4roii Lett.. 1981, 891. J. R . ScheKer. A w . C'hcw. Rcs., 1980, 13. 283. A . Canovas and J.-J. Bonet, Hrlr.. Clritii. Acto, 1980. 63, 2390.


Mfl

26 1

Me OAc

& O H

Me0

( I 60)

0

H

O& '0

(1611

162)

cyclic lactam (163) in t-butyl alcohol affords the lactam ether (1 64) presumably by trapping of an intermediate imine (165) formed from the biradical (166) by

g

HN 0

(163)

*

(Mb \

0

OCN

H

fyj? O

N H H

Me0 0

H OMe

kN H H

O

hydrogen abstraction. When the reaction is carried out in methanol this product (165) is accompanied by (1 67). The lactam (168) yields the isocyanate (169) when the irradiation is carried out in t-butyl alcohol but when methanol is used as solvent the ether (170) and the product (171) are formed, as well as a trace of the isocyanate (169). The lactams (172) and (173) afforded the products shown in Scheme 13 when irradiation was carried out in methanol. Irradiation in t-butyl alcohol gave only minor products which could not be separated from starting material." A review of the photocyclization of eneamides has been published.82 An ylide intermediate (174) is proposed as the key intermediate in the photocyclization of the enamino ketone (175) into the products (1 76) and ( 177).83 The photochemistry of enones has been reviewed by S c h ~ s t e r The . ~ ~ observation of orthogonal twisted triplet states has been reported from the laser flash A. Canovas, J . Fonrodona, J.-J. Bonet, M. C. Brianso, and J. L. Brianso, Helv. Chim. Acta, 1980,63, 82

83 R4

2380. I. Ninomiya and T. Naito, Kagaku No Ryoiki, Zokan, 1979, 69 (Chem. Abstr., 1980,93, 95447). D. Watson and D. R. Dillin, Tetrahedron Lett., 1980, 3969. D. I. Schuster, Org. Cliem., 1980, 42, 167.

262

Photochemistry

MeN

MeOH

&

O

hv

___)

MeOH

Me N

O b p J Me OMe

(173) Scheme 13

COMe

&Le \

m

-

+N

Me

(175)

( 174)

e

~

I Me

I Me

\

M

M I Me

(176)

( 177)

study of various en one^.^^ The lifetime of the transient is of the order of tens of nanoseconds and the degree of twist is dependent upon the rigidity of the molecule in question. The direct irradiation of the enone (178) results in a mixture of starting material and a new product (179) in a ratio of 1 : 3.2. The formation of the deconjugated product was not affected by oxygen but was suppressed when acetone was used as the solvent for the irradiation.86" Thus a singlet state is thought to be involved in the transformation. The enone (180) is formed when

( 178)

(179)

( 180)

(179) is irradiated in benzene solution. Such reactions as 1,3-migration are common in the photochemistry of b,y-unsaturated enones. 8 6 b The non-volatile fraction from the irradiation of this enone (178) contains four products identified as cyclobutane-type dimers of gross structure (18 1-1 83). Ketene and the phenol (184) are formed on irradiation of the enone epoxide (185)?' The mechanism for the formation of the phenol remains unsure even from the results of deuterium labelling experiments. The isomeric epoxide (186) is also photoreactive and yields the three products shown in Scheme 14. The formation of the cyclopentadiene (187) is due to the thermal rearrangement of tricyclic ether 85 86

*'

R. Bonneau, J . Am. Chem. SOC.,1980, 102, 3816. (a) B. Gioia, M. Ballabio, E. M. Beccalli, R. Cecchi, and A. Marchesini, J . Chem. Soc.. Perkin Trans. 2, 1981, 560. ( b ) see e.g. ref. 90. H. Hart, S.-M. Chen, S. Lee, D. L. Ward, and W.-J. H. Kung, J. Org. Chem.. 1980, 45, 2091.


263

M e M e Me

Me % ' Me Me 0

Me

Me Me (185)

(188). This compound is thought to arise via the ylide (189) formed on C-C bond cleavage in the epoxide ring. A study of the biradical (190) formed by the irradiation of the enone (191) has been

& Me@e Me

+

Me

Me

Me

6

+

/

Me

M e \ / Me

Me

(187)

Scheme 14 Me&Me

~k

Me

Me

Me

t 188) 0'

(190)

(191)

The irradiation of the enones (192-194) via a nn* excitation affords as the principal products (195-197), respectively, from 1,3-acyl migrations and (198200) from 1,2-acyl migrations. In contrast with this behaviour, the dieneone (201) undergoes 1,3- and 1,5-acylmigrations to yield the products (202) and (203). When nn* excitation is employed with (192 and 201) only decarbonylation occurs. The authors 8 9 suggest that the 1,3-acyl migrations occur from the excited singlet state,

**

(a) D . E. Seeger, E. F. Hilinski, and J. A. Berson, J . Am. Chem. SOC.,1981,103,720. (b)M. Rule, A. R.

89

Mathin, E. F. Hilinski, D. A. Dougherty, and J. A. Berson, J . Am. Chem. SOC..1979, 101, 5098. H. Eichenberger, K. Tsutsumi, G. de Weck, and H. R. Wolf, Helv. Chim. Acta, 1980, 63, 1499.

Photochemistry

264

priPAc al*, R

O

0

(192) R = Me or Pr'

(194)

(193)

(195) R' = Pr', R 2 = Me R' = Me, RZ = Pr'

&

0

Ac

(196)

0 0

whereas the 1,2-acyl migrations involve the triplet state: such tendencies have long been known. Interest continues in the ground-state control of photoreactions, i.e. the dependence on molecular conformation in the ground state. In cycloheptenes the more stable conformation is a chair which when photolysed will undergo a 1,3acyl migration, as exemplified in photolysis of the enone (204) to give the spiroketone (205)." In the more complex molecule (206), a similar rationale accounts for the formation of the single photoproduct (207). An X-ray crystal structure of this compound (207) proves that the conformation is as shown and

(204)

HO C=C

@ 0 (206)

*

(205)

@L

H*C (207)

J

(208)

that this will arise from the chair form (208) of the starting material." Acetonesensitized irradiation of the enones (209) leads to mixtures of the 1,3-acyl shift product (210) and the di-mmethane product (21 l), but the 1,3-acyl shift products 90

J . R. Williams and G . M. Sarkisian, J . Org. Cliem., 1980, 45, 5088.


265

alone are formed by direct irradiation." However when acetophenone was used as the sensitizer only the oxa-di-n-methane products were produced. It is clear from this study that the 1,3-acyl shift products formed in the sensitized experiments arise from stray light absorption by the starting material. Attempts to induce asymmetry in the product by the use of an optically active sensitizer were poor. Resolution of the starting material and acetophenone-sensitization afforded the (-)-product (212) from 1R,4S starting material (213a) and the (+)-product (214) 0

&R2

R'

'

R'

(209) R' = R2 = H R' = Me, R2 = H R' = H , R2 = Me

(212)

&o

R2y-J-y

R2

(211)

(210)

(2I3a)

(213b)

(214)

from the lS, 4 R starting material (213b). The stereospecificity of the reaction is in line with that predicted by the usual mechanism for the di-n-methane process. The sensitized irradiation (acetophenone) of the enones (215 ) brings about a regiospecific di-n-methane process to yield in each case one product identified as (216).92 R' R2 R 3 R4 R 5 R6

R4 0

(215 )

Me But But Me H H Me Me Bu'

H H 0-CH, C0,Me H H 0-CH, C02Me H H CH,-0 C0,Me M e H 0-CH, C0,Me H MeO-CH, C0,Me H M e H O Me C 0 , M e H MeO-CH, C0,Me H M e H O Me C 0 , M e H Me 0-CH,CO,Me

0

R'/ R2\

R3

(217)

R6 R6

R2 (216)

Me Me (218) R = C3H,

0 Me Me (219) R' = H, R 2 = Bu" R' = Bu", R2 = H

The enones (215) are converted into the aromatic compounds (217) by the loss of the ketene bridge. Full details 930f the use of the regiospecific di-n-methane 91

M. Demuth, P. R. Raghavan, C. Carter, K. Nakano, and K. Schaffner, Helv. Chim. Acta, 1980, 63,

92

H.-D. Becker and B. Ruge, J. Org. Chem., 1980, 45, 2189. G. Pattenden and D. Whybrow, J . Chem. Soc.. Perkin Trans. I , 1981, 1046.

2434. 93

266 Photochemistry reaction towards the synthesis of the natural product, taylorione (218) from (219) has supplemented the original note.94 Ciganek 9 5 has prepared the 9,lO-bridged ethenoanthracenes (220, 221). These compounds are photochemically reactive and on direct irradiation in THF solution are converted into the cyclo-octatetraenes (222,223). Sensitized (acetone)

(220) a; X = 0,Y = H, b;X=Y=O c; X = NMe, Y = 0

R R

b; R-R

= (CHI),

irradiation, on the other hand, brings about a di-z-methane conversion to semibullvalene derivatives e.g., (224 and 225) from (220c): see Scheme 15.

+

-

0-

(220c)

A

Scheme 15

Excitation of the ketone (226) brings about a 1,7-hydrogen transfer to afford the biradical intermediate (e.g., 227).96 Cyclization within this species yields the alkenyl-tetrahydrofurans (228) and (229) in the yields and ratios shown. The cyclization process is reasonably selective in that the geometry of the double bond is retained in the cyclized product. This was demonstrated for the enone (230) (a cis-trans mixture of ratio 1 : 3), which gave the cyclized products (231-234) (Scheme 16). Two principal products (235, 15%) and (236,60%) are obtained from irradiation of the ketone (237) in dioxan ~ o l u t i o n . ~Two ’ minor products (238) 94

95

96

’’

G . Pattenden and D. Whybrow, Tetrahedron Lett., 1979, 1885. E. Ciganek, J . Org. Chem., 1980, 45, 1505. H . A. J. Carless and D. J. Haywood, J . Chem. SOL-.,Chem. Commun., 1980, 657. J. Mattay, Tetrahedron Lett., 1980, 2309.


cz

R3 R' R

3

R2+

267

2

(226) a; R' = R2 = R 3 = H b; R' = R3 = H, R2 = Me

R2

(227)

R3

R2

R3

(228) (229) a; 1.4 : I (94"/,) b; 1.65:1 (85%) C; 0.6 :1 (80%) d; 1-5:l (88%)

c; R' = Me, R2 = R3 = H d; R' = R 2 = H , R3 = Me

Me OH

Mae? H

ratio 1:1.4:1.3:1

MepH

(234)

Scheme 16

and (239) were also detected. The intramolecular cycloaddition reaction affording (235) is not quenched by the addition of penta-1,3-diene, thereby suggesting that this reaction arises from the singlet manifold. The formation of the other products (236-239) is quenched and their formation is also influenced by the presence of tri-n-butyltin hydride. To account for these effects, Scheme 17 showing the formation of products (236, 238, and 239) is suggested.

(235)

(236)

(237)

(238)

(239)

Scheme 17

The enone (240) undergoes C-C bond fission in the oxiran ring to yield (241) on direct irradiation (254nm).98 This compound (241) is accompanied by the fission product (242) and by (243) and (244). 98

G . de Weck and H. R. Wolf, Helv. Chim. A c f a , 1981, 64, 224.

Photochemistry

268

3 Photoreactions of Thymines erc. A study of the photodimerization of the pyridones (245) in a micellar environment

has been reported.99The results show that there is an alignment of the molecules in the micelle. The pyrazinone derivative (246) is photochemically unreactive when it is irradiated in solution at room temperature.loOHowever when it is irradiated in the solid state at room temperature a [4 + 4l-dirner (247) is formed. R2

R' (245)

R' = CH2CH2C02H,R 2 = H, C,H,, or C,H,, R' = (CH2),C02H, R2 = H R' = (CH2),,C02H, R 2 = H

Me I

The acetone-sensitized irradiation of the bis-pyrimidine (248) yields the [2 + 21cyclized product (249). A chair-like conformation is adopted by the cycloheptane part of the molecule (249) in the solid and in solution."' The dimerization of the bichromophores (250) to yield the cycloadducts (25 1) was slow by comparison with the dimerization in analogous less heavily substituted systems. The slowness of the process is, it is thought, due to steric factors.102 99 loo lo' lo'

Y. Nakamura, T. Kato, and Y. Morita, Tetrahedron Lett., 1981, 1025. T. Nishio, N. Nakajima, and Y.Omote, Tetrahedron Lett., 1980, 2529. A. Rajchel and K. Golankiewicz, Pol. J . Chem., 1980, 54, 123 (Chem. Abstr., 1980, 93,70 500). K. Golankiewicz and L. Celewicz, Pol. J. Chem., 1979, 53, 2075 (Chem. Abstr., 1980, 93, 71 684).


269

v 0

0

(249)

0

de Mayo et al.lo3 have investigated the photoreactions of the aza-dienone (252a). Irradiation of (252a) at -70°C led to the formation of the bicyclic intermediate identified as (253a). Warming this intermediate to -40 "C brought about quantitative conversion into the intermediate (253b). This compound was stable in solution at 0 "C but at room temperature formed two oxazinones (252a) and (252b) in equal amounts. The irradiation of (252b) at -78°C gave the intermediate (253b). The authors l o 3 reason that (253b) is the thermodynamically stable intermediate and that the interconversion of (253a) into (253b) takes place

.o"r.h-- N N

yo

(252) a; R' = Ph, R2 = Me

b; R'

=

Me, R2 = Ph

R' (253) a; R' = Ph, R 2 = Me b; R' = Me, R2 = Ph

Me (254)

via the zwitterion (254). The bicyclic aza-compounds (255) can be prepared by the irradiation of the pyrimidones (256) in benzene solution.l o 4 The products (255) are thermally labile and can be readily converted into the quinoline derivatives (257).

(255) Ar = Ph (50%) Ar = p-tolyl (50%) Ar = p-anisyl (20%) 103

(256)

(257) R = H R = Me

R=MeO

P. de Mayo, A. C. Weedon, and R. W. Zabel, J . Chem. SOC..Chem. Commun., 1980, 881 T. Nishio, K. Katahira, and Y. Omote, Tetrahedron Lett., 1980, 2825.

27 0

Photochemistry

Irradiation of the pyrimidone (258) in methylamine+ther proceeds via ring closure to the tricyclic structure (259). Attack of methylamine on this molecule followed by ring opening (Scheme 18) affords the final product (260). Other examples of this process were reported. l o 5

(259)

Scheme 18

The regiospecific formation of the cyclobutene-type adduct (26 1) has been reported as a result of the photoaddition of diphenylacetylene to the cyanouracil (262).l o 6 The cycloaddition of 1-phenylprop-1-yne to the same substrate is reported to yield the cyclobutene (263) as the main product when Pyrex-filtered irradiation is used. The irradiation of the same compounds using 254nm light afforded the novel adduct (264), presumably formed by the secondary cyclization of the initially produced adduct (265). lo’ Indeed the sensitized irradiation of the uracil (262) and the propyne yields this adduct (265) as a 2-E-mixture as well as the cyclobutene (263). Direct irradiation of (265) affords the cyclized compound 0

0

Me

(263) ‘06

lo’

(264)

(245)

Y. Hirai, T. Yamazaki, S. Hirokami, and M. Nagata, Tetrahedron Lett., 1980, 3067. I. Saito, K. Shimozono, and M. Teruo, Fukusokan Kagaku Toronkai Koen Yoshishu, IZth, 1979, 161 (Chem. Abstr., 1980, 93, 45 547). I. Saito, K. Shimozono, S. Miyrazaki, K. Fukuyama, Y. Katsube, and T. Matsuura, Tetrahedron Lett., 1980, 2317.


27 1

(264). The photoreaction of the cyanouracil (262) with cyclo-octene, hex- 1-ene, and acetoxyethylene in acetonitrile yields the adducts (266a--c) and the rearranged adducts (267a-c). *'* The reaction is proposed to occur by the addition of the olefin to the excited state of the uracil yielding the biradical (268). This biradical can either ring close to yield the cycloadduct (266) or else cyclize to form

(266) a; R ' - R ~ = (CH,),, 35% b; R' = H, R2 = Bu", 40% C; R 1 = OAC, R2 = H, 60%

M e N k R ' O N R2 Me CN

O

A

(267) a; R ' - R ~ = (CHZ),, 52% b; R' = H, R2 = Bun, 42% C; R' = H, R2 = AcO, 10%

MTV

N

O

Me

(268)

N

N

Me

R2

N

(270)

(269)

a new biradical (269) and then (270) from which the cyano-migrated compounds (267) are obtained by bond cleavage. The reaction is temperature dependent as can be seen from the irradiation of cyclopentene with the uracil (262) where the cyclobutane (271, 26%) is the minor product at 20°C but becomes dominant at

M

e

N

Ph e

NL

20 "C

MeN

L

Me CN (27 1) 26% 56%

43% 15%

- 20 "C

L

Scheme 19

lower temperatures (-20 "C)(Scheme 19). When the reaction is carried out in ethanol the product formed is the imine (272) produced by trapping of the biradical [270, R'-R2 = (CH2)J. M

Ae

O

N Me

N

v NH

(272)

The adducts (273) are readily formed by the sensitized photocycloaddition of the azauracil (274) to the maleimides (275).'09 A [2 + 21-adduct is formed from I. Saito, K. Shimozono, and T. Matsuura, J . Am. Chem. SOC., 1980, 102, 3948. G. Szilagyi and H . Wamhoff, Angew. Chem. In?. Ed. Engl., 1980, 19, 1026.

212

Photochemistry M e N q

OAN" Me (273) R = Me or H

Br

(274)

(275)

the cycloaddition of thymine to 5,7-dimethoxy-coumarin. '' The cycloaddition of olefins to the diazaenone (276a) is reported to yield the cyclobutane-type adduct, e.g., (277) from 2-methylbut-2-ene. When the thioenone (276b) was used the cycloaddition yielded the adduct (278). l 1 Me

Me

Me (276) a; X = 0, R = H , Me, or Ph

b; X

=

S, R

=

(277)

H

The photoaddition of stilbene to caffeine (279) leads to the formation of six products (280-285). The first three products (280-282) can be readily accounted for by conventional [2 + 21-addition leading to (280) and (281) and a [4 + 21-addition followed by methylamine elimination giving (282). The other products are more difficult to explain, but the authors 'l 2 suggest that the biradical intermediates (286, 287) are involved in which various migrations and bond fissions occur. The fate of the missing carbon receives no comment.

''

.Ph

MeN

AN

O Me

'")

'" ' l2

Me

S. C. Shim and K. H . Chae, Photochern. Photohiol.. 1979, 30,349. Y. Kanaoka. M . Hasabe, and E. Sato. Fiikitsokm Koyciku loronkcii Koeri Yosliishu, 1979, 156 (Chem. Ahslr.. 1980. 93, 1679). G. Kaupp and H . - W . G r u u , .fiigczn. C'/ivrn. f r i t , Ed DigI., 1980. 19. 714.


273

A highly fluorescent uridine derivative (288a) has been prepared by the irradiation of the iodouridine (288b) in the presence of pyrene.'13 An analogous product (288c) is obtained when the irradiation is carried out in the presence of benzene. The acetone-sensitized photocoupling of 5-bromouridine (2884) with tryptophan has been studied. l4 The photochemical coupling of tryptophan (289) and 5-bromouridine (288e) in a frozen aqueous system yielded the single adduct (290)." A study of the photoreactions between bromouracil (291) and electronrich arenes (e.g., 292) has been reported.I16 0

H (288) a; R' = pyrenyl, R2-R2 = Me$ b; R ' = I , R Z - R 2 = Me,C c; R ' = phenyl, R2-R2 = Me,C d; R ' = Br, RZ-RZ = Me,C e; R ' = Br, R2 = H

(289)

OMe

The photoreaction of the flavin ( 93) with the amines (294,295) has been shown to yield a single photoproduct in each case identified as (296) and (297), respectively. When (298) is irradiated in the presence of hydrogen donors (e.g.,CH,OH) the reduced dimer (299) and the adduct (300) are formed, presumably via the intermediate radical (301).' l 8 Irradiation of the cytosine derivatives (302) in

'I5 116

'I8

I . Saito, S. Ito, T. Shiiimura, and T. Matsuura, Tetruhedron Lett., 1980, 21, 2813. S. Ito, I. Saito, and T. Matsuura, J . A m . Cheni. SOL'.,1980, 102, 7535. S. Ito, 1. Saito, H . Sugiyama, and T. Matsuura, Kokagaku Toronkai Koen YosAishu, 1979, 10 (Chem. Abstr., 1980, 93, 8476). S. Ito, I. Saito, and T. Matsuura, Tetrahedron, 1981, 37, 45. A. Krantz, B. Kokel, A. Claesson, and C. Sahlberg, J . Org. Chem., 1980, 45, 4245. Y . K d n d O k a , M . Hasebe, and Y . Hatanaka, Heterocycles, 1979, 13, 263 (Ckem. Ahstr., 1980, 93, 94474).

Photochemistry

274

propan-2-01 leads to the formation of the adducts (303). This reaction presumably involves the formation of the radical (304), by abstraction of hydrogen from the solvent followed by coupling.

(298)

(299)

(300) R

=

~

A

0 Me (302) R = NH,, NHMe,or NMe,

13 R

R N

(301)

CH,OH

N Me

Y

CMe,

(303)

H

0

N Me (304)

0 H x y i H M e P r

0

N H

(305)

The photodegradation of pentobarbital (305) in buffer solution at pH 11 has been studied.'*' The photoreactions of purines and related compounds has been reviewed.l 2 4 Photochemistry of Dienones Schaffner and Demuth lz2 have reviewed the photoreactions of conjugated cyclic dienones. 'Iy

Iz1

K . I . Ekpenyong and M. D. Shetlar, Photochem. Photobiof., 1979, 30, 455. H . Barton, J. Mokrosz, J. Bojarski, and M. Klimiczak, Pharmazie, 1980,35, 155 (Chem. Abstr., 1980, 93, 101426). M. Rafalska and G . Wenska, Wiad. Chem., 1980, 34, 9 (Chem. Abstr., 1980, 92, 215652). K. Schaffner and M. Demuth, Org. Chem., 1980, 42, 281.

Enone Cycloadditions and Rearrangements 275 Cross-conjugated Dienones.- From results obtained from the photorearrangement of the resolved dienone (306) the reaction yielding the lumiketone (307, 308) have been proved to involve the intermediacy of a zwitterion. The subsequent sigmatropic shift occurs with inversion of configuration of the migrating carbon.lz3 Details of the chemical trapping experiments relating to photorearrangement of the dienones (309), reported earlier in note have been published.’ 2 5 The zwitterion (310) in question derived from (309b) was successfully trapped with cyclopentadiene as the adducts (311) and (312). The methyl group in the adducts is endo which is proof that the carbon walk reaction takes place with inversion of configuration of the migrating carbon, in agreement with the work of Schu~ter.”~

Me

. H

(307)

(308)

Me R = Me b; R = CC13

(309) a; R

0-

6

,---.

Me CCl3

The quantum yields of the photochemical reactions of the dienone (313) have been shown to be solvent dependent with the efficiency enhanced in methanol and depressed in benzene. lZ6 The products from the reaction in methanol-benzene were the rearrangement product (3 14a) and the two methanol incorporation products (315a and b). The rearrangement product is obtained from both the sensitized and the direct irradiative conversions. It is of interest to note that the ground-state rearrangement of the zwitterion (3 16) yields the same products (3 14, 315) as are obtained in the photolytic process. From this it is reasoned that the excited-state process also arise via a zwitterionic process. In contrast with the

(313)

lz4 lz5 lz6

(314)a; R = CN b; R = OMe

(3 15a)

(3 15b)

D. I. Schuster, K. V. Prahbu, K. J. Smith, J. M. van der Veen, and H. Fujiwara, Tetrahedron, 1980, 36,3495. C. J. Samuel, J. Chem. SOC.,Chem. Commun., 1979, 275. C. J. Samuel, J. Chem. SOC.,Perkin Trans. 2, 1981, ?36. H. E. Zimmerman and R. J. Pasteris, J. Org. Chern., 1980,45,4864.

276

Photochemistry 0-

0

OMe

(317)

(3 16)

Ph Ph

(318)

(3 19)

foregoing, irradiation of the dienone (317) yields two photoenones (314b) and (3 18) as well as an unexpected product 3-methoxy-4,5-diphenylphenolderived from a phenyl migration.127There is, however, a preference for the formation of the enone (3 14b) over the enone (3 18) of 1.4 : 1 when benzene is used as the solvent. The fact that the enone (314b) is formed is proposed as evidence that not all the rearrangement reaction occurs via a zwitterion. Proof of this comes from the independent generation of the zwitterion (3 19) and the observation that this leads solely to the enone (314b). The cross-conjugated dienones (320) are readily converted by irradiation (254 nm) into lumiketones (321).lz8 Irradiation of these products (321) using Pyrex-filtered light and aqueous acetic acid gave the spirodienones (322). The lumiketone (324) can be prepared from (323) by irradiation under the same conditions as above. The subsequent irradiation of (324) in aqueous acetic acid was not as clean as the previous conversions and yielded the two products (325) and (326), as well as recovered starting material. The two dieneones (325) and (326) are formed from the lumiketone (324) however the spiroketone (325) is itself photolabile and yields starting material and the dienone (326). The rearrangements clearly involve the intermediacy of carbocation intermediates (327) which in

(320) R

=

Me or H

(323)

Me ....

(324)

Me (327)

”’ H. E. Zimmerman and R.J. Pasteris, J. Org. Chern., 1980, 45, 4876. lz8

D. Caine, C.-Y. Chu, and S. L. Graham, J. Org. Chem., 1980, 45, 3790.

Enone Cycloadditions and Rearrangements 277 some instances only rearrange in one mode or in others two possible pathways arise in competition. Direct irradiation of the steroidal dienones (328) in neutral media affords the expected lumiketones (329).12' The lumiketones (329a, b) are

0 (328) a; R' = OH,R 2 = H,R3 = COCH20H,R4 = OH b; R' = H,R2 = OH, R' = COCH20H,R4 = OH C;

R'

=

H,R2 = OH,R3 = COCH,,R4 = H

(329) a; 42% b; 78% c; 47%

(330)

themselves photolabile and are readily transformed into the cyclic ether (330). This product can be accounted for in terms of the accepted behaviour of the bicyclic ketone system and presumably involves intramolecular trapping of the zwi tterion (331) generated by fission of the cyclopropyl system in (329). When the steroidal dienones (328a, b) were irradiated in 50% acetic acid in water the products shown

yield from a; 20"," yield from b; 20'2;

a; 64"/ / O b; 50"/,

a; 16% b; 19%

Scheme 20

in Scheme 20 were isolated. The photorearrangement of betamethasone (332) affords the lumi-product (333) in good yield.'30 COCH20H

I3O

J. R. Williams, R. H . Moore, R. Li, and C. M. Weeks, J . Org. Chern., 1980, 45, 2324. T. Hidaka, S. Huruumi, S. Tamaki, M . Shimishi, and H. Minato, Yuktrgcrklc Zasshi, 1980, 100, 72 (Chern. Abstr., 1981, 94, 109 184).

27 8

Photochemistry

Irradiation of the tropolone (334a) as a complex with fj-cyclodextrin gave the isomer (335a, 64%) as the main product, accompanied by a small amount of (336a). A similar result was obtained from the photolysis of (334b) as a complex which yielded the two products (335b) and (336b). The photoisomers obtained from these reactions were optically active.

(334) a; R = O H b; R = OMe

(335) a; R b; R

(336) a; R = H b; R = Me

=H = Me

Compounds (337a, b) are formed initially from sensitized irradiation of the lactones (338a, b). 1 3 * The reaction is formally a 1,5-phenyl migration. Subsequent irradiation of (337) transforms it into the fused system (339) when the solvent used is protophilic. In other solvents the rearrangement of (338) follows a different path yielding the products (340). The use of optically active sensitizers has been

(337) a; R = H b; R = Me

(338) a; R b; R

R2 (340) R'

R'

'Ph

=H =

Me

(339)

k,,

= Ph, R2 = H, = H, R 2 = Ph,

R3 = H or Me R3 = H or Me

employed in a study of the phototransformation of racemic (337b).133 The isolation of optically active starting material indicates that enantiomer differentiation has occurred at the sensitization stage. 5 1,2-, 1,3-, and 1,4Diketones The photochemical addition of biacetyl to indene and furan affords the oxetans (341a) and (341b) as the major ~ r 0 d u c t s . lThis ~ ~ result confirms the earlier reports. 13', 36 From the kinetic study of these reactions and from the reaction of biacetyl with tetramethylethylene where ene products predominate it is clear that 13'

133

134

136

H. Takeshita, M. Kumamoto, and I. Kuono, BUN. Chem. SOC.Jpn., 1980, 53, 1006. N. Hoshi, H. Hagiwara, and H. Uda, Kokaguku Toronkui Koen Yoshishu, 1979, 14 (Chem. Abstr., 1980, 92, 214634). N. Hoshi, Y. Furukawa, H. Hagiwara, H. Uda, and K. Sato, Chem. Lett., 1980, 47 (Chem. Abstr., 1980, 93, 131 721). G. Jones, 11, M. Santhanam, and S.-H. Chiang, J . Am. Chem. Soc., 1980, 102, 6088. H.-S. Riang, K. Shima, and H. Sakurai, J. Org. Chem., 1973, 38, 2860. H.-S. Riang, K. Shimd, and H. Sakurai, Tetrahedron Lett., 1970, 1041.

Enone Cycloadditions and Rearrangements 279 the biacetyl triplet is operative. Extension of this work to include the reaction of biacetyl with cis-dimethoxyethylene as the addend has been made. This yields the four oxetans (342a-d) with the trans-pair (342a, b) predominating in a ratio of 2 : 1. The loss of stereochemistry in the olefin is further evidence that biacetyl triplets are involved in cycloaddition reactions. A new study of the photoreaction

Ac (341) a; R-R = ( C H d H ) , , X = CH2 b; R,R = H, X = 0

Me

Me

'OMe

(342a)

,&

"0Me

(342b)

,OMe

Ac (Q jo

Me M~ 'OMe (342c)

Me

3' ..

'OMe

Ac

(342d)

between biacetyl and tetramethylethylene has shown that the products from the reaction are those shown in Scheme 2 1. 3 7 A detailed kinetic study has shown that MeCOCOMe

-w++w++H+o 0

0

Scheme 21

an exciplex is involved produced by the quenching of the biacetyl triplets by the olefin. This interaction accounts for the lack of a significant deuterium isotope effect. A study of the photochemical behaviour of biacetyl in fluorocarbon solvents has been reported.138

+ Scheme 22 13' 13*

N. J. Turro, K. Shirna, C. Chung, C. Tanielian, and S. Kanfer, Tetrahedron Lett., 1980, 2775. E. J. Broomhead; K. A. McLauchlan, and J. C. Roe, J. Chem. SOC.,Perkin Trans. 2, 1980, 796.

280

Photochemistry

The dione (Scheme 22) reacts photochemically with aromatic aldehydes 139 in processes similar to the reactions between quinones and aldehydes. 140 Irradiation of the diketone (343) leads to the formation of the remarkable diol (344).141 The structure of this product was verified by X-ray analysis. The reaction, brought about by irradiation through Pyrex in various solvents, proceeds via the intermediate keto alcohol (343, a compound isolated at shorter reaction times. There is some doubt in the minds of the authors as to whether the reaction arises by hydrogen abstraction from the y- or the &-position.They propose that if the former occurs then the rearrangement by hydrogen migration to yield (1) is kinetically favoured.

(343)

(344)

Courtot 142 has reported some of the transformations encountered in the photochemistry of some chelates of P-diketones. A study of the photochemical interconversion of chelated enols of triacylmethanes has been reported. 43 The results of a study of the photochemical behaviour of the anhydrides (346) has been published. 144 The photoreactions of the thiolane-2,4-diones (347) have been studied. 145, 146 0

0 0 II II Ar CH,COCCH,Ph

14* 14'

14'

143 144

14' 146

R ' ~0 R '

K. Maruyama, Y. Narutama, A. Osuka, and H . Suzuki, Bull. Chem. SOC.Jpn.. 1980, 53, 2093. see e.g. A. Takuwa, Bull. Chem. SOC.Jpn., 1977, 50, 2973. D. W. Balogh, L. A. Paquette, P. Engel, and J. F. Blount, J . Am. Chem. SOC.,1981, 103, 226. P. Courtot, R. Pichon, and J. Le Saint, Bufl. Chim. SOC.Fr., 1980, 457. B. Couchouron, J. Le Saint, and P. Courtot, Bull. SOC.Chim. Fr., 1980, 381. A. A. M. Roof, H. F. van Woerden, and H . Cerfontain, J . Chem. SOC.,Perkin Trans. 2, 1980, 838. K. Saito and T. Sato, Bull. Chem. SOC.Jpn., 1979, 52, 3601. K. Saito and T. Sato, Chem. Lett., 1978, 307.


28 1

Scaiano et al.'47 have characterized two triplet states with different lifetimes in the photochemistry of o-phthalaldehyde (348). They believe that the products (349) and (350) arise from singlet state reactions although their data does not exclude the operation of a short-lived triplet state. Norrish Type I1 reactivity is shown by the formamide derivative (351a) when irradiated in t-butyl alcohol. The product formed from this reaction is the result of ring closing in the biradical intermediate (352) to afford the lactam (353).'48 When the formamide is Nmethylated (35 1b) two Norrish Type I1 hydrogen abstractions occur. One involves the abstraction of the formamide hydrogen yielding (353, R = Me), and the other proceeds by hydrogen abstraction from the N-methyl group affording (354). 0

acHo d

CHO

(348)

(349).

HN

RNKH 0 (351) a; R = H b; R = Me

o

'n'

0 (352)

0

RN*OH 0

PH

N CHO

Irradiation of the enedione (355) results in formation of the two acids (356a, b) and the lactone (357) when the reaction is carried out in benzene solution. 149 The formation of the lactone is presumed to involve the intermediacy of the biradical (358) within which a 1,2-phenyl migration occurs to yield product (357). A biradical (359) is also proposed as the key intermediate to the formation of the acids by way of the ketene intermediate (360) which is trapped by adventitious water. Further proof of the involvement of a ketene was obtained from experiments in methanol when the esters (356c, d) are obtained. Behaviour analogous to the above is also encountered with the ene diones (361). When the bridging chain is reduced as in (362) the irradiation yields only the quadricyclane (363).149An account of the photochemical cis-trans isomerization of (364) applied to an undergraduate experiment has been reported. The use of dibromo-N-methylmaleimidefor the photosubstitution of aryl compounds has been further studied. 147

"13

'*' I5O

J. C. Scaiano, M. V. Encinas, and M. V. George, J . Chem. Soc., Perkin Trans. 2. 1980, 724. H. Wehdi, Helv. Chim. Acta, 1980, 63, 1915. S. Lahiri, V. Dabrai, S. M. S. Chauhan, E. Chakachery, C. V. Kumar, J. C. Scaiano, and M. V. George, J. Org. Chem., 1980, 45, 3782. L. Poncini, Sch. Sci. Rev., 1980, 61, 520 (Chem. Absrr.. 1980, 92, 197228). K. M. Wdd, A. A. Nada, C. Szilagyi, and H. Wamhoff, Chem. Ber., 1980, 113, 2884.

282

Photochemistry

R2

(357)

(355)

(356) a; R' = C 0 2 H , R2 = H b; R' = H, R2 = C 0 2 H c; R' = C02Me, R2 = H d; R' = H, R2 = C 0 2 M e

(358)

&

C \\

0

(359)

(360)

0 Ph (361) a; n = 1 b;n=2

&::: phn (363)

0 Ph (364)

(362)

Maleimide and N-methylmaleimide both undergo dimerization yielding (365) when irradiated in carbon tetrachloride.lS2 When the irradiation is carried out in tetrahydrofuran oligomers are formed via a chain process.

(365) R = H or Me

(366) R

=H

or Me

The photoaddition of diketene to the anhydrides (366) yields the [2 + 21 adducts (367) and (368).153A study of the photocycloaddition of cyclohexene to maleic anhydride sensitized by an insoluble benzoylated polystyrene has shown that the technique is nearly as efficient as the use of free benzophenone.154 The cycloadducts (369) and (370) are obtained from the acetone-sensitized addition of 3,3-dimethylbut-l-yne to the anhydride (371). The product (372) is also found in 1the reaction mixture. This material is light sensitive and is converted by 152

153

P. Boule and J. Lemaire, J . Chim. Phys. Phys.-Chim. Biol., 1980, 77, 161 (Chem. Abstr., 1980, 93, 149 356). T. Kato, T. Chiba, and S. Tsuchiya, Chem. Pharm. Bull.. 1980, 28, 327 (Chem. Abstr., 1980, 93, 45 532).

154 155

J. L. Bourdelande, J. Font, and F. Sanchez-Ferrando. Tetrahedron Lett., 1980, 3805. W. Mayer, D. Wendisch, L. Born, and W. Hartmann, Chern. Ber., 1981, 114, 1287.

283


(369)

x; B u'

\

0 (372)

;F (370) MeMe 0

\\i

(371)

Se

:

Bu' Bu'

HMe 0

(373)

(374)

irradiation into the dimer (373). The [2 + 21-adduct (374) is obtained from the photoaddition of dimethylmaleic anhydride to selenophene. 5 6 Photocycloaddition of but-2-yne to the anhydride (375) yields the novel adduct (376, 36%). 157 This compound was subsequently chemically transformed into the pentaene (377). The photosynthesis of the adduct (378) obtained from the cycloaddition of acetylene to the anhydride (379) has been r e ~ 0 r t e d . I ' ~This adduct (378) was a key intermediate in the synthesis of the novel compound (380). 0

:=Meo2 Me0,C

0

0

C0,Me

The efficiency of triplet-triplet energy transfer to maleic acid has been studied with particular reference to the influence of P H . ' ~ ~ The photocyclization of the anhydride derivative (38 1) yields the naphthalene (382) after hydrolysis and esterification.I6O Irradiation of the epoxynaphthaquinone (383) leads to ring opening of the oxiran ring. When the reaction is carried out in the presence of xanthene, hydrogen abstraction leads to the formation of (384) and (385).16' Rearrangement also 156

Is'

161

C. Rivas, D. Pacheco, and F. Fargas, J. Heterocycl. Chem., 1980, 17, 11 51. R. Askani and B. Peleck, Tetrahedron Lett., 1980, 1841. T. Tsuji, Z. Komiya, and S. Nishida, Tetrahedron Lett., 1980, 3583. A. Gupta, R. Mukhtar, and S. Seltzer, J . Phys. Chem., 1980, 84, 2356. A. S. R. Anjaneyulu, P. Raghu, and K. V. R. Rao, Indian J. Chem., Sect. B, 1980, 19, 51 I (Chew. Abstr., 1980, 93, 220 132). K. Maruyama, S. Arakawa, A. Osuka, and H. Suzuki, Kokaguku Toronkai Koen Yoshishu, 1979, 24 (Chem. Abstr., 1980, 92, 197 663).

284

Photochemistry

Me0

HC OMe Ri

Me0 O M e R'

(381) (382) R' = 2,4,5-(MeO),C,H,; R2 = Br or M e 0

occurs to afford the quinone (386). In the more sterically crowded molecule (387), hydrogen abstraction from xanthene yielding (388) also takes place but rearrangement to (389), the ring-contracted product, dominates. Type I1 hydrogen abstraction reactions occur with the epoxyquinone (390) yielding (386a), the product of elimination, and (39 l), the cyclization product. Further irradiation of this

0

0

(383) R = H, Me, Et, Pr, or Pr'

(384)

%IH

0

0

0

0

(385)

H*

@ M $e 0

Me

R

(388) R = 9:xanthenyl or H

R

Ac

(389) or /I-OH

= u-

0 0

@J:

CH,CHR$

0

R2 R2

(390) R 1= Me, R2 = Ph or Me; R 1 = H, R 2 = Me

(391)

compound converted it into the products shown in Scheme 23. The photoringopening of epoxyquinones of the type (387) has previously been interpreted in

(391)

hv

R2 R2

Me Me Scheme 23


285

terms of the formation of the zwitterion (392).16' Intermolecular trapping of this intermediate accounts for the formation of the dimers (393) and (394) obtained from the photolysis of benzene solutions of the epoxyquinone (387). Further irradiation of the dimers (393 and 394) brings about their further transformation into the dimers, phthalides, (395) and (396).'63 Phthalides (397) are also formed from the irradiation of the adducts (398) in benzene solution. A mechanism involving Norrish Type cleavage as the first step is thought to be The adducts (398) are formed by the trapping of intermediate (392) by aldehydes. The

(392)

0

(393) 0

3 (394)

0

/ \

0

Me

(395)

0 (396)

(397)

(398) R = H,alkyl, or aryl

zwitterionic intermediate (392) is also thought to be involved in the formation of the oxygenated products (399) and (400) obtained from the irradiation (Pyrex

164

K. Maruyama and A . Osuka, Cliem. Left., 1979, 77 (Chem. Ahsfr., 1979, 90,167615). K. Maruyama and A. Osuka, J . Org. Cltem., 1980, 45, 1898. K . Maruyama, A. Osuka, and H. Suzuki, Clrem. Lett., 1979, 1477 (Ckem. Ahsfr., 1980,92, 214628).

286

Photochemistry

filter) of the epoxyquinone (387) in benzene.165 The trapping of the initially formed ylide (392) by singlet oxygen is thought to produce adduct (401). Thermal or photochemical transformation of this yields the observed products (399) and (400). Intermolecular trapping by ally1 alcohols (402) of an ylide intermediate can account for the formation of the adducts (403) from the epoxyquinone (404).'66

H ,C=CHCR:OH

(402) R 2 = H or Me

q HO

&; 0

0

R2 R 2

(404)R'

=

Me, Et, or Ph

(403)

The naphthalene- 1,3-dione derivatives (405) are photochemically transformed in benzene-t-butyl alcohol into the two products (406, 407).16' The reaction is proposed as a Norrish Type I1 process involving the biradical (408) as the key intermediate. The formation of both products can be accounted for from this intermediate either by bond formation or by the more unusual disproportionation to yield (407). A study of the dependence of product distribution with time has shown that while the olefinic product (407) can be produced from the biradical (408), there is also a secondary process in the direct reaction that cleaves the product (407) into the same biradical. The cleavage of this product is clearly dependent on the presence of the additional carbonyl function (perhaps via intramolecular energy transfer) since the acetate (409) is unreactive under the conditions of irradiation. 0

0

R4 R' R2 (405) a; R' b; R ' C;

165

''' 16'

R2 = M e H, R2 = Me R'-RZ = (CH,), =

=

(406)

(407) a; R 3 = Me, R4 = H b; R 3 = R4 = H C;

R3-R4

= (CH,),

K. Maruyama, A. Osuka, and H. Suzuki, J . Chem. SOC.,Chem. Commun., 1980, 723. K. Maruyama, A. Osuka, and H. Suzuki, Chem. Lett.. 1980, 919 (Chem. Abstr., 1981, 94, 30045). A. Osuka, M. H. Chiba, H. Shimizu, H. Suzuki, and K. Maruyama, J . Chem. SOC., Chem. Commun., 1980,919.


287

q R' R2 (408)

The irradiation of the dione (410) in methanol yields the epoxyketone (41 1).168 The authors suggest that an electron-transfer process is involved in the reaction which results in the formation of the methanol adduct (412), which dehydrates to yield the final product.

e M &

0 0

The photoaddition of N-ethylphthalimide (413) to cyclohexene in methanol affords the two adducts (414) and (415). The incorporation of methanol could result from trapping a radical ~ a t i 0 n . I ~Such ' a mechanism has been put forward for the formation of the products (416) and (417) from the phthalimide derivatives (418). The cyclized products (419, 420) are formed on the irradiation of the phthalimide derivatives (421a-c) in methanol.171In the case of 0

R' R2 I I

q

,

A2

R3R c, OMe l (416)

168 169

170 t7L

HO R 3 ~ 2 0 R' M e (417)

go

NCH2CH2C=C, R 0

(418)

R1 = R2 = R3 = H or Me

A. Schonberg, E. Singer, and P. Eckert, Chem. Ber., 1980, 113, 3094. H. Hayashi, S. Nagakura, Y. Kubo, and K. Maruyama, Koen Yoshishu-BunshiKozo Sogo Toronkai, 1979, 232 (Chern. Abstr., 1980, 93, 220 113). M. Machida, K. Oda, K. Maruyama, Y. Kubo, and Y. Kanaoka, Heterocycles, 1980,14,779 (Chem. Abstr., 1981, 94,3432). K. Maruyama, Y. Kubo, and T. Ogawa, Kokagaku Toronkai Koen Yoshishu, 1979, 268 (Chem. Abstr., 1980, 93, 70456).

288

& R2R '

Photochemistry Me

\

&..OMe R2,R1 @;RjR2

\

\

0

0 (419) a; 41% b; 54% c; 15%

0

(420) a; 41% b; 27% c; 54%

(421) a; R' = R2 = Me b; R' = R2 = Ph C; R' = H, R2 = Ph

(421c) the cyclized products were accompanied by the isomer (421, R 1 = Ph, R2 = H) of the starting material. When the reaction of (421c) was sensitized by benzophenone only cis-trans isomerization of the side-chain took place indicating that the cyclization process was a singlet-state reaction. The imidazoisoindolone (422) can be successfully prepared by the photocyclization of (423). 7 2 The phthalimides (424) photocyclize to yield the products (425). 7 3 The sulphur-containing phthalimides (426) yield the products (427) on irradiation.'74 Macrocyclic lactams (CZ8)are prepared in 2 6 5 7 % yield from the photocyclization of the phthalimides (428).1 7 5 Larger ring lactams, C,, and C38,

'

(422)

(423)

@:

(CH

NR R

R3

0

(425) R2 = Me, R3 = H R2-R3 = (CH,), or (CH,),

(424) n = 2 or 3 R' = R2 = Me,

R'-R2 = (CH,), or (CH,),

(426)

n = 5, 6, 8, 9, 10, or 12

(427)

112

J. D. Coyle, J. F. Challiner, E. J. Haws, and G . L. Newport, J . Heterocycl. Chem., 1980, 17, 1131.

173

M. Machida, H. Takechi, and Y. Kanaoka, Heterocycles, 1980, 14, 1255 (Chem. Abstr., 1981, 94, 47 286).

174

17s

Y. Sato, M. Wada, H. Nakai, Y. Hatanaka, and Y . Kanaoka, Fukusokan Kagaku Toronkai Koen Yoshishu, 22th, 1979, 151 (Chem. Abstr., 1980, 93, 1738). Y. Kanaoka, Y. Hatanaka, Y . Sato, M. Wada, and H . Nakai, Kokagaku Toronkai Koen Yoshishu, 1979, 266 (Chem. Abstr., 1980, 93, 70455).

Enone Cycloadditions and Rearrangements 289 were also produced from analogues of (428). Cyclization of (429) yielding macrocyclic lactones (c16, C18, C20,C,,, C25, and C27) was also r e ~ 0 r t e d . l ~ ~

(428)

(429)

Irradiation (254 nm) of the imide (430) brings about partial isomerization of the starting material to the trans-isomer (431).176This product is accompanied by the ring-contracted compounds (432) and (433). 769 7 7 Secondary irradiation of the

(433)

(434)

ring-opened compound (433) converts it into (432). From these results it is clear that the reaction proceeds by fission to the biradical (434) from which the isomerized starting material and the N-formyl derivative are derived. The scope of the reaction has been investigated. The usefulness of the cyclization process whereby N-formyl derivatives (e.g., 435) can be converted into azetidine diones R'-RZ = (CH,), or(CH2), R1 = R2 = Me R' = H, R2 = Me, Pr",Pr', Bun,or Bu' (435)

Scheme 24

was also studied (Scheme 24). The ring-expansion products (436a) are forrned on irradiation of the succinimides (437a).I These products are accompanied by the ring-contracted materials, the azetidines (438a). In some cases, as with the succinimides (437b), ring expansion did not take place and only azetidines (438b) were formed. The Norrish Type I1 fission of the N-alkyl side-chain is only important when the side-chain has a b-hydrogen. 177

17'

K. Maruyama, T. Ishitoku, and Y. Kubo, J. Org. Chem., 1981,46, 27. K. Maruyama, T. Ishitoku, Y. Koba, and T. Ogawa, Fukusokun Kaguku Toronkai Koen Yoshishu, 12th, 1979,46 (Chem. Absfr., 1980,93, 203 617). Y. Kanaoka, H. Okajima, and Y. Hatanaka, Kokuguku Toronkai Koen Yoshishu, 1979, 16 (Chem. Abstr., 1980, 93, 45 533).

290

Photochemistry

(436) a;

=

(437) a; R = Et, n = 2 or 4 b; R = Me, n = 2 or 4

Or

(438) a; n = 2 or 4, R = Et b;n=2or4,R=Me

6 Quinones An earlier report by Maruyama et al. described the formation of dimers (439) from the direct irradiation of the acetylquinone 18* In the presence of an electron-donating sensitizer (Rose Bengal) irradiation of the same quinone yields a different dimer assigned structure (441).18' A further account of the regio- and stereo-specific dimerization of the quinones (442) to yield (443) has been reported.182 The possibility of the involvement of an enol intermediate was considered. In one example, that of (444),dimerization failed and the cyclobutene derivative (455) was obtained via a Norrish Type I1 reaction.

0

" R'' C f O C H z R 3 0 (442) R 3 = H, Me, Et, Pr, or Bu, R 1 = H, Me, CI, or Br, R2 = H, or R'-RZ = (CH=CH),

R'

R2 (443) R4 = COCHzR3 OH

(pMe Me

0

OH

Photocyclization of the toluquinone (446) to (447) has been reported. The mechanism favoured by the authors 183 involves intramolecular hydrogen abstraction, proton transfer, and cyclization. 179

I8O 181 18'

183

K . Maruyama, N. Narita, and Y. Miyagi, Chem. Lett., 1979, 1033. K. Maruyama and N. Narita, J . Org. Chem., 1980, 45, 1421. Y. Miyagi, K. Kitamura, K. Maruyama, and Y. L. Chow. Chem. Lett., 1978, 33. Y. Miyagi and K. Maruyama, Kokagaku Toronkai Koen Yoshishu, 1979,26 (Chem. Abstr., 1980,92, 197841). K. Maruyama and T. Kozuka, Chem. Lett., 1980, 341 (Chem. Abstr., 1980,93, 70473).


29 1 The novel cage compounds (448, 449)are formed when duroquinone (450) is irradiated (Pyrex filter, benzene solution) in the presence of cycloheptatriene. 184* 185 The reaction takes place via the intermediate (451), which subsequently undergoes intramolecular cyclization to yield (448) or intermolecular addition of duroquinone followed by intramolecular cyclization to afford the

R C0,Me Me 0

OH (447)

(446) R = Me, Et, CO,Me, or (CH,), NHPh

0

Me

0 (448)

(450)

(449)

second product (449). A cage compound (452) was also obtained by irradiation of the quinone with the triene (453). The product indicates, however, that the triene undergoes photoisomerization to (454) before the addition to the quinone takes place. When cyclo-octatetraene is used as the addend, dimerization and isomerization yield (455) prior to the photoaddition to the quinone to yield (456).

(455)

(454) (456)

K . Ogino, T. Minami, S. Kozuka, and T. Kinoshita, J . Org. Chem., 1980, 45, 4694. K. Ogino, T. Minami, and S. Kozuka, J . Chem. Soc., Chrm. Commun., 1980, 480.

lB4

292

Photochemistry

A detailed study of the photochemical reaction of naphthaquinone with aldehydes has shown that the reaction occurs via an 'in cage mechanism' at low temperatures but at ambient temperatures a small part of the reaction arises from an 'out-of-cage' process. 186 Photocycloaddition of 2-methyl- and 2-ethyl-naphthoquinone to styrene yields three cyclobutane products (457,458) in which the.8-phenylisomer dominated. * 8 7 The ratio of 7-phenyl to 8-phenyl products was 1 : 6 for the methylquinone and 1 : 3.5 for the ethyl derivative. The authors l g 7 suggest that in these examples dipoledipole interactions overcome any adverse repulsions. Changes in the olefin brings about changes in the ratio of products. Thus with 2-phenylpropene the ratio

8

Ph

0

0

(457a)

0 (459)

(457b)

0 (460)a; R' = H,R 2 = AcO b; R' = AcO,R2 = H c; R' = Me,R2 = AcO

0 (458)

R2

_.

(461) a; R2 = H c; R 2 = Me

of 7: 8 isomers is 1 and with 1,l-diphenylethylene the ratio is about 2. Photoaddition of vinyl acetate to the methylquinone (459) yields the adducts (460a,b) regiospecifically.188 An analogous adduct (460c) is obtained when the olefin, isopropenyl acetate, adds to the same quinone. The adducts (460a, b) and (460c) undergo acid-catalysed conversion into the naphthofurans, (46 1a) and (46 lc), respectively. Irradiation of the quinones such as (462) with 1,l-diarylethylenes has been reported as a convenient one-pot synthesis of the benz[a]anthracene skeleton Scheme 25. This report is an extension of earlier work by the same 0

Scheme 25 lg6

K . Maruydma, A. Tdkuwa, S. Matsukiyo, and 0 . Soga, J . Chem. Soc., Perkin Trans. I, 1980, 1414. K . Maruyama and N. Naritd, Bull. Chem. SOC.Jpn., 1980, 53, 757. H. Liu and W. H. Chan, Can. J . Chem., 1980, 58, 2196.


293

(463)

(464)

authors.189-l g 2 A route to novel anthraquinones (e.g., 463) has been reported following the successful photoaddition of olefins (e.g., 464).l g 3 Further investigation into the reactions of quinone (462)has shown that low yields of

Me Scheme 26

products (Scheme 26) are obtained from irradiation in the presence of 1,ldicyclopropylethylene. 94 Interestingly no products were obtained from the addition reaction in which the cyclopropyl ring had opened. This fact is put forward as evidence for the operation of an ionic rather than a free-radical path. The photoaddition of the olefin (465)to the same quinone yields (466).Ig5 0

40SiMe3 R (465)

(466)

R

= Ph, 4-MeC6H,, or 2-thienyl

Phenanthraquinone (467)has been added photochemically to both alicyclic and bicyclic olefins.196 The nature of the products obtained is dependent upon the structure of the olefin. Thus with the bicyclic olefins (468470)the keto-oxetans (471473)are formed exclusively. The use of alicyclic olefins (474)as the addend I9O 191

19'

193

194

195

196

K. Maruyama, T. Otsuki, and K. Mitsui, J . Org. Chem., 1980, 45, 1424. K. Maruyama and T. Otsuki, Chem. Lett.. 1975, 87. K. Maruyama, T. Otsuki, and K. Mitsui, Bull. Chem. SOC.Jpn., 1976, 49,3361. K.Maruyama, K. Mitsui, and T. Otsuki, Chem. Lett., 1978, 323. K. Maruyama, T. Otsuki, K. Mitsui, and M. Tojo,J . Hererocycl. Chem., 1980,17,695 (Chem. Abstr., 1980, 93,239 128). K. Maruyama, M. Tojo,and T. Otsuki. Bull. Chem. SOC.Jpn.. 1980, 53, 567. K. Maruyama, M. Tojo, K. Matsumoto. and T. Otsuki, Chem. Lett.. 1980,859 (Chem. Abstr.. 1980, 93,239375). K. Maruyama, M. Muraoka, and Y. Naruta. J . Org. Chem., 1981, 46, 983.

Photochemistry

294

R3 (468) a; R' = R2 = H, n = 1 b; R' = R2 = H,n = 2 c; R'-R2 = 0, R3 = H, n = 1 d; R2-R3 = OCOCO, R' = H, n = 1

(467)

(469) a; R = H b; R-R = (CH=CH)2

(470)

(472)

(47 1)

also yields keto-oxetans (475) but these are accompanied by dioxins (476) and keto alcohols (477). In contrast, photoaddition of phenanthraquinone to the olefins

F

Y

@ (474) a; n = 1 b;n=2 c;n=3 d;n=4 e;n=8

0 W ) r . (475) a; 18% b; c; d; 20% e; -

(476) a; b; 29% c; 42% d; 56% e; 46%

\ +QIl

(477) a; 70% b; 59% c; 34% d; 6% e; 39%

(478) has been reported to yield the adducts (479).19' The photoaddition of the quinones (480) and (481) to the enzymes (482) yields the carboxamides (483), which undergo spontaneous ring closure to yield the adducts (484a) and (484b), respectively. The initial addition reaction presumably involves the formation of an oxeten which subsequently ring opens to (483). 19'

'98

P. Kertesz and J . Reisch, Arch. Pharm (Weinheim. Ger.), 1980, 313, 476 (Chem. Abstr., 1980, 93, 186 258). W. Verboom, A. V. E. George, L. Brandsma. and H. J. T. Bos, R e d . Trav. Chim. Pays-Bas, 1980.99, 29.


295

H p&CHZOR

H (479) R = H, 1 :5 cis :trans R = Bz, 1:lQ cis:trans

(478) R = H or Bz

8

By' R~CH =CHC=CNR:

/

(482)

R4

rONR!

CONR!

R' (483)

(484) a; R'-R3 = Rz-R4 = (CH=CH)2

b; R'

=

R2 = Bu', R 3 = R4 = H

The photocycloaddition of trans-piperylene to the quinone (485) yields the oxetan (486).199From a study of this and other dienes (e.g., cyclopentadiene and cyclohexa-l,3-diene), it was concluded that the addition involves an exciplex where both the singlet and the triplet states are involved.

& @ Ye

I

0

(485)

I

0

(486)

The study of the photochromism of a series of anthraquinone derivatives (487) has been reported.200The reaction involves the Norrish Type I1 hydrogen transfer from a neighbouring methyl group to a photoexcited carbonyl group yielding the enol(488). The photohydroxylation of anthraquinone in aqueous organic solvents has shown that both 1- and 2-hydroxyanthraquinone are produced.201- *04 A 199

'01

"' z03 '04

A. Ezaki, H. Inoue, and M. Hida, Kokagaku Toronkai Koen Yoshishu, 1979,164 (Chem. Abstr., 1980, 93, 7264). N. P. Gritsan, V. A. Rogov, N. M. Bazhin, V. V. Russkikh, and E. P. Fokin, izv. Akad. Nauk SSSR. Ser. Khim., 1980, 89 (Chem. Abstr., 1980, 93. 7382). 0.P. Studzinskii and A. V. El'tsov, Zh. Org. Khim., 1980,16,2117 (Chem. Abstr., 1981,94,83287). 0 .P. Studzinskii and A. V. El'tsov, Zh. Org. Khim., 1980,16, I101 (Chem.Abstr., 1980,93, 150035). 0.P. Studzinskii, R. P. Ponomareva, and V. N. Seleznev, izv. Vys. Uchebn. Zuved., Khim. Teknol., 1980, 23, 51 1 (Chem. Abstr., 1980, 93, 168 004). 0.P. Studzinskii and A. V. El'tsov, Zh. Org. Khim., 1980,16, I100 (Chem.Absrr., 1980.93, 168 005).

aR

296

Photochemistry

/

0 (487) R = H , 3 4 1 -cyclohexen-!-yl), 4-Me0, 3-cyclohexyl, 3-(2-nitro-l -cyclohexen-l-yI), or 4-CI.

0 (489) R = NH, or OH

detailed study of the photoreactions of amino- and hydroxy-anthraqwinones (e.g., 489) has been reported.205 Photoreactions of the quinones (490) have been described.206

205

K . Hamilton, J. A. Hunter, P. N. Preston, and J. 0. Morley, J . Chem. Soc., Perkin Trans. 2, 1980,

'06

Yu. E. Gerasimenko, N. T. Poteleshchenko, and V. V. Romanov, Zh. Org. Khim., 1980, 16, 1938 (Cliem. Abstr., 1981, 94, 47021).

1544.

Photochemistry of Olefins, Acetylenes, and Related Compounds ~~~

~~~

BY W. M. HORSPOOL

1 Reactions of Alkenes

Addition Reactions.-The photochemical conversion of the optically active aniline (1) into the indoline (2), and the methanol adducts (3, 4) of (l), have been described. Irradiation of the substituted naphthoic acid ( 5 ) yields the cyclized lactone (6). This is a key step in the synthesis of the quinone (7).2

OMe

OMe

(6)

(5)

0

(7)

Photoaddition of acetaldehyde to the stereoisomers of (8) gave only two (9) of the eight possible ad duct^.^ The acetyl group apparently enters specifically at C-4 frans- to the hydroxy-group. Addition products are formed when iminium salts (10) are irradiated in ethers or alcohol^.^ The mechanism of the addition involves an electron transfer as shown

'

B. Scholl and H.-J. Hansen, Helv. Chim. Acra, 1980, 63, 1823. R. G . F. Giles, M. K. Reuben, and G . H. P. Roos, S. Afr. J . Chem., 1979,32, 127 (Chem. Abstr., 1980, 93. 204403). 3. Srogl, M. Janda. F. Liska, and I. Stibor, Collect. Czech. Chem. Commun., 1980, 45, 888. J. Stavinoha, E. Bay, A . Leone, and P. S. Mariano, Tetrahedron Lett., 1980, 21, 3455.

297

298

Photochemistry M e C O e E

CHzOH

M e 0P O M e

Me0

(8)

(9)

in Scheme 1. The results obtained from a study of the photoaddition of electron-acceptor olefins e.g. acrylonitrile, to iminium salts (1 1) indicate that the reaction occurs by initial 1,2-addition to the aromatic ring5 The intermediate

QR1

CH, In.OH'

0

~

+

CH30& 1

I R2

\

R2

-

QRl+

+OH

/\

H R2

Q IG Z O "

R2

a/ % \ 2 0 H

R2 H

Scheme 1

Table 1 Products (13) formed by cycloaddition of olefn (CH,=CHCN) iminium salts (I 1) Salt (1 la) (1 lb) (1 lc) (1 Id)

to

Product (7; yield) (13a, 18%) ( 1 3b, 20%) ( 1 3 50%) ~ (134 5%)

adduct (12) rearranges to the spirocyclic amines (13) (Table 1). The anisyl compound (lle) is an exception to this generality and yields the abnormal cycloadduct (14).

'R

ClO,

HkR NC

H N & /NC J-

(11) a; R = Me

b:R=F R = CI d; R = Br e; R = OMe C;

aCN /I- McOC,,H,

(14)

R

299

Photochemistry of OZefins, Acetylenes, and Related Compounds

Hydrogen Migrations and Abstractions.-Morrison and Giacherio have reported the acid-catalysed photoisomerization of 2-alkylindenes (e.g., 15) into the corresponding alkylidene indans (e.g., 16). The reaction involves the singlet state of the indene since the triplet state yields only dimers. However, it is obvious from the failure of HCl to affect the fluorescence of the indenes that the interaction of the acid is with a state other than the simple singlet excited state. Further study has shown that the addition of a proton occurs at C-3 of the indene. Intramolecular hydrogen transfer has been demonstrated by deuterium labelling in the photorearrangement of the rigid homoallyl alcohol (17) into the aldehyde (18).7 ~\

M

W \

(1 5 )

(17)

(18)

C c

H

,

(16)

(19)

(20)

(21)

Irradiation of the deuteriated alcohol (19) affords the aldehydes (20) and (21) each containing one deuterium atom. Such an experiment indicates that the alcoholic hydrogen is abstracted. A similar experiment with the endo-exo mixture of alcohols (22) gave an analogous result with the two aldehydes (23, 24) each containing two deuterium atoms. The cyclized products (25a) and (25b) are

&OD D

R' = CO,H or CONH,, R2 = H b; R' = H, RZ = C02H or CONH,

(25) a;

(26) R

= CO,H

or CONH,

formed by the irradiation of the chlorinated tricyclic starting material (26).8 The reaction involves abstraction of hydrogen by the photoexcited double bond and bonding within the resultant biradical.

'

H. Morrison and D. Giacherio, J . Chem. Soc.. Chem. Commun., 1980, 1080. J. Studebaker. R. Srinivasan, J . A. Ors, and T. Baum, J . Am. CIwm. Soc., 1980, 102, 6872. J. Schmitzer, K. Hustert. H. Parlar, and F. Korte, Z . Naturforsch.. Teif B. 1980,35, 502 (Chem. Abstr., 1980, 93. 220 110).

300 Photochemistry Fission Processes.-Irradiation of the deuteriated mesylate (27) with 2 = 254 nm resulted in the formation of the products shown in Scheme 2.9 The recovered (27,

(27) R'

=

a; R = NHCOMe, 41% b; R = OMS. 7% Scheme 2

D, R2 = OMS

R = OMS, 17%

35%) was shown to be identical with starting material: the absence of deuterium migration suggests that the ion (28) is not a primary product. Kitamura et al."

(28)

have reported the synthesis of the compounds (29) following the irradiation of the olefin (30) in the presence of azide ion and dimethyl fumarate. The reaction is interpreted in terms of the formation of the ion (31) produced by the photoinduced ionization of the vinyl bromide. The ion is trapped by azide which presumably, on photoexcitation, produces an azirine. Ring opening of the azirine and trapping by the diester yields the observed products. The bromide (30a) yields the oxazole (32) when irradiated in the presence of azide and acetone. -0Me

"-.

R p-MeOC,H,

R p-MeOC6H4

R

R

XBr

(30) a; R =p-MeOC,H4 b; R = Ph c; R = Me

P+ (31)

Me (32) R = p-MeOC,H, cis-trans 1somerization.-The influence of triplet energy on the photo-equilibrium position of several /I-alkylstyrenes (33) has been studied.l19 l 2 The high ratio of the S. J. Cristol and R. M. Strom, J . Am. Chem. Soc., 1980, 102, 5577. T. Kitamura, S. Kobayashi, and H. Taniguchi, Kukagaku Toronkai Koen Yoshishu, 1979, 84 (Chem. Abstr., 1980, 92, 180331). T. Arai, H. Sakuragi, and K. Tokumaru, Kokuguku Toronkai Koen Yoshishu, 1979,112 (Chem. Abstr., 1980, 93, 70 606).

T. Arai, H. Sakuragi, and K. Tokumaru, Chem. Left., 1980, 261 (Chem. Abstr., 1980, 93, 70069).

Photochemistry of Olefins, Acetylenes, and Related Compounds

30 1

cis-t-alkylstyrene at the photostationary state was attributed to a lower rate constant for energy transfer to the cis-form than to the trans. The influence of oxygen upon the triplet-induced photostationary state composition of the olefin (34) has been as~essed.’~ The ‘betweenanenes’ (e.g., 35) present a novel class of compounds in which there has been some interest over the last few years. Marshall l4 has reviewed the area recently. Marshall and Black l 5 have reported the synthetic steps to some new examples (35)’ the key step in which is a photochemical cis-trans isomerization induced by irradiation in xylene or cyclohexane of the isomers (36). The ‘betweenanenes’(37) have been synthesized by the irradiation of the olefins (38).16 PhCH=CHR

Me

(33) R = Me, Et, Me2CH, M e X , or EtCMe,

M eMe bx2-naphthyl

(‘m a”?) (34)

(CH2),o

(CHdlo

(35)

n)2H & CrC(

(36)

(37)

m = 20, 22, and 26 a

m

(38) n = 8, 10, or 20 m = 6 , 8, or 18

The rate constants for the cis-trans isomerization of stilbene have been obtained.”. l 8 A study of the trans-cis isomerization of the stilbenes (39) using proton and fluorine CIDNP has been made.” Maciejewski 2o has published an account of a laboratory experiment based on the photoisomerization of cisstilbene.

R

5

c

(39)

L

R

(

=

H

3 / R 5

Or

F

pb \

/

(40)

A kinetic analysis of the behaviour of the styrene (40) upon irradiation using oxygen and azulene as quenchers has shown that the lifetime of the triplet state is

*’T. Arai, H. Sakuragi, and K. Tokumaru, Chem. Lett., 1980, 1335 (Chem. Abstr., 1981,94, 64815). l4 lS

l6

J. A. Marshall, Acc. Chem. Res., 1980, 13, 213. J. A. Marshall and T. H. Black, J . Am. Chem. SOC.,1980, 102, 7581. J. A. Marshall, M. Constantino, and T. H. Black, Synth. Commun., 1980,10,689 (Chem.Abstr., 1981, 94, 15 263).

l7

M. Sumitani, N . Nakashima, and K. Yoshihara, Chem. Phys. Lett., 1979, 68.

’* M. Sumitani, N. Nakashima, and K. Yoshihara, Kokuguku Toronkai Koen Yoshishu, 1979,40 (Chem. l9 2o

Abstr., 1980, 92, 163 331). T. V. Leshina, S. G. Belyaeva, V. I. Mar’yasova, R. Z. Sagdeev, and Yu. N . Molin, Dokl. Akad. Nauk. SSSR, 1980, 255, 141 (Chem. Abstr., 1981, 94, 102 547). A. Maciejewski, Mech. Kinet. Procesow Fizykochem., 1979, 89 (Chem. Abstr., 1980, 93, 131 529).

302

Photochemistry

104-150ns.2' The isomerization of the styrene (40) in the presence of electron acceptors has been reported.22

R

Ph

Po>

0

Ph (41) R

=

H , OAc, or OMe

(42)

(43)

A study of the excited-state properties of the trans- and cis-dianthrylethylenes (41) has been made.23 The cis-isomer photoconverts with low quantum yield (9 x into the trans-form. The reverse transformation does not take place. Irradiation of the crown ether (42) under various conditions yields the expected phenanthrene derivatives (50--60%) together with the cis-trans-isomer (43, 0.5%).24 Inoue et aE.25have described their study of the singlet sensitized isomerization of cyclo-octene. They 2 5 report that the use of methyl benzoate or other aryl esters results in the anomalously high trans-cis ratio of 0.25. This result is only anomalous if a triplet mechanism is operative but the authors 2 5 have shown that in this instance a singlet state is the active species. The same sensitizer has been used in a study of the photochemical behaviour of the diene (44), which is converted into the isomer (45) and subsequently into (46).26

0 (2(44)

(45)

(46)

2 Reactions involving Cyclopropane Rings Kaupp 27 has published a review in which reference is made to the di-n-methane reaction, a process which continues to yield interesting results. The di-n-methane 21

22

23 24 25

26

J. Saltiel and D. W. Eaker, Chem. Phys. Lett., 1980, 75, 209. G . Gennari, G. Cauzzo, G. Galiazzo, and M. Folin, J . Photochem., 1980, 14, 1 1 (Chern. Ahstr., 1981, 94, 3517). H. D. Becker, K. Sandros, and L. Hansen, J . Org. Chem., 1981, 46,82 1. M. Eichner and A. Merz, Tetrahedron Lett., 1981, 22, 1315. Y. Inoue, S. Takamuku, Y. Kunitomi, and H. Sakurai, J. Chem. SOC.,Perkin Trans. 2, 1980, 1672. S. Goto, S. Takamuku, H. Sakurdi, Y. Inoue, and T. Hakushi, J. Chem. SOC., Perkin Trans. 2 , 1980, 1678.

'' G . Kaupp, Angew. Chem. Int. Ed. Engl., 1980, 19, 243.

Photochemistry of OleJins, Acetylenes, and Related Compounds

303

Rb

R2

R' = RZ = H or HO (48) R 3 = H or Me rearrangement of the diene (47) into the pentacyclic compound (48) has been described.28 No products of bond homolysis or bond heterolysis were observed when the compounds (49) were irradiated in acetonitrile solution. 29 The products obtained were all of the di-n-methane type (50). The same reaction was observed when (49a) was irradiated in acetic acid. However, when (49b) was irradiated in (47)

(49) a; X

= HO b; X = AcO C: X = OCOEt

(50) a; X = OH b; X = AcO C;

X

=

,

OCOEt

( 5 1 ) a;

R' = AcO, RZ = H , 32';; b; R' = H,R 2 = AcO, 4%

Scheme 3 acetic acid the products (Scheme 3) were obtained. The propionate (49c) yielded the products shown in Scheme 4. The authors2' believe that the photoreactions are influenced by acid catalysis. (49c)

-&-

( ~ O C24: , ")

+ (49c, 47" ") + (5 1a, 4"/,) + (5 1b, 4%) Scheme 4

The acetone-sensitized irradiation of the bicyclo-octadienones (52) leads to the formation of a single photoproduct (53) in each case.3oThis product is presumed to arise from a di-n-methane reaction involving the bridging intermediate (54) exclusively, despite the polar substituents in the benzene ring. In constrast, similar irradiation of the compounds ( 5 5 ) leads to products, the nature of which is dependent upon the type and position of the polar substituent. The results are 28 29

30

I. Kasahara, H . Sugiyama, and M . Nitta, Kokagaku Toronkai Koen Yoshishu, 1979. 156 (Cliem. Abstr., 1980, 93, 7385). S. J. Cristol and R. D. Daussin, J . Am. Chern. Soc., 1980, 102, 2866. M.Kuzuya, E. Mano, M . Ishikawa, T. Okuda, and H . Hart, Tc.trrihcrlrori Lrrt.. 1981, 22. 1613.

304

Photochemistry

0

0

Ph

R3 R' ( 5 2 ) a; R' = R 2 = H, R3 = CN mdiS= 0.18 b; R' = R 3 = H, R2 = CN mdis = 0.17 c; R 3 = OMe, R' = R2 = H Qdiq = 0.19 d; R' = OMe, R2 = R 3 = H Qdis = 0.16

(53)

(54)

shown beside the appropriate structures (Scheme 5). Schnaffner and his coworkers 31 have examined further the photorearrangement of the barrelene 0

n

0

R2

0

II

Scheme 5 analogue (56) into the three isomeric semibullvalene products (57-59), Scheme 6. Their original proposal 32 was that two discrete biradical intermediates were presumably involved in the rearrangement process. They now report 3 1 that irradiations at 77K lead to a matrix which yields two e.s.r. spectra assignable to radical intermediates formed in the reaction. It is evident from this set of experiments that the reaction proceeds in a stepwise fashion via biradicals of the type shown in Scheme 6 . A study of the bridging selectivity shown in the compounds (60) has been reported (Scheme 7).33 The analysis of the reaction was carried out by spectroscopic means and the results are shown in Table 2. The preference for the type of bridging shown is dependent on the stabilization of the cyclopropyl radicals (61) and (62), i.e. whether the cyclopropane is stabilized or destabilized by the type of substituent at the bridgehead. A similar study has been carried out for the benzeno-bridged Compounds. Table 2 lists the findings. 31 32

33

K. Schaffner, M. Demuth, and D. Lernrner, J. Am. Chern. Soc., 1980, 102, 5407. M. Dernuth, C. 0. Bender, S. E. Braslavsky, H. Corner, V. Burger, W. Amrein, and K. Schaffner, Helv.Chim. Acta, 1979, 62, 847. M. Iwamura, H. Tukada, and H. Iwamura, Tetrahedron L x t i . , 1980, 21, 4865.

p:

Photochemistry of Olefins, Acetylenes, and Related Compounds /D

305

D

4

p

\

.COPh

I

\

J

P \C

--+ product

Scheme 7

(57) O (57)

P

h

Photochemistry

306 Table 2

Bridging selectivity for compounds (60a) and (60b) 3 3 Subs t it uent

(R2) Me0 AcO OCOPh But

Br Ph Ac Me CHO

Ethenoanthracene (604 path i path ii 0 100 0 100 0 100 0 100 0 100 100 0 29 71 29 71 12 88

Benzenoanthracene (60b) path ii path i 100 0 100 0 100 0 0 100 100 0 0 100 100 0 21 79 100 0

Prolonged irradiation of the tricyclic olefin (63) affords the spiro-compound (64) as the sole product.34 However, on shorter exposure times this compound is accompanied by the isomeric material (65). It is clear from a separate study that the irradiation of this dihydronaphthalene results in its conversion into the starting material (63). This compound (63) is also formed on irradiation of the isomeric compound (64) and (66). Both the products (64, 65) from the initial irradiation result from the migrations of the methylene unit on a methylene indene unit. Theoretical aspects are discussed.

Direct irradiation of the resolved ester (67) gave the optically active products (68-70), and the naphthalene (72). The two products (69) and (70) formally arise by 1,5-migrations of the methylene in both possible direction^.^' That the products obtained from these migrations preserved high optical purity is proposed

Bu'

(70)

(71)

as good evidence for the migration following the postulates of conservation of orbital symmetry and that the reactions occur with inversion of the configuration 34

35

H. E. Zimmerman and R. E. Factor, J . Am. Chem. Soc., 1980, 102, 3538. M. Kato, K. Takatoku, S. Ito, M.Funakura, and T. Miwa, Bull. Chem. SOC.Jpn., 1980, 53, 3648.

Photochemistry of Olefins, A cetylenes, and Related Compounds 307 of the migrating carbon. Irradiation of the diene (72) brings about a photochemical 1,5-sigmatropic migration to afford the product (73).36 The inversion in

(73)

(72)

configuration at the migrating carbon is as expected for a Woodward-Hoffman photochemically allowed process. However, the authors 36 raise the question of the applicability of the W.H. postulates to such a system since the thermal process also yields an inverted product. They 36 argue that a biradical intermediate could be involved since closure via a least motion pathway would lead to inverted configuration.

(74) a; R = Br b;R=CN c; R = OMe

(75)

Scheme 8

A study of the migratory aptitudes of aryl groups in the indenes (74) has been reported. 37 These results show that the substituted phenyl group migrates preferentially on triplet sensitization. The results obtained (Table 3) are broadly in Table 3 Migratory aptitudes for photorearrangement of indenes (74) 3 7 Indene (in hexane)

% Reaction

Ratio of (75):(76)

59

98:2 86: 14 95: 5

88 89

line with those obtained for other systems by Zimmerman et aL3* where a radicallike transition state was proposed. However, the present authors 37 have suggested an alternative interpretation that involves the intermediacy of an internal exciplex. Sensitized irradiation of the indene derivative (77) gives a quantitative yield of the cycloadduct (78).39An analogous product (79) is obtained from the irradiation of the indene (80). This product (79) is, however, accompanied by the two rearrangement products (81) and (82a). These products are thought to be formed by a 1,2-phenyl migration to afford the isoindene (83a), which thermally undergoes 1,5-hydrogen migrations to yield either (81) or (82a). The formation of the cycloadducts (78) and (79) is explained by crossed addition of the olefin unit to 36 3’

” j9

W. T. Borden, J. G. Lee, and S. D. Young, J. Am: Chem. SOC.,1980, 102,4841. C. Manning, M. R. McClory, and J. J. McCullough, J . Org. Chem., 1981, 46,919. H. E. Zimmerman, R. D. Rieke, and J. R. Scheffer, J. Am. Chem. Soc., 1967, 89. 2033; H. E. Zimmerman, R. C. Hahn, H. Morrison, and M. C. Wani, J . Am. Chem. Soc., 1965,87, 1138. A. Padwa and M. Pulwer, J. Am. G e m . SOC.,1980, 102, 6386.

308 Photochemistry the indene double bond. This behaviour is common in the photochemistry of hexa1,5-diene~.~' This crossed mode of cycloaddition is not followed by all the systems studied. Thus irradiation of the indene (84) gave the cycloadduct (85) as well as the rearranged indenes (82b) and (83b). An analogous adduct (86) is obtained from

@ \ $?R@R

\

Me H (81)

Me (82) a; R = H b; R = Me

Me (83) a; R = H b;R=Me

irradiation of the isomeric indene (87). The cycloadduct is presumably formed via the intermediacy of the biradical(88) since in this latter case it is accompanied by the olefin (89), which is presumably formed by disproportionation within the biradical (88). The cyclopropene (90a) undergoes dimerization to (9 1) when irradiated in benzene or hexane with Pyrex-filtered light.41 When the irradiation was carried out in the presence of a triplet quencher the dimerization product is absent and a new product (92a) is formed. A bicyclohexene (92b) is also formed from the irradiation of the cyclopropene (90b). The authors 4 1 suggest that the most likely route to these products is via an intermediate carbene (93). Further evidence for the existence of the carbene was obtained by trapping experiments in methanol 40 41

see W. L. Dilling, Chem. Rev., 1966, 66, 373. A. Padwa, T. J. Blacklock, R. Loza, and R. Polniaszek, J . Org. Chem., 1980, 45, 2181.


(90) a; R = H b; R = Me

(95)

(91)

(92) a; R = H b; R = Me

(93)

(97)

(96)

309

(98) a; R = H b;R=Me

Ph

when (94) and (95) were isolated from (90b). The behaviour of other cyclopropenes (96, 97) was also studied and these gave the indenes (98, 99) on direct irradiation. Under sensitized conditions the [2 21-adduct (100) was formed from (97). Direct irradiation of the cyclopropene (101) affords the two products (102) and (103): Scheme 9. The bicyclohexene (102) is likely to be formed from the

+

Ph

Ph

addition to the double bond of the carbene analogous to (93).42 A carbene mechanism is also thought to be involved in the formation of the butadiene product (104) obtained along with other products (Scheme 10) from the irradiation of (105).42 Diphenylcyclopropenes (106-108, Scheme 11) have been shown to quench the fluorescence of 9, lO-di~yanoanthracene.~~ When these compounds are irradiated in the presence of the anthracene, reaction products are obtained that are different from those obtained by either direct or triplet-sensitized irradiation. The route to products (Scheme 11) fits best with an electron-transfer process from the 42 43

A. Padwa, T. J. Blacklock, D. M. Cordova, and R. Loza, J. Am. Chem. SOC.,1980, 102, 5648. A. Padwa, C. S. Chou, and W. F. Riecker, J. Org. Chem., 1980,45, 4555.

Photochemistry

310

Ph

Me

Ph

Me Ph

Me

Scheme 10

Ph Ph +

@ph

Et

-k

&Ph

i&Ph

Ph

Me

Ph Et

Scheme 11

cyclopropene to the anthracene. The products formed are thus derived from reaction of the radical cation (e.g., 109-1 10). Sensitized irradiation of the arylcyclopropene (1 1 1) results in hydrogen abstraction to produce the intermediate biradical (1 l 2).44 This biradical can either undergo bond formation to yield (1 13), the principal product, or else undergo conversion into (1 14) which yields the minor product (1 15). The absence of dimethyl stabilization of the benzylic part of the biradical [derived from (1 16d)l affords a readily reactive species that exclusively cyclizes to (1 17) without ring opening. With the unsymmetrical cyclopropene (1 18) sensitized irradiation affords only the cyclized product ( I 19) clearly showing that hydrogen abstraction has resulted in the formation of biradical(120). The reaction is thus stereospecific with hydrogen transfer only to the methyl-bearing carbon. A similar study has been

31 1


m

Ph Me

Ph /

(121) R' = Ph, R2 = Me R' = Me, R2 = Ph

(122)

carried out on the alkyl derivatives (121). In these cases hydrogen abstraction appears to follow the same path with the formation of a biradical prior to cyclization and the formation of the final product (122). The influence of deuterium substitution on the reaction has shown that deuterium ends up in the expected endo-position of the product (123-1 24).44

Ph (1 23)

( 124)

Streith and Nastasi 45 have reviewed the photoreactions of three-membered rings. A study of the photo-ring-opening reactions of the azirines (125) has been reported.46 A CIDNP study of photoelectron transfer from cis- and trans-1,Z The evidence collected diphenylcyclopropane to chloranil has been carried from this study indicates that the intermediate involved is the radical cation (126), since no polarized rearrangement product was observed. The failure to observe reaction is in marked contrast to the behaviour when the cyclopropane is irradiated in the presence of 1,4-di~yanonaphthalene.~* 44 45

46

47 48

A. Pddwa and C. S. Chou, J. Am. Chem. SOC.,1980. 102, 3619. M . Nastasi and J. Streith, Org. Chem., 1980, 42, 445. K. Dietliker, W. Stegmann, and H. Heimgartner, Heterocycles, 1980, 14,929 (Chem. Abstr., 1980,93, 238 239). H. D. Roth and M . L. M. Schilling, J . Am. Chern. SOC.,1980, 102, 7956. P. C. Wong and D. R . Arnold, Tetrahedron Lett., 1979, 2101.

Photochemistry

312

PiPh-N (125)

( 126)

Srinivasan and his co-workers 49 have continued their study of the behaviour of olefinic compounds when irradiated at 185 nm (6.7 eV photons). The irradiation of (127) under such conditions gave the diene (128) and the internal cycloaddition product (129) as the only detectable volatile products. The irradiation of the endoadduct (130) also gave the diene (128) and the same cycloadduct (129) but in addition the di-n-methane product (1 3 la) was observed. This compound had previously been shown to result from irradiation of the diene (128).” Separate direct irradiation of this diene (128) also revealed that the other di-n-methane product (131b) was also formed at high conversions. The principal product from the irradiation of the endo-olefin (1 32) was the diene (133) and the adduct (1 34).

Several minor products were also detected but not identified. The exo-isomer (135) yielded the adduct (134) with no trace of the diene (133). Again several minor products were detected. A theoretical analysis of these systems was r e p ~ r t e d . ~ ’ Fission of a cyclopropane bond also occurs following the irradiation (254nm) of the tricyclohexene (1 36) in ethanol. The products formed are shown in Scheme 12. The dependence of the amounts of product on irradiation time showed that products (1 37 and 138) are the primary photoproducts and that the others are derived by secondary phot~lysis.~ 49

R.Srinivasan, J. A. Ors, K . H. Brown, T. Baum, L. S. White, and A. R. Rossi, J . Am. Chem. SOC.,

50

1980, 102, 5297. R. R. Sauers and A. Shurpik, J . Org. Chem., 1968, 33, 799.. A. P. Kouwenhoven, P. C. M. van Noort, and H. Cerfontain, Tetrahedron Lett., 1981, 22, 1745.

51

Photochemistry of Olejins, Acetylenes, and Related Compounds

& &

+

R' = H, R2 = Me =

products 2 unidentified

+

---+

R'

313

R' = OMe, R 2 = H R' = H,R 2 = OMe

Me, R' = H

Scheme 12 Patents have been lodged dealing with the photoconversion of the dihydrofurans (139) into the cyclopropane derivatives (140).5 2 * Intramolecular cycloaddition was not encountered during the photolysis of the 1,3-divinylcyclobutane (141a). The products formed from the reaction were identified as the cyclopropanes (142). With the substituted compounds (141b) only

R 0 2 C Me Me a

M

X x ( 139)

q

c

CO,R

X = CI or Br R = H or Me

(140)

JdR g

R-

R'

R/RR2

R = H,n = 1 b; R = C02Me, n = I c; R = CO,Me, n = 2

(142) R ' = CH=CH,, R 2 = H R' = H, R2 = C H S H ,

(14)

(1 45)

(141) a;

k

(143) a; R' = R = C02Me, R 2 = H b; R' = H, R = R2 = C 0 2 M e

cis-trans isomerization results in the formation of ( 143).54Increase in the ring-size to the cyclopentane derivative (141c) brings a profound change in the photoreaction and this molecuIe yields the [2 + 21-adducts (144, 145). 52

53 54

H. G . Schmidt, Ger. Offen., 2851 957 (Chern. Abstr., 1981, 94, 3785). H. G. Schmidt, USP, 4 198341 (Chern. Abstr., 1980, 93, 71 536). W. Trautrnann and H. Musso, Chem. Ber., 1981, 114, 982.

Photochemistry

314

The direct irradiation of the anion (146) using visible light (A > 450nm) leads to the formation of the cyclized product (147) formed by protonation of (148) and the formation of a polymer of undetermined c o n ~ t i t u t i o nWhen . ~ ~ the irradiation was carried out in the presence of benzophenone, thought to act as an electrontransfer agent, a quantitative yield of the cyclopropyl derivative (147) was obtained.

3 Diene Isomerization Baldry 5 6 , 5 7 has studied the influence of aryl substituents on the photoreactions shown by arylbutadienes (149). The author 5 6 * 5 7 concludes that the formation of the products (150), (151), and (152) correlates with the ground-state CT or CT’ substituent constant rather than with the excited-state constant nex.The mechanism for the formation of the products (150-1 55) was also discussed. Product (153) A

r

w

( 149)

Ar

Ar

=

% ( 1 50)

Ph, 3-MeC,H4, 4-MeC,H4, 2,4,6-Me,C6H,, 3-C1C,H4, 4-ClC6H4, 3-MeOC,H4, 4-MeOC,H4, or 4-Me2NC,H, A

r (151)

G

A

r

d

e

(152)

presumably arises by valence-bond isomerization of the diene. This is also reported 5 8 for the formation of (1 56) from 2,3-dimethylbuta-l,3-diene. In an effort to mimic the conditions encountered in ‘in vivo’ irradiation in the epidermis, the irradiation of 7-dehydrocholesterol (157) in various ordered lipid multilayers has been studied.59The results (Table 4 and Scheme 13) clearly show ” J6 57

59

D. H. Hunter and R. A. Perry, J. Chem. SOC.,Chem. Commun., 1980, 877. P. J. Baldry, J. Chem. SOC.,Pwkin Trans. 2, 1980, 805. P. J. Baldry, J. Chem. SOC.,Perkin Trans. 2, 1980, 809. A. V. Dolidze, M. V. Kodanashvili, and Kh. I. Areshidze, Izv. Akud. Nuuk. Gruz. SSR, Ser. Khim., 1980, 6 , 88 (Chem. Absrr., 1980,93, 149839). R. M. Moriarty, R. N. Schwartz, C. Lee, and V. Curtis, J. Am. Chem. SOC.,1980, 102, 4257.

Photochemistry of Olefins, Acetylenes, and Related Compounds Table 4 Products from irradiation of (1 57) in lipid multilayers System Dilauryl-L-a-phosphatidylcholine Distearyl-L-a-phosphatidylcholine Dimyristoyl-L-a-phosphatid ylcholine Dipalmitoyl-L-a-phosphatidylcholine Thin film Hexane solution

Filter quartz Pyrex quartz Pyrex quartz Pyrex quartz Pyrex quartz Pyrex quartz Pyrex

315

’’

(157)

(158)

(159)

(160)

(161)

(%I

(%I

(%I

(%I

(%)

88.1 82.8 89.2 83.3 85.2 81.9 88.5 81.9 96.4 100 27.2 46.4

8.2 6.45 7.0 6.15 9.2 6.3 7.2 6.2 2.7 0 20.7 21

0.6 0.43 0.87 0.97 1.9 1.1 1.3 1.3 0.87 0 4.9 3.3

0.95

2.1 7.9 2.0 6.7 2.7 9.1 2.2 8.5 0 0 2.1 8.5

2.4

0.9 2.8 1.0 1.6 0.6 1.9 0 0 44.9 19.9

(159)

1. i HO

HO’

the difference between the lipid reactions and the thin-film process in that conversions are lower in the thin film and the products (160) and (161) are absent. Irradiation in hexane solution shows that tachysterol(l60) is the major product, whereas in the lipid material this product is minor. The authors5’ suggest that the membrane effect discernible in these experiments is due to the influence on the opening of the starting material to the triene (1 58). Since rotation is restricted in the membrane conversion to (158) and (1 60) is disfavoured. The irradiation of the dehydrocholesterol analogues (1 62) results in the formation of the ring-opened vitamin D,

316

Photochemistry

compounds (163).60The ring-opening process and the 1,7-antarafacial hydrogenmigration path is the same as that encountered in the transformation of the parent. Further work by Moriarty and Paaren61 has included the study of the stereochemistry of the photochemical-thermal conversion of dehydrocholesterol into vitamin D,. They61 argue that the key to the stereochemical problem is the thermal 1,7-hydrogen transfer and have approached its solution by the synthesis of the deuterium-labelled dehydrocholesterol (164). Irradiation and thermal transformation affords the vitamin D, (165) with 26.4% hydrogen in the C-l9(Z) position. They argue that this transformation can only arise from a left-handed conformation of the triene (166) produced by photochemical ring-opening of the diene starting material.

&R

R '0 (162) a; R' b; R'

= R2 = Ac = Ac, R2 =

Me

Irradiation of 7,8-didehydrocholesterol (167) at 3 10-3 12 nm gave the previtamin D, (168, 20.4%),lumisterol, (169, 5.979, and vitamin D, (1 70, 69.7%).62 The position of the photoequilibrium between the cis- and the trans-isomer of vitamin D is dependent upon the energy of the triplet sensitizer employed.63 Vycor-filtered irradiation of the diene (1 67) in pentane afforded the triene (168) in a photoequilibrium of diene: triene 30: 70.64 When the diene (167) was irradiated at 270-330nm the triene was absent and the product was identified as the tricyclononene (169). Normally the diene (167) was prepared in situ by the decarbonylation of the ketone (170). This afforded a ready method for the preparation of large quantities of the diene and also permitted the successful " 61

62 63

'4

R. M. Moriarty and H. E. Paaren, J . Org. Chem., 1981,46, 970. R. M. Moriarty and H. E. Paaren, Tetrahedron Lett., 1980, 21, 2389. R. I. Yakhimovich and V. P. Vendt, Khim.-Farm. Zh., 1980, 14,93 (Chem. Abstr., 1980,93, 46993). J. W. J. Gielen, R. B. Koolstra, H. J. C . Jacobs, and E. Havinga, Red. Truv. Chim. Pays-Bus, 1980,99, 306. W. G. Dauben and M. S. Kellogg, J . Am. Chem. SOC.,1980, 102,4456.

317

Photochemistry of Olejins, Acetylenes, and Related Compounds 0

completion of preparative runs. At high conversions another product was isolated and identified as the cyclononene (171). The authors 64 endeavour to explain the wavelength dependence of the system as a result of facile closure of the triene (168) back to starting material. However, an additional feature of the system would suggest that the cyclohexadiene ring in (168) will be skew rather than planar. The temperature-dependent photochemistry of the system is in accord with this since the efficiency of ring-opening (167-1 68) increases with decreasing temperature. This is a further example of the control exercised on the photochemical reactivity of a molecule by the ground-state conformation. A reinvestigation of the photoreaction of (172) has shown that it is converted into the two products (173) and (174). The absence of (175) or (176) contrasts with the behaviour of diene (167). The reactions of the diene (172) did not show a wavelength dependence. The

&I$-J($J~(y \

H

H

H

(1 72)

( 173)

( 174)

(175)

(176)

two photoproducts formed from the irradiation of the diene (1 77) were identified as (178) and (179). The wavelength dependence of this system is not as marked as

H (177)

(1 78)

(1 79)

that seen for diene (167). However, it was seen that the irradiation at shorter wavelengths favoured the formation of the triene (178). In another study Dauben and Olsen 6 5 have further studied the question of ground-state conformation control of the photo-ring-opening of cyclohexadienes. They propose that ringopening will follow the path that involves the least motion. The ring-opening reactions of the dienes (180) and (181) are in accord with this postulate and yield the trienes (182) and (183), respectively. These trienes are very thermally labile and convert readily into (172) and (1 84). The diene (185), however, has been shown to yield the all-cis-triene (186). The authors 6 5 argue that the path followed by this diene (185) is dictated by the strain inherent in the bicyclic structure. The photochemical ring-closure of the trienes (182) and (183) afford the starting materials. However, triene (186) also yields the photoproduct (187). Dauben and 65

W. G . Dauben and E. G. Olsen, J . Org. Chem., 1980,45, 3377.

318

Photochemistry

rn

&& H

H

H

H

(1 84)

(1 85)

( 182)

QH

(1 86)

(187)

his co-workers 66 have published a review dealing with the photorearrangements of trienes. Direct irradiation at 254 nm of the acetal(l88) leads to two reaction modes, viz, valence-bond isomerization to yield (189, 3%), and bond fission to yield the Me Me

Me Me

0 1

0

Me

Me

(188)

M@Me

Me Me

(190)

(189)

biradical(l90) which ultimately affords products (191,4%E and 60x2).Acetonesensitized irradiation of (188) yields the same enones (191) as 2 - E isomers in 7% Me Me

Me

Me Me

0

(193)

(20%)

Me

254 nrn

CHz (9%)

(3%)

(10%)

(34%)

Scheme 14 66

W. G . Dauben, E. L. McInnis, and D. M. Michno, Org. Chem., 1980, 42, 91.


319

and 3%, respectively, as well as a low yield (9%) of the ketone (192).67A study of the photochemical behaviour of the acetal (193) was also carried out and direct irradiation was shown to yield the products indicated in Scheme 14. Irradiation of the sultone (194) in methanol affords the ring-opened products (195) and (196).68 Subsequent irradiation of these compounds brings about elimination of the S0,Me group and formation of the fluoranthene (197). This compound is thought to be the result of cyclization within the anion (198).

4 Reactions of Trienes and Higher Polyenes Direct irradiation of the benzcycloheptene (199a) gave the two isomeric products (200) and (201) in a temperature- and solvent-independent ratio of 95 : 5.69 The influence of substituents was obvious from the fact that the irradiation of (199b) exhibited solvent dependency and the yield of the products (200) and (201) showed an increasing predominance of the endo-product. The sensitized irradiation was less efficient.

\

/

-

(199) a; R' = CH,CO,Me b; R' = CN

(200)

Arnold and his co-workers 70 have reported the electron-transfer-induced photodimerization of 1,l-diphenylethylene. This reaction is thought to proceed to the triene (202a) which, in the absence of other reaction paths, undergoes hydrogen migration to afford the product (203).70When the reaction is carried out 67 69 'O

K. Murato, B. Frei, H. R. Wolf, and 0. Jeger, ffelv. Chim. Acra, 1980, 63,2221. J. L. Charlton and G. N. Lypka, Can. J. Chem., 1980, 58, 1059. H. Kobayashi, K. &to, M. Kato, and T. Miwa, Koen Yoshishu-Hibenzenkei Hokozoku Kagaku Torunkai Kozo Yuki Kadaku Toronkai,12th, 1979, 13 (Chem. Abstr., 1980, 92, 214528). D. R. Arnold, R. M. Borg, and A. Albini, J. Chem. SOC.,Chem. Commun., 1981, 138.

320

Photochemistry

a

in the presence of acrylonitrile, for example, the triene is trapped as the ene-adduct (204a). An analogous reaction sequence affords the adduct (202b) from the crossed addition of 1,l-diphenylethylene with methylpropene.

Ph Ph

RR (202) a; R b; R

@2CH2CN

=

Ph

=

Me

R R (204) a; R = Ph b ; R = Me

(203)

A study of the photoequilibrium involving 1,5-hydrogen transfer between the isomeric cycloheptatrienes (205a) and (205b) has been r e p ~ r t e d .The ~ influence of substitution in the aryl ring, e.g. (206), has also been studied.'* Irradiation of the diazepins (207) affords the bicyclic compounds (208).73This result, valence-bond isomerization, is in contrast with the thermal treatment of this compound which yields the 1,3-diazepins (209). These compounds undergo photochemical ring-closure to yield the bicyclic compounds (210). In some instances the bicyclic compounds of similar structure to (210) are also photolabile, as with (21 I), which on irradiation (254nm) yields the acetylene (212) and the imidazole (2 13). 74 R Q - R ' /

R3 (205) a; R ' = p-NMe,C,H,, R2 = C,H,, R 3 = H b; R' = H, R 2 = C,H,, 'R3 = p-NMe2C6H,

(206) R = H, F, C1, Br, Me, MeO. MeOC,H,CH=CH

C02Et (207) R ' = Me, R2 = H; R' = H, R2 = Me; R' = OMe, R2 = H; R' = H, R2 = OMe; R' = Me, R2 = Me; R ' = NHAc,R2 = H; R' = H , R 2 = NHAc;R' = NEt,, R Z = H

(208) 71

'' 73 74

(209)

(210)

W. Paulick, W. Abraham, and D. Kreysig, J . Prakt. Chem., 1980,322, 499 (Chem. Abstr., 1980, 93, 238 404). W. Abraham, K. Buck, and D. Kreysig, Z . Chem., 1980, 20, 214 (Chem. Abstr., 1980, 93, 238394). T. Tsuchiya, J. Kurita, and H. Kojima, J . Chem. Soc., Chem. Commun., 1980, 444. Y. Kobayashi, T. Nakano, M. Nakajima, and I . Kumadaki, Tetrahedron Lett., 1981, 22, 1369.

Photochemistry of Olefns, Acetylenes, and Related Compounds

(2 12)

(21 1)

321

(213)

Irradiation of perfluorocyclo-octatetraeneat 254 nm yields the anti- and syndienes (214) and (215).75 The ions (216) can be prepared by protonation of the corresponding 2,3homotropones in fluorosulphonic Irradiation (A > 360 nm, - 70 "C) of the ions leads to their isomerization. The selectivity shown in the photoisomerizations is attributed to the circumambulatory migration of the C-8 group via intermediates such as (2 17-2 19). Photoisomerization about the C- 1 - 4 and about the C-2-C-3 bond of the ally1 cations (220-222) has been r e p ~ r t e d : 'cf ~ the earlier preliminary report. 78 Childs 79 has reviewed the photochemical reactions of protonated unsaturated compounds.

I

I(

R2

R2

OH

R'

= R2 = H (217) b; R' = R2 = Me c; R' = Me, R2 = H

(216) a;

(220)

(2 18)

(22 1)

(219)

(222)

Barltrop et a1." have reported a study of the phototranspositions of alkylsubstit uted pyrylium cations. Sugawara and Iwamura have reported the photoproduction of the nitrene

''

75

A. C. Barefoot, tert., W. D. Saunders, J. M. Buzby, M. W. Grayston, and D. M. Lemal, J. Org. Chem., 1980, 45,4292.

76 77

78

l9 8o

*'

R. F. Childs and C. V. Rogerson, J . Am. Chem. Soc., 1980, 102, 4159. R. F. Childs and M. E. Hagar, Can. J . Chem., 1980, 58, 1788. R. F. Childs and M. E. Hagar, J . Am. Chem. SOC.,1979, 101, 1052. R. F. Childs, Rev. Chem. Intermed., 1980, 3,285 (Chem. Abstr., 1980, 93,203427). J. A. Barltrop, A. W. Baxter, A. C. Day, and E. Irving, J . Chem. Soc., Chem. Commun., 1980, 606. T. Sugawara and H. Iwamura, Kokaguku Toronkai Koen Yoshishu, 1979,78 (Chem. Abstr., 1980,93, 70 605).

322

& /

Photochemistry

/ \ - ,

NC

(223) from azatriptycene (224). The nitrene yields the azepine (225) and the adduct (226) when the reaction is carried out in the presence of tetracyanoethylene. 5 12

+ 21 Intramolecular Additions

Photocyclization of the methylenenorbornadienes (227a) and (227b) yields the quadricyclanes (228), which can be converted by ozonlysis into the two quadricyclanones (229).82The thermal cyclQadduct (230), obtained from the furan (23 1) and cyclo-octyne (232), undergoes photocyclization to yield the oxa-quadricyclane derivative (233).83This compound undergoes thermal conversion to the oxepin

Pr (227) a; R'-R' b; Rl-R'

=

(CH,),, R 2 = C 0 2 M e , R3 = H R 2 = H, R3 = CO,Me

= (CH,),,

AR3

Pri

83

H . P. Figeys, M. Destrebecq, and G . Van Lommen, Tetrahedron Lerr., 1980, 21, 2369. W. Tochtermann and P. Rosner, Tetrahedron Lett.. 1980, 21, 4905.


323

derivative (234). The influence of a coppper(1)-nitrogen catalyst on the conversion of norbornadiene to quadricylane has been assessed.B4A kinetic study of the behaviour of quadricyclane as an electron donor has been reported.85 Photocyclization of the alcohols (235) in the presence of ‘copper triflate’ has been reported to yield the products (236).86 The stereochemistry of the alcohols was not fully established but the results are interesting in that the stereochemistry of the hydroxy- group does not seem to play a major part in the reaction since either of the two isomers cyclize readily. The authorsB6 suggest that the coordinated copper ion is not intimately involved in the transition state leading to product. Irradiation of the dienes (237) and (238) brings about ring closure to the propellanes (239) and (240), respectively.” Irradiation of the related diene (241) gave only the isomeric compound (242) by a 1,3-hydrogen migration. The

84

K. Maruyama, K. Terada, Y. Naruta, and Y. Yamamoto, Chem. Lett., 1980, 1259 (Chem. Absfr.,

85

G. Jones, 11, S, Chiang, W. G. Becker, and D. P. Greenberg, J . Chem. SOC.,Chem. Commun., 1980,

86

J. E. McMurry and W. Choy, Tetrahedron Lett., 1980, 21, 2471. R. Bishop and A. E. Landers, Aust. J . Chem., 1979,32, 2615.

1981, 94, 64866). 681. 87

324

Photochemistry

Me Me (243A)

M;:

Me Me

Me (243B)

'Me

V

Me

Me

(243C)

1

IVY/

Me

Me

Scheme 15 X

I b*

14 (249)

eH2-

X = 0, N H , NMe, or NPh

Y = - CH,

Me

Photochemistry of Olefins, Acetylenes, and Related Compounds 325 germacrene system (243)afforded the products shown in Scheme 15.88 The type of cyclization mode adopted depends on the ground-state conformation. Thus conformation (243A)yields the adduct (244)whereas (243B) leads to the three products (245),(246),and (247),and conformation (2436)gives (247)and (248).89 Ashkenazi et al.'* have reported intramolecular cycloaddition in the cyclic structure (249) to afford the cycle of cage molecules (250).

6 Dimerization, Intermolecular Cycloaddition, and Reactions of Acetylenes The three dimers (251-253) are formed from the xylene-sensitized irradiation of cyclohexene. Regardless of the solvent used, the cis-trans-product (252) predominates. It is reasoned that the dimers are produced by a non-stereospecific

& & H H

H H

(25 1)

(252)

(253)

addition of cis- and trans-cycl~hexene.~~ Cycloheptene fails to yield dimers under the same condition. Various cyclobutane derivatives have been synthesized by the direct or sensitized irradiation of indene as shown in Scheme 16.The compounds were required for a detailed study of the electron-transfer-induced monomerization of the ad duct^.^^

Indene

I1 I'

& ' H

Illdene

h

F

13

X

Ph

H I

Scheme 16 The two adducts (254) and (255) are formed from the irradiation of trans93 The two adducts are stilbene in the presence of trans-3-phenylacrylonitrile. themselves photolabile and are converted into cis- and trans-stilbene and cis- and 88

89

90 91

92 93

P. J. M. Reijnders, R.G. van Putten, J. W. De Haan, H. N. Koning, and H. M. Buck, Red. Trav. Chim. Pays-Bas, 1980,99, 67. See also references 64-66 for other examples of conformational control. P. Ashkenazi, R.D. Macfarlane, W. A. Oertling, H. Wamhoff, K. M. Wald, and D. Ginsburg, Angew. Chem. Int. Ed. Engl., 1980, 19, 933. P. J, Kropp, J. J. Snyder, P. C. Rawlings, and H. G. Fravel, jun., J. Org. Chem., 1980, 45, 4471. T. Majima, C. Pac, and H. Sakurai, J. Am. Chem. Soc., 1980, 102, 5265. T. Kitamura, S.Toki, and H. Sakurai, Kokaguku Toronkai Koen Yo'oshishu,1979, 190 (Chem. Abstr., 1980,93,70806).

Photochemistry

326

trans-3-phenyiacrylonitrile.The authors 93 suggest that the steric interactions of the phenyl groups in (255) are greater than in (254). The regiospecific photocyclization of olefins (256) to cyanophenanthridine (257) yields the two adducts (258) and (259).94Photoaddition of 2-cyanopyridine to olefins affords the readily hydrolysable imines (260) isolated as the ketones (26 l).95

ph\dPh

ph\qPh Ph

Ph'

CN

'CN

(255)

(254)

(256) R'CH = CHR2 R' = R 2 = p-MeOC,H,, Me, PhO, or H

(257)

& NH

0

~

The benzophenone-sensitized addition of chlorofluoro-olefins (262) to indene has been The identity of the adducts (263) was established by detailed spectroscopic analysis. The mechanism of the addition is believed to involve biradicals such as (264). R'

R3

X

&jl \

y4

9s 96

*cCl, W \

L

F

2

H

S. Futamura, H. Ota, and Y. Kamiya, Chem. Letf., 1980, 655 (Chem. Ahstr., 1980, 93, 238631). I. Saito, K. Kanehira, K. Shimozono, and T. Matsuura, Tefruliedron Lett., 1980, 21, 2737. H . Kimoto, K. Takahashi, and H . Muramatsu, Bull. Chem. SOC. Jpn., 1980, 53, 764.

Photochemistry of OleJins, Acetylenes, and Related Compounds

327

Caldwell 9 7 has reported a method for the prediction of reactivity for allowed + 21 and [4 41 cycloaddition reactions. The triplet state of the alkyne (265) is involved in the photochemical reactions with di-isopropyl ether. The proof that a triplet is involved was obtained from quenching and sensitization studies. The products (266, 267) obtained from the reaction arise from hydrogen-abstraction and radical-combination reaction^.'^

+

[2

w~~

HC ECC0,Me

C0,Me

(265)

(266)

M e OMe k Me c o 2 M e (267)

The irradiation of benzisothiazole (268) in the presence of dimethyl acetylenedicarboxylate is thought to proceed by initial N-S fission to yield the biradical intermediate (269, Scheme 17). This intermediate is trapped by the acetylene to

(268) a; R ' = H , R2 = H b; R ' = H, R2 = CI C; R ' = CI, R 2 = H

(270)

CN (271 j

Scheme 17 yield the cis-trans mixture of esters (270) and the thiophen (271) as the main products of a complex reaction mixture. The details of the formation of products are shown in Scheme 1 7.99 With electron-rich-olefins, however, cycloaddition occurs with benzisothiazole (272) to yield the adduct (273), again as a result of trapping of a biradical such as (269).'0°

R'

"

,

d

R'

N

= R2 = H b; R' = Me. R2 = H C; R' = H . R 2 = C1

(272) a; R '

'9 98

99 loo

R. A. Caldwell, J . Am. Chem. SOC.,1980, 102, 4004. H. Hasegawa, A. Kimura, and M. Takayama, Wusedu Daigaku Rikoguku Kenkyusho Hokoku, 1979, 44 (Chem. Abstr., 1980, 92, 163 327). M. Sindler-Kulyk and D. C. Neckers, Tetrahedron Left., 1981, 22, 525. M. Sindler-Kulyk and D. C. Neckers, Tetruhedron Left., 1981, 22, 529.

328

Photochemistry

7 Miscellaneous Reactions The photochemical reversion of the cage compound (274) into the diene (275) has been studied by Mukai and his co-workers."' The process can be brought about by various catalysts such as ZnO or CdS. These experiments are related to the utilization of strained cage compounds as a means of energy storing. Mukai et al. l o 2 have further reported on their detailed study of the cycloreversion reactions of cage compounds (276) involving electron-transfer processes. Another report has described work with cationic sensitizers (277).'03

The cycloreversion of the cyclobutane (278) to the olefin occurs from the singlet state on irradiation at 265 nm. '04 Triplet-state reactivity is reported for cycloreversion using A = 347 nm. The isomerization of 1,2-diphenylcyclobutaneshas been used as a means of establishing the efficiency of electron-transfer processes in the phenanthreneedicyanobenzenesystem. l o 5 Meier and Kolshorn lo6 have reported the results obtained from a study of the conversion of oxirens and thiirens to the open-chain isomers. Photochemical rearrangement of the epoxyolefins (279, 280) gives the dihydrofuran derivatives (281, 282).'07 Direct irradiation of the epoxydiene (283) is reported to yield products derived from the fission of the C--C bond of the oxiran (Scheme 18). Other systems studied in this report are the trienes (284) and (285) whose photochemical behaviour is analogous to that reported for (283). Acetonesensitized irradiation of (289, however, yields products from the fission of a C - 0 Iol lo2

lo4 lo'

lo'

K. Okada, K. Hisamitsu, and T. Mukai, J. Chem. Soc., Chem. Commun., 1980, 941. T. Mukai, K. Sato, and Y. Yamashita, J. Am. Chem. Sor., 1981, 103, 670. K. Okada, K. Hisamitsu, and T. Mukai, Tetrahedron Left., 1981, 22, 1251. S. Takamuku and W. Schnabel, Chem. Phys. Lett., 1980, 69, 399. T. Gotoh, M. Kato, M. Yamamoto, and Y. Nishijima, J. Chem. Soc., Chem. Commun., 1981, 90. H. Meier and H. Kolshorn, Z. Nafurforsch., Teil B, 1980, 35, 1040 (Chem. Abstr., 1981, 94, 3515). W. Eberbach and J. C. Carre, Chem. Ber., 1981, 114, 1027.

Photochemistry of Olejns, Acetylenes, and Related Compounds

I-naphthyl

329

"C0,Me (278)

(279) a; R = H, fi = 1 b; R = CO,Me, n = 1 c; R = CO,Me, n = 2

(280)

(282)

(281) a; R = H , n = 1 b; R = CO,Me, n = 1 c; R = CO,Me, n = 2

bond (Scheme 19).lo8 C - 4 Bond fission also accounts for the photoinduced (254nm) formation of the ketone (286) from (287).lo9

(283)

Scheme 18

The regio- and stereo-selective ring opening of the oxaziridines (288) on photolysis to yield the lactams (289) has been reported.' l o The stereo-electronic

.

(286) lo'

lo9 'lo

(287)

-.

R

(288) n = 1, 2, 3, 4,8, 9; R = H n=Ior2;R=Me

A. P. Alder, H. R. Wolff, and 0. Jeger, Helv. Chim. Acra, 1981, 64, 198. D. Avnir and J. Blum, J. Heterocycl. Chem., 1980, 17, 1349. E. Oliveros, M. Riviere, and A. Lattes, N o w . J . Chim.,1979,3,739 (Chem.Abstr., 1980,92, 163 322).

330 Photochemistry control is due to rupture of a C--C bond that lies quasi-antiperiplanar to the nitrogen lone pair. The authors l o suggest that oxaziridines are intermediates in the photo-Beckman reaction. Irradiation of the chromene (290) in benzene afforded the styrene (291) and the ketene (292) which was detected by low-temperature i.r."' The presence of a ketene intermediate was confirmed chemically by irradiation of the chromene (290) in methanol when the ester (293) was obtained. The styrene photoproduct (291) is clearly a secondary product formed by the photodecarbonylation of the ketene to yield a carbene (294) which rearranges to the styrene. The route to the primary product (292) is thought to involve the conversion of the chromene into (295), which subsequently undergoes H or D transfer to affford the ketene (292). The o-xylylene intermediate (295) could not be trapped as a Diels-Alder adduct, presumably as a result of a rapid hydrogen-transfer process. The benzopyran (296) undergoes ring cleavage to yield (297) on irradiation in ethanol.'12 The product (297) is accompanied by the novel cyclized product (298), which is derived from (297) by a second photochemical step. The acetophenone-initiated reactions of tetrahydropyrans (299) have been described. l 3

Me

Me (290) R

=

H or D

(293)

Me (294)

Irradiation of the iodoalkane (300) in the absence of oxygen and with the removal of hydrogen iodide results in the formation of the alkene (301).'14 In contrast with this result, irradiation of the iodoalkene (302) yields a product from an ionic process. The reactions of the iodides (304-306) have been studied.' l 5 'I' 'I2

'I3

J. M . Hornback and B. Vadlamani, J . Org. Chem., 1980, 45, 3524. A. Bowd, J. Turnbull, and J. D. Coyle, J. Chem. Res. ( S ) , 1980, 202. B. W. Babcock, D. R. Dimmel, D. P. Graves, jun., and R.D . McKelvey, J. Org. Chem., 1981,46,736. J . L. Charlton, G . J. Williams, and G. N. Lypka, Can. J . Chem., 1980, 58, 1271. K. M . Saplay, R. Sahni, N. P. Damodaran, and S. Dev, Tetrahedron, 1980, 36, 1455.

Photochemistry of OleJins, Acetylenes and Related Compounds

331

I (300)

(301)

Quantum yields for the photodechlorination of insecticides of the type (307) have been obtained. Discussion of the mechanism in terms of C-CI bond fission and the generation of radical pairs was made.'16 Cristol and his co-workers ' I 7 have reported the results of the photolysis of the chloro-compounds (308). The results from this work have given an insight into the stereochemistry of the photochemical reactions.

(307) R

= CH=CH(CH,),,

n

= 1

4

(309) a; R = Br (308) a; R' = H, R 2 = C1, R 3 = H b; R = C1 b; R' = C1, R2 = H, R 3 = H c; R = OMe c; R' = H, R2 = C1, R 3 = M e 0 d; R = OEt d; R ' = H, R Z = R 3 = C1 e; R = OCHMe, f:R=OH

1-Haloadamantanes (309a, b) are formed from the ethers (309c-f) when they are irradiated in haloalkanes (CC1,Br or CCI,). ' 1 8 The phospholene (3 10) undergoes photofragmentation to afford 2,3dimethylbuta- 1,3-diene and (3 1 l ) , a product derived from the intermediate 'I6

'I7

'"

H. Parlar and F. Korte, Chemosphere, 1979,8, 873 (Chem. Abstr., 1980, 93, 70444). S. J. Cristol, R. J. Opitz, T. H. Bindel, and W. A. Dickenson, J. Am. Chem. Soc., 1980, 102, 7977. R. Perkins, Chem. Ind. (London), 1980, 700 (Chem. Abstr., 1981, 94, 83665).

332

Photochemistry

(312).'l9 The product (311) is also photolabile and is converted during the photolysis into the derivative (313). Irradiation of the cyclopentadiene (314) as a liquid or in solution a'ffords an 12' intermediate species identified as the free radical (31 Two reports have described the photochemical behaviour of triarylmethyl cations. 22* 5 ) . ' 2 0 9

5

Phi=S (312)

II PhP(OMe), (313)

Me

"'

IZo

H. Tomioka, S. Takata, Y. Kato, and Y. Izawa, J. Chem. SOC.,Perkin Trans. 2, 1980, 1017. A. G. Davies and J. Lusztyk, J. Chem. SOC.,Chem. Commun., 1980, 554. A. G. Davies and J. Lusztyk, J. Chem. SOC.,Perkin Trans. 2, 1981, 692. L. M. Tolbert, J . Am. Chem. SOC.,1980, 102, 3531. L. M. Tolbert, J . Am. Chem. SOC.,1980, 102, 6806.

4 Photochemistry of Aromatic Compounds ~

~

~~

BY J. D. COYLE

1 Introduction The interest in photoreactions that involve chemical change in an aromatic ring continues at a high level. Aromatic photosubstitution reactions have assumed a greater importance than they once had, but the classification of these reactions on a mechanistic basis is not easy because one of several different mechanisms may operate, and published information may not be sufficient to distinguish between the likely possibilities. However, it is clear that straightforward photochemical electrophilic substitution is as yet of very limited importance. Various thermal and photochemical rearrangements of the benzene ring have been reviewed including valence isomerization and ring transpositions, and, fairly briefly, a range of other reactions that can be classed formally as rearrangements.

2 Isomerization Reactions Valence-bond isomers of aromatic compounds (both 6-membered and 5-membered) that are stabilized by trifluoromethyl groups are reviewed,2 and it is concluded that both steric and electronic effects contribute to the stabilizing influence of the CF, group. A fascinating example is provided of a substituted Dewar benzene (1) that is more stable thermodynamically than the isomeric

'

BU'

Bu'

'".*B tu hv

+

CO,Me

Bu'

"'Q:g:;: Bu'

Bu'

(1)

benzene; the benzene can be generated by irradiating the Dewar benzene. Gasphase photoisomerization of trifluoro- and tetrafluoro-benzenes and of a tetrafluorotoluene gives mainly Dewar isomer^.^ However, the high-temperature ( > 1000 "C) thermal ring-transposition reactions of the three difluorobenzenes D. Bryce-Smith and A. Gilbert, in 'Rearrangements in Ground and Excited States', ed. P.de Mayo, Academic Press, New York, 1980, Vol. 3, p. 349. Y. Kobayashi and I. Kumadaki, Ace. Chem. Res., 1981, 14, 16. G. Maier and K. A. Schneider, Angew. Chem., Int. Ed. Engl., 1980, 19, 1022. B. Sztuba, E. Ratajczak, M. Pieniazek, A. Grzybala, and R. Janusz, Bull. Acad. Pol. Sci., Ser. Sci. Chim., 1979, 27, 581.

333

334

Photochemistry F

Q+pJ:.Q,;.l

F

F

QF=(J F

(2)

(e.g., 2) can best be rationalized5 on the basis of a benzvalene mechanism or something equivalent to it; one source of uncertainty in these results is that defluorination and polymerization occur to a large extent as competing processes. A theoretical description (based on INDO/S calculations) of the benzene-toDewar benzene isomerization suggests that the photoreaction is more likely to occur through a singlet state (which is in keeping with an earlier report that reaction occurs via S 2 benzene), although the thermal re-aromatization of Dewar benzene may give a small yield of triplet ( 3 B 1 , )benzene. On irradiation in solution 9-t-butylanthracene, unlike other 9-substituted anthracenes, gives a Dewar isomer (3), which reverts thermally to the parent anthracene (t+at 20 "C = 6.5 h).' Although the quantum yield is low (4 0.01), the absorption properties of this system make it more suited to further study for possible use in solar energy storage than many other photoisomerizations.

-

&

A , (3)

6

- 0.01

Photocyclization of the phenalenyl carbanion (4) can also be effected by visible light (A > 450nm), and the yield of the cyclized isomer is quantitative in the presence of benzophenone,8 which acts to suppress the competing electrontransfer and polymerization process. A pentafluoro-Dewar-pyridine, tentatively assigned the structure (5), has been isolated in very low yield from the complex mixture obtained in about 400 photolyses of pentaflu~ropyridine;~ its half-life is about 5 days at room temperature. Flash photolysis studies of pentafluoropyridine provide evidence for two azafulvene isomers (6) and (7), and it is suggested9 that an aza-benzvalene is the precursor to both the fulvenes and the Dewar isomer, although this mechanistic argument is quite speculative. The first hetero-benzvalene to be isolated and

'

L. T. Scott and J. R. Highsmith, Tetrahedron Lett., 1980, 21, 4703. M. Tsuda, S. Oikawa, and K. Kimura, h t . J . Quanrum Chem., 1980, 18, 157. H. Guesten, M. Mintas, and L. Klasinc, J . Am. Chem. SOC., 1980, 102, 7936. D. H. Hunter and R. A. Perry, J . Chem. SOC.,Chem. Commun., 1980, 877. E. Ratajczak, B. Sztuba, and D. Price, J . Photochem., 1980, 13, 233,

335

Photochemistry of Aromatic Compounds

characterized is that from tetrakis(trifluoromethy1)-l74-diphosphabenzene(8), and this isomer is quite stable at room temperature. 4-Alkoxypyridin-2-ones (9) undergo efficient photoisomerization to give bicyclic compounds, which on heating give a mixture of the original 4-alkoxypyridone and an isomeric 6-alkoxypyridone. Unlike many other pyridin-2-ones, the alkoxysubstituted derivatives show no tendency to undergo efficient [4 + 41photodimerization, and this accounts for the high yields of photoisomers that can be achieved. Further papers have appeared dealing with the photochemistry of OR

H 80-92%

0 II

Me

M~NHCCH=C/ \

N =C\

Me /

OMe

Me lo

Y . Kobayashi, S. Fujino, H. Hamana, Y. Hanzawa, S . Morita, and I. Kumadaki, J . Org. Chem., 1980, 45, 4683. C. Kaneko, K. Shiba, H. Fujii, and Y . Momose, J. Chem. Soc., Chem. Commun., 1980, 1 177.

336

Photochemistry

pyrimidin-4-ones. The trimethyl derivative (10) gives a bicyclic photoisomer that cannot be separated from unreacted pyrimidinone; however, its chemistry has been investigated and products isolated that result from abstraction of the methine proton by base (MeO-) or nucleophilic addition to the imino-group by methanol or methylamine. 2 * Dimethylpyrimidinones have also been studied, l4 as has the bicyclic derivative (1 1) that eventually gives an eight-membered lactam, 1 2 - l4 and a closely related sulphur-containing bicyclic system (12). In a slightly different heterocyclic system, an oxaza-bicyclic species (13) is an intermediate in the reversible photoisomerization of oxazinones.

MeNH,

cj?

H2

H

10% Me0

Ph

NH2

(R,R' = Me, Ph) (1 3)

Phototransposition reactions of hydroxypyrylium salts have been studied extensively, and now the first report has appeared l 7 of the corresponding reactions of pyrylium salts with only alkyl substituents. The reaction is efficient only when both C-3 and C-5 bear an alkyl group, and this is interpreted in terms of either an oxoniabenzvalene primary product (14) that re-aromatizes thermally in a concerted manner, or an oxabicyclohexenyl cation (1 5) whose formation involves an activation energy that is sensitive to the stability of the cation. These results are consistent with others from the irradiation of the pyrylium salts in water, where alternative, photohydration products are formed. Photorearrangemen t s of 5-membered heterocyclic aromatics are reviewed by Padwa. * Thiophen and 2-phenylthiophen photorearrangements are the subject

''

l3 l4

l5 l6

18

Y. Hirai, T. Yamazaki. S. Hirokami. and M. Nagata, Tetrahedron Lett., 1980, 21, 3067. S. Hirokami. T. Takahashi. M. Nagata, Y. Hirai, and T. Yamazaki, J . Org. Chenr., 1981, 46, 1769. S. Hirokami, Y . Hirai, T. Takashi, M. Masanori, and T. Yamazaki, Kokuguku 7oronkui Koen Yoshishu, 1979, 12 (Chem. Ahstr., 1980. 92, 197 575). T. Kato. N. Katagiri, U. Izumi, Y . Miura, T. Yamazaki. and Y. Hirai, Heterocycles, 1981, 15, 399. P. de Mayo, A. C . Weedon, and R. W. Zabel, J . Client. Soc.. Cltenr. Commun., 1980, 881. J . A. Barltrop, A. W. Baxter, A. C. Day, and E. Irving, J . Chern. Soc., Cltem. Cnmmun.,1980, 606. A. Padwa. in 'Rearrangements in Ground and Excited States', ed. P. de Mayo, Academic Press, New Ynrk. 1980, Vol. 3, p. 501.

337


40

+

r

I

(14)

of an ab initio MO calculation,'g and it is concluded that two singlet excited states are involved, followed by cleavage of the C-S bond or by 'flapping' of the five ring atoms. Photoreaction of thiophens with amines gives pyrroles, and in an attempt to elucidate the mechanism of this reaction N-substituted 5azabicyclo[2.1.O]pentenes (16) have been prepared 2o from the corresponding sulphur compounds (in turn derived by photoreaction of tetrakis(trifluor0methy1)thiophen) and also cyclopropenyl imines (17). Neither of these species gives pyrroles in thermal reactions, although (16) rearranges to pyrroles on irradiation. It is proposed2' that the thiophenlamine reaction goes by way of nucleophilic attack by the amine on a 5-thiabicyclo[2.1.O]pentene intermediate (18), with initial attack at the thiirane ring as shown or at the double bond.

RNH, S

n-

NHR SH

ASH

RNH

The well documented photorearrangement of isoxazoles to oxazoles has been investigated theoretically,*' 2 2 and it is suggested that excitation of the aclyazirine 9

l9 2o

22

T. Matsushita, Y. Osamura, H. Tanaka and K. Nishimoto, Kokugaku Toronkai Koen Yoshishu, 1979, 114 (Cfiem.Abstr., 1980, 92, 180 534). Y . Kobayashi, A. Ando, K. Kawada, and I. Kumadaki, J . Org. Chem., 1980, 45, 2968. H. Tanaka, T. Matsushita, Y. Osamura, and K. Nishimoto, Kokagaku Toronkai Koen Yoshishu, 1979, 176 (Chem. Abstr., 1980,92, 197664). H. Tanaka, T.Matsushita, Y. Osamura, and K . Nishimoto, Int. J . Quantum Chem., 1980, 18,463.

338

Pho tochemistry

Q

-&

N-0

a

"R,a',"3+

N

N O 35% (R = H)

(20)

(12: R

62% (R = Me)

intermediate (19) to S1 (n,n* state associated with c----O) leads to isoxazole formation, whereas excitation to S , (n, n* state associated with C=N) gives the oxazole. The previously reported reaction of the bicyclic isoxazoles (20) has now 2 3 been described as a synthetic route to bridged oxazoles and imidazoles. Interestingly, with the isoxazolo[4,5-~]pyridines (21) a different formulation is used 24 for the intermediate as an acylnitrene species rather than an acylazirine, apparently on D

.

N-N

D

H O A

'CI

\R

(22) X = 0, NBz

= NMeNHMe

37-800/,

the basis of the alternative products (triazine or pyrazole) formed by intramolecular trapping of the intermediate. The mesoionic dithioles (22) undergo a similar 1,2-phototransposition of ring atoms,25 but it is proposed that a bicyclic valence isomer is an intermediate in this process. In the case of (22; X = 0), 23 24

25

E. M . Beccalli, L. Majori, A. Marchesini, and C. Torricelli, Chem. Lett., 1980, 659. G. Adembri, A. Camparini, D. Donati, F. Ponticelli, and P. Tedeschi, Tetrahedron Lett., 1981, 22, 2121. H . Tezuka, T. Shiba, N. Aoki, K. Iijima, and H . Kato, Kokagaku Toronkai Koen Yoshisl7~4,1979, 8 (Chern. Abstr., 1980, 92, 197661).

Photochemistry of Aromatic Compounds 339 tetraphenyl-l,4-dithiin and tetraphenylthiophen are also formed by way of an initial [4 + 4lcycloaddition of the original dithiole. Two further papers in a series on the generation of nitrilimines (RC=&NR’) by irradiation of sydnones suggest that the reactive excited state is a (n,n*) triplet state,26 and demonstrate again the use of the reactive nitrilimines in the synthesis of heterocyclic compounds.*’ In continuing studies on the formation of thiirens from 1,2,3-thiadiazoles (23), the parent thiiren has been characterized 28 in a lowtemperature matrix after photolysis of (23; R = R’ = H). Product analysis in experiments with 3C-substituted substrates suggests 29 that thiiren is formed to a considerable extent thermally but to a lesser extent photochemically from (23; R = H, R’ = Ph).

(23)

Finally in this Section, the saga continues of the photolysis of sym-tetrazines, with a report 30 that complexes between a nitrile (RCN) and HCN, or between two molecules of nitrile, can be formed and studied in a low-temperature matrix by irradiation of appropriately substituted tetrazines. 3 Addition Reactions A review 3 1 of the photochemistry of alkaloids includes reactions in which addition to an aromatic compound or substitution in an aromatic ring occurs. The second part32 of a review of the thermal and photochemical addition of dienophiles to arenes and their vinyl- and hetero-analogues covers additions to styrenes, stilbenes, and related systems. There is once again little to report in the way of photoaddition reactions to aromatic compounds that involve cleavage of the aromatic ring. Benzene can be ‘photomineralized’ (i.e. converted to carbon dioxide) by photolysis on silica or similar s ~ b s t r a t e s .More ~ ~ usefully for the synthetic chemist, pyridine-N-oxide (24) or its 4-methyl analogue undergo facile ring-cleavage on irradiation in the presence of aqueous amine, to give reasonable yields of 5-aminopenta-2,4dienenitriles.34

026

’’ 28

29

30 31

32 33 34

2-30;,

(24) G. Eber, S. Schneider, and F. Doerr, Bey. Bunsmges. Phys. Chem., 1980, 84, 281. K. H. Pfoertner and J. Foricher, Helv. Chim. Actn, 1980, 63, 653. A. Krantz and J. Laureni, J. Am. Chem. Soc., 1981, 103,486. U. Timm, U. Merkle, and H. Maier, Chem. Ber., 1980, 113, 2519. J. Pacansky and H. Coufd, J. Phys. Chem., 1980, 84, 3238. S. P. Singh, V. I. Stenberg, and S. S. Parmar, Chem. Rev., 1980. 80, 269. T. Wagner-Jauregg, Synthesis, 1980, 769. J. Schmitzer, S. Gaeb, and F. Korte, Chernosphere, 1980, 9, 663. J. Becher, L. Finsen, 1. Winckelmann, R. R.Koganty, and 0. Buchardt, Tetruhedron, 1981, 37, 789.

340

6

RR'NH

6 &

&NRRl+

or

NRR'

Photochemistry +

NRR'

NRR'

(25)

,$ F

RR'NH hv

F

F

,

\

F

/

F

F

(26)

The photoreaction of fluorobenzene (25) and the difluorobenzenes (26) with tbutylamine or diethylamine gives mixtures of 1 : 1 adducts arising mainly by 1,2addition to the ring,35 although with p-difluorobenzene the major products are derived by 1,4-addition. In all cases, products are also formed by substitution of a fluorine atom, and this is the only reaction for hexafluorobenzene and diethylamine. In a subsequent paper,36 the reactions of other substituted benzenes with these amines are described, and again addition and substitution products are both formed. Addition predominates for PhR (R = Me, C1, or CF,) and for rn- or p fluorotoluene; substitution is a major reaction for PhR (R = C1 or CN) and for anisoles and fluorotoluenes. A new type of acyclic adduct (27) is isolated from the product mixture from toluene and t-butylamine, and this may be formed by ringopening of an initial 1,2-adduct with a subsequent hydrogen shift.

(28)

In aqueous solution, phenylphosphonic acid gives phosphoric acid on prolonged irradiation, and an intermediate bicyclic species (28) has been identified;3 this represents an unusual acyclic 1,3-addition to a substituted benzene, related to the photohydration reactions of benzene itself and of pyridinium salts. Photoreduction of naphthalenes (and also of phenanthrene or anthracene) by sodium borohydride can be effected in the presence of an electron-acceptor such as rn- or p-di~yanobenzene.~'The naphthalenes are reduced to 1,4-dihydro35 36 37

A. Gilbert and S. Krestonosich, J . Chem. Soc., Perkin Trans. I , 1980, 1393. A. Gilbert, S. Krestonosich, and D. L. Westover, J . Chem. Suc., Perkin Trans. I , 1981, 295. M . Takahashi, J. Migita, and S. Takano, Nippon Noyaku Gakkaishi, 1980,5407 (Chem. Abstr., 1981, 94, 93 469). M . Yasuda, C. Pac, and H. Sakurai, J . Org. Chem., 1981, 46, 788.


34 1

compounds (29), although 1-methoxynaphthalene also gives some 1,2-dihydroproduct (30), and 2-methoxynaphthalene gives a product (3 1) that incorporates part of the sensitizer molecule. The use of substituted borohydride reducing agents has been in~estigated:~’ product distributions are affected by the choice of reagent. 1,4-Dicyanonaphthalene gives products by photoaddition with toluene;40 one adduct (32) arises by straightforward 1,2-addition to the ring, and the other (33)

apparently by a subsequent reaction between a benzyl group and an unsaturated nitrile grouping. Replacement of one cyano-group by benzyl also occurs to a 39

M. Yasuda, C. Pac, and H . Sakurai, Kokagaku Toronkai Koen Yoshishu. 1979, 262 (Chem. Abstr.,

40

1980, 93, 94 535). A. Albini, E. Fasani, and R. Oberti, J. Chem. SOC.,Chem. Commun., 1981, 50.

342

Photochemistry

rn \

/

/

C6H12 hv’ 77

&+&

’\

/

/

/

(34)

certain extent. Photoreduction of anthracene in cyclohexane at 77 K gives 9,lOdihydroanthracene and 9-cyclohexyl-9,1O-dihydroanthracene(34), as well as 9cycl~hexylanthracene.~~ Similar photoadducts arise when phenanthrene is irradiated in glassy methylcyclohexane or in microcrystalline cyclohexane dispersed in liquid n i t r ~ g e n : ~as ’ shown previously, the reaction is biphotonic and involves an upper excited triplet state of the aromatic hydrocarbon. A principal product formed by irradiating quinoline-2-carbonitrile (35) in acidified aqueous propan-2-01 has two quinoline rings linked through the 2 4 ’ positions and has lost both cyano-groups. The mechanism put forward 43 for this formal 1,2-addition reaction begins with electron transfer from propan-2-01 to an upper triplet state of protonated ( 3 9 , followed by attack on a second (groundstate) molecule of (35). A photophysical study 44 of the photoreduction of acridine hv

Pr’OH, aq. HCI

’

ONH

(35)

H (36) 36%

19% 41

42

43 44

M . Lamotte, R. Ldpouyade, J. Pereyre, and J. Joussot-Dubien, J . Chem. Soc., Chem. Commun., 1980, 725. M . L’amotte, R. Lapouyade, J . Pereyre, and J. Joussot-Dubien, C . R . Hebd, Seances Acad. Sci., Ser. C, 1980, 290, 21 I . T. Caronna, S. Morrocchi, and B. M . Vittimberga, f. Org. Chem., 1981, 46, 34. K . Okutsu and M. Kobayashi, fosai Shika Daigaku Kigo, 1979.8,215 (Chern.Absrr., 1980,93,45 404).

Photochemistry of Aromatic Compounds 343 by amines suggests that a singlet exciplex is involved that can be derived from the (n,n*) state or from the (n,n*) state depending on the solvent. Acridine also undergoes photoaddition of acetaldehyde to give an acetyldihydro-product (36),45 and phenazine (37) reacts in a similar way, although it gives a ring-substituted product as well as the photoadduct. The photoreduction of mono-protonated phenazine in aqueous solution gives the dihydrophenazine radical cation via the lowest excited singlet state,46 and water is oxidized to hydrogen peroxide. Octahydrophenazine (38) behaves like phenazine in giving the NN'-dihydroderivative on irradiation in the presence of propan-2-01, or the radical cation in water;47 this report is of interest in that it provides an example of the photoreduction of a fairly simple substituted pyrazine.

H

(39)

40%

(R = Pr)

The well known photoalkylation of N-heterocyclic aromatic compounds has been extended 48 to sym-triazolo[4,3-b]pyridazine(39); the substitution can be effected by photoaddition of an alcohol followed by heating the initially formed adduct. Photocycloaddition reactions are not observed for diphenylmethane (40) unless either a charge-transfer complex between (40)and, for example, maleic anhydride is involved, or a species such as excited N-ethylmaleimide initiates reaction by attack on an aromatic ring of (40).49 In both of these examples cycloaddition occurs in a 1,Zmanner to only one of the aromatic rings. Interaction between the two phenyl groups is thought to provide a mechanism for dissipating energy in the S , state of diphenylmethane. With benzene and an electron-deficient alkene, 1,2photocycloadducts predominate, and the same is true for electron-deficient aromatic substrates. So hexafluorobenzene gives 1,Zadducts as major products on 45 46

47 48 49

M . Takagi, S. Goto, and T. Matsudd, Bull. Chem. SOC.Jpn., 1980, 53, 1777. H. Kawata, Nihon Kaigaku Nojuigukuba Ippan Kyoyo Kenkyu K i p , 1979,15,27 (Clzem. Abstr., 1980, 93, 177 113). F. Benayache, Y. Gounelle, and J. Jullien, J . Chem. Res. ( S ) , 1981, 158. D. H . Brown and J . S. Bradshaw, J. Org. Chem., 1980,45, 2320. A. Gilbert and J. C. Lane, J . Chem. Soc., Perkin Trans. I , 1981, 142.

344

Photochemistry 0

irradiation with indene or 1,2-dihydronaphthalene, and alkoxypentafluorobenzenes (4 1) with cyclopentene give 1,2-~ycloadductsand products derived by further photochemical ring-closure. 5 0 Pentafluoropyridine (42) behaves in a similar way with cy~loalkenes,~' except that no 1 : 1 adducts are isolated, but only 2 : 1 products arising from further reaction with alkene. OR

2148% 51

B. Sket and M. Zupan, Croat. Chem. Acta, 1979, 52, 387. M. G. Barlow, D. E. Brown, R. N. Haszeldine, and J. R. Langridge, J. Chem. SOC.,Perkin Trans. I , 1980, 129.


345

Details are now presented 5 2 of studies on the benzene-furan system, in which a + 2]cycloadduct (43) and a [4 4ladduct (44) are the major products; adduct (44)can be converted thermally or photochemically into (43). This photoaddition is the first example involving two monocyclic aromatic compounds; benzene and thiophen give products in only very low yield on irradiation.

+

[2

m0" do: & (43)

(44)

h"

\

/

,

J"\

OH-,

/

(45) 36%

\

/

76%

The 1,2-photocycloaddition of acrylonitrile to naphthols or their methyl or trimethylsilyl ethers produces cyclobutane adducts (e,g., 4 9 , and these can be cleaved with base.53 This provides a synthetic route to (1- or 2-cyanoethy1)substituted derivatives of the original naphthol. 1-Cyanonaphthalene (46) gives both 1,2-cycloadductsto the ring and a C=N cycloadduct on irradiation with 1,2dimethylcycl~pentene,~~ and the two reactions proceed by way of different singlet excited states of the aromatic nitrile. The photophysics of this system has been studied p r e v i o ~ s l y ,but ~ ~ this is the first report in which the photoproducts are characterized. An intramolecular version of the reaction starting with the the major one substituted 1-cyanonaphthalene (47) gives two 1,2-~ycloadducts,~~

CN

4 = 0.03 52 53

" "

''

J. C. Berridge, A. Gilbert, and G. N. Taylor, J . Chem. SOC.,Perkin Trans. 1, 1980, 2174. I. A. Akhtar and J. J. McCullough, J. Org. Chem., 1981, 46, 1447. F. D. Lewis and B. Holman, J . Phys. Chem., 1980, 84, 2328. D.V. O'Connor and W. R. Ware, J. Am. Chem. SOC.,1979, 101, 121. J. J. McCullough, W. F. MacInnis, C. J. L. Lock, and R. Faggiani, J . Am. Chem. SOC.,1980,102,7780.

346

Photochemistry

arising by attack at positions 1 and 2, and the minor one by reaction at positions 3 and 4. Solvent effects on the weak exciplex emission from systems containing an aromatic nitrile and furan or an alkene are reported.57 The 1,2-photocycloaddition reactions of methyl phenanthrene-9-carboxylatewith styrenes are proposed 5 8 to go by way of singlet exciplexes, partly on the basis of results from fluorescence studies of compounds such as (48). 6-Cyanophenanthridine (49) behaves like its

(49)

Ar = p-C,H,OMe

84%

16%

phenanthrene analogue on irradiation with alkenes, and by way of an exciplex intermediate provides a route to azetidines and a z ~ c i n e s .6~o ~ . p-Xylene sensitizes the cis-trans-isomerization of cyclohexene, but with cycloheptene (50) the major products are cycloadducts involving 1,3-addition to the

(58

” 58

59

ho

+ 22%)

H. Sakurai, Prepr. Div. Pet. Chem., Am. Chem. Soc.. 1979. 24, 143. H. Sakuragi, H. Itoh, T. Arai, and K. Tokumaru, Kokngrrkrc Toronkrri Koen Yoshishu, 1979, 188 (Chem. Ahsrr., 1980. 93, 70450). S Futamura, H. Ota, and Y. Kamiya, Chem. Left., 1980, 655. S. Futamura, H . Ota, and Y . Kamiya, Kokriguku Toronkai Koen Yoshishu, 1979. 272 (Chem. Abstr., 1979.93, 113518).

347


aromatic ring.61 A detailed study 6 2 of the 1,3-photocycloaddition of cis-cyclooctene (51) to PhR (R = Pri, But, or OMe) or p-MeC,H,R (R = Pr' or OMe) suggests that both of the previously proposed mechanistic pathways are required to account for the selectivity of the reaction. The extent of participation of initial meta-bonding in the arene or of initial 1,3-addition of the alkene to the arene seems to be governed by both steric and electronic effects. An intramolecular version of this reaction has been investigated 63 for various substituted benzenes: with 5-phenylpent-1-ene (52), three 1,3-~ycloadductsare formed, but 1,4-addition

(52)

l p

=0.11

0.023

0.02

$ = 0.23

(53)

predominates for phenethyl vinyl ether (53). The balance between 1,3- and 1,4cycloaddition, and the preferred positions of attack on the ring, depend not only on the length of the linking group between the benzene ring and the alkene unit, but also on the nature of the linking group, i.e. whether or not it contains oxygen, and the position of the oxygen in the chain. An intramolecular photocycloaddition involving the substituted benzene (54) has been, employed 64 in a synthesis of acedrene.

(54)

65%

In a detailed report 6 s of the photoreactions of dienes with benzene, it is shown that with 1,4-dienes one of the double bonds generally adds 1,3-(meta-) to the benzene ring, although evidence is presented for the formation of 1,4-(para-)adducts as well. Rigid 1,3-dienes such as 1,2-dimethylenecyclohexane(55) give regioselectively meta- and para-adducts that involve both of the double bonds in the diene; flexible 1,3-dieneslead to complex mixtures of products. 1,2-Dienes such 61

63 64

65

P. J. Kropp, J. J. Snyder, P. C. Rawlings, and H. G. Fravel, J . Org. Chem., 1980, 45, 4471. M. Dadson, A. Gilbert, and P. Heath, J . Chem. Soc., Perkin Trans. 1, 1980, 1314. A. Gilbert and G . N. Taylor, J . Chem. Soc., Perkin Trans I , 1980, 1761. P. A. Wender and J . J . Howbert, J. Am. Chem. SOC.,1981, 103, 688. J. C. Berridge, J. Forrester, B. E. Foulger, and A. Gilbert, J . Chem. SOC., Perkin Trans. I , 1980,2425.

Photochemistry

348

(55)

major

as allene (56) give predominantly para-adducts, which is unusual for the reactions of benzene with simple alkenes. A brief report 6 6 of the irradiation of naphthalene with trans-cyclo-octene suggests (without evidence) that a 1,3-cycloadduct (57) is involved as an intermediate in the isomerization of the cyclo-octene.

+

Q

There are several reports this year of photocycloaddition reactions between polycyclic aromatic hydrocarbons and 1,3-dienes. Anthracene (58; R = H) or 9cyanoanthracene (58; R = CN)give [4 + 41 and [4 + 2ladducts on irradiation with buta-1 ,3-diene,67but the different product ratios and temperature effects are used to support the previously proposed biradical mechanism for the reaction. Another report from the same group deals with anthracene-hexa-2,4-dieneand 9-phenylanthracene-penta-1,3-diene or cyclohexa-1,3-diene systems; in the case of 9-phenylanthracene (59) and cyclohexa-1,3-diene, two [2 + 2]cycloadducts involving a terminal aromatic ring are isolated, as well as the more usual [4 + 21 and [4 + 4ladducts involving the central ring. Irradiation of substituted anthracenes 66 67 68

Y . Inoue, T. Hakushi, and N. J. Turro, Kokagaku Toronkai Koen Yoshishu, 1979, 152 (Chem. Abstr., 1980, 92, 214 553). G . Kaupp and H. W. Grueter, Chem. Ber., 1980, 113, 1458. G. Kaupp and E. Teufel, Chem. Ber., 1980, 113, 3669.


349

15%

41%

17%

(R,R'

= H, Me, Ph, Br, CN)

32--63%

+

with cycloheptatriene (60) provides [4 + 21, [4 + 41, and [4 + 6]cycloadducts, as well as other products;69 the selective formation of particular product types is rationalized on the basis of orbital and steric interactions. Yang has shown '* that the initial concentration of the arene has a large effect on product ratios ([4 + 41 versus [4 + 21) in the reaction of 9,lO-difluoroanthracene with 2,5-dimethylhexa-2,4-dieneY and this effect is also found with anthracene (61) and cyclohexa-l,3-diene, which [like 9-phenylanthracene (59) and cyclohexa-1,3-diene] gives a minor product involving [2 + Zladdition to a 69

O'

H. Kondo, M . Mori, and K. Kanematsu, J . Org. Chem., 1980, 45, 5273. N. C. Yang, H . Shou, T. Wang, and J. Masnovi, J . Am. Chem. Soc., 1980, 102, 6652.

350

Photochemistry

10%

terminal ring of anthracene, as well as another minor product involving [4 + 2]cycloaddition to a terminal ring. The photoreactions of dibenzanthracenes have already been studied with cyclohexa-l,3-diene, and similar reactions are now reported 7 1 with cyclopentadiene to give mixtures of [4 + 21 and [4 + 4]cycloadducts with well defined stereochemistry. Although 9,lO-endoperoxides can be formed readily in anthracene systems, the corresponding benzene compounds are not common. Cycloaddition of hexamethylbenzene with singlet oxygen is shown to give an endoperoxide (62), although this reacts quickly with more singlet oxygen to give a hydroperoxyderi~ative.~~

* \

/

/ OOH

(62)

The photodimerization of 2-pyridones is a [4 + 4]cycloaddition process, and it is reported 7 3 that the length of the alkyl chain in N-(cu-carboxyalkyl)-2-pyridones (63) governs the ratio of cis: trans dimers when the process is carried out in micellar solution. Photocyclization that involves 1,4-addition to a styrene moiety is included in a more general review 74 of photosensitization in organic synthesis. In a trapping

’’ G . Kaupp and H. W. Crueter, Chem. Ber., 1980, 113, 1626. ’’ C. J . M. Van den Heuvel, A. Hofland, H . Steinberg. and T. J. De Boer, R e d . Trav. Chim. Pays-Bas, ”

1980, 99. 275. Y. Nakamura. T. Kato, and Y. Morita, Tetrahedron Lett., 1981, 22, 1025.

74

A. Albini, S~.nthessis,1981, 249.


351

R (63) R =(CH,),COOH

Ph Ph

&

Ph

4-

(R

)==

=

Ph

-@

C,Ht&):

R R

Me, Ph)

ICH,=CHX

R R

dx (X= CN, C0,Me)

\

R R

experiment using acrylonitrile or methyl acrylate, the formation of products (64) is taken as evidence for the proposed triene intermediate in the electron-transfer sensitized photodimerization of 1,l -diphenylethylene or in the cross-cycloaddition between 1,l-diphenylethylene and 1-methylpropene. A related [4 + 2]cycloadduct is formed photochemically from N-methyl-2-phenyl-maleimide (65), accompanying a number of [2 + 2]cycloadducts involving only the maleimide double bond.76 The [4 2ladduct is also produced on prolonged heating of (65). A reaction that bears some resemblance to the styrene reaction is the formation of spiro-indanes

’’

+

GMe hv

d

Ph’

[2 + 21 dimers

+ 0

0

x (Y = F, Br, C1, Me, OMe) 75

76

(X

= CN,

C0,Me)

(66) 5-50%

D. R. Arnold, R . M. Borg, and A. Albini, J. Chem. Soc., Chem. Commun., 1981, 138. K. Ichimura, S. Watanabe, K . Ueno, and H. Ochi, Nippon Kagaku Kuishi, 1980, 846 (Chem. Abstr., 1980, 93, 185 480).

352

Photochemistry

(66) on irradiation of 2-aryl- I-pyrrolinium salts in the presence of electronacceptor alkenes. 77 However, the proposed mechanism starts with [2 + 2]photocycloaddition of the alkene to the aromatic ring. [2 + 2lCycloaddition to five-membered heterocyclic aromatic compounds is well documented. Examples reported this year include the formation of azetidine adducts (67) by irradiation of 3-(p-cyanophenyl)-2-isoxazolinewith furan or thiophen (and also with benzene);78 benzophenone-sensitized reaction of selenophen with dimethylmaleic anhydride (68) to give 1 : 1 and 1 : 2 ad duct^;^' and oxetan formation from benzophenone and 1-acylimidazoles (69), thiazoles, or isoxazoles.8o

COR

COR

(69)

34-41%

Closer investigation of the photoreaction between benzo[b]thiophenes and dimethyl acetylenedicarboxylate reveals 81 that the unrearranged photoadduct (70) can be isolated if longer-wavelength radiation is excluded, and that (70) shows a charge-transfer absorption band (A,,, 3 6 6 3 6 9 nm), which is responsible for the facile conversion to the previously observed rearranged photoadducts when 366 nm radiation is available (as in the output of a medium-pressure mercury arc). 3-Phenyl- 1,2-benzisothiazoIe (7 1) gives a 1,4-benzothiazepin on irradiation with ethyl vinyl ether,82 consistent with initial S-N bond cleavage rather than ”

7a

P. S. Mariano and A. Leone-Bay, Tetrahedron Lett.. 1980, 21, 4581. T. Kumagai, Y. Kawamura, K. Shimizu, and T. Mukai, Koen Yoshishu-Hibenzenkai Hokozoku Kagaku Toronkai (oyobi) Kozo Yuki Kagaku Toronkai 12th. 1979, 317 (Chem. Abstr., 1980, 92, 197 557).

79

8’

*’

C. Rivas, D. Pacheco, and F. Vargas, J . Hetercycl. Cliem., 1980, 17, 1151. T. Nakano, W. Rodriguez, S. Z. de Roche, J. M. Larrauri, C. Rivas, and C . Perez, J . Heterocycf. Chem., 1980, 17, 1777. S. R. Ditto, P. D. Davis, and D. C . Neckers, Tetrahedron Lett., 1981, 22, 521. M. Sindler-Kulyk and D. C . Neckers, Tetrahedron Lett., 1981, 22, 529.


353 C02Me

d

R

+

Me02C-C~C-C02Me

PhCOMe. hv &C02Me

'

S R (70)

(71)

80%

cycloaddition to the C=N bond. This proposal is supported by the observation that 1,2-benzisothiazoleitself reacts with dimethyl acetylenedicarboxylate to give two isomeric ring-opened products and a cyano-substituted benzo[b]thiophen (72). Further work by the same group shows that 2-phenylbenzothiazole (73) may also undergo bond cleavage, this time of a C-S bond to give in the presence of alkenes a 1,5-benzothia~epin;~~ the reaction is stereospecific.

mf

+

MeOzC-CCrC-CO,Me 602Me (30% cis

+ 50% trans) C02Me

+

p

C

0

2

M

e

CN

4 Substitution Reactions Many examples of photosubstitution reactions in aromatic systems are reported, and it is not easy to group the reactions on a mechanistic basis (in part because 83 84

M. Sindler-Kulyk and D. C. Neckers, Tetrahedron Lett., 1981, 22, 525. M . Sindler-Kulyk and D. C. Neckers, Tetrahedron Lett., 1981, 22, 2081.

Photochemistry

354

many papers are concerned with synthetic rather than mechanistic investigations). Reactions in which direct electrophilic substitution occurs in the excited state are very rare; however, nucleophilic substitution can take place by several mechanisms, including initial electron transfer from the aromatic compound to give an aromatic radical cation. Attack by a radical on the excited state of an aromatic compound is again a rare occurrence, but the reactions of photochemically generated radicals with ground-state aromatics are included briefly at the end of this section. Electrophilic substitution in excited-state aromatics is the subject of only one report, concerned with a photophysical investigation of hydrogen4euterium exchange in 1-metho~ynaphthalene.~~ hv (R

= F) RR’NH (R, R’ = Et or R = H:

(74)

\

R’

= Bu‘)

hv(R

7H(X)Me

= H)

(X = OEt, NHEt, NEt,)

+

Irradiation of 2-fluoropyridine (74;R = F) with t-butylamine or diethylamine gives (di)alkylaminopyridine as the sole product, formed by nucleophilic photosubstitution.86 With triethylamine a more complex mixture of products is formed. Pyridine itself (74; R = H) reacts with diethylamine, triethylamine, or diethyl ether to give 2- and 4-substituted pyridines that reflect attack on the a-methylene group in the aliphatic component; this process involves a formal hydrogenabstraction step from the activated CH, group by an excited-state aromatic. A full report has now appeared 87 of the reactions of alkenes with 3-chlorotetrafluorowhere insertion pyridine (75), and also with 3,5-dichloro-2,4,6-trifluoropyridine, F

77%

8 1-90%

(of ethylene) into the carbon-halogen bond or replacement of chlorine by cycloalkyl (cyclopentyl or cyclohexyl) is the major reaction. The chlorine in these ”

”

S. Tobita and H. Shizuka, Koen Yoshishu Bunshi Kozo Sogo Toronkai, 1979,228 (Chem. Abstr., 1980, 93, 185503). A, Gilbert and S. Krestonosich, J. Chem. SOC.,Perkin Trans. I , 1980, 2531. M . G. Barlow, R. N. Haszeldine, and J. R. Langridge, J . Chem. SOC., Perkin Trans. I , 1980, 2520.

355


compounds is readily replaced by hydrogen on irradiation in hydrogen-donor solvents such as ethanol or diethyl ether, a reaction that is similar to the photodechlorination of (po1y)chlorobiphenyls. On irradiation, amines readily replace a hydrogen (or halogen) in a wide range of nitroindazoles (e.g., 76), and in a few cases ethanol similarly gives rise to YO2 NHMe

NHR

(77)

up to 56%

+

Q-fyJNO2 \

+

OH\ NHR up to 25%

& y o 2

\

o \ up to 28%

ethoxyindazoles by nucleophilic photosubstitution.88 However, with 2-nitrodibenzodioxin (77), attack by amine occurs at the C-0 position to give substituted diphenyl ethers or an N-alkyl-2-nitrophenoxazine(which is the sole product in non-polar solvents);89it is proposed that a triplet excited state of the dibenzodioxin forms an exciplex with the amine, which in polar solvents dissociates to give solvated radical ions. This reaction is related to the photoSmiles rearrangement, the mechanism of which is the subject of several reports.

The photorearrangement of I-anilino-o-(p-nitrophen0xy)alkanes(78) to N-(pnitropheny1)-o-anilinoalkan-1-01sis shown to proceed by way of a radical ion pair and a Meisenheimer complex, both of which are observed in flash photolysis experiment^.^^. 91 In a simpler system, the Smiles rearrangment of the " 89

92

P. Bouchet, R. Lazaro, M. Benchidmi, and J. Elguero, Tetrahedron, 1980, 36, 3523. M. A. Leoni, G. F. Bettinetti, G. Minoli, and A. Albini, J . Org. Chem., 1980, 45, 2331. K. Yokoyama, R. Nakagaki, J. Nakamura, K. Mutai, and S. Nakagura, Bull. Chem. Suc. Jpn., 1980, 53, 2472. K. Yokoyama, R. Nakagaki, J. Nakamura, S. Nakagura, and K. Mutai, Koen Yoshishu Bunshi Kozo Sogo Toronkai, 1979, 236 (Chem. Abstr., 1980, 93, 220 114). K. Mutai and K. Kobayashi, Bull. Chem. SOC.Jpn., 1981, 54, 462.

Photochemistry

356

0-, m-, or p-isomers of 2-(nitrophenoxy)ethylamine has been studied.93 The 0-and p-isomers undergo a Smiles rearrangement thermally, but photochemically this is not important; instead the o-compound gives a mixture of unidentified products, and the p-compound (79) gives two products in which the amine nitrogen has

NHCH,CH,OH OH

OCH,CH ,N H (79)

14%

aq NaOH hv

~

25%

6

OCH,CH,NH,

NHCH,CH,OH

(80)

= 0.23

become bonded to the adjacent ring atom. The m-compound (80) does not undergo the Smiles rearrangement on heating, but the rearrangement does occur photochemically. These results are thought to have a wider significance, because they suggest that in intermolecular nucleophilic photosubstitutions involving alkoxy-nitrobenzenes, electron-transfer interaction between the nitro-group and the nitrogen lone pair (of the nucleophile) may be important; this is not possible in the intramolecular reactions studied, and a more direct nucleophilic attack on the ring may occur. Photocyanation of aromatic compounds is dealt with in several papers this year. In the presence of an electron acceptor such as p-dicyanobenzene, aromatic hydrocarbons such as naphthalene (8 I), substituted naphthalenes, phenanthrene, or anthracene give mixtures of products on irradiation with sodium cyanide.94 The major products involve substitution of hydrogen by cyanide or addition of hydrogen cyanide to the aromatic hydrocarbon. When oxygen is present, the product mixture is less complex, and a good yield of cyano-substituted compound is obtained. It is proposedg4 that the aromatic radical cation is involved in the CN I

18%

(81)

44%

OMe

OMe

OMe

(82)

13%

CN 11%

93

94

G. G. Wubbels, A. M. Halverson, and J. D. Oxman, J. Am. Cheni. Suc., 1980, 102, 4848. M. Yasuda, c'. Pac, and H. Sakurai, J. Chem. Suc., Perkin Trans. I, 1981, 746.

357


mechanism, and a similar conclusion is reached 95 in a mechanistic study of the photocyanation of naphthalene and biphenyl. The latter study is concerned more with the reaction in the absence of added electron acceptor, and it is suggested that a singlet excimer is then involved, which dissociates into radical ions before the attack by cyanide ion. An extension of work on the photosubstitution by cyanide in anisole (82) supports previous conclusions about the mechanism in the presence or in the absence ofp-di~yanobenzene,'~ and it also shows that polyethylene glycol can replace a crown ether as co-solvent (with dichloromethane) for the reaction. A mechanistic link is proposed 97 between the photoreduction of chloro-aromatics such as p-chloroanisole (83) and photosubstitution, involving aromatic radical OMe

61 (83) CN -,M

OMe

, ~

OMe

OMe 13%

79%

O

H

~

OMe

OMe

OMe

4%

OMe 5%

CN 89%

cations and anions; the anions can lead to overall photoreduction, and the cations to the replacement of chlorine by methoxy (from methanol solvent) or by cyano (from added cyanide). Replacement of cyano by hydrogen in a photosubstitution reaction is not as frequently encountered as the reverse process, but the dicyanopyrazine (84), and a related compound with a crown ether group attached to the phenyl ring, undergoes an efficient photoreaction in which first one cyano group is replaced and hv

Ar

CN

(84) (Ar.= C,H,(OMe),]

Ar

CN

79% 95 96 97

Ar

80%

9%

N. J. Bunce, J. P. Bergsma, and J. L. Schmidt, J. Chem. Soc., Perkin Trans. 2, 1981, 713. N. Suzuki, K . Shimazu, T. Ito, and Y. Izawa, J. Chem. Soc., Chem. Commun., 1980, 1253. J. P. Soumillion and B. de Wolf, J . Chem. Soc., Chem. Commun., 1981, 436.

3 58

Photochemistry

then the second The reaction is thought to proceed by way of an aromatic radical anion, which loses cyanide ion: the resulting radical then abstracts hydrogen from the solvent. Dicyanobenzenes react with amines in a different way, however; o-dicyanobenzene (85), or the p-isomer (but not the m-isomer), on irradiation with primary, secondary, or tertiary amines gives products in which one cyano-group is replaced either by the amine linked through the cx-position or by an alkyl group of the amine.99 The first product arises by initial electron transfer (in an exciplex) followed by proton transfer, combination of radicals and elimination of HCN; the alkylated product is formed by subsequent photoreaction of this initial product, again initiated by electron transfer. The analogous substitution reaction of 2-cyanoquinoline in ethanol was reported some time ago, l o o and now an investigation of the effect of a magnetic field on the reaction of 1-cyanoisoquinoline (86) suggests that a triplet radical pair is a likely reaction intermediate. O 1 The same reaction occurs with 4-cyanopyridine (87) and pent-4en-1-01 or hex-5-en-1-01 in neutral solution,'02 but in the presence of HCl attack occurs instead at the ethylenic bond of the alcohol to give products having chlorohydroxy-substituted alkyl chains. Chloroalkyl substituted pyridines (without the OH group) are formed in the reaction of (87) with alkenes in the presence of HCl. l o 2 The same research group reports l o 3 that photosubstitution products are formed from 2- or 4-cyanopyridine (88) with simple alkenes in the absence of acid, in contrast to an earlier report that showed no such allylic substitution products.

HO CN

Q

+

CH,=CH(CH,),OH (n = 3, 4)

'"*

Y

(CH,),$H=CH,

Q Q

(88) 98

99 loo

lo'

7-60%

M. Tada, H. Hamazaki, and H. Hirano, Chem. Lett., 1980, 921. M. Ohashi, K. Miyake, and K. Tsujimoto, Bull. Chem. SOC.Jpn., 1980, 53, 1683. N. Hata, I. Ono, S. Matono, and H. Hirose, BuK Chem. SOC.Jpn., 1973, 46,942. N. Hata and Y. Yamada, Chem. Lett., 1980, 989. T. Caronna, A. Clerici, D. Coggiola, and S. Morrocchi, Tetrahedron Lett., 1981, 22, 2115. R. Bernardi, T. Caronna, S. Morrocchi, and P. Traldi, Tetrahedron Lett., 1981, 22, 155.

Photochemistry of Aromatic Compounh

359

Fluorenol(89) is reduced photochemically by triethylamine to give fluorene in high yield;lo4a small amount of 9-ethylidenefluoreneis also formed. Other amines are effective, although the yields are generally lower, and 9-acetoxyfluorene also reacts to give fluorene in rather low yield. The photoreduction reaction is related formally to the photoreduction of dicyanopyrazine (84). An apparently straightforward replacement of hydrogen by nitro in the photolysis of butyl phydroxybenzoate (90) in aqueous sodium nitrite is shown to be more complex,105 and it seems possible that the initial attack is by HO' radicals, followed by reaction with N02.

84%

COOBu I

9%

YOOBu

OH

4 = 0.012 Nucleophilic photosubstitution with enolate anions continues to attract attention. p-Dihalobenzenesreact to give doubly substituted products (91),Io6 although 0

C'

+ 61

RCOCH,-

Rd 0

(91) 65%

(R = But)

there can be complications caused by the fact that the anion derived from the initial photoproduct can act as a nucleophile towards the excited state of the chloroaromatic. The use of o-iodoanisole (92) in this reaction provides a route to benzo[b]furans, and 3-amino-2-chloropyridine(93) similarly leads to azaindoles.108A detailed mechanistic investigation l o 9 of the reaction with ketone and ester enolates highlights the competition between substitution and hydrogen-atom transfer from the enolate anion to a transient phenyl radical; the same report lo4

lo6 lo'

'09

M. Ohashi, Y. Furukawa, and K. Tsujimoto, J. Chem. Soc., Perkin Trans. I , 1980, 2613. Y. Usui and H. Shimizu, Nippon Kugaku Kaishi, 1979, 1636 (Chem. Abstr., 1980,92, 180305). R. A. Alonso and R. A. Rossi, J . Org. Chem., 1980,45,4160. R. Beugelmans and H. Ginsburg, J . Chem. Soc., Chem. Commun., 1980, 508. R.Beugelmans, B. Boudet, and L. Quintero, Tetrahedron Lett., 1980, 21, 1943. M. F. Semmelhack and T. Bargar, J. Am. Chem. Soc, 1980, 102, 7765.

360

Photochemistry I hv

U O M e (92)

\

RCOCH,-'

(It ='H, Me,

40-100%

100%

Pr', But)

(93)

(R = Me, Pri, But)

23-100%

(94) 25-35%

shows that intramolecular reactions of this type can give products (e.g., 94) with new rings of up to ten atoms. Polychloromethanes can take part in photochemical electron-transfer reactions with aromatic compounds, leading (in alcohol as solvent) to products with oxygenated one-carbon substituents. It is reported that ruthenocene (95), like ferrocene, gives the corresponding ethoxycarbonyl, formyl, or ethoxymethyl compounds when irradiated with carbon tetrachloride , chloroform, or dichloromethane, respectively. Carbazole (96) behaves in a similar way with CCl,, and the

C1 (97)

major products are 1- and 3-ethoxycarbazole;l 1 in a hydrocarbon solvent the reaction is diverted to produce mainly N-(trichloroviny1)carbazole (97) by way of further reaction with trichloromethyl radical. In contrast, NN-dialkylanilines give amino-substituted diphenylmethanes as major products on irradiation in CH,Cl,, 'lo

''I

A. Sugimori, M.Matsui, T. Akiyama, and M. Kajitani, Bull. Chem. SOC.Jpn., 1980, 53, 3263. B. Zelent and G . Durocher, J . Org. Chem., 1981,46, 1496.

Photochemistry of Aromatic Compounds 361 and further examples of aromatic amine and phenol systems are reported 1 1 * to provide similar product ranges in low yield. Dialkylanilines irradiated in the presence of acrylonitrile give ring-substituted products with ortho- or para-groups

incorporating one (MeCHCN) or two (NCCH,CH,CH,&HCN) molecules of the unsaturated nitrile;' l 3 a product of intramolecular cyclization (98) is also formed.

R2

(R = Me, Et)

(98)

Pyridinecarboxylates (99) give photosubstitution products on irradiation with alcohols; the products have alkyl or alkoxy substituents, and the product ratios depend on the absence or presence of added mineral acid. A mechanistic rationalization is presented,'l4P based on the involvement of a triplet excited state located largely on W or a triplet located largely on the ring (for alkylation), and a singlet excited state (for alkoxylation). The reaction of pyridinecarboxylic acids in the presence of transition-metal ions is reported: l 6 pyridine-2-carboxylic acid gives pyridine and 2,2'-bipyridyl with iron(rn), but 2pyridone with copper(@; pyridine-3-carboxylic acid (1 00) with Fe"' gives a dehydrodimer without decarboxylation.

'

Me COOMe

(99)

COOMe

Me0 up to 88%

Irradiation of aqueous solutions of 5-methylphenazinium salts yields the 10hydro cation radical and the 1-hydroxy-derivative (101) in a stoicheiometric 2 : 1 ratio. An e.s.r. study '17 suggests that free hydroxyl radicals are not likely to be involved in the reaction. A more extensive study l a shows that addition of water 112

T. Latowski, E. Latowska, B. Poplawska, M. Przytarska, M. Walczak, and B. Zelent, Pol. J . Chem.,

113

H. Terashima, S. Toki, and H. Sakurai, Kokagaku ToronkaiKoen Yoshishu, 1979,264 (Chem.Abstr.,

114

T. Sugiyama, E. Tobita, K. Takagi, S. Akiyama, Y. Kumagai, K. Yagi, G . P. Sato, and A. Sugimori, Kokagaku Toronkai Koen Yoshishu, 1979, 114 (Chem. Abstr., 1980, 93, 70 449). T. Sugiyama, E. Tabita, K. Takagi, M. Sato, Y. Kumagai, S. P. Sato, and A. Sugimori, Chem. Letr.,

1980, 54, 1073. 1980,93, 70454). 115

1980, 131. 116

T. Takada, T. Kimura, and A. Sugimori, Kokagaku Toronkai Koen Yoshishu, 1979, 206 (Chem.

117

Abstr., 1980, 93, 70452). V. S. F. Chew and J. R. Bolton, J. Phys. Chem., 1980,84, 1903. V. S. F. Chew, J. R. Bolton, R. G. Brown, and G. Porter, J . Phys. Chem., 1980, 84, 1909.

118

362

Photochemistry

to the excited phenazinium cation gives a strongly oxidizing species that can be intercepted by added reagents. Related to this reaction, synthetic proof is presented 'I9 that the photoproduct from lumichrome in aqueous solution is 9hydroxylumichrome (I 02). Similar hydroxylation occurs on irradiation of Nsubstituted alloxazinium cations,' 2o although at lower pH some hydroxylation at C-6 also occurs.

Interest continues in the photoreactions of quinones, especially anthraquinones, in which substitution occurs in one of the aromatic rings. In the 1,4naphthoquinone series, irradiation of an aqueous solution of sodium 1,4-naphthoquinone2-sulphonate gives a mixture of products including the 5-hydroxy-compound: 12' the effects of pH, irradiation wavelength, solvents, and radical scavengers are described. Replacement of halogen by butylamino in anthraquinone (103) is NHAc

0 (103)

Br

N HAc

0

NHBu

reported 22 to proceed through a triplet charge-transfer excited-state of the substrate. Substitution of halogen in 1-chloroanthraquinone on irradiation in aqueous sulphuric acid gives the l-hydroxyq~inone,'~~ and in both of these reactions the 1-halo-isomers are inactive, possibly because they lack low-lying charge-transfer states. 22 Nitro-groups in aminonitroanthraquinones such as (104) can be replaced by hydroxyl,'24*125 although in this system the oxygen of 119 120 121

B. Te Nijenhuis, A. C. Mulder, and W. Berends, Recl. Trav. Chim. Pays-Bas, 1980, 99, 115. R. R. Dueren, R. H. Dekker, H. I. X. Mager, and W. Berends J . Phofochem., 1980,13, 133. S . Hashimoto and M. Mouri, Sci. Eng. Rev., Doshisha Univ., 1980, 21, 39 (Chem. Abstr., 1980, 93, 2 13 2 16).

122

123

124 125

M. Tajima, H. Inoue, and M. Hida, Nippon Kagaku Kuishi, 1979, 1728 (Chem. Absrr., 1980, 92, 2 14 527). K. Seguchi and H. Ikeyama, Chem. Lett., 1980, 1493. 0 . P. Studzinskii and A. V. El'tsov, Zh. Org. Khim., 1979, 15, 2597 (Chem. Abstr., 1980, 93, 7885). 0. P. Studzinskii and A. V. El'tsov, Zh. Obshch. Khim., 1980, 50, 2575 (Chem. Abstr., 1981, 94, 120 526).

Photochemistry of Aromatic Compounds 0

(104)

363

NHR

0

NHR

(R = H,Me)

the OH group presumably can come from the nitro-group, since benzene can be used as a solvent for the irradition. The photohydroxylation of anthraquinone itself in 77% sulphuric acid gives largely (62%) 2-hydroxyanthraquinone, with a small amount of the 1-hydroxyisomer.126 A mechanism involving electron transfer to the (n,n*) triplet state of anthraquinone is propo~ed,'~'followed by attack of the hydroxyl radical soformed on ground-state quinone. A product investigation of the reaction in 96% H,SO, shows that the 2-hydroxyquinone is formed as its sulphate ester,128and that, in the absence of oxygen, reduction products derived from the radical (105) are obtained. In 77% acid and in the presence of boric acid, the 1,4-dihydroxyquinone (106) is formed in high yield from l-hydroxyanthraquin~ne.~~~

&&-+& /

, &OH \

96%H+, hv

/

0

O \

80%

\

a

/

\

/

OH (105)

(106) 81%

2-aminoanthraquinone can be made in a similar manner by irradiating anthraquinone with ammonia in aqueous propan-2-01 in the presence of air, 30 although the yield is only 33%. Similar reactions between 1- or 2-hydroxyanthraquinone and ammonia or methylamine give amino-substituted derivatives (e.g., 107); again an electron transfer from amine to quinone is postulated as the first

IJ1

0.P. Studzinskii and A. V. El'tsov, Zh. Org. Khim., 1980,16, 1100 (Chem. Abstr., 1979,93, 168005). 0.P. Studzinskii and A. V. El'tsov, Zh. Org. Khim., 1980,16,2117 (Chem. Abstr., 1981,94,83 287). A. D. Broadbent and J. M. Steward, J. Chem. Soc., Chem. Commun.,1980, 676. 0.P. Studzinskiiand A. V. El'tsov, Zh. Org. Khim., 1980,16, 1101 (Chem. Abstr., 1979,93, 150035). 0.P. Studzinskii, A. V. El'tsov, and Yu. K. Levental, Zh. Obshch. Khim., 1980,50,435 (Chem.Abstr., 1980, 93, 7286). 0. P.Studzinskii, R. P. Ponomareva, and V. N. Seleznev, I n . Vyssh. Uchebn. Zuved., Khim. Khim. Techno/., 1980, 23, 511 (Chem. Abstr., 1980, 93, 168004).

364

Photochemistry

step in the reaction of the excited state. Substitution in 1-hydroxyanthraquinone with sodium sulphite gives mixture of the 2-, 4-, and 2,4-di-~ulphonates,'~~ but selectivity is greater when amino-substituents are present. 1-Aminoanthraquinone (108) gives exclusively the 2-sulphonate with Na,S03 and the 2-thiolate with

& 0

;:x,

&XNa

(X=S,SO,)

/

\

0

0

(108)

70-100%

Na,S; 2-aminoanthraquinone with sulphite gives only the 3-sulphonate. The lower selectivity with hydroxyquinones is attributed 32 to partial ionization of the OH group in the reaction medium. A homolytic cleavage mechanism with aryl radicals as intermediates is generally accepted for the photodehalogenation reactions of haloaromatics, and this type of reaction is included in a review 133 of modern methods of aryl-aryl bond formation. An example of such bond formation is seen in the photolysis of 0-or p (but not rn-) chlorobenzonitrile, or of tetrachloro- or tetrafluoro-phthalonitrile (109), in the presence of methoxybenzenes; this leads to the formation of biaryls, in

6 Ncm F

+

F \ F (109)

CN

h v ,

F OMe

\ /

\ /

\

OMe

CN F

OMe 36%

some cases in reasonable yield.134 At 193nm, the photolysis of simple halobenzenes occurs from a state derived from S, (PhC1) or from S , , S,, or S , (PhBr).135 In the benzene, naphthalene, and biphenyl series in solution the preferred reaction pathway for aromatic carbon-halogen bond homolysis involves the aromatic triplet state, provided that the triplet energy is close to the required bond-dissociation energy; 36 this is not so for 1-chloronaphthalene, and an 132

K . Hamilton, J. A. Hunter, P. N. Preston, and J. 0. Morley, J . Chem. SOC.,Perkin Trans. 2, 1980, 1544.

13' 134

135 136

M. Sainsbury, Tetrahedron, 1980, 36, 3327. K. A. K. Al-Fakhri, A. C. Mowatt, and A. C. Pratt, J . Chem. Sot., Chem. Commun., 1980, 566. A. Freedman, S. C. Yang, M. Kawasaki, and R. Bersohn, Kokagaku Toronkai Koen Yoshishu, 1979, 232 (Chem. Abstr., 1980, 92, 180338). N.J . Bunce, J. P. Bergsma, M. D. Bergsma, W. De Graef, Y. Kumar, and L. Ravandl, J . Org. Chem., 1980,45, 3708.

Photochemistry of Aromatic Compounds 365 inefficient singlet-state reaction occurs in this case. A triplet state reaction is also proposed for the photodehalogenation reaction of the chlorotoluenes in the presence of ethane,13' and an initial quantum yield of 0.7-1.0 is estimated for this system. p-Dichlorobenzene on irradiation in benzene gives 4-chlorobiphenyl, and on further photolysis this gives p-terphenyl.' 38 p-Dibromobenzene (110) behaves in a similar way,139and flash photolysis studies reveal the cyclohexadienyl radical intermediates, and quenching studies point once again to a triplet mechanism. Br

x (1 1 I )

15--81%

(X= C1, Br; n = 2-10)

A mechanistic study 140 of the photoreactions of (p-ha1ophenoxy)alkyl bromides (1 11) yields some surprising results. First, despite the commonly encountered triplet nature of many aryl-halogen homolytic cleavage reactions, these compounds appear to react by way of an excited singlet state. Secondly, cleavage of the much weaker aliphatic carbon-bromine bond is seen in only one case, although intermolecular sensitization of such cleavage is possible using benzene as sensitizer. Photodehalogenation of a wide range of substituted dichlorobenzenes in methanol is reported to give the corresponding monochlorobenzenes.I4' 142 There is little that is new this year on the photochemistry of polychlorobiphenyls, except that the differing selectivity towards chlorine loss in neutral or alkaline solution (reported previously for polychlorobenzenes) is confirmed for b i p h e n ~ 1 s . lThe ~ ~ major difference is that the preference for loss of ortho-C1 in neutral solution becomes a competition between ortho- and para-C1 loss in the presence of alkali. Polychlorobiphenyls are used as examples in a paper 144 that gives equations to determine quantum yields in solution for situations where products act as inner filters in competing for light absorption. 1

13'

'" 140 14' 142 143

144

Y.Koso, T. Ichimura, T. Hikida, and Y. Mori, Kokakagu Toronkai Koen Yoshishu, 1979,170 ( C h m . Absir., 1980,92, 197 578). K. Chikasawa and M. Uyeta, Chem. Pharm. Bull., 1980, 28, 57. C. L. Pederson and C. Lohse, Acta Chem. Scand., Ser. B, 1979, 33, 649. R. S. Davidson, J. W. Goodin, and G. Kemp, Tetrahedron Lett., 1980, 21, 291 1. M. Mansour, H. Parlar, and F. Korte, Chemosphere, 1980, 9, 59. M . Mansour, S. Wawrik, H. Parlar, and F. Korte, Chem.-Ztg., 1980, 104, 339. T. Nishiwaki, M.Usui, and K. Anda, Tokyo-toritsu Kog-vo Gijutsu Senta Kenkvu Hokoku, 1980, 133 (Chem. Abstr., 1980, 93, 113 514). N.J. Bunce, J. Phorochem., 1981, 15, 1.

Photochemistry

366

Irradiation of thyroxine (1 12) liberates iodine prior to more extensive photodegradation. 14’ Polyhaloheteroaromatic compounds are shown 146 to undergo dehalogenation on irradiation, and in some cases a product (e.g., 113) of attack on

68%

(114)

the solvent is also identified. Tetrachloro-4-(phenylthio)pyridine (1 14) and similar (ary1thio)pyridines give benzothienopyridines on irradiation, by attack of the photogenerated aryl radical on the phenyl group of the substituent. Aromatic hydrocarbons can be readily substituted by radicals that are generated photochemically. A typical example is the reaction of N-methyldibromomaleimide and 4,4‘-bipyridyl,which gives a 3,8-phenanthroline-5,6-dicarboximide (1 15). This example is from a report 14’ that deals with many similar reactions

Q’

hv

d

Br’ QMe0

#;Me

N’

(115) 42%

between cyclic derivatives of dibromomaleic acid and aromatic compounds. 5Bromo-I ,3-dimethyluracil{116)reacts with electron-rich aromatics to give 5-aryl1,3-dimethyluracilsin a similar way,148although here a charge-transfer mechanism is proposed rather than a simple homolytic cleavage of a carbon-halogen bond in the uracil, Similar substitutions occur with indole derivatives,14’ and ‘4b

’*’ 14’

S. Koya, Kirakanta Igaku, 1979, 29, 341 (Chem. Absfr., 1980, 93. 131 762). J . Bratt, B. Iddon, A. G. Mack, H. Suschitzky, J. A. Taylor, and B. J. Wakefield, J . Chem. SOC., Perkin Trans. I , 1980, 648. K. M. Wald, A. A. Nada, G. Szilagyi, and H. Wamhoff, Chem. Ber., 1980, 113, 2884. S. Ito, I. Saito, and T. Matsuura, Tetrahedron, 1981, 37, 45. S. Ito, I. Saito, and T. Matsuura, J . Am. Chem. SOC.,1980, 102, 7235.


:$Br+

0 (1 16)

aRq‘ -%

367

NMe

(R = Me,OMe)

NAO Me

4M5%

between 5-iodo-1,3-dimethyluraciland pyrene or phenanthrene. 5-Iodo- or 5bromo-uridine can also be coupled in this way to benzene, pyrene,’” or tryptophan;”’ in the last example the product (117) is formed only in a frozen aqueous solution. These reactions feature in a general review l S 2of the photochemistry of 5-bromo- and 5-iodo-uracil.

(R = ribosyl)

[R’= CH2CH(NH,)C0,H]

(1 17)

Me

Reports of the substitution of aromatic hydrocarbons by radicals derived by photolysis of peroxides include the photoreaction of peracetic acid and xylenes,’ 5 3 which gives products of ring and side-chain substitution by methyl or hydroxyl radicals; mechanistic studies of the photodecomposition of dibenzoyl peroxide in toluene to give, amongst other products, dimethylbiphenyls through the dimerization of (benzy1oxy)methylcyclohexadienyl radicals (1 18); s4 the reaction of toluene with phenyl or methyl radicals generated photochemically from dibenzoyl or diacetyl peroxide;155and the formation of naphthyl benzoates and phenylnaphthalenes in the naphthalene-sensitized photolysis of dibenzoyl peroxide.’56 The photolysis of the a-azohydroperoxide (1 19) in substituted benzenes (PhR; R = MeO, C1, NO,, or Me) gives hydroxylated products RC,H40H in isomer

’

lS1

lS2 154

’”

I. Saito, S. Ito, T. Shinmura, and T. Matsuura, Tetrahedron Lett., 1980, 21, 2813. S. Ito, I. Saito, H. Sugiyama, and T. Matsuura, Kokaguku Toronkai Koen Yoshishu, 1979, 10 (Chem. Absrr., 1980, 93, 8476). F. Hutchinson and W. Kohnlein, Prog. Mol. Sub-cell. Biol., 1980, 7 , 1. K. Tomizawa and Y. Ogata, To-yodaKenkyu Hokoku, 1980, 1 (Chem. Abstr., 1980, 93, 185 648). Y. Sakaguchi, H. Hayashi, and S. Nakagura, Bull. Chem. SOC.Jpn., 1980,53, 3059. Y. Ogata, K. Tomizawa, K. Furata, and H. Kato, J . Chem. Soc., Petkin Trans. 2, 1981, 110. A. Kitamura, H. Sakuragi, M. Yoshida, and K. Tokumaru, Bull. Chem. SOC. Jpn., 1980, 53, 2413.

Photochemistry

368

6

N-CH,

,OOH Ph

COOH

0

hv

HZOZ

’

FH \

(120)

Br (1 19)

ratios that are consistent with the formation of hydroxyl radicals as intermediates. s’ Hydroxylation also occurs on irradiating benzoic acid in the presence of hydrogen peroxide; salicyclic acid (120) is a major product at low conversion.l S 8 Other photohydroxylations are the formation of 2,5-dichloro-6nitrophenol (121) as the major product on photolysis of p-dichlorobenzene with nitric oxide in air,’” and the related formation ofp-nitrophenol, along with other

’

(122)

Cl

c1

c1

61

20%

phenols, from bromobenzene and nitrogen oxides in air.’60 In the absence of nitrogen oxides, the main products from bromobenzene are phenol and pbromophenol. 16* ortho-Hydroxylation occurs when the quinoxalin-2-one (1 22) is irradiated in sunlight.161 When the charge-transfer complex between hexamethylbenzene (123) and oxygen is irradiated (313 nm) in methanol, a methoxymethyl derivative and pentamethylanisole are formed. 16’ These are not the products obtained when singlet oxygen attacks (123): see structure (62). Finally in this section, an example of substitution in benzene by a phosphorus-centred radical is seen in the formation of 0-ethyl diphenylphosphinate(124) y s one of the products of photolysis of 0ethyl S-propyl phenylphosphonothibilte in benzene. 63 15’

16’ 16’ 16’

N . Narita, T. Tezuka, and W. Ando, Kokagaku Toronkai Koen Yoshishu, 1979, 198 (Chem. Abstr., 1980, 93, 25 562). Y. Ogata, K. Tomizawa, Y. Yamashita, and K. Takagi, Kokagaku Toronkai Koen Yoshishu, 1979, 120 (Chem. Absrr., 1980, 92, 180334). K . Nojima and S. Kanno, Chemosphere, 1980, 6, 437. K. Nojima, T. Ikarigawa, and S. Kanno, Chemosphere, 1980, 9, 421. M. J. Haddadin, J. Makhluf, and A. A. Howi, Heterocj&s, 1980, 14, 457. K. Onodera, H. Sakuragi, and K. Tokumaru, Tetrahedron Lett., 1980, 21, 2831. H. P. Benschop, C. A. G . Konings, D. H. J. M. Platenburg, and R. D e n , J . Chem. SOC.,Perkin Trans. 2, 1980, 198.

369

Photochemistry of Aromatic Compounds ,OMe

(123)

Eta,P/p 'hP

?Me

24% hv

+

'SPr

5 Intramolecular Cyclization Reactions A good review of the 4a,4b-dihydrophenanthrenesformed by photocyclization of

stilbenes has appeared,'64 which includes details of evidence for the stereochemistry at the ring junctions. A stilbene (1 25) substituted with a long-chain

carboxyalkyl group has been used as a probe for investigating conditions in vesicle solution^,'^^ the variables measured being the fluorescence and photoisomerization (trans + cis) quantum yields; a phenanthrene is also formed in the irradiation. Stilbene units incorporated into crown ethers (1 26) provide a substrate for the formation of new crown ethers with one or two phenanthrene rings.'66

(

+ 340 nm

Me0 \

Me (1)

H

Me0 \ (2)

unstable o-quinodimethane, which undergoes intramolecular [4 + 2]Cycloaddition to (2). This can be readily converted to (+)-oestrone. In a flash photolysis study of the photoreduction of chloranil to tetrachlorohydroquinone,solvent and isotope effects have been interpreted in terms of

' a lo

l2 l3

K. S. Peters, S. C. Freilich, and C. G. Schaeffer, J. Am. Chem. SOC.,1980, 102, 5701. P. G. Stone and S. Cohen, J. Am. Chem. SOC.,1980, 102, 5685. S. M. Fredericks and M. S. Wrighton, J . Am. Chem. SOC.,1980, 102, 6166. N. Kambe, K. Kondo, and N. Sonoda, Chem. Lett., 1980, 1629. N. Kambe, K. Kondo, S. Murai, and N. Sonoda,Angew. Chem., Int. Ed. Engl., 1980, 19, 1008. J. C. Scaiano, Chern. Phys. Lett., 1980, 73, 319. G. Quinkert, W. D. Weber, U. Schwartz, and G.Duerner, Angew. Chem., Int. Ed. Engf., 1980, 19, 1027.

Photochemistry

396

a charge-transfer mechanism.l4 E.s.r. data obtained from measurements on the photoreduction of frozen solutions of some diphenoquinones by amines suggest the existence of radical pairs in liquid solution." Photoreduction of 1,Znaphthoquinone by acetaldehyde proceeds by a mechanism involving the initial radical pair, as shown l 6 by measurements of 'H CIDNP and of the change of product distribution with temperature. However, at 20 "C at least 6.7% occurs by addition of a free acyl radical to the quinone in its ground state. In some related work,17 strong evidence has been obtained for secondary polarization of 1,4-naphthosemiquinone radicals during photoreduction. The temperature dependence of the chemical decay rate constant showed that the termination process is diffusion controlled. The photoinduced reduction of some quinones by zinc porphyrin and also by its tetraphenyl derivative has been studied in micellar systems. The mean time for intramicellar electron transfer has been established as 0.2 p,and for duroquinone the rates of entry and exit from the micelle have been found to be 5 x 10" M - sand 6 x lo5 M - s- ', respectively. Quinones possessing long chains are less mobile and partial charge separation could be achieved. Irradiation of anthraquinone in aqueous sodium dodecyl sulphate leads to anthraquinol and the surfactantanthrahydroquinone ether as major products via the triplet state of the anthraquinone. CHMeR

I F'h%N,CHMeR 0

HS Me

ha

MeOH

(3) R = Me, Et

Ph 0 e < H M e R

On irradiation in MeOH, (3; R = Me or Et) undergoes 7-hydrogen abstraction followed by intramolecular radical reaction to give a B-lactam. However, excitation in the nn* region of the thiocarbonyl group does not induce this transformation, suggesting that photocyclization of the thioxoacetamides proceeds from upper excited states as in the case of thiones.20

2 Reduction of Nitrogen-containing Compounds The first results have been reported 2 1 of the synthesis of 1,l'-bis[3(trimethoxysilyl)propyl]-4,4'-bipyridinium bromide and of its use in the derivatization of Pt or p-type Si electrodes. In the dark, p-type Si is blocking to reduction but illumination with light of greater energy than the band gap results in reduction of the surface-confined reagent. This surface will reduce a variety of species such as Fe(y5-C5Hs)2+in MeCN, or [Ru(NH&I3+ in water, and is l4 l5

l7 l9

'' *'

T. Nanun, T. Iwata, H. Kobayashi, and T. Morita, Koen YoshishuBunshi Kozo Sogo Toronkai, 1979, 230. G. G. Lazarev, 0. B. Lantratova, Yu. A. Ivanov, I. E. Pokrovskaya, and M. V. Serdobou, tzv. Akad. Nauk SSSR, Ser. Khim., 1980, 942. K. Maruyama, A. Takuwa, S. Matsukiyo, and 0. Soga, J. Chem. Soc., Perkin Trans. I , 1980, 1414. S. Frydkjaer and L. T. Muus, Chem. Phys., 1980, 51, 335. M. P. Pileni and M. Graetzel, J . Phys. Chem., 1980, 84, 1822. V. Swayambunathan and N. Periasamy, J, Photochem., 1980, 13, 325. H. Aoyama, S. Suzuki, T. Hasegawa, and Y. Omote, J. Chem. Soc., Chem. Commun., 1979, 899. D. C. Bookbinder and M. S . Wrighton, J. Am. Chem. Soc., 1980, 102, 5123.

397 capable of undergoing many thousands of redox cycles without significant deterioration. The mechanism of the CdS-sensitized photoreduction of heptylviologen has been investigated and is thought to occur by transfer of a photoexcited electron from the conduction band of the CdS to the absorbed heptylviologen.22Addition of surfactants was observed to enhance the reaction rate. The methylviologen dimer (4) undergoes a photoinduced two-electron Photo-reduction and -oxidation

[

M e N x C H 2 ] C2 H 2 4C10, (4)

reduction by propan-2-01, a process which leads exclusively to the stable radical cation dimer.23 An intramolecular process seems to be involved. Methylviologen itself has also been photoreduced in an alcoholic medium 24 as well as in the solid phase adsorbed on cellulose paper.25 Other polysaccharides such as starch and cotton wool were found to be similarly effective. The kinetics and mechanism of the photoreduction of water to hydrogen have been investigated26 in a system containing methylviologen and haematoporphyrin as sensitizer in an aqueous micellar solution together with a reducing agent such as (HOCH,CH,),N or HSCH2CH20H. Hydrogen was found to be evolved if the system contained hydrogenase or colloidal Pt as catalyst. Irradiation of solutions of methylviologen containing cysteine and cationic micelles into which Zn" tetrasulphophthalocyanine had been incorporated leads 2 7 to irreversible reduction of the viologen. The non-sulphonated phthalocyanine was found to be a more efficient photosensitizer for this reaction. Kinetic studies have shown a strong dependence of the initial rate on cysteine concentration and on pH, and the reaction probably involves reductive quenching of the cysteine to give the radical anion of the zinc complex, together with the cysteine radical cation. A study has been made of the kinetics of the photoreduction of methylviologen by zinc tetraphenylporphyrin triplets in mixed micelles containing the functional surfactant N-dodecyl-Nmethylviologen ( 5 ) and cetyltrimethylammonium chloride.28It was found that the back electron-transfer from reduced (5) to oxidized zinc tetraphenylporphyrin could be intercepted if a donor such as NADH was cosolubilized in the micelle, and in fact irreversible reduction of ( 5 ) and production of hydrogen has been successfully achieved. Sensitized irradiation of the amphiphatic viologens (6; n = 10, 12, 14, or 16) using a Ru" trisbipyridine-type complex in the presence of edta brings about its photoreduction. Bilayer systems give the best yields and

(6)

*' 23 24

'' 26 27

F. D. Saeva, G. R. O h , and J. R. Harbour, J . Chem. SOC., Chem. Commun., 1980,401. M. Furve and S. Nozakura, Chem. Lett., 1980, 821. M. Kaneko, H. Araki, and A. Yamada, Sci. Pap. Inst. Phys. Chem. Res. (Jpn). 1979, 73, 67. M . Kaneko, J. Motoyoshi, and A. Yamada, Noture (London), 1980, 285, 468. I. Okura and K. T. Nguyen, J . Chem. Soc., Faraday Trans. I , 1980, 76, 2209. J. R. Darwent, J. Chem. SOC.,Chem. Commun., 1980, 805. M. P. Pileni, A. M. Braun, and M. Raetzel, Photochem. Photobiol., 1980, 31, 423.

398 Photochemistry examination of electron transport across the lipid bilayer using several electron carriers revealed that dialkylalloxazines were the most satisfactory.29 Aliphatic amines have been found'O to quench the fluorescence of acridine efficiently and a linear relationship has been demonstrated between the logarithms of the Stern-Volmer quenching constants and the ionization potentials of the amines. The photoreduction of the acridine occurs in 20% Me,COH-MeCN via an exciplex formed between the ground state of the amine and the acridine '(n,n*) state and in 20% Me,COH-C,H, via the '(n,n*) state of the acridine. A quantitative study has been reported 31 of the photoreactivity of 2-nitrophenazine with tertiary amines. Excitation to the '(n,n*) state leads via a non-emitting complex (7) to abstraction of hydrogen from the a-carbon atom of the amine to

(7)

give the 2-nitrophenazinyl radical. Photoreductive acylation of phenazine has been observed 3 2 on irradiation of the parent heterocycle in the presence of aldehydes, and leads to N-acylated 5,lO-dihydrophenazineas product. The mechanism of the transformation has not yet been investigated but it is suggested that it may be related to the reductive photoalkylation of acridine by aliphatic carboxylic acids, and its analogy to pyruvate dehydrogenase activity is discussed. Deoxygenation reactions have been recorded for same methoxyquinoline and methoxyisoquinoline N-oxides.3 3

3 Miscellaneous Reductions Irradiation of aromatic hydrocarbons such as phenanthrene, anthracene, naphthalene, and certain substituted naphthalenes in the presence of NaBH, and rn- or p-(NC),C,H, promotes a Birch-type photoreduction.34* 3 5 The reaction seems to occur by electron transfer from the excited singlet state of the arene to the electron acceptor giving the arene radical cations, which are then reduced by the borohydride. Other reducing agents such as NaBH,, NaBH,CN, and NaBH(OMe), have been found to be effective and all lead to different isomer ratios. In a mechanistically related reaction, both fluoren-9-01and the corresponding acetate are reported 36 to be photoreduced to the parent hydrocarbon in the presence of aliphatic amines. The products arise by photoinduced electron transfer followed by proton transfer from the amine. The yield depends on the structure of the amine and increases in the order primary < secondary < tertiary amine. In 29

30 31

32 33 34

35 36

T. Matsuo, K . Takuma, K. Itoh, and K. Sakura, Kokagaku Toronkai Koen Yoshishu, 1979, 244 K. Okutsu and M. Kobayashi, Josai Shika Daigaku Kiyo, 1979, 8, 215. A. Albini, G. F. Bettinetti, and G. Minoli, J. Chem. SOC.,Perkin Trans. I , 1980, 191. M. Takagi, S. Goto, and T. Matsuda, Bull. Chem. SOC. Jpn., 1980, 53, 1777. A. Albini, E. Fasani, and L. M. Dacrema, J. Chem. Soc., Perkin Trans. 1, 1980, 2738. M. Yasuda, C. Pac, and H. Sakurai, Kokagaku Toronkai Koen Yoshishu, 1979, 262. M. Yasuda, C. Pac, and H. Sakurai, J . Org. Chem., 1981,46, 788. M. Ohashi, Y. Furukawa, and K. Tsujimoto, J . Chem. Soc., Perkin Trans. I , 1980, 2613.

399 pyrene-amine systems, a study has been made of H-atom transfer via the heteroexcimer state.37Using flash phatolysis, the transient exciplexes originating from 2,7-di-t-butylpyrene with 3,4,6-(Me,C),C,H,NH,, and from pyrene and PhNHEt have been observed. In all cases, steric hindrance to electron transfer appears to be less important than steric hindrance to atomic hydrogen transfer. Photo-oxidation and photoreduction of the zinc tetraphenylporphyrin radical cation have been described.38 The disproportionation equilibrium [equation (l)] Photo-reduction and -oxidation

2ZnTPPt, C10,-

ZnTPP2', 2C10,-

+ ZnTPP

(1)

was investigated by flash photolysis and the values obtained for the forward and backward rate constants are 1.2 x 1 0 5 ~ - ' s - ' and 1.4 x l o l o M u I - ' S - ' , respectively. Metalloporphyrinshave been used 39 to catalyse the photoreduction of water in a system consisting of Zn" porphyrins, and colloidal Pt together with methylviologen, edta, or N-phenylglycine. The efficiencies far exceed those obtained for the [Ru(bipy),12+ system. Cetyltrimethylammonium bromide, SDS, and Tween 20 micelles have been used4* to solubilize alkylanthraquinones in the photoreduction of electron acceptors such as (8) and ferricyanide in an aqueous medium. Irradiation of

M e a M Mee Me

I

optically active 2,3-trans-3-hydroxyflavanones in anhydrous ethyl acetate is reported 41 to give free phenolic flavanone analogues. This is a photochemical equivalent of a Clemmensen reduction and is important as it constitutes a general method of direct access to optically pure flavanones in moderate yield. A comparison has been published 42 of the photodechlorinations of chloroderivatives of benzene, naphthalene, and biphenyl. Numerous mechanisms are possible for reductive dechlorinationsin general, but for chloroacenes the reaction seems to occur by triplet-state homolysis of the A r 4 1 bond provided that the triplet energy is close to the bond-dissociation energy. This is not the case for 1chloronaphthalene, however, and an inefficient reaction occurs from the singlet state. In a quantitative study of the photoreduction of 0-ethyl S-n-propyl phenylphosphonothioate (9),irradiation at 254nm has been shown to lead to a mixture of 0-ethyl phenylphosphinate, propanethiol, 0-ethyl phenyl37

I. Karaki, T. Okada, N. Mataga, Y. Sakata, and S. Misumi, Kokagaku Torondai Koen Yoshishu, 1979,

38

W. Potter, R. N. Young, and G . Levin, J . Am. Chem. SOC., 1980, 102, 2471. G. McLendon and D. S. Miller, J. Chem. SOC.,Chem. Commun., 1980, 533. G . V. Fomin, M. M. Shabarchina, and Yu. Sh. Moshkovskii, Zh. Fiz. Khim., 1980,54, 2400. J. H. Van der Westhuizen, D. Ferreira, and D. G. Roux, J . Chem. SOC.,Perkin Trans. I , 1980, 1003. N. J. Bunce, J. P. Bergsma, M. D. krgsma, W. De Graaf, Y. Kumar, and L. Ravanal, J . Org. Chem.,

34. 39 40 41

42

1980,45, 3708.

400

Photochemistry

phosphonothioic acid, and propane.43 These compounds are formed by photoreductive cleavage of the P-S or S--C bond (+ = 0.14 or 0.05, respectively). The rate of these photoreductions is not influenced by the H-donor capacity of the solvent, suggesting that the reaction proceeds without prior H-abstraction, but rather by direct homolysis of the excited state of (9). The intermediate radical [EtO(Ph)P(O)]’ has been detected by e.s.r. in support of this conclusion. Several new photochemical hydrogen-abstraction reactions of epoxynaphthoquinones have been described 44 (Scheme 1) and various other transformations of a broadly similar nature are also reported. 0

R

=

H, Me, Et, Pr, or Me,CH

a,R 0

+

+

9, 9’-bixanthenyl

OH

0 Scheme 1

4 Singlet Oxygen Reviews have appeared on photo-oxidation and toxi~ity,~’ and on the involvement of singlet oxygen in the photofading of dyes.46 A study of solvent deuterium isotope effects on the lifetime of singlet moleqular oxygen has found that on going from MeCN and CHC1, to the corresponding perdeuteriated analogues, the lifetime increases by at least an order of magn i t ~ d e . ~These ’ results suggest that an earlier treatment of the quenching of singlet oxygen by solvent interactions may need revision.48The lifetime of singlet oxygen has been measured 49 in different solvents by monitoring the luminescence decay time at 1270nm using palladium mesoporphyrin as sensitizer. Deactivation occurs by exchange of electronic energy to overtones of vibrations of CC, CH, and OH groups of solvent molecules. In some related works0 the same authors report lifetime studies that suggest that the 1588nm luminescence is a result of the electron-vibrational transition IAg(vl = 0) -+ 3Z,-(v = 1). Quenching of singlet oxygen luminescence by chlorophylls, porphyrins, carotenoids, and lipids has been 43

44

” 46

47

48 49

H . P. Benschop, C. A. G . Konings, D. H. J. M. Platenburg, and R. Deen, J . Chem. SOC.,Perkin Trans. 2, 1980, 198. K. Maruyama, S. Arakawa, A. Osuka, and H. Suzuki, Kokagaku Toronkai Koen Yoshishu, 1979,24. C . S. Foote, Mol. Basis Environ. Toxic., 1980, 37. T. Kitao, Kagaku Kogyo, 1980, 31, 1035. P. R. Ogilby and C. S. Foote, J . Am. Chem. SOC.,1981, 103, 1219. D. R. Kearns and P. B. Merkel, J . Am. Chem. SOC.,1972, 94,7244. I. M. Byteva and K. I. Salokhiddinov, Biqfizika, 1980, 25, 358. K. I. Salokhiddinov, B. M. Dzhagarov, I. M. Byteva, and G . P. Gurinovich, Chem. Phys. Letr., 1980, 76, 85.

Photo-reduction and -oxidation

401

examined51 in H,O and in D20, and the results suggest that the lifetime is independent of the nature of the solvents and is about 500s. Complexes of porphyrins, e.g. tetraphenylporphine (TPP), with highly charged metal ions such as FeII', Mn"' , Sn'" , and AlI", the synthetic dimer of TPP (p-0x0-bis-FeTPP), and Fen'-mesoporphyrin IX dimethyl ester have been used 5 2 to quench the luminescence of singlet molecular oxygen. Stern-Volmer kinetics are obeyed, and with the monomeric iron and manganese porphyrins, quenching is probably by energy transfer from singlet oxygen to the 7t-d levels of the quenchers. An attempt has been made to establish the efficiency of energy transfer from singlet oxygen by use of steady-state yield data. 5 3 Triplet-sensitized reactions of singlet oxygen with 2,5di-butylfuran were investigated for benzophenone, acridine, and anthracene. In no case was unit efficiency observed and the ketone was established as being a significantly poorer sensitizer for singlet-oxygen production than either of the other compounds. Excited states of porphyrins and metalloporphyrins are quenched by 0, in protic and aprotic solvents. E.s.r. studies suggest54 that superoxide ion and singlet oxygen are formed in quenching processes of nett electron and excitation energy-transfer, respectively. The partitioning ratio is quite different from that obtained with Rose Bengal, and singlet oxygen is the major product. The yield of singlet oxygen in the quenching of triplet states of aromatic compounds by molecular oxygen has been reported. This was found to decrease along the series 9,lO-diphenylanthracene > fluorene > 9-methylanthracene > phenanthrene > acenaphthene > p-terphenyl > anthracene > fluorenone > Ph,CO > Ph,N, and confirmed the importance of CT states in triplet quenching by 02. The reactions of oxygen (2l0,) and oxygen (Z3PJ)with halomethanes have been examined,s6 and for O(2'0,) with CF,Cl, CF,Br, CF31, and CHF,Cl, the dominant channel is abstraction yielding a halogen oxide. Reactions of O(2'0,) closely parallel those of singlet methylene and an efficient mechanism appears to exist for the quenching of O(2l0,) to the ground state. A kinetic study of the reactions of singlet molecular oxygen with organic compounds has established that the second-order rate constants are in the order olefins and monomers > carbonyl compounds > saturated hydrocarbons. For the olefins examined, agreement is found with the data obtained in this study and the known agreement between electron density at the unsaturated centre and the quantum yield for oxidation. An equation has been derived for the quantum yield of photoperoxidation of unsaturated organic molecules, and has been applied to lipoic acid inhibition of the self-sensitized photoperoxidation of 1,3-diphenylisobenzofuranin acetonitrile.58 Evidence has been presenteds9 to suggest that in benzene solution photoperoxidation of 1,3-diphenylisobenzofuran proceeds with formation of 51 52

53 54

55 56

"

59

A. A. Krasnovskii, Zh. Prikl. Spektrosk., 1980, 32, 852. E. A. Venediktov and A, A. Krasnovskii, Biojizika, 1980, 25, 336. A. A. Gorman, I. R. Could, and I. Hamblett, Tetrahedron Lett., 1980, 21, 1087. G. S. Cox, D. G. Whitten, and C. Giannotti, Chem. Phys. L e f f . ,1979, 67, 511. V. B. Ivanov, B. G. Kuprashvili, and 1. L.Edilashvili, Khim. Vys. Energ., 1980, 14, 280. M. C. Addison, R. J. Donovan, and I. Garraway, Faraday Discuss. Chem. SOC.,1979, No. 67, 286. R. K. Datta and K. N. Rao, Indian J. Chem., Secf. A , 1979, 18, 102. B. Stevens and K. L. Marsh, J. Chem. Res., (S), 1980, 290. B. Stevens, J. A. Ors, and C. N. Christy, J. Phys. Chem., 1981, 85, 210.

402

Photochemistry

endoperoxide as primary product. This, however, further reacts with the triplet state of 1,3-diphenylisobenzofuranto give a secondary product, which is hitherto unidentified. However, it is concluded that at moderate concentrations this diene exhibits normal stoicheiometic behaviour as an O,( 'Ag) acceptor. The stereochemistry of singlet-oxygen capture by cyclopentadiene rings fused to norbornyl and norbornenyl frameworks has been investigated 6o and shown to proceed only with moderate endo-stereoselectivity. Energetic factors arising from the ionization potential of lo2( 16.12eV) appear to be responsible, since this value differs considerably from that of the nl(S)energies of normal dienophiles (10.5-1 1.5 eV) and the n,(S) energies of the diene substrates (9.6-10.0eV). The disparate nature of the singlet molecular oxygen energy is the cause of the inability of the reagent to distinguish between the advantages of endo-attack relative to exo-bonding. A design has been described 6 1 for an inexpensive apparatus for the measures) exponential processes, and its use has ment of the lifetimes of long-lived (> been illustrated by an example in the study of photo-oxidation.

5 Oxidation of Aliphatic Compounds Kinetic data have been published 6 2 for the photo-oxidation of air-saturated cyclohexane, and a radical mechanism has been described to explain the results. The photosensitized oxidation of the 19-norsteroid 1 1P-chloro-17a-19norpregn-4-en-20-yn-17-01 has been shown 6 3 to lead to the mixture of products in Scheme 2, but a satisfactory rationalization of the stereoselectivity has not yet

&+HO

@ HO

oH

Scheme 2

been made. Evidence has also been presented by the same authors to suggest that in the photosensitized oxidation of a related 19-norsteroid, a pseudoaxial tertiary hydrogen atom is less readily abstracted than a pseudoaxial secondary hydrogen atom.64Even though the substrate is an unactivated alkene, the structure of one of the products implies that some of the singlet oxygen reacts via the dioxetan pathway. An interesting example of remote oxidation has a ~ p e a r e d . ~ 6o 61 62

63

64

L. A. Paquette, R. V. C. Carr, E. Arnold, and J. Clardy, J. Org. Chem., 1980, 45, 4907. S. Joly, J. C. Andre, F. Baronnet, and R. L. Lyke, Oxid. Commun., 1980, 1, 175. L. G. Galimova, S. 1. Maslennikov, and A. I. Nikolaev, Izv. Akad. Nuuk SSSR,Ser. Khim., 1980, 2464. K. H. Schonemann, N. P.Van Vliet, and F. J. Zeelen, Reel. Truv. Chim. Pays-Bas, 1980, 99, 91. J. A. M. Peters, K. H. Schonemann, N. P. Van Vliet, and F. J. Zeelen, J. Chem. Res., ( S ) , 1979,402. D. Wolner, Tetrahedron Lett., 1979, 4613.


403

I

b (10) Z = CH,O, CONH, or SO,

Photoinitiated free-radical chlorination of ( 10) using phenyliodine dichloride is directed exclusively to the C(9) position, probably as a result of the conformation of the steroid placing the C(l) complexed to the template iodine atom close to the C(9) hydrogen. Dehydrochlorination then places a double bond in the C(9)-C( 1) position.

CH2CH2CH2CH0

H

H

CH,CH,CH,CHO

The singlet oxygenation of trans-cyclo-octene has been investigated and leads to the products shown (Scheme 3). Treatment of this mixture with Ph,P is found to increase the (1 2) :(13) ratio suggesting the stereospecific formation of (1 1) as the initial product of the reaction.66*" This is the first example of dioxetan formation in a molecule which carries sterically accessible and abstractable allylic hydrogen atoms, and does not have electron-donating substituents. In protic media, the singlet oxygenation of cr-pinene has been examined and has been found to be partially deviated towards the formation of bifunctional compounds such as hydroperoxymenthene (14; R = OH) and acetamidohydroperoxymenthene (14; R = NHAc). These observations support a zwitterionic mechanism.68 Photooxidation of bicyclopropylidene in CDC1, using tetraphenylporphyrin has been reported to give the spiro-compounds (15) and (16). It is suggested that the reaction proceeds initially to form the intermediate 1,4-zwitterion (17), which is in equilibrium with the perepoxide (18), and, which can undergo a cyclopropylcarbinyl-to-cyclobutylring enlargement.69 Oxidation of the strained olefins (19) has been examined 'O and found to lead to a wide range of different

'' Y. Inoue T. Hakushi, and N. J. Turro, Kokuguku Toronkai Koen Yoshishu, 1979, 150. 67

'* 69 'O

Y. Inou and N. J. Turro, Tetrahedron Lett., 1980, 21, 4327. P. Capdevielle and M. Maumy, Tetrahedron Lett., 1980, 21, 2417. A. De Meijere, G . Rousseau, and J. M. Conia, Tetrahedron Lett.. 1980, 21, 2501. A. A. Frimer and A. Antebi, J . Org. Chem., 1980,45, 2334.

Photochemistry

404 Me

(14)

(1 5 )

(16)

(17)

(18)

(19) R = C02Et, COMe, or H

products, which seem to have been derived by secondary rearrangements of an initially formed hydroperoxide and epoxide. However, singlet oxygen does not appear to be involved, and the products are thought to have arisen from a freeradical process. The failure of singlet oxygen to react may be due to the relatively high ionization potential of cyclopropenes. In this connection it may be significant that cyclopropenes epoxidize only slowly and that the rates of both epoxidation and singlet-oxygen photo-oxygenation are known to decrease with ionization potential. The stereoselective addition of singlet oxygen to the 8-isopropylidenetricyclo[3.2.1.02~4]octanes(20) and (21) has been discussed in terms of Walsh and n

/31)

R' = R2 = H R = R' = bond, R2 = H R = R' = bond, R2 = cyclopropyl

(20) R

=

\L'i

orbital interactions. 7 1 Following irradiation in acetone and reduction with Me$, mixtures of alcohols are obtained whose ratios seem to imply that the endocyclopropane ring of (20)has a similar effect on the selectivity as does the double bond of (21). lt is also suggested that the Walsh orbital interacts with the orbital of the exocyclic double bond more strongly than the orbital of the endocyclic double bond of (21). The singlet-oxygen oxidation of the vinylcyclopropane (22) in the presence of diphenyl sulphide has been reported to give a cis-glycol on cleavage of the dioxetan intermediate.72 This observation has necessitated revision to (23) of the structure of the azido-alcohol formed during the photosensitized oxygenation of (22)in the presence of N3-. No peroxidic products have been detected from contact of singlet oxygen and anti- 1,2,3,4,5,6,7,8-octahydro-1,4,5,8-dimethanonaphthalene (sesquinorbornene) (24). However, (24) does react with mchloroperbenzoic acid and with the oxygen photosensitized by biacetyl gives (25). It appears, therefore, although the presence of the bridge atoms in (24)still permit reaction at one end of the double bond, they seem to inhibit concerted reaction.73 71 72

73

K. Okada and T. Mukai, Tetrahedron Lett., 1979, 3429. T. Hatsui and H. Takeshita, Bull. Chem. SOC.Jpn., 1980, 53, 2027. P. D. Bartlett, A. J. Blakeney, M. Kimura, and W. H. Watson, J . Am. Chem. SOC.,1980, 102, 1383.


(24)

405

(25)

The formation of 1,2-dioxolanes has been reported74 to occur by photooxidation of (Z,Z)-octadeca-9,12-dienoicacid methyl ester (methyl linoleate). These compounds are predominantly of &configuration and arise from an alkenylperoxy radical cyclization. It is suggested that b,y-unsaturated lipid hydroperoxides in general may cyclize stereoselectively in this way, and that this may be significant in the enzymatic formation of prostaglandin hydroperoxides. The reduction products of the hydroperoxides resulting from singlet-oxygen oxidation of methyl linoleate have been characterized.7 5 Methyl 1O-hydroxytrans-8-cis-12-octadecadienoate was detected among the products and was proposed as a test to probe the involvement of singlet oxygen in biological oxidations. Certain fatty acids have been shown to act as sensitizers for the oxidation of methyl linoleate, and the initiation is induced by those fatty acids having a conjpgated oxodiene system which produce start radicals.76 This is supported by the observation that fatty acids having a conjugated triene system, which absorbs in the same region as the oxodiene, are ineffectivesensitizers. A study has also been made of modes of hydroperoxidation in the photo-oxygenation of unsaturated fatty acid esters such as methyl oleate and methyl arachidonate.” (2,E)-Tetradeca-9,ll-dienyl acetate is the main component of the sex pheromone of the female Egyptian cotton leaf worm and on photo-oxidation this has been found7* to undergo cyclization of the furan (26); Scheme 4. Singlet oxygenation of cis&-cyclo-octa- 1,5-diene produces 6-hydroperoxycyclo-octa-1,4-diene and on further oxidation 5,8-dihydroperoxycyclo-octa-1,3diene. Since reduction of this hydroperoxide with Ph,P leads to cis-5,8-dihydroxycyclo-octa-1,3-diene, the whole sequence represents a convenient synthetic entry into 5,8-difunctionalized oxygen derivatives of cyclo-octa-1,3-diene. A highly stereoselective method has been developed for the cis-oxygenation of cycloheptyl systems.80 This involves irradiation of methanolic solutions of 1-acetoxycyclohepta-3,5-diene in the presence of haematoporphyrin as sensitizer to give

’’

74 75 76

l7 78 79 *O

E. D. Mihelich, J . Am. Chem. SOC.,1980, 102, 7141. M.J. Thomas and W. A. Pryor, Lipidr, 1980, 15, 544. U. Semmler, R. Radtke, and W. Grosch, Fette, SeiJen, Ansrrichm., 1979, 81, 390. N. A. Khan, J . Bangladesh. Acad. Sci., 1978, 2, 77. A. Shani and J. T. Klug, Tetrahedron Lert., 1980, 21, 1563. W. Adam and B. H. Bakker, Tetrahedron Lett., 1979, 4171. D. M. Floyd and C. M. Cimarusti, Tetrahedron Lett., 1979, 4129.

406

Photochemistry

(z.E)-EtCH=CHCH=CH(CH,),OAc 4

(E. E)-EtCH=CHCH=CH(CH,),OAc

1

kr. 0,

Scheme 4 0

OAc

H OAc

(27)

AcO H

(29)

(28)

(27) as the major product arising from attack syn to the acetoxy-substituent, together with (28) and (29). Triplet-sensitized irradiation of cis- or trans-vitamin D is known to establish a photostationary state between the two isomers and it is now reported " that in the presence of oxygen highly selective photo-oxygenation of the trans-isomer occurs. The difference in reactivity between these geometric isomers is paralleled in their behaviour towards maleic anhydride and may have applications in the synthesis of hydroxylated vitamin D metabolites. Several 6,19-epidioxy vitamin D derivatives (30) have also been prepared by dye-sensitized photo-oxygenation. The biological activity of these compounds has been examined and a significant degree of Ca transport found.82A study has also been made of the photosensitized oxidation of abietic Oxygen functionalization of some norcaradienes or cycloheptatrienes has been communicated. Thus the endoperoxides (31) and (32) have been obtained from the corresponding h y d r ~ a r b o n s . ' ~An investigation has also been made of the photosensitized oxidation of 7-methoxycycloheptatriene. The product, a [4 + 2]cycloadduct (33), could be thermally isomerized to 4-methoxytropone. 8L

82

83 84

J. W, J. Gielen, R. B. Koolstra, H. J. C. Jacobs, and E. Havinga, Red. Trav. Chim. Pays-Bas, 1980,99,

306. S. Yamada, K. Nakayama, H. Takayama, A. Itai, Y. litaka, S. Moriuchi, F. Tsuruki, and Y. Otawara, Tennen Yuki Kagobutsu Toronkai Koen Yoshishu, 22nd. 1979, 25. A. Fukuchi, H. Negishi, and H. Kanno, Tokyo Gakugei Daigaku Kiyo, Dai-Cbumon, 1979,31, 127. W. Adam, M . Balci, B. Pietrzak, and H. Rebollo, Synthesis, 1980, 820.

407


..u-..,,

R'O.

Mc

Similar photo-oxidation procedures can be used to prepare 4-hydroxytropone and 3-methoxytropone. Sensitized photo-oxidation of the vinylallenes CH,=C=CRCR'=CH, [R = Bu, R' = H; R = (CH,),Me, R' = Me] and 3-(cyclohex-1-en- 1-yl)penta-1,Zdiene have been found 86 to lead to the tetrahydropyranones (34) and (35). 1,2-Dioxetans are reported to be products of the OMe

(31) R

=

Me, Et, or CHMe,

Rb

(33)

(32) Et

R'

(34)

(35)

singlet oxygenation of ketene silyl acetals and are formed together with the expected or-peroxy esters RO,CCH(CMe,)OOSiMe,. The dioxetan undergoes a chemiluminescent thermolysis and rearranges to Me,CCHO and the Mperoxyester. Formation of this product is interesting in that it represents the first example of a thermal transformation of 1,2-dioxetans in which the peroxide bond is p r e ~ e r v e d . ~ ~ Two papers have appeared on the singlet photo-oxygenation of enol ethers. In the first of these,88the (+)-methoxymethylenefenchanes (36) were found to give 85 86 87

88

M. Yagihara, Y. Kitahara, and T. Asao, Bull. Chem. SOC.Jpn., 1980, 53, 236. M. Malacria and J. Gore, Tetrahedron Lett., 1979, 5067. W. Adam, J. Del Fierro, F. Quiroz. and F. Yany, J . Am. Chem. SOC.,1980, 102, 2127. E. W. Meijer and H. Wynberg, Tetrahedron Lett., 1979, 3997.

408

Photochemistry

two pairs of isomeric 1,2-dioxetans. Methoxymethyleneadamantane has similarly been converted to a dioxetan. Examination of the chemiluminescence produced on thermal decomposition of these dioxetans has enabled a comparison to be made of light- and chemically-induced circular polarization of luminescence. Sensitized photo-oxidation of silyl enol ethers of cyclic ketones has also been i n ~ e s t i g a t e d . ~ ~ Following a prototropic ene-reaction and subsequent reduction and solvolysis, or,B-unsaturated (37) and a-hydoxyketones (38; R = H) were produced. A competing silatropic ene-reaction leads to the formation of or-silyloxy ketones (38; R = Me$) and the partition between these different pathways was found to be dependent on such considerations as ring size, configuration, and substitution pattern.

= H, R' = OMe; (37) (38) R = H or Me$ R = OMe, R' = H Although simple acetylenes do not react with singlet oxygen that has been generated using methylene blue or Rose Bengal in MeOH, photosensitized oxygenation of aryl acetylenes is reported" to occur in the presence of some cyanoaromatics and yields benzils (Scheme 5). Diphenylacetylene (39) also

(36) R

+

Rvo RAO '

t I

1

I

hP, 0,

RCOzH Sheme 5

undergoes efficient photo-oxidation using dicyanoanthracene as sensitizer but does so only inefficiently if tetracyanoanthracene (40) is used.g1 This is because the oxidation occurs largely by reaction of (39 ?) with 0, :, and in the second case no 0, is formed. In the presence of acids and bases, the reaction is catalysed because protonation of the radical anion (40') suppresses back-electron transfer to (39 ?) as does nucleophilic addition of pyridine to (39?). Irradiation of cis- and transdiphenylcyclopropane in the presence of electron acceptors such as chloranil, 1,489 90 91

E. Friedrich and W. Lutz, Chem. Ber., 1980, 113, 1245. N. Berenjian, P. De Mayo, F. H . Phoenix, and A. C. Weedon, Tetrahedron Lett., 1979,4179. S. L. Mattes and S. Farid, J . Chem. SOC.,Chem. Commun., 1980, 457.

Photo-reduction and -oxidation 409 dicyanonaphthalene,or 9-cyanophenanthrene have been reported 9 2 to lead to the formation of radical ion pairs. The structures of the triplet state and radical ions are somewhat uncertain and the available evidence is unable to distinguish between the ‘closed’ and ‘open’ structures for the cyclopropane bond. However, substantial spin density does appear to be present at the benzylic position in the radical cations suggesting that one of the ring bonds may be very weak. The photolysis, and photo-oxidation of normal saturated aldehydes has been examined. In the range 10-’-10-*~ it has been shown that the triplet states deactivate principally by self-quenching, and that self-quenching of the singlet state represents a more efficient initiation process than triplet ~elf-quenching.~~ The same authors also find that self-quenchingis the only important deactivation path of the triplet state of branched aldehyde^.^^ The photolysis of aldehydes adsorbed on porous Vycor glass has been observed to decrease in the order Me,CHCHO > > PrCHO > EtCHO > > MeCHO and this is unaffected by oxygen. However, under these conditions photo-oxidation occurs at a rate which is dependent on the oxygen pressure. The species 0, and 0, derived by glass photosensitization, are considered as possible photo-oxidation intermediate^.^' Reports have also appeared of ketone photo-oxidation.96 Photolysis of menaquinone (41; R = CH,CH=CMe,) gives a mixture of the hydroperoxide (41; R = CH=CHCMe,OOH) and the trioxane (42) in a reaction that may involve 0

trapping of oxygen by a quinone-olefin exciplex or a 1,4-preoxetane biradical species. Irradiation of b-ionone in an oxygen atmosphere but in the absence of sensitizers has been shown97 to lead to a mixture consisting of unreacted pionone, 2,3-epoxy-/?-ionone (4573, 2,6,6-trimethyl-2,3-epoxycyclohexylideneacetaldehyde (2%) and dihydroactinidiolide (3%). Rate constants have also been determined 98 for the reaction of chalcone with singlet oxygen, and the dyesensitized photo-oxygenation of chalcones into aurones has been de~cribed.’~ Irradiation of 3a,5-cyclo-5a-cholestan-7-onein methanol gives a 7-oxasteroid.* O0 This phototransformation of an oxosteroid into an oxasteroid in the presence of oxygen appears to be a new type of reaction of excited cyclic ketones. 92 93 94

95 96

97 90

99

loo

H. D. Roth and M. L. M. Schilling, J . Am. Chem. SOC.,1980, 102, 7956. L. M. Coulangeon, G . Guyot, and J. Lemaire, J. Chim. Phys., Phys.-Chim. Biol., 1980, 77, 497. L. M. Coulangeon, G . Guyot, and J. Lemaire, J. Chim. Phys., Phys.-Chim. Biol., 1980, 77, 217. M. Anpo, Y. Ueda, A. Kanno, and Y. Kubokawa, Kokagaku Toronkai Koen Yoshishu, 1979, 60. R. M. Wilson, T. F. Walsh, and S. K. Gee, Tetrahedron Lett., 1980, 21, 3459. H. Etoh and K. h a , Agric. Biol. Chem., 1979,43, 2593. M. Nowakowska and J. Kowal, Bull. Acad. Pol. Sci. Ser. Sci. Chim., 1979, 27, 409. A. Sharma, S. S. Chibber, and H. M. Chawla, Indian J . Chem., Sect. B., 1980, 19, 905. H. Suginome and C.-M. Shea, Bull. Chem. SOC.Jpn., 1980, 53, 3387.

Photochemistry

410

In the presence of FeCl,, photo-oxidation of trisubstituted cyclic olefins in pyridine-benzene has been reported lo' to give gem-dichloroketones from which methyl ketones possessing a terminal triple bond can be obtained by dehydrochlorination. For example, under these conditions 1-methylcyclohexene has been converted l o 2 into (43), an important intermediate in the preparation of brevicomin (44). These reactions have been interpreted in terms of a long-range

(43)

electron-transfer mechanism. At present, no experimental evidence is available concerning the nature of the light-absorbing species, but it seems quite probable that this might be FeC1, modified by olefin co-ordination and s o l ~ a t i o n . The '~~ reaction could, therefore, be visualized as proceeding according to Scheme 6. C

~

F

e

~

~

h

O

,

Scheme 6

Irradiation of certain hydroxyacids, e.g. lactic, glycolic, or 2-hydroxybutanoic acids in the presence of Cu" ions, brings about oxidation of the hydroxyl function with formation of Cu'. At pH > 1, the dominant photoprocess is oxidative decarboxylation, and the presence of free-radical scavengers is found to suppress formation of the a-keto acids. O4 The photoassisted dehydrogenation and dehydration of aliphatic alcohols on ZnO and TiO, surfaces at room temperature has been studied.lo5 The former process occurs via co-ordinatively unsaturated O2- sites, and evidence has been found for photoassistance in the cleavage of the C,-C, bond. An examination of the photocatalytic oxidation of isobutene and butane on these same metal oxides at temperatures between 100-300 "Chas shown l o 6 that local interactions in the catalysts are more important than collective interactions. Heterogeneous photooxidation of alkanes has been reported l o 7 to lead to alcohols and olefins, which are further oxidized into ketones and aldehydes in a process in which the oxidizing agent appears to be surface-lattice, u.v.-activated oxygen. Products of a more intense oxidation are sometimes formed, and it is suggested that in these cases adsorbed and u.v.-activated oxygen is participating. A mechanism has been proposed l o * to explain the heterogeneous photocatalytic oxidation of hydrocarbons in oxygen-containing solutions at platinized TiO,. This is based on the photogeneration of hydroxyl radicals at the TiO, surface [equations (2>--(4), where h + = hole]. However, another paper suggests that the lo'

Io4 lo'

lo' lo'

A. Kohda and T. Sato, Kokagaku Toronkai Koen Yoshishu, 1979, 194. E. Murayama, K. Nagayoshi, and T. Sato, Kokagaku Toronkai Koen Yoshishu, 1979, 196. A. Kohda, K. Ueda, and T. Sato, J . Org. Chem., 1981, 46, 509. R . Matsushima, Y. Ichikawa, and K. Kuwabara, Bull. Chem. SOCJpn., 1980, 53, 1902. J . Cunningham, K. Hodnett, and D . J. Morrissey, Rev. Port. Quim., 1977, 19, 158. L. V. Lyashenko, Katal. Katal., 1979, 17, 6 . N . Djeghri and S. J. Teichner, J . Catal., 1980, 62, 99. I. Izumi, W. W. Dunn, K. 0.Wilbourn, F.-R. F. Fan, and A. J. Bard, J. Phys. Chern., 1980,84,3207.

Photo-reduction and -oxidation TiO,

H,O

+ h+

RH + H O

hv

-H'

41 1

+ h+

e-

HO

+ H+

ROH

(2)

(3) (4)

fundamental step in the activation process is the creation of a neutral atomic oxygen activated species.'0g This may arise from neutralization of an adsorbed 0-ion by a photoproduced hole, h'. The photo-oxidative degradation of polypropylene and stabilization by hindered amines has been reviewed.' l o A study has appeared of the effect of pcarotene on the photoreactivity of anthracene in hexane solution and a kinetic scheme has been proposed to account for the photochemical and photophysical processes that occur on irradiation at 365 nm. Quenching rate constants have been determined between p-carotene and singlet oxygen. Some characteristics have been communicated of the sensitized photo-oxidation of abietic acid contained in a vinyl butyl ether-butyl methacrylate-methacrylic acid copolymer.' l 2 At 400 nm and using eosine and methylene blue as sensitizers, the results show that up to 13% incorporation of abietic acid, uniform photo-oxidation occurs along the matrix, but that above 13%, oxygen diffusion is hindered by oxidation products.

''

6 Oxidation of Aromatics Hexamethylbenzene has been photo-oxidized by singlet oxygen in a two-step process and each step consumes one molecule of oxygen. Step one is a [4 + 2lcycloaddition and this is followed by an ene-reaction to give (45); 0 /I

Me

OOH (45)

''

pentamethylbenzene behaves similarly. A recent paper l4 on the irradiation of the hexamethylbenzene-oxygen charge-transfer complex reported results that were in conflict with earlier work of Wasserman. These discrepancies have now been investigated and accounted for in terms of the wavelength of the incident light leading to production of different excited species. Singlet oxygen has also been found to react with all possible isomers of mono- and di-methylnaphthalenes

''

'lo 'I1

"*

'I3

' l4 'I5

J. M. Herrmann and P. Pichat, Geterog. Katal., 1979, 4th, Pt. 1, 21. D. J. Carlsson, K. H. Chan, A. Garton, and D. M. Wiles, Pure Appl. Chem., 1980, 52, 389.

M. Nowakowska, Makromol. Chem., 1980, 181, 1013. L. Ya. Tantsyura and N . G . Kuvshinskii, Fund. Om.Opt. Pamyati Sredy, 1978, 9, 132. C. J. M . Van den Heuvel, A. Hofland, H. Steinberg, and T. J. De Boer, Recl. Trav. Chim. Pays-Bas, 1980, 99, 275. C. J. M. Van den Heuvel, H. Steinberg, and Th. J. de Boer, Recl. J . R . Neth. Chem. SOC.,1977, %, 157. H. H.Wasserman, P. S. Mariano, and P. M. Keehan, J. Org. Chem., 1971, 36, 1765. K. Onodera, H. Sakuragi, and K. Tokumaru, Tetrahedron Lett., 1980, 21, 2831.

412

Photochemistry

’

with the exception of 2-methylnaphthalene. l 1 Endoperoxides are formed by 1,4or 5,8-attack. Dioxetans are also intermediates in the photosensitized oxygenation of indene and of acenaphthylene, and their reduction leads to substantial amounts of the expected cis-glycols.l Irradiation of Ph,C==CHOMe produces a complex mixture whose constituents all arise from decomposition of the initial endoperoxide.’lg Photoaddition of oxygen to (46) has been reported to give (47). 0

0

Interestingly, further photolysis of (47) involves an irreversible decomposition of low quantum yield, which occurs via S,(n,n*) or T , (n,n*), together with a photoreversible reaction to give ground-state (46) via S , (n,n*). This strongly supports the state-correlation diagram predictions of the concerted photocleavage of endoperoxides.12’ The INDO method has been used to study the lightstimulated interaction of anthracene and oxygen in various geometries, and interactions in the ground and first excited states are classified according to the principle of orbital-symmetry conservation. ” Calculations on the anthracene-Ni model catalyst show that the photo-oxidation is catalysed by transition metals. Photo-oxygenation of alkylbenzenes can be initiated by electron transfer. Thus irradiation of p-xylene in the presence of 9,lO-dicyanoanthracene gives ptolualdehyde and p-toluic acid in a radical chain process 1 2 2 (Scheme 7). Irradiation of (48) in the presence ofp-dicyanobenzene and an aromatic hydrocarbon such as phenanthrene has been found123to lead to ring cleavage. This process is induced by n-complex formation between (48) and the aromatic hydrocarbon radical cation generated by electron transfer to the p-dicycanobenzene. Photoredox reactions can thus provide another route for ring cleavage of cyclobutanes. In MeCN the products of photocoxidation of Ph,G=--H,, cis- and transPhCH=CHPh, and Ph,C=CPh, using 9,lO-dicyanoanthracene and 9-cyanoanthracene as sensitizers include benzophenone, benzaldehyde, epoxides, and products of cis-trans-isomerization. 24 A correlation is established between the rate constants for electron-transfer processes and those determined from the acceptor concentration-dependence of product formation. These observatiqns appear to implicate a sensitizer radical anion that subsequently reduces 0, to 0,.

‘I9 120 12‘

”*

lZ3 124

C. J. M. Van den Heuvel, H. Steinberg, and T. J. D e Boer, R e d . Trav. Chim. Pays-Bas, 1980,99, 109. T. Hatsui and H. Takeshita, Bull. Chem. Sor. Jpn., 1980, 53, 2655. D. S. Steichen and C. S. Foote, Tetrahedron Lett., 1979, 4363. R . Schmidt, W. Drews, and H . D. Brauer, J . Am. Chem. SOC.,1980, 102, 2791. M . Ceppan, L. Lapcik, M . Liska, and P. Pelikan, Eur. Polym. J., 1980, 16, 607. I. Saito, K. Tamoto, and T. Matsuura, Tetrahedron Lett., 1979, 2889. T. Majima, C. Pac, and H. Sukurai, J . .4m. Chem. SOC.,1980, 102, 5265. J . Ericksen and C. S. Foote, J . Am. Chem. SOC.,1980, 102, 6083.

-

Photo-reduction and -oxidation - DCA

I)"

413

'DCA*

X DCA:

+

+

(exciplex)

R D C H 2 0 0 '-_.'

termination

1

Products

Scheme 7

Evidence has been presented

25

that suggests that the oxidation of trans-stilbene

to benzaldehyde using methylene blue as sensitizer does not involve singlet oxygen,

but rather proceeds by the mechanism shown (Scheme 8). Dye-sensitized photooxygenation of 1-phenylcyclobuteneto 3-benzoylpropanal and 2-phenyl-3-hydroperoxycyclobutene has been reported to occur via singlet oxygen. A third product l-(2-hydroxyphenyl)cyclopropanecarboxaldehyde may arise from superoxide anion. MB+

4 * M B& OMB* +

TS+

ISC(

c

2PhCHO

'MB*

TS

lo2 --+

-N.R.

Scheme 8

Oxidative photocyclization of 1-(2-naphthyl)-2-(3-phenanthryl)ethylene has been carried out in a chiral liquid crystal and an optically active helicene obtained. 27 A synthetically useful conversion of 2-(/3-arylvinyl)pyrazines to azaphenanthrenes has also been described using the same oxidative procedure. The position at which ring closure occurs is dependent on the structure of the aryl group.

'

L. E. Manring, J. Ericksen, and C. S. Foote, J. Am. Chem. SOC., 1980, 102, 4275. M. Sakuragi and H. Sakuragi, Chem. Lett., 1980, 1017. "' A. Okami, H. Sakuragi, and K. Tokumaru, Kokugaku Toronkai Koen Yoshishu, 1979, 184. 12* A. Ohta, K. Hasegawa, K. Amano, C. Mori, A. Ohsawa, K. Ikeda, and T. Watanabe, Chem. Pharm. Bull., 1979, 27, 2596.

414 Photochemistry Irradiation of o-nitrobenzaldehyde in benzene gives o-nitrosobenzoic acid (4 0.5) in a process that occurs via a triplet state having a lifetime of 0.6 ns, and the transient enol(49). A mechanism is proposed 12' and this is outlined in Scheme 9. The kinetics of the photo-oxidation of benzaldehyde have been studied in the liquid phase and the rate constants extracted found to be in close agreement with those obtained from the photodecomposition of PhC0,OH. 13*

-

N=O

I -0 Scheme 9

Benzoic acid has been reported 1 3 1 * 32 to be photo-oxidized in the presence of H 2 0 2 ,but if [H,O,]/[PhCO,H] c 10 complete reaction is suppressed by the inner filtering effect of polyhydroxylated aromatics, and complete decomposition is only achieved for ratios >25. In the early stages of the reaction, the products are salicylicacid together with some phenol and benzene, and at longer reaction times, lower aliphatic diacids such as CH,(C0,H)2 appear. The photo-oxidation of a-benzoylbenzyl ethers has been found to occur in the solid phase as well as in solution, and takes place by mechanistically distinct routes. Scheme 10 has been suggested to account for the crystalline-phase PhCOCH(0R)Ph -.!!-L [ PhC ( =0) C H (0R)Ph] SOlld

PhC0,R

+

PhC0,H

+-

[PhC(=O)-OO-CH(OR)Ph]

Scheme 10

processes. Photo-oxidation of various methoxynaphthalenes in the presence of lead tetra-acetate gives a wide range of products including acetoxy derivatives, dimers, 0- and p-quinones, and polysubstituted derivatives. 34 A substratereagent complex seems to be involved and the site of the initial attack appears to be influenced by the location of the methoxy-group. 129

130 lJ1 132

133 134

M. V. George and J. C. Scaiano, J. Phys. Chem., 1980, 84,492. T. Shirotsuka, M. Sudoh, and H. Fukawa, Kagaku Kogaku Ronbunshu, 1980, 6, 53. Y. Ogata, K. Tomizawa, and Y. Yamashita, J. Chem. Soc., Perkin Trans. 2, 1980, 616. Y. Ogata, K. Tomizawa, and Y. Yamashita, Kokagaku Toronkai Koen Yoshishu, 1979, 120. H. Tomioka and Y. Izawa, J. Chem. SOC.,Chem. Commun., 1980,445. E. R. Cole, G. Crank, and B. J. Stapleton, Aust. J . Chem., 1979, 32, 1749.

Photo-reduction and -oxidation 415 Irradiation of anthraquinone in aqueous organic solvents leads to 2-hydroxyanthraquinone together with some of the corresponding 1-hydroxy-isomer. The transformation seems to involve electron transfer from HO- or H,O to the anthraquinone in its 3(n.n*) excited state followed by attack of HO' on unexcited starting material. 35 Photohydroxylation of hydroxyanthraquinones in 75% ~ ~study has been made of the variations of H,SO, has also been d e ~ c r i b e d . 'A fluorescenceand photo-oxidation quantum yields of o-phenylphenolat differential pH. Oxygen inhibits the recombination of the solvated electron and PhO and electron scavengers, such as Cd2+ and NO3-, also increase the quantum yield for disappearance of irradiated o-phenylphenol. 37 Examination of the sensitized photo-oxygenation of a group of coumarins has shown 138 that those bearing a 4hydroxyl group undergo cleavage of the heterocyclic ring; absence of the hydroxyl group suppresses this reaction. It has been suggested that these reactions may

'

HO

Scheme 11

involve a dioxetan intermediate (Scheme 1 1). Photo-oxygenation of epoxynaphthoquinone (50) has been described and may occur by a mechanism involving addition of singlet oxygen to a transient carbonyl ylide. 13' The mechanism of the photoinitiated oxidation of alkylbenzenesulphonates in aqueous media has been discussed.140 Results have been presented that show that furan endoperoxides such as (51)

13'

139

14*

0.P. Studzinskii and A. V. El'tsov, Zh. Org. Khim., 1980, 16, 2117. 0. P. Studzinskii and A. V. El'tsov, Zh. Org. Khim., 1980, 16, 1101. L. M. Coulangeon, G. Perbet, P. Boule, and J. Lemaire, Can. J. Chem., 1980,58, 2230. S . S. Chibber and R. P. Sharma, Indian J. Chem., Sect. B, 1979, 18, 538. K. Maruyama, A. Osuka, and H. Suzuki, J. Chem. SOC.,Chem. Commun., 1980, 723. V. Chekulaev and M. Gubergrits, Eesri NSV T e d . Akad. Toim. Keem., 1980,29, 157. M. L. Graziano, M. R. Iesce, and R. Scarpati, J . Chem. SOC..Perkin Trans. I , 1980, 1955.

416

Photochemistry

can be obtained in quantitative yield by dye-sensitized photo-oxidation of 3methoxycarbonylfurans at - 15 "C. Studies have been reported of the photooxidation of furans in aprotic solvents 4 2 and of a fluorescein-photosensitized oxidation of furan derivatives in methanolic and reversed micellar solutions. Aniline seems to enhance the photo-oxidation of 1,3-diphenylisobenzofuranin methanol and to inhibit the reaction in dodecylammonium propionate reversed micelles. The predominant pathway appears to be a Type I1 oxidation involving singlet oxygen, but addition of aniline promotes oxidation by introducing a competitive radical mechanism (Type I). However, in the reversed micelle, aniline quenched the singlet oxygen leading to inhibition. 143 - 145 7 Oxidation of Nitrogen-containing Compounds The selectivity of tertiary amine oxidations using singlet trans-stilbene has been investigated 146 in the cases of Et,NMe, Me,NEt, and Me,NCHMe,. A relatively non-selective deprotonation of the aminium radical is shown by the stilbene radical anion and the selectivity of the oxidation appears to be due to a stereoelectronic effect, which is most evident when two or three alkyl groups are highly branched. In the photosensitized oxidation of 3-diazocamphor in either MeCN or PhCN as solvent the amide (52) is produced. The formation of this amide strongly supports the intermediacy of a carbonyl oxide intermediate. 14' Me Me

(52) R = Me or Ph

Oxidation of benzophenone N-alkylimine in propan-2-01 is reported to occur on irradiation in a stream of oxygen and gives PhCH,OH, PhCH,NHCHPh,, Ph,CO, and PhCH,NH,. It is suggested that the reaction proceeds through an initial light-induced 1,3-H transfer (Scheme 12). Phenyl-substituted 1,3oxazepins (53) undergo photosensitized oxygenation in CCI, to form various products, all of which can be derived from the peroxides (54) and (55).149 Ph

CH2Ph

>=.'

Ph

h I' 2-PrOH

PhCH=NCHPhz

Scheme 12 142 143 144 145 146

14' 14' 149

W. Grimminger and W. Kraus, Liebigs Ann. Chem., 1979, 1571. N. Miyoshi and G. Tomita, Z. Natuforsch., Teil. B., 1979, 34, 1552. N . Miyoshi and G. Tomita, Kokagaku Toronkai Koen Yoshishu, 1979, 146. N. Miyoshi and G. Tomita, Z. Naturjorsch., Teil. B., 1980, 35, 107. F. D. Lewis and T.-I. Ho, J . Am. Chern. SOC.,1980, 102, 1751. K. Okada and T. Mukai, Teirahedron Lett., 1980, 21, 359. K. N. Mehrotra and G. P. Pandey, hdian J. Chem., Sect. B., 1979, 18, 475. A . Tokida, K. Okada, and T. Mukai, Fukusokan Kagaku Toronkai Koen Yoshishu, IZrh, 1979, 221.


417

R'

R'

Ph

R'

Ph

Ph

(53)

(55)

(54)

The photocyclization of diphenylamine shows a pH dependence and gives carbazole, or if the solution is degassed, carbazole and tetrahydrocarbazole. 5 0 Similar behaviour is also observed for p-Me,CHNHC,H,NHPh. The mechanism of the oxidative photocyclization of N-methyldiphenylamine to N-methylcarbazole has been examined in the presence of surfactants and the bimolecular found to dehydrogenation of the intermediate 4a,4b-dihydro-N-methylcarbazole be enhanced. This appears to be the result of the difference in oxygen solubility between the organic and aqueous solutions. In contrast to an earlier published result, 152 diphenylamine is now reported 53 to undergo photo-oxidation using chlorophyll as sensitizer to give N-phenyl-p-benzoquinonimineas primary product. m-Hydroxydiphenylaminebehaves similarly, 54 and singlet oxygen has been confirmed to participate in this system. Irradiation of dibenzylaniline and CBr, in a poly(viny1 chloride) matrix has been found to lead to the formation of a triplet exciplex between the two compounds. This then dissociates to give final products which themselves sensitize the photo-oxidation of the dibenzylaniline. 5 5 A review on the dye-sensitized photo-oxygenation of indole derivatives has appeared.'', At low temperature, dioxetan (56) has been obtained 157 from the dye-sensitized oxygenation of indole (57) (Scheme 13) and zwitterionic intermediates have been trapped 1 5 8 using nucleophiles such as MeOH, EtOH, and

'

''

'

'

'

Me

Me

(57)

(56)

Scheme 13

Pr'OH. Hydroperoxyindolineshave been trapped by reduction with KBH,.' 59 In the photo-oxidation of aqueous indole-3-acetic acid and of its methyl ester using various sensitizers at different pHs, cleavage by singlet oxygen appears to compete with hydroperoxidation of the CH, group. 160 The mechanism of photo-oxidation of bacteriochlorophyll C derivatives has also been examined.16' D. Lopez, P. Boule, and J. Lemaire, Nouv. J. Chem., 1980, 4, 615. N. Roessler and T. Wolff, Photochem. Photobiol., 1980, 31, 547. M.S. Ashkinazi, V. E. Karpitskaya, and B. Ya. Dain, Russ. J . Phys. Chem., 1964, 38, 1571. R. Kumar, W. R. Bansai, and K. S. Sidhu, Indian J. Chem., Sect. B., 1980, 19, 373. N. Ram and K. S. Sidhu, Can. J . Chem., 1980,58, 2073. A. D. Grishina and G. M. Chernov, Khim. Vys. Energ., 1980, 14, 28. T. Hino and M. Nakagawa, Kagaku No Ryoiki Zokan, 1980, 177. I J 7S. Matsugo, I. Saito, and T. Matsuura, Kokagaku Toronkai Koen Yoshishu, 1979, 202. 15' 1. Saito, Prepr., Div. Pet. Chem., Am. Chem. SOC.,1979, 24, 95. 1 5 9 C. Amsterdamsky and J. Rigaudy, Tetrahedron Lett., 1980, 21, 3187. F. Guerri and R. Martinez-Utrilkd, Rev. R. Acad. Cienc. Exactas, Fis. Nat. Madrid, 1979, 73, 596. 161 R. F. Troxler, K. M. Smith, and S. B. Brown, Tetrahedron Lett., 1980, 21, 491.

418

Photochemistry

Regiospecific oxidation of substituted 1-benzyl-3,4-dihydroisoquinolines to give the corresponding 1-benzoyl compounds has been achieved using singlet oxygen.16* Solvent trapping experiments failed to provide evidence for a zwitterionic peroxide intermediate and it is concluded that either the reaction occurs via a dioxetan or that, if formed, the zwitterionic intermediate is too short lived to be trapped. The photo-oxidation of 2-(Zquinolyl)indan- 1,3-dione (58) to phthalic acid, quinoline-2-carboxaldehyde,and quinoline-2-carboxylicacid has been found to be both self- and Rose Bengal-sensitized. A mechanism has been suggested involving attack of singlet oxygen on the central double bond.163 lO-Methyl-9methylene-9,lO-acridane undergoes methylene blue-sensitized oxygenation at - 78 “C with the formation of three chemiluminescent compounds, the most stable

(58)

(59)

of which is 3,3,7,7-bis( 1O-methyl-9’,9’-acridanyl)-1,2,5,6-tetraoxocane,a dioxetan dimer.164A paper has appeared which describes a general photo-oxygenation procedure for the regiospecific introduction of an oxygen function at position 13 of the photoberberine alkaloids.1658-Azapurines are reported 166 to be photooxidized to the 6-0x0-derivative(59) probably via a hydrate intermediate, and some triazapentalenes undergo 16’ self-sensitized photo-oxidative ring cleavage to the epoxyketone (60) (Scheme 14). By contrast if Me = H, use of Rose Bengal as sensitizer leads to (61). ,COMe

. I

OHC--CH=CH, N-N

(61) Scheme 14 162 163 164 165

166 16’

N. H. Martin, S. L. Champion, and P. B. Belt, Tetrahedron Lett., 1980, 21, 2613. N. Kuramoto and T. Kitao, J. Chem. Soc., Perkin Trans. 2, 1980, 1569. E. H. White, N. Suzuki, and W. H. Hendrickson, Chem. Lett., 1979, 1491. Y.Kondo, J. Imai, and H. Inoue, J. Chem. SOC.Trans. I , 1980, 91 1. F. Kazmierczak, Pol. J . Chem., 1980, 54, 1333. A. Albini, G. F. Bettinetti, G. Minoli, and S. Pietra, J . Chem. SOC.,Perkin Trans. I , 1980, 2904.

419


8 Miscellaneous Oxidations The photo-oxidation of sulphur compounds appears to be a field in which there is increasing interest. Tamagaki 16' has presented evidence to refute an earlier claim 16' that singlet oxygen is solely responsible for the photo-oxidation of di-tbutylthioketone. This new work suggests two distinct paths for the transformation namely singlet-oxygenoxidation to give a sulphine, and oxidation to a ketone via a biradical intermediate. Di-t-butyl thioketone is also reported to undergo photooxidation to (Me,C),C=S=O and (Me,C),CO on irradiation in various aerated solvents.170*171 In the case of thione (62, R = S), irradiation in CH,Cl,-MeOH containing 1% crosslinked polystyrene-anchored Rose Bengal under an atmosphere of oxygen gave a mixture from which the sulphine (62, R = S=O) (4.5%)

R

together with 3% of the corresponding ketone could be is01ated.l~~ This mechanism is, however, not claimed to be general. Rate comparisons have been made for the singlet-oxygen oxidation of the C=S function in various thione compounds, e.g. thioamines, thioureas, and thiocarbonates. Again, steric effects and other evidence strongly suggest that photo-oxidation to the ketones proceeds via a sulphine intermediate. 73 The nature of the intermediates produced by the photosensitized oxygenation of organic sulphides has also been investigated. Competitive studies have been made 174 of the oxidation of pairs of compounds of structure (4-RC6H,),S, R = H, 02N, C1, Me, or MeO, using intermediates formed by photosensitized oxidation of Et,S and PhCN2COPh. A Hammett correlation established that the oxidizing intermediates were electrophilic and most probably were a persulphoxide and a carbonyl oxide, respectively. Dibutyl sulphide has been found 75 to undergo photo-oxidation to BuzSO on sensitization by chrysene. A peroxide intermediate is involved, which reacts further with either a sulphoxide product or with the starting sulphide. Photosensitized oxygenation of a-ketoketene mercaptals has been described 76 and these give dioxetanols, which subsequently collapse to carboxylic acids. Photo-oxidation of the mesoionic compounds (63) and (64)gives ring-cleavage products via endoperoxides 177 and irradiation of tetrathiatetracene and of its selenium analogue in halocarbon solvents leads to radical cation salts. 17'

I7O

17' 17' 174

17' 17'

178

S. Tamagaki, R. Akatsuka, M. Nakamura, and S. Kozuka, Tetrahedron Lett., 1979, 3665. R. Rajee and V. Ramamurthy, Tetrahedron Lett., 1978, 5127. V. J. Rao and V. Ramamurthy, Indian J . Chem., Sect. B., 1980, 19, 143. V. J. Rao and V. Ramamurthy, Curr. Sci., 1980,49, 199. S. Tamagaki and K. Hotta, J . Chem. Soc., Chem. Commun., 1980, 598. S. Tamagaki, R. Akatsuka and S. Kozuka, Mem. Fac. Eng., Osaka City Univ., 1979, 20, 97. W. Ando, Y. Kabe, and H. Miyazaki, Photochem. Photobiol., 1980, 31, 191. G. Cauzzo, G. Gennari, F. Da Re, and R. Curci, Gazz. Chim. Ital., 1979, 109, 541. W. Ando, S. Kohmoto, Y. Nakata, and Y. Haniyu, Kokagaku Toronkai Koen Yoshishu, 1979, 22. H. Kato, K. Tani, H. Kurumisawa, and Y. Tamura, Chem. Lett., 1980, 717. M. Masson, P. Delhaes, and S. Flandrois, Chem. Phys. Lett., 1980, 76, 92.

420

Photochemistry

phpph

Ph

.-/

-0

-0

"Ph

Chloride ions have been photo-oxidized to gaseous chlorine using anthraquinonesulphonic acid and anthraquinonemethanesulphonic acid in aqueous solution. 7 9 The reaction involves transfer of an electron from the halide to the triplet state of the quinone (4 = 0.1--0.13), and in the presence of oxygen the semiquinone radical can be oxidized to ground-state anthraquinone and the whole cycle repeated. In this way partial storage of radiation energy as chemical energy can be achieved. The photosensitized oxidation of I - by anthracenesulphonates appears to proceed by two pathways,'80 sensitizer-peroxide formation which appears to be important for low values of [I-], and direct attack by singlet oxygen which dominates at high values of [I-]. Flash photolysis at 380 nm reveals the presence of a sensitizer-peroxy radical, which is most likely to be of the type AOO, and, which could be an intermediate in the reaction of A0, with I - . By monitoring at 450nm, 10,- is shown to be an intermediate in the photo-oxidation reaction. Several papers have appeared on the photo-oxidation of porphyrins and related compounds. Irradiation of the two water-soluble derivatives of zinc porphyrin, 5,10,15,20-tetra-p-sulphonatophenyl-and 5,10,15,2O-tetra-p-N-methylpyridiniochloride, gives their triplet states, which in the presence of electron donors such as edta are quenched reductively, and in the presence of acceptors such as methylviologen are quenched oxidatively.' The cationic porphyrin will sensitize the photoreduction of water to hydrogen and this offers an attractive alternative to the use of inorganic complexes such as [Ru(bipy)J2+. Photolysis of chlorophyll a or b acting as excited donor together with an electron acceptor such as p-benzoquinone in solvents of low or medium polarity give rise to a triplet exciplex. This decays with formation of solvated radical ions and the effect of solvent polarity has been examined over the range E = 3-20. Unsensitized photo-oxygenation of magnesium tetraphenylporphyrin has been reported to lead to oxidative ring cleavage yielding a bilitriene.18, The transformation is suppressed in the presence of 8carotene or a-tocopherol, which suggests that singlet oxygen is involved. However, although the mechanism of formation of the bilitriene is unclear, it seems reasonable to assume that a zwitterionic peroxide is initially formed and that this reacts with MgTPP to give an epoxide. The photo-oxygenation of oxodipyrromethene is reported to be self-sensitized and to involve singlet oxygen. l g 4 A group of substituted p-benzophenones of the form CH,kEt,Br-, cH2k(C8Hl.,)$r-, p-RC+,H,COPh (R = CH,kEt,q-, CH,NMe,(C,,H,,)Br-, OCl,H,,NMe,Br-) have been shown 185 to be more

'

18*

lS5

H. D. Scharf and R. Weitz, Tetrahedron, 1979, 35, 2255. K . K. Mukherjee and A. K. Gupta, Indian J. Chem., Sect. A., 1979, 17A,332. K. Kalyanasundarum and M. Graetzel, Helv. Chim. Actu, 1980, 63, 478. N. E. Andreeva and A. K. Chibisov, Teor. Eksp. Khim., 1979, 15, 668. T. Matsuura, K. Inoue, A. C. Ranade, and 1. Saito, Photochem. Photobiol., 1980, 31, 23. Y.-T. Park, Taehan Hwahakhoe Chi., 1980, 24, 146. S. Tazuke, Y. Kawasaki, N. Kitamura, and T. Inoue, Chem. Left., 1980, 251.

Photo-reduction and -oxidation 42 1 efficient sensitizers than benzophenone as measured by their ability to photooxidize leuco crystal violet to crystal violet in MeCN. This property is ascribed to the ease of the primary electron transfer from the dye to the triplet excited state of benzophenone. The effect of oxygen on the photodecomposition of rhodamine dyes in ethanol solution has been investigated, and found to increase the stability of the dye solutions.186 A review has appeared on the current status of chemiluminescence. 87

V. A. Mostovnikov, G. R. Grinevich, and A. L. Shalimo, Dokl. Akad. Nauk BSSR, 1980,24, 596. K. D. Gundermann, Proc.-Int. Symp. Anal. Appl. Biolumin. Chemilumin., ed. E. Schram and P. Stanley, State Print. and Publ. Inc., Westlake Village, Ca, 1978, 37.

6 Photoreactions of Compounds containing Heteroatoms other than Oxygen BY S.

T. REID

1 Nitrogen-containingCompounds

Useful reviews on the photochemistry of imides, the photoreactions of alkaloids,2 and selected aspects of photochemically induced preparative heterocyclic chemistry have been published.

'

Rearrangements.-Z,E-Photoisomerization about the carbon-nitrogen double bond has been the subject of further investigations, and the role of both inversion and rotation in this process has been demonstrated the~retically.~E -+ Zphotoisomerization has been observed in (E)-2-hydroxyiminocyclododecanone,5 whereas in singlet excited (E)-/?-ionone oxime ethyl ether (l), isomerization competes with 1,Shydrogen migration to give the 2-isomer (2) and (2)-retro-yionone oxime ethyl ether (3), respectively.6 The results obtained from a study of the E % Z-photoisomerization of the 0-methyl ether of 2-acetylnaphthalene oxime in various microemulsions illustrate the importance of interfacial processes in colloidal systems. Me (yJ/f Me LNPEt

___* /IF

Mp I

Me

OEt

(2)

(1)

+-

PN/

Me Me

(:v

Both direct and triplet-sensitized photoisomerization of pyridylhydrazones has been reported, and a syn-anti-photoisomerization of the carbon-nitrogen double bond has been shown to be responsible for the photochromism observed

'

'

P. H. Mazzocchi, Org. Photochem., 1981, 5, 421. S. P. Singh, V. I. Stenberg, and S . S. Parmar, Chem. Rev., 1980, 80, 269. H. Wamhoff, L. Farkas, H. J. Hupe, A. A. Nada, P. Sohar, G. Szilagyi, H. C. Theis, and K. M. Wald, Kern. Kozl., 1979, 52, 393. P. Russegger, Chem. Phys. Lett., 1980, 69, 362. S. McLean, J. Wong, and P. Yates, J. Chem. SOC.,Chem. Commun., 1980, 746. P. Baas, H. Cerfontain, and P. C. M. Van Noort, Tetrahedron, 1981, 37, 1583. I. Rico, M. T. Maurette, E. Oliveros, M. Riviere, and A. Lattes, Tetrahedron, 1980, 36, 1779. L. L. Costanzo, U. Chiacchio, S. Giuffrida, and G. Condorelli, J . Photochem., 1980, 13, 83. L. L. Costanzo, U. Chiacchio, S. Giutfrida, and G. Condorelii, J. Photochem., 1980, 14, 125.

422

Photoreactions of Compounds containing Heteroatoms other than Oxygen

423

in the 2-arylhydrazones of certain 2-substituted 1,2-diketones.l o Syn-antiphotoisomerization has been confirmed in the 2-phenylhydrazones of some 1,2,3triketones. l 1 Irradiation of 3or-acetoxy-5a-androstan- 17-one acetylhydrazone (4) leads to the formation of the corresponding 2-isomer ( 5 ) and in the presence of -NH Ac

oxygen to the lactams (6) and (7). Pathways accounting for the formation of these lactams have been proposed but not substantiated. The methylthiomethyl nitrone (8) undergoes reversible E Z-photoisomerization on irradiation in deuteriochloroform.l 3 Prolonged irradiation of the E-isomer affords the oxazole (9); the proposed pathway is outlined in Scheme 1. Other photoproducts arising by SMe I

HO

SMe

N-0-

H+ Ph

Ph

?Me

H SMe

4

x H Ph Ph

0

N-OH

-Hzo~

HPh

Ph

(9)

Scheme 1

carbon-sulphur bond homolysis have been described. The photochromism of certain aryl-substituted acyclic azines is also the result of an analogous E + Zphotoisomerization,14 and the process has been shown to be singlet derived.15 The Z-Ziminodiazene 1-oxides (10) are converted on irradiation (A > 300 nm) into the corresponding E-isomers (1 1); irradiation (A < 300 nm), however, results in cleavage and the formation of phthalimidonitrene (12) and nitroso-compounds (13). l6 1-Amino-2-phthalimido-diazene1-oxides are reported to undergo similar transformations.

’

lo l1 l2 l3

l4

l6

”

R. Pichon, J. Le Saint, and P. Courtot, Terrahedron, 1981, 37, 1517. P. Courtot, T. Pichon, and J. Le Saint, J. Chem. SOC.,Perkin Trans. 2, 1981, 219. H. Suginome and T. Uchida, J. Chem. SOC.,Perkin Trans. 1, 1980, 1356. N. S. Ooi and D. A. Wilson, J. Chem. Res. ( S ) , 1980,366. K. Appenroth, M. Reichenbkher, and R. Paetzold, J. Photochem., 1980, 14, 39. K. Appenroth, M. ReichenbEher, and R.Paetzold, J . Phorochem., 1980, 14, 51. L. Hoesch and B. Koppel, Helv. Chim. Acra, 1981, 64, 864. L. Hoesch, Helv. Chim. Acta, 1981,64, 890.

424

Photochemistry

N=N '0-

Me,C

N-N

+

R-NO (13)

0 (12)

The photoisomerization of azo-compounds continues to attract attention. Evidence that photoisomerizationof certain steroidal-substitutedazo-compounds proceeds by way of an inversion mechanism has been described.18 Full details have now been reported of the photorearrangement of 1,2-diaza-(Z)-cyclo-oct-1ene (14) to the E-isomer (15), and analogous transformations have been observed

(14)

(15)

in cis- and trans-3,8-dimethyl-1,2-diaza-cyclo-oct-1-ene. Photoisomerization has also been reported in trans- 1-(3,5-di-t-butyl-4-hydroxyphenyl)-2-phenyldiazene, and transient species, detected on flash photolysis in viscous solution of several trans-4-nitro-4-(dialkylamino)azobenzenes,are believed to be lowest trans-(n, n*) triplet states.21Other examples of E -+ 2-photoisomerization have been reported in azobenzene derivatives.22.23 E-Azobenzene is virtually planar, whereas in Z-azobenzene one of the phenyl groups occupies a plane at an angle of 56" to the plane of the second phenyl group and the azo-nitrogen atoms. Irradiation of complex molecules to which an azobenzene function has been added can therefore be accompanied by profound conformational changes. This approach has been employed to study several biochemically-related problems. Artificial photoresponsive membranes have been constructed by incorporating amphiphatic alkylammonium salts containing azobenzene chromophores into dipalmitoylphosphatidylcholine l i p ~ s o r n e s2.5~ ~ ~ Photocontrol of micellar catalysis has been effected in a similar fashion using the photoresponsive surfactant (1 and the hydrolysis of p-nitrophenyl acetate l9 2o 21 22

23

f4 " 26

U. Kolle, H. Schatzle, and H. Rau, Photochem. Photobiol., 1980, 32, 305. C. G. Overberger and M . 4 . Chi, J . Org. Chem., 1981,46, 303. E. Hofer, Z . Naturforsch., Teil B. 1980, 35, 233. H. Gtkmer, H. Gruen, and D. Schulte-Frohlinde, J . Phys. Chem., 1980,84, 3031. U.-W. Grummt and H. Langbein, J . Photochem., 1981, 15, 329. H. J. Timpe, U. Mueller, and J. Franze, Z . Chem., 1980, 20, 440. K. Kano, Y. Tanaka, T. Ogawa, M. Shimomura, Y. Okahata, and T. Kunitake, Chem. Lett., 1980, 421. T. Kunitake, N. Nakashima, M. Shimornura, Y. Okahata, K. Kano, and T. Ogawa, J. Am. Chem. SOC.,1980, 102, 6642. S. Shinkai, K. Matsuo, M. Sato, T. Sone, and 0. Manabe, Tetrahedron Lett., 1981, 22, 1409.

Photoreactions of Compoundr containing Heteroatorns other than Oxygen 425 catalysed by /3-cyclodextrin can be photoregulated in the presence of an azobenzene moiety.27.2 8 The conformational changes induced by light in the and azobenzene-containingply@-glutamic acid) ( 17) are completely re~ersible,~' similar photoisomerizations in crown ethers have been employed in the control of ion extraction and ion t r a n ~ p o r t . ~ ' - ~ ~ -NH-CH-CO-

CH, I

C=O NH

I Ph (17)

New examples of well established photo-induced rearrangements arising by electrocyclic pathways have been reported. A classification for such processes in systems containing heteroatoms has been proposed.33 1H-1-Benzazepines are readily converted on irradiation in tetrahydrofuran into dihydrocyclob~t[b]indoles,~~ whereas the 4,6a-dihydro[1,2]diazeto[1,4-a]pyrroles (18) are formed preferentially on irradiation of the 3H- 1,Zdiazepines (19).35A high yield

(19)

R' = Rz = Me; R 1= H,RZ = Me or Ph

(18)

preparation of 5-alkoxy- and 5-acetoxy-3-oxo-2-azabicyclo[2.2.0]hex-5-enes (20), without any competing [,4 + ,4] photodimerization, has been achieved by irradiation of the corresponding 2-pyridones (21),j6 and several 1-aryl-4,6diphenyl-2(1H)-pyrimidin-2-ones (22) have been similarly converted in benzene into the bicyclic photoisomers (23).37In contrast, the imines (24) are obtained on 27

29 'O

'' " 33 34

"

'' ''

A. Ueno, K. Takahashi, and T. Osa, J . Chem. SOC.,Chem. Commun., 1980, 837. A. Ueno, K. Takahashi, and T. Osa, J. Chem. SOC.,Chem. Commun., 1981, 94. 0.Pieroni, J. L. Houben, A. Fissi, P. Costantino, and F. Ciardelli, J . Am. Chem. SOC.,1980,102,5913. S. Shinkai, T. Nakaji, Y. Nishida, T. Ogawa, and 0. Manabe, J . Am. Chem. Soc., 1980, 102, 5860. S. Shinkai, T. Nakaji, T. Ogawa, K. Shigematsu, and 0. Manabe, J. Am. Chem. SOC.,1981,103, 11 1. M. Ship, M. Takagi, and K. Ueno, Chem. Leu., 1980, 1021. 0. Kikuchi, Tetrahedron Lett., 1981, 22, 859. M. Ikeda, K. Ohno, T. Uno, and Y. Tamura, Tetrahedron Lptf., 1980, 21, 3403. C. D. Anderson and J. T. Sharp, J. Chem. SOC..Perkin Trans. I , 1980, 1230. C. Kaneko, K. Shiba, H. Fujii, and Y. Momose, J . Chem. SOC.,Chem. Commun., 1980, 1177. T. Nishio, K. Katahira, and Y. Omote,Tetrahedron Lett., 1980, 21, 2825.

Photochemistry

426

R3

-Et,O

R4

(22) Ar

=

Ph, p-MeC,H4, or p-M&C,H,

(23)

irradiation of unsubstituted 1-arylpyrimidin-2(lH)-ones (25) in benzenemethan01;~'evidence supporting the pathway outlined in Scheme 2, in preference

(25) Ar = Ph, p-MeC,H,, or p-MeOC6H4

+ N

MC

lAr

o c N'H (24)

Scheme 2

to an alternative one involving bicyclic isomers, has been described. A bicyclic intermediate (26) has previously been proposed to account for the photoinduced transformation of 2,3,6-trimethylpyrimidin-4-one(27) to the /3-methoxy-p-lactam

(28) in methanol. The intermediacy of (26) has now been verified by irradiation in liquid ammonia-ether solution at -40 0C,39 and application of this reaction sequence to the ring-fused pyrimidin-4-one (29) affords a novel route to the azocine (30) as shown in Scheme 3.40 38 39 40

T. Nishio, K. Katahira, and Y. Omote, J . Chem. Soc., Perkin Trans. 1 , 1981, 943. S. Hirokami, T. Takahashi, M. Nagata, Y. Hirai, and T. Yamazaki, J . Org. Chem., 1981,46, 1769. Y. Hirdi, T. Yamazaki, S. Hirokami, and M. Nagata, Tetrahedron Lett.. 1980, 21, 3067.


427

Gi2 - s:i2 0 Me

H 0 Me Scheme 3

Bicyclic valence isomers (31) and ring-opened ketens (32), characterized spectroscopically, have been obtained by low-temperature irradiation of the oxazinones (33),41 and analogous oxa-azabicyclo[2.2.0]hexenones have been shown to be intermediates in the photoinduced ring-scrambling of other oxa~inones.~~ R'

(33) R' = H, R2 = R3 = H or Me R' = R2 = Me, R 3 = H or Me R1 = But, R2 = Me, R3 = H

R'

R'

(31)

Examples of nitrogen-containing analogues of the stilbene-to-dihydrophenanthrene electro-cyclization and related transformations have been reported. Thus, photocyclization of 1-(2-pyridy1)-2-arylpyridiniumsalts affords benzo[c]pyridi[ I ,2-a]-1,8-naphthyridinyliumcations;43similar cyclizations have been observed in ind~lylpyridylethylenes,~~ in 4-(5)arylethenylimidazoles,4s and in 2(pyridylvinyl)chromen-4-ones,which, on irradiation in benzene in the presence of oxygen, yield 12H-[l]benzopyrano[1,2-f or h]-isoquinolin-12-ones and -quinolin12-0nes.~~ Related transformations include the photodehydrocyclization of the perchlorate salt (34) to give the 7H-indolo[l ,2-a]quinoliniumsalt (35),47the synthesis 41

42 O3 O4

45

" "

G . Maier and U. Schafer, Liebigs Ann. Chem., 1980, 798. P. de Mayo, A. C. Weedon, and R. W. Zabel, J . Chem. SOC.,Chem. Commun., 1980, 881. A. R. Katritzky, Z. Zakaria, and E. Lunt, J . Chem. Soc., Perkin Trans. 1, 1980, 1879. D. Pelaprat, R. Oberlin, I. L. Guen, J. B. Le Pecq, and B. P. Roques, J . Med. Chem., 1980,23, 1330. G . Lindgren, K. E. Stensio, and K. Wahlberg, J . Heterocycl. Chem., 1980, 17, 679. I. Yokoe, K. Higuchi, Y. Shirataki, and M. Komatsu, J . Chem. SOC.,Chem. Commun., 1981, 442. K. B. Soroka and J. A. Soroka, Tetrahedron Lett., 1980, 21,4631.

428 Photochemistry of 12-acetoxybenzo[c]phenanthridines from substituted styryli~ocarbostyrils,~~ and the rather surprising conversion in high yield of the enamines (36) into the 11methoxyindoloquinolizidines(37).49

M e ’Me (34)

Me0

(35)

JqJQ,

(36) R’ = R2 = H R’ = C1, R2 = H R’ = H, R2 = OMe

(37)

The application of enamide photocyclization to the synthesis of heterocycles has again been reviewed.” The key step in the total synthesis of the photoberberine alkaloid, xylopinine, is the conversion by photocyclization and [1,5]hydrogen migration of the enamide (38) into 8-oxoprotoberberine (39) in 73% yield.’l Enamides of the N-aroylenamine type, which contain an electron-withdrawing substituent in the aromatic ring, undergo both photochemical and thermal cyclization,5 2 whereas the benzofuran derivative (40) is converted on irradiation in an aprotic solvent into the trans-fused product (41) by a pathway involving conrotatory cyclization and [1,5]suprafacial hydrogen migration. s3

Me0

___,

OMe (38)

OMe (39)

Diarylamines are known to undergo analogous photoinduced electrocyclizations; N-phenyl-1,2,3,4-tetrahydro-S-naphthylamine, for example, is con48

Y. Harigayd,

s. Takamatsu, H. Yamaguchi, T. Kusano, and M . Onda, Chem. Pharm. Bull., 1980,

28, 2029. 49

A. Rahman and M. Ghazala, Heterocycles, 1981, 16, 261.

’’ I. Ninomiya and T. Naito, Heterocycles, 1981, 15, 1433. T. Kametani, N. Takagi, M. Toyota, T. Honda, and K. Fukumoto, Heterocycles, 1981, 16, 591. ’’ ’’ T. Naito and 1. Ninomiya, Heterocycles, 1980, 14, 959. 51

Y.Kanaoka and K. San-nohe, Tetrahedron Lett., 1980, 21, 3893.

Photoreactions of Compoundr containing Heteroatoms other than Oxygen

429

verted in this way into 1,2,3,4tetrahydro-1 1H-benzo[a]carbazole.54 The photocyclization of N-aryl enamines has similarly been employed in the synthesis of 2,3dihydroindoles. A detailed study of the reaction mechanism has revealed that in acyclic enamines such as (42), cis-trans-isomerization competes with cyclization.

The zwitterion (43) has been detected by flash photolysis. Reverse reactions have also been observed, but these are suppressed at lower temperatures. This cyclization has been used in the synthesis of substituted indolines as shown, for example, for enamine (44)in Scheme 4.56Analogous photocyclizations have been

H

Scheme 4

observed in N-aryl enamino ketone^;^'. ” thus, on irradiation, the 2-anilinocyclohex-Zenone (45) is converted into the tetrahydrocarbazoles(46)and (47) by the pathway outlined in Scheme 5.” 54

55 56

” 58

R. J. Olsen and 0. W. Cummings, J. Hetermycl. Chem.. 1981, 18, 439. T. Wolff and R. Waffenschmidt, J . Am. Chem. Soc., 1980, 102,6098. A. G. Shultz and C.-K. Sha, Tetrahedron, 1980,36, 1757. J. C. Amould, J. Cossy, and J. P. Pete, Tetrahedron, 1980, 36, 1585. D. Watson and D. R. Dillin, Tetrahedron Lerr., 1980, 21, 3969.

Photochemistry

430

(47) Scheme 5

An unusual 1,7-electrocyclic ring closure has been observed in the diazoalkane

(48) to give the diazepine (49).59 In contrast, irradiation of the isomeric N-

+gp

(49)

(48)

(50)

diazoalkane (50) affords products derived only from an intermediate photochemically generated carbene. Photorearrangement of 3-(N-methylanilino)-2Hazirine (51) leads to the formation of the nitrile ylide (52), which has been trapped as the oxazoline (53) and as the 1,2+triazoline (54) by reaction with the appropriate dipolarophiles.60 Photorearrangements of heterohexa- 1,3,5-trienesto five-membered heterocycles have been reviewed.6 Me I Me P h ” k + N

A

Me\

+

N-CEN-C,,

Ph’

Me

-/

Me (52)

Me

(53)

Further studies of the photorearrangement of five-membered heterocycles have been described. The isoxazole-oxazole rearrangement has previously been shown

’’ D. P. Munro and J. T. Sharp, J. Chent. Soc., Perkin Trans. 1, 1980, 1718. 6o 61

K. Dietliker, W. Stegmann, and H. Heimgartner, Heterocycles. 1980, 14, 929. M. V. George, A. Mitra, and K. B. Sukumaran, Angew. Chem., Int. Ed. Engl., 1980, 29, 973.

431 to involve 2H-azirine intermediates. Indeed, Pyrex-filtered irradiation of the isoxazolophanes (55) affords the corresponding 2H-azirines (56).62 3-Methylisoxazolo[4,5-clpyridines are similarly converted on irradiation into 2rnethyloxazol0[4,5-c]pyridines.~~The 4-hydrazino-derivative (57), however, has


(55)

R

=H

Me

or Me

(56)

NHMe hv

Me (58)

(57)

been reported to undergo a different photorearrangement to give the 1,2dihydropyrido[3,2-e]-1,2,4-triazine (58); a common intermediate is probably involved. Results of a molecular orbital study of isoxazole-oxazole photoisomerization have been published.64 Not surprisingly the allyloxazolinone (59) Ph

Ph

co, hv

Me&Me

r

‘Me p

M

e

Me (61)

(59)

I”.

FMe

Ph

0

N

&Me

(60)

hv

(62) R = Ph, p-M&&, 62

c4

or p-M& C&

Ph (63)

E. M. Beccalli, L. Majori, A. Marchesini, and C. Torricelli, Chem. Lett., 1980, 659. G. Adembri, A. Camparini, D. Donati, F. Ponticelli, and P. Tedeschi, Tetrahedron Lett., 1981, 22, 2121. H. Tanaka, T. Matsushita, Y. Osamura, and K. Nishimoto, Int. J . Quantum Chem., 1980, 18, 463.

432

Photochemistry

behaves differently on irradiation and is converted via a symmetry-allowed 1,3sigmatropic rearrangement into the isomer (60)."' The oxazolinone (59) was itself prepared by addition of carbon dioxide to the nitrile ylide, generated in turn by irradiation of the 2H-azirine (61). A 1,5-sigmatropicrearrangement is preferred on irradiation of the photolabile pyrrolines (62) and results in the formation of ringexpanded products (63),66 whereas competing photochemically induced benzyl migrations have been observed in N-substituted 3-pyrazolin-5-0nes.~' Two pathways appear to be implicated in the transposition reactions of 3cyano-1-methylpyrazole (64)."* The first, which leads to the imidazole (65), is believed to involve 2,5-bonding followed by a nitrogen 'walk', whereas the second proceeds by way of the azirine (66) and yields the isomeric imidazole (67); both processes are illustrated in Scheme 6. Sensitization and quenching experiments CN

p N N' I Me

hv

6'"-

CN

M e - N N e

N I Me

I

+N I

Me (65)

Me (67)

%heme 6

suggest that the reactive excited state of the pyrazole has the singlet z,z* configuration. The possible role of 'Dewar' pyrroles or cyclopropenyl imines as intermediates in the photorearrangement of tetrakis(trifluoromethy1)pyrroleshas also been inve~tigated;~' the valence-bond isomer (68), for example, does seem to be involved as an intermediate in the conversion of the N-phenylpyrrole (69) into the cyclobutindole (70).

65

" 68 69

A. Padwa, M. Akiba, L. A. Cohen, and J. G. MacDonald, Tetrahedron Lett., 1981, 22, 2435. T. Debaerdemaeker, W.-D. Schroer, and W. Friedrichsen, Liebigs Ann. Chem., 1981, 502. G. Singh, D. Singh, and R. N. Ram, Tetrahedron Lett., 1981, 22, 2213. J. A. Baritrop, A. C. Day, A. G . Mack, A Shahrisa, and S. Wakamatsu, J . Chem. SOC.,Chem. Commun.. 1981, 604. Y . Kobayashi, A. Ando, K. Kawada, and I. Kumadaki, J . Org. Chem., 1980,45, 2968.

Photoreactions of Compounh containing Heteroatoms other than Oxygen

433

A novel photorearrangement has been observed in the 3-amino-4-(phenylthio)sydnones (7 1) and yields the isomeric 2-aza- 1,3-diazoniacyclopentadiene-1,4diolates (72); the proposed route is outlined in Scheme 7.70

I

I NR2

NR 2

'*\

RhC'

1 11u

N=O

R

Few new examples of photorearrangement in six-membered heterocycles have been reported. Irradiation of pentafluoropyridine in the gas phase affords the 'Dewar' isomer with a half-life of 5 days at room temperature." Two transients, thought to be isomers of azafulvene, were detected on flash photolysis. The conversion of the lactam (73) into the seco-steroid (74) on irradiation in t-butyl alcohol is viewed as arising via an electrocyclic ring-opening process, followed by addition of solvent, as shown in Scheme 8.72 Spectroscopic evidence for the

-0

(73)

Ha}

MeJCO

-0 HyJ}

'

0

(74)

Scheme 8

intermediacy of the 2,4-diazabicyclo[3.1.O]hex-2-(3)ene (75) in the photoisornerization of the I ,4-(3,4)-dihydropyrimidine (76) has been published.73 The

'* 71

72

73

H. Gotthardt and F. Reiter, Chem. Ber., 1981, 114, 1737. E. Ratajczak, B. Sztuba, and D. Price, J . Phofochem.. 1980, 13, 233. A. Canovas, J. Fonrodona, J.-J. Bonet, M. C. Brianso, and J. L. Brianso, Helv. Chim.Acta, 1980,63, 2380. R. E. van der Stoel, H. C. van der Plas, and G. Geurtsen, J . Heferocycl., 1980, 17, 1617.

Photochemistry effect of substituents on the regioselectivity of di-z-methane rearrangement in 5,6benzo-2-azabicyclo[2.2.2]octadienones has been examined,74 and 1,2,4,6,7pentakis(trifluoromethyl)-3,5-diazatricyc10[4.1 .0.02*7]hept-J-ene(77)is converted, on irradiation in ether, into the isomer (78); various mechanisms have been considered for this transformation. 7 5 On further irradiation, the bicycle (78) undergoes cleavage to the imidazole (79)and hexafluorobut-2-yne.

434

(76) R

= p-CF,C,H,

(75)

R R

'C~FR hv R

N

R H (77) R

=

CF,

-

R

I ) - R

hv

R

R E (78)

R

+

R-CEC-R

H (79)

Oxaziridines are of interest in their own right and as intermediates in various photorearrangements. It has been shown that the nature of the nitrogen substituent does not affect the regioselectivity of lactam formation on irradiation of spiroo~aziridines.'~ The oxaziridine (80) has been proposed without any real evidence as an intermediate in the photoinduced transformation of trans-canadine N-oxide

(81) to the lactam (82) and the formamide (83).77 The photorearrangements of heteroaromatic N-oxides have, in general, been rationalized in terms of intermediate oxaziridines, although in most cases, definite evidence for the existence of 74

75

76 77

M. Kuzuya, E. Mano, M. Ishikawa, T. Okuda, and H. Hart, Tetrahedron Lett., 1981, 22, 1613, Y. Kobayashi, T. Nakano, M. Nakajima, and 1. Kumadaki, Tetrahedron Lett., 1981, 22, 1369. E. Oliveros, M. Riviere, and A. Lattes, J . Heterocycl. Chem., 1980, 17, 1025. P. Chinnasamy, R. D. Minard, and M. Sh,amma, Tetrahedron, 1980, 36, 1515.


435

such species is lacking. The previously reported ring opening of pyridine N-oxide (84) in aqueous solution in the presence of secondary amines to give the 5-amino2,4-pentadienenitriles(85) and (86) has been developed as a preparative method.78

(86)

(85)

(84)

A two-step synthesis of Chydroxyindole derivatives (87) has also been reported and involves photorearrangement of isoquinoline N-oxides (88) via oxaziridines (89) to the benzoxazepines (go), followed by treatment with acid, as shown in Scheme 9.'' In a separate study, 3,l-benzoxazepines have been shown to undergo THCO,R

(88) R

=

rHC02R

Et or CH,Ph

(89)

?H

N HC02R

C02R (87)

(90)

Scheme 9

a novel photoinduced ring-contraction to yield 3-formylindoles. An oxaziridine (9 1) has been detected on irradiation of 6-cyanophenanthridone5-oxide (92) in an ethanol or 2-methyltetrahydrofuran matrix at 77K and is an intermediate in the formation of 5-ethoxyphenanthridone (93) and 6-cyanophenanthridine (94), respectively.'l 6-Cyano-3,1-dibenzoxazepine (95) was also obtained, presumably via an axygen 'walk' process involving oxaziridine (96). 1- and CAzaphenanthrene N-oxides undergo solvent-dependent photorearrangement, yielding naphtho- 1,3oxazepines in aprotic solvents and benzoquinolin-1(2H)-ones in aqueous solution.** A biphotonic process via an oxaziridine has been observed in pyrazine NN-di~xide;'~the likely product is 2,s-dihydroxypyrazine. Oxaziridines are also reported to be intermediates in the photodecomposition of chlordiazepoxide 78

79 80

81

82

83

J. Becher, L. Finsen, I. Winckelmann, R. R. Koganty, and 0. Buchardt, Tetrahedron, 1981,37, 789. C . Kaneko, W. Okuda, Y. Karasawa, and M. Somei,Chem. Left., 1980, 547. C. Kaneko, H. Fuji, S. Kawai, A. Yamamoto, K. Hashiba, T. Kimata, R. Hayashi, and M. Somei, Chem. Pharm. Bull., 1980, 28, 1157. K. Tokumura, H. Goto, H. Kashiwabara, C. Kaneko, and M. Itoh, J . Am. Chem. SOC.,1980, 102, 5643. A. Albini, G. F. Rettinetti, and G. Minoli, J. Chem. SOC.,Perkin Trans. 2, 1980, 1159. H. Kawata, S. Niizuma, and H. Kokubun, J . Photochem., 1980, 13, 261.

436

Photochemistry

I OEt (93)

(94)

C1

Ph (97)

0-

I 0. (98)

(97) 84 and the nitroxyl radical (98).85 Examples of oxygen-atom transfer have been observed on irradiation of heteroaromatic N-oxides.86- 8 8 Azomethane imines undergo an analogous photoinduced cyclization to give diaziridines. The dihydroisoquinoline derivative (99), for example, is converted on irradiation in cyclohexane or benzene into the diaziridine the transformation is thermally reversible. In contrast, the pyrazolidinone azomethine imines (101) undergo photoreversible conversion into the diaziridines (102), providing in this way a useful reversible photochromic system.g0The analogous photoisomerization of a pyrene-substituted pyrazolidinone azomethinimine has 84

86

89

P. J. G. Cornelissen and G. M. J. Beijersbergen van Henegouwen, Pharm. Weekbl. Sci.Ed., 1980, 2, 547. G. I. Shchukin, I. A. Grigor’ev, and L. B. Volodarskii, Izv. Akad. Nauk SSSR, Ser. Khim., 1980, 1421. Y.Ogawa, S. Iwasaki, and S. Okuda, Tetrahedron Lett., 1981, 22, 2277. A. G. Rowley and J. R. F. Steedman, Chem. Ind. (London), 1981, 365. M . N. Akhtar, D. R. Boyd, J. D. Neill, and D. M. Jerina, J. Chem. Sot:., Perkin Trans. I , 1980, 1693. G. Tomaschewski, U. Klein, and G. Geissler, Tetrahedron Lett., 1980, 21, 4877. G. Tomaschewski, G. Geissler, and G . Schauer, . I Prakt. . Chem., 1980, 322,623.


431

(99)

R3 R3

hv

hv

also been described.” The first authenticated example of a triaziridine, 1ethoxycarbonyl-trans-2,3-di-isopropyltriaziridine(103), has been prepared in a similar fashion;92 irradiation of isomeric acylazimines (104) gave a species with a half-life of 3.5 days at room temperature to which the triaziridine structure (103) has been assigned. Pyridine and quinoline N-imides undergo related ring-expansion reactions via diaziridines to afford diazepines. The regiospecific synthesis of 3-methoxy-1,2diazepines (105) has been achieved in this way by irradiation of ylides (106).93

OY”-

Such ring-expansion reactions have previously been limited to ylides possessing an electron-withdrawing substituent on nitrogen. Now, the tricyclic Niminopyridinium ylides (107) have been reported to give the tricyclic 1H-1,2diazepines (108) by the pathway outlined in Scheme Quinoline N-imides (109) having an electron-donating substituent in the 6- or 8-position are converted on irradiation into the 3H-l,3-benzodiazepines (1 intermediates (1 11) and 91

92

93 94

”

A. Klirnakova, M. V. Koz’menko, G. Tomashewskii,and M. G. Kuzmin, Khim. Vys. Energ., 1980,14, 149. C. Leuenberger, L. Hoesch, and A. S. Dreiding, J . Chem. Sor., Chem. Commun., 1980, 1197. T. Kiguchi, J.-L. Schuppiser, J.-C. Schwailer, and J. Streith, J. Org. Chem., 1980, 45, 5095. Y. Yamashita and M. Masumura, Chem. Lett., 1980, 621. T. Tsuchiya, S. Okajima, M. Enkaku, and J. Kurita, J. Chem. Soc., Chem. Commun., 1981. 211.

Photochemistry

438

R'

MeOH

Me

'

Ph

Ph

R2F +N

R3

R'

hv

R

2

W

R3

-N

R N,N

1

\

CO,Et

k02Et (111)

(109) R' = Me, R3 = H, RZ = OMe, NMe,, or Me R' = R3 = Me, R2 = H R' = R3 = H, R2 = O M e

N-CO Et

R3

R'

R3

(1 12) are believed to be involved. Analogous quinoline N-imides having an electron-donating group in other positions or having an electron-withdrawing group are not converted into diazepines, whereas 1H-l,3-benzodiazepines are formed in a novel two-step photorearrangement from isoquinoline N-acylirnide~.'~ The photoinduced formation of pyrazole derivatives from pyrazine and pyrimidine N-imides and of pyrrole derivatives from pyridazine N-imides is thought to involve cyclization to a diaziridine, followed by ring expansion, photoisomerization to the triazabicyclo[3.2.0]heptadiene system, and elimina t i ~ n . The ~ ' photocyclization of the phenol betaine (1 13) to the 8,lkycloberbine (1 14) has been employed in a novel synthesis of (+)-f~maricine.~*

Me0

hv ____,

'' T. Tsuchiya, M. Enkaku, and S. Okajima, Chern. Phum. Bull., 1980,28,2602. 97

98

T. Tsuchiya, J. Kurita, and K. Takayama, Chem. Phum. Bull., 1980,28,2676. M. Hanaoka, S. Yasuda. Y. Hirai, K. Nagami, and T. Imanshi, Herertwycles, 1980, 14, 1455.


439

Oxaziridines are accepted as intermediates in the photorearrangements of oximes to amides and lactams. The formation of host-guest complexes in acetophenone oxime derivatives that incorporate a crown ether moiety has been shown to stimulate triplet-derived 2-E-isomerization and to depress singletderived oxaziridine formation.99 Low yields of lactams (1 15)--(117) have been obtained on irradiation of ~-nor-5a-androstan-16-one oxime (118) in methano1.'O0 The unusual formation of lactam (1 17), in which the chirality of the

H

(115)

(1 18)

+

~

(1 16)

C

E

(117)

+ N G

\

C

q \

N

\ (1 19)

+

-

L

(120)

N

+

g E i 2 0 H

\H

H (121)

(122)

migrating carbon centre is not retained, supports the intervention of a ring-opened intermediate. The major products of this photoreaction are the seco-nitriles (1 19)--(122) arising, it is suggested, by competing ionic carbon-carbon bond cleavages. a-Fission is not observed, however, on irradiation of 3a,5cyclo-5acholestan-7-one oxime (123) in methanol, the major products being the parent ketone (124) and the isomeric lactams (125) and (126);'" these results are in

(125) 99

loo lo*

M. Tada, H. Hirano, and A. Suzuki, Bull. C k . SOC.Jpn.. 1980,53,2304. H. Suginome and T. Uchida, Bull. Chem. Soc. J p . . 1980,53,2292. H. Suginome and C.-M.Shea, J. Chem. SOC.,Perkin Trans. I , 1980, 2268.

(126)

Photochemistry

440

agreement with the suggested mechanism for the 'normal' photo-Beckmann rearrangement. Lactam formation also predominates on irradiation of steroidal p,y-unsaturated ketone oximes. The photorearrangement of o-nitrobenzaldehyde (127) to o-nitrosoknzoic acid (128) has been re-examined. l o 3 the mechanism of this conversion remains uncertain, but a transient species has been detected and tentatively assigned the

a'"" -

H,O

hv

,

a'''" N- OH I

NO2

( 127)

I 0-

OH

I

Scheme 11

structure (129); the proposed pathway is outlined in Scheme 11. This transformation has been used as the basis for a photolabile protecting group. Irradiation of the o-nitrobenzylidene acetal-containing disaccharide (1 30), for example, followed by mild oxidation with trifluoroperacetic acid (to effect OMe

i, hv ii, CF,CO,H

H',"

I c=o

6"".

oxidation of the nitroso-group), gave the partially protected disaccharide (1 3 1) with a free hydroxy-group at C(3).'04 Other similar applications have been described. l o 6 The photocyclization of certain o-nitrophenyl alkyl ethers (1 32) to give benzoxazoles (133) is also thought to involve intramolecular hydrogen abstraction by the nitro-group as shown in Scheme 12.''' Other miscellaneous photorearrangements reported include the isomerization of l o 5 7

Io3

lo4 Io5 lo6 lo'

H. Suginome, N. Maeda, Y. Takahashi, and N. Miyata, Bull. Chem. SOC.Jpn., 1981, 54, 846. M. V. George and J. C. Scaiano, J . Phys. Chem., 1980, 84, 492. P. M . Collins and V. R. N . Munasinghe, J . Chem. Soc., Chem. Commun.. 1981, 362. E. Ohtsuka, S. Tanaka, and M. Ikehara. Nucleic Acid Chem., 1978, 1, 401. A. D. Broom and D. G . Bartholomew, ivucleic Acid Chem., 1978, 2, 771. S. Oguchi and H. Torizuka, Bull. Chem. SOC.Jpn., 1980,53, 2425.


(132) R = H, Me, or Ph

441

OH

-0

0-

(133) Scheme 12

aryl isocyanides to aryl cyanides,"* examples of photo-Smiles rearrangement, log*loo and photo-Fries rearrangement of N-arylcarbamates. Rearrangements in nitrogen-containing compounds originating from excitation of a carbonyl group merit brief discussion in this Section as well as in Part 111, Chapter 1. Norrish Type I cleavage is responsible for the conversion of 2aminopyrrolin-5-ones (134) into aminocyclopropylisocyanates (135);' the products are isolated as the dimethylurea derivatives (136) by reaction with dimethylamine. The bis(2-aminopyrrolin-5-ones)(137) undergo a similar photorearrangement to form bis(isocyanates) (1 38). The azetidine-2,4-dione (1 39) has been

'''

''

6

NMe

hv

I

R (134) R = Me or Ph 0

0

J)(ziz=o I

R (135)

Me NH 2

I

R

(1 34)

(137)

prepared by irradiation of N-methylcyclohexane-1,Zdicarboximide( 140) in acetonitrile;' N-formyl-N-methylcyclohexene-1-carboxamide(141) has been shown to be an intermediate in this transformation and the proposed mechanism is shown in Scheme 13. l4 Competitive Type I and Type I1 processes have been observed in N-acylpyrrolidones.

'

lo'

Io9 'Io

'I2

'I5

''

J. H. Boyer, V. T. Ramakrishnan, K. G. Srinivasan, and A. J. Spak, Chern. Left., 1981, 43. K. Mutai and K. Kobayashi, Bull. Chern. SOC.Jpn., 1981, 54, 462. G. G. Wubbels, A. M. Halverson, and J. D. Oxman, J. Am. Chem. Soc., 1980,102,4848. J. E. Herweh and C. E. Hoyle, J. Org. Chern., 1980, 45, 2195. B. J. Swanson, G. C. Crockett, and T. H. Koch, J . Org. Chem., 1981, 46, 1082. K. Maruyama, T. Ishitoku, and Y. Kubo, J. Org. Chem., 1981,46, 27. K. Mayuyama, T. Ishitoku, and Y. Kubo, Chem. Left., 1980, 265. M. Machida, H. Takechi, A. Sakushima, and Y . Kanaoka, Heterocycles. 1981, 15, 479.

Photochemistry

442

-

hv

L

hv

0

Scheme 13

2-(N-Methylanilino)acetophenones undergo Type I1 cyclization on irradiation in diethyl ether to give 1,3-diarylazetidin-3-01~. Analogous cyclizations were observed in 2-(N-methylanilino)-2'-acetonaphthone and 2-(N-methylanilino)-ltetralone. Likewise, the heteroaryl N-methylanilinomethyl ketones (142) are converted on irradiation in diethyl ether, into isomeric 3-heteroaryl- 1phenylazetidin-3-01s (143),' and N-benzyl-a-aminoacetophenonesgave cis-2,3diarylazetidin-3-01s on n -+ n* excitation.' l 8 OH Ph,

hv

N- CH2-C-R ------+ I II Me 0 (142) R = 2-fury1, benzo[b]furan-2-yl, 2-thienyl, 1 -methylpyrrol-2-yl, or 2,4-dimethylthiazol-5-y1

Ph' (1 43)

RZ

or

R'

GR3 0

(144) R' = R3 = Ph,(145) R' = R2 = R3 = Me (146) R' = R2 = R3 = Me R2=H ' R' = Ph, R 2 = R3 = Me R' = Ph, R2 = R 3 = Me R' = R3 = Ph, R2 = H

Competing pathways to p-lactams (144) and oxazolidin-4-ones (145) were observed on irradiation of N-alkyl-a-oxoamides (146). Similar photoreactions have previously been reported for NN-dialkyl-a-oxoamides, but in the present case the reactions are less clean with many unidentified by-products. A novel intramolecular hydrogen abstraction from a formyl group is apparently responsible for the photorearrangement of N-phenacylformamide (147) to the /?-lactam (148). 120 &Hydrogen.abstraction, followed by cyclization of the biradical thus formed, has

''

K. L. Allworth, A. A. El-Hamamy, M. M . Hesabi, and J. Hill, J . Chem. Soc., Perkin Trans. I , 1980, 'I'

'I8

'I9

1671. M . M . Hesabi, J. Hill, and A. A. El-Hamamy, J . Chem. SOC., Perkin Trans. I , 1980, 2371. H. G. Henning, J. Fuhrmann, and U. Krippendorf, Z . Chem., 1981, 21, 36. H. Aoyama, M. Sakamoto, and Y. Omote, J . Chem. SOC., Perkins Truns. 1, 1981, 1357. H. Wehrli, Helv. Chim. Acfa, 1980, 63, 1915.

Photoreactions of Compounh containing Heteroatoms other than Oxygen

443

been observed to occur readily in the Mannich base (149) to give the imidazoline (150), whereas E- and t-hydrogen abstractions are preferred in N-aminoalkylphthalimides yielding hexahydropyrazines and hexahydro- 1,$-diazepines, respectively.122A mechanism involving a radical ion has been proposed to account for the latter transformation.

N

0 ( 149)

(150)

2-Dialkylaminocyclohex-2-enonesalso undergo intramolecular hydrogen abstraction on irradiation, but the delocalized biradical thus formed cyclizes in a different sense to afford a-ketoazetidines as shown, for example, in Scheme 14 for

Scheme 14

diethylaminocyclohex-2-enone(15 l).' 23 For reasons that are not entirely clear, 2benzylaminocyclohex-2-enone (1 52) is unexpectedly converted on irradiation in diethyl ether into a mixture of isomeric a-ketoaziridines (153) and (1 54). 124 NNDibenzyl- and NN-diallyl-P,y-unsaturatedamides (1 55) undergo photocyclization to give the corresponding pyrrolidin-2-ones (1 56) and (1 57); 25 intermediate lZ1

''' lZ3 lZ4 If5

J. D. Coyle, J. F. Challiner, E. J. Haws, and G. L. Newport, J . Heterocycl. Chem., 1980, 17, 1 131. M. Machida, H. Takechi, and Y. Kanaoka, Heterocycles, 1980, 14, 1255. J. C. Amould, J. Cossy, and J. P. Pete, Tetrahedron, 1981, 37, 1921. J. Cossy and J. P. Pete, Tetrahedron Lett., 1980, 21, 2947. H . Aoyama, Y. Inoue, and Y. Omote, J . Urg. Chem., 1981, 46, 1965.

Photochemistry

444 O

H

O

H

___)

R

R

I

I H ZC\ ,CHzR

.CH

\ ,CH,R

--,h

Me

I'

PhG O Me Me

P

N

h V O Me Me

( I 55) R = Ph or CH=CH,

( 1 58)

Me Me

Me Ph

CH2R

CH2R

( 156)

(157)

biradicals (158), formed in this case by an unprecedented 1,6-intrarnolecular hydrogen transfer to the alkene, appear to be implicated. An initial cyclization to the oxazoline (159) is involved in the photodecomposition of 'propyzamide' (160),'26 and the conversion of dialdehyde (161) into ( )-cis-alpinigenine (162) is the result of photoinduced enolization followed by thermal [,4 + ,2] cycloaddition. 127 R-C-NH-C-CECH 0 II Me I

hv

___+

I Me ( 1 60) R

p,.

Me

-N

Me

= 3,4-C1,C,H3

(1 59)

Me0 M e o r N h 4 e hv ___*

Me0

OMe

Meo

'H dM e 0 - OMe (162)

Addition.-Examples of photodimerization arising by [,2 + ,2] cycloaddition have been reported in unsaturated nitro-compounds 12' and the effect of solvent lZ6 12'

128

P. Meallier, B. Pouyet, J. Badin, J. Bastide, and C. Coste, Chemosphere, 1980, 9, 105. S. Prabhakar, A. M. Lobo, M. R. Tavares, and I. M. C. Oliveira, J . Chem. SOC.,Perkin Trans. I , 1981, 1273. Y. Slavcheva, V. V. Perekalin, E. S. Lipina, and 2. F. Pavlova, Zh. Org. Khim., 1980, 16, 2413.

Photoreactions of Compounds containing Heteroatoms other than Oxygen 445 on such dimerizations in maleimide and N-methylmaleimide has been investigated.12’ An intramolecular equivalent process has been observed in the 1,l’trimethylbisuracil (163), which on irradiation is converted into the cyclobutane derivative (164).130

H

O

O

H

FN N -(CH 2)3-N

O% ( 163)

HI;,-. &

do’” O

(164) D

1,3-Diacetylimidazolin-2-0ne(165) undergoes [z2 + .2] cycloaddition to ethylene on irradiation in acetone to give the cis-fused adduct (166).13’ In a separate study, good yields of cyclobutane derivatives were obtained by photoaddition of 1,3-diacetylimidazolin-2-oneto cyclopentene, dihydropyran, and 2metho~y-3,4-dihydropyran.~~~ Irradiation of N-benzoylindole (167) in the Ac

Ac

Ac ( 165)

CH ,==CHCO,Me

COPh ( 167)

presence of methyl acrylate gave a stereoisomeric mixture of dihydrocyclobut[b]indoles (168),133whereas photoaddition of N-isobutenylpyrrolidine to dimethyl fumarate takes place only in non-polar solvents.134 The preferred stereochemistry of the photoadducts, (169) and (170), of 3-ethoxycarbonyl-2phenyl-2-pyrroline4,5-dione(1 71) with substituted alkenes has now been firmly established by chemical and spectroscopic means;13’ styrene and butadiene principally form 7-excpisomers, whereas ethyl vinyl ether and vinyl aetate afford 7-endo-adducts. P. Bouk and J. Lemaire, J. Chim. Phys.. Phys. Chim. Biol., 1980, 77, 161. K. Golankiewicz and L. Celewicz, Pol. J . Chem., 1979, 53, 2075. K.-H. Scholz, J. Him, H.-G. Heine, and W. Hartmann, Liebigs Ann. Chem., 1981, 248. R. A. Whitney, Tetrahedron Lett., 1981, 22, 2063. lJ3 M. ikeda, K. Ohno, T. Uno, and Y . Tamura, Tetrahedron Lett., 1980, 3403. IJ4 F. D. Lewis, T.-I. Ho, and R. J. DeVoe, J . Org. Chem.,1980, 45, 5283. 13’ T. Sano, Y. Horiguchi, and Y. Tsuda, Heterocycles, 1981, 16, 359.

”’

IJo

Photochemistry

446

The 5-trimethylsilyl group has been shown to have a profound effect on uracil photocycloaddition reactions. 36 Irradiation of the uracil (172), for example, in SiMe,

hv

AN O

AN

O

R’ = R2 = Me or -(CH2)5R’ = H, R2 = Me

(172)

R2

H H R’ (1 73)

propene, isobutylene, or methylenecyclohexane gave only the head-to-tail adduct (173). Photocycloaddition of 6-cyanouracil (174) to alkenes gave, in addition to normal cyclobutane derivatives, products arising by migration of the cyanogroup. 37 The proposed mechanism for this transformation is illustrated in Scheme 15 for cyclopentene;adducts (175) and (176) were obtained on irradiation

’

-

M e . 5

0A

N Me ( 1 74)

hv

cyclopentene

CN

M e . 5 7 0 N’O CN Me

I

__+

M e N 5 - 0 Me

CN

(175)

in acetonitrile, whereas the imine (I 77) was the major product on irradiation in ethanol. Adducts (178) and (179), arising by [,2 + %2]process, and the pyridine (180), formed by [,4 + ,2] cycloaddition followed by methylamine elimination, have been obtained on irradiation of caffeine (181) in the presence of stilbene (182).138The competing but unprecedented formation of photoproducts (183)(185) has also been observed. The photocycloaddition of 5-fluorouracil to 5,7dimethoxycoumarin has been described,’39 and five nucleoside4’13‘

13’ 13’ 139

C. Shih, E. L. Fritzen, and J. S. Swenton, J . Org. Cliem.. 1980, 45. 4462. 1. Saito, K. Shimozono, and T. Matsuuri. J. Am. Chem. Soc., 1980, 102, 3948 G. Kaupp and H.-W. Griiter, Angew. Cheni.. Int. Ed. Engl., 1980. 19. 714. S. C. Shim. C. S. Ra. and K. H. Chae, Bull. Korean Chem. Soc.,-1980,, 1, 121.


0

0

+

+

O

N Me

447

MTk:>R O

N Me (184) R (185) R

Ph

(183)

= Ph = CH,Ph

hydroxymethyl-4,5’,8-trimethylpsoralencycloadducts have been obtained on irradiation of psoralen with native double-stranded DNA. 140 Intermolecular hydrogen-bonding in alkenyl-substituted 2-pyridones brings carbon-carbon double bonds into close proximity and thus facilitates [,2 + ,2] cycloaddition.14’ Contrasting photocycloadditions have been reported in 4methoxy-Zpyridone (1 86);14* irradiation in acetone in the presence of electronrich alkenes affords the 3-azabicyclo[4.2.0]ot4en-2-ones( 187), whereas with R

“ . O d H

hv

f---

@R

N

H

O

(187) R = Me,, CH,OAc,

or OMe

hv

, ( 186)

(1 88) R = C0,Me or C N

electron-deficient alkenes the 2-azabicyclo[4.2.0]oct-4-en-3-ones(188) are obtained. An analogous [,2 + ,2] photoaddition of 4-methoxyquinol-2-one to ethylene 143 and further examples of the photoaddition of 4-hydroxyquinol-2-one to alkenes 144 have been published. In a molecular orbital study of the photocycloaddition of quinol-Zone to alkenes, the calculated regioselectivity has been I4O 14’ 14’ 143

K. Straub. D. Kanne, J. E. Hearst, and H. Rapport, J. Am. Chem. SOC.,1981,103, 2347. P. Beak and J. M. Zeigler, J. Org. Chem., 1981,46,619. H. Fuji, K. Shiba, a 4 C. Kaneko, J. Chem. Sm., Chem. Commun., 1980, 537. C. Kaneko, T. Naito, and N. Nakayama, Chem. Pharm. Bull., 1981,29, 593. T. Naito and C. Kaneko, Chem. Pharm. Bull., 1980,uI, 3150.

Photochemistry

448

+

found to correlate with experimental results.145 [ ~ 2 ,2] Cycloadditions of isoquinol-1(2H)-ones to alkenes have also been accomplishedphotochemically;14‘ reaction of 4-acetoxy isoquinol-l(2H)-one (189) with acrylonitrile, vinyl acetate, and methylenecyclohexane, for example, proceeds in high yield to give a mixture of diasterioisomeric adducts (190).

Examples of intramolecular [,2 + ,2] cycloaddition are common and frequently occur more efficiently than related intermolecular cycloadditions. N-Methylmethacrylimide (191) undergoes reaction of this type on irradiation in acetonitrile to give cis- 1,3,5-trimethyl-3-azabicyclo[3.2.O]heptane-2,4-dione( 192) in 66% yield. 14’ An acetone-sensitized intramolecular cycloaddition in the ester (193)

hv

Me

Me 0

‘

0

-Ac

Me 0 reroc,ji!. Clicwr.. 1980, 17, 825. W . A . Feld. R . Paessum. and M . P. Serw. J . H c t i v w j d . Cliim.. 1980. 17. 1309. U . Iiniin. U . Merkle, and H. Meier. Clwrn. Bar.. 1980. 113. 2519.

477

Photoelimination

Photoelimination of nitrogen from 2,5-diphenyltetrazole (52) in an ether-pentane-ethanol glass at 77 K gave a product identified spectroscopically as diphenylnitrilimine (53).33 Dimerization of this species was observed on heating to 160-175K to give the alkene (54). Diphenylnitrilimine, generated in the same fashion, has also been trapped by ethanol as the adduct (55),34 and intramolecular addition of a nitrilimine to an alkene was observed on irradiation of the oallyloxyphenyltetrazole (56) as shown in Scheme 6. Ph I

+ -

C=N-N-Ph -

N2

0

I

I

Ph

Scheme 6

3 Elimination of Nitrogen from Diazo-compounds

The photoelimination of nitrogen from diazo-compounds provides a simple and versatile route for the generation of carbenes. The reactions of such carbenes are easily studied under various conditions. The relative amounts of carbene-derived products arising by 1,2-hydrogen migration, ( 5 7 ) and (58), and 1.2-phenyl migration, (59), on irradiation of 1,2-diphenyl-I-diazopropane (60), have been Ph

Me

+ -+Phxph

XPh N2

H

Me

(57)

(60)

(61)

Ph#Me H Ph

+

Ph

Me

Ph

H

+( (59)

(58)

(62)

found to vary with t e m p e r a t ~ r eIrradiation .~~ of the diazocycloalkene (61) affords the cyclohexadiene (62) and products arising by carbene addition to a l k e n e ~ . ~ ~ This decomposition, like those of other diazoalkanes, evidently involves the S , 33

34 3s 3h

H. Meier. W. Heinzelmann, and H. Heimgartner. Chiiwiu. 1980, 34. 504. H. Meier. W. Heinzelmann. and H. Heimpartner. Chhiu. 1980. 34, 506. H. Tomioka, H. Ueda, S. Kondo. and Y. Izawa, J . Aiu. C/tiw. Snc.. 1980. 102, 7817. G. R. Chambers and M. Jones, J. Aiii. Clierw. Sol... 1980, 102. 4516.

Photochemistry

478

state. The oxidation products obtained by irradiation of 3-n-butyl-3-phenyldiazirine in the presence of m-chloroperbenzoic acid are derived mainly from the intermediate 1-diazo- 1- ~ h e n y l p e n t a n e , ~and ~ products arising by singlet methylene insertion into the sulphur-hydrogen bond are formed on irradiation of diazomethane-hydrogen sulphide mixtures. 38 Particular interest has been shown in the reactions of photochemically generated arylcarbenes. A study of the photodecomposition of phenyldiazomethane in 2-chloropropane has revealed that carbon-chlorine bond insertion of singlet phenylcarbene predominates at low temperature in solution, whereas carbon-hydrogen bond insertion is preferred in a rigid matrix.39 The principal products of irradiation of diazoalkane (63) are phenylacetylene (64)and the cyclobutene (65), even in the presence of alkene~.~'At lower temperatures, however, carbene addition predominates as shown, for example, with isobutene as shown in Scheme 7.

\

Nz

-Nz hv

'

Ph

4:-

PhCzCH

+

"0

Ph

(63)

(64)

(65)

Me Scheme 7

The interconversion of photochemically generated singlet and triplet diphenylmethylene' has been investigated using methanol and isoprene as selective trapping agent^.^' Supporting evidence for a carbene singlet-triplet equilibrium is provided by a study of the addition of diphenylmethylene to cis- and truns-1,2di~hloroethylene.~~ Singlet addition affords the corresponding cyclopropane with greater than 90% stereospecificity, whereas triplet addition is accompanied by rearrangement and affords the alkene (66) as shown in Scheme 8. It has also been reported that pulsed excimer laser-induced excitation of diphenyldiazomethane affords certain photoproducts, namely 9,10-diphenylanthracene,9,lO-diphenylphenanthrene, and tetraphenylethylene, which have not been detected in conventional lamp-induced i r r a d i a t i ~ n .The ~ ~ rate of reaction of photochemically generated triplet phenylmethylene, diphenylmethylene, and fluorenylidene in isobutene has been monitored using e.s.r. s p e c t r o ~ c o p y . ~ ~ 37 38 j9

40 41

42

43

M . T. H. Liu. G. E. Palmer, and N. H . Chishti, J . Cliem. Snc.. Perkin Trms. -7. 1981, 53. C. W. Whang. H. L. Kao. and S. Y. Ho, J . Chin. Cliem. Sac. ( TciipciJ, 1980, 27. 137. H. Tomioka, S. Suzuki. and Y. Izawa, Ciieni. Lett., 1980. 293. R. A. Moss and W. P. Wetter. Tetraliedron Lett., 1981. 22, 997. K. B. Eisenthal. N. J. Turro. M. Aikawa. J. A. Butcher, C. DuPuy, G . Hefferon. W. Hetherington, G . M. Korenowski. and M. J. McAuliffe, J . Am. Clieni. Soc.. 1980. 102, 6563. P. P. Gaspar, B. L. Whitsel. M. Jones, and J. B. Lambert, J . Am. Cheni. Soc., 1980, 102. 6108. N. J. Turro, M. Aikawa, J. A. Butcher, and G. W. Griffin. J . Am. Client. Soc., 1980, 102, 5127. C.-T. Lin and P. P. Gaspar. Tetrahedron Lett.. 1980, 21, 3553.

Pho toeIimination Ph

Ph

):

)=N2 Ph

’

Ph

-

-

479

CI

Ph >: Ph

ci

+Cl

Ph Ph

>7

PhZC* CI

Ph

PI

)= CHCHCI,

c1

Ph (66) Scheme 8

Singlet and triplet fluorenylidenes have been generated and observed spectroscopically as transient products of irradiation of diazofluorene in a~etonitrile.~’ As a result, it has proved possible to calculate the rate of intersystem crossing and the rate constants for reaction of both carbenes with alkenes and alcohols. Reaction of singlet fluorenylidene (67) with alkenes affords cyclopropanes as the major product, as shown for methyl methacrylate in Scheme 9.46 Surprisingly,

Me

Scheme 9

such cyclopropanations have been shown to be non-stereo~elective,~~ and further studies are obviously necessary to elucidate fully the nature of the reaction intermediates. 1-Phosphoryl-substituted2-vinylcyclopropanes have been prepared by the addition of photochemically generated carbenes to 2,3-dimethylbuta~iiene.~~ Similarly, benzophenone-sensitized photodecomposition of the dimethyl ( r diazoalky1)phosphonates (68) in the presence of diketen (69) affords E- and Z-1substituted 1 -(dimethylphosphono)-5-oxaspiro[2.3]hexanes (70) and (7 1).49 Rearrangement of the carbene (72), leading to the formation of short-lived 45

46 47 48

49

J. J. Zupancic and G. B. Schuster, J. Am. Clicvii. Sot., 1980. 102, 5958. J . J. Zupancic and G. B. Schuster. J . din. Clicwi. Soc.. 1981. 103. 944. J . J . Zupancic. P. B. Grasse, and G . B. Schuster, J . Am. C l i m . Sol... 1981. 103, 2423. G. Mans and R. Hoge, Liebigs Ann. Cheni.. 1980, 1028. T. Kato. N. Katagiri, and R. Sdto, J . Org. Clicwi., 1980, 45, 2587.

480

(68) R = H, Me. Ph, p-MeOC,H,, or p-NO,C,H,

(69)

1

PhCHO

Ph (75)

(diphenylmethy1ene)phenylphosphane oxide (73), has been observed on photoelimination of nitrogen from (diazobenzy1)diphenylphosphane oxide (74): s the oxide (73) can be trapped as the adduct (75) with benzaldehyde. 4E- and 4Z-ethyl diazoethylidenecyanoacetates (76), on irradiation in benzene, are converted viu loss of nitrogen into the cyclopropene (77) and the furan (78), respectively.s2 2,5Diazocyclopentadienylidene (759, generated by irradiation of 2-diazo-2Hit imidazole (go), is biradical in character in contrast with ~yciopentadienylidene;~~ readily undergoes reaction with benzene derivatives to give 0-, rn-, and psubstituted 2-phenylimidazoles (8 1). CN

M . Regitz and H. Eckes. Chrnt. Bcv-., 1980, 113, 3303. ’ M. Regitz and H. Eckes, Tetrulirdron, 198 1, 37. 1039. ’’ C . Guiborel, R. Danion-Bougot, R . Danion. and R. Carrie, Terrcrlterlron LLJrt., 1981, 22, 441.

50

s3

N . Rru and J . Vilarrasa, C/imi. Lett., 1980. 1489.

Photoelimination 48 1 The study of the mechanism and synthetic applications of photodecomposition of diazoketones has continued to attract attention. There is already much indirect evidence for the existence of an r-0x0-carbene interconversion on photoelimination of nitrogen. A study of unsymmetrically substituted r-diazoketones (82) and (83) has now established that not only are singlet x-0x0-carbenes (84) and Ph-C-S-R II 0

Ph-C-C-R II II 0 N2

(84)

(85) in equilibrium, but that these rearranged carbenes can be trapped with a l k e n e ~The . ~ ~observation that irradiation of azibenzil-' 3 C 0 in methanol yields partially scrambled methyl diphenylacetate and unscrambled azibenzil adds further support to the intermediacy of an oxiren and virtually eliminates the possibility of any involvement of the bicyclic intermediate (86).55The carbene generated by irradiation of azibenzil (87) has been intercepted with diphenylmethanimine leading to the formation of the cyano ether (88);56 the proposed pathway is shown in Scheme 10. The amido-ether (89) is also formed, presumably Ph-C-C-Ph II II 0 Nz (87)

Ph-C-c-Ph II 0

-

Ph Ph'

'C=C=O

Ph

Ph

Ph

\ /

Ph

Ph

Ph

0 Ph II CH-C- NHf Ph / OMe Ph

Ph

\

(89)

Scheme 10

by way of a photo-WoIff rearrangement, followed by successive additions of imine and methanol. Numerous examples of photochemically induced Wolff rearrangements have been described. In a detailed study of several a-diazoketones, it has 54

"

H. Tomioka, H . Okuno, S. Kondo, and Y. izawa, J . Ant. Cheni. Soc., 1980, 102, 7123 M . A. Blaustein and J. A. Berson, Terrnlierlron Lett., 1981, 22. 1081. K. N. Mehrotra and G. Prasad, Bull. Ciiem. Sou. Jpn., 1981, 54, 604.

482

Pho t ockemist ry

been reported that Wolff rearrangement to form ketens takes place directly viu the excited singlet state of the sym-2 c ~ n f o r m e r . ~The ' sym-Econformer, however, on excitation undergoes photoelimination of nitrogen and yields products characteristic of singlet carbenes. Ring contraction has been observed on irradiation of 3diazothiochroman-4-one (90) in methanol to give the dihydrobenzo[b]thiophen ester (91) and the spiro-compound (92),'* and various unusual products have been obtained on photoelimination of nitrogen from the z-diazoketone of 2,2,5,5tetramethylthiolane-3,4-dione (93).59In particular, diazoketone (93) is converted 0

M e v MM e Me (93)

on irradiation in benzene into the dihydrothiophen (94). A Wolff rearrangement has also been observed on irradiation in methanol of the diazoketone (95) to give esters (96) and (97) of tricyclo[4.2.0.0' .4]octane.60 The effect of substituents on the temperature dependence of z-carbonyl-carbene reactivity has been examined using carbenes generated by low-temperature photolysis of methyl diazophenylacetate.6 A correction to the literature on the photoreaction of isopropylidene diazomalonate (98) with 1,3,3-trimethyIcyclohexane (99) has been reported.62The photoproduct, originally thought to be a cyclopropane derivative, has now been shown to be the cyclobutanone (1OO), the formation of which presumably involves a photo-Wolff rearrangement as illustrated in Scheme 11. Substituent effects observed in the product distribution of diazo-amide photochemistry have been ascribed to conformational factors;63 the b-lactam, oxindole, and Wolff rearrangement products appear to arise directly from the excited singlet state of the sym-2 form of the diazo-amide itself.

'' 5y 60

" b2 63

H . Tomioka. H. Okuno, and Y. Izawa. J . Org. Cltcwt., 1980, 45, 5278. Y. Tamurd, H . Ikeda, C. Mukai. S. M. M. Bayomi, and M. Ikeda, C h m . Pltmv. Bull., 1980,28. 3430. J . Bolster and R. M . Kellogg, J . Org. CIteni., 1980, 45, 4804. S. Wolff and W. C. Agosta, J . Clieni. Soc., Clicwi. Conintun.. 1981, 1 18. H . Tomioka, H . Okuno, and Y. Izawa, J . Cltcwi. Soc.. Perkin Truns. 2, 1980. 1636. R. V . Stevens. G. S. Bisacchi, L. Goldsmith, and C. E. Strouse. J . Org. Cltmi., 1980, 45. 2708. H . Tomioka. M . Kondo, and Y . Izawa, J . Org. Chcw., 1981, 46, 1090.

483

Photoelimination

hv. MeOH

Me (95)

(96)

(97)

Scheme I I

Irradiation of the pyrazoline diazo-amide (101) in methanol affords a mixture of isomeric methyl 3-phenylazobut-2-enoates ( 1 0 2 y 4 Details of the precise mechanism implicated in this transformation are uncertain, but the process must presumably involve ring opening of the intermediate carbene (1 03). A carbeneinsertion reaction is observed on irradiation of the diazo-amide (104) to give the novel p-lactam (105).65

Me

Me N=N

Ph

Ph

)=CHCO,Me Me

(105) 64

65

S. N. Ege, E. J. Gess. A. Thomas. P. Umrigar. G. W. Griffin. P. K. Das, A. M. Trozzolo, and T. M. Leslie, J. Clieni. Soc., Clwn. Commun.. 1981. 1263. G . M. Bright, M. F. Dee, and M. S . Kellogg, Heterocycles, 1980, 14, 1251.

484

Photochemistry

2-0x0-carbenes are formed on irradiation of o-naphthoquinonediazides in alcohols;66 the singlet species undergoes ring contraction yielding indenecarboxylates, whereas triplet carbenes are converted into naphthols. The photoreactions of o-quinonediazides have been r e ~ i e w e d . ~ ' Esters and thioesters of (dansy1diazomethyl)methylphosphinic acid undergo carbene insertion reactions in high yield on irradiation;68 their fluorescent properties make them suitable reagents for photoaffinity labelling studies. 4 Elimination of Nitrogen from Azides The photoreactions of azides can in most cases be rationalized in terms of intermediate nitrenes. Irradiation of t-butyl azide (106) in nitrogen matrices at 12K gave the imine (107), but no evidence was obtained for a nitrene intermediate.69 Photoelimination of nitrogen from 4-azido-2-pyrolinones provides a new synthetic route in high yield to 3-cyano-2-azetidines, as shown, for example, for the pyrrolinone (108) in Scheme 12.70 Zwitterionic intermediates have been Me I .Me-C-N3

Me, ,Me ,C=N Me

h1'

I

Me

proposed. A thermally unstable azacyclobutadiene is thought to be implicated in the conversion of tri-t-butylcyclopropenyl azide (109) into the acetylene (1 10) and the nitrile (1 11) on irradiation in an argon matrix.71

(109)

(1 10)

(1 11)

Further examples of the preparation of 2H-azirines by irradiation of a$unsaturated azides have been r e p ~ r t e d . 'The ~ azirine (112) has been proposed as an intermediate in the photoreaction of 6-azido- 1,3-dimethyluracil (1 13) with 66 67

68 69

70

R.P. Ponomareva, A. M.Komagorov, and N. A. Andronova, Zh. Org. Khim.,1980, 16, 146. R.P. Ponomareva, A. M. Komagorov, and 0. P. Studzinskii. Izv. Vvssh. Uchebn. Zaved., Khim. Khim. Tekhnol., 1980, 23, 812. J. Stackhouse and F. H. Westheimer, J. Org. Chem., 1981, 46, 1891. I. R. Dunkin and P.C. P. Thomson, Tetrahedron Lett., 1980, 21, 3813. H. W. Moore, L. Hernandez, D. M. Kunert, F. Mercer, and A. Sing, J . Am. Chem. Soc., 1981, 103,

11

1769. G. Maier and U. Schafer, Liebigs Ann. Chem., 1980, 798.

71

K . Isomura, S. Noguchi, M. Saruwatari, S. Hatano, and H. Taniguchi, Tetrahedron Lett., 1980, 21, 3879.

Photoelimination

485

I

Me

I

(’ 12)

(114)

R = Ph, 3-MeC6H,, 4-MeC6H,, PhCH,, or MeS

0

Me Scheme 13

tetrazoles (1 14) to give the 6-tetrazolyluracils (1 15): 7 3 further irradiation gave the 3-substituted fervenulins (1 16) as shown in Scheme 13. Many photoreactions of aryl azides can be interpreted as arising v i a unstable ring-fused azirines. The formation of the 6,7-diaminobenzothiazoles(1 17) and the 6-amino-8H-thiazolo[5,4-c]azepines (1 18) on irradiation of the corresponding 6azidobenzothiazoles (1 19) in diethylamine can be explained in this way, as shown in Scheme 14.74An alternative explanation for the photodecomposition of phenyl azide (120) at low temperatures has recently been advanced and involves the formation of an intermediate 1-azacyclohepta-1,2,4,6-tetraene (121). Further evidence for this pathway is to be found in a study of the photodecomposition of phenyl azide in acetic acid:75the azepin-Zone (122) is believed to arise in this way, as shown in Scheme 15. The formation of the same azepin-Zone on irradiation of phenyl azide in the presence of ‘naked’ acetate anion has been reported;76 the nature of the intermediate in this transformation is still open to question, but both benzazirine and 1-azacyclohepta- 1,2,4,6-tetraene intermediates are considered possible. In contrast, irradiation of the azide (123) in an argon matrix at 10K affords, on the basis of spectral evidence, the cyclic carbodi-imide (124).77 273 74

” 76

”

K. Hirota, K. Maruhashi, T. Asao, and S. Senda, Heterocycles, 1981, 15, 285. P. T. Gallagher, B. Iddon, and H. Suschitzky, J. Chem. Soc.. Perkin Trans. 1, 1980, 2362. H. Takeuchi and K. Koyama, J. Chem. Soc., Chem. Commun., 1981, 202. R . Colman, E. F. V. Scriven, H. Suschitzky, and D. R. Thomas, Chem. Ind. ( L o n h n ) , 1981, 249. H.-W. Winter and H. P. Reisenauer, Angen,. Chem., Inr. Ed. Engl., 1980, 19, 566.

!A2' N3

(1 19)

..a-R ElR Photochemistry

486

R

= H,

!!

N

Me, SMe, SPh, or CI

1

Et,NH

Scheme 14

Azidophenazine is converted, on irradiation in acetonitrile in the presence of amines, into 2-alkylamino-1 -aminophenazines and 2-aminophenazine. Singlet nitrene, formed by direct irradiation of the pyrazole (1 25), undergoes cyclization in high yield to give the 5H-pyrazolo[1,2-a]benzotriazol-4-iuminner salt ( 126).79 An alternative reaction pathway is preferred on triplet-sensitized

hi-. sens

(1 27) 78 79

( 125)

( 126)

G. F. Bettinetti, E. Fasani, G. Minoli, and S. Pietra, Gazz. Chim. ital., 1980, 110, 135. A. Albini, G. F. Bettinetti, and G. Minoli, Chem. LRtt., 1981, 331.

487 photodecomposition leading, presumably via a radical mechanism, to the dihydropyrazine (1 27). 1,3-Dimethyl-SH-pyrazolo[ 1‘,2’: 1,2]triazol0[3,2-a]phenazin-4-ium inner salt is similarly formed from the corresponding azide via either singlet or and the indazolo[3,2-b]triplet l-(3,5-dimethylpyrazolyl)phenazinyl-2-nitrene,80 benzothiazole (128) is a product of irradiation of the azide (129).*’ Photoelimination

(129)

(1 28)

The phenazine (130) was unexpectedly formed in low yield in addition to the benzo[c]cinnoline (13 1) on irradiation of the 2,2’-diazidobiphenyl (1 32).82 The proposal of intermediate (133), arising presumably by two successive nitrene additions to the phenyl nuclei, lacks conviction. Triazinylnitrene, generated by photoelimination of nitrogen from 2-azido-4,6-dimethoxy- 1,3,5-triazine ( 134),

(133) Me0

Me0

‘7kN3

N

F N

Me0

( 1 34)

f

O

R

NF“ Y N F N D R

Me0 (135)

has, however, been shown to add intermolecularly to alkylbenzenes to give the corresponding N-triazinylazepines (1 35).83 The nitrene (1 36), formed either by irradiation of the azide (137) or by photofragmentation of 1-azatriptycene ( 1 38), undergoes analogous conversion into the indenoacridine (139) by the route shown in Scheme 16;84in the presence of acetic acid, the acridine is further converted into A . Albini, G. F. Bettinetti, and G. Minoli, J . Chem. Soc.. Perkin Trcins. 1 , 1981, 4. D. Hawkins, J. M. Lindley, I. M. McRobbie, and 0. Meth-Cohn, J . Cliem. Soc., Perkin Trms. I , 1980, 2387. ” 83 84

A. Y a k , Bull. Chem. SOC.Jpn., 1980, 53, 2933. S. Tamura, H. Imaizumi, Y. Hashida, and K. Matsui, Bull. G e m . So

Me Me

152)

Me Me (1 53)

(1 56).94 The alcohol (1 57) was also obtained and is formed via the 5-norbornene-2endo-diazonium ion. 3-, 5, 6-, and 7-Methylnorbornane-2-diazonium ions have been generated as exo-endo-mixtures by photodecomposition of the corresponding methyl-2-norbornanone tosylhydrazones under similar condition^.^^

&

L& NdOH +HOp.J+Q,

N-NHTs

OH

OH

( 154)

(1 55)

( 1 56)

( 1 57)

Few studies of p-toluenesulphonylhydrazonesthemselves have been reported. The major products of p-tosylhydrazone derivatives of aryl and r,B-unsaturated carbonyl compounds have now been shown to be azines and sulphones, the formation of the former being preferred in benzene and the latter in methanol.96 Interest continues to be shown in the photodecomposition of diazonium salts,97*98 and aryldiazonium tetrafluoroborates have been recommended as potential photoaffinity labelling reagents for protein^.^' The key step in a recent synthesis of pyrazofurin involves the photodecomposition of the diazopyrazole (1 58) to give the hydroxypyrazole ( 1 59). l o o 2-Azahypoxanthine (160) is the major

AcO OAc (1 58) 44

" "" " H

" ''')

AcO OAc ( 159)

W. Kirmse. N . Knopfel, K. Loosen, R . Siegfried.and H . -J. Wroblowsky, C h ~ i i iBcr., . 1981. 114, 1187. W. Kirmse, M . Hartmann, R. Siegfried. H.-J. Wroblowsky. B. Zarig, and V. Zellmer, C / i f ~ 7B.w . , 1981. 114, 1793.. F. Bellesia. R. Grand]. U . M . Pagnoni. and R. Trave. J . Clriw. Res. / S ) . 1981. 112. D. Rehorek. F. Walkow. and J. Marx. Z . C h m ~ . 1980, , 20. 416. D. Isac, M . Mracec. N . Prosteanu, and Z. Simon. R i v . Roitnr. C/rim., 1981, 26, 29. B. L. Kieffer, M. P. Goeldner. and C. G. Hirth, J . Cl7cw. SOC.,Cltcw. Coninitin., 1981, 398. J . G. Buchanan, A. Stobie, and R . H . Wightman. J . Clicwr. Soi..,C/ri.ni. Coiirnrun., 1980, 916.

49 1

Photoelimination CONH,

N 2+

'-'

H

0-

(161)

(160)

( 1 62)

product of irradiation of 5-diazoimidazole-4-carboxamide( 161) in aqueous solution at pH 1 or pH 7.4-1 2. l o ' 4-Carbamoylimidazolium-5-olate (1 62) is formed, presumably via a carbene, at intervening pH values. 6 Photoelimination of Carbon Dioxide N-Alkyl-N-nitroso a-amino-acids (163), on irradiation in solution or in the solid state, are converted into amidoximes (164) with eliminatipn of carbon dioxide. l o 2 r-0x0-carboxylic acids undergo oxidative photodecarboxylation via a pathway thought to involve electron transfer. O 3 Photoelimination of carbon dioxide from esters has also been observed. Hindered biphenyls have been prepared'in this way

'

R-N-CH,CO,H , I -co, ' NO (163) R = Me, Et, CHMe,, or (CH,),Ph

HNR OH \ / /C=N

H (164)

0

hV ___)

- co,

(1 65) R = OMe or C0,Me

from substituted methyl benzoates. ' 0 4 Similarly, the dilactones (1 65) are converted on irradiation into the [2.2]paracyclophanes (166);"' the nature of the substituent has a profound effect on the efficiency of these transformations: electron-donating groups strongly enhance the formation of paracyclophanes. Photodecomposition of maleic anhydride in the gas phase has been reported to give ethylene, carbon dioxide, and carbon monoxide. O6 The fragmentation is believed to proceed via internal conversion to a vibrationally excited ground state. Photoelimination of carbon dioxide has also been observed in perfluoro-nbutanoic anhydride O 7 and in perfluorosuccinic anhydride to give tetralo' lo'

Io3 lo4

lo' '06 lo'

J. K. Horton and M. F. G. Stevens, J. Clicwi. Soc.. Perkin Truns. I , 1981. 1433. Y. L. Chow, D. P. Horning, and J. Polo, C m . J . Chem.. 1980, 58, 2477. R. S. Davidson, D. Goodwin, and G. Turnock, Tetrrilierlron Lett., 1980, 21 4943 R. Luedersdorf. J. Mai, and K. Praefcke, Z. Nrrturfimdi.. Ted. B, 1980, 35. 1420 M. Hibert and G. Solladie, J. Org. Clieni., 1980. 45, 4496. R. A. Back and J. M. Parsons, Cm. J. Chem.. 1981, 59, 1342. C. J. Stock and E. Whittle, J. Cheiii. Soc.. Frircrdiiy Trims. 1. 1980. 76, 496.

Pho tochemistry

492

fluoroethylene. l o 8 Carbon dioxide is formed together with other radical-derived products on irradiation of various acyl peroxides. Irradiation of the 4-sulphenylated 2,3-dimethylisoxazolin-5-ones ( 167) is accompanied by the loss of carbon dioxide and leads to the formation of the sulphurstabilized iminocarbenes (1 68), which can be intercepted by methanol as shown in Scheme 17.' l 2 Evidence for the formation of an organic fulminate has, at last,

''

(167) R

=

Ph, 2-naphthyl, CH,CH=CH,, CH,CH,OH, or CH,CH,OAc

(168)

SR

SR Scheme 17

'

been described. I 3 Irradiation of the 4-oximinoisoxazol-5(4H)-one (169) in an argon matrix as 1 0 K gave a species identified spectroscopically as phenyl fulminate ( 1 70).

7 Fragmentation in Organosulphur Compounds Photoreactions arising by carbon-sulphur bond homolysis have again been described. Thus, irradiation of 2-methylthio-5-alkyluracils in aqueous solution affords the corresponding 4-0x0-5-alkylpyrimidines. I4 Multilayered paracyclophanes have similarly been synthesized from the corresponding cyclic sulphides by photochemically induced removal of sulphur in the presence of triethyl phosphite.' I 5 An oxidative step must be involved in the photodecomposition of the fungicide, quinomethionate (171), in benzene to give, with loss of sulphur and carbon monoxide, the quinoxalinedione (1 72) and the methylquinoxalines ( 1 73) and ( 1 74). '

''

P. E. Watkins and E. Whittle, J . C h i . Soc., Fiirirtliij. Trrins. I. 1980, 76,503. J . Y. Nedelec and D. Lefort. Tetrrrhethon, 1980. 36. 3199. A. Kitamura. H . Sakuragi, M . Yoshida. and K. Tokumaru. Bull. C h i . Soc. Jpn., 1980. 53, 1393. 111 A . K 'itainura. H . Sakuragi, M . Yoshida. and K. Tokumaru. Bull. Chcwi. Soc. Jpn., 1980. 53. 2413. l'' T. Sasaki, K . Hayakawa, and S. Nishida, J . C / i o i ) i . Soc., Clicwt. C o t i i n i u t ~ . .1980, 1054. 'IJ C . Wentrup, B. Gerecht, D. Lagua, H , Briehl. H.-W. Winter, H. P. Reisenauer, a n d M . Winnewisser, J . Org. Chwi., 198 1, 46,1046. ''-I K . Golankiewicz, M . Szajda. a n d E. Wyrzykiewicz, Pol. J . C%ern.,1980, 54,363. 115 H. Machida. H. Tatemitsu, T. Otsubo, Y. Sakata, and S. Misumi, Bull. Clicw. SOC.J p . , 1980, 53.

lo'

'(Iy

'lo

IIh

2943. T. Clark and R. S. T. LoeRler. Prstic Sci.. 1980, 11, 45 1.

493

Pho toelimination

H

(173) R’ = H , R2 = Me (174) R’ = Me, R2 = H

( 172)

Carbon-sulphur bond homolysis has been shown to be, in addition to sulphur-sulphur bond homolysis, a primary process in the photolysis of disulphides in solution. Sulphur-sulphur bond homolysis is, however, responsible for the establishment of an equilibrium between various alkyl disulphides on irradiation. Other liquid-phase studies of the photodecomposition of acyclic alkyl disulphides have been reported,’ 1 9 * I 2 O and the quantum yield for the formation of methyl ethyl disulphide from methyl disulphide and ethyl disulphide has been determined. The disulphide ( I 75), obtained by photo-oxidation of 6-mercapto- 1,3-dimethyllumazine, undergoes photorearrangement to the dithiin derivatives (1 76) and ( 1 77) by way of initial sulphur-sulphur bond homolysis. 2 2 The photodecomposition of 2.2’-dithiodibenzoic acid derivatives has also been examined. Irradiation of

’

’’

’*

’

mi

MeCHO’ il I’

OC”” S-C-Me II

‘I7

I”

I2O I22

123

G . H. Morine and R. R. Kuntz, Pliotoclieni. Photohiol.. 1981, 33, 1. D. Gupta and A. R. Knight, Ccrtt. J . Clieiti., 1980, 58. 1350. D. Gupta, Inctirm J . Clieni., Sect. B, 1980, 19, 206. D. Gupta, lntlicrn J . CIieni., Sect. B, 1980, 19, 328. D. Gupta, Indim .I. Clieni., Sect. B, 1980. 19, 371. A. Heckel and W. Pfleiderer, Tetrcrhedron Lett., 1981. 22. 2161. B. Kohne, K. Praefcke, and C. Weichsel. Plio.sp1ioru.s Sulfitr, 1979, 7 . 21 I .

494

Photochemistry

organic disulphides in aldehydes resulted in reductive fission of the sulphur-sulphur bond and leads to the formation of an equimolecular mixture of the corresponding thiol and the thiol ester.'24 The cyclic disulphide (178) is converted in this way on irradiation in acetaldehyde into the S-acetylated dithiol (179). A photoinitiated radical chain mechanism has been proposed.

Dihydrothiadiazole 1,l -dioxides ( 180) undergo photoelimination of sulphur dioxide on irradiation to give the azines (181),'25 and the conversion of 2-ptoluenesulphonyloxycyclopent-2-enone( 182) in to 2-hydroxy-3p-tolylcyclopent-2enone ( 1 83) on irradiation is believed to proceed viu photoelimination of sulphur dioxide from an intermediate diketosulphone. ' 2 6 Singlet-state photodecomposition of alkyl arenesulphones in various solvents affords alkanols, aromatic hydrocarbons, and sulphur dioxide. 12' Further irradiation of the methyl sulphonates (184) and (185), obtained by photoinduced ring opening of the sultone

12* 125

12'

M. Takagi, S. Goto, M. Tazaki, and T. Matsuda, Bull. Cliem. Sot.. Jpn., 1980, 53, 1982. H . Quast and F. Kees, Chem. Ber., 1981, 114, 787. K. Tomari, K. Machiya, I. Ichimoto, and H . Ueda, Agric. B i d . Chem., 1980, 44, 2135. J. P. Pete and C. Portella, Bull. Sot.. Chim. Fr., 1980, 11, 275.

495

Pho toeliminution

(1 86), yields 12-hydroxy-1 l-phenylbenzolj]fluoranthene ( 1 87), ' 2 8 and the conversion of unsaturated sultones into furan derivatives by formal elimination of sulphur dioxide has been described. 29 Competing photodecomposition pathways have been observed in sulphonamides and sulphonylureas, 30 and the photohydrolysis of sulphonamides, viu the formation of donor-acceptor ion pairs with electron-donating aromatic compounds, has been reported. l 3 Irradiation of N-tosylmethylphenethylamine (188) in the presence of veratrol (189) in ethanol, for example, gave methylphenethylamine (190) in 66% yield. This procedure has also been employed in the selective detosylation of lysine peptides. Elimination of COS is effected on irradiation of o-phenylene thioxocarbonate (191) in an argon matrix, leading to the formation of cyclopentadienylidene keten (192);' 3 2 no transient species corresponding to an intermediate benzoxiren was detected.

'

'

0

CH ,CH2-N -Me Ts I

+

8 Miscellaneous Decomposition and Elimination Reactions Fragmentation and elimination reactions that cannot be included in any of the above categories are briefly reviewed in this Section. It has not proved possible to classify these processes, but analogous reactions are grouped together. Products arising by carbon-nitrogen bond homolysis have been obtained on irradiation of N-benzyldiphenylamine, 3 3 dimers of 2,4,5-triphenylimidazolyl,3 4 and N-aIkyl-4-(carboalkoxy)pyridinylradicals. ' The pyrazoline carbonyl ylides (193) are formed on irradiation of the oxirans (194),'36 and substituted 3,4epoxycycloalkenes have been converted photochemically into the corresponding 2,3-dihydrofurans. 3 7 The major products, in order of decreasing amounts, of the photolysis (A = 147 nm) of 1,l-dimethylcyclopropanehave been shown to be isobutene, ethylene, hydrogen, buta- 1,3-diene, 2-methylbuta- 1,3-diene, propylene, allene,

'

'

'

J. L. Charlton and G . N. Lypka, Can. J . Cliem., 1980, 58, 1059. H. Itokawa, T. Tazaki, and S. Mihashi, Heferocycles, 1981. 15, 1105. B. Weiss, H.Diirr, and H. J. Haas, Angew. Cltem.. Inr. Ed. Engl., 1980, 19, 648. ''I T. Hamada, A. Nishida, Y . Matsumoto, and 0. Yonemitsu, J . Am. Cltem. Soc., 1980, 102, 3978. ''' M . Torres, A. Clement, and 0. P. Strausz, J . Org. Cliem.. 1980, 45, 2271. M. Z. A. Badr, M. M. Aly. and A. M. Fahmy, Can. J . Chem., 1980, 58, 1229. T. Goto, H. Tanino, and T. Kondo, Cltem. Lett., 1980, 431. 13' K. Takagi and Y. Ogata, J . Otg. Chem., 1981, 46, 989. 13' S. N. Ege, E. J. Gess, A. Thomas, P. Umrigar, G . W. Griffin, P. K. Das, A. M. Trozzolo, and T. M. Leslie, J . Chem. Soc., Chem. Commun., 1980, 1263. *''W. Eberbach and J. C. Carrt, Chem. Ber., 1981, 114, 1027. 129

"'

Plio tocheniist ry

496

I

I

Ph

Ph (193)

( 194)

methylacetylene, and acetylene;’ 3 8 up to ten primary processes have been postulated. Irradiation (3. = 185 nm) of cis- or rruns-bicyclo[6.1 .O]nonane gave nona-l,8-diene together with small amounts of cis- and trans-cyclononenes.’ 3 9 Examples of [2 + 2]photocycloreversions of cyclobutane derivatives have been reported. 140-142 Transformations arising by photoinduced nitrogen-chlorine bond homolysis have again been observed. The Hofmann-Loftler-Freytag reaction of N-chloro-Lamino-acids, for example, affords &chlorinated intermediates which can be cyclized to proli lines,'^^ and the N-chloroamine (195) is converted on irradiation

Me” “CI

into the iminocholestane (1 96). 144 Irradiation of N-chloroammonium perchlorate and hexane in trifluoroacetic acid gave monochlorohexanes in high yield with a striking preference for the 2-isomer; 145 a free-radical chain reaction with hydrogenatom abstraction by the tertiary aminium radical has been proposed. Intramolecular photoelimination of HCI, HBr, and HI, often initiated by carbon-halogen bond homolysis, has again been widely used in the synthesis of heterocycles and alkaloids. 6-Acetyl- 1,2-dimethoxy-4H-5,6,6a,7-tetrahydrobenzo[&]thieno[2,3-g]quinoline (l97), for example, has been obtained in this way by irradiation of the bromothiophen ( 198). 46 Analogous photocyclizations have been employed in the synthesis of ( )-oliveroline, 14’( +)-domesticine, 14*

+

13H 13Y

I40 141

I 4’

143 144

155

J . B. BinkewicL. M. Kaplan. and R. D. Doepker. Cm. J. C/rcw~..1981. 59. 537. R. Srinivasan. J. A. Ors. and T. Baum. J. Org. Chcwr.. 1981. 46. 1950. K. Okada. K . Hisamitsu. and T. Mukai. J. C % c w . Sot.., C/riw. C01711171111.. 1980. 941. K. Okada. K. Hisamitsu. and T. Mukai. Tcvrtrhc,tirori Lc,/t., 1981, 22. 1251. S. Takunuku and W. Schnabel. CIICIJI. P h ~ x f*i,//.. . 1980. 69. 399. S. L. Titouani. J.-P. Lavergnr. Ph. Viallefont. and R. Jacquier. T m w h l h m . 1980. 36. 2961. A . X1. Farid. .I.McKenna. and J. M. McKennn. J . Chcw~.Soc. Ptrk.. 1979. 1. I3 I. S. E. Fuller, J. R. L. Smith, R.0. C. Norman, and R. Higgins, J . Chem. Soc.. Perkin Truns. 2. 1981,

545. I46 14-

148

S. Jeganathan and M. Srinivasan, //tt/io/r J. Clrcwr.. See./. B, 1980. 19. 1028. S. V. Kessar. Y. P.Gupta. V. S. Yadac. M. Nwrula. and T. Mohammad. Tc~/rci/ictiri~ri LCV/..1980. 21. 3307. B. R. Pai, H . Suguna, S. Natarajan, P. K. Vanaja, and R. Meenakumari, Indian J . Chem., Sect. B, 1979. 17. 525.

497

Pho toeliminat ion

I1 I'

MeOH-H,O

'

a:1,R2fJlL1' 3

I

0-JI2

-2.L

I

R' (199) R ' = Me, R 2 = H. Bu", or Ph R' = H, R 2 = H, Me, or Ph R ' = CH2Ph, R 2 = H

I

R'

R'

(200)

(201)

'

apogalanthamine analogues, 49 and certain phenanthridones. 5 0 Treatment of N alkyl-N-acyl-o-chloroanilines( 199) with excess lithium di-isopropylamide and irradiation of the resulting carbanions (200) provides a general and efficient route to oxindoles (201), 5 1 and a mechanism involving homolytic fission assisted by radical complexation has been proposed to account for the photocyclization of 5(2-halogenopheny1)- 1,3-diphenylpyrazoIes. 5 2 Intramolecular photoelimination of HCI from N-chloroacetamide derivatives is also a useful and versatile approach to the synthesis of aza-heterocycles. The Nalkyl-N-chloroacetyl derivatives (202), for example, undergo photocyclization to (203),'53 and the conversion of the N the I ,2,3,4-tetrahydroisoquinolin-3-ones chloroacetamide (204) into the lactam (205) is the key step in a synthesis of 20-deethylcatharanthine. 5 4 Intermolecular photoeliminations of HX of potential

'

OMe

OMe

7m+ Me0 (202) R

Me0 =

Me, CMe,, or CH,Ph

(203)

*o T& H

144

50

15'

Is' Is'

Is4

C02Me

C0,Me

S. Kobiyashi. M . Kihara, and T. Shingu. Ydugcrh-ir Zasslii. 1980, 100. 302. B. R . Pal, H. Suguna, B. Geetha. and K. Sardda, Inclitrri J . Clr~wi.,S c ~ r B. . 1979, 17, 503. J . F. Wolfe, M. C. Sleevi, and R . R. Goehring. J . Aiii. Clwrn. Soc.. 1980. 102, 3646. J . Grimshaw and A. P. de Silva, Can. J . Cliewi., 1980, 58. 1880. T. Hamada. Y. Okuno. M . Ohniori, T. Nishi, and 0. Yonemitsu, Clicvir. P h ~ r r i i i Bu//., . 1981, 29. 128. R . J . Sundberg and J . D. Bloom. J . Org. Clicw., 1980, 45. 3382.

498 Pho todiemistrjt synthetic value have also been described.' 55-' 6 1 Nb-Acetyltryptophan methyl (207), for example, unester (206) and 2',3'-O-isopropylidene-5-bromouridine dergo reaction on acetone-sensitized irradiation to give the substituted uridine (208). 6 2

Hop I1 I'

- HBr

X0

Me Me

(207)

Many other photochemically induced decomposition reactions arising by carbon-halogen bond homolysis have been reported, but these are essentially radical processes having no special photochemical significance and so are not reviewed in detail in this report. Attention should be drawn, however, to the accumulating evidence for both radical and ionic intermediates in such transformations. 6 3 - 1 6 5

'' 15H

lho Ihl

I" Ih3

lh4

Ih5

K. M. Wald, A. A. Nada, G. Szildgyi. and H. Wamhoff. Clicvii. Bc~r..1980. 113, 2884. K. Maruyama, M. Tojo. H. Iwamoto. and T. Otsuki, Clicwi. Leu.. 1980. 827. K. Maruyama. M. Tojo. K. Matsumoto. and T. Otsuki. Clicw. Lptt., 1980, 859. I. Saito. S. Ito. T. Shinmura. and T. Matsuura, Tktnrlidron Lcrt.. 1980, 21. 2813. S. Ito. I. Sdito. and T. Matsuura. Tc~trcrhirlrori,1981. 37. 45. K. Maruyama, T. Otsuki. K. Mitsui. and M. Tojo, J. H c w r o q d . Cliciii.. 1980. 17, 695. M. Terashima, K. Seki. C. Yoshidd. and Y. Kanaoka. Hc~fcwc,sclc~s. 1981. 15. 1075. S. Ito. 1. Saito, and T. Matsuura. J. An?. Clicw. Sol... 1980. 102. 7535. P.C. Purohit and H. R. Sonawane. T~~trcrhc.tlrort. 1981. 37. 873. B. J. Swdnson. J. C. Kutzer. and T. H. Koch, J. h i . Clicwr. Soc.. 1981. 103. 1274. J. L. Charlton. G. J. Williams. and G. N. Lypka. C w . J . Chcwi.. 19x0, 58. 1271.

Part IV POLYMER PHOTOCHEMISTRY By N. S. Allen

1 Introduction The format of this year’s report is unchanged. The past twelve years’ growth in the field of polymer photochemistry has continued, not least because of the industrial applications in such fields as photopolymerization. In fact, a new journal specifically devoted to polymer photochemistry is now available (see later references). Modern techniques such as laser flash photolysis, time-resolved emission, and derivative spectroscopy are being used to unravel the complex photophysical and photochemical processes involved in polymers. 2 Photopolymerization Photopolymerization is now a well established and highly efficient industrial process. Since the last report, some twenty-four review articles have appeared. Arthur has compiled two excellent reviews on the photoinitiated grafting of monomers onto cellulose and vinyl polmers.2 Mechanisms and commercial applications of photografting are discussed. Crivello, an international authority on cationic photopolymerization, has reviewed recent developments in photoinitiation by sulphonium salts.3 Hayashi on the other hand has reviewed both cationic and anionic photopolymerization initiated by charge-transfer complexe~.~ Several review articles have appeared on the commercial aspects of photopolymerization in coatings technology. These include discussions on the present status and f ~ t u r e applications,6,~ * and a comparison of the energy requirements between ultraviolet and electron-beam ~ u r i n g .Marechal ~ l o has reviewed his own work on the use of dyes in accelerating U.V. curing, whereas Hasegawa has reviewed four-centre-type photopolymerizations in the solid state. Interest continues in the u.v.-initiated curing of epoxy-resins 1 2 - l4 and inks.15.l6 Several general articles on U.V.curing have appeared,”-” and Bayer has given an overview of the subject.” Other review articles of interest include

’ lo I’

l3 l4

“ l9

2o

”

J. C. Arthur, jun., in ‘Developments in Polymer Photochemistry’, ed. N. S. Allen, Applied Science Publishers Ltd., London, 1980, Vol. 1, Chap. 3, p. 69. J. C. Arthur, jun., in ‘Developments in Polymer Photochemistry’, ed.N. S. Allen, Applied Science Publishers Ltd., London, 1981, Vol. 2, Chap. 2, p. 39. J. V. Crivello, in ‘Developments in Polymer Photochemistry’, ed. N. S. Allen, Applied Science Publishers Ltd., London, 1981, Vol. 2, Chap. I , p. 1. K. Hayashi, J. Radiat. Curing, 1980, 7 , 11. T. Sugimoto, Toso To Toryo, 1980,32445. C. Loucheux, Double Liaison-Chim. Paint, 1980,27, 263. K. Inomata, Shikizai Kyokaishi, 1980, 53, 530. G. E. Green and B. P. Stark, Chem. Br., 1981, 17, 228. Y. Hishino, Shikizai Kyokaishi, 1980, 53, 537. E. Marechal, Pure Appl. Chem., 1980, 52, 1923. M. Hasegawa, PoljJm.Prepr., Am. Chem. Soc., Div. Polvm. Chem., 1979, 20, 430. I. A. Provina, T. S. Yushchenko, and A. V. Uvarov, Lakokras. Mater. Ikh. Primen., 1980, 2, 313. B. Passalenti, S. Vargiu, and S. Bollani, Ind. Vernice. 1979, 33, 3. W. R. Watt, Am. Chem. Soc., 1979, 114, 17. K. Hashimoto and S. Saraiya, Am. Inkmuker, 1981,59, 20. A. Van Neerbos, Adhesion, 1980, 24,413. J. W. Prane, Polvm News, 1980, 6, 265. N. Fukumara, Kumi To Purasuchikku, 1979, 7 , 8 . K. K. Kogyo and A. Denka, Kumi To Parasuchikku, 1977, 5 , 30. H.Akiyama, Kumi To Parasuchikku, 1979, 7 , 24. W. G. Bayer, Tech. Pup. Assoc. Finish. Proc., S.M.E., (Ser) F.C., 1979, F.C. 79-203.

50I

502

Photochemistry

flash xenon curing,22 photosensitized c r ~ s s l i n k i n g , and ~ ~ photoinitiators for paint. 24 On a more commercial note, articles have appeared on photocurable pressuresensitive adhesives,25.26 trigger curing of epo~y-resins,~'and development of a photocolorimeter for monitoring cure rates.28 role of carbonyl compounds in Photoinitiated Addition Polymerization.-The initiating photopolymerization continues to be an area of prolific research. Laser flash photolysis has provided a valuable insight into both the photophysical and photochemical processes involved in carbonyl-initiated photopolymerizations. For example,,Fouassier and co-workers 29- 3 3 have found that carbonyl-initiated vinyl polymerization proceeds faster in a micellar system2' and an example of this interesting effect is shown in Table 1. Laser flash photolysis3' has shown that Table 1 Activity of photoinitiators with methyl acrylate 4 2 Photoinitiator"

Benzophenone Benzophenone + (triethylamine)b Fluorenone Benzoin Benzoin methyl ether Benzoin isopropyl ether Benzil 4,4'-Bis(dimethylamino)benzophenone Benzil diethyl ketal "1.57 & O . O I m ~ l d r n - x~ 10'.

Conversion at 10 min (%) 0.1 62.7 0.2 15.8 59.8 33.5 0.2 3.9 80.3

b4.64moldm-3 x lo2.

the presence of the micelle enhances the initiation step. The rate of propagation was found to be unaffected by the micelle. The workers have also studied the photoinitiating behaviour of various aromatic carbonyl compounds in THF solution.3'* 32 Using laser flash photolysis they determined the rate constants of several processes. For example, for benzoin the substituted benzyl radical was found to interact more strongly with THF than the unsubstituted benzyl radical, as shown in Scheme 1. The triplet lifetimes of the aromatic carbonyls were also found to be reduced at very low THF concentration^.^^ In another study the same group of workers33 have also studied vinyl polymerization by the well known 22

23

'' " 26

''

'' 29 30

31

32 33

E. Blank, J . Radiat. Curing, 1980, 7 , 15. M. Sierocka, J. Paczkowski, A. Wrzyszczynski, and A. Zakrzewski, Pr. Wydz. Nauk. Tech.,Bvdgoskie TOM', Nauk. Ser. A , 1980, 14, 67. R. Kirchmayr, G. Berner, and G . Rist, Farbe Lack, 1980, 86, 224. W. C. Perkins, J . Radiat. Curing, 1980, 7 , 4. J. Schields, Adhesion, 1977, 1, 165. R. A. Gardiner, Tech, Pap. SOC.Mnnuf. Eng., ( S e r ) Ad., 1979, AD79-917. R . W. Bush, A. D. Ketty, C. R. Morgan, and D. G . Whitt, J . Radiat. Curing, 1980, 7 , 20. A. Merlin and J. P. Fouassier, Polymer, 1980, 21, 1363. D. J . Longnot, A. Merlin, P. Jacques, and J. P. Fouassier, Makromol. Chem., Rapid Commun:, 1980, 1, 687. A. Merlin and J. P. Fouassier, Mukromol. Chemie, 1980, 181, 1307. A. Merlin, D. J. Longnot, and J. P. Fouassier, Polym. Bull., 1980, 2, 847. A. Merlin, D. J. Longnot, and J. P. Fouassier, Pofym. Buff.,1980, 3, 1 .

- -

Polymer Photochemistry 'DMPA ,DMPA

'MPA

'DMPA OCH,

+ *{*

&*

6)

0

kq

@:H3

I

THF

~

OCH,

503

k, > 10'os-l

OCH,

OCH, L + THH F * k, = 2 . 5 ~1041 mol-1s-1 I OCH, Scheme 1

benzophenone-amine system. In contrast to a previous theory 34 these workers find no evidence for an excited charge-transfer complex. Instead they propose the following mechanism involving an amine free radical as the initiating radical (Scheme 2).

Ketyl' +THF' MMA* f BP

\MMA

J

MMA' BP +Amine

Ketyl' + Amine' Scheme 2

MM A'

-1

8

Decker and Fizet3j have developed a novel laser nephelometry method for monitoring continuously by the kinetics of facile photopolymerizations. Figure 1 A

Lamp HPK 125

U.V.

Photodiode BPY 13

Figure 1 Laser-nephelometry device for investigation of photopolymerizations (Reproduced by permission from Makromol. Chem., Rapid Commun.,1980, 1, 637) 34

35

J. B. Guttenplan and S . G. Cohen, Tetrahedron Lett.. 1972, 2163. C. Decker and M. Fizet, Makromol. Chem., Rapid Commun., 1980, 1, 637

Photochemistry

504

shows the device used. The helium-neon laser analysing source emits light that is not absorbed by the monomer or photoinitiator. The laser beam passes through the quartz reaction cell and into a photodiode detector. The U.V. mercury lamp induces polymerization in the cell resulting in a translucent white gel. As the turbidity grows, the analysing laser beam is increasingly absorbed and the transmitted light decreases rapidly. The curves of percent transmittance against time then reflect the kinetics of polymerization, an example of which is shown in Figure 2 for the polymerization of trimethylolpropane triacrylate in propan-2-01.

Time in seconds

Figure 2 Transmission of the laser beam as a function of the irradiation lime in the photopolymerization of trimethylolpropane in propan-2-01 (20g 1 - ') (Reproduced by permission from Makromol. Chem., Rapid Commun., 1980, 1, 637)

Schnabel and co-workers 36 have examined the behaviour of aromatic carbonyl compounds in laser flash photolysis. For l-pheny1-2-hydroxy-2-methyl-propan1one (1) in the absence of a hydrogen-atom donating solvent, or-cleavage to give (2) and (3) was the dominant initiating step. CH,

I HO-C-C-Ph I II H,C

0

(1)

:'" -% HO-C.

I C'H,

(2)

+

C-Ph II 0 (3)

Naito et af.37 have examined the photopolymerization of methyl methacrylate initiated by poly(3-methyl-3-buten-2-one).Again or-cleavage was found to be the dominant initiating step. The photoinitiated polymerization of methyl methacrylate by benzophenone derivatives has been found to depend upon the nature of the substituent, which in turn influences the activity of the sernipinacol 39 36

37

j9

J. Eichler, C. P. Herz, 1. Naito, and W. Schnabel, J . Photochem., 1980, 12, 225. I. Naito, IS. Koga, H. Hashiuchi, and A. Kinoshita, Kobunshi Ronbumhu, 1979, 36, 777. I. 1. Dilung, V. M. Granchak, and V. P. Sherstyok, Tezisy Dokl. Ukr. Resp. Konf. Fiz. Khim, 12th. 1977, 212. V. M . Granchak, P. A. Kondratenko, V. P. Sherstyok, and I. I. Dilung, Vvsokomol. Soedin., Ser. A . 1980, 22, 1865.

Polymer Photochemistry 505 Essentially electron-donor substituents retarded polymerization, whereas electron-acceptor substituents accelerated the process. In fact, these workers obtained a good correlation between the Hammett cr values of the substituents and the polymerization rate. Remaining with benzophenone, the photopolymerization of 1,3,5-trithianehas been found to be inhibited by amines and also the absence of oxygen," whereas in the hydrogen peroxide-initiated photopolymerization of methyl methacrylate-benzophenone has been found to be a powerful accelera t ~ r .In ~ the l latter study different solvents were found to have different effects on initiation. In solvents giving low conversions, degradative initiator transfer was found to be a dominant process. The search for more efficient carbonyl photoinitiators continues to be an active area of research. Clarke and Shanks 42 have compared the photoinitiating efficiencies of several carbonyl systems using methyl acrylate as monomer, and it is found that benzil diethyl ketal is the most efficient system. Pappas and Lam43 have shown that methylsulphonate derivatives of benzophenone are more efficient photoinitiators of the polymerization of diethylene glycol divinyl ether than benzophenone itself, whereas Gupta et aZ.44 have found that 4,4'-divinylbenzophenone polymer is a better photosensitizer than benzophenone for the cycloaddition of benzo[b]thiophene with ethylene dichloride. Turro and co-workers 4 5 have found that the emulsion polymerization of styrene proceeds faster and to higher conversions when initiated by light in the presence of aromatic carbonyl compounds. Clearly, this work emphasizes the importance of U.V. methods in improving the efficiency of industrial processes. Other workers have examined the influenceof light intensity, temperature, and reaction time on the benzoin methyl ether photoinitiated polymerization of ~tyrene.'~High conversion without a sacrifice in the molecular weight was obtained by operating the reactor at a metastable state. Interestingly, the curing of polyesters by benzil-amine mixtures has been found to be hardly affected by the concentration of the benzil." This work would tend to confirm the mechanism of Fouassier et al.," where the amine radical was found to be the main initiating species. In the photodimerization of omono- and a,o-di-anthrylpolystyrenes, both inter- and intra-molecular excimer formation was found to be important.48 Other studies of intert include the photopolymerization of NN-methylenediacrylamide by anthraquinone-/.?sulphonates in the presence of bisdiazo methyl acrylate by alkoxysubstituted benzophen~nes,~~ and methyl methacrylate by pyromellitic dianhydride and anthracene. O0

41

42 43

44

" 46 47 48

S. Andrzcjewska and A. Zuk, Mater. Kauf. Ogolnopol. Symp. Polim. Siarkowsych, Ist, 1978, 38. P. Gosh, G. Mukhopadhyay, and R. Gosh, Eur. Polym. J., 1980, 16,457. S. R. Clarke and R. A. Shanks, J . Macromol. Sci., Chem., 1980, 14, 69. S. P. Pappas and C. W. Lam, J. Radiat. Curing, 1980, 7 , 2. S. N. Gupta, L. Thijs, and D. C. Neckers, Macromolecules, 1980, 13, 1037. N . J. Turro, M. F. Chow, C. J. Chung, and C. H. Tung, J. Am. Chem. Soc.. 1980, 102, 7391. H. T. Chen, C. N. Kuan, S. Settachayanon, and P. A. Chartier, AIChEJ. 1980, 26, 672. J. Mleziva and V. Cennak, Congr. FATIPEC, 1980, 15th, (1) 360. I. Mita, H. Ushiki, A, Okamoto, and K. Horie, Polym. Prepr.. Am. Chem. Soc., Div. Polym. Chem., 1979, 20, 1045.

49

G. V. Formin and P. I. Mordvintsev, Zh, Fiz. Khim., 1980, 54, 1877. A. Borer, R. Kirchmayr, and G . H. Rist, Magn. Reson. Relat. Phenom., Proc. Congr. AMPERE, 20th. 1979, 167.

E. G. Varisova and N . S. Vshiutseva, Issled. Obl. Khim. Vysokomol. Soedin. Neftekhim, 1977, 73.

506

Photochemistry

Transition-metal carbonyls have been found to exhibit some unusual behaviour with various systems.52.53 In one study 53 the presence of a halogen-donating solvent was found to be essential in the photopolymerization of phenylacetylene. The results of this work are shown in Table 2 where it can be seen that the tungsten carbonyl is particularly effective in carbon tetrachloride. Table 2 Polymerization of phenylacetylene by Group VZA metal carbonyls” No. 1 2 3 4 5 6 7

Catalyst W(CO), Mo(CO), Cr(CO), W(CO), W(CO), W(CO), W(CO),

Solvent CCl, CC1, CCl, Toluene CCl, CCl, CCI,

Zrradn. time, h 1 1 1 1 0 1/2 2

Convn.

%

R”

92.9 7.9 0.0 0.0 0.0 90.7 96.4

76900

78800 76600

“Polymerized at 30°C for 24h after catalyst solutions were irradiated at 30°C: [MI, [Cat] = 1OmM.

=

1.0~,

Clarke and Shanks 54 have examined the influence of sample thickness on the benzoin photoinitiated polymerization of butyl acrylate. They found that as the photoinitiator concentration increases so the extent of polymerization become less susceptible to changes in sample thickness. Grauchak et al. have successfully photopolymerized acrylic monomers in polyamide matrices with aromatic carbony1 compounds. In the photocycloaddition of olefins to poly(4,-vinylbenzophenone) and its copolymers with styrene, the rate of addition was found to be independent of the glass transition temperature suggesting that large-scale molecular motion is unimportant in this photoreaction. 56 The photopolymerization of methyl methacrylate using a quinoline-chlorine charge-transfer complex has been investigated. Bulk polymerization was found to follow normal free-radical kinetics, whereas in solution variable monomer exponents were observed depending on the nature of the solvent. The kinetic nonideality in solution was attributed to retardation and initiator termination via degradative chain-transfer involving solvent-modified initiating complexes and chain radicals. Similar observations were made in the photopolymerization of methyl methacrylate by a dimethylaniline-nitrobenzene complex.5 8 Remaining with methyl methacrylate photopolymerization by N-benzylpyridinium chloride in methylene dichloride is believed to be initiated by a chlorine atom formed from the decomposition of a charge-transfer complex.5 9 The presence of the halogen-

’’ V. A. Padgorodetskaya, Issled 061. Khim. Vysokomol. Soedin. Nefrekhim, 1911, 12. 53 54

55

T. Masuda, Y. Kuwane, K. Yamamoto, and T. Higashimura, Polym. Bull., 1980, 2, 823. S. Clarke and R. A. Shanks, Polym. Photochem., 1981, 1, 103. V. M. Grauchak, V. P. Sherstynk, T. 1. Viktorova, and I. I. Dilung, Tezisy. Dokl. Ukr. Resp. Kauf. Fiz. Khim, 12th. 1971, 212.

56

” 5E

s9

D. A. Holden and J. E. Guillet, J . Polym. Sci.,Polvm. Chem. Ed., 1780, 18, 565. P. Gosh and S. Chakraborty, Makromol. Chem., 1980, 181, 2597. P. Gosh and N. Mukherji, Eur. Pol-vm. J., 1981, 17, 541. K. Tabuchi, H. Okazaki, K. Inoue, T. Okubo, and T. Tanigaki, Niihama Kogyo Koto Semmon Gakko Ciyo, Rikogaku Hen, 1980, 16, 80.

Polymer Photochemistry 507 containing solvent was found to be essential for polymerization. Two independent groups of workers 60*6 1 have postulated the involvement of a charge-transfer complex in the photoinitiated copolymerization of styrene with maleic anhydride. Conversion was found to be a maximum at 405 nm in tetrahydrofuran.60 Complex formation was believed to occur between the maleic anhydride and the solvent in both investigations. Other workers have identified the free-radical species (4)---(6) in the photopolymerization of styrene-maleic anhydride.62 H,C-CH

\ oc,I ,co

0

HOCH~-HC--CH

oc,I ,c'\o 0

HC-CH

I t,.2\ \ ()-C.(-)C-O 0

The photopolymerization of N-vinylcarbazole by perylene-l,4-dicyanobenzene is believed to involve electron transfer.63 Quantum yields were found to be higher in electron-transfer sensitization than in other systems. One study of interest is the photopolymerization of acrylonitrile by nickel chloride-dimethyl formamide and hydrochloric acid. Unfortunately, the role of the acid could not be explained. The role of sulphur-containing compounds in photopolymerization appears to have attracted some interest. Bis(~-methylpyridazinyl)-3,3'-disulphide has been found to initiate the photopolymerization of styrene but inhibits the thermal p ~ l y me r iz atio n .~~ The role of thiyl radicals (PhS -) in photoinitiated polymerization of vinyl monomers by aromatic thio-compounds has been postulated by several workers.65*66 In one study,66 flash photolysis was used to identify the nature of the radical. Sulphur-containing monomers such as 4-methyl-2(viny1thio)thiazole67 and thiocyclanes 6 8 have been photopolymerized and copolymerized with other vinyl monomers. Luca et have devised a mathematical model for the photopolymerization of 2,3-dimethylbutadiene and thiourea. In the cyclic acetal-photosensitized polymerization of styrene and methyl methacrylate, the conversion was found to increase with an increase in the number of cyclic acetal groups in the initiating Asakura et al.71have described in detail the homo- and co-polymerization of P-allyloxypropionaldehydeby direct photoexcitation. Although no mechanism was postulated it was certainly free radical in nature. Triallylidene sorbital (7) has also been found to polymerize by direct photoexcitation by the radical mechanism shown in Scheme 3.72 6o 61

63 64

'' 67 68 69 'O

71

72

M. Raetzsch and G. Schicht, Acta Pol?/m..1980, 31, 419. E. Borsig, D. Hlubocka, and A. Romanov, Acta Pol.vm., 1980, 31, 407. J. Barton, I. Capek, and J. Tino. Makromol. Chem., 1980, 181, 255. N. Kitamura and S. Tazuke, Bull. Chem. Soc., Jpn., 1980, 53. 2594. T. Eda, C. Y. Huang, Y. Matsubara, M. Yoshihara, and T. Maeshima, J . Macromol. Sci., Chem., 1980, 14, 1035. S. Hayama, M. Ikehata, M. Takeishi, and S. Niino Kobunshi Ronbunshu, 1980, 37, 255. 0. Ito and M. Matsuda, Polym. Prepr.. Am. Chem. Soc., Div. Polym. Chem., 1979, 20, 562. H. Ohnishi and T. Otsu, J . Macromol. Sci., Chem., 1980, 14, 1015. A. A. Mochalov, Issled. Obi. Khim. Vysokomol. Soedin. Neftekhirn, 1977, 72. C. h c a , A. Popa, and F. Vitan, Bull. Inst. Politech. Iasi, Sect. 2, Chim. Ing. Chim., 1980, 25, 5 5 . T. Ouchi, N. So, and Y. Kornatsu, J . Macromol. Sci., Chem., 1980, 14, 277. J. I. Asakura, Y. Matsubara, M. Yoshihara, and T. Maeshima, . I Macrornol. . Sci.,Chem., 1980, 14, 803. T. Ouchi and M. Imoto, Polym. Prepr., Am. Chem. SOC.,Div. Polym. Chem., 1979, 20, 670.

Photochemistry

508 H,C-CH-HC-CH-HC-CH, I I I I 0, ,o 0, o , CH CH I I CH=CH, CH=CH (7)

HlC-

I

0,

CH-HC-

o, CH

I

I CH=CH,

I

0,

I 0,

I

/o

CH I CH=CH,

CH-HC-7H2 I I 0,dO

o, CH

I CHLCH,

C I CH=CH,

k i n g - o pcnmg

H,C-CH-HC-CH-HC-CH,’ I I I I I 0, /O 0, / O 0, 40 CH CH C I I I CH=CH, CH=CH, CH=CH,

‘(7)

, Polymer

Scheme 3

At high light intensities, the photopolymerization of methyl methacrylate has been found to deviate from the square-root law.73Radical termination at high light intensities was believed to be dominant. The photopolymerization of propylene oxide by arenediazonium salts has been found to depend markedly on the pretreatment of the monomer. 74 Several workers have observed the production of long-lived radicals in the photoinitiated polymerization of N-methylacrylamides 7 5 and propane- 1,3-diol bis(methacrylogloxyethy1carbonate). 76 In the former study, post-polymerization was observed in dioxan but not in benzene. Other studies of interest include the photoinitiated polymerization of polyionenes bearing pendant (9-anthry1)methyl groups,77 water-soluble polyesters based on sulphonimide oligourethane acrylates with methyl metha~rylate,~’unsaturated groups, polyesters,80and the telomerization of ethylene and dimethylformamide.81 In the photopolymerization of allylic and acrylic monomers, the presence of polythiols was found to enhance the process in the presence of oxygen.82 On a more commercial note, Ohtsuka et aLE3have developed light focusing plastic rods prepared from the photocopolymerization of methyl methacrylate with vinyl

’*

’3 74

T. Y . Yu, L. H . Wang, H. S. Bu, H. S. Li, and Y. L. Zhao, Kao Fen. Tzu Tung Hsun, 1980, 1, 10. T. S. Bal, A. Cox, T. J. Kemp, and J. P. Murphy, Pliotogr. Sci., 1978, 26, 49. H. Tanaka, T. Sato, and T.Otsu, Mcrkromol. Chem., 1980, 181,2421. T. E. Rudnitskaya, 0. Ya. Grinberg, A. A, Dubinskii, A. P. Shvedchikov, B. G . Dzantiev, and Ya. S. Lebedev., Khim. Vw. Energ., 1980, 14, 126. Y. Suzuki and S. Tazuke, Mncromolecules. 1980, 13, 25. J . M . Novnan and R. C. McCorkey, Polym. Prepr., Am. Chem. Soc., Div. Polym. Chem., 1978,19,407. A. P. Karnaukh, R. I. Dryagileva, I. A, Pronina, and Yu. I. Spirin, Vvsokomol. Soedin, Ser. B, 1980,

l5

76

’’ ” 79

22, 570. ‘O

81

83

A. V. Shevchuk, V. G . Matyushova, and N. A. Luneva, Plrst. Massey, 1980, 11,46. T. Gascard, B. Dederichs, and A. Sam, Tenside Deterg., 1981, 18, 17. C. R. Morgan and A. D. Ketley, J . Radicrt. Curing, 1980, 7, 10. V. Ohtsuka, Y. Koike, and H. Yamazaki, Appl. Opt., 1981, 20, 280.

Polymer Photochemistry

509

benzoate, whereas Chartier and Chen 84 have developed a system for controlling the initiation and polymerization of vinyl monomers, and Kolek and Hammill 8 5 have prepared u.v.-curable polyesters with good electrical properties. Photopolymerization in the solid state at ambient and cryogenic temperatures has attracted considerable interest. The amphilic diacetylene derivative pentacosa10,12-olignoic acid in the form on multilayers has been investigated by Fouassier et aLE6Interestingly, 3,3-distearyl thiocarboxyamine iodide was found to act as a sensitizer only if it was included into the multilayers by a co-spreading technique. was found The lattice packing of cyclo-octatriaconta-l,3,9,11,17,19,25,27-0ctayne to have a marked effect upon its solid-state photop~lymerization,~~ and a diacetylene derivative has been polymerized as rigid monolayers at a gas-water interface.88 There has been active interest in the low-temperature photopolymerization of diacetylene crystals such as hexa-2,4-diyne- 1,6-diol di-p-toluenesulphonate. These include, e.~.r.~’* optical and kinetic ~tudies.’~From e.s.r. work the structures of the diradical dimer and trimer initiators were established as shown in Scheme 4.’l The photopolymerization of 2,4-heptadecadiynoic acid and phenazine has been studied and monitored by p h o t o c o n d u ~ t i o nElectron .~~ transfer was believed to be important in initiation. Using molecular-orbital structures the photopolymerization of alkadiynes was shown to be allowed and a [2+2]-photocycloaddition process has been used to describe the topochemical polymerization of chiral 9 5 The solid-state polymerization of acrylonitrile has been inpolyrner~.’~. vestigated at cryogenic temperatures using NNN’ZV-tetramethyl-p-phenylenediamine as initiat~r.’~, 97 Surprisingly, efficient polymerization occurred owing to an electron-transfer process. Also of interest is the observation that formaldehyde undergoes photopolymerization at cryogenic temperatures to give polyoxymeth~lene.’~Other studies of interest include a discussion on crystalline-lattice control in photopolymerization,gg polymerization of surfactant polystyrene derivatives in monolayers,”’ copolymerization of 4-(methacryloyloxy)chalcone with NN-dimethylaminoethyl methyacrylate for use as a reverse osmosis membrane,lO’ and the curing of resins onto solid alumina surfaces.lo2

’’

84 85

86 87

88

P. A. Chartier and H. T. Chen, Polym. Eng. Sci., 1980, 20, 1197. R. L. Kolek and J. L. Hammill, J . Radiat. Curing, 1980, 7, 3 . J. P. Fouassier, B. Ticke, and G. Wegner, Isr. J . Chem., 1979, 18, 227. K. C. Yee, Polym. Prepr., Am. Chem. Soc., Div. Polym. Chem., 1978, 19, 165. D. R. Day, H. Ringsdorf, and J. B. Lando, Polym. Prepr., Am. Chem. SOC.,Div. Polym. Chem., 1978, 19, 16.

89

90 91

92 93 94 95

96

” 98

99 loo lo’ lo’

R. Huber and M. Schmoerer, Chem. Phys. Lert., 1980, 72, 10. C. Bubeck, H. Sixl, and W. Neumann, Chem. Phyx., 1980, 48, 269. C. Bubeck, W. Hersel, W. Neumann, H. 5x1, and J. Waldmann, Chem. Phys., 1980, 51, 1 . H. Niederwald, H. Eichele, and M. Schwoerer, Chem. Phys. Lett., 1980, 72, 242. F. Braunschweig and H. Baessler, Ber. Bunsenges. Phys. Chem., 1980,84, 177. J. K. Burdett, J . Am. Chem. SOC.,1980, 102, 5458. L. Addadi, C. D. Cohen, and M. Lahav, Charged React. Polym., 1979, 5, 183. G. N . Gerasimov, S. M . Dolotov, and A. D. Abkin, Radial. Phys. Chem., 1980, 15, 405. S. M. Dolotov, G. N. Gerasimov, and A. D . Abkin, Dokl. Akad. Nauk. SSSR, 1980, 250, 384. S. M. Dolotov, 0. A. Yuzhakov, G. N . Gerasimov, and A. D. Abkin, Vysokomol. Soedin.. Ser. B, 1980, 22, 575. M. Hasegawa, Kobunshi N o Kin0 Sekkei To Sono Oyo Shinpojumi, 1980, 1 . 0. G. Whitten and P. R. Worsham, Org. Coat. PIasr. Chem., 1978,38, 572. W. Karwai, Kobunshi Ronbunshu, 1980, 37, 157. K . Nate and T. Kobayashi, J . Coat. Technol., 1980, 52, 57.

510

Photochemistry

R

-.’ R

* ’

R’

.& .

R

/c.

I R

d R

R R

RNL

R

Schematic representation of the structure of the intermediates. n is the number of monomer units. (a) DR ( 2 d n < 5) e.g. dimer, (b) AC (2 < n < 6) e.g. trimer, (c) MO ( 3 d n < 7) e.g. trimer, (d) DC ( 3 < n < 10) e.g. trimer, (e) C (10 < n < 30) e.g. short pol-vmer, (f) SP (30 < n < 50) e.g. polymer. Scheme 4

Smets and c o - w o r k e r ~ ’have ~ ~ examined in depth direct and radical-induced cationic photopolymerizations. The latter mechanism is interesting and the authors quote as an example the cationic polymerization of butyl vinyl ether in the presence of phenylazotriphenylmethane and a silver salt with a non-nucleophilic anion, such as silver hexafluorophosphate. Scheme 5 shows initial radical production to give a triphenylmethane radical followed by electron transfer with the silver salt to give a complex. Unfortunately, such a free-radical process *03

G. Smets, A. Aerts, and J. Van Erum, P o l p i . J . , 1980, 12, 539.


51 1

2 6h + N1 +

Ph-N=N-CPh3

Ph,C

+

Ag+PF,-

+ AgPF,

-CH,-eH

I

Ph,C+PF,-

_+

Ph,k

+

Ag

+ ........ ...... +

-CH,-CH-OC4H9

OC4H9

+

Ag

PF,Scheme 5

although quite efficient, is sensitive to oxygen and therefore commercially unattractive. Crivello and Lam continue to be highly active in the search for new cationic photoinitiators. Some of the most recent include dialkylphenacylsulphonium salts lo4** O 5 and triarylsulphonium salts bearing a thiophenoxysubstituent lo6, lo' with the general structures (8) and (9,' MX, = BF,-, PF,-,

AsF,-, SbF,-, ClO,-, etc.), respectively. In the case of the latter photoinitiators their efficiencies were found to be very much dependent upon the position of substitution of the thiophenoxy-group. This effect is shown in Figure 3 for the polymerization of cyclohexene oxide. lo' The para-substituted derivative gave the highest conversion probably owing to the absence of steric hindrance. In another study lo* the same workers have found that the reactivity of triphenyl sulphonium salts decrease in the order Ph,S+SbF,- 2 Ph,S+AsF,- 2 Ph3S+PF6- 2 Ph,S+BF,- for the photopolymerization of cyclohexene oxide. Ledwith and coworkers t O9 have reported ion-pair dissociation equilibria for iodonium and sulphonium, which are believed to be important for gaining an understanding of their photoinitiation behaviour. Ledwith ' l o has also reported on the use of p,pdimethoxy-#I-phenylactophenoneand di-p-tolyliodonium hexafluorophosphate as an effective initiator for the photopolymerization of THF. Several objections have been raised regarding two earlier papers published by Kennedy and Diem on the photopolymerization of isobutylene by TiCl,. Here an olefin-TiCl, complex was postulated as the initiator. According to Gandini et ai. the paper contains

'' ''

loo lo5

lo'

lo'

'I1 '13

'

J. V. Crivello and J. H. W. Lam, Polym. Prepr., Am. Chem. SOC.,Div. Polym. Chem., 1979,20, 415. J. V. Crivello and J. H. W. Lam, J . Polym. Sci., Polym. Chem. Ed., 1980, 18, 1021. J. V. Crivello and J. H. W. Lam, J . Polym. Sci., Polym. Chem. Ed., 1980, 18, 2677. J. V. Crivello and J. H. W. Lam, J . Polym. Sci.,Polym. Chem. Ed., 1980, 18, 2697. J. V. Crivello and J. H. W. Lam, Org. Coat. Plast. Chem., 1978, 39, 31. A. Ledwith, S. Al-Kass, D. C. Sherrington, and P. Bonner, Polymer, 1981, 22, 143. A. Ledwith, Makromol. Chem., Suppl., 1979, 3, 348. J. P. Kennedy and T. Diem, Polym. Bull., 1978, 1, 29. T. Diem and J. P. Kennedy, J. Macromol. Sci. Chem., 1978, 12, 1359. A. Gandini, H. Cheradame, and P. Sigwalt, Polym. Bull.. 1980, 2, 731.

512

Photochemistry

-i

80

-

70

-

60

0

2

4 0 kred-Tm(mh.)

8

10

Figure 3 Photopolymerization of cyclohexene oxide at 20 "C using 0.021 M diflerent sulphonium salt photoinitiators (Reproduced by permission from J. Polym. Sci., Polym. Chem. Ed., 1980, 18, 2697)

three major discrepancies: (ij the mechanism of TiC1, photolysis was partly inferred; (iij the reaction scheme of the photogenerated cocatalyst is in total conflict with known experience; and (iiij the explanation of photopolymerization in terms of a condensation mechanism is highly questionable. Apparently there has been no rebuttal in the literature from Kennedy and Diem and consequently the reporter can only assume at this juncture that Gandini et al. are correct in their criticisms. Tabata and co-workers have investigated the photodimerization of Nvinylcarbazole in benzonitrile and nitrobenzene solvents. In aerobic benzonitrile the mechanism of initiation was essentially cationic, whereas in anaerobic solution it was a radical process. Using picosecond laser photolysis it was shown that cyclodimerization occurs through a diffusion-controlled encounter collision of the excited singlet state of the vinylcarbazole with an oxygen molecule, producing a vinylcarbazole radical cation and an oxygen radical anion as shown in Scheme 6. The oxygen radical anion is believed to be the initiator. In nitrobenzene, only 'I4

K. Hamanoue, H. Teranishi, M. Okamoto, Y . Furakawa, S. Tagawa, and Y . Tabata, J . Polym. Sci., Polym. Chem. Ed., 1980, 18, 91. S. Tagawa and Y . Tabata, Polym. Prepr., Am. Chem. Soc., Div.Polym. Chem., 1979,20, 411.


4 ISC

VCZ hv (VCZ*)singlet

513

-

(VCZ*):riplct

(VCZt)solv+ (0,;)solv Scheme 6

radical polyherization

-

dimerization

cationic polymerization took place and was independent of oxygen. In this case a contact charge-transfer complex is believed to be important, giving rise to the charged radical ions shown in Scheme 7. VCZ +PhNO,

-

CT complex -% (VCZ f - - -PhNO, ) Scheme 7

-

(VCZ:

)solv

+ (PhNO,

)solv

Hayashi has investigated in some detail the ionic photopolymerization of styrene monomers. Free ion lifetimes measured by pulse electrical conductivity measurements were found to agree with those calculated from steady-state conductance measurements. Other studies of interest on radical addition polymerization include the photodimerization of polymers containing thymine bases, l 7 diene polymerization by terbium complexes,' l8 polymerization of vinyl acetate, l9 and preparation of light-sensitive polyacrylates.120

'

Photografting.-Photografting of monomers onto cellulose continues to be a topic of considerable activity and industrial importance. Reinhardt and Arthur 21 have produced wrinkle-resistant cotton fabric by photografting N-methylolacrylamide monomer from an aqueous solution onto the fabric (see also reference 147). The efficiency of the process was apparently greater when the cotton-monomer solution was irradiated wet than when it was dry. Herold and Fouassier 122 have grafted methyl methacrylate onto cotton using aromatic carbonyl photoinitiators. These workers found that the presence of THF enhances the percentage photograft through its hydrogen-atom donating properties (Scheme 8).

'

R'+M R"+M R'+THF

---

RM' R'M' RH+THF' R"+THF R'H+THFr THF-M' THF'+M R'+Cell RH +Cell' Cell' +'DMPA 3DMPA i-Cell Cell'+M Cell-M' Scheme 8 'I6

''.' 120

'" 122

K. Hayashi, Polym. J., 1980, 12, 583. Y. Kita, Y. Inaki, and K. Takemoto, J. Polym. Sci., Polym. Chem. Ed., 1980, 18, 427. S. R. Rafikov, G. A. Tolstikov, B. Yu. Monakov, N. A. Vakhrnsheva, D. D. Afonichev, and V. P. Kazakov, Dokl. Akad. Nauk, SSSR, 1980,251,919. C . Simionescu and M. Bezdadea, Bul. Inst. Politech. Iasi., Sect. 2, Chim. Ing. Chim., 1980, 25, 93. Z. K, Brzozonski, B. Jozwik, and J. Kielkiewiez, J. Appl. Polym. Sci., Appl. Pofyrn. Syrnp., 1979, 35, 377.

R. M. Reinhardt and J. C. Arthur, Tex. Res. J.,1980,50,261; R.M. Reinhardt and J. A. Harris, Tex. Res. J., 1980, 50, 139. R. Herold and J. P. Fouassier, Angew. Makromol. Chem., 1980,86, 123.

Photochemistry

514

Guthrie and co-workers 123 have used an anthraquinone dye to photosensitize the grafting of N-vinyl-2-pyrrolidone onto cotton. The dye (10) sensitizes in two

ways depending upon the pH of the system. At low pH, where protonation would occur, hydrogen-atom abstraction would occur through the quinone group of the dye, whereas at high pH hydrogen abstraction would occur through the vinyl group resulting not only in grafting but also homopolymerization. Takahashi et a1.'24-126have reported on the photografting of vinyl monomers onto preoxidized cellulose. In one study'26 the rate of grafting decreased in the order methyl acrylate > methyl methacrylate > vinyl acetate > acrylonitrile > styrene. Flame-resistant textiles have been made by a continuous photografting process using a vinyl phosphonate.' 27 The photografting of methyl methacrylate onto nylon-6 has been found to occur only in the presence of fructose.'28 Other sugars do not appear to have been investigated and no mechanism was proposed. Also, the thermal stability of the polymer was considerably reduced by the grafting process. Other studies of interest include the photografting of vinyl acetate onto poly(methy1 methacrylate), 29 methacrylic acid onto high-density polyethylene,' 30 vinyl monomers onto polypropylene, l 3 and acrylic acid onto poly(viny1 alcohol) and starches. 3 2 Bellobono et al. have successfully photografted acrylated azo dyes onto polyamide and polypropylene fibres, whereas Guthrie and co-workers 34 have developed a novel water-soluble grafting photosensitizer, 4-(sulphomethy1)benzil sodium salt.

'

'

'

'

Photocrosslinking.-A considerable number of research papers have appeared in this area. One article of special interest by Damen and Neckers 1 3 5 describes a series of styrene-divinylbenzene copolymers, which not only recognize their origins, but which are also capable of guiding a subsequent photochemical 123 124

125

126 12' 12* 129

130

131 13* 133

134

F. I. Abdel-Hay, P. Barker, and J. T. Guthrie, Makromof. Chem., 1980, 181, 2063. A. Takahashi, Y. Sugahara, and S. Takahashi, Kogakuin, Daigaku Kenkyu Hokoku, 1980,48,46. A. Takahashi and S. Takahashi, Seni, Gakkaishi, 1980,36, T397. A. Takahashi and S. Takahashi, Kobunshi Ronbunshu, 1980, 37, 151. J. A. Harris, E. J. Keating, and W. R. Goynes, J . Appl. Polym. Sci., 1980, 25, 2295. A. K. Mukherjee and H. R. God, Man-Made Text., India, 1980, 23, 301. Y. P. Shim, J. S. Kim, and J. K. Lee, Polfimo, 1980, 4, 138. M. Mikhailov and I. Ibeva, God. Vissh. Khim-Tekhnol. Inst. Burgas. Bulg., 1979, 13, 47. C. H. Ang, J. L. Garnett, R. Levot, A. M. Long, andT. N. Yen, J . Polym. Sci., Polym. Lett. Ed, 1980, 18, 47 1 . D. Trimnell and E. I. Stout, J . Appf. Polym. Sci., 1980, 25, 2431. I. R. Bellobono, T. Tolusso, E. Selli, and A. Berlin, J . Appl. Polym. Sci., 1981, 26, 619. P. Barker, J. T. Guthrie, A. Godfrey, and P. N. Green, J. Appl. Polym. Sci.. 1981, 26, 521. J. Damen and D. C. Neckers, J . Am. Chem. Soc., 1980, 102, 3265.


515

reaction in a stereochemicaldirection. This is believed to be the first ever example of a 'photochemical template effect'. These authors have converted stereoisomeric a-truxillic (1 l), fl-truxinic (12), and 6-truxinic acids (13) into polymerizable monomers. These were than copolymerized with an excess of styrene and divinylbenzene to form highly crosslinked polymers. Removal of the truxillate or truxinate esters by acidic hydrolysis in methanol leaves two benzyl alcohol groups in the cavity (Table 3). Treatment of the hydrolysed polymers (14) with an excess of trans-cinnamoyl chloride yielded the polymer (15) as shown in Scheme 9. Table 3 Synthesis of memory-containing viny2 polymers 35 Monomer composition in mol % Polymer @ a-(14) @ $-( 14) @ - (1 4)

X

Template monomer, X bis(vinylbenzy1)-a-truxillate

5.0 5.0 4.8

bis(vinylbenzyl)-B-truxin~te bis(vinylbenzyl)-d-truxinate

Styrene 29.8 30.0 45.1

DVB

ZHydrolysis 30 50

65.2

65.0 50.1

30

Hydrolysis of the template molecule to completion. No additional truxillate or truxinate ester could be subsequently removed.

+

$'""

phxH H

H

p x 02CHH

COCl

= a$, or 6)

H

x =a

- 7 z

4\ 0 0

Ph

b3o=ct5

0 0

A0

\ /

0

+

I

db

b

Ph

0 0

0 0

I

Ph

4

\

HCI-CH,OH

HOOC

[Jj + COOH (1 1)

\\

COOH COOH

Ph

0 Ph

Ph

IHCI-CH,OH

6" + (11)

H O W Ph Ph

Ph

(12)

(13)

Scheme 9

4

516

Photochemistry

Irradiation of these polymers in degassed benzene produced mixtures of photodimers that would be released from the polymer by acid hydrolysis. Decout et a/. 36 - 38 have prepared a wide range of photocrosslinkable vinyl polymers containing pyridine N-oxide and aromatic N-oxide groups. The actual mechanism is not clear, but is believed to involve coupling of radicals, supposedly formed by hydrogen abstraction by the atomic oxygen or oxygen radical anion generated in the film by photochemical cleavage of the N-oxide bond. In another article,13' the same workers found the order of photosensitivity of the N-oxide polymers decreases in the order 4-vinylpyridine N-oxide > 4-vinylquinoline Noxide > p-NN-dimethylaminostyrene N-oxide > 2-methyl-5-vinylpyridine Noxide. Other photocrosslinkable polymers developed by these workers include copolymers of methyl methacrylate with cyanocinnamylydene-pyridinium groups '40 and pyridinium dicyanomethylide groups. 41 Photocrosslinkable elastomers have been developed by previously grafting photosensitizer molecules onto the polymer backbone. 142 Modification was performed by a Friedel-Crafts reaction and the subsequent crosslinking reaction was found to be extremely efficient even at low concentrations of grafting. In the preparation of photocrosslinkable polymers bearing propargyl and ally1 groups the presence of a hydroxygroup in the para-position of styrene was found to be essential for stabilizing the polymer towards oxidation. 143, 144 The photocrosslinking of poly(4-bromoacetylstyrene) in the solid phase has been found to be enhanced by the presence of divinylbenzene, ethylene glycol diacrylate, and trimethylolpropane tria ~ r y 1 a t e . l14'~ ~Wrinkle-resistant . cotton has been made by Reinhardt et al.14' by polymerizing with poly(glycidy1 methacrylate) followed by crosslinking (see also reference 121). Poly(viny1 alcohol) has been photocrosslinked with terephthalic aldehyde according to Scheme 10.148 The photocrosslinking of poly(viny1 alcohol) cinnamate has been associated with cycloaddition between polymer-bound cinnamoyl groups.'49 Only half of the reactive sites, however, undergo this reaction; the rest remain intact. Apparently site geometry is believed to control reactivity. In a study of the photosensitized polymerization of cyclic acetals,' 5 0 a terpolymer of vinyl formal-vinyl acetate-vinyl alcohol underwent decomposition, while poly(Zviny1-1,3-dioxolane) and poly(2-vinyl-4-hydroxy methyl- 1,3dioxolane) were crosslinked (Scheme 1 1).

'

'

136

13' 13' '39

140 141

143 144

145

14' 14'

150

.I.L. Decout, A. L. Combier, and C. Loucheux, J . Pol-vm. Sci., Polym. Chem. Ed., 1980, 18, 2371. J . L. Decout, A. L. Combier, and C. Loucheux, J . Pol-vm. Sci., Pol-vm. Chem. Ed., 1980, 18, 2391. J . L. Decout, A. L. Combier, and C. Loucheux, Photogr. Sci. Eng., 1980, 24, 255.

J. L. Decout, A. L. Combier, and C. Loucheux, Photogr. Sci.Eng., 1979, 23, 309. C. Roucoux, C. Loucheux, and A. L. Combier, J. Appl. Polym. Sci., 1981, 26, 1221. J. J. Cottart, C. Loucheux, and A. L. Combier, J . Appl. Polym. Sci.,1981, 26, 1233. J. A. Bouquet, J. B. Donnet, J. Faure, J. P. Foudssier, B. Haidar, and A. Vidal, J . Polym. Sci., Polym. Chem. Ed., 1980, 18, 765. M . Kato and Y. Yoneshige, Kobunshi Ronbunshu, 1980, 37, 243. M. Kato and Y. Yoneshige, J . Radial. Curing, 1980, 7 , 23. M. Tsunooka, H. Sasaki, and M. Tanaka, Kobunshi Ronbunshu, 1980,37, 249. M . Tsunooka, H. Sasaki, and M. Tanaka, J. Polym. Sci., Polym. Lett. Ed., 1980, 18, 407. R. M . Reinhardt, J. C. Arthur, and L. L. Muller, J. Appl. Polym. Sci.,1980, 25, 933. J. Poldvka, M. Uker, L. Lapcik, M. Ceppan, J. Valasck, and B. Havlinova, Chem. Zvesti, 1980, 34, 780. P. L. Egerton, E. Pitts, and A. Reiser, Macromolecules, 1981, 14, 95. T. Ouchi, C. Sato, and T. Yamamoto, J . Macromol. Sci., Chem., 1980, 14, 265.


bI

H-C-0'

6+

I 6/.o,

H"

I

I

CH2-CH-CH2-CH-

I

CH2-CH-CH2-CHI

Scheme 10

-CH2-CHI

-CH2-CHI

o/ceo I I H2C-CHR

___, -hv H-

O O L O

I I H2C-CHR

-CH2-CHI 4% 0 OCH,CHR

-CH2-CHI C /\ *CH2CHR0 0 k i n g

Network Polymer

Scheme 11

H

Photochemistry

518

Several studies have appeared on the photocrosslinking of polymers by diazides. l 5 - 5 3 These include polyphenylenes and poly(phenylquinoxoa1ines).5 2 In the former case photocrosslinking occurred in the absence of oxygen, whereas in the second case photocrosslinking was inhibited by oxygen owing to the formation of nitrenes, which underwent reaction with oxygen to form peroxyradicals. These peroxy-radicals apparently inhibited the crosslinking. Benzophene has been found to be ineffective in the photocrosslinking of certain types of polyester resins, 5 4 whereas an oligo-carbonate methacrylate of xylitol has been found to be highly suitable for the preparation of resins of high photosensitivity.lSs Pan and Morawetz lS6 have examined the rate constants for the acylation of aromatic amine groups in polymers dispersed by crosslinking, whereas Negishi et ~ 1 . ' ~have ' studied the influence of molecular motion on the photocrosslinking of poly(alky1 methacrylate)-aromatic bisazide systems. In the photocrosslinking of a copolymer of tri-n-butylstannyl methacrylate with maleic anhydride a supermolecular transformation involving anhydride and organotin segments was observed,' 5 8 whereas photodimerization has been observed in the photopolymerization of butadiene monolayers.'59 Crivello and Lam and Watt 161 have studied the photocrosslinking of epoxy-resin systems. In the former study cationic photoinitiators were found to be very effective. Many studies have appeared dealing with the properties of crosslinked polymer systems. These include adhesion of epoxy-acrylates onto tin-plate, 6 2 adhesion of isocyanate and epoxy-resin coatings,163adhesion of butadiene-acrylate rubbers onto metals, glass, and ceramics,164 adhesion of acrylic, thiol, and polyester resins to aluminium bodies,'65 and the mechanical and physical properties of photocrosslinkable poly(viny1 cinnamate), vinyl-divinyl copolymers,168 polythiols,' 6 9 acrylates, epoxies, and thiols,' 7 0 epoxy resins,"' polyesters on wood,' 7 2

''

'

151

15'

.

153

154 155

15' Is'

159

I6l 162 164

l'' I"

16' 169

V. M. Trenshnikov, N. V. Frolova, A. V. Oleinik, and Yn. D. Semehikov, Fiz.-Khim. Osnovy. Sinteza Pererab. Polim. (Gorkii). 1979, 4, 76. V. M . Trenshnikov, T. V. Kudoyavtseva, A. V. Oleinik, V. A. Sergaev, and Yn. A. Chernomordik, Vysokomol. Soedin., Ser. A , 1980, 22, 830. V. M. Trenshnikov, N. V. Frolova, N. V. Karayakin, and A. V. Oleinik, Vysokomol. Soedin., Ser. A , 1980. 22, 1443. V. Cermak and J. Mleziva, Poiimerz, 1979, 24, 401. E. Keitners, R. Pernikis, N. Veinberg, I. Zaks, and V. P. Karlivans, Latv. PSR Zinat. Akad. Vestis. Khim. Ser., 1979, 5 , 553. S. S. Pen and H. Morawetz, Macromolecules, 1980, 13, 1157. N. Negishi, T. Suzuki, M. Momiyama, and I. Shinohara, Kobunshi Ronbunshu, 1980, 37, 549. Z. M. Rzaev, A. T. Aliev, S. Z. Rizaeva, S. G. Mamedova, M. R. Kiselev, and U. Kh. Agaew, Vysokomol. Soedin., Ser. B, 1980, 22, 831. A. Barraud, C. Rosilio, and A. Ruaudel-Teixier, Polym. Prepr., Am. Chem. SOC.,Div.Polym. Chem., 1978, 19, 179. J. V. Crivello and J. H. W. Lam, Am. Chem. SOC., Symp. Ser., 1979, 114, 1. W. R. Watt, Am. Chem. SOC.,Symp. Ser., 1979, 114, 17. A. Neerbes, C. A. M. Hoefs, and E. A. Giezen, Congn. FATIPEC, 1980, 15th (I), 1-319. A. Noomen, Congn. FATIPEC, 1980, 15th (I), 1-346. V. V. Kadykov and D. A. Kochkin, Kuuch Rezinu, 1980, 11, 59. G. M. Lucas, A. Patsis, and D. A. Bolon, J. Radiat. Curing, 1980, 7, 4. M. Koshiba, T. Yamaoka, and T. Tsunoda, Kobunshi Ronbunshu, 1980, 37, 227. T. Yamaoka, J. Rudiat. Curing, 1980, 7, 4. M. M. Micko and L. Paszner, J . Rudiat. Curing, 1980, 7, 1. H. Kanehiro and T. Hanyuda, Shikizai Kyokaishi, 1980, 53, 140. D. A. Bolon, G. M. Lucas, D. R. Olson, and K. K. Webb, J. Appl. Polym. Sci., 1980, 25, 543. Y. Suzuki, T. Fujimoto, S.Tsunoda, and K. Shibayama, J. Macromol. Sci.,Phys., 1980, 17, 187. E. M. Garyachaya and V. F. Kashan, Izv. Vyssh. Uchebn. Zuved. Lesn. Zh., 1980, 4, 71.


519

and acrylourethanes.173Barrett 174 has described the use of a number of methods for measuring the degree of cure of photopolymers. Other studies of interest include the photocrosslinking of urea resins,175polyesters,176paint films,’ 77 epoxy resins,’ 78 i~ocyanates,”~ooligoester rnaleates,l8O and substituted methacrylates. 81 3 Optical and Luminescence Properties Several interesting review articles have appeared by authorities in the field. de Schryver 8 2 has discussed general photophysical processes in polymers including photopolymerization, and Schnabel 8 3 has reviewed energy-migration processes. Ciardelli et have reviewed optically active polymers and Prabhakarran 18’ has discussed model materials for photo-orthotropic-elasticity.Stress analysis of composites through photo-anisotropic elasticity has been examined by Jacob. 186 Several research papers have appeared on optically active polymers. 18’- lg2 Chiellini et ul.187i18* have prepared optically active copolymers of N-vinylcarbazole with menthyl acrylate-methacrylate and menthyl acrylate-methacrylate with spaced carbazole monomers. Farina has also prepared optically active polymers by inclusion polymerization. Other optically active polymers that have been prepared include polyethylenimine containing L-proline and thymine 191 and copolymers of 9-vinylcarbaxole and menthyl vinyl ether.’ 9 2 Labsky et al.lg3have studied the photochromic behaviour of spiropyrans. For example, 1’,3‘,3’-trimethyl-6-nitrospiro(2H-1-benzopyran-2,2’-indoline) undergoes the configurational change shown in Scheme 12.

’

Scheme 12 173 174 17s

176 177 178 179

180

181

182

183 184

185

186 187 188 1 UY

I 90 191

192 I93

J. R. McDowell, Radiat. Phys. Chem., 1979, 14, 883. J. L. Barrettt, J. Radiat. Curing, 1979, 6, 20. V. V. Panov, Zb. Ref. Semin. Prokroky Vyrobe Ponziti Lepide Drevopriem, 1979, 4, 83. R. L. Kolek and J. L. Hammill, Plast. Compd., 1979, 2, 52. A. C. J. Van Oosterhaut, Double Liaison-Chim. Paint, 1980, 21, 135. W. R. Watt, Org. Coat. Plast. Chem., 1978, 39, 36. V. G. Matyushova, A. V. Shevehuk, P. V. Datsenko, and S . L. Melnikova, Vysokomol. Soedin., Ser. A , 1980, 22, 1233. A. S. Rat, A. E. Chermyan, and V. D. Gerber, h k o k r a s . Mater. Ikh. Primen, 1980, 3, 27. J. C. Dubois and A. Eranian, Plast. Electron Microelectron (J. Etud. Group. Primot. Connaiss Plast.) , 1978, 187. F. C. de Schryver, Makromol. Chem., Suppl., 1979, 3, 85. W. Schnabel, Pure Appl. Chem., 1979,51, 2373. F. Ciardelli, E. Chiellini, and C. Carlini, in ‘Optically Active Polymers’, Vol. 5 of Charged and Reactive Polymers, ed. E. Selegny, D. Reidel, Boston, 1979, p. 83. R. Prabhakaran, Fibre Sci. Technol., 1980, 13, 1. K. A. Jacob, J. Ind. Inst. Sci., 1980, 62, 129. E. Chiellini, R. Solaro, G. Galli, and A. Ledwith, Macromolecules, 1980, 13, 1654. E. Chiellini, R. Solaro, F. Ciardelli, G. Galli, and A. Ledwith, Polym. Bull., 1980, 2, 577. C. G . Overberger and Y . Morishima, J. Polym. Sci., Polym. Chem. Ed., 1980, 18, 1433. M. Farina, G. D. Silvestro, and P’. Sozzani, Makromol. Chem., Rapid Commun., 1981, 2, 51. C. G. Overberger and Y . Morishima, J. Polym. Sci.,Polym. Chem. Ed., 1980, 18, 1433. E. Chiellini, R. Solaro, A. Ledwith, and G. Cali, Eur. Polym. J., 1980, 16, 875. J. Labsky, F. Mikes, and J. Kalal, Polym. Bull., 1980, 2, 785.

520

Photochemistry

Photoelectron spectra of molecularly doped polyacetylenes have been examined,194and the thermal degradation of PTFE has been studied by the same technique. The spectroscopic properties of poly( 1,6-di-p-toluene sulphonyloxy2,6hexadiyne) have been examined in the solid state and solution.196The polymer chains were found to exist in two forms; a quasicrystalline form with properties close to those of a single crystal and a chain-extended-form occurring in solution and colloidal suspension. Chapoy and co-workers 19' have examined the spatial disposition of a probe molecule in uniaxially orientated poly(N-vinylcarbazole) by dichroic absorption. They found that the visible dichroic absorption of the probe was related only to the amorphous regions of the polymer. Surprisingly, the probe was found to align itself perpendicularly to the stretching direction. Of particular interest are a few articles by Nuyken and Talskylg8 and Allen and coworkers 99-2oo on the use of u.v.-visible derivative spectroscopy for analysing polymer films. This technique has been shown to have several advantages over normal zero-order spectroscopy, particularly for resolving the absorptions due to mixtures of impurities or additives. An example of this outstanding effect is shown in Figure 4 for polyethylene made using an aromatic peroxide. All the impurity chromophores are seen to be clearly resolved. The conformation of polypeptides Absorbance (----I

2nd Derivative (-)

2.0

1.o

0.5

0.0 Wavelength (nm)

u.v.-visible absorption Figure 4 Normal (zero) (- -- -) and second-order derivative (-) spectra of low-density polyethylene film made using an aromatic peroxide (100 pm thick) (Reproduced by permission from Chem. Ind. (London), 198 1, 28 1) H. R . Thomas, W. R. Salaneck, C. B. Duke, E. W. Plummer, A. J. Heeger, and A. G. MacDiarmid, Polymer, 1980, 21, 1238. 195 D. Betteridge, N. R. Shoko, M. E. A. Cudby. and D . G. M. Wood, Polymer, 1980, 21, 1309. ' 9 6 D. Bloor, D . N. Batchelder, J. Ando, R. T. Read, and R. J. Young, J. Poivm. Sci., Polvm. Phys. Ed., 1981, 19, 321. IY7 L. L. Chapoy, R. K. Sethi, P. R. Sorensen, and K. H. Rasmussen, Polym. Photochem., 1981, 1, 131. 19' 0. Nuyken and G. Talsky, Poldvm.Bull., 1980, 2, 719. 19' N . S. Allen, Polq'm. Pliotocltem., 1981. 1, 43. N. S. Allen, K. 0.Fatinikun, and T. J. Henman, Chem. fnd. (London), 1981, 119. 19'


52 1

has been studied by circular dichroism,201 and photochromism in polymers has been related to the free-volume theory.202 The luminescence properties of polymers continue to be widely used for investigating degradation processes. Stuckey and Roberts 203 have examined the luminescence and photo-oxidation properties of copolymers of poly(ethy1ene terephthalate+V-sulphonyl dibenzoate) yarns. They found that the presence of the sulphonyl linkages sensitize photo-oxidation of the polyester. The luminescence studies ruled out an energy-transfer process. Dellinger and Roberts '04 report a similar study on copolymers of butylene terephthalate and oxytetramethylene terephthalate; but in this case they concluded that singlet oxygen generation could be important owing to the long-lived nature of the triplet terephthalate chromophores. However, the mechanism was highly speculative and completely lacked any experimental evidence. Davidson and Roberts 2 0 5 have classified the luminescence characteristics of a wide range of bromine-containing fire-retardants, and Selwyn and Scaiano '06 have characterized the triplet state of pol y @-methoxyacry lophenone). The chemi- and thermo-luminescence of polymers have also been widely investigated as an analytical probe for degradative and oxidative processes. The chemiluminescence of poly(viny1 methyl ether) in the absence of oxygen has been associated with the decomposition of surface hydroperoxide groups. 2 0 7 Oxyluminescence has been used to study polymer composition.208 It was found that the spectra of the block copolymers of styrene, polybutadiene, and their copolymers resembled that of the polybutadiene phase (Figure 5). It was suggested that the surface composition of the copolymer resembles that of polybutadiene. The oxyluminescence of nylon-6,6 has been associated with non-stationary alkyl peroxy radicals in the polymer '09 whereas the thermoluminescence of irradiated aliphatic oligesters has been associated with two phenomena, viz, recombination of acyl radicals and recombination of an ester cation with trapped electrons.210 There appears to be some conflict in the literature regarding the origin of thermally stimulated current in anionic polystyrene. Neumann and Macknight 2 1 have associated it with a simple viscosity effect unlike other workers who have associated it with some molecular origin. 2 1 The activation energy of polymer mobility has been measured using radio-thermoluminescence and a correlation has been found between radio-thermoluminescence intensity and gel fraction in low density polyethylene.2l4 The chemiluminescence of stressed polymers has

'O'

'03 '04 '05

'06 '07

'08 '09 'lo

'I1 'I' '13

A. Ueno, J. Anzai, K. Takahashi, and T. Osa, Kobunshi Ronbunshu, 1980,37, 281. C. D. Eisenbach, Ber. Bunsenges. Phys. Chem., 1980,84, 680. W. C. Stuckey and C. W. Roberts, J . Appl. Polym. Sci., 1981,26, 701. J. A. Dellinger and C. W. Roberts, J . Polym. Sci., Polym. Chem. Ed., 1980, 18, 3129. T. E. Davidson and C. W. Roberts, J. Appl. Polym. Sci., 1980, 25, 2439. J. C. Selwyn and J. C. Scaiano, Polymer, 1980, 21, 1365. K. Naito and T. W. Kwei, J . Polym. Sci., Polym. Chem. Ed., 1980, 18, 1635. K. Naito and T. W. Kwei, Macromolecules, 1980, 13, 1018. G. A. George and S. Z. Riddell, J . Macromol. Sci., Chem., 1980, 14, 161. M. Tsumura, S. Takahashi, N . Omi, and Y. Hama, Radiat. Phys. Chem., 1980, 16, 67. R. M. Neumann and W. J. MacKnight, J . Polym. Sci., Pol-vm. Phys. Ed., 1981, 19, 369. G. Lacabanne, P. Goyand, and R. F. Boyer, J. Polym. Sci., Pol.vm. Phys. Ed., 1981, 19, 369. V. A. Aulov and N. F. Bakeev, Dokl. Akad. Nauk. SSR, 1980,255, 1400. I. Mikhaleevd and S. Jipa, Radiochem. Radioanal. Lett., 1980, 43, 19.

522

Photochemistry I 06 0

POLYBUTADIENE

105

104

In V

Io3

102

Figure 5 Oxyluminescence of polystyrene, polybutadiene, and their copolymers. Ordinate, counts per second (Reproduced by permission from Macromolecules, 1980, 13, 1018).

’

been used to elucidate the mechanochemical contribution to polymer ageing,2 whereas other studies have dealt with carrier traps in crystalline polymers,216 effect of environment on thermoluminescence,2l 7 electroluminescence of poly(viny1 chloride),21 and triboluminescence of poly(methy1 methacrylate) in laser irradiati~n.~”The photoconductivity of dyed nylon films has been investigated using a transverse field The peak photocurrent was found to be proportional to the actual power of the light quanta absorbed. Polymer photochemistry has now moved into the solar energy field involving water photolysis. Japanese workers 2 2 1 - 2 2 4 have discovered that certain ruthenium trisbipyridyl complexes with viologen-containing polymers have the ability to generate molecular hydrogen. Electron migration along the polymer chain is believed to be an important process in the mechanism. The photophysics and photochemistry of polymers and doped polymers continue to be widely investigated by luminescence spectroscopy. Intermolecular energy-transfer processes and their importance in various photochemical applications such as a photopolymerization, polymer mobility, and photostabilization D. L. Fanter and R. L. Levy, Org. Coat. Plast. Chem., 1978, 39, 599. M . Ieda, Y. Suzuoki, and T. Mizutani, Conf. Rec. IEEE Int. Symp. Elect. Insul., 1980, 158. ’I7 D. L. Fanter, R. L. Levy, and K. 0. Lippold, Org. Coat. Plast. Chem., 1978, 39, 6 0 3 . ‘IU P. Cracium. An. Univ., Timisoara,. Ser. Stiite Fiz. Chem., 1979, 17, 15. ’Iy N. P. Norikov, Ukr. Fiz. Zh., 1980, 25, 1956. 2 2 0 D. B. Freeston. C. H. Nicholls, and M. T. Pailthorpe, Polym. Photochem., 1981, 1, 85. 2 2 1 T. Nishyima, T. Nagamura, and T. Matsuo, J . Polym. Sci.. Polym. Lett. Ed., 1981, 19, 65. 22’ H. Kamogawa, T.Rui, and M. Navasawd, Chem. Lett., 1980, 9, 1145. 2 2 3 T. Matsuo, T. Sakamoto, and T. Nishyima, Kokagaku Toronkai Koen Yoshishu, 1979, 98. 224 T. Shimizu and K. Fukni. Koenshu-Kvoro Daigaku Nippon, Kagaku Seni Kenkvrusho, 1979,36, 101. 215

’’‘


523

have been reviewed by Owen.225Holden and Guillet 226 have reviewed the use of luminescence for studying polymer structure and mobility. Excimer formation in polymers continues to be an important area of study. Ledwith and co-workers 2 2 7 have made an important observation that carbazole-containing polymers do not exhibit excimer formation unless the carbazole units are linked to the molecular backbone. The migration of singlet and triplet excitons in vinylcarbazole polymers has been shown to have a strong influence on both their luminescence properties and photochemical reactions.228 In copolymers of N-vinylcarbazole and 1vinylnapthalene, monomer, excimer, and exciplex emissions were observed. 229 Ledwith and co-workers 230 have studied in some depth the emission properties of a range of different poly(N-ethyl-vinylcarbazole) polymers. Interestingly, poly(Nethyl-3-vinylcarbazole) was found to exhibit a much higher excimer-to-monomer fluorescence than the 2- and 4-substituted isomers owing to its higher isotactic content. A similar observation was made by G ~ i l l e tand ~ ~co-workers on naphthyl ester polymers and copolymers with methyl acrylate and methacrylate. In this case, intramolecular excimer fluorescence was found to be greater in the more flexible polyacrylates. In butyl-substituted vinylnapthalene polymers it is interesting to note that excimer formation was significantly suppressed by the steric effect of the butyl According to de Schryver and c o - w ~ r k e r sa, simple ~~~ kinetic scheme based on intermolecular excimer formation is not sufficient to describe the kinetics of excimer formation of polymers in solution. Using poly(2vinylnapthalene) the decay of the excimer fluorescence suggests the presence of more than one stabilized excited-state complex. Liao and Morawetz 234 have examined excimer formation from dichromophoric residues situated in poly(ethy1ene oxide). Apparently the activation energy for excimer formation was found to be the same in the polymer as in low molecular weight analogues. Thus, crankshaft-type motions in the polymer would appear to offer no hindrance to excimer formation. Excimer formation in poly(wmethy1styrene)has been found to be higher than in polystyrene,235but differences in excimer formation in isotactic and atactic polystyrenes were found to be variable.236In the latter study, excimer formation was found to be intimately related to the exciton diffusion length in the polymer chain. Temperature effects on excimer formation in polystyrenes and polysiloxanes have Seen studied. 2 3 7 Although low temperatures favour excimer formation, high temperatures favour their dissociation. Steric effects were found E. D. Owen, in ‘Developments in Polymer Photochemistry’, ed. N . S. Allen, Applied Science Publishers Ltd., London, 1980, Vol. 1 , Chap. 1, p. 1. 2 2 6 D. A. Holden and J. E. Guillet, in ‘Developments in Polymer Photochemistry’, ed. N . S. Allen, Applied Science Publishers Ltd., London, 1980, Vol. 1, Chap. 2, p. 27. 2 2 7 A. Ledwith, N . J. Rowley, and S. M. Walker, Polymer, 1981, 22, 435. 2 2 8 A. N. Faidysh, V. V. Slobodyanik, and V. N. Yashuk, J . Lumin., 1979, 21, 85. 2 2 9 W. R. Cabaness, Y. K. Cheng, and R. Ganzalez, Pol-vm. Prepr., Am. Chem. Soc., Div. Po17vm.Chem., 1978, 19, 561. 230 M. Keyanpour-Rad, A. Ledwith, and G . E. Johnson, Macromolecules, 1980, 13, 222. 231 L. M. Aubry, D. A. Holden, Y. Merle, and J. E. Guillet, Macromolecules, 1980, 13, 1138. 2 3 2 T. Nakahira, T. Sakuma, S. Iwabuchi, and K. Kojima, Makromol. Chem., Rapid Commun., 1980,1, 413. 2 3 3 K. Demeyer, M. Van Der Auwerner, L. Aerts, and F. C. de Schryver, J . Chim. Phys., 1980, 77, 6. ”’T. P. Liao and H. Morawetz, Macromolecules, 1980, 13, 1338. 23’ L. Bokobza and L. Monnerie, Polvmer, 1981, 22, 235. 236 T. Ishii, T. Handa, and S. Matsunago, J . Polym. Sci., Polym. Phys. Ed., 1979, 17, 811. 237 S. K. Wu, Y. C. Jiang, and J. F. Rabek, Pol.vm. Bull., 1980, 3, 319. 225

Photochemistry

524

to be important in phenyl-substituted methacrylate polymers. 238*239 Increasing the number of phenyl groups in the side chain was found to induce excimer formation. The results were interpreted in terms of excimer formation between non-nearest neighbours. Pyrene-excimer formation has been used as a probe to study terminally-substituted p ~ l y s t y r e n e . ~The ~ ' corrected value for the rate constant for end-to-end cyclization was found to depend upon the degree of polymerization of the polymer. Excimer formation in poly(2-vinylnaphthalene) Both has also been found to depend upon the molecular weight of the p01ymer.~~' singlet and triplet excimers were formed with increasing molecular weight. Polymers containing pendant 3-pyrenylmethyl groups also give excimer emision,^^^ and Nishijima and Yamamoto 243 discuss excimer formation in various polymerxopolymer systems. Polymer-blend compatibility has been investigated using excimer emission for polystyrenes and poly(alky1 phenyl ethers) 244 and aromatic vinyl polymers with poly(alky1 met ha cry late^).^^' Time-resolved emission spectroscopy has provided valuable information on the nature of excited states in polymers. Two distinct types of excimers have been observed in pol y(N-vinylcarbazole) using picosecond time-resolved fluore ~ c e n c eThe . ~ ~sandwich-type ~ excimer emitting at 420 nm was formed in several nanoseconds, whereas a second excimer emitting at 375nm was formed immediately after a 10ps electron pulse. (Scheme 13). Similar observations were also

\i

(-M-M-)

'I,

J\

(375nm)

(-M-M-)+ hv,, (-M-M-) (420nm) Scheme 13 +Main pathway, -- -+ minor pathway, JIMF) other energy-loss processes, (-M-M-): polyvinylcarbazole (PVCZ),-M-M-*: excited singlet state of PVCZ before relaxation, (-M-M-*): relaxed excited singlet state of PVCZ, D,: sandwich-type excimer of PVCZ, D,: so-called second excimer of PVCZ 238

239 240 241

242

243 244 245

246

E. A. Abuin, E. A. Lissi. L. Gargallo, and D. Radic, Eur. Polym. J., 1980, 16, 1023. E. A. Abuin, E. A. Lissi, L. Gargallo, and D. Radic, Eur. Polvm. J . , 1980, 16, 793. M. A. Winnik, T. Redpath, and D. H. Richards, Macromolecules, 1980, 13, 328. N . Kim and S. E. Webber, Macromolecules, 1980, 13, 1233. H. Ooki, K. Sato, and S. Tazuki, Kokagaku Toronkai Koen Yoshrshu, 1979, 30. Y. Nishijima and M. Yamamoto, Polym. Prepr., Am. Chem. Soc., Div. Polym. Chem., 1979,20, 391. F. Mikes, H. Morawetz, and K. S. Dennis, Macromolecules, 1980, 13, 969. C. W. Frank, M. A. Gashgari, P. Chutikamontham, and V. J. Haverly, Stud. Phys. Theor. Chem., 1980, 10, 187. S. Tagawa, M. Washio, and Y. Tabata, Chem. Phys. Lett., 1979, 68,276.

525 made by Ghiggino et ~ 1 . ’ ~ and ’ Phillips et In the latter study, however, a third excimer site was observed at 370nm which does not interconvert to the normal sandwich excimer. Scheme 14 was proposed for comparison with that of Tagawa et al. above. Several fluorescent states were also observed in poly(Nvinylcarbazole) using laser flash photolysis.249


main pathway minor pathway Scheme 14 D, is identiJiedas the low-energy sandwich-type excimer, D, as the high-energy dimer, and (MM)* as “re1axed”monomer. D, and (MM)* are populated rapidly ( < 10 ps) by an exciton diflusion mechanismfrom the initially excited monomer M*, and D, isformed from (MM)* (but not from D2*) with a rise time of about 2ns

Time-resolved emission studies on copolymers of 1-vinylnaphthalene and methyl methacrylate indicate a third emitting species other than the expected monomeric or excimer forms.’” Similar observations were made for copolymers of 1-vinylnaphthalene and methyl acrylate,’ and copolymers of acenaphthalene and methyl methacrylate.2s2 Similar studies on homopolymers of vinylnaphthalene and naphthyl methacrylate found that dual exponential functions were unable to account for the decays of monomeric and excimeric erni~sions.~’~ Fluorescence decay curves for poly(acenaphtha1ene) are shown in Figure 6 as an e~arnple.’’~ Decay curves recorded in the region of monomer emission and in the region of excimer emission are displayed along with the excitation pulse. Comparison of curves (b) and (c) clearly demonstrates that the lifetime of the monomer is considerably less than that of the excimer. Consequently, the monomer and excimer species are capable of differentiation by means of timeresolved emission spectroscopy. Two emitting singlet states have also been observed in p~ly(phenylacetylene).~~~ In some naphthalene-containing polymers, long-lived monomer emission was observed.’ s6 The emission was not associated, however, with thermal dissociation of the polymeric excimer, but results from singlet naphthalene being unable to form an excimer within the excited state

’

24’

248

249

K. P. Ghiggino, D. A. Archibald, and P. J. Thistlethwaite, J . Polym. Sci., Polym. Lett. Ed., 1980, 18, 673. A. J. Roberts, C. G . Cureton, and D. Phillips, Chem. Phys. Lett., 1980, 72, 554. H. Masuhara, S. Ohwada, N. Mataga, A. Itaya, K. Okamoto, and S. Kusabayashi, J. Phys. Chem., 1980,84,2363.

Phillips, A. J. Roberts, and I. Soutar, J . Polym. Sci.. Polym. Phys. Ed., 1980, 18, 2401. ’” D. D. Phillips, A. J. Roberts, and I. Soutar, Polymer, 1981, 22, 293. 252

2s3 254

255 256

D. Phillips, A. J. Roberts, and I. Soutar, Eur. Polym. J., 1981, 17, 101. D. Phillips, A. J. Roberts, and I. Soutar, Polymer, 1981,22,427; R. D. Burkhart, R. G . Aoiles, and K. Magoini, Macromolecules, 1981, 14, 91. D. Phillips, A. J. Roberts, and I. Soutar, J . Polym. Sci., Polym. Lett. Ed., 1980, 18. 123. J. R. MacCallum, C. E. Hoyle, and J. E. Guillet, Macromolecules, 1980, 13, 1647. D. A. Holden, P. Y. K. Wang, and J. E. Guillet, Macromolecules, 1980, 13, 295.

526

Photochemistry

I

T IME

Figure 6 Fluorescence decay curves for undegassed poly (acenaphthylenr) solution (THF, 298 K): (a) excitation pulse, (b) monomer decay (analysed at 325 nm), ( c ) excimer decay (analysed at 450 nm) (Reproduced by permission from J. Polym. Sci., Polym. Lett. Ed., 1980, 18, 123)

lifetime. Singlet electronic-energy transfer has been found to be very efficient in poly( 1-naphthylmethyl methacrylate) 2 5 7 and poly[2-(-naphthyl)ethyl methacrylate] containing anthracene end 2 5 9 A Forster mechanism is believed to be involved. Exciplex formation in polymers has also attracted some interest. The effect of chain binding on the reactivity of naphthyl groups towards intermolecular exciplex formation with triethylamine has been investigated in p ~ l y a m i d e s5.9~The intermolecular exciplex interaction involving a chain-bound reactive group was found to be sensitive to the flexibility of the intervening chain. Exciplex dissociation in the poly(N-vinyl carbazole)-dimethyl terephthalate system has been foundSo occur through the carbazole triplet state,260and other workers have observed the quenching of the same exciplex by an applied electric field.261The same system has also been characterized by nano- and pico-second flash photolysis.262The latter technique indicates that molecular complexation is absent prior to excitation and occurs by a diffusional process following excitation of the polymer. Exciplex formation in a copolymer of p-NN-dimethy1-aminostyrene-pcyano-styrene was found to be significantly higher than in a model system.263* 264 Fluorescence polarization studies have also provided valuable information on excimer formation, energy migration, and molecular mobility in polymers. The role of hydrophobicity was analysed for mixtures of poly(methacry1ic acid) and poly(N-vinyl-2-pyrrolidone) in solution,265 and the motion of 8-anilino-lnaphthalenesulphonic acid covalently bound to poly(methacry1ic acid) has been 257 258 259 2hD 261

262

263 2h4

D. A. Holden and J. E. Guillet, Macromolecules, 1980, 13, 289. J . E. Guillet, Polym. Prepr., Am. Chem. Soc., Div. Polym. Chem., 1979, 20, 395. J . A. Ibemesi, J. B. Kinsinger, and M. A. El-Bayoumi, J . Macromol. Sci., Chem., 1980, 14, 813. U . Lachish and D. J. Williams. Macromolecules, 1980, 1322. M. Yokoyama, Y. Endo, A. Matsubura, and H. Mikawa, Pol-vm. Prepr., Am. Chem. Soc., Div. Pol~~m Chem., . 20, 399. U . Lachish, R. W. Anderson, and D. J. Williams, Macromolecules, 1980, 13, 1143. K . Iwai, M . Furne, S. Nazakura, Y . Shirota, and H. Mikawa, Polym. J . , 1980, 12, 97. M. Furue, Y. Ito, S. Nozakura, K. Iwai, and F. Takemura, Kokagaku Toronkai Koen Yoshishu, 1979, 32.

265

H . Ohno and E. Tsnuchida, Makromol. Chem., Rapid Commun.. 1980, 1, 591.


527

investigated by the same workers.266 Soutar and co-workers 267 have examined intramolecular excimer formation in acenaphthalene-methyl acrylate copolymers. Excimer formation was found to be enhanced by an increase in the degree of substitution in the comonomer. Energy migration was found to be less in acenaphthy lene-me thacrylat e than in acen aph th ylene-met hy 1 methacrylate as detected by fluorescence polarization. Phosphorescence depolarization has been found to be valuable for investigating relaxation phenomena in labelled poly(methy1 methacrylate).268 Ester group motion, for example, was found to occur at temperatures in the vicinity of the @-relaxationof the polymer. David et al.269 have also examined acenapthylene-methyl methacrylate copolymers by fluorescence polarization. Fluorescence polarization has been used to measure segmental orientation in stretched p o l y i ~ o p r e n e .Two ~ ~ ~ deviations from the classical theory of rubber elasticity were observed. The first involves an extra orientation of dry networks owing to the existence of weak nematic-like interactions between segments and the second is a saturation of orientation at high elongations that is associated with local conformational changes in the polymer. Mobility in hydroxyethyl cellulose and poly(ethy1ene oxide) tagged with fluorescein has been investigated and found to be much greater in the latter sy~tern.’~’ Relaxation phenomena in styrene and 9-vinyl anthracene polymers,’ 7 2 9-methylanthracene solubilized in poly(methacry1ic acid),273 polystyrene,274 formyl styrene-methyl methacrylate copolymer,’ poly(methacry1ic acid) containing spirobenzopyranindan side groups,’76 polystyrene and poly(methy1 methacrylate) with anthracenoid groups,277 copolymers of phenylazo-substituted aspartic and oligester-acrylates 279 have been studied using luminescence and optical methods. The photoreduction of a fluorescent probe auramine 0 in poly(methy1methacrylate) has been found to be very dependent upon the physical state of the polymer.280The rate of photoreduction was found to be reduced at temperatures higher than the Tgof the polymer owing to enhanced radiationless deactivation processes of both the excited singlet and triplet states of the probe. Triplet-energy migration and transfer processes have been studied to some extent. The efficiency of the decay of the triplet-triplet of excited poly(2vinylnaphthalene) by an added quencher, piperylene, has been found to decrease with an increase in the molecular weight of the polymer.281 An increase in the 266 267

268

269 270 271

272 ’13 274

’15 276 277

’” 279 280

H. Ohno and E. Tsnuchida, Makromol. Chem., Rapid. Commun., 1980, 1, 585. R. A. Anderson, R. F. Reid, and I. Soutar, Eur. Polym. J . , 1980, 16, 945. H . Rutherford and I. Soutar, J . Polym. Sci.,Polyrn. Phys. Ed., 1980, 18, 1021. C. David, D . Baeyens-Volant, and M. Piens, Eur. Polym. J . , 1980, 16, 431. J. P. Jarry and L. Monnerie, J . Polym. Sci., Polym. Phys. Ed., 1980, 18, 1879. H. Elmgren, J . Polym. Sci., Polym. Lett. Ed., 1980, 18, 351. J. Fuhrmann and R. Leicht, Colloid Polym. Sci.. 1980, 258, 631. K. L. Tan and F. E. Treloar, Chem. Phys. Lett., 1980, 73, 234. A. E. C. Redpath and M. A. Winnik, J . Am. Chem. SOC.,1980, 102, 6869. I. P. Zydt’kov and V. V. Mogil’nyi, Zh. Prikl. Spektrosk., 1980, 32, 49. M. Irie, A. Menju, Y. Hirano, and K. Hayashi, Kokagaku Toronkai Koen Yoshishu, 1979, 56. M. G . Krakovyak, E. B. Milovskaya, G . D. Rudkovskaya, L. V. Zamoiskaya, V. B. Lushchik, and G . D. Anan’eva, Vysokomol. Soedin., Ser. A , 1980, 22, 143. A. Ueno, K. Takahashi, J. Anzai, and T. Osa, Macromol. Chem. Phys., 1981, 182, 693. Yu. V. Zelenev and Yu. M. Sivergin, Acta Polym., 1981, 32, 75. G. J. Kettle and I. Soutar, Polym. Photochem.. 1981, 1, 123. J. F. Pratte, W. A. Noyes, jun., and S. E. Webber, Polym. Phorochem., 1981, 1, 3; J. F. Pratte and S. E. Webber, Polym. Prepr., Am. Chem. SOC.,Div. Polym. Chem., 1979, 20, 927.

528 Photochemistry density of the polymer coil in solution was associated with this effect. Alkyl substitution in poly(2-naphthylalkyl methacrylate) was found to have a favourable effect on triplet energy migration in the polymer.282Triplet energy migration has been shown to control the photochemistry of polymers containing phenyl vinyl ketone and o-tolyl vinyl ketone The average ‘residence time’ of the triplet exciton in any chromophore was found to be about 30 ps. Photoenolization of the o-tolyl vinyl ketone moieties provided an energy sink, thereby reducing the degree of photodegradation. Triplet-state photosensitizers based on polyb-(trifluoroviny1)benzophenonel and polyb-(trifluoroviny1)-acetophenone] have been described284 and triplet energy transfer in styrene-methyl methacrq late copolymers has been studied using triphenylene and coronene as triplet ~ I i m e r s . ~ ~ ~ Diffusion-controlled intramolecular reactions in polymers have been described by Cuniberti and Perico.286 Singlet energy transfer has been studied in polycarbonate resins using laser flash photolysis and phenyl salicylate as a q ~ e n c h e rThe . ~ ~quenching ~ results suggest that facile migration of singlet energy occurs in the polymer. Both singlet and triplet states were observed in picosecond laser flash photolysis of 2-hydroxy-3allyl-4,4’-dimethoxybenzophenone copolymerized with methyl methacrylate.288 Laser flash photolysis of polymers containing pendant 1-pyrenyl groups resulted in the production of dense populations of fluorescent most of which decayed by S-S annihilation. A similar study was carried out on poly(Nvinylcarbazole) 2-( 1-pyrenylmethyl)-propene-1,3-diol d i a ~ e t a t e . ~ ~ ~ Isomerization has been studied in polymers containing aromatic azo-groups. For example, E i ~ e n b a c h ~has ~ ’ investigated isomerization of azo-groups in poly(ethy1 acrylate) and found the process to be very dependent on the crosslinking density. Photoinduced reversible pH changes in poly(carboxy1ic acid)-azo dye complexes were found to be very dependent upon the composition of the 293 Cis-trans isomerization of azobenzene has been used as a tool to enforce conformational changes in crown ethers and polymers.294 Conformational changes in poly(L-glutamic acid) containing photochromic side groups have been investigated.2 9 282

T. Nakahira, S. Ishizuka, S. Iwabuchi, and K. Kojima, Makromol. Chem., Rapid Commun., 1980, 1, 759.

283 284 285

286

”’

J. P. Bays, M. V. Encinas, and J. C. Scaiano, Macromolecules, 1980, 13, 815. N . Asai and D. C. Neckers, J . Org. Chem., 1980, 45, 2903. A . N. Jassim, J. R. MacCallum, and T. M. Shepherd, Eur. Polym. J . , 1981, 17, 125. C. Cuniberti and A. Perico, Conv. Ital. Sci. Macromol. ( A t t i ) , 1979, 182. A. Gupta, R. Liang, J. Moacanin, R. Goldbeck, and D. Kilger, Macromolecules, 1980, 13, 262. A. Gupta, A. Yavronian, S. di Stefano, C. D. Merritt, and G . W. Scott, Macromolecules, 1980, 13, 821.

290 291 292

293

294 295

H. Masuhara, S. Ohwada, Y . Seki, N. Mataga, K. Sato, and S. Tazuki, Photochem. Photobiol., 1980, 32, 9. H. Masuhara, S. Ohwada, Y. Seki, N . Mataga, A. Itaya, K. Okamoto, S. Kusaabayashi, K. Sato, and S. Taguke, Kobunshi Ronbunshu, 1979, 36, 281. C . D. Eisenbach, PoIymer, 1980, 21, 1175. N . Negishi, K. Tsunemitsu, T. Suzuki, and I. Shinohara, Kobunshi Ronbunshu, 1980,37, 293. N . Negishi, T. Matsuo, K. Tsunemitsu, and I. Shinohara, Polym. Prepr., Am. Chem. Soc., Div. Polym. Chem., 1979, 20, 1017. S. Shinkai, T. Nakaji, Y . Nishida, T. Ogawa, and 0. Manabi, J. Am. Chem. Soc., 1980, 102, 5860. 0. Pieroni, J. L. Houben, A. Fissi, P. Costantino, and F. Ciardelli, J . Am. Chem. Soc., 1980, 102, 5913.

529


Fluorescence spectroscopy has also been widely used for investigating microviscosity in carbohydrate^,^^^ deformation of poly(viny1 composition of rare-earth metal-containing polymers,298 crystallinity in polyolefins 300 and p o l y c a r b o n a t e ~ ,hydrophobicity ~~~ in crosslinked polystyrene gels,3o2polymerization of methyl methacrylate doped with pyrene, 303 lubricants in fibres,304and photocrosslinking of tris(bipyridine)ruthenium complexes doped in polymers. 305 Other luminescence studies of interest include diffusion in labelled polystyrene,306 tunnelling in polyethylene,307and aggregation of eosin in polyvinyl acetate. 308 Hamanoue et aL309have studied photoreactions of nitroanthracene derivatives in poly(methy1 methacrylate). In the presence of triethylamine, anthryloxy anions were formed, whereas in its absence only the anthryloxy radical was formed. However, in the monomer only the anthryloxy radical was formed even in the presence of the amine. The microscopic medium polarity of the methyl methacrylate by the polymerization process was believed to be responsible for this effect. Finally, photoinduced charge separations have been observed in polymers containing pendant tris(bipyridy1)ruthenium chlorine complexes. l o 2999

4 Photodegradation and Photo-oxidation Processes The photodegradation and photo-oxidation of polymer systems is still a subject of considerable scientific and technological activity. A number of general review articles have appeared on the subject. Allen and McKellar 311 have reviewed the interactions of light with polymers, and Shalaby 312 has written a comprehensive review on all the chemical, physical, and environmental aspects of polymer photodegradation. Three other reviews of interest have also a ~ p e a r e d . ~ ' ~ - ~ ' ~

Polyo1efins.-Polyolefin oxidation continues to be a subject of considerable controversy. Wiles and co-workers * have written a comprehensive review of polyolefin photo-oxidation mechanisms with particular emphasis on the role of 296 29'

298 299

300

H. Elmgren, J. Polym. Sci.,Polym. Lett. Ed., 1980, 18, 815. Yu. V. Brestkin, E. S. Edilyan, N. G. Bel'nikevich, G. Mann, and S. Ja. Frankel, Actu Polym., 1980, 31, 646. Y. Ueba, E. Banks, and Y. Okamoto, J. Appf. Polym. Sci., 1980,25, 2007. J. Fuhrmann and M. Hennecke, Mukromol. Chem., 1980, 181, 1685. M. Hennecke and J. Fuhrmann, Colloid Polym. Sci., 1980, 258, 219.

L. S . Bogdan, Zh. Prikl. Spektrosk., 1980, 32, 937. K. Horie, I. Mita, J. Kawabata, S.Nakahama, A. Hirdo, and N. Yamazaki, Pofym. J., 1980,12.319. 303 I. I. Kalechits, M. G. Kuz'min, V. P. Zubov, and V. A. Kabdnov, Dokl. Akud. Nauk. SSSR, 1981, 256, 407. 304 N. P. Chekrii, Khim Volokna, 1980, 4, 31. j o 5W. Kawai, Kobunshi Ronbunshu, 1980, 37, 303. 306 I. Mita, K. Hone, and M. Masuda, Polym. Bull., 1981, 4. 369. 307 V. A. Aulov, Dokl. Akud. Nauk. SSSR. 1980, 254,910. 308 I. P.Zharkov, P. A. Kondratenko, and M. V. Kurik, Opt. Spektrosk. 1980, 49, 523. '09 K. Hamanoue, S. Hirayama, T. Hidaka, H. Ohya, T. Nakayama, and H. Teranishi, Pofym. Photochem., 1981, 1, 57. 310 M. Kaneko, A. Yamada, and Y. Kurimura, Inorg. Chim. Acta, 1980, 45, 73. 311 N. S. Allen and J. F. McKellar, Chem. Br., 1980, 16, 480. S. W. Shalaby, J. Polym. Sci.,Macromol. Rev., 1979, 14, 419. 3 1 3 L. Gansel, Tekstif, 1979, 28, 804. 314 S. C. Shim and S. K. Chang, Pollimo. 1979, 3, 342. 315 D. M. Wiles, J. Appl. Pol-vm. Sci., Pol-vm. Symp., 1979, 35, 235. 316 A. Garton, D. J. Carlsson, and D. M.Wiles, in 'Developments in Polymer Photochemistry', ed. N. S. Allen, Applied Science Publishers Ltd., London, 1980, Vol. 1, Chap. 4. p. 93. jol

jo2

530

Photochemistry

the solid-state environment in controlling radical reactivity. Slobadetskaya 3 1 has also reviewed polyolefin photo-oxidation processes with particular emphasis on the prediction of their service life. Wiles and co-workers 318 have examined the role of peroxy-radicals in polyolefin photo-oxidation. They suggest that radical recombination processes have a high probability even if they escape the primary polymer cage. The occurrence of secondary cage-recombination processes was considered. Vasilenko et aL3 have also studied the role of free radicals in polyethylene photo-oxidation. They found that the quantum yield for C-H bond rupture was 10-100-fold higher than for C-C bond rupture. In the photo-oxidation of radiation-modified polyethylene, the formation of carbonyl groups was associated with diene formation in the Frank321 has reported on the lifetimes of free radicals during the intermittent exposure of polypropylene. The initiation mechanism of polyolefin photo-oxidation is still unsettled. According to Karpukhin et al,322the rate of photo-oxidation of polyethylene is controlled more by hydroperoxide than carbonyl groups. G ~ i l l e ton , ~the ~ ~other hand, has produced evidence to show that carbonyl groups photosensitize the breakdown of hydroperoxides in polyolefin photo-oxidation. But both Allen 324 and Verdu325 have produced evidence to show that polymer oxygen or unsaturation-oxygen charge-transfer complexes are important precursors of hydroperoxide formation in the photo-oxidation of polyolefins. For example, prior destruction of photoactive carbonyl and hydroperoxide groups in polyolefins by pre-irradiation in an inert atmosphere was found to have‘no effect on the subsequent rate of p h o t o - ~ x i d a t i o n . ~ ~ ~ Vink 3 2 6 has produced evidence in total conflict with previous experience which is suggested to show that the photo-oxidation of polypropylene is a bulk reaction rather than a surface phenomenon. ESCA studies, however, have shown that the photo-oxidation of polypropylene is clearly a surface phenomenon.327In a recent study by Kollmann and Wood 328 the photo-oxidation of polypropylene was found to be dependent upon the intensity of the light source. Thus, for unstabilized polymer the rate was proportional to 1°-5,whereas for stabilized polymer the rate was proportional to I0.*-O.’ . There appears to be some conflict in the literature as to whether chemical changes during the photo-oxidation of polyolefins correlate with the changes in mechanical properties.329,330 This has always been a difficult

’” E. Slobodetskaya, Usp. Khirn., 1980, 49, 1594.

318

319

320 321

322

323

324 325 326 327

328 329 330

A. Garten, D. J. Carlsson, and D. M. Wiles, Macrornol. Chern., 1980, 181, 1841. V. V. Vasilenko, E. R. Klinshpont, V. K. Milinchuk, and L. I. Iskakov, Vysokomol. Soedin., Ser. A , 1980, 22, 1770. V. P. Pleshanov, V. V. Vasilenko. S. M. Berylant, E. R. Klinshpont, and V. K . Milinchuk, Vjsokomol. Soedin., Ser. A , 1980, 22, 1622. H. P. Frank, Kunstst. Fortschrittsber., 1979, 5, 5 3 . 0.N. Karpukhin, E. M. Slobodetskaya, and T. V. Magamedova. Vykomol. Soedin..Ser. B, 1980,22, 595. J. E. Guillet, Pure Appl. Chem., 1980, 52, 285. N. S. Allen, Polym. Deg. Stab., 1980, 2, 155. J. Verdu, Eur. Polym. J . , 1980, 16, 565. P. Vink, J . Appl. Polym. Sci., Appl. Polyrn. Symp.. 1979, 35, 265. J . Peeling and D. T. Clark, Polym. Deg. Stab., 1981, 3, 177. T. M. Kollmann and D. G . M. Wood, Polym. Eng. Sci.,1980, 20, 684. G. Akay, T. Tincer, and H. E. Ergoz, Eur. Pol-vm. J . , 1980, 16, 601. S. Orban, Kunstst. Fortschrittsber., 1979, 5, 119.


53 1

problem, and in the author's experience it should be assumed that no correlation exists. Only the particular property changes desired should be monitored for a particular application. Reprocessing effects have been studied by Sadrmohaghegh and S ~ o t t . ~ They ~ ' found that alternating processing and ultraviolet-exposure cycles have a more severe effect on photo-oxidation than repeated reprocessing. This effect is believed to be due to the formation of vinyl unsaturation in the polymer by Norrish Type I1 photolysis (Scheme 15), which considerably decreases

TH2

-CH2C-CH-CH2I -CH2C-CH-CHz-

-CH~C-~H-CH, II CHZ

< 0,-RH

II

Crosslinking

OOH CHzI -CH2C-CH-CH2II CH2

CH2C-CHO II

+ *CHzChain-scission

Scheme 15

the thermal oxidative stability of the polymer. Mathur et have found that the thermal stability of polypropylene is inversely proportional to the concentration of photo-oxidized groups, which would tend to confirm the work on re~ycling.~ Other studies of interest on polyolefins include determination of supramolecular structure,333 influence of rotational moulding,334 comparison of natural and accelerated weathering,335 and measurement of gel formation on photocrosslinking.336

'

Poly(viny1 halides).-Vink and Van Bloois 337 have reviewed the general mechanism of photo-oxidation of PVC. Boyd-Cooray and Scott 3 3 8 have shown that hydroperoxides are primary initiators in the photo-oxidation of poly(viny1 chloride). At low processing temperatures, hydroperoxides are believed to be 33'

332 ' j 3

334 335

336 337 338

C. Sadrmohaghegh and G. Scott, Eur. Polym. J., 1980, 16, 1037. A. B. Mathur, V. Kumar, and G. N. Mathur, Ind. Polym. Radiat., Proc. Symp., 1979, 143. D. A. Akhemedzade, E. I. Markova, and N. F. Ozhavibekov, Sb. Tr. Inst. Nefekhim. Protsessov, im Yu. G. Mamedalieva, Akad. Nauk Ar. SSR, 1980, 11, 104. B. A. Golender, V. P. Shein, and S . Ya. Kleinman, Plust Massy. 1980, 11, 36. S. Khadzhidocheva, L. Peeva, and V. Tsveteva, Kunstst. Fortschrittsber., 1980, 279. Yu. I. Dorofeev and V. E. Skurat, Dokl. Akad. Nauk. SSSR, 1979, 249, 1142. P. Vink and F. I. Van Bloois, Overdruk Wit Plastica, 1975, 5, 167. B. Boyd-Cooray and G. Scott, Polym. Deg. Stab., 1981, 3, 127.

532 Photochemistry formed, whereas at higher temperatures carbonyl and unsaturation predominates and tend to control the subsequent photoinitiated oxidation of the polymer. Verdu et aZ.339have studied the photosensitized oxidation of PVC and propose the involvement of unsaturated sites as initiators. The unsaturated groups are believed to originate from thermolabile groups such as a-chloroperoxides or #l-chloroketones. Rabek and co-workers 340 have examined the photosensitized oxidation of PVC. They also believe unsaturation plays a vital role in photoinitiated oxidation and have proposed the following detailed mechanistic scheme to account for both radical formation and the observed carbonylic products (Scheme 16). According to the same group of polyene sequences may also

+ -CH2-CH-I

-CH-(CH=CH),,-l-CH-

-

c1

+

-cH,-(cH=cH),-,-~H-

-~H-cH-

I

CI

b

I 0 -CH2-eH-CH2-CH-

I CI

+ 0,

I

-CH2-CH-CH2-CH-

+

I CI

H

I

6

0 I 0

I 0

I

-CH2-CH-CH2-CH-

I

I + RH + -CH2-CH-CH2-CH-

+ R.

CI H

I

0 I 0 I -CH2-CH-CH2-CH-

6 I

% -CH2-CH-CH2-CH-

I CI

I

+ HOB

c1 OH

I

b

-CH2-CH-CH2-CH-

+ Rm

I -CH2-CH-CH2C1 H

C1

Scheme 16

339 340

341

J . Verdu, A. Michel, and D. Sonderhof, Eur. Polym. J., 1980, 16, 689. J . F. Rabek, G . Canaback, and B. Ranby, J . Appl. Polym. Sci., Appl. Polym. Symp., 1979,35, 299. J. F. Rabek, B. Ranby, B. Ostensson, and P. Flodin, J. Appl. Polym. Sci., Appl. Polym. Symp., 1979, 35, 299.

Polymer Photochemistry 533 photosensitize the formation of singlet oxygen in the polymer (Scheme 17). Owen et 343 have made some dramatic observations which indicate unequivocally ~

1

.

~

~

~

3

fCH=CHj-

+

'0,___* -CH-CH=CHI OOH Scheme 17

that polyene sequences play a key role in the photoinitiated oxidation of PVC. Polyenes in degraded PVC samples were found to exhibit some astonishing spectral changes in solution which have been associated with the prototropic equilibrium shown in Scheme 18. In one experiment the absorption spectrum of chemically

aCH2CHCICH=CH-CH=CHCH2CHCl* -H+/

/+H+

~CH~CHCICH-CH-CH-CH~CH~CHCIO

+ +H+T

l-H+

-CH2CCl=CH-CH=CH-CH2CH2CHCl@ The overall result would be

-(CH=CH)r(CH=CH)r

__*

-(CH=CH)oy

Scheme 18

degraded PVC showed a dramatic increase in the visible region in dichloromethane on standing. This effect was illustrated in Volume 12. Subsequent photo-oxidation experiments showed that these strongly absorbing species are extremely photosensitive. The photobehaviour of these species in the presence of aromatic carbonyls was also studied in solution. Benzophenone, for example, was a powerful sensitizer in dichloromethane, whereas in THF there was an induction period in the presence of oxygen. The induction period was associated with the build-up in solvent THF radicals, which inhibited photoreaction of the polyenes by reaction with oxygen. Polyene structures have also been invoked in the photodegradation of various other poly(viny1 halides), such as poly(viny1 bromide) and poly(viny1 iodide).344Polyenyl radicals have also been observed at room temperature during the photo-oxidation of Pvc.345

"' E. D. Owen, I. Pasha, and F. Moayyedi, J . Appl. Polym. Sci., 1980, 25, 2331. 343 344

345

E. D. Owen and 1. Pasha, J . Appl. Polym. Sci., 1980, 25, 2417. M. Yamamoto, M. Yano, and Y. Nishijima, Kobunshi Ronbunshu, 1980, 37, 319. N. L. Yang, J. Liutkus, and H. Haubenstack, Am. Chem. SOC.. Symp. Ser., 1980, 142, 35.

534

Photochemistry

Other studies of interest on PVC photo-oxidation include the influence of light intensity,346 chlorination,347 solvent and inhibition of dehydrochlorination at the surface layers.349 The chlorination process destabilized the PVC. Polystyrenes.4euskens and Davis 3 5 0 * 3 5 1 have reviewed their work on the mechanism of the photo-oxidation of polystyrene. It would appear that carbonyl groups are responsible for the sensitized photolysis of hydroperoxide groups, as with polyolefins. Quantum yields of hydroperoxide photolysis were found to be significantly higher in the presence of aromatic ketones. Ranby and Lucki 3 5 2 have discussed in some depth their work on the photo-oxidation of polystyrene and present some novel evidence for the formation of hydroxylated products (Scheme 19). Ring-opening reaction schemes were also proposed to account for photoyellowing: see earlier Volumes. have also used model compounds such as 3-phenylpentane for Ranby et investigating the mechanisms of photo-oxidation of polystyrene. The photooxidation of polystyrene has been investigated in solution by a number of workers. Woolinski 3 5 4 has observed the development of unsaturation and implicated the involvement of singlet oxygen in the mechanism of photo-oxidation, whereas Easton and M a ~ C a l l u m ~invoke ~ ~ " the involvement of polymer-solvent complexes in initiation. The photo-oxidation of polystyrene has been found to have a kinetic chain length of 103-104.355b ESCA has provided valuable and novel information in the surface changes during the photo-oxidation of polystyrene. 3 5 6 Initially C--O groups are formed followed by carbonyl, carboxyl, and carbonate groups. Ring-opening reactions were also observed, but the bulk of the polymer remains virtually unaffected. Light scattering 3 5 7 a and laser flash photolysis 3 5 7 b techniques have also been applied to the study of polystyrene photo-oxidation. The photo-oxidation of polystyrene has also been investigated using gel permeation chromatography 3 5 8 and dielectric techniques.359The former indicated initial high rates of chain scission followed by crosslinking, whereas in the latter the presence of oxygen caused a dramatic increase in the dielectric constant of the polymer. Waligora et al.360have studied the sensitized photo-oxidation of polystyrene by a,b-enones. These chromophores introduced an induction period due to D. Braun and S. Kull, Angew. Makromol. Chem.. 1980, 85, 79. C. Decker and M. Balandier, Makromol. Chem., Rapid Commun., 1980, 1, 389. 34a J. Polanka, L. Lapcik, and J. Valasek, Chem. Zvesti, 1980, 34, 63. 349 T. G. Fedoseevn, L. D. Strelkova, E. 0.Krats, V. P. Lebedev, and K. S. Minsker, Plast. Massv, 1980. 7, 28. G. Geuskens and C. David, Pure Appl. Chem., 1979, 51, 2385. 3s1 G. Geuskens, J . Chim. Phys., 1980, 77, 487. 352 B. Ranby and J. Lucki, Pure Appl. Chem., 1980, 52, 295. 353 J. Lucki, J. F. Rabek, and B. Ranby, J . Appl. Polym. Sci., Appl. Polym. Sci., 1979, 35, 275. 3 5 4 L. Wolinski, Makromol. Chem.. 1980, 18, 2335. 3 5 5 ( a ) M. J. Easton and J. R. MacCallum, Polym. Deg. Stab.. 1981, 3, 229; (b) S. I. Kingina and A. I. Mikhailov, Dokl. Akad. Nauk. SSR, 1980, 253, 1150. 3 s b J. Peeling and D. T. Clark, Polym. Deg. Stab., 1981, 3, 97. 3 5 7 ( a ) W. Schnabel, Po[ym. Eng. Sci., 1980,20,688; (b)S . Tagawd and W. Schnabel, Makromol. Chem., Rapid Commun., 1980, 1, 345. 35R B. Wandelt, J. Brzezinski, and M. Kryszenski, Eur. Polym. J., 1980, 16, 583. '" N. A. Weir and T. Milkie, J . Appl. Polym. Sci., Appl. Pol.vm. Sci., 1979, 35, 289. 360 B. Waligora, M. Nowakowska, and J. Kowal, Polym. J . , 1980, 12, 767. 346 34'


535

I". MeCH,CMe

+

'H

H I

b

0

I 0

I

0

b

OH

I

ONo' H

I

I

C'

Me-C,

,CH2

I

J.

1 Me I MeCH,-C-0-OH

H

b

I O H I I Me -C -CkH,

6"

k

0.

I

MeCH,-C-Me

I". b

I Me-C-CH=CH,

8I.

+ H,O 4tHd

0 II MeCH,C

RH

OH I Me-y-CH=CH,

+'R

6""

0 II

Me-C

(yoH

Scheme 19

trans cis isomerization followed by rapid oxidation. The photo-oxidation of polystyrene blended with poly(2,6-dimethyl-1,Cphenylene oxide) 361, 3 6 2 and N--+

36'

362

J. P. Tovborg Jenson and J. Kops, J . Polym. Sci., Polvm. Chem. Ed., 1980, 18, 2737. B. Wandelt and M.Kryszewski, J . Appl. Pol-vm. Sci., Appl. Pol-vm. Svmp., 1979, 35, 361.

536

Photochemistry

ethylmaleimide 363 has also been studied. In the former studies there is an increase in the rate of photo-oxidation of the poly(2,6-dimethyl-1,4-phenylene oxide) due to energy transfer from the polystyrene. The photo-oxidation of poly(p-methylstyrene) has been studied initiated by azobis-is~butyronitrile.~~~ The effects of polymer concentration, light intensity, initiator concentration, and oxygen pressure were related by the following expression:

-!!?!

~ ( 0 2 ) '

(Polymer)0.6 (AlBN)0.95 (]o)l.os

dt

High-impact polystyrene has also been studied by a number of workers. Ghaemy and have correlated changes in infrared with impact strength during photo-oxidation. Thermal treatment has a deleterious effect on the photo-oxidation of ABS 366 and DSC 367a has been found useful for determining the amount of unoxidized polybutadiene in the terpolymer. Another study includes the measurement of hardness. 3 6 7 b Polyacry1ics.-Gupta et al.368 have investigated in some detail the mechanism of photodegradation of poly(methy1 methacrylate) using various spectroscopic techniques and they have confirmed, for example, the presence of the radical species shown in Scheme 20 during photodegradation. These workers found that bond scission occurs as a result of direct excitation of the ester carbonyl group absorbing at 254nm. Panke and Wunderlich 369 have examined the molecular weight changes during the photo-oxidation of poly(methy1 methacrylate) and found that the kinetic chain length is limited by termination reactions between the depolymerizing radicals and other small mobile radicals. Grassie and Davidson 3 7 1 have found that whereas copolymerization of maleic anhydride decreases the rate of chain scission of methyl methacrylate during exposure to 254 nm light, copolymerization of vinyl ketones accelerates the rate. In the latter case the rate of chain scission passes through a maximum at 2 0 30% ketone content. Copolymers of methyl methacrylate and a-chloroacrylonitrile are also photolysed rapidly by 254nm light.372 Scission at the C-C1 bond is primarily responsible for photodegradation. Defects in poly(methy1 methacrylate) 374 The introduction of 4induced by laser photolysis have also been chromanone groups into poly(methy1methacrylate) imparts some improvement in 3703

363

364 36s 366

367

368 369

370 371

372 373

374

I . K. Chernova, S. S. Leshchenko, V. P. Golikov, and V. L. Karpov, Vysokomol. Soedin., Ser. A , 1980, 22, 2175. N. Weir and T. H. Milkie, Polym. Deg. Stub., 1980, 2, 225. M. Ghaemy and G. Scott, Polym. Deg. Stub., 1981, 3, 233. W. Y. Chiang, Ta T'ung Hsuch Pav, 1979, 9, 129. (a) H . E. Blair, D. J. Boyle, and P. G. Kellcher, Polym. Eng. Sci., 1980, 20, 995; ( b ) H. H. Racke, Kunststoffe, 1980, 70, 76. A. Gupta, R. Liang, F. D. Tsay, and J . Moncanin, Macromolecules, 1980, 13, 1696. D. Panke and W. Wunderlich, J . Appl. Pol.vm. Sci., Appl. Polym. Symp., 1979, 35, 321. N. Grdssie and A. J. Davidson, Pof-vm.Deg. Stab., 1981, 3, 25. N. Grassie and A. J. Davidson, Pofym. Deg. Stab., 1981, 3, 45. N. Grassie and A. S. Holmes, Polym. Deg. Stab., 1981, 3, 145. A. A. Manenkov, V. S. Nechitailo, and A. S. Tsapvilov, Izv. Akad. Nauk. SSSR, Ser. Fiz., 1980, 44, 1770. N. P. Novikov and L. N. Trukhanova, Fiz.-Khim. MekA. Muter., 1980, 16, 31.

537

Polymer Photochemistry y

3

y

-CHz-CI C ‘0-CH,

h,, __+

8

3

tCHZ-C$ I f-

k,

k2 V

I

C*

d

-CH,-C-

+ bCH,

s

I

+ eOOCH, 1

HCOOCH,

1

k41 y

-CH,-c-

c, d + e0H3

CH,OH

CH4

k.1

y-43

3

-CH2-c-

7H3

t‘H3

743 -CHz-C-

+CO

-CH2-c-

+ co, y

-CH2-C-

3

k6

7H-I -CH,-C* I COOCH,

7H3 CH2=C-

7H3

+

k,

y

-7’

(PR. RAD.) COOCH, 2

CH2=C + (PR. RAD.) I COOCH,

Scheme 20

light stability.375 In copolymers of poly(ester-urethanes) with poly(methy1methacrylate) the presence of the urethane links and ester groups were found to be unimportant in determining the rate of p h o t o - ~ x i d a t i o nAn . ~ ~e.s.r. ~ study 377 on the photo-oxidation of poly(acry1amide) has identified the formation of propionamide radicals, and the photolysis of sodium acrylate has been studied by vi~cornetry.~~~ Polyamides-Copolyamides derived from truxillic acid are highly photosensitive by the mechanism shown in Scheme 21.379*380 The effect of pH on the photodegradation rate indicates that protonation in the first excited singlet state accelerates ring cleavage. 375

3’6 3’’ 378 37q

380

H. Matsuda, A. Ninagawa, and Y. Tokunaga, Kenkyu Hokoku-Asahi Garasu Kogyo Giiutsu Shoreikai, 1979, 34, 47. J. A. Simms, Polym. Sci. Technol., 1980, 11, 137. U. Ramelow and B. M. Baysal, J. Appl. Polym. Sci., Appl. Polym. Symp., 1979, 35, 329. T. Saito, Jpn, J. Appl. Phys., 1980, 19, 2501. G. G. Aloisi, U. Mazzucato, P. Maravigna, G . Montaudo, A. Recca, and M. Scarnporrino, Chim. Ind., 1979, 61, 800. P. Maravigna, G . Montaudo, A. Recca, E. Scamporrino, G. G. Aloisi, and U. Mazzucato, J. Polym. Sci., Polym. Lett. Ed., 1980, 18, 5 .

Photochemistry

538

hv

+H'-

Scheme 21

Infrared has been used for investigating the photodegradation of polyamide whereas several other workers have studied mechanical changes.382- 384 A comprehensive review has appeared on polyamide photoageing.

Poly(Z,6-dimethyl-l,4phenylene oxide) (PPO).-The photo-oxidation of this polymer has attracted some interest. Wandelt 386 has found that the photoinitiated oxidation of PPO depends upon the mobility of one more unit in the polymer chain. A marked increase in the rate of photo-oxidation of the polymer occurs in the temperature range 45-40 "C, which corresponds with the p-relaxation phenomena. Chain mobility markedly controls the diffusion of oxygen. From detailed analysis of the products of PPO photo-oxidation the following reaction 388 hydroperoxide photolysis schemes have been proposed to account for (Scheme 22) and quinone photoreaction with aromatic aldehydes to give aromatic esters, for example (1 6) (Scheme 23). The three chromophores are formed during 3879

PCH,COC

-

[PCH,O"OHI-

PCHO

\ PCH,O' +

+

H20

'OH

Scheme 22

processing of the polymer. Direct absorption of light by the phenylene oxide units also occurs. Zinc isopropylxanthate has been found to be a photostabilizer in PPO, whereas the cobalt form was a p h o t o s e n s i t i ~ e r . ~ ~ ~ Polyurethanes.-Rek and Bravar 390- 392 have proposed the following mechanism to account for the photo-oxidation of polyurethanes (Scheme 24). Direct photolysis of N-C and C - 0 bonds are believed to be the primary photochemical steps

"' 3g3 384

385

386 388

389 390

392

I. S. Polikarpov, Zaved Teknol. Legk. Prom. Sti., 1979, 22, 21. S. Yano and M . Murayama, Nippon Reoraji Gakkaishi, 1980, 8, 84. Y . W. Mai, D. R. Head, B. Cotterell, and R. W. Roberts, J. Muter. Sci., 1980, 15, 3057. S. Yano and M. Murayama, J. Appl. Polym. Sci., 1980, 25, 433. A. L. Margoiin and L. M. Postnikov, Usp. Khim., 1980, 49, 1106. B. Wandelt, Polym. Bull., 1981, 4, 199. Z. Slama, E. Svejdova, and J. Majer, Makromol. Chem., 1980, 181, 2449. J . Petrij and Z. Slama, Makromol. Chem., 1980, 181, 2461. R. Chandra, B. P. Singh, S. Singh, and S. P. Handa, Polymer, 1981, 22, 523. V. Rek and M. Bravar, Cell. Noncello Polyurethanes, Inst. Conf., 1980, 845. V. Rek and M. Bravar, Kunstst. Fortschrittsber., 1980, 5, 107. V. Rek and M. Bravar, J. Elast. Plast., 1980, 12, 245.

539


0

+

0

0

followed by the formation of aromatic amino, azo, and carbonyl structures. Lipskerova and Mel’nikov 393 have proposed a similar mechanism. Aromatic urethanes have been stabilized by complexation of peroxides in the polymer394 and the effect of prior y-irradiation has been investigated, on polyurethane^.^^^ The ageing of polyurethane coatings has been investigated,396 and light-stable integral skin foams have been developed for polyurethanes. 3 9 7 Creep behaviour of polyurethanes on ultraviolet exposure has also been investigated.398 Rubbers.-Golub and Rosenburg 399 have proposed the following general mechanism to account for the loss of unsaturation during the photodegradation of 1,2poly(cis- and trans-hexa-1,4-dienes). The reaction (Scheme 25) is believed to occur through cyclization of the double bond. Chandra and co-workers 400, 401 have investigated aldehyde production during the photo-oxidation of butyl rubber. Diphenyl ally1 mercury was an effective stabilizer for the polymer but it did not inhibit aldehyde formation. Clearly, the aldehyde production must be a side product and has little importance in the 393

394 395

396

397 398 399 400 401

E. M. Lipskerova and M. Ya. Mel’nikov, Dokl. Akad. Nauk. SSSR, 1980, 253, 1154. V. A, Kosobutskii, M. N. Kurganera, 0. G. Tarakanov, and V. K. Belyakov, Vysokomol. Soedin., Ser. A , 1980, 22, 1264. E . M. Lipskerova and M. Ya. Mel’nikov, Khim. Vys. Energ., 1980, 14, 143. M. V. Karyakina, V. V. Luk’yanova, N. V. Mairova, and A. Kalnavais, Mod$ Polim. Muter., 1979, 8, 102. H. Horacek and 0. Volkert, Angew. Mukromol. Chem., 1980, 90, 109. A. K. Aleksandvova, V. F. Stepanov, and S. E. Vaisberg, Kuuch. Rezina, 1980, 11, 30. M. A. Golub and M. L. Rosenberg, J . Polym. Sci., Polym. Chem. Ed., 1980, 18, 2543. R. Chandra, B. P. Singh, and S. Singh, Indian J. Chem., Sect. A , 1980, 19, 527. R. Chandra, J . Indian Chem. Soc., 1981, 58, 49.

Photochemistry

540 O-CH2-CH2-R-

H

i

1.1

I -R'-N'

+

L+"RI-

+ -R~NH-NH-R~-

*CH2-CH2-R-

+

L + 2RO'+ TH2-CH2-R-

+

-R'-

CO,

-R'N=NR'NH,

+

+ 2ROH

CH,=CH-R-

0 I1

li

-R'-N-C' I H

1 -R'-N'

I H R' R

4-

+ CO

*O-CH2-CH2-R-

'

C H 2 0 +*CH2-R-

L + 0, = =

+

O O C H -R-

aromatic part from di-isocyanate aliphatic part from polyglycol Scheme 24

If,

-RCHO

+ 'OH

-m

Scheme 25

photodegradation mechanism. Lala and Rabek 402 have proposed that hydroperoxides are the key initiators in the photo-oxidation of poly(buta-l,4-diene). Ranby and co-workers403 have studied the effect of various active oxygen species on poly(buta- 1,2-diene). Interestingly all the species attacked the polymer causing marked crosslinking. In the photosensitized oxidation of polyisoprene it has been found that the presence of an OH group in an allylic position to a double bond causes considerable deactivation of the group towards singlet-oxygen attack.404 *02

*03 404

D. Lala and J. F. Robek, Eur. Polym. J . , 1981, 17, 7. J. Lucki, B. Ranby, and J. F. Rabek, Eur. Polym. J., 1979, 15, 1101 C. Tanielian and J. Chaineaux, Eur. Polym. J . , 1980, 16, 619.

Polvmer Photochemistry

54 1

Other studies of interest on rubbers include weathering 405 and photolysis in the far ~ l t r a v i o l e t . ~The ’ ~ resistance of rubbers to ultraviolet attack has been found to decrease in the order neoprene > polybutadiene > p o l y c h l ~ r o p r e n e . ~ ~ ~

Natural Polymers-Two comprehensive review articles have appeared on wool 408 and cellulose 409 photodegradation. Holt and Milligan 410* 4 1 have examined the photo-oxidation of serine, threomine, and cystine side chains in wool. Serine is converted into a-carboxyglycine, cystine to a-formylglycine, and threomine to r-acetylglycine. Waters et have shown that the ph’otodegradation of wool is due to disulphide bond scission and main-chain cleavage. Polikarpov and Kottyar 413 have used polarography for studying the photooxidation of wool. Aqueous polysaccharide gels have been investigated by Phillips and cow o r k e r ~ These . ~ ~ ~workers found that the photochemical processes in gels were the same as in solution suggesting that the gel structure is fluid. Nickel and copper ions have been found to inhibit the photodegradation of silk, whereas zinc and chromium ions accelerate the process.415 Other studies of interest include surface photoreactions on the fibre stalk of e.s.r. studies on polypeptide p h o t o l y s i ~ , ~photoyellowing ~’ of silk studied by ATR,418 and the photodiscoloration of w001.4’9-421 Miscellaneous Polymers.-Buchanan and McGill 42 have investigated in detail the photodegradation of poly(viny1 esters). First results indicated that there is a close relationship between the photodegradation of poly(viny1 esters) and model ester compounds. The following mechanisms were proposed to account for carboxylic acid formation (Scheme 26), ketone formation (Scheme 27), and aldehyde formation (Scheme 28). It is seen that two mechansims, one involving hydrogen abstraction by the acyl radical formed in a Norrish Type I cleavage process (Scheme 29), and the other involving an intramolecular hydrogen abstraction by an excited carbonyl group followed by fragmentation have been proposed to account for aldehyde formation. 405 406

407 408

409

410 411

R. Vesely and 2.Prauseova, Kunstst. Fortschritfsber., 1980, 5, 27. Yu. I. Dorofeev and V. E. Skurat, Khim. Vys. Energ., 1980, 14, 431. E. M. Abdd-Bary and E. A. Abdel-Razik, Proc. Int. Rubber Conf.,1979, 970. C. H. Nicholls, in ‘Developments in Polymer Photochemistry’. ed. N. S. Allen, Applied Science Publishers Ltd., London, 1980, Vol. 1, Chap. 5, p. 125. P. J. Baugh, in ‘Developments in Polymer Photochemistry’, ed. N. S. Allen, Applied Science Publishers Ltd., London, 1981, Vol. 2, Chap. 5 , p. 165. L. A. Holt and B. Milligan, Text. Res. J., 1980, 50, 387. B. Milligan and L. A. Holt, Fibrous Proreins, Sci. Ind. Med. Asp. Proc. Inr. Conf. 4th. 1979, 1980, 2, 203.

412

413

415 416 417

418 419 420 421

422

P. J. Waters, N. A. Evans, L. A. Holt, and B. Milligan, Quinquenn. Int. Wool. Test. Res. Conf. (Pup.) 6rh, 1980, Fiche, 13, D, 7. L.S. Polikarpov and G. I. Kottyar, Tekst. Prom-Sti (Moscon), 1980, 12, 26. D. J. Wedlock, G. 0. Phillips, and J. K. Thomas, Polymer J., 1979, 11, 671. F. Shimiza, Zoku Kenshi No Kozo, 1980, 485. H. Banmann, Quinquenn. Int. Wool Text. Res. Conf. (Pap.) 6th, 1980, Fiche, 14, F, 5. F. Y. Lion, M. Kuwabara, and P. Riesz, J. Phys. Chem., 1980, 84, 3378. A. Watanabe, M. Tagawa, and R. Osawa, Kaseiguku Zasshi, 1979, 30,706. K. Umchara and N. Minemura, Rinsan Shikenjo Geppo (Hokkaido), 1979, 331, 15. K. Umchara, N. Minemura, and T. Suganuma, Rinsan Shikenjo Geppo (Hokkaido), 1979, 327, 15. L. L. Lamparski, R. H. Stehl, and R. L. Johnson, Environ. Sci. Techno(., 1980, 14, 196. K. J. Buchanan and W. J. McGill, Eur. Polvm. J.. 1980. 16, 309. 313, and 319.

542

Photochemistry -CH H4‘YHe

-CH2-CH0 I

P -

*

/Ill

*.

> o, C

___+

0.0,

I

R

4

eCH H QCHI I :o

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