Photochemistry (SPR Photochemistry (RSC)) (Vol 30)

Photochemistry Volume 30

J-4

A Specialist Periodical Report

Photochemistry

Volume 30

A Review of the Literature Published between July 1997 and June 1998 Sen ior Reporter A. Gilbert, Department of Chemistry, University of Reading, UK Reporters N.S. Allen, Manchester Metropolitan Unversity, UK A. Cox, University of Warwick, UK 1. Dunkin, University of Strathclyde, Glasgow, UK A. Harriman, Ecole Europeenne Chimie Pdymeres Ma teriaux, Strasbo u rg, France W.M. Horspool, University of Dundee, UK A.C. Pratt, Dublin City University, Ireland

RSK

ROYAL SOCIETY OF CHEMiSTRY

ISBN 0-85404-420-5 ISSN 0556-3860 Copyright 0The Royal Society of Chemistry 1999 All rights reserved Apart from any fair dealing for the purposes of research or private study, or criticism or review as permitted under the terms of the UK Copyright, Designs and Patents Act, 1988, this publication may not be reproduced, storedor transmitted, in any form or by any means, without the prior permission in writing of The Royal Society of Chemistry, or in the case of reprographic reproduction only in accordance with the terms of the licences issued by the appropriate Reproduction Rights Orgunizution outside the UK.Enquiries concerning reproduction outside the terms stated here should be sent to The Royal Society of Chemistry at the addressprinted on this page.

Published by The Royal Society of Chemistry, Thomas Graham House, Science Park, Milton Road, Cambridge CB4 OWF, UK Typeset by Computape (Pickering) Ltd, Pickering, North Yorkshire, UK Printed and bound by Athenaeum Press Ltd, Gateshead, Tyne and Wear, UK

Contents

Introduction and Review of the Year By Andrew Gilbert Part I

1

Physical Aspects of Photochemistry Photophysical Processes in Condensed Phases By Anthony Harriman

13

1

Introduction

13

2

General Aspects of Photophysical Processes

13

3

Theoretical and Kinetic Considerations

15

4

Photophysical Processes in Liquid or Solid Media 4.1 Detection of Single Molecules 4.2 Radiative and Nonradiative Decay Processes 4.3 Amplitude or Torsional Motion 4.4 Photophysics of Fullerenes 4.5 Quenching of Excited States 4.5.1 Energy-transfer Reactions 4.5.2 Electron-transfer Reactions

18 18 18 22 23 25 26 21

5

Applications of Photophysics

29

6

Advances in Instrument Design and Utilization 6.1 Instrumentation 6.2 Data Analysis

30 30 32

References

33

Part I1

Organic Aspects of Photochemistry

Chapter 1

Photolysis of Carbonyl Compounds By William M. Horspool

59

1

Norrish Type I Reactions

59

2

Norrish Type I1 Reactions 2.1 1,5-Hydrogen Transfer 2.2 Other Hydrogen Transfers

61 61 62

3

Oxetane Formation

64

Photochemistry, Volume 30 0The Royal Society of Chemistry, 1999 V

Contents

vi

4

Chapter 2

Miscellaneous Reactions 4.1 Decarbonylation and Decarboxylation 4.2. Reactions of Miscellaneous Haloketones 4.3. Photo Reactions of Esters and Photodeprotection 4.4. Other Fission Processes

65 65 70 71 74

References

75

Enone Cycloadditionsand Rearrangements: Photoreactions of Dienones and Quinones By William M. Horspool

78

Cycloaddition Reactions 1.1 Intermolecular Cycloaddition 1.1. I Open-chain Systems 1.1.2 Additions to Cyclopentenones and Related System s 1.1.3 Additions to Cyclohexenones and Related Systems 1.2 Intramolecular Additions 1.2.1 Intramolecular Additions to Cyclopentenones 1.2.2 Additions to Cyclohexenones and Related Systems

78 78 78

Rearrangement Reactions 2.1 m,P-Unsaturated Systems 2.1. I Hydrogen Abstraction Reactions 2.1.2 Radical Addition Reactions 2.1.3 Miscellaneous Processes 2.2 P,y-Unsaturated Systems 2.2.1 The Oxa Di-n-methane Reaction and Related Processes 2.2.2 Miscellaneous Processes

88 88 88 89 92 94

3

Photoreactions of Thymines and Related Compounds 3.1 Photoreactions of Pyridones 3.2 Photoreactions of Thymines etc.

97 97 98

4

Photochemistry of Dienones 4.1 Cross-conjugated Dienones 4.2 Linearly Conjugated Dienones

101 101 101

5

1,2-, 1,3- and I ,4-Diketones 5.1 Reactions of 1,2-Diketones 5.2 Reactions of 1,3-Diketones 5.3 Reactions of 1,4-Diketones 5.3.1 Phthalimides and Related Compounds 5.3.2 Fulgides and Fulgimides

103 103 105 106 107 109

1

2

82 83 84 84 85

94 95

vii

Contents

6

Chapter 3

Chapter 4

Quinones 6.1 o-Quinones 6.2 p-Quinones

110 110 110

References

114

Photochemistry of Alkenes, Alkynes and Related Compounds By Williurn M. Horspool

119

1

Reactions of Alkenes 1.1 cis,trans-Isomerization 1.1.1 Stilbenes and Related Compounds 1.2 Miscellaneous Reactions 1.2.1 Addition Reactions 1.2.2 Electron Transfer Processes 1.2.3 Other Processes

119 119 120 122 122 123 124

2

Reactions Involving Cyclopropane Rings 2.1 The Di-n-methane Rearrangement and Related Processes 2.2 Other Reactions Involving Cyclopropane Rings 2.2.1 SET Induced Reactions 2.2.2 Miscellaneous Reactions Involving Three-membered Ring Compounds

126 126 128 128 129

3 Reactions of Dienes and Trienes 3.1 Vitamin D Analogues

130 135

4

(2+2)-Intramolecular Additions

137

5

Dimerization and Intermolecular Additions

138

6

Miscellaneous Reactions 6.1 Miscellaneous Rearrangements and Bond Fission Processes

141 141

References

144

Photochemistry of Aromatic Compounds By Alan Cox

149

1

Introduction

149

2

Isomerisation Reactions

149

3

Addition Reactions

157

4

Substitution Reactions

163

5

Cyclisation Reactions

166

6

Dimerisation Reactions

171

... Vlll

Chapter 5

Contents

7

Lateral Nuclear Shifts

173

8

Miscellaneous Photochemistry

174

References

178

Photo-reduction and exidation By Alan Cox

188

1

Introduction

188

2

Reduction of the Carbonyl Group

188

3

Reduction of Nitrogen-containing Compounds

198

4

Miscellaneous Reductions

202

5

Singlet Oxygen

206

6

Oxidation of Aliphatic Compounds

207

7

Oxidation of Aromatic Compounds

209

8

Oxidation of Nitrogen-containing Compounds

213

9

Miscellaneous Oxidations

219

References

Chapter 6

Photoreactions of Compounds Containing Heteroatoms Other

than Oxygen

220

230

By Albert C. Pratt

Chapter 7

1 Introduction

230

2

Nitrogen-containing Compounds 2.1 E,Z-Isomerisations 2.2 Photocyclisations 2.3 Photoadditions 2.4 Rearrangements 2.5 Other Processes

230 230 232 24 1 249 251

3

Sulfur-containing Compounds

265

4

Compounds Containing Other Heteroatoms 4.1 Silicon and Germanium 4.2 Phosphorus 4.3 Other Elements

277 277 282 284

References

285

Photoelimination By Ian R. Dunkin

296

1

296

Introduction

Contents

Part 111

ix

2

Elimination of Nitrogen from Azo Compounds and Analogues

296

3

Elimination of Nitrogen from Diazo Compounds and Diazirines 3.1 Generation of Alkyl and Alicyclic Carbenes 3.2 Generation of Aryl Carbenes 3.3 Photolysis of a-Diazo Carbonyl Compounds

298 298 300 302

4

Elimination of Nitrogen from Azides and Related Compounds 4.1 Aryl Azides 4.2 Heteroaryl Azides

302 303 305

5

Photoelimination of Carbon Monoxide and Carbon Dioxide 5.1 Photoelimination of CO and C02 from Organometallic Compounds

305 306

6

Photoelimination of NO and NO2

310

7

Miscellaneous Photoeliminations and Photofragmentations 7.1 Photoelimination from Hydrocarbons 7.2 Photoeliminations from Organohalogen Compounds 7.3 Photofragmentations of Organosilicon and Organogermanium Compounds 7.4 Photofragmentations of Organosulfur and Organoselenium Compounds 7.5 Photolysis of o-Nitrobenzyl Derivatives 7.6 Other Photofragmentations

312 312 313 316 317 318 320

References

322

Polymer Photochemistry By Norman S.Allen

33 1

1 Introduction

33 1

2 Photopolymerisation 2.1 Photoinitiated Addition Polymerisation 2.2 Photocrosslinking 2.3 Photografting

33 1 332 336 34 1

3 Luminescence and Optical Properties

342

4 Photodegradation and Photooxidation Processes in Polymers 4.1 Polyolefins 4.2 Poly(viny1 halides) 4.3 Poly(acry1ates) and (alkyl acrylates) 4.4 Polyamides and Polyimides 4.5 Poly(alky1and aromatic ethers)

354 354 355 355 355 356

Contents

X

4.6 4.7 4.8 4.9 4.10 4.1 1 4.12

Part IV

Polyesters Silicone Polymers Polystyrenes and Copolymers Polyurethanes and Rubbers Photoablation of Polymers Natural Polymers Miscellaneous Polymers

358 358 358 359 360 361 361

5

Photostabilisation of Polymers

362

6

Photochemistry of Dyed and Pigmented Polymers

363

Rejerences

363

Photochemical Aspects of Solar Energy Conversion By Alan Cox

389

1

Introduction

389

2

Homogeneous Photosystems

389

3

Heterogeneous Photosystems

39 1

4

Photoelectrochemical Cells

393

5

Biological Systems

394

Rejkrences

395

Author Index

398

Introduction and Review of the Year BY ANDREW GILBERT

As usual, the chapter and references of the papers cited in this Introduction and Review can be found by using the Author Index. The tremendous activity directed towards the synthesis and photochemistry of fullerenes noted in previous years is possibly abating. Nonetheless, interesting accounts of the photoinduced behaviour of these fascinating molecules continue to appear. Areas of current importance appear to be the synthesis of water soluble materials (see inter alia Bourdelande et al.; and Crooks et al.) and the incorporation of fullerenes into multicomponent arrays. In the latter context, Guldi et al. have reported on the competition between through-bond and through-space interactions for various fullerenes - ferrocene dyads. More generally, photoelectron transfer to C60 continues to be a major area attracting considerable attention (Sasaki et al.; and Fukuzuh et al. inter alia) Non-resonant two-photon fluorescence spectroscopy is a new field of laser spectroscopy which has particular relevance to the in situ study of biomolecules. The technique can be readily adapted for the investigation of two-photon anisotropy of large molecules dispersed in membranes and has been reviewed by Callis. The application of fluorescence to monitor chiral resolution of enantiomers (Grady et al.; Stockman et al.), and the possible discrimination between enantiomers from the electron transfer quenching of excited states continue to attract attention (Tsukahara et al.). Xie et al. and Takeuchi et al. report on the development of new systems for chiral recognition of targeted substrates. There has been a considerable increase in the interest in design of fluorescent sensors for the recognition of molecules in solution and da Silva et af. have reviewed this rapidly expanding area. In the past, there has been surprisingly little concern regarding the possibility of fast energy migration amongst the chromophores of supramolecular assemblies but Muller and Stock have now reported on this subject and have formulated an expression for the temporal dependence of the distribution of the excited states of structurally identical chromophores in bichromophoric compounds. Dovinchi and Chen have reviewed recent advances in photophysical processes of single and isolated molecules with particular reference to applications in analytical chemistry and to the combination of single molecule detection with capillary electrophoresis. Despite the enormous volume of literature which has appeared over the years concerned with the photoreduction of benzophenone in solution, interesting observations and comments continue to be reported for this system, and the importance of exciplex-type intermediates in the reaction has been stressed Photochemistry, Volume 30 0The Royal Society of Chemistry, 1999 1

2

Photochemistry

(Marciniak et al.; and Shizuka). Kotani et af. and Miyasaka et af have reported the important finding that similar rate versus energy gap profiles to those described earlier for systems in solution are observed for charge-transfer complexes adsorbed onto porous glass. These data indicate that high frequency vibrational modes control the rate of charge recombination in such complexes, a situation which questions the validity of applying Marcus-type theory to intimate donor-acceptor complexes. Singlet singlet energy transfer to a porphyrin from a covalently-bound carotenoid has been described by Debreczney et al. and surprisingly, this transfer occurs from the very short lifetime Sz state in at least one example. Striplin et al. in a departure from the usual theme, have described energy transfer from porous silicon to adsorbed metal polypyridine complexes, and the photochemistry of a number of rigidly linked dyads which allow the study of geometry effects to be studied has been described (Sumida et al.; and Dieks et af.).A new triad in which naphtho- 1,4-quinone and tyrosine units are linked to a central porphyrin chromophore is reported by Evstigneeva and Grihkov, and a two-colour laser has been used in a novel approach to control the rates of electron transfer in multicomponent molecular systems (Gosztola et af.). Three-photon excitation combined with single photon counting fluorimetry gives a powerful approach to the selective study of fluorescent molecules, and the technique has been applied to the investigation of several scintillators (Hatrick et al.). Publications of the more organic aspects of photochemistry are now considered. A two-photon process for a-cleavage has been suggested from a laser flash study of the photochemistry of acetone (Markaryan), and irradiation of (1) is reported to yield the alkene (2) both in benzene solution and in the solid state (Kim et af.).The site of &-hydrogenabstraction from the amides (3) (Lindemann et af.) and of the regiochemistry of the keto ester (4) (Hasegawa et al.) are considered to be controlled to some extent by the heteroatom, and for the first time the regiochemistry of the addition of triplet carbonyl compounds to alkenes has been interpreted in terms of hard and soft acid-base systems (Sengupta et al,).

Me

CN (1)

Me

CN

(2)

As in previous years, there have been a number of accounts published describing the use of the photochemistry of enones as a key step in the synthesis of target systems. For example, the adduct ( 5 ) from the addition of ethene to the lactam (6) has been elaborated by Tsujishima et al. to provide a route to ~-2-(2carboxycyclobuty1)glycine derivatives, and the popular target molecule, ( & )-

Introduction and Review of the Year

3

grandisol(7) has been obtained using (-)-quinic acid as the starting material in a photochemical procedure (Matsuo et ul.). In contrast to many enone systems, the principal reaction of the esters (8) is one of dimerisation rather than intramolecular (2n + 271) photocycloaddition (Piva-Le Blanc et ui.) but the latter process does occur with (9) and the product (10) provides a key intermediate towards the natural product (+)-ligudentatol (1 1) (Haddad and Salmon).

c>SU

(9)

Diastereoselective photoinduced electron transfer initiated cyclisation of unsaturated esters such as (12) and (13) gives the cyclic alkanols (14) and (15) respectively (Pandey et ul.),and the intramolecular cycloaddition of (16) produces the complex enone (17) which undergoes photorearrangement to the pentacyclic compound (18) on prolonged irradiation (Kalena et uZ.). Ito et uZ. report a novel coupling reaction from studies into the photochemistry of mixed crystals of 1,2,4,5tetracyanobenzeneand benzyl cyanide, and the pyridones (19) which crystallise to give a chiral space group are photochemically converted in the solid state into j3-lactams (20) in good yield and with reasonable ee's (Wuet d.). A

Photochemistry

4

two-laser technique for irradiating reaction intermediates has been used to provide yet further evidence for the mechanistic steps in the photo-Fries reaction (Jimenez et ul.), and the bisaryne (21) is reported to be formed from the dianhydride (22) photochemically in an argon matrix by using a KrF laser (Moriyama and Yabe).

p';

0

I H (19) R = Me, MeO, Br or CI

&o

A+

0

N\

H

(20)

0

0

(22)

Irradiation of (23) yields the isomer (24) by a concerted 1,3-alkyl migration on an ally1 moiety which Rodriguez and Shi claim to be the first example of a rearrangement from a cembrane to a pseudoterane skeleton. In solution, the dibenzonorbornadiene (25) gives the cyclo-octatetraene (26) while in the solid phase only the pyrrole derivative (27) is formed which is suggested by Scheffer and Ihmels to result from steric effects within the crystal. The Dewar paracyclophanes (28) ring open to their benzenoid isomers on irradiation in a glass at 77 K but, interestingly, for (28) with R' = CN and R2 = H, the aromatic compound undergoes the first reported thermal cyclisation back to (28) on warming to room temperature (Okoyuma et d ) . Irradiation in the charge-transfer band of the

NH2

H2N)

H

Introduction and Review of the Year

5

complex of acenaphthylene and tetracyanoethene in solution yields no products, but co-crystallised samples with the same wavelength light form the (27t + 27t) cycloadduct (29) exclusively (Haga et al.), and mixed crystals of acridine and phenothiazine (3:4 ratio respectively) give (30) photochemically but in solution the dihydrodimer (3 1) is also formed (Koshima et al.). H

H

Gade and Porada have described a new procedure for the determination of quantum yields of a reversible photoisomerisation, and a novel adiabatic pathway has been suggested for the trans-cis photoisomerisation of di-(anaphthy1)ethene (Budyka et d.). Scavarda et al. report that irradiation of 4hydroxybenzonitrile in deoxygenated water isomerises from the triplet state to 4hydroxyisobenzonitrile by way of an intermediate which may possibly be the azirine and this yields the product in a secondary photochemical rearrangement. The anti-Bredt ( 2 + ~ 2 ~ tricyclic ) adducts (32) are formed from the sensitised irradiation of the bichromophoric compounds (33), and the first report has appeared of the formation of a 11.11 paracyclophane (34) (Tsuji et al.). The efficient conversion of the ubiquinol-benzoin adduct into (36) and (37) is considered by Stowell et al. to be significant for the study of rapid electrontransfer events in ubiquinol oxidising enzymes. Chiang et al. have described the photoconversion of the cyclopropanone (38) into N-(pentafluoropheny1)phenylethynamine and (39) for which there is no precedent, and a new photosensitive amine protecting group based on o-hydroxy-trans-cinnamic acid has been reported by Wang and Zheng. The first fluorescence and fluorescence quantum yields from the excited state of the radical anion of 1,4-benzoquinone have been reported by Cook et al., and electron transfer from aromatic donors to the S, state of chloranil giving the singlet radical ion pair has been observed on the fs/ps time scale (Hubig et al.). A series of porphyrin quinones having variable acceptor strengths of the quinone moiety has been synthesised by Dieks et al. and may be considered to be wellsuited as biomimetic model compounds for studying photochemically-induced electron transfer in photosynthesis. The usual number of publications have appeared within the review year concerning the reactions of singlet oxygen, and Huang et al. have published an order of effectiveness of metal phthalocyanines for the generation of this species. The ethenyl hydrogens of the twisted 1,3-diene (40) have unusually high reactivity towards O,('A,) (Mori et al.),and Maras et al. have described a convenient route

Photochemistry

6

%OM.

M Me0 (35)

e

I I O

OMe

0

0

\

(36)

Ph

\ QN,

OMe

(37)

H Ph \ / /c=C, C02H F5 H (39)

to ( k )-talo-quercitol and ( f)-ribo-quercitol from the reaction of cyclo-l,4-diene with singlet oxygen. Irradiation of the norbornadiene (41) produces the expected quadricyclane which undergoes a secondary photoreaction to give (42) by a (2 + 2 + 2) cyclisation followed by a [ 1.51-hydrogen shift (Ivakhnenko et d).The efficient photodimerisation of the sterically hindered 1,4-dihydropyridine (43) in the solid CMe3

Introduction and Review of the Year

7

state is considered to result from a disordered packing region (“buffer zone”) which maintains the crystal structure in the monomer but allows conformational change in the pyridine ring to avoid steric effects in the photoreaction (Marubayashi et al.). A sequence of (2x + 2x) photocycloadditiodretro-Mannich fragmentation/Mannich closure in the vinylogous amide (44)provides the key procedure in the synthesis of the pentacyclic ring system of the anti-leukaemia marine alkaloid, manazamine A (Winkler et al.). CO(CH2)3CS(CH&,COzEt

If

A general method for producing highly efficient photoreactions initiated by electron-transfer quenching of excited states has been described by Chen et al. and it has been report by Engel et al. that the y-perester radical (45) produced cyclises to from irradiation of t-butyl-4-methyl-4-(t-butylazo)peroxypentanoate, give the y-lactone sufficiently slowly to allow the azoperester precursor to be used as a photochemical bifunctional initiator. Donati et al. have described an access to the new isoxazolo-[4,5-dJ- and -[4,5-e]-diazepines (46) and (47) respectively by irradiation of the diazide (48) in methanol, and a nitrobenzyl linker incorporated at different positions in a fraction of the oligomers during the split synthesis combinatorial approach has been used to initiate photochemical cleavage of the oligomers on a bead (Burgess et al. ). 2,3,4,5-Tetraphenylsilacyclopentadienylidene, the first silylene incorporated into a silole ring, has been generated by irradiation of 7-silanorbornadiene and norbornene precursors at 77 K (Kato et al.). Me Me+OLOCMe3

0

A comprehensive theoretical study has been made of the potential energy surfaces and reaction pathways of the singlet and triplet states associated with the photolysis of 2,3-diazabicyclo[2.2.l]hept-2-ene(Yamamoto et al.). All possible

8

Photochemistry

processes have seemingly been considered and the reactions are proposed to evolve through a network of 18 ground and excited state species, 17 intermediates and 10 “funnels” where internal conversion or intersystem crossing may occur, but for the transimt triplet intermediate observed experimentally, the best candidate is considered to be the 3(nn*) - 3(~n*)species. The first triplet diazatrimethylenemethane (49) has been observed from the photolysis of (50) (Quast et d), and in agreement with much experimental evidence and theoretical data, it is proposed from studies of (51), that diazirines open by C-N cleavage and the resulting diazirinyl diradicals may recombine, form diazo compounds, cleave to give carbene (+N2), or rearrange to cyclobutenes (+N2) (Platz et a/.). 1,2’-Biazulene derivatives, which are difficult to obtain, can be formed in yields around 90% from the irradiation of (52) in the presence of azulene or its alkyl and photolysis of 9-diazo-1-fluorenylmethanol (53) gives derivatives (Lin et d), yields of the aldehyde (54) in excess of 95% (Kirmse and Krzossa).

Shimizu et al. report that while [2.2] paracyclophane (55) undergoes twophoton dissociation in low temperature matrices by way of the triplet state, in the gas phase, the efficient two-photon process proceeds via a hot molecule formed by internal conversion from the initially formed singlet excited state. The photocleavage of 2-nitrobenzyl ethers and ester has been widely reported and has now been evaluated as a deprotection methodology for indoles, benzimidazole, and 6-ch1orourdcil (Voelker et al.). The mechanism of the cleavage of such compounds is considered to involve the o-quinonoid intermediate, but previously these had only been deduced from transient electronic spectra produced in flash photolysis experiments. Infrared spectral data from photochemical studies of 2nitrobenzyl methyl ether in argon and nitrogen matrices have now been published which confirm that the intermediate does indeed have the o-quinonoid structure

introduction and Review of the Year

9 OMe

OH OH

M e 2 N e ( ! I+ A I e N M e 2 Me Me

OH OH

Me-+N>t-tGN+-Me Me Me

(56) (Dunkin et a!.). Interestingly, the irradiation of a mixture of the two pinacols (57) and (58) in acetonitrile induces efficient fragmentation of the central carboncarbon bond in both compounds in a chain process (+ = 9 & 1) initiated by single electron transfer quenching of (57) by (58) (Caen et al.). Again this year, the tremendous interest in “polymer photochemistry” is reflected in the considerable number of publications reviewed in Part I11 of this Volume. Eklund et al. report on the photopolymerisation of C6o-fullerene (see also Burger et al.), and polymeric fullerene hydrides have been synthesised which have the potential for storage of hydrogen (Lawson et al.). Konno et al. have observed that compared to thermally polymerised acrylate monomers (room temperature), the photoinduced free radical process gives high yields of stereoregular syndiotactic polymers, and a new light emitting polynorborene has been synthesised by a ring-opening metathesis of coumarin-containing derivatives (Tlenkopatchev et al.). In the presence of N, N-dimethyl-4-toluidine, a series of novel N-phenylmaleimides are found to undergo rapid photopolymerisation (Xu et a/.), and the first report of the curing of polydimethylsiloxanes having epoxynorbornyl units has appeared (Lecamp et al.). A novel method of molecular switching through surface photochromism has been described by Seki et al. from their studies into systems having polyacetylene monolayers cast onto an azobenzene monolayer. Konigstein and Bauer have discussed pathways for hydrogen production based on electron transfer using new homogeneous catalysts and with ascorbic acid as the sacrificial donor, and a range of new dithiolene complexes have been investigated for their abilities to promote the photo-oxidation of water (Lyris at al.). In heterogeneous photosystems, a new photochemical catalyst has been described for the production of hydrogen from water using visible light (Park and Lim), and a new three-layered structure also capable of splitting water comprises a monolithic polypyromellitimide film, a second layer of this polymer incorporating [Ru(bpy)3I2’ and the third layer is [Ru(bpy)J2+ with EDTA.2Na and dispersed ultrafine platinum (Swarnkar et al.). A new type of photocell based upon the dye sensitisation of thin films of Ti02 nanoparticles in contact with a non-aqueous liquid electrolyte has been described (Frank et a/.), and in a further new solar cell, a UV filtering photocatalyst layer (preferably anatase) is situated on the light incident side of the cell (Oka).

Part I Physical Aspects of Photochemistry By Anthony Harriman

Photophysical Processes in Condensed Phases BY ANTHONY HARRIMAN

1

Introduction

The format of this chapter follows that adopted last year. The first section deals with the general aspects of photophysical properties of molecules in condensed phase, with particular emphasis being given to supramolecular systems. This is followed by a review of progress made in the theoretical description of photophysical events and of the kinetic models used to describe photophysical processes taking place in solution. The third section reviews the many different types of photophysical event that might accompany deactivation of an excited state while a separate section is concerned with possible applications for molecular photophysics. The final section describes advances made with instrumentation and data analysis. Regretably, shortage of space prohibits a full listing of all the relevant literature that has appeared during the review period. 2

General Aspects of Photophysical Processes

The complementary features of laser flash photolysis and pulse radiolysis have been reviewed'*2while the application of electron spin polarization techniques to the measurement of molecular photophysics in solution has been highlighted.3 have been The fundamental aspects of luminescence and chemiluminescen~e~~~ considered in detail and particular attention has been given to the theory of spontaneous emission.697A comprehensive review of the dynamics of the fluorescence Stokes shift has appeared' and the underlying theory for radiative migration of electronic excitation energy has been considered by special reference to the fluorescence of Rhodamine 101 in ethanol.' Attention has been paid to the possibility of extracting a statistical temporal signature of quantum chaos from time-resolved fluorescence decay curves" while other studies have concentrated on the implications of gelatin fluorescence for photography.' The technique of non-resonant two-photon fluorescence spectroscopy has been reviewed.12 This is a new field of laser spectroscopy, having particular relevance to the in situ study of biological molecules, that can be readily adapted for examination of twophoton anisotropy of large molecules dispersed in membranes. The mechanism for light-induced hydrogen atom abstraction by n,n* excited states has been ~o ns i der ed'~while . '~ separate studies have addressed the issue of Photochemistry, Volume 30 0The Royal Society of Chemistry, 1999 13

14

Photochemistry

ultrafast proton-transfer reactions. '',I6 Application of femtosecond spectroscopy to solvation and electron-transfer dynamics continues to be an attractive subject.l7,I8 Recent attention has focussed on the dynamics of geminate recombination in charge-transfer complexe~'~ and in geminate radical pairs2' and of nonergodic reactions2' Theoretical models have been presented to account for the selectivity of organic singlet and triplet photoreactions.22 Other studies23have considered the implications of vibronic coupling for light-induced electrontransfer processes occurring in multicomponent supramolecular systems. Marcus theory has been applied to electrochemiluminescence24and quantum beats have been reported25in the recombination of radical ion pairs, as caused by hyperfine interaction in the radical anions. Interest has been shown in the development of protecting groups that can be cleaved by photochemical electron-transfer reactions26and in the use of polarized light to attain stereocontrol of reactive encounter^.^^ The possible discrimination between enantiomers by way of electron-transfer quenching of excited states continues to attract attention,28 as does the application of fluorescence spectroscopy to monitor chiral resolution of e n a n t i o m e r ~ .Several ~ ~ ' ~ ~ new systems have been developed for chiral recognition of targeted substrate^.^"^^ The interconversion of enantiomers has been monitored by time-resolved chiroptical luminescence s p e ctr o ~c o p y~ while ~ a theory has been proposed to account for the special case of circularly polarized fluorescence emanating from chiral nematic liquid crystals.34Circularly polarized luminescence has also been reported from rigid complexes of chiral macrocyclic tetranaphthylamide~.~~ Considerable attention has been given to the study of those systems in which light is used to engineer a conformational change in a large molecule. Such effects are important in certain biological systems and the effect of solvent on the conformational equilibrium of previtamin D has been described.36 Related studies have been devoted to following the a-helix-to-coil transformation for a series of photochromic polypeptide^.^^ Several artificial phototropic systems have been d e ~ e l o p e d ~in ~ -which ~' light is used to drive a largescale conformational change. The mechanism and dynamics of the transformation have been followed for the photoejection of a guest from a macrocyclic host and of its subsequent reentry into the cavity.38The photochemistry of many supramolecular assemblies has been considered in terms of energy or electron transfer between the reactive s ~ b u n i t s .A ~ ~strategy - ~ ~ has been proposed for the construction of extended 2D and 3D arrays that display long-range magnetic ordering and for which there are interesting photophysical properties." During the past year there has been a tremendous upsurge in interest in the design of fluorescent sensors for the recognition of target molecules in solution and the field has been comprehensively reviewed. 51 Because of its great biomedical significance, attention has focussed on the detection of nitric oxide by fluorescence t e c h n i q ~ e s The . ~ ~ development of photozymes for water purification has been reviewed.53 Attempts to better understand natural photosynthesis and to construct artificial models54955 continue to be important areas of modern photochemistry. The photophysical properties of certain bacteriochlorophylls56and carotenes57 have been reported while the mechanisms of electron58and energy59transfer in natural

i: Photophysical Processes in Condensed Phases

15

photosynthetic systems have been reviewed. Particular attention has been given to the design of artificial photosystems that mimic the manganese-containing enzyme of PS2 that is responsible for water oxidation in green plant^.^-^^ Most of these photosystems use a powerful oxidant to photo-oxidize a simple manganese complex but they lack the ability to store oxidizing equivalents that is an inherent feature of the natural organism. Progress is being made in this area, however, and many of the important spectroscopic features of the natural manganese cluster can now be duplicated in model systems.67

3

Theoretical and Kinetic Considerations

One of the great strengths of photochemistry is the close interplay between experimental work and theoretical analysis and there has been a constant evolution of the theoretical framework for many types of photochemical processes. A model has been proposed6* for the specific case where proton transfer is coupled to light-induced electron transfer in a polar solvent, with proton transfer being sequential or concerted to the electron-transfer event. Semiclassical and quantum mechanical treatments have been given for nonadiabatic photodissociation dynamics, with particular reference to interference effects.69A complete thermodynamic classification has been presented that describes orientational relaxation in both excited and ground states following Franck-Condon transition^.^' The photophysical properties of styrene and indene have been explained in terms of a combined molecular mechanics and valence bond meth~dology,~' wherein the geometry of the excited state is fully optimized before calculation of the various potential energy surfaces. Quantum mechanical approaches, based on the LCAO MO SCF method, have also been used to calculate the photophysical properties of complex heteroaromatic corn pound^.^^ Electron-transfer processes continue to play a central role in molecular photophysics and there remains much fundamental information to be learned before we have a complete understanding of the mechanism of such reactions. Although it has been known for many years that intramolecular charge recombination can lead to population of both the ground state and the triplet excited state of the chromophore little is known about the mechanism of this latter process. It has now been found that the two recombination steps possess quite disparate attenuation factors for through-bond electron t ~ n n e l l i n g .An ~ ~ evaluation has been made of the electronic coupling matrix elements for electron exchange in mixed-valence complexes74while an expression has been derived for the dependence of the rate of self-exchange on the extent of electron delocalization in the corresponding mixed-valence ~omplex.~'Path integral calculations have been used to follow the charge-transfer events that follow from laser excitation of these mixed-valence complexes.76 The calculations indicate that the strong electronic interaction between the metal centres gives rise to very fast oscillations in the electronic state population as the wave function oscillates coherently between donor and acceptor, It is suggested that the Fermi golden rule might not be applicable to such systems. Other theoretical evaluations of charge-transfer

16

Photochemistry

effects in solution77 and in weakly coupled conjugated polymers78 have been described. Detailed information about the nuclear79 and solvent8' re-organization energies that accompany electron transfer is critical for a deeper insight into the reaction mechanism and evaluation of these parameters is an important subject. Replacing the solvent bath with a protein scaffold, as in photosynthetic bacterial reaction centres, introduces additional complications for understanding the dynamics of electron-transfer events. Attention has been given to modelling the non-linear dynamics of photosynthetic reaction centres8' and to estimating the importance of protein relaxation dynamics on the rate of electron transfer from the bacteriochlorophyll special pairsB2 Increasing attention is being paid to the possibility of calculating the fluorescence properties of large molecules, especially for those cases where chargetransfer interactions are likely to be important.83 Calculations have also been made to gauge the significance of incorporating vibronic transitions into the expression for ultrafast solvation of excited state dye molecules in polar solvents.84385Experimental studies have addressed the mechanisms by which rapid re-orientations6 and ~ o l v a t i o n ~ ~ of- ~dye ' molecules occur in organized media and in polar solution. Particular attention has been given to seeking a better understanding of the transient dynamics of the solvatochromic shift in binary solvents.90 The role of the excitation lifetime in controlling the initial distribution of electron-transfer products has been considered." Given the widespread interest in the photophysics of supramolecular assemblies wherein numerous identical chromophores are built into a large array it is surprising to find that little concern has been shown about the possibility of fast energy migration amongst the chromophores. This subject has now been examined9*and an expression has been formulated for the temporal dependence of the distribution of the excited states of structurally identical chromophores in bichromophoric molecules. The expression describes the temporal dependence of emission anisotropy in cases where dissipative iriteractions between the chromophores can take place, A combined quantum mechanical and classical description of non-adiabatic photoprocesses, such as internal conversion, has been given.93 The model might be useful for looking at interconversion between high-lying excited states. Advances in kinetic theory, with particular reference to fluorescence quenching in fluid solution, have been while the advantages of monitoring fluorescence quenching by way of stimulated emission have been stressed. lo' A theoretical expression has been given for resonance energy transfer occurring in dense dispersive media"* and separate calculations have been concerned with the possibility of energy transfer taking place via higher-energy excited states. lo3 Limitations to the analysis of fluorescence quenching techniques have been raisedIo4 while a kinetic model has been presented for the photomodulated transport of species across liquid membranes. ' 0 5 Quenching of excited singlet and triplet states by molecular oxygen has been examined for systems where the second-excited triplet states lies close in energy to the first-excited singlet state. Io6 Other studies have reported anomalously high rates of bimolecular fluorescence quenching that could be ascribed to the effects of static q~enching."~A kinetic model has been proposed for the slow photo-

1: Photophysical Processes in Condensed Phases

17

tautomerization of free-base porphyrins. '08 Numerous studies lo9-' l 5 have considered the kinetics of fluorescence quenching in terms of structural or environelectrolyte mental effects, such as temperature,"6i' l7 solvent,' 18-12' composition,'22 or viscosity.123 Additional studies have addressed the issue of non-diffusional formation of e ~ c i m e r sand ' ~ ~the relaxation behaviour of excitedstate complexes.125y126 The influence of secondary structure on the decay properties of fluorescent donor-acceptor labelled peptides has been c o n ~ i d e r e dwhile '~~ the fluorescence of chlorophyll in concentrated solution has been re-examined.128 Particular attention has been given to the kinetics of triplet-triplet annihilation in fluid ~ o l u t i o n ' ~and ~ - 'to ~ ~the various factors that influence the rate of reverse electron transfer in charge-transfer complexes133or radical ion pairs. 134 Diffusional processes available to transient species formed during photochemical processes, especially hydrogen-atom abstraction reactions, have been reviewed'35 and it has been shown that the diffusion coefficients depend markedly on the nature of the surrounding solvent. 13' Photophysical processes involved in the formation of twisted intramolecular charge-transfer (ICT) states continue to be of considerable interest and to receive intense investigation. Theoretical studies have addressed the structure of the ICT state in amino-substituted benzenes'37.'38 while the dual fluorescence of dialkylaminobenzonitrile has been examined in different solvents and as a function of t e m p e r a t ~ r e . ' ~ ~Coupling -'~' between the close-lying S1 and S2 energy levels in dimethylaminobenzonitrile has been detected by picosecond emission anisotropy and related to internal twisting of the amino group.'42 Numerous derivatives of dimethyaminobenzonitrile have been s t ~ d i e d ' ~ in ~ -order ' ~ ~ to determine the structural requisites for dual fluorescence. Similar ICT state formation occurs in diphenylamino-substituted biphenyl'49 and in N,N-dimethyladen~sine~~' while triple fluorescence has been found for certain benzonitriles substituted with tetraazacyclotetradecyl rings. 5 1 y 1 52 The dynamics of ICT state formation have been monitored for amino-substituted oxadiazoles and ketones'53 while the effects of pressure-tuning of the solvent relaxation time on the rate of internal rotation of the ICT state have been At high viscosity, it appears that the rate of ICT state formation greatly exceeds the solvent relaxation time. The importance of hydrogen bonding in controlling ICT state formation has been ~ t r e s s e d ' ~while ~ . ' ~ the ~ involvement of the excited triplet state has been 15* noted for ICT states formed from 4-amino-N-methylphthalimide. Ultrafast intramolecular charge transfer occurs in the excited singlet state of trans-4-dimethylamino-4'-cyanostilbene,followed by trans-to-cis isomerization by way of a highly polar ICT state.'59 The activation barrier for isomerization increases with increasing solvent viscosity in nonpolar solvents but the specific effect of viscosity cannot be separated from polarity effects in alcohols or polar nitriles. Competing photoisomerization also occurs in 4-dialkylamino-9-styrylacridines. 6o Several reports have addressed the photoprocesses occurring in the push-pull polyenes 1617162where both one- and two-photon effects have been observed and where complex formation has been noted at high concentration. The absence of dual fluorescence from 4-dimethylaminophenylacetylenehas been a t t r i b ~ t e d 'to ~ ~a large energy gap between S1 and S2 levels but ICT state

'

18

Photochemistry

formation has been detected for N,N-dimethylaminophenyI-4'-cyanophenylacetylene by virtue of picosecond laser spectroscopy measurements. 9,9'-Dianthrylmethanol shows complicated fluorescence behaviour that depends markedly on temperature and solvent polarity due to the co-existence of local n,n*, excimer, and ICT states.'65 The results have been considered in terms of different molecular conformations for which the degree of orbital overlap between the aryl rings can vary over a wide range. Internal conversion in 1aminonaphthalene derivatives has been linked to twisting of the amino group, even in nonpolar solvents, and the activation energy has been measured.'66 In polar solvents, ICT state formation begins to compete with internal conversion but there are interesting effects caused by pre-twisting of the donor group. Formation of an ICT state has also been invoked to explain the photophysical properties of 4-( 1H-pyrrol-1-yl)benzoic acid. 167 4

Photophysical Processes in Liquid or Solid Media

4.1 Detection of Single Molecules - The most elegant photophysical processes are undoubtedly those associated with single or isolated molecules and such studies have become possible over the past few years by way of selective laser excitation and ultrasensitive fluorescence detection. Recent advances in this field have been reviewed,'68 with particular reference to applications in analytical chemistry and to the combination of single-molecule detection with capillary electrophoresis. Detection of single molecules, such as r h ~ d a r n i n e 'or ~ ~cowmarin'70 dyes in water has been described under conditions that permit measurement of the fluorescence lifetime by way of one-photon laser excitation. A mechanism for the two-step photolysis of coumarin dyes has been proposed on the basis of fluorescence correlation spectroscopy and transient absorption. I7O Fluorescence anisotropy has been applied at the single-molecule levelI7' in order to elicit information about the rotational diffusion of isolated molecules and about their interaction with specific solutes. Counting of single molecules on microchip devices,'72 fused silica,'73 and nan~ part i cl es'~~ has been described while the fluorescence decay characteristics of single molecules near to a surface have been monitored under conditions of variable interaction with the surface.'75 Methods for improving the spatial resolution of the technique have been d e ~ c r i b e d ' ~while ~ - ' ~ related ~ studies have indicated the advantages of dispersing the fluorophore in a m i ~ r o d r o p l e tor ' ~ flowing ~ sample stream. I8O Single-molecule detection by way of two-photon absorption spectroscopy has been reported. 1 8 * 4.2 Radiative and Nonradiative Decay Processes - The use of cyclodextrins or surfactant dispersions to promote room-temperature phosphorescence from organic molecules is a particularly simple but elegant way in which to characterise triplet excited state^.'^^-'^^ This field has been greatly extended by the synthesis of modified cyclodextrins bearing chromophoric groups that can be included into the cavity.190-'92Additional studies have reported binding constants for the

1: Photophysicul Processes in Condensed Phases

19

inclusion complex formed with various small organic molecule^,'^^-'^^ including a r ~ t a x a n e ,and ' ~ ~described how the host modifies the photophysical properties of the included guest .200-202 Diffuse-reflectance laser flash spectroscopic studies have been performed with the solid-state complex.196i200 Because of their relevance to natural photosynthetic organisms, there is a long and well-established history associated with the photophysics and photochemistry of tetrapyrrolic pigments. Such interest has been stimulated in recent years by the application of these pigments as sensitizers for photodynamic therapy of tumours. The mechanism for the singlet oxygen sensitized delayed fluorescence from certain phthalocyanines has been re-examined203while the photophysical properties of many new phthalocyanines have been reported.204-2'0Most attention has been given to improving the optical properties of the pigment, notably by moving the absorption bands to longer wavelength, or in solubilizing the chromophore in such a way as to improve its biocompatibility. The origin of the violet emission observed from some phthalocyanines has been discussed.2' Similar studies have been made with the corresponding metallop~rphyrins~'~-~'~ Many different laser dyes have been and with their protonated studied by flash photolysis studies, partly because of the increased use of such compounds as fluorescent labels in biochemistry. The photophysical properties of several rhodamine dyes have been reported2199220 and the characteristics of the SI-S, absorption spectra have been discussed in terms of the lasing characteristics of the dye. Several new members of the rhodamine family have been synthesized and fully characterized in solution2*' and in the presence of amines.222 In polymeric media, the importance of two-photon excitation has been stressed and its pressure dependence measured.223 A new class of acridine-1,&dione-based laser dyes224has been introduced and their photophysical properties have been recorded. Coumarin dyes have often been used as probes for dynamical Stokes shift measurements and several amino-substituted coumarins have been examined by ultrafast upconversion fluorescence spectroscopy.225Extremely fast intramolecular relaxations take place following laser excitation and it has been possible to monitor breaking and reformation of various hydrogen bonds formed with the surrounding solvent. Related studies have described an excitation energydependent spectral relaxation in coumarin 153 in selected solvents226and the effects of solvent on the spontaneous emission characteristics of 7-diethylamino4-methylcoumarin have been reported.227The lasing properties of several new coumarin dyes have been described.228 The photophysical properties of polyacene molecules depend markedly on the number of rings and the fluorescence behaviour of hexacene has now been compared with that of earlier members of the series.229A similar comparison has been made of the photophysical properties of catacondensed aromatic polycycles.230Fluorescence from an upper-excited singlet state has been described for benz[a]azulene derivative^^^' while the fluorescence properties of some antiaromatic molecules have been described in Several t h i o p y r y l i ~ mand ~~~ p y r y l i ~ r nsalts ~ ~ ~ have been studied and the effects of various substituents attached to the heterocycle have been examined in terms of the triplet yield. A full evaluation of the photophysical properties of 4-aminonaphthalimide, and its

'

20

Photochemistry

alkylated derivatives, has appeared235that includes the effects of solvent polarity and viscosity. The fluorescence properties of several amines have been dewhile laser flash photolysis techniques have been used to study the photoreactions of 4-tolyltrifluoromethyI~arbene.~~~ 4-Nitroaniline has potential applications as a photoinitiator and its photophysical properties have been recorded in the presence of a tertiary amine.239Separate reports have addressed the photophysical properties of coelenteramide analogs,240methyl red,241benzylP-naphthyl ~ u l f o x i d eacyl , ~ ~ phosphine ~ and triphenylphosphines.2a It has been reported245that the phosphorescence spectrum of 4-hydroxy-3-methoxybenzaldehyde exhibits a temperature-dependent hysteresis due to the co-existence of different molecular conformations. The transient intermediate observed during laser flash photolysis of ketoprofen shows the combined properties of a ketyl radical and a ~ a r b a n i o n Photophysical .~~~ properties have been reported for 3 -a~a f lu o r e n o n edinaphthyl ,~~~ ketone,248b i a n t h r ~ n eand , ~ ~pyridimethi~nes.~~' ~ There have been several interesting reports concerning the photophysical properties of biologically-relevant molecules recorded in fluid solution. Thus, the fluorescence properties of the nucleic acid bases have been recorded251and the excited singlet state lifetimes of purines and pyrimidines in aqueous solution have been found to be ca. 7 and 2 ps, respectively. A theoretical explanation has been provided for the vastly different fluorescence properties displayed by the isomers adenine and 2 - a m i n o p ~ r i n e .The ~ ~ ~ fluorescence properties of cysteine and cystine have been measured and compared with theoretical calculations253while the photophysics of p-carotene and related compounds have been reviewed.254A quantitative evaluation has been made of the triplet absorption spectra of several carotenoid pigments on the basis of triplet sensitization with a n t h r a ~ n eThe .~~~ photophysical properties of several N-substituted 1,8-naphthalimides and 1,4,5,8naphthaldimides have been recorded256and used as a basis by which to better understand the biological applications for such chromophores. An examination of dipolar relaxation around indole has revealed257both a slow fluorescence component and a fast relaxation process that depends on excitation wavelength. Flash photolysis studies of 4',7-dihydroxyflavylium perchlorate have shown that cis-trans isomerization is not the determining step in conversion of the molecule into trans-~halcone.~~' The photochemistry of 1- and 9-naphthyl glyoxylic acids has been interpreted in terms of an ionic mechanism for photodecarb~nylation~~~ while the triplet state properties of flavone and flavanone have been compared.260 Since the availability of ultrafast laser spectroscopic techniques, increasing attention has been given to characterizing upper-lying excited singlet states. Using fluorescence upconversion spectroscopy, the lifetime of the S2 state of zinc tetraphenylporphyrin has been measured at 2.35 ps in ethanol.261 Similar measurements262made with malachite green in water place the lifetime of S2 at 0.27 ps but the lifetime is longer in more viscous solvents. Internal conversion from S2 into S1 in coumarin 481 in cyclohexane is reported263to occur with a lifetime of 220-280 fs while the origin of the second-excited singlet state in dimethyldiazirine has been examined by high-resolution fluorescence spectrocopy.^^ Emission has been observed265from unrelaxed vibrational levels in the S2 state of thiocoumarin, where the S2 lifetime is ca. 1 ps, while the application of

I : Photophysical Processes in Condensed Phases

21

two-colour (two-laser) spectroscopy to probe the photochemistry of upper-lying excited states has been recommended.266The temperature dependence267of the photophysical properties of 3-chloro-7-methoxy-4-methylcoumarinhas been related to the energy gap between the two lowest-lying excited singlet states. Related studies have addressed the issue of reversible triplet energy transfer between excited states of comparable triplet energy268and the importance of upper-lying triplet states in controlling the photophysical properties of fluorenone derivatives has been noted.269 Photoinduced intramolecular proton transfer makes a major contribution towards nonradiative deactivation of the excited singlet state of salicylic acid and its derivative^.^^'-^^^ Similar photoreactions, leading to transient formation of an enol, have been reported for 5-methyl-1,4-na~hthoquinone,~~~ h~pericin,*~~ 2-(2’-aminophenyl)ben~irnidazole,2~~ ortho-hydroxy deriva2’-hydro~ychacone,2~~ tives of 2,5-diarylo~azole,2~~ and anthralin.280 Proton transfer tautomerism in 3-hydroxyisoquinone is promoted by dual hydrogen bonding to suitable substrates, in both ground and excited states.281 The involvement of rotational processes in the intramolecular proton-transfer cycle of 2-(2-hydroxyphenyl)imidazo[1,Za]pyridine has been monitored by picosecond transient absorption measurements.282Photoinduced proton transfer is responsible for the lack of fluorescence from 8-hydro~yquinoline~~~ while the effects of organized media on excited-state proton transfer in 2-(2’-pyridy1)benzimidazole have been deDeuterium isotope effects have been noted for the fluorescence properties of phenylpyridines and interpreted in terms of protonation of the excited state.285 The phototropic behaviour of l’-(purin-6-yl)-3-methylimidazolium chloride in water has been described in terms of the Forster cycle.286Hydrogen bonding between the fluorophore and solvent can promote nonradiative decay of the excited state and the mechanisms of such processes have been explored for aminoanthraquinone~,~~~ aminofluorenones,2886,ll -dihydroxynaphthacene-5,12d i ~ n e , ~acridine’~ 1,8-di0ne,~” and mono-functionalized hydroxybenzophenones.29’ 5,5’-Dimethyl-[2,2’-bipyridyl]-3,3’-diol undergoes single and double proton transfer on very fast time scales.292The rate of proton transfer is independent of the nature of the solvent for aprotic solvents but the proton transfer rate depends on viscosity for protic solvents.293A direct measurement of the rate of bimolecular acid-base reactions has been made for several pairs of naphthol photoacids and carboxylate bases.294A full kinetic analysis has been made of proton-base recombination processes.295Interaction between 7-hydroxycoumarin and tertiary amines leads to highly selective proton transfer296while hydrogen bonding of tyrosine to amide-like ligands is reported297to affect the fluorescence properties of the amino acid. Similarly, binding to serum proteins can perturb the photophysical properties of triarylmethane dyes due to restricted rotation.298 Extremely fast double proton transfer has been described for the 7-azaindole dimer in benzene.299Other studies have noted unusual photophysical properties for closely-spaced pairs of p ~ r e n or e ~anthracene ~ m o l e ~ u l e s and ~ ~ for ’~~ self~~ Photodissociation of assembled complexes containing metaIlop~rphyrins.~~-~~~ ~ ~ ~ the importance of methoxybenzenes occurs under UV laser p h o t o l y ~ i swhile

22

Photochemistry

internal rotation in controlling the photophysical properties of tyrosine model compounds has been stressed.309 Three reports have described the solvent dependence for the (blZg+) + (a'A& emission of molecular oxygen in solution,310-312 Quenching of the emission of singlet molecular oxygen by diary1 telluride^,^'^ dialkyl di ~ ul f i des , ~and '~ naphthal~cyanines~'~ has been described. Simultaneous quenching of both triplet and singlet states of naphthalene derivatives by oxygen has been observed during separation of geminate Lightinduced generation of superoxide ions in solution has been r e p ~ r t e d . ~ ' ~ . ~ ' '

4.3 Amplitude or Torsional Motion - Many molecules undergo a light-induced change in conformation that provides a facile means for nonrddiative deactivation of the first-excited singlet state, Such geometry changes might be small, as in the slight twisting around a connecting bond that optimizes ICT state formation, or large-scale, leading to the formation of an isomer. In either case, the process tends to be extremely fast and competitive with other forms of excited-state decay. Various aspects of the photoisomerization process have been r e ~ i e w e d , ~ ' ~ - ~ ~ although a unified theory for large-scale torsional motion in a viscous medium is still lacking. Photoisomerization of the rhodopsin chromophore has been considered in terms of a transient electric field associated with a change in local charge that accompanies geometrical displacement.323A crucial feature of this model concerns the coupling of torsional motion, vibrational interactions, and electronic effects associated with the surrounding amino acids into a single theoretical description. The effects of temperature and local viscosity on the rotational diffusion of simple organic molecules have been examined by way of molecular-mechanics simulations and time-resolved fluorescence spectroscopy.324 A comprehensive study of the solvent dependence of the photophysical properties of 9,9'-bianthryl shows that the fluorescence lifetime is essentially constant in low polarity solvents.325In more polar solvents, light-induced electron transfer occurs to form a perpendicular ICT state having D2d symmetry and which is weakly fluorescent. Reports have appeared that describe the photoisomerization of 4nitr~benzaldehyde,~~~ 5 - h y d r o ~ y t r o p o l o n e4-hydro~ybenzonitrile,~~* ~~~~ methylbenzonitrile, 329 and cinnamaldehyde.330 Because of their structural relevance to the retinal pigments, considerable attention has been given to the photoisomerization of polyenes in solution. Ab initio calculations have been made for isomerization of a Schiff base having five conjugated double bonds in the polyene backbone331 while the dynamics for light-induced and thermal isomerization of hexatriene have been measured in cyclohexane solution.332The lifetime of the first-excited singlet state of the cisisomer is believed to be ca. 200 fs and this species decays to form a mixture of vibrationally-excited ground-state rotamers that rapidly converts into the stable distribution of isomers. Photoisomerization of the corresponding I ,6-diphenyl1,3,5-hexatriene has been considered for both the excited singlet333and triplet334 states; in this latter case there are indications for a quantum chain reaction at high concentration. The alkali metal salts of the a,o-diphenylpolyenylic carbanions exist in ether solution as mixtures of tight and loose ion pairs.335The loose ion pairs undergo isomerization from the first-excited singlet state by way of an

I : Photophysicul Processes in Condensed Phuses

23

activated process for which the Arrhenius parameters have been measured by time-resolved fluorescence spectroscopy using the Daresbury synchrotron source. Despite its short lifetime, the excited singlet state of 1,6-diphenyl-l,3,5-hexatriene reacts by way of light-induced electron transfer in the presence of suitable electron acceptors336 while its photophysical properties are affected by the presence of substituents in the phenyl rings.337The fluorescence properties of hexamethylsexithiophene have been interpreted in terms of increased conjugation in the excited state caused by ultrafast planarization of the molecule.338 Extremely rapid ring-opening reactions are known to occur for certain cycloa l k e n e ~ . ~ ~ ~ ~ ~ ~ Quantum yields for the reversible photoisomerization of donor-acceptor substituted 1,2-diet hyn ylethenes and tetraet hynyle t henes have been reported. 341 Several studies have described the photoisomerization of m e r ~ c y a n i n e s , ~ ~ ~ . ~ o x a car b o ~y an in e s ,and ~ ~ ~c a r b ~ c y a n i n e s . ~ There ~ ~ , ~is~growing ~ evidence that isomerization of such molecules can take place via higher excited states.346 Photoisomerization of azobenzene is very fast;347photolysis of cis-azobenzene leading to product formation on time scales of 170 fs and 2 ps whereas the corresponding trans-isomer reacts on time scales of 320 fs and 2.1 ps.348These latter results are interpreted in terms of the Si n-n* excited state undergoing rapid inversion at one of the N atoms. In fact, the early time dynamics of isomerization of trans-azobenzene have been investigated by resonance Raman spectroscopy349 and it appears that, within 30 fs of excitation, the major geometrical changes are localized on N=N and C-N stretching vibrations. Substituted azobenzenes also undergo reversible photoisomerization, both in solution350 and in LangmuirBlodgett films,35’and provide a facile means for the construction of photoresponsive chelating macro cycle^.^^^^^^^ The photoisomerization of cis-stilbene continues to attract attention and the importance of both vibrational coherence354and solvent polarity355in controlling the dynamics of the process has been stressed. The photophysical properties of numerous derivatives of stilbene have been recorded in solution in order to better define the nature of the isomerization step.356-36’Additional studies have considered the effects of attaching freely-rotating or rigid substituents to the isomerizing bond362and the effects of mixing between S1 and S2 levels are known to be important.363Many other aryl-substituted ethenes undergo photoisomerization, with the rate depending on the nature of the terminal g r o ~ p s . ~A~ ” ~ ~ detailed examination366of the photoisomerization dynamics has been made for cis- 1-(2-anthryl)-2-phenylethene at different temperatures and the importance of triplet state formation has been explained. Involvement in an upper-lying singlet excited state has been invoked to explain the unusual fluorescence properties of aryl-substituted styrenes.368

Photophysics of Fullerenes - Interest in the synthesis, derivatization, and photochemistry of the various fullerenes continues but perhaps the fervour of earlier years is passing. These materials display important photophysical properties and it is clear that they can serve as unique components in supramolecular assemblies. A special has been devoted to the photophysics and photo-

4.4

24

Photochemistry

chemistry of fullerenes while recent advances in the field have been reviewed.374A critical comparison of the properties of parent and substituted fullerenes has appeared375and the various photoreactions leading to structural modification of fullerenes have been reviewed.376A theoretical examination of the triplet state characteristics of the higher fullerenes, including excited state geometries, excitation energies and Jahn-Teller splitting energies, has been presented.377Photoinduced electron-transfer reactions of carbon clusters have been reviewed378and compared to similar reactions undertaken by aromatic carbonyl compounds.379 Photophysical properties have been reported for the higher f ~ l l e r e n e s and ~~~~~~' for several hydrogenated f ~ l l e r e n e sTriplet-triplet .~~~ annihilation takes place for fine particles of c60 but is suppressed in favour of light-induced electron transfer when electron donors are present.383 Formation of c60 radical ions can be monitored by EPR spectroscopy under conditions that show reaction between the radical cations and solvent molecules.3s4Transient oxidation of fullerenes has also been followed by laser flash photolysis techniques.385 Numerous studies have been concerned with the luminescence properties of fullerenes in solution or solid phase.386-393 An important issue yet to be solved for the various fullerenes concerns the need to prepare samples that are genuinely soluble in water. Several approaches continue to be advocated, including coating the particle with a polymer wrapping,394but progress in this area is slow. Other methods for solubilizing the fullerene particles include forming inclusion comp l e ~ e or s ~using ~ ~ surfactant dispersion^.^'^ Functionalization of fullerenes with hydrophilic groups increases solubility but can lead to irreversible formation of clusters.397Capping the hydrophilic groups with surfactant residues restricts selfassociation. Fullerenes are susceptible to attack by many different types of r a d i ~ a l ' ~ ~while ' ~ ~ ' the excited triplet state readily enters into electron-transfer reaction^.^^^-^'^ Likewise, fullerenes function as efficient quenchers for many other excited states formed in fluid solution.409"' The photophysical properties of many different adducts of c60 have been recorded and compared with those of the parent c ~ m p o u n d .2-42 ~ ' Particular attention has been given to the ability of these derivatives to sensitize formation of singlet molecular oxygen and to enter into light-induced electron-transfer processes. One of the more interesting aspects of fullerene photochemistry concerns the incorporation of such units into multicomponent arrays that display intercompartment energy or electron transfer. Competition between through-bond and through-space interactions has been reported for various fullerene-ferrocene with the importance of intramolecular reactions depending on the nature of the connecting bridge. Bimolecular electron transfer from fullerene to ferrocene also occurs for fullerene derivatives containing a nitroxido Photoactive dyads have been synthesized in which a fullerene is linked to ruthenium(I1) tris(2,2'-bipyridyl) c ~ m p l e x e s . Laser ~ ~ ~ flash * ~ ~ photolysis ~ studies indicate that light-induced charge separation takes place when the metal complex is illuminated, with the lifetime of the redox pair depending on the length and type of bridging unit used to connect the reactants. Intramolecular electron transfer also occurs from an appended porphyrin to Cm and several such dyads have been With zinc porphyrin-fullerene dyads, a variety of

'

I : Photophysical Processes in Condensed Phases

25

processes follow from selective excitation of the porphyrin moiety. Thus, rapid singlet-singlet energy transfer occurs from the porphyrin to populate the lowestenergy singlet excited state localized on the fullerene. The fate of this latter excited state depends on the energetics of the system. Thus, fast intramolecular electron abstraction from the nearby porphyrin occurs in polar solvents but intersystem crossing to the triplet manifold dominates in nonpolar media. The triplet state localized on the fullerene unit can participate in reversible energytransfer processes with the excited triplet state of the porphyrin. These latter studies have been extended to include photoactive triads comprising fullerenep~rphyrin-carotene~~”~~~ or fullerene-porphyrin-pyromellitimideunits.433 Both triads display sequential electron-transfer events that lead to long-range charge separation across the molecule. 4.5 Quenching of Excited States - Photobleaching of dyes during illumination in chlorinated solvents results in transient formation of free Intramolecular photoaddition reactions have been observed for a family of styrene-spacer-amine compounds, where the spacer is a rigid amide interspersed between flexible alkane chains.436Several reports have addressed the mechanism of the photoreduction of benzophenone in and the importance of exciplex-type intermediates has been stressed. Certain halogenated naphtho- 1,4quinones abstract a hydrogen atom from phenolM0 and the reaction has been monitored by laser flash photolysis and CIDEP techniques. The mechanism by which azoalkanes are photoreduced by amines has been investigateda1 and, as found earlier for benzophenone, hydrogen-atom abstraction and charge-transfer compete as modes for deactivation of the excited triplet state. Exciplex formation, involving amino donors, has been described for numerous systems,M2-446including reagents bound on the surface of silica gel.447 Interaction between thiacyanine and acridine orange also leads to exciplex formation in premicellar surfactant medium, but once the critical micelle concentration is reached exciplex formation is suppressed in favour of intermolecular energy transfer.M8 The dynamics of charge recombination in charge-transfer complexes represents an extremely important and general area of photophysics and there is still doubt about how the rate varies with thermodynamic driving force. Charge separation and recombination have now been monitored for several types of charge-transfer complex adsorbed onto porous glassM9~450 under conditions where no solvent is present. Similar rate vs energy-gap profiles are observed to those found earlier in polar solvents, indicating that high frequency vibrational modes control the rate of charge recombination in such complexes. This is an extemely important finding since it calls into question the validity of applying Marcus-type theory to intimate donor-acceptor complexes. Other studies have addressed the photoprocesses occurring in closely-spaced, donor-acceptor c ~ m p l e x e s . ~ Related ~’-~~~ work has been concerned with the effects of ion pairing on the efficiency of lightinduced electron-transfer reactions455and specific cation effects have been noted. Electron-transfer quenching has been reported for donor-acceptor pairs in l i q ~ i d ~ ’ ~and - ~ solid ’ ~ states.459 In many cases, energy- and electron-transfer processes compete as the major

26

Photochemistry

route for deactivation of excited states and resolving the overall reaction mechanism can be hazardous. Often, the two processes can be distinguished by virtue of their different response to solvent polarity460or to structural facets.461 For photoactive dyads having the terminals tethered by a flexible chain, there is the additional need to distinguish between intramolecular and intermolecular quenching.462Such realizations allow construction of systems capable of displaying tandem energy-transfer and electron-transfer processes.463 4.5.I Energy-transfer Reactions - Many elaborate multicomponent molecular arrays have been engineered over the past few years in an effort to mimic the light-harvesting complexes found in natural photosynthetic organisms. Such artificial systems can also be considered as prototypes for molecular-scale photoelectronic devices in which selective excitation causes vectorial energy transfer along the molecular axis. Although the available mechanisms for excitation energy transfer between closely-spaced chromophores are well established there remains considerable uncertainty as to how best to assemble these artificial arrays. Most synthetic arrays are built from porphyrin-based modules and it is known that varying the nature of the cation housed in the porphyrin ring can modulate the energy-transfer process.464The rate of energy transfer also depends on the type of porphyrin nucleus465and on any substituents attached to the connecting bridge.466In the latter case, it appears that the rate of through-bond energy transfer is remarkably sensitive to the orientation of bridging phenyl rings and this can be affected by the presence of bulky substituents. Several hydrid porphyrin dimers have been s y n t h e ~ i z e d and ~~~'~~~ used to study both singlet and triplet energy-transfer processes. A cascade of triplet energy-transfer steps has been established for a carotenoid-porphyrinpyropheophorbide triad molecule.470 Highly efficient intramolecular singletsinglet energy transfer from a covalently-linked carotenoid to a porphyrin chromophore has been described for a series of dyads.47' It is suggested that energy transfer occurs predominantly via the Forster-type Coulombic mechanism involving the first-excited singlet state of the carotenoid as energy donor. Surprisingly, in view of its very short lifetime, energy transfer occurs from the S2 level of the carotenoid in at least one case.471Intermolecular energy transfer has been reported for porphyrin-based systems in s o l ~ t i o n and ~ ~ in~ Langmuir-~~~ Blodgett layers.475 Flexible arrays of porphyrinic chromophores have been constructed as simple models of natural light-harvesting c ~ m p l e x e s . ~ ~ ~ Intramolecular energy transfer has been reported for dyads built from 1,8naphthalimide and 1,3,4-0xadiazole Reversible energy transfer between monomeric and dimeric forms of rhodamine 6G in ethylene glycol has been observed479and the concentration dependence of the overall fluorescence quantum yield has been modelled by MonteCarlo simulations. Triplet energy transfer in disordered polymers has been analyzed on the basis of Bawler's model in which the trap energies have a Gaussian di~tribution.~~' Energy transfer has also been observed in monolayers48' and for photoswitchable molecular triads.482The structural requirements for efficient energy transfer from a carotenoid to chlorophyll have been

I : Photophysical Processes in Condensed Phases

27

elucidated483 while the solvent dependence of energy transfer from triplet benzophenone to naphthols and methoxynaphthalene has been investigated.484It was observed that the rate of intermolecular triplet energy transfer depends on both viscosity and polarity of the solvent, with the latter effect being due to perturbation of the relative energy levels of x,n* and n,x* excited states. Intramolecular energy transfer has also been reported for dyads based on ruthenium(I1) polypyridine With covalently-linked arenes, localization of the triplet energy depends on the nature of the arene. Thus, with naphthalene the triplet state remains on the ruthenium(I1) polypyridine but efficient intramolecular triplet energy transfer occurs when the arene is a n t h r a ~ e n eWith . ~ ~ ~a covalently-bound pyrene fragment, the two triplet states are almost isoenergetic and reversible triplet energy transfer takes so that the triplet lifetime of the metal complex is prolonged. In a marked variation on the usual theme, energy transfer has been observed from porous silicon to adsorbed metal polypyridine complexes.488

4.5.2 Electron-transfer Reactions - Quenching of fluorescence from organic dyes in solution by inorganic anions is known to proceed by way of bimolecular electron-transfer Electron transfer has also been implicated in many other bimolecular quenching reaction^,^^'-^^^ including the quenching of naphthalene fluorescence by nucleic acid components.495An interesting effect of how the relative size of the reactants can affect the outcome of fluorescence quenching in solution has been described498with respect to the quenching of fluorescence of aryl hydrocarbons by thiocyanate. The Marcus inverted region has been observed for a bimolecular electron-transfer reaction in which emission from ruthenium(I1) polypyridine complexes is quenched by phenolate ions.499 The effects of both internal and external heavy atoms on the efficiency of bimolecular electron-transfer reactions have been explored500by reference to the fluorescence quenching of thiopyrylium salts by halogenated benzenes. A popular method for distinguishing between electron- and energy-transfer quenching is to freeze the solution into a solid glass where energy transfer is likely to Intermolecular electron transfer can occur on very fast time scales at high concentrations of quencher or when the quencher is also the solvent.503 More useful mechanistic information is obtained from intramolecular electrontransfer reactions if the kinetics for the electron-transfer step can be isolated from the effects of diffusion. The main stimulus for making such studies is the urge to design systems that mimic some of the essential features of the photosynthetic reaction centre complex and much attention has focussed on the study of porphyrin-based photoactive dyads. Thus, a series of N-alkylporphyrins linked to a quinolinium cation has been synthesized and found to display a rich variety of photo reaction^.^^ The singlet excited state of the quinolinium cation operates in both intramolecular energy- and electron-transfer reactions while the excited singlet state of the porphyrin transfers an electron to the appended quinolinium cation. Several new porphyrin-quinone dyads have been s t ~ d i e d , ~ ' ~including -~' cyclophane-derived systems where the reactants are held in a face-to-face orienta-

28

Photochemistry

tion506,507 Particularly important examples are provided by the rigidly-linked dyads509,5'0where the effects of geometry can be studied. Certain closely-spaced dyads undergo fast charge separation for which the rate is essentially activationless509 whereas slight separation of the reactants renders the electron-transfer event sensitive to temperature and solvent polarity. A series of rigidly-linked porphyrin-quinone dyads built around cis- or trans- 1,4-disubstituted cyclohexylene bridges has been synthesized for which exact geometries are a~ailable.~" Structural information has also been obtained for the folded conformations of some zinc(I1) pyropheophytin-anthraquinonedyads in solution from 2D N M R studies.512Light-induced electron transfer has been observed with porphyrinferrocene dyads assembled onto a gold Building photoactive porphyrin-based dyads by way of non-covalent linkages continues to be an attractive 5 14-5 17

This work has been extended to include the study of porphyrin-based triads and higher-order analogues by the attachment of additional redox-active groups. A new triad has been introduced in which the central porphyrin chromophore is equipped with naphthoquinone and tyrosine The dynamics of successive electron-transfer steps occurring in a carotenoid-porphyrin-dinitronaphthalenedicarboximide (C-P-Nim) triad have been elucidated5I9 and compared with those of the corresponding P-Nim dyad. In benzonitrile, the final charge-separated state of the triad survives for 430 ns and is formed with a quantum yield of 0.33. It is noted that light-induced electron transfer does not occur from the firstexcited singlet state of the carotenoid moiety. The effect of an internal hydrogen bond on the dynamics of electron transfer in carotenoid-porphyrin-naphthoquinone (C-P-NQ) triads, and the corresponding P-NQ dyads, has been evaluated520and the importance of sequential electron and proton transfers has been stressed. Stepwise electron transfer has been described for a ZnC-ZnP-ZnP-I tetrad comprising zinc chlorin (ZnC), zinc porphyrin (ZnP), and pyromellitimide (I) units.52' The lifetime of the fully-separated state is ca. 230 ps in tetrahydrofuran at room temperature. A novel approach to controlling the rates of electron transfer in these multicomponent molecular systems involves the use of twocolour laser excitation spectroscopy.522This technique has been applied to the selective excitation of tetrads comprising two donor-acceptor pairs and it is shown that the photogenerated electric field associated with formation of a transient ion-pair inhibits formation of the second ion pair. Numerous studies have been concerned with further evaluation of how the environment affects the rate of electron transfer. It has been shown that the rate of electron transfer through a donor-(amidinium-carboxy1ate)-acceptor salt bridge is about 100-fold slower than electron transfer in the corresponding donor-(carboxylate-amidinium)-acceptor system.523 The .effects of temperatUre524,525 and selective d e ~ t e r a t i o n ~ on* ~the rates of charge separation and/or charge recombination have been explored while electron-transfer reactions occurring along helical or oligonucleotides528 have been monitored. Similarly, the dynamics of electron-transfer reactions have been studied for reactants adsorbed onto micelle surfaces,529incorporated in porous glasses,530 bound to silica gel,S3' or interspersed into dry gelatin.532 This latter study has

I : Photophysicul Processes in Condensed ?%uses

29

revealed a marked difference in reactivity between gelatin in the random coil and a-helical forms. Light-induced electron transfer has also been reported in organic-inorganic multilayer composites533 and across liquid-liquid junctions.534.535 Electron transfer along conjugated polyenes is extremely fast536but the rate can depend on the nature of the solvent for through-space electron tunnelling.537 Intramolecular electron transfer has been observed in several non-porphyrinic dyads and triads.538-543Thus, intramolecular electron transfer involving an anilido group as electron donor has been described540while the effects of chain length on exciplex formation and electron-transfer rates have been described for some styrene-spacer-amine dyads.54' An unusual effect of bidirectionality has been observed for I-(4-~yanopheny1)-4-(cyanomethylene)piperidinein different solvents538caused by competitive electron transfer occurring through the CTor 71: bonds of the organic framework. Two charge-transfer states are formed, corresponding to electron donation to either acceptor, before electron exchange occurs to form the thermodynamic distribution. Photoinduced electron transfer in a constrained bicyclic structure has been d e ~ c r i b e d . ~ ~ There have been several reports describing intramolecular electron transfer in dyads formed from transition metal complexes. The effect of hybridization of the bridge on the rate of through-bond electron exchange, hole transfer and electron delocalization has been described for ethanylene, ethenylene, and ethynylene bridges separating terminal metal terpyridine complexes.545 Electron transfer proceeds through a salt bridge separating two different ruthenium(i1) polypyridine complexes546while certain r h e n i ~ m ( 1 )or ~ ~~~o p p e r ( 1 )complexes ~~~ have been found to effect unusually long-lived charge-separated states. Electrontransfer events that follow excitation of ruthenium(I1)-rhodium(II1) terpyridylbased dyads have been described.549 Other studies have concerned electron transfer in triads constructed from transition metal c ~ m p l e x e s . ~ ~ ' - ~ ~ ~

5

Applications of Photophysics

The study of photophysical processes, especially time-resolved luminescence spectroscopy, provides unique opportunities to explore elaborate molecular systems, to selectively transfer information at the molecular level, to label biological materials, and to design analytical protocols. A great number of molecular systems have been proposed as luminescence sensors for species dissolved in solution but most systems have poor sensitivity and little, if any, selectivity for particular substrates. The most popular design feature involves complexation of a cation to a luminophore in such a way as to switch on or to extinguish emission, usually by perturbing an intramolecular electron-transfer reaction. Such systems have been reviewed in detai1554-559 while alternate design protocols have been p r o p o ~ e d . ~Many ~ . ~ ~new ' sensors have been reported that respond, with varying levels of success, to and/or In several cases, the mechanism for sensory action has been established by laser flash photolysis studies and binding constants have been determined. Related lumines-

30

Photochemistry

cence sensors are available for the in situ determination of oxygen concentrations,573-580 although the operating principle of the device requires only that molecular oxygen quenches a long-lived excited triplet state. Other types of environmental sensors have been designed to detect volatile organic compounds,58' aryl hydrocarbons,582petroleum,5833584 sugars,585and water.5867587 Photophysical processes have been adapted to provide systems for the measuremen t of temperature, 588-590 critical micellar concentrations, 591*592 micropolarity and microviscosity of organized media,593and sol-gel transition points.594-s98 Other systems have been used to probe the mobility of materials in monolayer assembles599and the microenvironmental pH in highly-charged polymers.600 Several systems are available for in situ monitoring of free radical-induced polymerization6013602 and changes in refractive index603or mobility604of polymer films. A simple system has been developed that allows monitoring of stress induced in polymer films upon exposure to light.605Models have been proposed for photofacilitated transport across liquid membranesm6and for imaging liquid drops and jets.607 Methods for establishing dipole moments of ground and excited states have been considered 608 and a fluorescence probe for lipid organization has been described.609A fluorescence method has been used to measure the thickness of the water layer formed when a hydrophobic plastic slides across ice6'' and the results have been used to better understanding the physics of skiing. The methodology used for luminescence dating of rock art has been described.61' Applications of fluorescenceprobes in cellular biology have been r e ~ i e w e d ~ ' ~ - ~ ' ~ while labelled polypeptides6I5and proteins6I6 have been described. Detection of DNA fragments has been considered by several a ~ t h o r s , ~including ' ~ - ~ ~ ~the quantitative estimation of low concentrations of DNA in drinking water. A phosphorescence-based method623has been used to study refolding of disulfide reduced RNase TI. 6

Advances in Instrument Design and Utilization

Photophysics depends critically on the availability of appropriate instrumentation and adequate computational protocols, as well as a ready supply of suitable molecular systems. As the systems become more complex it becomes necessary to design new instruments and to improve procedures for data analysis. A necessary part of this improvement concerns increasing the reliability and precision of existing facilities. 6.1. Instrumentation - A methodology has been devised for comparing the features of fluorescence spectrometer^.^^^ The technique of fluorescence recovery after photobleaching has been applied to the special case of transport across an interface625 while gain spectroscopy has been used to study solute-solvent exciplexes.626A strategy for replacing the excitation monochromator from commercial spectrofluorimeters with an acousto-optic device has been proposed627and tested by studying the fluorescence properties of merocyanine dyes.

I : Photophysical Processes in Condensed Phases

31

The main advantage of this technique relates to the improved optical purity of the excitation source. The concept of continuous measurement of resonance fluorescence has been discussed and improvements in the experimental methodology have been suggested.628Several reports have focussed on ways to increase the spatial resolution of near-field scanning optical microscopes, with special reference to measurements made at interface^.^^^-^^' A methodology has been developed that permits detection and manipulation of individual microdroplets with a fluorescence microscope.632Two-photon fluorescence spectroscopy is now an established technique, especially in biophysics, and several developments have been r e p ~ r t e d . This ~ ~ ~technique - ~ ~ ~ has been applied to the study of DNA-dye and resonance energy transfer in labelled b i ~ m a t e r i a l s Three.~~~ photon excitation has been combined with single-photon counting fluorometry to give a very powerful approach to the selective study of fluorescent molecules.639 The technique has been applied to the study of several scintillators and makes use of a 120 fs excitation pulse from a Ti-sapphire laser.@’ Two new microchannel plate photomultipliers have been described for spaceand time-correlated, single-photon counting that possess temporal resolution around 75 psa’ An apparatus for making double-pulse fluorescence lifetime measurements has been reported.642 A workstation for fluorescence imaging microscopy has been designeda3 that is completely automated and constructed from readily available parts. Several 2D fluorescence lifetime imaging spectrometers have been d e s ~ r i b e d and ~ - ~applied ~ ~ to various problems. Time and wavelength fluorescence detectors have been designed for use with capillary zone electrophoresisa8 and high-performance liquid chromatography.6497650 It is now possible to record an entire fluorescence decay profile during HPLC elution. Several designs have been given for the construction of inexpensive frequencydomain f l u ~ r o m e t e r s . ~ ”Such - ~ ~instruments ~ have been used for making fluorescence-lifetime imaging measurements652and for flow cyt0rnet1-y.~~~ Magnetic field effects continue to provide important information about the dynamics and mechanisms of charge-recombination reactions. Several experimental setups have been improved and described in detai1,654-663 including the application of ultrahigh magnetic fields655and phase-locked detection.656Techniques for recording absorption and fluorescence spectra under an applied electric field have been The technique of photochemically-induced dynamic nuclear polarization has been comprehensively reviewed666and its potential application to many different problems in organic photochemistry has been stressed. The corresponding CIDEP technique has been been applied to quenching One of the most important experimental techniques to appear in the last few years has been transient grating spectroscopy and this methodology has numerous important applications. The technique has been used to measure the quantum yield for photodissociation of diphenyl disulfide,668and compared to photoacoustic and transient absorption spectoscopic methods. Additional studies have used transient grating spectroscopy to monitor the energetics and dynamics of charge separation of an ion pair into free ions.669The approach permits direct measurement of the enthalpy change accompanying formation of the free ions

32

Photochemistry

and, consequently, the mechanism can be addressed in great detail. Translational diffusion processes can be followed by the transient grating method, allowing determination of diffusion coefficients for numerous radicals670 and unstable photo isomer^.^^' Time-dependent anisotropy measurements have also been made for several photoexcited f u l l e r e n e ~A. ~double-pulse ~~ fluorescence technique has been described that permits facile measurement of rotational diffusion times in solution.67' The main advantage of this technique, apart from its simplicity of operation, is that it does not require fast-time response detectors. A thermal lens spectrometery has been constructed that is highly sensitive to the presence of low concentrations of aggregated dye in equilibrium with monomer.674 Lateral diffusion of cell surface proteins can be monitored by interferometric fringe patterns during photobleaching recovery.67s This technique seems to be more reproducible than the more commonly used method of spot fluorescence recovery. A common problem in photophysics concerns the inner-filter effect that prevents the study of optically dense materials. A way round this problem might be to use the total internal reflectance technique of evanescent wave fluorescence spectroscopy.676 The technique of stimulated nuclear polarization has been applied to light-induced electron-transfer reactions.677 Laser-induced photoacoustic calorimetry has been used to measure enthalpy and volume changes during photolysis of methylcobalamin in neutral aqueous solution.67s Diffuse-reflectance laser-flash photolysis techniques have been used to monitor solid-state photo reaction^^^^^^^^ while an experimental approach for the use of high pressures in quenching studies has been described.68' This latter setup might have particular applications to the study of enantioselective quenching. A two-colour spectral hole-burning technique has been developed and applied to zinc tetrdphenylchlorin.682 Several new far-red absorbing dyes have The technique of femtosebeen proposed for spectral hole burning cond hole-burning spectroscopy has been used to monitor nonradiative decay between exciton states that occurs on a time scale of cu. 120 fs.685

Data Analysis - The basis of molecular fluorescence and phosphorescence spectrometry has been reviewed with special emphasis on the detection of trace constituents in biological and chemical systems.686A detailed analytical procedure has been formulated687 that evaluates fluorescence quenching in micellar media where the fluorophore can migrate between micelles. A method has been devised for the multicomponent analysis of absorption and emission spectra that allows extraction of spectra for pure components from complex mixtures.688 Attention has been given to the procedures used to calibrate modern fluorescence s p e c t r o p h o t ~ m e t e r sand ~ ~ ~to the simultaneous recording of spectral, temporal and polarized emission spectra.690 Analysis of time-resolved fluorescence decay records, using computer simulation, has been considered69' while various methods used for deconvolution of the instrument response function have been critically compared and evaluated.692 An analytical procedure for frequencydomain multidimensional fluorescence spectroscopy has been provided693and a treatment has been given694 for measuring fluorescence lifetimes using noisemodulated light. A directly modulated CCD imaging device has been developed 6.2.

I : Photophysical Processes in Condensed Phases

33

which is suitable for frequency-domain phosphorescence measurements up to ca. 400 kHz.695 A general kinetic scheme has been proposed for intermolecular two-state photoreactions that covers such processes as excimer formation, acid-base equilibria, fluorescence indicators and sensors, and quenching phenomena.696 The time dependence of fluorescence anisotropy in the region of pure electronic transitions from the molecular ground state has been examined697and a system has been outlined that allows the rapid acquisition of lifetime-resolved fluorescence images.698Software for controlling a time-resolved fluorescence instrument, as well as for data storage and analysis, has been presented.699An improved system for fluorescence anisotropy measurements has been described7" while a model for the statistical analysis of single-molecule detection has been given.701 Methods used for the analysis of time-resolved delayed emission and transient Raman spectra have been reviewed.702A theoretical model has been advanced that permits estimation of two-photon absorption cross-sections for photochromic molecules703while fast Fourier transformations have been applied to pyrene f l u o r e s c e n ~ eTheories .~~ have been developed for studying the size effect in fluorescence correlation spectroscopy705and for the measurement of diffusion coefficients by this t e~ hni que. ~Total '~ internal reflection fluorescence has been applied to the problem of counting molecules at solid/liquid interfaces707and adsorbed onto cellular surfaces.708Analytical routines have been devised for determining the distribution of fluorophores in mixed mono layer^^^^ and in A protocol has been established that permits evaluation of the mi~elles .~~' microviscosity of micellar media on the basis of measuring the rotational and transitional diffusion coefficients of included dyes as a function of temperature." Techniques for measuring diffusion coefficients by conventional recovery of dye photofading have been reviewed712 while the use of reaction-induced birefringence provides an interesting alternative approach to obtaining the same informat i ~ n .A ~ ' new ~ family of xdnthene dyes that fluoresce strongly in the far red region of the spectrum has been introduced714and their potential application as biological probes has been stressed.

'

7

References

1.

J. F. Wishart, A h . Chem. Ser., 1998,254 (Photochemistry und Radiution Chemistry),

2.

J. R . Miller, K . Penfield, M. Johnson, G . Closs, and N. Green, Adv. Chem. Ser., 1998,254 (Photochemistry and Radiation Chemistry), 161. K. A. McLauchlan, J. Chem. SOC.,Perkin Trans. 2, 1997,2465. S . W. S. McKeever and R. Chen, Radiat. Meus., 1998,27,625. S. A. Soper, I. M. Warner, and L. B. McGown, Anal. Chem., 1998,70,4778. L. P. Knight, Phys. Scr., T, 1997, T70,94. D. T. Pegg, Phys. Scr., T, 1997, 770, 106. L. W. Ungar and J. A. Cina, Adv. Chem. Phys., 1997,100, 171. M. N. Berberan-Santos, E. J. N. Perreira, and J. M. G. Martinho, J. Fluoresc., 1997, 7, 119s.

1.

3. 4. 5. 6. 7. 8. 9.

34 10. 11. 12. 13. 14.

15. 16. 17. 18.

19. 20. 21. 22. 23. 24. 25. 26. 27. 28. 29. 30. 31. 32. 33. 34. 35. 36. 37. 38. 39. 40. 41. 42. 43.

Photochemistry

J. Wilkie and P. Brumer, J. Chem. Phys., 1997,107,4893. C. G. B. Cole and J. J. Roberts, Imaging Sci. J . , 1997,45, 145. P. R. Callis, Annu. Rev. Phys. Chem., 1997, 48,271. W. M. Nau, Ber. Bunsenges-Ges., 1998,102,476. W. M. Nau, G. Greiner, J. Wall, H. Rau, M. Olivucci, and M. A. Robb, Angew. Chem., Int. Ed. Engl., 1998,37, 98. A. Douhal, Science, 1997,276, 22 1. L. G. Arnaut and S. J. Formosinho, Wiley Ser. Photosci. Photoeng., 1997, 2 (Homogeneous Photocatalysis), 55. M. Glasbeek, Czech. J, Phys., 1998,48,417. Y. Gauduel and H. Gelabert, Adv. Chem. Ser., 1998, 254 (Photochemistry and Radiation Chemistry), 33 1. F. P. X. Everdij and D. A. Wiersma, Femtochem. Femtobiol.: Ultrafast React. Dynamics. Nobel Symp., 1997,101,488, V. Sundstroem, Imperial College Press, London. E. Gershgoren, U. Banin, and S . Ruhman, J. Phys. Chem. A , 1998,102,9. E. W.-G. Diau, J. Herek, Z. H. Kim, and A. H. Zewail, Science, 1998,279,847. M. Klessinger, Pure Appl. Chem., 1997,69,773. J. F. Endicott, M. A. Watzky, X. Song, and T. Buranda, Coord. Chem. Rev., 1997, 159,295. A. Kapturkiewicz, Adv. Electrochem. Sci. Eng., 1997,5, 1 . V. A. Bagryansky, V. I. Borovkov, Y. N. Molin, M. P. Egorov, and 0. M. Nefedov, Mendeleev Commun., 1997, 132. A. Banerjee and D. E. Falvey, J. Org. Chem., 1997,62,6245. K.-H. Gericke, C. Kreber, and J. L. Rinmenthal, J. Phys. Chern. A, 1997,101,7530. K. Tsukahara, C. Kimura, J . Kaneko, K. Abe, M. Matsui, and T. Hara, Inorg. Chem., 1997,36,3520. T. Grady, T. Joyce, M. R. Smyth, D. Diamond, and S . J. Harris, Anal. Commun., 1998,35, 123. T. G. Stockman, C. A. Klevickis, C. M. Grisham, and F. S. Richardson, J. Mol. Recognit., 1996, 9, 595. J.-W. Xie, Y.-Q. Zhai, Z.-P. Yang, and J.-X. Huan, Huaxue Xuebao, 1997,18,1447. M. Takeuchi, S. Yoda, T. Imada, and S. Shinkai, Tetrahedron, 1997,53, 8335. D. P. Glover-Fischer, D. H. Metcalf, T. A. Hopkins, V. J. Pugh, S. J. Chisdes, J. Kankare, and F. S . Richardson, Inorg. Chem., I998,37,3026. H. Shi, B. M. Conger, D. Katsis, and S. H. Chen, Liq. Cryst., 1998,24, 163. R. S. Dickens, J. A. K. Howard, J. M. Moloney, D. Parker, R. D. Peacock, and G. Siligardi, Chem. Commun., 1997, 1747. 0 . G. Dmitrenko, 1. P. Terenetskaya, and W. Reischl, J. Photochem. Photohiol. A , 1997,104, 113. L. V. Natarajan, T. M. Cooper, and D. Stilzel, Mol. Cryst. Liq. Cryst. Sci. Technol., Sect. A , 1997,298, 205. ‘4. C. Benniston, A. Harriman, and D. S. Yufit, ,4ngw. Chem., Int. Ed. Engl., 1997, 36,2356. J.-P. Collin, P. Gavina, V. Heitz, and J.-P. Sauvage, Eur. J. Inorg. Chem., 1998, 1. T. Shikata, S. Imai, and Y. Morishima, Langmuir, 1997, 13, 5229. N. Armaroli, F. Diederich, C. 0. Dietrich-Buchecker, L. Flamigni, G. Marconi, J.-F. Nierengarten, and J.-P. Sauvage, Chem.- Eur. J., 1998,4,406. M. Tamura and A. Ueno, Chem. Lett., 1998,369. D. G. Hamilton, J. E. Davies, L. Prodi, and J. K. M . Sanders, Chem.-Eur. J., 1998, 4,608.

I : Photophysiwl Processes in Condensed Phases 44. 45. 46. 47. 48. 49. 50. 51.

52. 53. 54. 55. 56. 57. 58. 59. 60. 61. 62. 63. 64. 65. 66. 67. 68. 69. 70. 71. 72. 73. 74. 75. 76. 77. 78.

35

L. Moggi and M. F. Manfrin, Suprumol. Chem. Anions, I997,32 1. M. D. Ward, Chem. SOC.Rev., 1997,26,365. I. Yamazaki, N. Ohta, A. Osuka, and M. Mimura, Hyomen, 1997,35,418. K. Mizuno and Y. Inoue, Kohuguhu, 1997,25,36. V. Balzani, A. Credi, and M. Venturi, Coord Chem. Rev., 1998,171,3. A. Bar-Haim and J. Klafter, J. Phys. Chem. B, 1998,102, 1662. S. Decurtins, H. W. Schmaile, R. Pellaux, A. Hauser, M. E. van Arx, and P. Fischer, Synth. Met., 1997,85, 1689. A. P. da Silva, H. Q. N. Gunaratne, T. Gunniaugsson, A. J. M. Huxley, C. P. McCoy, J. T. Rademacher, and T. E. Rice, Chem. Rev., 1997,97, 1515. T. Rieth and K. Sasamoto, Anal. Cummun., 1998,35, 195. J. E. Guillet, N. A. Burke, and M. Nowakowska, Mucrornol. Symp., 1997,118, 527. A. Osuka, N. Mataga, and T. Okada, Pure Appl. Chem., 1997,69,797. A. Osuka, Kihan Kagaka Sosetsu, 1997,31, 120. K. Teuchner, H. Steel, D. Leupold, A. Scherz, D. Noy, I. Simonin, G. Hartwich, and H. Scheer, J. Lumin., 1997, 72-74,612. S . L. Cardoso, Quim. Nova, 1997,20,535. L. G. Arnaut and S. J. Formosinho, J, Photochem. Photobiol, A , 1997, I 1 1, 11 1. J. T. M. Kennis, A. M. Streltsov, S. I. E. Vulto, T. J. Aartsma, T. Nozawa, and J.Amesz, J. Phys. Chem. B, 1997,101,7828. A. Magnuson, H. Berglund, P. Karall, L. Hammarstroem, B. Aakermark, S. Styring, and L. Sun, J. Am. Chem. SOC.,1997,119, 10720. T. K. La1 and R. Mukherjee, Znorg. Chem., 1998,37,2373. S . M. Gorun, R. T. Stilbrany, and A. Lillo, Znorg. Chem., 1998,37,836. H. Berglund-Baudin, L. Sun, R. Davydov, M. Sundahl, S. Styring, B. Aakermark, M. Almgren, and L. Hammarstroem, J. Phys. Chem. A , 1998,102,2512. L. Sun, H. Berglund, R. Davydov, T. Norrby, L. Hammarstroem, P. Korall, A. Boerje, C. Philouze, K. Berg, A. Tran, M. Andersson, G. Stenhagen, J. Maartensson, M. Almgren, S. Styring, and B. Aakermark, J, Am. Chem. SOC., 1997,119,6996. C. E. Dube, D. W. Wright, P. J. Bonitatebus Jr., S. Pal, and W. H. Armstrong, J. Am. Chem. SOC.,1998,120,3704. L. Sun, L. Hammarstroem, T. Norrby, H. Berglund, R. Davydov, M. Andersson, A. Boerje, P. Korall, C. Philouze, M. Almgren, S. Styring, and B. Aakermark, Chem. Commun., 1997,607. M. T. Caudle, J. W. Kampf, M. L. Kirk, P. G. Rasmussen, and V. L. Peoraro, J. Am. Chem. SOC.,1997,119,9297. J.-Y. Fang and S. Hammes-Schiffer, J. Chem. Phys., 1997,107,5727. D. Romstad, G. Granucci, and M. Persico, Chem. Phys., 1997,219,21. V. S . Pavlovich, J. Appl. Spectrosc., 1997,64,764. F. Bernardi, M.Olivucci, and M. A. Robb, J. Phys. Chem. A , 1997,101,8395. A. E. Obukhov, Laser Phys., 1997, 7, I 102. M. R. Roest, A. M. Oliver, M. N. Paddon-Row, and J. W. Verhoeven, J. Phys. Chem. A, 1997,101,4867. B. Gholamkhass, K. Nozaki, and T. Ohno, J. Phys. Chem. B, 1997,101,9010. E. L. Bominaer, C. Achun, S. A. Borshch, J.-J. Girerd, and E. Muenck, Znorg. Chem., 1997,36,3689. D. G . Evans, A. Nitzao, and M. A. Ratner, J. Chem. Phys., 1998,108,6387. P. L. Nordio, A. Polimeno, and G. Saielli, J. Photochem. Photobiol. A , 1997, 105, 269. M. W. Wu and E. M. Conwell, Chem. Phys., 1998,227, 11.

36 79. 80. 81. 82. 83. 84. 85. 86. 87 88. 89. 90. 91. 92. 93. 94. 95. 96. 97. 98. 99. 100. 101. 102. 103. 104. 105. 106. 107. 108. 109. 110. 111. 112. 113. 114. 115. 116.

Photochemistry A. Yoshimura, K. Nozaki, andT. Ohno, Coord. Chem. Rev., 1997,159,375. J. Najbar, Bull. Pol. Acad. Sci.. Chem., 1997,45, 79. A. Goushcha, M. Kapoustina, and V. Kharkyanen, J. Tech. Phys. (Warsaw), 1997, 38,283. A. J. A. Aquino, P. Beroza, J. Reagan, and J. N. Onuchic, Chem. Phys. Lett., 1997, 275, 181. A. B. J. Parusel, R. Schamschule, and G. Koekler, Ber. Bunsenges-Ges., 1997, 101, 1836. Y. Ho, Y. Xiong, Z. Wang, Q. Zhu, and F. Kong, J. Phys. Chem. A , 1998, 102, 4266. C.-P. Hsu, Y. Georgievskii, and R. A. Marcus, J. Phys. Chem. A, 1998,102,2658. M. Choi, D. Jin, H. Kim, T. J. Kang, S. C. Jeoung, and D. Kim, J. Phys. Chem. B, 1997,101,8090. P. van der Meulen, A. M. Jonkman, and M. Glasbeek, J. Phys. Chem. A , 1998,102, 1906. G . Saielli, A. Polimeno, P. L. Nordio, P. Bartolini, M. Ricci, and R. Righini, J. Chem. Soc., Faruduy Trans., 1998, 94, 121. N. K. Petrov, A. Wiessner, and H. Staerk, J. Chem. Phys., 1998,108,2326. A. I. Burschtein and A. Y. Sivachenko, J. Photochem. Photobiol. A , 1997,109, 1. V. A. Morozov, Zh. Fiz. Khim., 1998, 72, 119. U. Muller and G. Stock, J. Chem. Phys., 1997,107,6230. M. Yang, S. Lee, and K. J. Shin, J. Chem. Phys., 1998,108, 1 17. V. V. Sapunov, Opt. Spektrosk., 1997,83, 749. A. V. Barzykin and M.Tachiya, J. Phys. Chem. B, 1998,102, 1296. G. Cosa and C . A. Chesta, J. Phys. Chem. A, 1997,101,4922. A. I. Burschtein and P. A. Frantsuzov, J. Chem. Phys., 1997, 107,2872. S. Taen, J. Chem. Phys., 1998,108,6857. I. Frank, J. Hutter, D. Marx, and M. Parrinello, J. Chem. Phys., 1998, 108,4060. F. Tanaka, J. Chem. Phys., 1998, 109, 1084. J. R. Lakowicz and I. Gryczynski, Top. Fluoresc. Spectrosc., 1997,5, 305. A. Y. Sechin, A. N. Starostin, Y. K. Zemtsov, D. I. Chekhov, and A. G. Leonov, J. Quant. Spectrosc. Raciiut. Trurufer, 1997,58,887. M. N. Berberan-Santos, E. N. Bodunov, and J. M. G. Martingo, Opt. Spektrosk., 1997,83, 378. Y . Rakicioglu, M. Young, and S . G. Schulman, Anal. Chim. Acta, 1998,359, 269. T. L. Longin, C. A. Koval, and R. D. Noble, J. Phys. Chem. B, 1998,102, 1036. C. Wirp, J. Bendig, and H. D. Brauer, Ber. Bunsen-Ges., 1997,101,961. S. Icli, H. Icil, and I. Gurol, Turk. J. Chem., 1997,21, 363. V. A. Kuz’mitskii, Khim. Fiz., 1996, 15,61. Y.-H.Zhang, B. Jiang, andX.-K. Jiang, Chin. J. Chem., 1997, 15, 395. A. I. Burschtein and E. Krisinel, J. Phys. Chem. A , 1998, 102, 816. E. Szajdzinska-Pietek and M. Wolszczak, J. Photochem. Photobiol. A, 1998, 112, 245. C. E. Bunker, Y.-P. Sun, and J. R. Gord, J. Phys. Chem. A , 1997,101,9233. K. Weidemaier, H. L. Tavernier, and M. D. Fayer, J. Phys. Chem. B, 1997, 101, 9352. F. Caruso, E, Donath, and H. Moehwald, J. Phys. Chem. B, 1998,102,201 1. H. Rosenbluth, B. Weiss-Lopez, and A. F. Olea, Photochem. Photobiol., 1997, 66, 802. S. Sinha, R. De, T. Ganguly, A. K. De, and S. K. Nandy, J. Lumin., 1987, 75,99.

I : Photophysicul Processes in Condensed Phases

37

125. 126. 127.

T. P. Giraddi, J. S. Kadadevarmath, G. C. Chikkur, M. C. Rath, and T. Mukherjee, J. Photosci., 1997,4,97. G. P. Zanini, H. A. Montejano, J. J. Cosa, and C. M. Previtali, J. Photochem. Photobiol. A, 1997, 109, 9. P. Chen and T. J. Meyer, Chem. Rev., 1998,98, 1439. C. G. Clark and M. Z. Hoffman, Coord. Chem. Rev., 1997,159,359. S. V. Kuznetov, M. Bazin, and R. Santus, J. Photochem. PhotobiuI. A , 1997,103, 57. P. Piotrowiak, A h . Chem. Ser., 1998, 254 (Photochemistry and Radiation Chemistry), 219. W. Jaeger, S. Schneider, and J. W. Verhoeven, Chem. Phys. Lett., 1997,270,50. V. M. Reyes, C. S. Renamayer, I. Pierola, J. C. Lima, E. C. Melo, and A. L. Macanita, Chem. Phys. Lett., 1998,287, 379. I. V. Rubtsov and K. Yoshihara, J. Phys. Chem. A, 1997,101,6138. J. Prochorov, J. Mol. Struct., 1997,404, 199. G. Hungerford, F. Donald, D. J. S. Birch, and B. D. Moore, Biosens. Bioelectron.,

128.

R. S. Knox, P. D. Laible, D. A. Sawicki, and M. F. J. Talbot, J. Lumin., 1997, 72-74,

129.

L. V. Levshin, G. A. Ketsle, G. V. Mel’nikov, and Y. D. Lantukh, J. Appl. Spectrosc., 1997,64, 639. E. A. Ermilov, 0. L. Markovskii, and I. M. Gulis, J. Appl. Spectrosc., 1997,64, 642. I. M. Gulis, E. A. Ermilov, and S. A. Sakharuk, J. Appl. Spectrosc., 1997,64,354. B. Nickel, H. E. Wilhelm, and C. P. Janesch, Opt. Spektrosk., 1997,83,584. Y. Kimura, Y. Takebayashi, and N. Hirota. J. Chem. Phys., 1998,108, 1485. S. Sekiguchi, Y. Kobori, K. Akiyama, and S . Tero-Kubota, J. Am. Chem. Soc.,

117. 118. 119. 120. 121. 122. 123. 124.

1997,12, 1183. 580.

130. 131. 132. 133. 134.

1998,120, 1325.

138. 139.

M. Terazima, Kokugaku, 1997,24, 12. K. Okamoto, N. Hirota, and M. Terazima, J. Phys. Chem. A, 1998,102, 3447. A. L. Sobolewski, L. Andrzej, and W. Domcke, J. Photochem. Photobiol. A, 1997, 105, 325. R. Schamschule, A. B. J. Parusel, and G. Kohler, Internet J. Chem., 1998, I , 5. A. Mordzinski, A. Sobolewski, L. Andrzej, and D. H. Levy, J. Phys. Chem. A, 1997,

140. 141.

A. Kawski and G. Piszcek, Z. Nuturforsch., A: Phys. Sci., 1997,52,409. A. Polimeno, P. L. Nordio, P. Bartolini, M. Ricci, and R. Riggini, Chem. Phys.,

142. 143.

J. J. Fisz and A. van Hoek, Chem. Phys. Lett., 1997,27,432. K. A. Zachariasse, M. Grobys, Th. Van der Haar, A. Hebecker, Y. V. Tl’ichev, 0.Morawski, I. Roeckert, and W. Kuehnle, J. Photochem. Photobiol. A, 1997,105,373. Y. V. Il’ichev, W. Kuehnle, and K. A. Zachariasse, J. Phys. Chem. A, 1998, 102,

135. 136. 137.

101,8221.

1997,223, 51.

144.

5670.

145. 146. 147. 148. 149.

G. Koehler, K. Rechthaler, G. Grabner, R. Luboradzki, K. Suwinska, and K. Rotkiewicz, J. Phys. Chem. A , 1997, 101,8518. S. Delmond, J.-F. Letard, R. Lapouyade, and W. Rettig, J. Photochem. Photobiol. A , 1997,105, 135. D. Braun, W. Rettig, S. Delmond, J.-F. Letard, and R. Lapouyade, J. Phys. Chem. A, 1997,101,6836. F. D. Lewis and T. M. Long, J. Phys. Chem. A, 1998,102,5327. W. Verbouwe, L. Viaene, M. Van der Auweraer, F. C. De Schryver, H. Masuhara, R. Pansu, and J. Faure, J. Phys. Chem. A , 1997,101,8157.

38 150. 151. 152. 153. 154. 155. 156. 157. 158. 159. 160. 161. 162. 163. 164. 165. 166. 167. 168. 169. 170. 171. 172. 173. 174. 175. 176. 177. 178. 179. 180. 181.

Photochemistry

B. Albinsson, J. Am. Chem. Soc., 1997, I 19,6369. L.-S. Choi, Chem. Commun., 1998,893. G. E. Collins, L.-S. Choi, and J. H. Callahan, J. Am. Chem. Soc., 1998, 120, 1474. A. P. Klishchenko, M. A. Senyuk, S. A. Tikhomirov, and G. B. Tolstorozhev, Opt. Spektrosk., 1997,83,664. N . Kometani, 0. Kajimoto, and K. Hara, J. Phys. Chem. A , 1997,101,4916. K. Hara, D. Bulgarevich, S. Dmitry, and 0. Kajimoto, Ber. Bunsenges-Ges., 1997, 101,1443. Y. H. Kim, D. W. Cho, N. W. Song, D. Kim, and M. Yoon, J. Photochem. Phorobiol. A , 1997, 106, 161. Y. Kim, B. I. Lee, and M. Yoon, Chem. Phys. Lett., 1998,286,466. S . Aich, C. Raha, and S. Basu, J. Chem. Soc., Faraday Trans., 1997, 93,2991. Y. V. Il’ichev and K. A. Zachariasse, Ber. Bunsenges-Ges., 1997, 101,625. U.-W. Grummt, E. Birckner, H. Lindauer, B. Beck, and R. Rotomskis, J. Photochem. Photobiol. A, 1997, 104, 69. A. P. Klishchenko and I. N. Koziov, J. Appl. Spectosc., 1997,64, 126. E . Abraham, J. Oberle, G. Jonusauskas, R. Lapouyade, K. Minoshima, and C. Rulliere, Chem. Phys., 1997,219, 73. K. A. Zachariasse, M. Grobys, and E. Tauer, Chem. Phys. Lett., 1997,274,372. Y . Hirata, Chem. Phys. Lett., 1997,278, 133. C. Cornelissen-Gude and W. Rettig, Chem. Phys., 1998,229, 325. K. Susuki, H. Tanabe, and H. Shruka, J. Phys. Chem. A , 1997,101,4496. P. R. Bangal, S. Chakravorti, and G. Mustafa, J. Photochem. Photobiol. A , 1998, 113, 35. N. J. Dovinchi and D. D. Chen, Single-Mol. Opt. Detect., Imaging Spectrosc., 1997, 223. C. Zander, M. Sauer, K. H. Drexhage, J. Wolfrum, L. Brand, C. Eggeling, and C. A. M. Seidel, Proc. SPIE-Int. Soc. Opt. Eng., 1997, 2980 (Advances in Fluorescence Sensing Technology III), 107. C. Eggeling, L. Brand, and C. A. M. Seidel, Bioimuging, 1997,5, 105. T . Ha, J. Glass, Th. Enderle, D. S. Chemla, and S. Weiss, Phys. Res. Lett., 1998,80, 2093. J. C. Fister 111, S. C. Jacobson, L. M. Davis, and J. M. Ramsey, Anal. Chem., 1998, 70,43 I . W. P. Ambrose, P. M. Goodwin, J. Enderlein, D. J. Semin, and R. A. Keller, Proc. SPIE-Int. Soc. Opt. Eng., 1998,3270 (Methodsfor Ultrasensiiive Detection), 190. T. Basche, J. Lumin., 1998, 76,263. M . Xiao and X. Chen, J. Phys. Soc. Jpn., 1998,67,351. C. Zander and K. H. Drexhage, Proc. SPIE-Int. SOC. Opt. Eng., 1997, 2980 (Advunces in Fluorescence Sensing Technology III), 546. M. A. Bopp, G. Tarrach, M. A. Lieb, and A. J. Meixner, J. Vuc. Sci. Technol. A , 1997,15, 1423. S. C. Hill, M. D. Barnes, W. B. Whitten, and J. M. Ramsey, Appl. Opt., 1997,36,4425. M . D. Barnes, N. Lerner, C.-Y. Kung, W. B. Whitten, J. M. Ramsey, and S. C. Hill, Opt. Lett. , 1997,22, 1265. A. Van Orden, M. P. Machara, P. M. Goodwin, and R. A. Keller, Anal. Chem., 1998, 70, 1444. C. Zander, L. Brand, C. Eggeling, K. H. Drexhage, and C. A. M. Seidel, Proc. SPIE-Int. SOC.Opt. Eng., 1997,2980 (Advances in Fluorescence Sensing Technology III), 552.

I: Photophysiml Processes in Condensed Phases 182. 183. 184. 185. 186. 187. 188. 189. 190. 191. 192. 193. 194. 195. 196. 197. 198. 199. 200. 201. 202. 203. 204. 205. 206. 207. 208. 209. 210. 21 1. 212.

39

C. Eggeling, J. Widnegren, R. Rigler, and C. A. M. Siedel, Anal. Chem., 1998, 70, 265 I. W.-Y. Lin, Huuxue, 1997,55, 59. X.-Z. Du, Y. Zhang, Y.-B. Jiang, L. R. Lin, X.-Z. Huang, and G.-Z. Chen, J. Photochem. Photobiol. A, 1998,112, 53. J. Xie, D. Huang, J. Xu, and G. Chen, Chin. Sci. Buff.,1997,42, 1468. X.-Z. Du, Y.B. Jiang, X.-Z. Huang, and G.-Z. Chen, Chin. Chem. Lett., 1997, 8, 431. X.-Z. Du, Y. B. Jiang, X.-Z. Huang, and G.-Z. Chen, Spectrochim. Acta, Part A, 1997,53,671. K. Nakashima and S. Yasuda, J, Photochem. Photobiol. A, 1997,111,249. A. S . Carretero, C. C. Blanco, A. F. Gutierrez, and A. M. De La Pena, Appf. Spectrosc., 1998,52,420. A. Ueno, Kikun Kagaku Sosetsu, 1997,31,44. J. W. Park, S. E. Park, B. A. Lee, and S.-Y. Lee, Chem. Lett., 1997, 1043. T. Aoyagi, A. Ueno, M. Fukushima, and T. Osa, Macromol. Rapid Commun., 1998, 19, 103. X. Shen, M. Belletele, and G. Durocher, J. Phys. Chem. B, 1998,102, 1877. S. Mitra, R. Das, and S. Mukherjee, J. Phys. Chem. B, 1998,102,3730. S . Monti, S. Sortino, G. De Guidi, and G. Marconi, New J. Chem., 1998,22, 599. M. Milewski, M. Sikorski, A. Maciejewski, M. Mir, and F. Wilkinson, J. Chem. Soc., Faraduy Trans., 1997,93,3029. B. D. Wagner and P. J. MacDonald, J. Photochem. Photobiol. A , 1998,114, 151. E. L. Roberts, J. Dey, and I. M. Warner, J. Phys. Chem. A, 1997,101,5296. R. De, S. Sinha, and T. Gunguly, Nuovo Cimento SOC.Itul. Fis. D, 1997,19,955. M. Mir, F. Wilkinson, D. R. Worrall, J. L. Bourdelande, and J. Marquet, J. Photochem. Photobiol. A , 1997,II, 241. S. De Feyter, J. van Stam, F. Imans, L. Viaene, F. C. De Schryver, and C. H. Evans, Chem. Phys. Lett,, l997,277,44. S . Akimoto, €3. Nishizawa, T. Yamazuki, I. Yamazaki, Y. Hayashi, M. Fujimaki, and K. Ichimura, Chem. Phys. Lett., 1997,276,405. A. A. Krasnovskii Jr., Y. Fu, M. E. Bashtanov, S. Murphy, and C. S. Foote, Opt. Spektrosk., 1997,83,616. R. A. Kipp, J. Simon, M. Beggs, H. E. Ensley, and R. H. Schmehl, J. Phys. Chem. A, 1998,102,9659. N. Kobayashi, N. Sasaki, and H. Konami, Inorg. Chem., 1997,36,5674. E. Liu, J. Huang, Z. Dai, S.Yang, Y. Wu, N. Chen, J. Huang, Z. Huang, J. Sun, and J. Xu, WujiHuaxue Xuebuo, 1997,13,411. M. Aoudia, G. Chang, V. 0. Kennedy, M. E. Kenney, and M. A. J. Rodgers, J. Am. Chem. SOC., 1997,119,6029. G. X. Xiong, S. Y. Shen, J. P. Ya, Q. F. Zhou, and H. J. Xu, Chin. J. Chem., 1997, 15,443. S . Foley, G. Jones, R. Liuzzi, D. J. McGarvey, M. H. Perry, and T. G. Truscott, J. Chem. Soc., Perkin Trans 2, 1997,1725. N. Kobayashi, Y. Yoshikawa, 0. Ito, H. B. Goodbrand, and J. Mayo, Chem. Lett., 1998,423. Y. Kaneko, Y. Nishimura, N. Takane, T. Arai, H. Sakurago, N. Kobayashi, D. Matsunaga, C. Pac, and K. Tokumaru, J. Photochem. Photobiol. A, 1997,106,177. A. V. Savitskaja, E. A. Lukjanetz, S. N. Dashkevich, and E. A. Markarova, Proc. SPZEInt. SOC.Opt. Eng., 1997,2980 (Advances in Fluorescence Sensing Technology), 352.

40 213. 214. 21 5. 216. 217. 218. 219. 220. 221. 222. 223. 224. 225. 226. 227. 228. 229. 230. 231. 232. 233. 234. 235. 236. 237. 238. 239. 240. 241. 242.

Photochemistry

M. Li, J. Zou, Z. Xu, and X. You, Spectrochim. Acta, Part A, 1997,53,2109. E. Vogel, M. Broring, S. J. Weghorn, P. Scholz, R. Deponte, J. Lex, H. Schmickler, K. Schaffner, S. E. Braslavsky, M. Muller, S. Porting, C. J. Fowler, and J. L. Sessler, Angew. Chem., Inl. Ed. Engl., 1997,36, 1651. W. Freyer, H. Stiel, M. Hild, K. Tauchner, and D. Leopold, Photochem. Photobiol., 1997,66, 596. E. Balasubramaniam and P. Natarajan, J. Photochem. Photobiol. A, 1997,103,201. P. Lopez-Cornejo and S. M. B. Costa, Langmuir, 1998,14,2042. V. N. Knyukshto, K. N. Solovyov, and G. D. Egorova, Biospectroscopy, 1998, 4, 121. P. C. Beaumont, D. G. Johnson, and B. J. Parsons, J. Chem. Soc., Furaduy Trans., 1998, 94, 195. P. C. Beaumont, D. G. Johnson, and B. J. Parsons, J. Photochem. Photobiol. A , 1997,107, 175. T. Lopez Arbeloa, F. Lopez Arbeloa, 1. Lopez Arbeloa, A. Costela, L. GarciaMoreno, and J. M. Figuera, J. Lumin., 1997, 75, 309. S. Becker, I. Gregor, and E. Thiel, Chem. Phys. Lett., 1998,283,350. Z . A. Dreger, G. Yang, J. 0. White, Y. Li, and H. G. Drickamer, J. Phys. Chem. B, 1998,102,4380. N. Srividya, P. Ramamurthy, and V. T. Ramakrishnan, Spectrochim. Acta, Part A , 1998,54,245. T. Gustavsson, L. Cassara, V. Gulbinas, G. Gurzadyan, and J.-C. Mialocq, J. Phys. Chem. A , 1998,102,4229. W. C. Flory and G. J. Blanchard, Appl. Spectrosc., 1998,52,82. D. Sastikumar and V. Masilamani, Proc-Indian Acad. Sci., Chem. Sci., 1997, 109, 325. M. K . Desai, S. K. Manon, and Y. K. Agrawal, Mol. Cryst. Liq. Cryst. Sci. Technol., Sect. C, 1997,8, 329. N. Nijegorodov, V. Ramachandram, and D. F. Winkoun, Spectrochim. Actu, Part A, 1997,53,1813. N. Nijegorodov and D. F. Winkoun, Spectrochim. Actu, Part A, 1997,53,2013. H. Yamaguchi, S. Sato, M. Yasunam, T. Sato, and M. Yoshinobu, Spectrochim. Actu, Part A , 1997,53, 2471. A. Falchi, C. Gellini, P. R. Salvi, and K. Hafner, J. Phys. Chem. A, 1998,102, 5006. F. Morlet-Savary, S. Parret, J. P. Fouassier, K. Inomata, and T. Matsumoto, J. Chem. Soc., Faraday Trans., 1998,94,745. Y. Chen and S.-K. Wu, J. Photochem. Photobiol. A, 1997,102,203. S . L. Dmitruk, S. L. Druzhinin, R. A. Minakova, A. I. Bedrik, and B. M. Uzhinov, Russ. Chem. Bull., 1997,46,2027. J. M. Zwier, P. G. Waring, A. M. Brouwer, D. Bebelaar, and W. J. Buma, J. Am. Chem. SOC.,1997, I19, 11525. S. Yamamoto and H. Habara, Chem. Lett., 1997,757. A. Admasu, A. D. Gudmundsdottir, M. W. Platz, D. S. Waqtt, S. Kwaitkowski, and P. J. Crocker, J. Chem. Soc., Perkin Trans 2, 1998, 1093. A. Costela, I. Garcia-Moreno, J. Dubrin, and R. Sastre, J. Photochem. Photobiol. A, 1997, 109, 77. R. Saito, T. Hirano, H. Niwa, and M. Ohashi, J. Chem. Soc., Perkin Trans. 2, 1997, 1711. S. Mukherjee and C. B. Subbash, J. Chem. Soc., Faraday Tram., 1998,94,67. Y. Guo, A. Darmanyan, and W. S. Jenks, Tetrahedron Lett., 1997,38, 8619.

1: Photophysical Processes in Condensed Phases

243.

41

S. Jockusch, I. V. Koptyug, P. F. McGarry, G. W. Sluggert, N. J. Turro, and D. M. Watkins, J. Am. Chem. SOC.,1997,119, 11495. 244. P. Changenet, P. Plaza, M. M. Martin, Y. H. Meyer, and W. Rettig, Chem. Phys., 1997,221,311. 245. A. Nishigaki, U. Nagashima, A. Uchida, I. Ohnishi, and S. Ohshima, J, Phys. Chem. A , 1998,102, 1108. 246. L. J. Martinez and J. C. Scaiano, J. Am. Chem. Soc., 1998,119, 11066. 247. L. Biczok, Reuct. Kinet. Catal. Lett., 1997,61,57. 248. S . V. Jovanovic, D. G. Morris, C. N. Pliva, and J. C. Scaiano, J. Photochem. Photobiol. A, 1997,107, 153. 249. D. E. Nicodem and M. F. V. da Cunha, J. Photochem. Photobiol. A , 1997,107, 169. 250. M. M. Alam, M. Fujitsuka, A. Watanabe, and 0. Ito, J. Chem. Sac., Perkin Trans. 2, 1998,817. 251. T. Haupl, C. Windolph, T. Jochum, 0. Brede, and H. Hermann, Chem. Phys. Lett., 1997,280,520. 252. A. Broo, J. Phys. Chem. A, 1998,102, 526. 253. H. F. Hameka, J. 0. Jensen, K. K. Ong, A. C. Samuels, and C. P. Vlahacos, J. Phys. Chem. A, 1998,102, 361. 254. S . L. Bondarev, J. Appl. Spectrosc., 1997,64, 1. 255. B. 0. Neilsen, K. Jorgensen, and L. H. Skibsted, J. Photochem. Photobiol. A , 1998, 112, 127. 256. B. M. Aveline, S. Matsugo, and R. W. Redmond, J. Am. Chem. SOC.,1997, 119, 11785. 257. M. Vincent, J. Gallay, and A. P. Demchenko, J. Fluoresc., 1997, 7, 107. 258. F. Pina, M. J. Melo, R. Ballardini, L. Flamigni, and M. Maestri, New J. Chem., 1997,21,696. 259. C . Laurich, H. Gorner, and H. J. Kuhn, J. Photochem. Photobiol. A , 1998, 112, 29. 260. T. Nakayama, T. Shimizu, Y. Torii, S. Miki, and K. Hamanoue, J. Photochem. Photobiol. A , 1997, I I I, 35. 261. G. G. Gurzadyan, T.-H. Tran-Thi, and T. Gustavsson, J. Chem. Phys., 1998, 108, 385. 262. M. Yoshizawa, K. Suzuki, A. Kubo, and S. Saikan, Chem. Phys. Lett., 1998,290,43. 263. J. T. Kang, K. Ohta, K. Tominaga, and K. Yoshihara, Chem. Phys. Lett., 1998,287, 29. 264. T.-S. Kim, K. Kyu, C. Sang, S. Young, and I. Kwak, J. Chem. Phys., 1997, 107, 8719. 265. M. Szymanski, A. Maciejewski, J. Kozlowski, and J. Koput, J. Phys. Chem. A , 1998, 102,677. 266. W. G. Megimpsey, Trends Org. Chem., 1997,6,233. 267. J. Seixas de Melo, R. S. Becker, F. Elisei, and A. L. Macanita, J. Chem. Phys., 1997, 107,6062. 268. M. Yamaji, K. Okada, B. Marcinisk, and H. Shizuka, Chem. Phys. Lett., 1997,277, 375. 269. R. S. Murphy, C. P. Moorlag, W. H. Green, and C. Bohne, J. Photochem. Photobiol. A, 1997,110, 123. 270. H. C. Joshi, H. Mishra, and H. B. Tripathi, J. Photochem. Photobiol. A , 1997, 105, 15. 271. F. Lahmani and A. Zehnacker-Rentien, J. Phys. Chem. A , 1997,IOI,6141. 272. J. Catalan and C. Diaz, J. Phys. Chem. A , 1998, 102,323.

42 273, 274. 275. 276. 277. 278. 279. 280. 281. 282. 283. 284.

285. 286. 287. 288. 289. 290. 291. 292. 293. 294. 295. 296. 297. 298. 299. 300. 301. 302. 303. 304.

Photochemistry

P. B. Bisht, M. Okamoto, and S. Hirayama, J. Phys. Chem. B, 1997,101,8850. G . S . Denisov, N. S. Golubev, V. M. Schreiber, S. S. Shajakhmedov, and A. V. Shurakhina, J. Mol. Struct., 1997,436, 153. Y. Chiang, J. A. Kresge, B. Ht."iung, P. Schunemann, and J. Wirz, Helv. Chim. Actu, 1997,80, 1 106. D. S. English, K. Das, K. D. Ashby, J. Park, J. W. Petrich, and E. W. Castner Jr., J. Am. Chem. Soc., 1997,119, 11585. T. Arai and Y. Norikano, Chem. Lert., 1997, 339. S. Santra and S. K. Degra, Chem. Phys., 1998,226,285. A. 0. Doroshenko, E. A. Posokhov, V. M. Shershukov, V. G. Mitina, and 0. A. Ponomarev, High Energy Chem., 1997,31, 388. S. Moller, K. B. Andersen, J. Spanger-Larsen, and J. Waluk, Chem. Phys. Lett., 1998,291,51. C.-Y. Wei, W.-S. Yu, P.-T. Chou, P.-T. Hung, C.-P. Chang, and T.-C. Lin, J. Phys. Chem. B, 1998,102, 1053. A. Douhal, Ber. Bunsenges-Ges., 1988,102,448. E. Bardez, I. Devol, B. Larry, and B. Valeur, J. Phys. Chem. B, 1997,101,7786. M. C. Rath, D. K. Palit, and T. Mukherjee, J. Chem. Soc., Furaday Trans., 1998,94, 1189. F. Deng, J. Kubin, and A. C. Testa, J. Photochem. Photobiol. A , 1997,104,65. G. Wenska, B. Skalski, M. Insinka, S Paszyc, and R. E. Verrall, J. Photochem. Photobiol. A , 1997,108, 135. T. Yatsuhashi and H. Inoue, J. Phys. Chem. A , 1997,101,8166. T. Yatsuhashi, Y. Nakajima, T. Shimaoa, and H. Inoue, J. Phyx Chem. A , 1998, 102,3018. M. C. Rath and T. Mukherjee, J. Chem. Soc., Furuduy Trans., 1997,3331. B. Venkatachalapathy, P. Ramamurthy, and V. T. Ramakrishnan, J. Photochem. Photobiol. A , 1997,111, 163. A. C. Bhasikuttan, A. K. Singh, D. K. Palit, A. Y. Sapre, and J. P. Mittal, J. Phys. Chem. A, 1998,102,3470. D. Marks, H. Zhang, and M. Glasbeek, J. Luminesc., 1998, 76, 52. D. Marks, H. Zhang, M. Glasbeek, P. Borowicz, and A. Grabowska, Chem. Phys. Lett., 1997,275, 370. E. Pines, B.-Z. Magnes, M. J. Lang, and G. R. Fleming, Chem. Phys. Lett., 1997, 281,413. E. Pines, D. Tepper, B.-Z. Magnes, D. Pines, and T. Barzek, Ber. Bunsenges-Ges., 1998,102,504. H. Mizoguchi, K. Kubo, T. Sakurai, and €I. Inoue, Ber. Bunsenges-Ges., 1997, 101, 1914. J. K. Lee and R. T. Ross, J. Phys. Chem. B, 1998,102,4612. M. S. Baptista and G. I. Indig, J. Phys. Chem. B, 1998,102,4678. S . Takeuchi and T. Tahara, Chem. Phys. Lett., 1997,277,340. 0.Oishi, S. Yamashita, M. Ohno, S. Lee, G. Sugihara, andN. Nishino, Chem. Phys. Lett., 1997,269, 530. K. Nishiyama, T. Honda, H. Reis, U. Muelier, K. Muellen, W. Baumann, and T. Okada, J. Phys. Chem. A , 1998,102,2934. A. Schuetz and T. Wolff, J. Photochem. Photobiol. A , 1997,109,251. Z. Lin, S. Priyadarshy, A. Bartko, and D. H. Waldeck, J. Photochem. Photobiol. A , 1997,110, 131. M . Aoudia and M. A. J. Rodgers, J. Am. Chem. Soc., 1997,119, 12859,

I : Photophysical Processes in Condensed Phases 305. 306. 307. 308. 309. 310. 31 1 . 312. 313. 314. 315. 316. 317. 318. 319. 320. 321. 322. 323. 324. 325. 326. 327. 328. 329. 330. 331. 332. 333. 334. 335. 336. 337. 338. 339. 340.

43

J. M. Kroon, R. B. M. Koehorst, M. van Dijk, G. M. Sanders, and E. J. R. Sundholter, J. Muter. Chem., 1997, 7,615. N. C. Maiti, S. Mazumdar, and N. Periasamy, J. Phys, Chem. B, 1998,102, 1528. M. Kimura, K. Nakada, Y. Yamaguchi, K. Hanabusa, H. Shirai, and N. Kobayashi, Chem. Commun., 1997, 1215. M. Fujiwara and K. Toyami, J. Chem. Phys., 1997,107,9354. W. Wieslaw, S. Krystyna, C. Cezary, L. Leszek, and M. Alicja, J. Photochem. Photobiol. A, 1997,102, 189. A. P. Losev, S. M. Bachilo, and I. N. Nichiporovich, J. Appl. Spectrosc., 1998,65, 1 . D. Weldon, B. Wang, T. D. Poulsen, K. V. Mikkelsen, and P. R. Ogilby, J. Phys. Chem. A , 1998,102, 1498. P.-T. Chou, Y.-C. Chen, C.-Y. Wei, S.-J. Chen, H.-L. Lu, and T.-H. Wei, J. Phys. Chem. A, 1997,101,8581. P. Serguievski and M. R. Detty, Organometallics, 1997,16,4386. E. L. Clennan, D. Wang, C. Clifton, and M.-F. Chen, J. Am, Chem. Soc., 1997,119, 9081. M. E. Bashtanov and A. A. Krasnovskii Jr., High Energy Chem., 1997,31,338. A. L. Mamaev, V. V, Korolev, N. M. Bazhin, and S. V. Morozov, Chem. Phys. Lett., 1998,289,247. M. Weng, M.-H. Zhang, and T. Shen, J. Chem. Soc., Perkin Trans. 2, 1997,2393. M. Weng, M.-H. Zhang, and T. Shen, J. Photochem. Photobiol. A , 1997,108, 159. M. Ikegami and T. Arai, Kokagaku, 1997,26,42. J. Troe, Pure Appl. Chem., 1997,69,841. M. S . Kurdoglyan, Opt. Spektrosk., 1997,82,581. M. R. V. Sahyun and J. T. Blair, J. Photochem. Photobiol. A , 1997,104,179. H. Kikuchi and H. Suzuki, J. Phys. Chem. B, 1997,101,6050. G. S. Jas, Y. Wang, S. W. Pauls, C. K. Johnson, and K. Kuczera, J. Chem. Phys., 1997,107,8800. G. Grabner, K. Rechthaler, and G. Koehler, J. Phys. Chem. A , 1998,102,689. H. Gorner, J. Photochem. Photobiol. A , 1998,212, 155. J. J. Paz, M. Moreno, and J. M. Lluch, J. Chem. Phys., 1997,107,6275. F. Scavarda, F. Bonnichon, C. Richard, and G. Grabner, New J. Chem., 1997,21,1119. P. J. MacLeod, A. L. Pincock, J. A. Pincock, and K. A. Thompson, J. Am. Chem. Soc., 1998, 120,6443. R. J. Olsen, J. Photochem. Photobiol. A, 1997,103,91. M. Garavelli, T. Vreven, P. Celani, F. Bernardi, and M. A. Robb, J. Am. Chem. Soc., 1998,120, 1285. S. H. Pullen, N. A. Anderson, L. A. Walker 11, and R. J. Sension, J. Chem. Phys., 1997,107,4985. Y. Sonada, H. Morii, M. Sakuragi, and Y. Suzuki, Chem. Lett., 1998,349. J. Saltiel, S. Wang, D.-H. KO,and D. A. Gormin, J. Phys. Chem. A , 1998,102,5383. R. N. Young, B. Brocklehurst, and C. E. Oliver, J. Photochem. Photobiol. A , 1997, 102, 163. F. Schael, J. Kuester, and H.-G. Loehmannroeben, Chem. Phys., 1997,218, 175. G . Pistolis and A. Malliaris, Chem. Phys., 1998,226, 83. K. S. Wong, H. Wang, and G. Lanzani, Chem. Phys. Lett., 1998,288,59. A. M. Muller, S. Lochbrunner, W. E. Schmid, and W. Fuss, Angew. Chem., Int. Ed. Engl., 1998,37, 505. S . H. Pullen, N. A. Anderson, L. A. H. Walker, and R. J. Sension, J. Chem. Phys., 1998,108,556.

44

341. 342. 343. 344. 345, 346. 347. 348. 349. 350. 351. 352. 353. 354. 355. 356. 357. 358. 359. 360. 361. 362. 363. 364. 365. 366. 367. 368. 369. 370. 371.

Photochemistry

R. E. Martin, J. Bartek, F. Diederich, R. R. Tykwinski, E. C. Meister, A. Hilger, and H.-P. Luthi, J. Chem. SOC.,Perkin Trans. 2, 1998,233. A. K. Chibisov and H. Goerner, J. Photochem. Photobiol. A, 1997,105,261. A. I. Tolmachev, Y . L. Slominski, and M. A. Kudinova, Zh. Nauchn. Prikl. Fotogr., 1997,42, 54. D. Pevenage, D. Corens, W. Dehaen, M. Van der Auweraer, and F. C. De Schryver, Bull. Soc. Chim. Belg., 1997, 106, 565. E. S. Voropai and M. P. Samtsov, Opt. Spektrosk., 1997,82, 577. S. Reindl and A. Penzkofer, Chem. Phys., 1998,230,83. J. Wachtveitl, T. Naegele, B. Puell, W. Zinth, M. Krueger, S. Rudolph-Boehner, D. Osterhelt, and L. Moroder, J. Photochem. Photobiol. A, 1997,105,283. T. Nagele, R. Hoche, W. Zinth, and J. Wachtveitl, Chem. Phys. Lett., 1997,272,489. N. Biswas and S . Umapathy, J. Chem. Phys., 1997,107,7849. S. Mukherjee and S. C. Bera, J. Photochem. Photobiol. A, 1998,113,23. E. Markava, D. Gustina, G . Matisova, I. Kaula, I. Muzikanto, M. Rutkis, and L. Gerca, Suprumol. Sci., 1997,4, 369. R. Tahara, T. Morozumi, H. Nakamura, and M. Shimomura, J. Phys. Chem. B, 1997,101,7736. M. V. Alfinov, A. 1. Vedernikov, S. P. Gromov, Y . V. Fedorov, and 0. A. Fedorova, Russ. Chem. Bull., 1997,46,2099, D. K. Palit, A. Z. Szarka, N. Pagliano, and R. M. Hochstrasser, Ultrufust Processes Spectrosc. [Proc. Int. ConJ], 1996, 9,75. N. R. King, E. A. Whale, F. J. Davis, A. Gilbert, and G. R. Mitchell, J. Muter. Chem., 1997,7,625. S . Dobrin, A. Starakhin, P. Kaszynski, and J. Waluk, Opt. Spektrosk., 1997,83,669. H. E. Wilhelm, H. Gebert, and W. Regenstein, 2. Nuturforsch., A: Phys. Sci., 1997, 52, 837. V. Papper, D. Pines, G. Likhtenshtein, and E. Pines, J. Photochem. Photobiol. A , 1997, I l l , 87. V. Strehmel, C. W. Frank, and B. Strehmel, J. Photochem. Photobiol. A , 1997, 105, 353. W. J. Oldham Jr., Y. J. Miao, R. Lachicotte, and G. C. Bazan, J. Am. Chem. Soc., 1998,120,419. S. Dobrin, P. Kaszynski, and J. Waluk, J. Photochem. Photobiol. A , 1997,105, 149. G. Strati and P. Piotrowiak, J. Photochem. Photobiol. A, 1997,105,255. S. M. Bachilo, E. V. Bachilo, and T. Gillbro, Chem. Phys., 1998,229,75. E. J. Shin, E. Y . Bae, S. H. Kim, H. K. Kang, and S. C. Shin, J. Photochem. Photobiol. A, 1997,107, 137. V. Raj Gopal, V. Jayathritha, G. Saroja, and A. Samanta, Chem. Phys. Lett., 1997, 270, 592. J. Saltiel, Y . Zhang, and D. F. Sears Jr., J. Am. Chem. SOC.,1997, 119, 11202. L. Latterini, F. Elisei, G. G. Aloisi, and M. A. J. Rodgers, J. Phys. Chem. A, 1997, 101,9870. G . G . Aloisi, F. Elisei, L. Latterini, G. Marconi, and U. Mazzucato, J. Photochem. Photobiol. A , 1997,105,289. M. F. Budyka, 0. D. Laukhina, and V. F. Razumov, Chem. Phys. Lett., 1997,279, 327. T. Arai, Y . Hozumi, 0. Takahashi, and K. Fujimori, J. Photochem. Photobiol. A , 1997,104, 85. E. J. Shin and S. W. Choi, J. Photochem. Photobiol. A , 1998,114,23.

I: Photophysical Processes in Condensed Phases

45

Z. Li and S. Wu, J. Lumin., 1997, 7,237. Special Issue: Fullerenes, Photoexcited States and Reactive Intermediates, Part I . ed. D. M. Guldi, P. V. Kamat, and K.-D. Asmus, Res. Chem. Intermed., 1997,23. 374. Y.-P. Sun, Mol. Suprumol. Photochem., 1997, I , 325. 375. L. Juha, V. Hamplova, Z. Pokorna, J. Kodymova, 0. Spaiek, J. Krasa, K. Lang, P. Kubat, F. P. Boody, E. Koudoumas, S. Couris, I. Stibor, T. Gareis, 0. Kothe, and J. Daub, Proc.-Electrochem. Soc., 1997, 97, 56. 376. J. Mattay, C. Siedschlag, G. Torres-Garcia, L. Ulmer, C. Wolff, M. Fujisuka, A. Watanabe, 0. Ito, and H. Luftmano, Proc.-Electrochem. Soc., 1997,97,326. 377. M. Kallny, K. Nemeth, and P. R. Surjan, J. Phys. Chem. A , 1998,102, 1261. 378. 0.Ito, Reza Kenkyu, 1997,25,776. 379. S . Fukuzumi, Res. Chem. Intermed., 1997,23, 519. 380. P. V. Kamat and D. M. Guldi, Proc.-Electrochem. SOC.,1997, 97,203. 381. R. V. Bensasson, E. Bienvenue, J.-M. Janot, E. J. Land, and P. Seta, Chem. Phys. Lett., 1998,283,221. 382. D. K. Palit, H. Mohan, and J. P. Mittal, J. Phys. Chem. A, 1998, 102,4456. 383. M. Fujitsuka, H. Kasai, A. Masuhara, S. Okada, H. Oikawa, H. Nakanishi, A. Watanabe, and 0. Ito, Chem. Lett., 1997, 121 1 . 384. Y. L. Hwang and K. C. Hwang, Huaxue, 1997,55,53. 385. M. Fujitsuka, A. Watanabe, 0. Ito, K. Yamamoto, and H. Funasaka, J. Phys. Chem. A, 1997,101,7960. 386. M. Ichida, M. Sakai, T. Yajima, and A. Nakamura, J. Lumin., 1997, 72,499. 387. J . S. Ahn, K. Suzuki, Y. Iwasa, and T. Mitani, J. Lumin., 1997, 72,464. 388. V. V. Kveder, V. D. Negrii, E. A. Steinman, A. N. Izotov, Y. A. Ossip’yan, and E. K. Nikolaev, Zh. Eksp. Teor. Fiz., 1998,113, 734. 389. I. Akimoto, J. Azuma, M. Ashida, and K. Kan’no, J. Lumin., 1998, 76,206. 390. T. Ohno, K. Matsuishi, and S. Onari, J. Appl. Phys., 1998,83,4939. 391. Y. Wang, Y. Yang, Y. Guo, R. Gan, J. Wang, Y. Sun, and G. Chen, Proc. SPIE-Int. SOC.Opt. Eng., 1998,3175 (Thin Film Physicsand Applications), 104. 392. J. Qian, J. Song, C. Xu, S. Qian, and W. Peng, Zhongguo Jiguang, 1997, A24,251. 393. V. A. Gaisin, B. S. Kulinkin, and B. V. Novikov, Vestri. St.-Petersbg. Univ., Ser. 4. Fiz. Khim., 1997, 113. 394. Y.-P. Sun, B. Kiu, and G. E. Lawson, Photochem. Photobiol., 1997,66, 301. 395. J. L. Bourdelande, J. Font, R. Gonzalez-Moreno, and S. Nonell, J. Photochem. Photobiol. A , 1998,115,69. 396. E. R. Crooks, J. Eastoe, and A. Beeby, J. Chem. Soc., Faraday Trans., 1997, 93, 4131. 397. D. M. Guldi and K.-D. Asmus, Proc. Electrochem. Soc., 1997,97,82. 398. C . Wang and S. Yao, Huaxue Wuli Xuebuo, 1998,II, 146. 399. L. Juha, V. Hamplova, Z. Pokorna, K. Lang, P. Kubat, I. Stilbor, and F. P. Brody, Proc. Electrochem. SOC.,1997,97, 256. 400. Z. R. Lian, S. D. Yao, W. Z. Lin, W. F. Wang, and N. Y. Lin, Radiut. Phys. Chem., 1997,50,245. 401. S. D. Yao, W. Z. Lin, Z. R. Lian, W. F. Wang, and N. Y. Lin, Rudiat. Phys. Chem., 1997,50,249. 402. S . Michaeli, V. Meiklyar, B. Endeward, K. Mobius, and €3. Levanon, Res. Chem. Intermed., 1997,23, 505. 403. V. A. Nadtochenko and E. F. Brazgun, Russ. Chem. Bull., 1997,46, 1074. 404. S. Fukuzumi, M. Patz, T. Suenobu, A. Ishida, and K. Mikami, Proc.-Electrochem. SOC.,1997, 97,45.

372. 373.

46 405. 406. 407. 408. 409. 410. 41 1. 412. 41 3. 414. 415. 41 6. 41 7 41 8. 419. 420. 421. 422. 423. 424. 425. 426. 427. 428. 429. 430. 431. 432. 433.

Photochemistry

L. Biczok, N. Gupta, and H. Linschitz, J. Am. Chem. SOC.,1997,119, 12601. J. Qiao, X. Yuan, and W. Jin, Shanzi Daxue Xuebao, Ziran Kexuebuo, 1998,21,147. D. M. Guldi, J. Phys. Chem. B, 1997,101,9600. M. Alam, A. Watanabe, and 0. Tto, J. Photochem. Photobiol. A, 1997,104, 59. T. Nojiri, M. Alam, H. Konami, A. Watanabe, and 0. Ito, J. Phys. Chem. A, 1997, 101,7943. Y . Sasaki, M. Fujitsuka, A. Watanabe, and 0. Ito, J. Chem. SOC.,Faruday Trans., 1997,93,4275. M. I. Sluch, I. D. W. Samuel, and M. C. Petty, Chem. Phys. Lett., 1997,280,215. R. V. Bensasson, E. Bienvenue, C. Fabre, J.-M. Janot, E. J. Land, S. Leach, V. Leboulaire, A. Rassat, S. Roux, and P. Seta, Chem.-Eur. J., 1998,4,270. H. Mohan, L. Y. Chiang, and J. P. Mittal, Res. Chem. Intermed., 1997,23,403. H. Mohan, D. K. Palit, J. P. Mittal, L. Y. Chiang, K.-D. Asmus, and D. M. Guldi, J. Chem. Soc., Faraday Trans., 1998,94,359. C. Carvaja, M. Maggini, M. Rossi, G. Scorrano, and A. Toffoletti, Appl. Magn. Reson., 1997,12,477. P. V. Kamat, D. M. Guldi, D. Liu, K. G. Thomas, Y. Biju, S. Das, and M. V. George, Proc.-Electrochem. Soc., 1997, 97, 122. D. K. Palit, H. Mohan, P. R. Birkett, and J. P. Mittal, J. Phys. Chem. A, 1997, ZOI, 5418. M. Moggini, S. Mondini, G. Scorrano, M. Prato, F. Paolucci, P. Ceroni, S. Roffia, and D. M. Guldi, Proc.-Electrochem. SOC.,1997,97, 325. C. Luo, M. Fujitsuka, A. Watanabe, 0. Tto, L. Gan, Y. Huang, and C.-H. Huang, J. Chem. Soc., Faraday Trans., 1998,94,527. A. W. Jansen, A. Khong, M. Saunders, S. R. Wilson, and D. I. Schuster, J. Am. Chem. SOC.,1997,119,7303. M. Ohno, N. Koide, H. Sato, and S. Eguchi, Tetrahedron, 1997,53,9075. D. M. Guldi, M. Maggini, G. Scorrano, and M. Prato, Res. Chem. Intermed., 1997, 23,561. D. M. Guldi, M. Maggini, G. Scorrano, and M. Prato, Fullerenes, Fullerene Nunostruct., Proc. Int. Wintersch. Electron. Prop. Novel Muter., loth, ed. H. Kuzmany, World Scientific, Singapore, 1996, pp 487-491. F. Conti, C. Corvaja, M. Maggini, F. Piu, G. Scorrano, and A. Toffoletti, Appl. Magn. Reson., 1997, 13, 337. D. M. Guldi, M. Maggini, S. Mondini, G. Scorrano, and M. Prato, ProcElectrochem. Soc., 1997,97,89. D. M. Guldi, M. Maggini, S. Mondini, G. Scorrano, and M. Prato, Proc. SPIE-Int SOC.Opt. Eng., 1997,3142 (Fullerenes and Photonics I V ) , 96. I. G. Sahonov, P. S. Baran, and D. 1. Schuster, Tetrahedron Lett., 1997,38, 8132. T. D. M. Bell, T. A. Smith, K. P. Ghiggino, M. Ranasinghe, M. J. Shepard, and M. N. Paddon-Row, Chem. Phys. Lett., 1997,268,223. H. Imahori and Y. Sakata, Mv. Muter., 1997,9, 537. D. Gust, T. A. Moore, and A. L. Moore, Res. Chem. Intermed., 1997,23,621. D. Gust, T. A. Moore, A. L. Moore, P. A. Liddell, D. Kuciauskas, J. P. Sumida, B. Nash, and D. Nguyen, Proc.-Electrochem. SOC.,1997,97,9. D. Carbonera, M. Di Valentin, C. Corvaja, G. Agostino, G. Giacometti, P. A. Liddell, D. Kuciauskas, A. L. Moore, T. A. Moore, and D. Gust, J. Am. Chem. Soc., 1998,120,4398. H. Imahori, K. Yamada, M. Hasegawa, and S. Taniguchi, Angew. Chem., Int. Ed. Engl., I997,36, 2626.

I : Photophysical Processes in Condensed Phases 434. 435. 436. 437. 438. 439. 440. 441. 442. 443. 444. 445. 446. 447. 448. 449. 450. 451. 452. 453. 454. 455. 456. 457. 458. 459. 460. 461. 462. 463. 464. 465. 466.

47

A. Mortensen and L. H. Skibsted, Free Radical Rex, 1997,26,549. K. Iwata and H. Hamaguchi, Bull. Chem. Soc. Jpn., 1997, 70,2677. F. D. Lewis, J. M. Wagner-Brennan, and J. M. Denari, J. Photochem. Photobiol. A , 1998,112, 139. B. Marciniak, E. Andrzejewska, and G. L. Hug, J. Photochem. Photobiol, A , 1998, 112,21. H. Shizuka, Pure Appl. Chem., 1997,69,825. K. Okada, M. Yamaji, and H. Shizuka, J. Chem. Soc.. Furaday Trans., 1998, 94, 861. I. Amada, M. Yamaji, M. Sase, H. Shizuka, and T. Shimokage, Res. Chem. Intermed., 1998,24, 8 1 . W. Adam, J. N. Moorthy, W. M. Nau, and J. C. Scaiano, J. Am. Chem. SOC.,1997, I 19,6749. A. I. Novaira, C. D. Borsarelli, J. J. Cosa, and C. M. Previtali, J. Photochem. Photobiol. A , 1998, I15,43. T. Nakayama, S. Akimoto, I. Yamazaki, and K. Hamanoue, J. Photochem. Photobid. A, 1997,104, 77. D. Burget and P. Jacques, Chem. Phys. Lett., 1998,291,207. Y. H. Lee and M Lee, Bull. Korean Chem. Soc., 1997,18, 1054. P. Bortolus, S. Monti, G. Galiazzo, and G. Gennari, Chem. Phys., 1997,223,99. G. Zhang, J. K. Thomas, A. Eremenko, T. Kikieva, and F. Wilkinson, J. Phys. Chem. B, 1997, IOI, 8569. A. Goswami and M. Kanta Pal, Collids Surf., 1998,138, 123. S . Kotani, H. Miyasaka, A. Itaya, Y. Hamanaka, N. Mataga, S. Nakajima, and A. Osuka, Chem. Phys. Lett., 1997,269,274. H. Miyasaka, S. Kotani, A. Itaya, G. Schweitzer, F. C. De Schryver, and N. Mataga, J. Phys. Chem. B, 1997,101,7978. H. A. Staab, D. Q. Zhang, and C. Krieger, Liebigs Ann. I Reel., 1997,1551. T. Fiebig, W. Kuhnle, and H. Staerk, Chem. Phys. Lett., 1998,282,7. F. Schael and H. G. Loehmannsroeben, J. Photochem. Photobiol. A , 1997,105,317. G . Jones I1 and X. Qian, J. Phys. Chem. A, 1998,102,2555. C. D. Clark and M. Z. Hoffman, J. Photochem. Photobiol. A , 1997,111,9. S . Icli, H. Icil, D. G. Whitten, C. Sayil, and I. Dityapak, J. Lumin., 1997, 75, 353. A. 0. Doroshenko, V. T. Skripkina, V. M. Schershukov, and 0. A. Ponomaryov, J. Fluoresc., 1997, 7 , 10I . N. A. Bayri and 0. Kocsk, Turk. J. Chem., 1997,21, 172 E. Bosch, S. M. Hubig, S. V. Linderman, and J. K. Kochi, J. Org. Chem., 1998,63, 592. T. Fournier, S. M. Tavender, A. W. Parker, G. D. Scholes, and D. Phillips, J. Phys. Chem. A , 1997,101,5320. Y. L. Chow, Y.-H. Zhang, M. X. Zheng, and A. Rassat, Chem. Phys. Lett., 1997, 2?2,47 1 . X. Yan, M. Weng, M. Zhang, and T. Shen, Dyes Pigm., 1997,35,87. M. Fagnoni, M. Melia, and A. Albini, J. Phys. Org. Chem., 1997, 10, 777. F. Li, S. Gentemann, W. A. Karlsbeck, J. Seth, J. S. Lindsey, D. Holten, and D. F. Bocian, J. Mater. Chem., 1997, 7 , 1245. J.-P. Strachan, S. Gentemann, W. A. Karlsbeck, J. Seth, J. S. Lindsey, D. Holten, and D. F. Bocian, J. Am. Chem. Soc., 1997,119,11191. J.-P. Strachan, S. Gentemann, W. A. Karlsbeck, J. Seth, J. S. Lindsey, D. Holten, and D. F. Bocian, Inorg. Chem., 1998,37, 1191.

48 467. 468. 469. 470. 471. 472. 473. 474. 475. 476. 477. 478. 479. 480. 481. 482. 483. 484. 485. 486. 487. 488. 489. 490. 491. 492. 493, 494. 495. 496. 497. 498.

Photochemistry

E. I. Zenkevich, V. N. Koyukshto, A. M. Shulga, V. A. Kuzmitsky, V. I. Gael, E. G. Levinson, and A. E. Mironov, J. Lumin., 1997, 75, 229. S. Kawahata, I. Yamazaki, Y. Nishimura, and A. Osuka, J. Chetn. Soc., Perkin Trans. 2 , 1997,479. K. M. Kadish, N. Guo, E. Van Caemelbecke, A. Froijo, R. Paolesse, D. Monti, P. Tagliatesta, T. Boschi, L. Prodi, F. Bolletta, and N. Zaccheroni, Inorg. Chem., 1998,37,2858. A. A. Krasnovskii Jr., M. E. Bashtanov, N. N. Drozdova, P. A. Liddell, A. L. Moore, T. A. Moore, and D. Gust, J. Photochem. Photobiol. A , 1997,102, 167. M. P. Debreczney, M. R. Wasielewski, S. Shinoda, and A. Osuka, J. Am. Chem. Soc., 1997,119,6407. J. Ho, M. Zhang, and T. Shen, Sci. Chinu, Ser. B: Chem., 1997,40,380. W. Zhao, Y.-J. Hou, W.4. Wang, B.-W. Zhang, and Y. Co, Chin. J. Chem., 1998, 16, 7. J. Delaire, C. Giannotti, and J. Zakrzewski, J. Photochem. Photobiol. A , 1998,112,205. Z. Zhang, A. L. Verma, K. Nakashima, M. Yoneyama, K. Iriyama, and Y. Ozaki, Lungmuir, 1997, 13, 5726. G. Vaijayanthimala and V. Krishnan, J. Porphyrins Phthulocyunines, 1997, I , 17. M. R. Shortreed, S. F. Swallen, Z.-Y. Shi, W. Tan, Z. Xu, C. Davadoss, J. S. Moore, and R. Kopefman, J. Phys. Chem. B, 1997,101,6318. H. Tian, W. Ni, J. Su, and K. Chen, J. Photochem. Photobiol. A , 1997,109,213. P. Bojarski and L. Kulak, Asiun J. Spectrosc., 1997, I , 107. K. Hisada, S. Ito, and M. Yamamoto, J. Phys. Chem. B, 1998,102,4075. T. Morita, S. Kimura, and Y. Tmanishi, Langmuir, 1998,14, 171. H. Tian, K. Yang, andX. Luo, J. Photochem. Photobiol. A , 1997,110,253. Y .Yamano, M. Mimuro, and M. Ito, J. Chem. Soc., Perkin Truns I , 1997,2713. T. Tanaka, M. Yamaji, and H. Shizuka, J. Chem. Soc., Faraduy Truns., 1998, 94, 1179. L. Flamigni, N. Armaroli, F. Barigelletti, V. Balzani, J.-P. Collin, J.-0. Dalbavia, V. Heitz, and J.-P. Sauvage, J. Phys. Chem. B, 1997,101,5935. G . J. Wilson, A. Launikonis, W. H. F. Sasse, and A. W.-H. Mau, J. Phys. Chem. A , 1997,101,4860. J. A. Simon, S. L. Curry, R. H. Schmehi, T. R. Schatz, P. Piotrowiak, X. Jin, and R. P. Thummel, J. Am. Chem. SOC.,1997,119, 11012. D. R. Striplin, C. G. Wall, B. W. Erickson, and T. J. Meyer, J. Phys. Chem. B, 1998, 102,2383. M. Mac, Bull. Pol. Acad. Sci., Chem., 1997,45, 53. P. Ray, S. C. Bhattacharya, and S. P. Moufik, J. Photochem. Phtobiol. A , 1997, f0.5, 69. L. A. Al-Hassan and F. S. Al-Amro, J. Photochem. Photobiol. A , 1998,112, 165. S . G. Bertolotti and C. M. Previtali, J. Photochem. Photobiol. A , 1997, 103, 1 15. D. K. Palit, A. V. Sapre, and J. P. Mittal, Chem. Phys. Lett., 1997,269, 286. N. Manoj, K. Ajit, and K. R. Gopidas, J. Photochem. Photobiol. A, 1997,109, 109. G . Wanaska, Pol. J. Chem., 1997, 71, 797. W. Bergmark, S. Hector, G. Jones 111, C. Oh, T. Kumagai, S. Hara, T. Segawa, N. Tanaka, and T. Mukai, J. Photochem. Photobiol. A , 1997,109, 119. M. Suzuki, T. Ikeno, K. Osoda, K. Narasaka, T. Suenobu, S. Fukuzumi, and A. Ishida, Bull. Chem. Soc. Jpn., 1997, 70,2269. C. Sato, K. Kikuchi, H. Ishikawa, M. Iwahashi, H. Ikeda, Y. Takahashi, and T. Miyashi, Chem. Phys. Lett., 1997,276,210.

I : Photophysical Processes in Condensed Phases

49

P. Thanasekaren, T. Rajendren, S. Rajagopal, C. Srinivasan, R. Ramaraj, P. Ramamurthy, and B. Venkatachalapathy, J. Phys. Chem. A , 1997,101,8195. 500. S. S. Jayanthi and P. Ramamurthy, J. Phys. Chem. A, 1998,102,51 I . 501. S . Sinha, R. De, and T. Ganguly, Spectrochim. Actu, Part A, 1998, M A , 145. 502. S. Sinha, R. De, and T. Ganguly, J. Photochem. Photobiol. A, 1998,112, 13. 503. H. Shirota, H. Pal, K. Tominaga, and K. Yoshihara, J. Phys. Chem. A, 1998, 102, 3089. 504. K. Tsukahara, K. Ito, M. Matsui, M. Subo, and 0. Yoshaki, Chem. Phys. Lett., 1997,281,261. 505. P. K. Malnen, A. Y. Tauber, J. Helnja, and P. H. Hynninen, Liebigs Ann. I Recl., 1997, 1801. 506. H. A. Staab, A. Feurer, C. Krieger, and A. S. Kumar, Liebigs Ann. I R e d , 1997, 2321. 507. H. A. Staab, R. Hauck, and B. Popp, Eur. J. Chem., 1998,631. 508. A. P. Losev, S. M. Bachilo, D. I. Volkovich, Y. S. Avlasevich, and K. N. Solov’yov, J. Appl. Spectrosc., 1997,64, 62. 509. J . P. Sumida, P. A. Liddell, S. Lin, A. N. Macpherson, G. R. Seely, A. L. Moore, T. A. Moore, and D. Gust, J. Phys. Chem. A , 1998,102,5512. 510. H. Dieks, M. 0. Senge, B. Kirste, and H. Kurreck, J. Org. Chem., 1997,62, 8666. 51 1. G. Elger, H. Mossler, P. Tian, E. Johnen, M. Fuhs, H. Kurreck, and K. Mobius, Nukleonika, 1997,42,293. 512. J. Helaja, A. Y. Tauber, I. Kilpelainen, and P. H. Hynninen, Mugn. Reson. Chem., 1997,35,619. 513. K. Unsaki, T. Kondo, Z.-Q. Zhang, and M. Yamagida, J. Am. Chem. SOC., 1997, I 1 9,8367. 514. M. H. Wall Jr., P. Basu, T. Buranda, B. S. Wicks, E. W. Findsen, M. Ondrias, J. H. Enemark, and M. L. Kirk, Inorg. Chem., 1997,36,5676. 515. H. Imahori, K. Yamada, K. Yoshizawa, K. Higawara, T. Okada, and Y. Sakata, J. Porphyrins Phthalocyanines, 1997, I , 55. 516. E. Kaganer, E. Joselevich, I. Willner, Z. Chen, M. J. Gunter, T. P. Gayness, and M. R. Johnson, J. Phys. Chem. B, 1998,102, 1159. 517. M. C. Feiters, M. C. T. Fyfe, M. V. Martinez-Diaz, S. Menzer, R. J. M. Nolte, J. F. Stoddart, J. M. van Kan, and D. J. Williams, J. Am. Chem. SOC.,1997,119,8119. 518. R. P. Evstigneeva and A. A. Grihkov, Dokl. Akud. Muuk, 1997,357,779. 519. Q . Tan, D. Kuciauskas, S. Lin, S. Stone, A. L. Moore, T. A. Moore, and D. Gust, J. Phys. Chem. B, 1997,101,5214. 520. S.-C. Hung, A. N. Macpherson, S. Lin, P. A. Liddell, G. R. Seely, A. L. Moore, T. A. Moore, and D. Gust, A h . Chem. Ser., 1998, 254 (Photochemistry and Radiation Chemistry), 177. 521. A. Osuka, S. Marumo, T. Okada, S. Taniguchi, N. Mataga, T. Ohno, K. Nozaki, I. Yamazaki, and Y. Nishimura, J. Photosci., 1997,4, 113. 522. D. Gosztola, M. P. Niemczyk, and M. R. Wasielewski, J. Am. Chem. SOC.,1998, 120,5118. 523. J. P. Kirby, J. A. Roberts, and D. G. Nocera, J. Am. Chem. Soc., 1997,119,9230. 524. N. A. Sadovskii, M. G. Kuzmin, H. Gorner, and K. Schaffner, Chem. Phys. Lett., 1998,282,456. 525. D. Wiedenfeld, M. Bachrach, T. M. McCleskey, M. G. Hall, H. B. Gray, and J. R. Winkler, J. Phys. Chem. B, 1997, 101,8823. 526. C. A. Slate, D. R. Striplin, J. A. Moss, P. Chen, B. W.Erickson, and T. J. Meyer, J. Am. Chem. SOC.,1998,120,4885.

499.

50 527. 528. 529. 530. 531. 532. 533. 534. 535. 536. 537. 538. 539. 540. 54 I 542. 543. 544. 545. 546. 547. 548. 549. 550. 551. 552. 553. 554. 555.

Photochemistry A. Knorr, E. Galoppini, and M. A. Fox, J. Phys. Org. Chem., 1997,10,484. K. Fujimoto, H. Sugiyama, and I. Saito, Tetrahedron Lett., 1998,39,2137. K, Weidemaier, H. L. Tavernier, K. T. Chu, and M. D. Fayer, Chem. Phys. Lett.,

1997,276, 309. D. Wang, M. Hu, L. Hu, L. Zhao, Y. Hamanaka, N. Mataga, S. Nakajima, and A. Osuka, Chem. Phys. Lett., 1997,269,274. D. R. Worrall, S. L. Williams, and F. Wilkinson, J. Phys. Chem. B, 1997,101,4709. G. J. Smith, A. Harriman, A. D. Woolhouse, T. C. Haskell, and T. H. Barnes, Photochem. Photobiol., 1998,67, 101. S . W. Keller, S. A. Johnson, E. H. Yonemoto, E. S. Brigham, G. B. Saupe, and T. E. Mallouk, Adv. Chem. Ser., 1998,254 (Photochemistry and Radiation Chemistry), 359. X.-Z. Song, S.-L. Jia, M. Miura, J.-G. Ma, and J. A. Shelnutt, J. Photochem. Photobiol. A, 1998,113,283. S . V. Lymar, R. F. Khairutdinov, V. A. Sukova, and J. R. Hurst, J. Phys. Chem. B, 1998,102,281. H. Port, A. Hartschuh, T. Hirsch, and H. C. Wolf, J. Luminesc., 1997, 72,75. M. B. Zimmt, Chimia, 1997,SI, 82. S . Depaemelaere, F. C. De Schryver, and J. W. Verhoeven, J. Phys. Chem. A , 1998, 102,2109. H. Zhang, M. Zhang, and T. Shen, Sci. China, Ser. B: Chem., 1997,40,449. S. R. Greenfield, D. J. Gosztola, and M. R. Wasielewski, J. Phys. Chem. A , 1997, 101,4939. F. D. Lewis, J. M. Wagner-Brennan, and J. M. Denari, J. Phys. Chem. A, 1998,102, 519. B.-W. Zhang, Y. Cao, J.-W. Bai, and J.-R. Chen, J, Photochem. Photobiol. A , 1997, 106, 169. S. Li, H. Tian, Q. Zhou, Z. Li, and H. Su, Chin. Sci. Bull., 1997,42, 1619. Y.-S. Chen, J. W. Kampf, and R. G. Lawton, Tetrahedron Lett., 1997,38, 7815. A. C. Benniston, A. Harriman, V. Grosshenny, and R. Ziessel, New J. Chem., 1997, 21,405. J. A. Roberts, J. P. Kirby, S. T. Wall, and D. G. Nocera, Inorg. Chim. Acta, 1997, 263, 395. R. Ziessel, A. Juris, and M. Venturi, Chem. Commun., 1997, 1593. M. Ruthkosky, C. A. Kelly, M. C. Zaros, and G. J. Meyer, J. Am. Chem. Soc., 1997, 119, 12004. M. T. Indelli, F. Scandola, L. Flamigni, J.-P. Collin, J,-P. Sauvage, and A. Sour, Inorg. Chem., 1997,36,4247. M. D. Hossain, M. Wage, H. Monjushiro, B. Gholamkhass, and K. Nozaki, Chem. Lett., 1997,573. J. A. Treadwey, P. Chen, T. J. Rutherford, F. R. Keene, and T. J. Meyer, J. Phys. Chem. A , 1997,101,6824. S . E. Ronco, D. W. Thompson, S. L. Gahan, and J. D. Petersen, Inorg. Chem., 1998, 37,2020. B. W. Pfennig, J. K.Goertz, D. W. Wolff, and J. L. Cohen, Inorg. Chem., 1998, 37, 2608. A. P. da Silva, H. Q. N. Gunaratne, T. Gunnlaugsson, A. J. M. Huxley, and J. T. Rademacher, NATO ASI Ser., Ser. C , 1997,492 (Chemosensors of Ion and Molecule Recognition), 143. A. P. da Silva, H. Q. N. Gunaratne, T. Gunnlaugsson, A. J. M. Huxley, C. P. Mccoy, J. T. Rademacher, and T. E. Rice, Adv. Suprumol. Chem., 1997,4, I .

I: Photophysical Processes in Condensed Phases 556. 557. 558. 559. 560. 561. 562. 563. 564. 565. 566. 567. 568. 569. 570. 571. 572. 573. 574. 575. 576. 577. 578. 579. 580. 581. 582. 583. 584. 585. 586. 587.

51

J. N. Demas and B. A. DeGraff, J. Chem. Educ., 1997,74,690. Y. Shen and B. P. Sullivan, J. Chem. Educ., 1997, 74,685. L. Fabbrizzi, G. Francese, M. Liorhelli, P. Pallavicini, A. Perotil, A. Poggi, D. Succhi, and A. Taglietti, NATO ASI Ser., Ser. C, 1997, 492 (Chemosensorsof Ion and Molecule Recognition), 75. B. Valeur, F. Badaoui, E. Bardez, J. P. Lefevre, and A. Soulet, NATO ASI Ser., Ser. C, 1997,492 (Chemosensorsof Ion and Molecule Recognition), 195. J. D. Winkler, C. M. Bowen, and V. Michelet, J. Am. Chem. SOC.,1998, 120, 3237. I. K. Lednev. T.-Q. Ye, R. E. Hester, and J. N. Moore, J. Phys. Chem. A, 1997,101, 4966. K . Meuwis, N. Boens, F. C. De Schryver, M. Ameloot, J. Gallay, and M. Vincent, J. Phys. Chem. B, 1998,102,641. S. Sasaki, Y. Ando, M. Dejima, Y.Arikawa, and I. Korube, Anal. Chem., 1998,31, 555. G. J. Mohr, S. Drawler, K. Tranasel, F. Lehmann, and M. E. Lippitsch, And. Chim. Acta, 1998,360, 119. J . Yoon, N. E. Ohler, D. H. Vance, W. D. Aumiller, and A. W. Czernik, NATO ASI Ser., Ser. C, 1997,492 (Chemosensorsof Ion and Molecule Recognition), 189. J. Yoon, N. E. Ohler, D. H. Vance, W. D. Aumiller, and A. W. Czernik, Tetrahedron Lett., 1997,38, 3845. F. Unob, Z. Asfari, and J. Vicens, Tetrahedron Lett., 1998,39,2951. J. M. Price, W. Xu, J. N. Demas, and B. A. DeGraff, Anal. Chem., 1998, 70,265. A. P. da Silva, H. Q. N. Gunaratne, T. E. Rice, and S. Stewart, Chem. Commun., 1997,1891. P. D. Beer, F. Szemes, V. Balzani, C. M. Sala, M. G. Drew, S. W. Denti, and M. Maestri, J. Am. Chem. SOC.,1997,119, 11864. D. Parker, K. Senanayake, and J. A. G. Williams, Chem. Commun., 1997,1777. L. Fabbrizzi and I. Faravelli, Chem. Commun., 1998,971. K. A. Kneas, W. Xu, J. N. Demas, and B. A. DeGraff, Appl. Spectroscop., 1997,51, 1346. N . E. Azoz and J. J. Birmingham, J. Fluoresc., 1997, 7,227. K . P. McNamara, X. Li, A. D. Stull, and Z. Rosenweig, Anal. Chim. Acta, 1998,36, 73. F. Alava-Moreno, M. J. Valencia-Gonzalez, A. Sanz-Medel, and M. E. Diaz-Garcia, Analyst, 1997,122,807. A. Mills and F. C. Williams, Thin Solid Films, 1997,306, 163. N. Valesco-Garcia, M. J. Valencia-Gonzdez, and M. E. Diaz-Garcia, Analyst, 1997, 122, 1405. S.-K. Lee and 1. Okura, Anal. Sci., 1997,13,535. H. Chuang and M. A. Arnold, Anal. Chim. Acta, 1998,368,83. M. A. Mansour, W. B. Connick, R. J. Lachioette, H. J. Gysling, and R. Eisenberg, J. Am. Chem. SOC.,1998, 220, 1329. W. K. Hartmann, M. A. Mortellaro, D. G. Nocera, and Z. Pikramenou, NATO AS1 Ser., Ser. C, 1997,492 (Chemosensorsof Ion and Molecule Recognition), 159. S. H. Lieberman, Field Anal. Chem. Technol., 1998,2,63. G. Ellingsen and S. Fery-Forgues, Rev. Inst. Fr. Pet., 1998,53,201. H. Shinmori, M. Takeuchi, and S. Shinkai, J. Chem. SOC.,Perkin Trans 2, 1998,847. Q. Chang, Z. Murtaza, J. R. Lakowicz, and G. Rao, Anal. Chim. Acta, 1997,350,97. J . M. Costa-Fernandez, M. E. Diaz-Garcia, and A. Sanz-Medel, Sens. Actuators, B, 1997, B38,103.

52 588.

589. 590. 591. 592. 593. 594. 595. 596. 597. 598. 599. 600. 601. 602. 603. 604. 605. 606. 607. 608. 609. 610. 61 I. 612. 613. 614. 61 5. 616. 617. 618. 619. 620. 621. 622. 623. 624. 625.

Photochemistry

C. Parigger, D. H. Plemmons, R. J. Litchford, and S.-M. Jeng, Opt. Lett., 1998, 23, 76. A. Kawaski, Asian J. Spectrosc., 1997, I , 27. K. B. Migler and A. J. Bur, Polym. Eng. Sci., 1998,38,213. J. van Stam, S. Depaemelaere, and F. C. De Schryver, J. Chem. Educ., 1998, 75,93. K.-Y. Wong and W. W.-S. Lee, J. Photochem. Photobiol. A , 1997,102,231. R. Zana, L. In, H. Levy, and G. Duportail, Langmuir, 1997,13,5552. T. A. Kikteva, B. V. Zhmud, N. P. Smirnova, A. M. Eremenko, Y. Polevaya, and M. Ottolenghi, J. Collid InterJace Sci., 1997,193, 163. L. Zheng, W. R. Reid, and J. D. Brennan, Anal. Chem., 1997,69,3940. I. Black, D. J. S. Birch, D. Ward, and M. J. Leach, J. Fluoresc., 1997, 7, I 11. C. M. Marchi, S. A. Bilmes, and R. M. Negri, Lungmuir, 1997,13,3665. A. N. Diaz, J. Lovillo, and M. C. R. Peinado, Chem. Muter., 1997, 9,2647. N. Kimura and T. Araiso, Mol. Cryst. Liq. Cryst. Sci. Technol., Sect. A, 1997, 294, 149. Y. Agi and D. R. Walt, J. Polym. Sci., Part A; Polym. Chem., 1997,35,2105. S . Hu, R. Popielarz, and D. C. Neckers, Macromolecules, 1998,31, 4107. G. Moad, D. A. Shipp, T. A. Smith, and D. H. Solomon, Macromolecules, 1997,30, 7627. S. Morino and K. Horie, ACS Symp. Ser., 1997, 672 (Photonic and Optoelectronic Polymers), 260. M. H. Klopffer, L. Bokobza, and L. Monnerie, Macromol. Symp., 1997,119, 119. T. Shiga, T. Narita, T. Ikawa, and A. Okada, Polym. Eng. Sci., 1998,38,693. T. L. Longin, C. A. Koval, and R. D. Noble, Polym. Muter. Sci.Eng., 1997, 77,278. K. T. Chojnacki and D. A. Feikema, Appl. Opt., 1998,37,4034. N. Srividya, P. Ramamurthy, and V. T. Ramakrishnan, Spectrochim. Acta, Part A , 1997,53, 1743. M. Viard, J. Gallay, M. Vincent, 0. Meyer, B. Robert, and M. Paternostre, Biophys. J., 1997, 73, 222 1. H. Strausky, J. R. Krenn, A. Leitner, and F. R. Aussenegg, Appl. Phys. B: Lasers Opt., 1998,66, 599. R. Roberts, G. Walsh, A. Murray, J. Olley, R. Jones, M. Morwood, C. Tuniz, E. Lawson, M. Macphail, D. Bowdery, and I. Naumann, Nature, 1997,387,696. A. Bafter, J. Fluoresc., 1997, 7,99. J. Slavik, J. Lumin., 1997, 72, 575. G. Bendas, K. Schubert, and P. Nuhn, Pharmazie, 1998,53,43. M. Sisido, A h . Photochem., 1997,22, 197. K. A. Giuliano and D. L. Taylor, Trends Biotechnol., 1998,16, 135. M. Collini, G. Chirico, M. E. Bianchi, and G. Baldini, J. Lumin., 1997, 72,585. R . Sjoeback, C. M. Gustafsson, and M. Kubista, J. Lumin., 1997, 72, 610. J. Dapprich, N. G. Walter, F. Salingue, and R. Staerk, J. Fluoresc., 1997, 7, 87. D. Boturyn, A. Boudali, J.-F. Constant, E. Defranoq, and J. Lhomme, Telrahedron, 1997,53,5485. Y. Hamaguchi, M. Iwai, T. Uchida, H. Shimada, and M. Mitsuhashi, J. Environ. Health, 1997,60, 14. K. Yamana, S. Kumamoto, and H. Nakano, Chem. Lett., 1997, 1 173. Y. Kai and T. Maeda, J. Phys. Soc. Jpn., 1998,67, 1486. Instrumentation for Molecular Fluorescence Spectrometry, Anulyst, 1998,123, 1649. E. P. Browne and T. A. Hatbridge, NASA Con$ Publ., 1996, (Third Microgruvity Fluid Physics Conference), 667.

1: Photophysical Processes in Condensed Phases 626. 627. 628. 629. 630. 631. 632. 633. 634. 635. 636. 637. 638. 639. 640. 641. 642. 643. 644.

645.

646. 647. 648. 649. 650. 651. 652. 653.

53

L. Vetrivel and B. M. Sivaram, Proc. SPIE-Int. Soc. Opt. Eng., 1997,2980 (Advances in Fluorescence Sensing Technology III) , 360. A. George and G. Patonay, Talanta, 1997,45,285. G. N . Jones and C. T. Lee, J. Mol. Opt., 1998,45,283. S. A. Safvi, J. Liu, and T. F. Kuech, J. Appl. Phys., 1997,82, 5252. A. Kramer, T. Hartmann, and R. Eschrich, Ultramicroscopy, 1998, 71, 123. H. Monobe, A. Koike, H. Muramatsu, N. Chiba, N. Yamamoto, T. Ataka, and M. Fujihira, Ultramicroscopy, 1998, 71,287. S. Arnold, S. Holler, and G. L. Goddard, Muter. Sci. Eng. B, 1997,48, 139. Z. Zhang, G. J. Sonek, X. Wei, M. W. Berns, and B. J. Tromberg, Jpn. J. Appl. Phys., Part 2, 1997,36, L1598. L. Avanessian and V. Hovanessian, Proc. SPIE-Int. Soc. Opt. Eng., 1997, 2980 (Advances in Fluorescence Sensing Technology III), 42. J. R. Lakowicz, I. Gryczynski, H. Malak, and Z. Gryczynski, Proc. SPIE-Int. Sor. Opt. Eng., 1997,2980 (Advances in Fluorescence Sensing Technology III), 368. P. Allcock and D. L. Andrews, J. Chem. Phys., 1998,108,3089. W . G. Fisher, E. A. Wachter, F. E. Lytle, M. Armas, and C. Seaton, Appl. Spectrosc., 1998,52, 536. J. D. Bhawalkar, J. Swiatkiewicz, S. J. Pan, J. K. Sumarahundu, W. S. Liou, G. S. He, R. Berezney, P. C. Cheng, and P. N. Prasad, Scanning, 1996,18,562. D. A. Hatrick, A. Volkmer, Y. Bai, and D. J. S. Birch, Proc. SPIE-Int. Soc. Opt. Eng., 1997,2980 (Advances in Fluorescence Sensing Technology III), 48. A. Volkmer, D. A. Hatrick, and D. J. S. Birch, Meas. Sci. Technol., 1997,8, 1339 K . Kemnitz, L. Pfeifer, R. Paul, and M. Coppey-Moisan, J. Fluoresc., 1997, 7, 93. A. H. Buist, M. Muller, E. J. Gijsbers, G. J. Brackenhoff, T. S. Sosnowski, T. B. Norris, and J. Squier, J. Microsc., 1997, 186,212. F. R. Boddeke, L. K. Van Geest, and I. T. Young, Proc. SPIE-Int. Soc. Opt. Eng., 1997,2980 (Advances in Fluorescence Sensing Technology III), 35. K . Dowling, S. C. W. Hyde, N. P. Barry, J. C. Dainty, P. M. W. French, A. J. Hughes, M. J. Lever, A. K. L. Dymoke-Bradshaw, and P. A. Kellett, Proc. SPIEInt. Soc. Opt. Eng., 1997, 2980 (Advances in Fluorescence Sensing Technology I I I ) , 20. H. Itoh, A. Evenzahev, K. Kinoshita, Y. Inaguki, M. Toshimori, T. Hiroshi, F.Akira, H. Tadashi, T. Hayakawa, and A. Kusumi, Proc. SPIE-Int. SOC.Opt. Eng., 1997,2980 (Advances in Fluorescence Sensing Technology III), 12. D. McInskey, K. Suhling, and D. J. S. Birch, Proc. SPIE-Int. Soc. Opt. Eng., 1997, 2980 (Advances in Fluorescence Sensing Technology III) ,400. M . E. Lippitsch, S. Draxler, and D. Kieslinger, Sens. Actuators, B, 1997,38,96. A. Fultz, T. M. Branch, and V. Majidi, Microchem. J., 1997,57,231. E. Moutiez, P. Prognon, G, Mahuzier, P. Bourrinet, S. Zehaf, and A. Dencausse, Analyst, 1997,122, 1347. M . A. Dvorak, G. A. Oswald, M. H. Van Benthem, and G. D. Gillispie, Anal. Chem., 1997,69,3458. R. Levy, E. F. Guignon, S. Cobane, E. St. Louis, and S. M. Salvador, Proc. SPIEInt. Soc. Opt. Eng., 1997, 2980 (Advances in Fluorescence Sensing Technology III), 81. T . W. J. Gadella Jr., A. Van Hoek, and A. J. W. G. Visser, J. Fluoresc., 1997, 7, 35. J. A. Steinkamp, H. A. Crissman, B. E. Lehnert, N. M. Lehnert, and C. Deka, Proc. SPIE-Int. Soc. Opt. Eng., 1997, 2980 (Advances in Fluorescence Sensing Technology III), 96.

54 654. 655. 656. 657. 658. 659. 660. 661. 662. 663. 664. 665. 666. 667. 668. 669. 670. 671. 672. 673. 674. 675. 676. 677. 678. 679. 680. 681. 682. 683. 684. 685. 686. 687. 688.

Photochemistry

S. Aich and S. Basu, J. Phys. Chem. A , 1998,102,722. K. Nisizawa, Y. Sakaguchi, H. Hayashi, H. Abe, and G. Kido, RIKEN Rev., 1997, 15,49. S. Aich, S. Basu, and D. N. Nath, J. Photochem. Photobid. A , 1997, 109,95. J. C. Scaiano, S. V. Jovanovic, and D. G. Morris, J. Photochem. Photobiol. A , 1998, 113, 197. S. Aich and S. Basu, Chem. Phys. Lett., 1997,28,247. T. Nakai, M. Tani, S. Nishio, A. Matsuzaki, andH. Sato, Chem. Lett., 1997,795. N. K. Petrov, W. Kuehale, T. Fiebig, and H. Staerk, J. Phys. Chem. A, 1997, 101, 7043. T. Fiebig, W. Kuehnle, and H. Staerk, J. Fluoresc., 1997, 7,29S. M. H. Kleinman, T. Shevchenko, and C. Bohne, Photochem. Photobiol., 1998, 67, 198. M. Sacher and G. Grampp, Ber. Bundsenges-Ges., 1997,101,971. N. Ohta, T. Ito, S. Okazaki, and I. Yamazaki, J. Phys. Chem. B, 1997,101, 10213. S. Umeuchi, Y. Nishimura, I. Yamazaki, H. Murakami, M. Yamashita, and N. Ohta, Thin SolidFilms, 1997,31,239. M . Goez, Adv. Photochem., 1997,23,63. A. N. Savitsky, S. N. Batchelor, and H. Paul, Appl. Magn. Resun., 1997,13,285. Y. Kimura, K. Sugihara, M. Terazima, and N. Hirota, Bull, Chem. Sue. Jpn., 1997, 70,2657. E . Vauthey and A. Henseler, J. Photochem. Photobiol. A, 1998,112, 103. K. Okamoto, N. Hirota, and M. Terazima, J. Phys. Chem. A , 1997,101,5269. M . Terazima, J. Phys. Chem. A, 1998,102,545. D. V . Khodyakov, I. V. Rubtsov, and V. A. Nadtochenko, Res. Chem. Intermed., 1997,23,479. J. R. Torga, J. L. Etcheverry, and M. C. Marconi, Opt. Commun., 1997,143,230. M . Fischer and J. Georges, Spectrochim. Acta, Part A , 1997,53, 1419. B. G. Barisas, H. M. Munnelly, and D. A. Roess, Proc. SPIE-Int. SOC.Opt. Eng., 1997,2980 (Advances in Fluorescence Sensing Technology III), 523. J. A. Elliott, G. Rumbles, A. J. De Mello, and H. L. Anderson, Muter. Res. SOC. Symp. Pruc., 1997,464 (Dynamics in Small Confining Systems III), 295. Y. Yamakage, T. Nagashima, K. Mineda, H. Murai, and T. Azumi, Appl. Magn. Reson., 1997,12,441. L, B. Luo, G. Li, H. L. Chen, S. W. Fu, and S. Y. Zhang, J. Chem. Soc., Dulton Trans., 1998,2103. M. Barra and K. A. Agha, J. Photochem. Photobiol. A, 1997,109,293. S. Hishimoto, J. Chem. Soc., Faruday Trans., 1997,93,4401. C . L. Maupin, S. C. J. Meskers, H. P. J. Dekkers, and J. P. Riehl, J. Phys. Chem. A, 1998,102,4450. S. Salhi, S. G. Koulikov, C. Bied-Charreton, and J.-F. Galaup, J. Lumin., 1998, 78, 187. I. Renge, H. Wolleb, H. Spahni, and U. P. Wild, J. Phys. Chem. A , 1997,101,6202. B. Plagemann, I. Renge, A. Renn, and I. P. Wild, J. Phys. Chem. A, 1998,102, 1725 M. D. Edington, R. E. Riter, and W. F. Beck, J. Phys. Chem. B, 1997,101,4473. E. L. Wehry, Molecular Fluorescence and Phosphorescence Spectrometry, in Hundbook Instrum. Tech. Anal. Chem,. ed. F.A. Settle, Prentice Hall, Upper Saddle River, NJ, 1997, pp 507-539. M. R. Gehlen, Chem. Phys., 1997,224,275. M. Dalibart, Talanta, 1997,44,223 1 .

I : Photophysical Processes in Condensed Phases

55

D. H. Leaback, J. Fluoresc., 1997, 7,55. L. A. Kelly, J. G. Trunk, and J. C. Sutherland, Proc. SPIE-Int. Soc. Opt. Eng., 1997, 2980 (Advances in Fluorescence Sensing Technology I I I ) , 2. 691. V . Apanasovich, E. G. Novokov, and N. N. Yatskov, Proc. SPIE-Int. Suc. Opt. Eng., 1997,2980 (Advances in Fluorescence Sensing Technology III), 516. 692. Z. Y. Zhang, T. Sun, K. T. V. Grattan, and A. W. Palmer, Proc. SPIE-Int. Soc. Opt. Eng., 1997,2980 (Advances in Fluorescence Sensing Technology III), 90. 693. S. L. Neal, Anal. Chem., 1997,69,5109. 694. V . M. E. Schenkeveld and I. T. Young, J. Fluoresc., 1997,7,55. 695. C. G. Morgan, A. C. Mitchell, J. G. Murray, and E. J. Wall, J. Fluoresc., 1997, 7,65. 696. A. Molski and N. Boens, J. Phys. Chem. A, 1997, 101, 5124. 697. V. A. Morozov, Opt. Spektrosk., 1997,83,227. 698. P. C. Schneider and R. M. Clegg, Rev. Sci. Instrum., 1997,68,4107. 699. C. Dusan Jr., C. Dusan, and S. Libusa, J. Fluoresc., 1997, 7,45. 700. I. Gryczynski, Z. Gryczynski, and J. R. Lakowicz, Proc. SPIE-Int. Soc. Opt. Eng., 1998,2256 (Advances in Optical Biophysics), 40. 701. J. Enderlein, D. L. Robbins, W. P. Ambrose, P. M. Goodwin, and R. A. Keller, Proc. SPIE-Int. SOC. Opt. Eng., 1997, 2980 (Advances in Fluorescence Sensing Technology III) , 4 6 1. 702. J. C. Fister I11 and J. M. Harris, Anal. Chim. Acta, 1997,348, 31 1. 703. A. A. Angeluts, N. IL. Koreteev, S. A. Magnitskii, 1. A. Ozheredov, and A. P. Shukuronov, Proc. SPIE-Int. Soc. Opt. Eng., 1998, 3347 (Optical Recording Mechanisms and Media), 228. 704. M. Itaguki, M. Hosono, and K. Watanabe, Anal. Sci., 1997,13, 891. 705. K . Starchov, J. Zhang, and J. Buffie, J. Collid. Interface Sci., 1998,203,289. 706. R. L. Hansen, N. R. Zhu, and J. M. Harris, Anal. Chem., 1998, 70, 1281. 707. R. L. Hansen and J. M. Harris, Anal. Chem., 1998, 70,2565. 708. J. S. Burmeister, L. A. Olivier, W. M. Boitchert, and G. A. Truskey, Biomaterials, 1998, 19,307. 709. M. T. Martin and D. Mobius, Supramol. Sci., 1997,4,381. 710. T. Asakawa, A. Sareta, and K. Miyagishi, Colloid. Polym. Sci., 1997,275,958. 71 1. N. C . Maiti, M. M. G, Krishna, P. J. Britto, and N. Periasamy, J. Phys. Chem. B, 1997,101, 11051. 712. J . M. Kavaleski and M. J. Wirth, Anal. Chem., 1997,69,600. 713. A. Morita and Q. Tran-Cong, Physica A (Amsterdam), 1997,242,377. 714. J. Arden-Jacob and K. H. Drexhage, J. Fluoresc., 1998,7,91. 689. 690.

Part II Organic Aspects of Photochemistry

1

Photolysis of Carbonyl Compounds BY WILLIAM M. HORSPOOL

As in previous years there is a continued swing away from the more traditional areas of study. This feature is obvious not oniy in this chapter but also in the other two compiled by this reviewer. Interest in organic photochemistry is clearly not on the wane, however, and there are still as many publications as in past years. Some topics of general interest have been addressed during the past year. Thus the results from a study of exchange interactions between donors such as triphenylamine and N,N,N',N'-tetramethylbenzidine and ketonic acceptors (xanthone, duroquinone and 2,3-dimethoxy-5-methylbenzoquinone) have been published.' The influence of so-called spectator molecules (e.g. pyridine) upon the intrazeolite chemistry of ketones such as benzophenone, xanthone and p methoxy-Pphenylpropiophenonehas been studied.2 The results of the irradiation of the radical cation of dimethylformamide in a matrix at 77 K have been publi~hed.~ A laser-flash examination of the ketones (1-3) has been carried out? The photochemical reactions of some a-aryloxyacetophenones have been studied and the results obtained compared and contrasted with those obtained from thermolysis experiment^.^ Many products were obtained from these reactions. aPhenoxyacetophenone undergoes photochemical changes when it is irradiated as a complex with fkyclodextrin either in the solid state or in aqueous solution.6 In the solid state a-fission occurs and products of recombination are formed. In solution hydrogen abstraction is the principal reaction.

1

Norrish Type I Reactions

A laser flash study of the photochemistry of acetone has examined the polarization induced by irradiati~n.~ The author suggests that this study shows the

Photochemistry, Volume 30 0The Royal Society of Chemistry, 1999

60

Photochemistry

possibility of a two photon process for a-cleavage. Ketones such as (4) are often used as initiators in industrial polymerization processes under high light intensity irradiation conditions. Faria and Steenken have examined the photoreactivity of such compounds in polar solvents using laser light sources.* They have observed that on irradiation of (4) at 248 nm Norrish Type I fission occurs to yield the radical ( 5 ) . Second photon irradiation at 308 nm brings about the formation of the cation (6) by oxidation of the radical. The authors suggest that such a step might also be involved in industrial photocuring. 0 OMe II I Ph-C-C-Ph I OMe (4)

OMe I Ph-CI OMe

(5)

OMe I PhC' I OMe (6)

A CIDNP study of the irradiation of (7) has shown that a-fission occurs on irradiation.' The resultant radical (8) eliminates diethyl phosphoric acid and yields the radical cation (9). When irradiation is carried out in methanol this species is trapped as the ether (10). Other products are methyl benzoate and the acetal(l1). A laser irradiation study of the reaction of acetophenone with amines constrained in NaY zeolites has been carried out and evidence has been collected that shows that ketyl and amino radicals are formed by hydrogen abstraction pathways. lo

The photochemical reactions of the ketones (12) which are used as sunscreens in cosmetics has shown that degradation is considerable when they are irradiated as thin films. Norrish Type I reactions dominate affording benzoic acid derivatives.' I A study of the biradicals formed on flash photolysis of the ketone (1 3) has been reported.12 The reaction involves a Norrjsh Type I process and yields an acyl-ketyl biradicai that transforms into an alkyl-ketyl biradical by decarbonylation.

R*

'

(12) R' = R2 = Pr' R' = But, R2 = Me0

a 0 Me R'

(13)

OH

IIII: Photolysis of Carbonyl Compounds

2

61

Norrish Type I1 Reactions

2.1 1,SHydrogen Transfer - The Norrish Type I and Type I1 photochemical behaviour of pentan-2-one constrained in zeolite cavities has been studied.13 The series of ketones (14) all undergo Norrish Type I1 elimination of acetophenone when irradiated.14 A study of intramolecular energy transfer was carried out using these compounds. Wessig and co-workers have examined the photochemical reactivity of the bridged ketones (15).15 Ring-size was found to be one of the controlling factors on the outcome of the reactions. The ketone (16) undergoes Norrish Type I1 hydrogen abstraction. However, a cyclobutanol is not formed in this case but instead the resultant l,.l-biradical (17) fragments to yield the alkene (18).16 The reaction is reasonably efficient and a quantum yield of 0.2 was measured for the reaction in benzene as solvent. The same reaction is observed when (16) is irradiated in the solid state. H 0

(14) Ar = Ph, n = 3,4,5, 7, 10 or 11 Ar = 2-naphthyl, n = 3, 4, 5 6 , 7, 9, 10, 11 or 14 Ar = 4-biphenyly1, n = 3-7, S 1 1 or 14

Me

CN

CN

OH

Me NC

Me

Considerable interest continues to be shown in photoenolization reactions. Results from the study of reaction volume changes in the photoenolization of 2methyl benzophenone have been reported. l7 o-Benzylbenzophenone (1 9) is photochemical reactive and undergoes a Norrish Type I1 transformation into an enol.'* Cyclization of this intermediate affords the cyclobutenol (20) quantitatively. A detailed study of the factors that control the formation of o-xylylenes (the photoenols) by the photoenolization of alkylphenyl ketones such as (19) and (21) has been reported. The product selectivity appears to correlate with the geometries of the twisted xylylene triplet state. l9 The photoenolization of the aldehyde (22, R = H) and ketone (22, R = CH3) has been reported.*' The photoenol (23, R = H) can be obtained from the aldehyde and cycloaddition of acrolein yields the dihydronaphthalene derivative (24). The photoenol of the ketone (23, R = CH3) undergoes ring closure to the cyclobutenol (25). The cyclobutenol is thermally reactive and can be ring opened to reform the enol that can also undergo thermal cycloaddition reactions with suitable dienophiles. The synthetic utility of such photoenolization reactions continues to be of interest. Thus, the photochemistry of the aldehydes (26) has been examined using

Photochemistry

62 Me

Ph

Ph

OMe 0

Ph

OMe

OMe OH

OMe

Pyrex-filtered irradiation in de-aerated acetonitrile solution. The resultant enols can be trapped by dimethyl maleate to yield the adducts (27) and (28) in the ratios and yields shown.21Trapping of the enols can also be acomplished using dimethyl acetylenedicarboxylate or ethyl propiolate as the dienophile. A study of the phototautomerism of methyl salicylate (29) into (30) at 77 K has been carried out and this again involves a 1$-hydrogen transfer.22 Interestingly, the authors report that triplet state emission occurs from the transient keto form (30). The influence of aryl substituents (p-Me and p-MeO) upon the photochemically induced intramolecular proton transfer in salicylic acid has also been studied in

(26) n=1,2or3

(27)

Ratio Yield (YO)

06Me

12: 1 15: 1 3:l OYoMe

(28)

10 70 40

2.2 Other Hydrogen Transfers - Irradiation (h =- 300 nm) of the ketoamines (31) in methanol solution results in the formation of the cyclopropanols (32) via the triplet excited state of the arylketo function.24 The reactions involve 1,4hydrogen transfer processes and the yields range from modest to good. The

MI: Photolysis of Carbonyl Compounds

63 HO R2 R3

NR2'

R2

R3

R4 Yield (YO)

Morpholino

H H H H H

H H H

H CN F Ci Br

H

H

46

75

43 42 20

authors reason that the regioselectivity involved, where hydrogen abstraction occurs from the site next to the amino function, must be due to preferred chargetransfer interaction between the benzoyl and the amino groups. The hydrogen abstraction reactivity of the benzophenone derivatives (33) involves a 1,6-transfer and has been studied in various solvents.25The key step on irradiation is the formation of the corresponding 1,5-biradical produced on hydrogen abstraction from the 8-methylene group of the ether function. When the irradiations are carried out in benzene the furanols (34) are formed in 80-94% by ring closure of the 1,5-biradical. The ratio of cis:trans-isomers ranged from 12:1 to 1:O dependent upon the substituent R. The yields of products were poorer in acetonitrile than in methanol and a decreased selectivity was also observed. A further study of the photochemical cyclization of the arylketones (35) has sought to evaluate the effects of solvents and substituents on the outcome of the reactions.26The cyclizations follow the normal &hydrogen abstraction path that leads to the benzofuranols (36). 0

(33) R = H, Me, Et, Pri, Ph, CH=CH2, CN

(34)

(35) (36) R' = H, Me, Et or Pri, R2 = CH2Phor CH2CQEt

&-Hydrogen abstraction is the outcome of irradiation of the amides (37) in methylene chloride solution.27The site of the hydrogen abstraction is controlled to some extent by the presence of hetero atom. The resultant 1,6-biradical undergoes cyclization to afford (38) and (39) with high diastereoselectivity as

Photochemistry

64

ph 350 nm.53 In the presence of t-butylthiol the products formed were identified as the cyclopropane derivatives (81) and (82). With different hydrogen donors such as tri-n-butyltin hydride the products obtained are cyclopropenes (83) and (84). The cyclopropane (85) is also photoreactive and in THF/water yields the cyclopropane (86). The authors suggest that the cyclopropene double bond in (80) is particularly prone to undergo addition reactions and that the thiol adds prior to the photochemical decarboxylation. Iminocarbene (87) are formed by the loss of carbon dioxide on irradiation of the dihydroisoxazoles (S8).54 The irradiation can be effected by either 254 or 300 nm but the best conditions involve the latter wavelength with (88) in acetone or acetonitrile solution. The yields for some of the compounds studied are shown in Scheme 3. Some level of substituent dependency is obvious from the variation in

Mi:Photolysis of Carbonyl Compounds

69

the yields of the oxazoles obtained. The thio analogues (89) are similarly reactive and yield the thiazoles (90), again in reasonable yields.55The path to the thiazoles occurs in competition with a reaction mode leading to the formation of the oxazines (91).55

Me PhCH2 Ph Me Ph

H H Me Ph Me

C02Et C02Et CGEt H H

Scheme 3

65 88 30 29 24

70

Photochemistry

A study of matrix isolated 1,2,3,4-benzenetetracarboxylicdianhydride has provided evidence for the formation of 1,3,5-he~atriyne.~~ The possibility of the formation of C6H2 by photochemical extrusion of carbon dioxide and carbon monoxide was discussed.

4.2 Reactions of Miscellaneous Haloketones - Acetyl chloride undergoes photochemical loss of HCl when irradiated either neat or in a matrix.57 Irradiation of 3-chloropropanoyl chloride in a matrix using wavelengths greater than 230 nm yields 3-chloro- I ,2-propenone and acryloyl chloride as the principal photochemical products.58 Further studies on the photochemical reactivity of a-haloacetophenone derivatives have been reported. The results in the present publication have shown that the acetophenone derivatives (92)undergo a variety of reactions but the one of interest is the Favorskii type rearrangement where by a 1,2-aryl migration occurs to yield an acyl cation that can form a carboxylic acid d e r i ~ a t i v e .The ~~ investigation examined the influence of media on the outcome of the reaction and some of the results are illustrated in Scheme 4.The best yields of carboxylic acids, the products formed via the acyl cation path, are obtained in aqueous acetonitrile. The singlet states of the ketones (93) and (94) are reactive and undergo elimination of halide to form aroylmethyl radicals.60 These then rearrange to arylacetyl radicals by a 1,2-aryl migration. Subsequent decarbonylation yields the arylinethyl radicals (95)and these have been detected spectroscopically. 0 Ar

Ar

Ar-CQR

aq. acetone (i) (ii)(R=H) (iii) 37 24 16 10

24 47

43 14

29 23 14 31

aq. CH3CN (i) (ii)(R=H) (iii) 14 14 9 6

47 70 54 35

18 11 8 18

Scheme 4 Br

The ester (96) undergoes electron transfer photochemistry on irradiation in acetonitrile solution in the presence of the amine (97).61The SET process brings about the expulsion of bromide and produces the radical (98). This radical undergoes ring expansion by the path illustrated in Scheme 5 to yield the final product (99). This product can be accompanied by varying amounts of the

IIl I : Photolysis of Carbonyl Compounds

71

t COz Et

(104)

Yield

2

TMS

2 2 1 1

Et H TMS TMS TMS

CH;!

coH20 0

NHBoc

(YO) Ratio E : Z

74 61 72 68 64 51

3:l 1:l

-

5:3 3:l

-

reduced ester (100) and the dimer (101). However, these reaction paths can be suppressed by the addition of water to the reaction system with the best yields of (99) being obtained by radiation in 30% aqueous acetonitrile. Irradiation of the iodoketones (102) under electron transfer conditions (with triethylamine as the donor and acetonitrile as solvent) brings about C-I bond fission and the formation of the radical (103).62 These radicals undergo cyclization with the alkyne moiety in the side chain to yield ultimately the products (104) in the yields shown. 4.3 Photo Reactions of Esters and Photodeprotection - Laser irradiation at 183 nm of a series of alkyl acetates has been reported.63The aryl phenylacetates (105) undergo photo-Fries reactions when irradiated in acetonitrile solution.@ The reactivity is appreciably more selective when they are irradiated within the cavities in NaY zeolites. Under these conditions only the ortho photo-Fries product is formed. The oxime derivative (106) undergoes N-O bond fission when the compound is irradiated on a micellar surface.65Such bond fission results in

72

Photochemistry

both 1,3- and 1,5-benzoyloxy migration to afford products such as (107) from the former process. These products are also accompanied by the decarboxylation product (108). A detailed analysis of the influence of benzyl alcohol and of the presence of bromide ion (a heavy atom) on this fission were also described. The outcome of the photolyses of the esters (109) and (110) in pentasil or faujasite zeolites has been shown to be extremely sensitive to the zeolite structure.66 A mechanistic study of the single electron transfer reactivity of the esters (1 1 1) has been reported.67

(105) A r = Ph Ar = pMeC6H4 Ar = oMeC6H4

(108) R = l-naphthyl

(106)

0

Considerable interest has been shown in derivatives of esters that can be photodeprotected. One of the more common of these is the 3’,5’-dimethoxybenzoin ester system. A reinvestigation of the photochemistry of this system has suggested that the reaction does not involve attack by the carbonyl oxygen on the dimethoxy substituted benzene ring.68Instead from the detailed examination, it is proposed that a charge transfer, or perhaps an electron transfer, occurs between the electron-rich dimethoxy substituted ring and the carbonyl group within (1 12), for example. This results in the formation of the cation (1 13) with the release of the acid group. Deprotonation of (1 13) affords the furan byproduct. A new method has been described for the protection of amino acids with a photoremovable This procedure involves the conversim of the amino acid into the phenacyl derivative (1 14). Irradiation of (1 14) in a buffered aqueous

+ CH3CO2-

R (112) R = Me, PhCH2, Ph or But

(1 13)

73

IIil: Photolysis of Carbonyl Compounds

solution results in the release of the amino acid and the transformation of the phenacyl group into a phenylacetic acid. The reaction proceeds by way of the triplet state from which there is intramolecular displacement of the amino acid moiety as represented in (1 15). The resultant intermediate (1 16) undergoes ring opening by attack of water to afford thep-hydroxyphenyl acetic acid as the byproduct of the deprotection. The use of single electron transfer activation has been applied to this area of study and in particular to the phenacyl esters (1 17).70 These undergo cleavage with the release of the acid by a path in which an electron is transferred on irradiation from amines such as (1 18) to yield the radical anion

&

HO (114) R = - C H ~ C H Z C H ~ ) ; ~ H ~ R = -CH&HCO2I NH3+ R = -CHNHCOCHCH3

LOGoMeI

I

NH3+

CH3

0 PhCMe II +

Ph

Me0

0

Scheme 6

0

0

OH

(117) R =

A,,,.,, H

I OMe

NMe2

0

OH

74

Photochemistry

intermediate (1 19). This undergoes fission to yield the anion radical pair (120) from which acetophenone and the carboxylic acids are formed in excellent yield. One example of this process is shown in Scheme 6 where the yield of 3methoxycyclohexane carboxylic acid is quantitative. Related to this work is the report dealing with the photochemistry of phenacyl protecting group^.^' These simple systems such as (121) undergo cleavage to phenylacetic acid and acetophenone. The efficiency of the reaction is solvent dependent and irradiation in benzene, for example, fails to yield products. However, when a hydrogen donating reagent, such as 2-propanol or tri-n-butyltin hydride, is present the irradiations are very efficient. The authors suggest that a hydrogen abstraction rather than a C-0 bond cleavage is involved as the primary photochemical step. Thus irradiation affords the radical (122) which is trapped by, for example, an isopropoxy radical. The intermediate (123) then collapses to the observed products.

Other Fission Processes - Considerable use is being made of radical reactions in organic synthesis. For example, Deng and Kutateladze have described a novel method for the synthesis of esters.72This involves the irradiation of the ester (124) in the presence of terminal alkenes. Unfiltered light from a medium pressure mercury arc lamp results in the fission of the S-methylene bond and the formation of a radical which adds to the alkenes. The yields obtained are reasonable with acetonitrile as the solvent. Other solvents such as methanol or ethanouwater can also be used. Yields of the products obtained are shown in Scheme 7. 4.4

Yield (YO) 70 0

n=l

84

n = 3 90

0

21

45

Scheme 7

The acetone-sensitized decarbonylation of E-( 1S),2(S) (125a) has been studied. The principal reaction is the formation of the 2(S),3(R)-cyclopropane (126a).73 Other products (127a), (128a) and (129a) are also formed in low yield. The reaction arises from the triplet state and this was confirmed by using Michler's ketone as the sensitizer and by quenching experiments. A similar selectivity is

75

IIII: Photolysis of Carbonyl Compounh

k2

R’ (125) a: R’ = R2 = CH20Bz b: R’ = CH~OBZ,R2 = H

(126)

a: 53

b: 86

(127) 17

-

R’ (128) 19 10

R’

R2

(129) 5 Yield (YO) Yield (YO)

-

reported for the 2(S)-ketone (1 25b) which affords the cyclopropane (126b) as the principal product. This reaction is more selective and only one by-product (128b) is formed. The photochemical aromatization of the bicyclodienones (1 30) has been reported.74 The major products obtained were identified as (131) and arose by extrusion of ketene.

References

5

1. 2.

3. 4.

5. 6. 7. 8. 9. 10. 11. 12. 13.

14. 15.

S. Sekiguchi, Y. Kobori, K. Akiyama and S. Tero Kubota, J. Am. Chem. Soc., 1998, 120, 1325. J. C. Scaiano, M. Kaila and S. Corrent, J. Phys. Chem., 1997,101, 8564. M. Ya. Mel’nikov, V. N. Belevskii, S. I. Belopushkin and 0. L. Mel’nikova, Russ. Chem. Bull., 1997,46, 1245 (Chem. Abstr., 1997,713770). S . V. Jovanovic, D. G. Morris, C. N. Pliva and J. C. Scaiano, J. Photochem. Photobiol. A , 1997,103, 153 (Chem. Abstr., 1997,127,240808). A. E.-A. M. Gaber, Bull. Pol. Acad Sci., Chem., 1997,44,235 (Chem. Abstr., 1997, 437582). N. C. De Lucas and J. C. Netto-Ferreira, J. Photochem. Phorobiol. A, 1997, 103, 137 (Chem. Abstr., 1997,127,72894). Sh. A. Markaryan, Arm. Khim. Zh., 1996,49,71 (Chem. Abstr., 1998,256773). J. L. Faria and S. Steenken, J. Chem. Soc., Perkin Trans. I , 1997, I 153. A. Gugger, B. Batra, P. Rzadek, G. Rist and B. Giese, J. Am. Chem. Soc., 1997, 119, 8740. J. C. Scaiano, S. Garcia and H. Garcia, Tetrahedron Lett., 1997,38, 5929. W . Schwack and T. Rudolf, GIT Lab. J., 1997, 17 (Chem. Abstr., 1997,595520). 0. B. Morozova, A. V. Yurovakaya, V. Alexandra, Y. P. Tsentalovich, R. Z. Sagdeev, T. Wu and M. D. E. Forbes, J. Phys. Chem. A, 1997,101,8803. H. Yamashita, N. Sato, M. Anpo, T. Nakajima, M. Hada and H. Nakatsuji, Stud. SurJ Sci. Catal., l997,105B, 1141 (Chem. Abstr., 1998,128, 183387). P. Klan and P. J. Wagner, J. Am. Chem. SOC.,1998,120,2198. P. Wessig, J. Schwarz, D. Wulff-Molder and G. Reck, Monatsh. Chem., 1997, 128, 849 (Chem. Abstr., 1997,127,331378).

76 16. 17. 18. 19. 20. 21. 22 23. 24. 25. *

26. 27. 28. 29. 30. 31. 32. 33. 34. 35. 36. 37. 38. 39. 40. 41. 42. 43. 44. 45. 45. 46. 47. 48. 49.

Photochemistry

T. Y. Kim, E. S. KO, B. S. Park, H. Yoon and W. K. Chae, Bull. Korean Chem. Soc., 1997,18,439 (Chem. Abstr., 1997,127,65424). M. Terazima, J. Phys. Chem. A , 1998,102,545. M. Sobczak and P. J. Wagner, Tetrahedron Lett., 1998,39,2523. P. J . Wagner, M. Sobczak and B.4. Park, J. Am. Chem. SOC.,1998,120,2488. G. A. Krauss and G. Zhao, Synlett, 1995,541. T. J . Connolly and T. Durst, Tetrahedron, 1997,53, 15969. J . Catalan and C. Diaz, J. Phys. Chem. A, 1998,102,323. F. Lahmani and A. Zehnacker-Rentien, J. Phys. Chem., 1997,101,6141. W. Weigel, S. Schiller and H.-G. Henning, Tetrahedron, 1997,53,7855. E. Sharshira, M. Essam, M. Okamura, E. Hasegawa and T. Horaguchi, J. Heterocycl. Chem., 1997,34,861 (Chem. Abstr., 1997,127, 161648). E. M. Sharshira and T. Horaguchi, J. Heterocycl. Chem., 1997, 34, 1837 (Chem. Abstr., 1998, 128, 180290). U. Lindemann, G. Reck, D. Wulff-Molder and P. Wessig, Tetrahedron, 1998, 54, 2529. T. Hasegawa, Y. Yamazaki and M. Yoshioka, J. Photosci., 1997,4,7 (Chem. Abstr., 1997,127, 121403). S. A. Fleming and J. J. Gao, Tetrahedron Lett., 1997,38, 5407. T . Bach, J. Schroder, T. Brandl, J. Hecht and K. Harms, Tetrahedron, 1998, 54, 4507. T. Bach and J. Schroder, Liebigs AndRecueil, 1997,2265. T . Bach, , Liebigs AmlRecl., 1997, 1627. D. Sengupta, A. K. Chandra and M. T. Nguyen, J. Org. Chem., 1997,62,6404. C. R. Silva and J. P. Reilly, J. Phys. Chem. A , 1997,101, 7934. T. S. Sorensen and F. Sun, Can. J. Chem., 1997,75, 1030. D. Leinweber and H. Butenschon, Tetrahedron Lett., 1997,38,6385. J. C. Netto-Ferreira, V. Wintgens and J. C. Scaiano, J. Braz. Chem. SOC.,1997, 8, 427 (Chem. Abstr., 1997,620850). G. Maier, H. P. Reisenauer and R. Ruppel, Angew. Chem., Znt. Ed. Engl., 1997, 36, 1862. N. Sahoo, Orient J. Chem., 1997,13,53 (Chem. Abstr., 1997,428330). F . Nakashini, J. Nagasawa, M. Yoshida and H. Abdedaal, J. Photopolym. Sci. Technol., 1997,10,25 (Chem. Abstr., 1997,127,227215). H. Koshima, H. Nakagawa and T. Matsuura, Tetrahedron Lett., 1997,38,6063. H. Koshima, K. L. Ding, Y. Chisaka and T. Matsuura, J. Am. Chem. Soc., 1996, 118, 12059. Y. Ito, Synthesis, 1998, 1. Z . Zhou, W. Jiang and W. Liu, Huanjing Kexue, 1997, 18, 35 (Chem. Abstr., 1997, 683592). F. Benoit-Marquie, E. Puech-Costes, A. M. Braun, E. Oliveros and M.-T. Maurette, J. Photochem. Photobiol., A, 1997,108,73 (Chem. Abstr., 1997,127,285784). J . Cossy, S. BouzBouz and A. Hakiki, Tetrahedron Lett., 1997,38,8853. L. J . Martinez and J. C. Scaiano, J. Am. Chem. Soc.. 1997,119,11066. S. Monti, S. Sortino, G. De Guido and G. Marconi, J. Chem. SOC.,Faraday Trans., 1997,93,2269. Y. Kawai and K. Matsubayashi, Chem. Pharm. Bull., 1998, 46,131 (Chem. Abstr., 1998,128, 184585). C. Laurich, H. Gorner and H. J. Kuhn, J. Photochem. Photobiol. A, 1998, 112, 29 (Chem. Abstr., 1998, 128, 160840).

IIII: Photolysis of Carbonyl Compounds 50. 51. 52. 53. 54. 55. 56. 57. 58. 59. 60. 61. 62. 63. 64. 65. 66.

67. 68. 69. 70. 71. 72. 73. 74.

77

D. R. Prudhomme, Z. Wang and C. J. Rizzo, J. Org. Chem, 1997,62,8257. D. H. R. Barton and W. S. Liu, Tetrahedron, 1997,53, 12067. D. H. R. Barton and W.-S. Liu, Tetrahedron Lett., 1997,38,367. M . Cano, G. Fabrias, F. Camps and J. Joglar, Tetrahedron Lett., 1998,39, 1079. R. H. Prager, J. A. Smith, B. Weber and C. M. Williams, J. Chem. Soc., Perkin Trans. I , 1997,2665. R. H. Prager, M. R. Taylor and C. M. Williams, J. Chem. Soc., Perkin Trans. I , 1997,2673. M. Moriyama and A. Yabe, Chem. Lett., 1998,337. B. Rowland and W. P. Hess, J. Phys. Chem. A , 1997,101,8049. N. Pietri, J. Piot and J.-P. Aycard, J. Mol. Strucf., 1998, 443, 163 (Chem. Abstr., 1998, 198458). D. D. Dhavale, V. P. Mail, S. G. Sudrik and H. R. Sonawane, Tetrahedron, 1997,53, 16789. M. Hall, L. Chen, C. R.Pandit and W. G. McGimpsey, J. Photochem. Photobiol. A , 1997,111,27 (Chem. Abstr., 1998,128, 121513). E. Hasegawa, Y. Tamura and E. Tosaka, J. Chem. Soc., Chem. Commun., 1997, 1895. C.-K. Sha, K. C. Santhosh, C.-T. Tseng and C.-T. Lin, J. Chem. Soc., Chem. Commun., 1998,397. M. Wasche, U. Bruckner and E. Linke, Laser Med., Vortr. 10. Tag. Dtsch, Ges. Lmermed 12. Int. Kongr., 1995,645 (Chem. Abstr., 1997,127, 168900). C. H. Tung and Y. M. Ying, J. Chem. Soc.. Perkin Trans. 2, 1997, 1319, T. Kaneko, K. Kubo and T. Sakurai, Tetruhedron Lett., 1997,38,4779. C.-H. Tung and Y.-M. Ying, Res. Chem. Intermed., 1998,24, 15 (Chem. Abstr., 1998, 78146). M. P. D. De Costa, P. K. Cumaranatunga and K. A. D. Sriyanimallika, J. Natl. Sci. Counc. Sri Lanka, 1997,25, 127 (Chem. Abstr., 1998,128,47936). Y. Shi, J. E. T. Corrie and P. Wan, J. Org. Chem., 1997,62,8278. R. S. Givens, A. Jung, C. H. Park, J. Weber and W. Barlett, J. Am. Chem. Soc., 1997,119,8369. A. Banerjee and D. E. Falvey, J. Org. Chem., 1997,62,6245. A. Banerjee and D. E. Falvey, J. Am. Chem. SOC.,1998,120,2965. L. X. Deng and A. G. Kutateladze, Tetrahedron Lett., 1997,38,7829. J. Ramnauth and E. Lee-Ruff, Can. J. Chem., 1997,75, 518. A. A. Bogachev and L. S. Kobrina, Russ. J. Org. Chem., 1997, 33, 681 (Chem. Abstr., 169148).

2

Enone Cycloadditions and Rearrangements: Photoreactions of Dienones and Quinones BY WILLIAM M. HORSPOOL

1

Cycloaddition Reactions

1.1 Intermolecular Cycloaddition - Cycloaddition reactions continue to be a valued route to compounds that are key intermediates in the synthesis of natural products or other compounds of general interest.

I. 1. I Open-chain Systems - Several reports over the last few years have made use of the pentenoate (1) in photochemical cycloaddition reactions. Typical of these

4 CGMe Me02C Me (5) 43%

C02Me

+

Me

3.5%

8%

9 3%

1.5%

Scheme 1

/

' Me

he

Me

C@Me

Me Me

(2)

Photochemistry, Volume 30 0The Royal Society of Chemistry, 1999 78

Me

/

(3)

OMe

MeQ-Me

(6)

CMe20H

M2: Enone Cycloadditions and Rearrangements

79

studies is a description of a route to Sollasin a (2) and Sollasin d (3).' This utilized the cycloaddition reaction of (1) to the butenoate (4) as shown in Scheme 1. Several compounds were obtained from this reaction, all of which arise by (2+2)photocycloaddition to yield a cyclobutane intermediate. Ring-opening then affords the products isolated as illustrated in Scheme 1. The subsequent transformation of the major adduct ( 5 ) results in the completion of the synthetic approach to the targeted natural products. The cycloaddition of the same 2,4dioxopentanoate (1) as its enol to terpinolene has been described and has been used as a route to a total synthesis of racemic a-chamigren-3-0ne.~ Another report describes the addition of methyl 2,4-dioxopentanoate (1) to alkenes and the adduct obtained from 1,5-dirnethyI-6-methylene cyclohexene has been transformed into Hinesol(6) and related compound^.^ Interest in the control that environment can exert on (2+2)-cycloaddition reactions is still being shown. A recent study has examined the dimerization of the cinnamic acid derivatives (7) in the presence of surfactant vesicles in water.4 The surfactants used are the N-oxides (8) with varying alkyl chain lengths. The dimerization affords p- and 8-truxinic and y-truxillic acids. The yields of the adducts as shown are reasonable with a preponderance of the truxillic acid type. These results are illustrated in Scheme 2. The yields of cyclodimers decrease with decreasing molar ratio of the acid to the surfactant. The irradiation of monolayers of 4-octadecyloxy-E-cinnamic acid and 4-octadecyloxy-E-cinnamideon a water surface has been ~ t u d i e dThe . ~ cycloaddition reactions that occur reflect the packing within the monolayers. The cinnamic acid derivative yields p-truxinic acids while the cinnamides undergo only cis-trans isomerization. Other workers have reported the dimerization of cinnamic acid in mixed crystals composed of cinnamic acid and the pentafluoro derivative (9).6 The orientation within the crystal is such that the phenyl group interacts with the pentafluorophenyl group

pcQH C02H

H 0 2 C bCO2H +A+ (7) ArArxC02H = Ph or pMeOCsH4

Ar

14

16

5 5 6

Scheme 2

L

C4H Yield (YO)

n (in 8) 12

C02H +

12 16 17

Ar Ar = Ph 25 38 31

80

Photochemistry

thus ensuring the orientation within the crystal. Irradiation for several hours affords an 87% yield of the truxinic acid (10). D'Auria and Racioppi have reported that the arylacrylonitriles (1 1) undergo facile (2+2)-cycloaddition when subjected to benzophenone-sensitized irradiation in acetonitrile s ~ l u t i o n .The ~ products obtained from this treatment and the yields obtained are shown under the appropriate structures in Scheme 3. Again a mixture of addition types is encountered in line with results obtained from the cycloaddition reactions with the cinnamic acids. Dimerization of the nitrile (12) was also studied and yielded the two adducts (13) and (14). Irradiation of 3(estran- 16-y1)acrylates and 2-(estran- 16-y1)vinyl ketones brings about the formation of dimers and also isomerization of the unsaturated side chains.'

18% 24%

Ar = MeO

Photochemical cycloaddition of dimethyl fumarate and dimethyl maleate to the psoralen (1 5) has been reported.' The adducts formed are presumed to be of the (2+2)-type illustrated by (16) where addition to the furan ring has occurred. The photodimerization of a,w-bis(4-methylcoumarin)tetraethylene glycol is regiospecific and only the syn head-to-tail dimer is formed."

Further examples of the photoaddition of alkenes to the diketonatoboron difluoride (17) have been published." The irradiations are carried out in 1,4dioxane or acetonitrile as solvent and use 350 nm light. Irradiation times are relatively long (20 h) but result in the formation of the expected adducts. Thus addition of the alkenes (18) affords the 1,Sdiketones (19). These arise by ring opening of the initially formed cyclobutane adducts [e.g. (20)]. Similar results are

IIl2: Enone Cycloudditionsand ReurrangemenIS

F\

7

Ph O

81

q

P

h

PhQPh

R (18) R

= HorMe

R CN (19) R = H or CH3

(21) X-CH2, R = M e X=O, R = H

obtained with the enones (21) which give (22) and (23). Margaretha and coworkers have reported that irradiation of angelicin in benzene with 2,3dimethylbut-2-ene results in the formation of a cyclobutane adduct. l 2 The solid state dimerization of three polymorphic forms of (24) has been reported.I3 From these irradiations, the dimer (25) is obtained when light in the range 320400 nm is used. The principal product (25) is obtained in 58% yield and is accompanied by several minor products. Another report of the photochemical reactivity of (24) has shown that irradiation in solution brings about aromatization quantitatively. l4 In the crystal, however, irradiation of the (4R",1'RS)-(24) affords the dimer (25). Apparently this dimerization in the crystalline phase is possible because of extra space within the crystal, but this is not so with crystals

/-\

H

(24) X = CH or N

gN

Me02C Me

C02Me

H

Me

82

Photochemistry

of (26) and this fails to dimerize. The photochemical addition of ethyl 2,2dimethyl-5-0~0-5,6-dihydro-2H-pyridine1-carboxylate to 2,3-dimethylbut-2-ene has been investigated. Ethyl 5-0x0- 1a,2,5,5a,6,6a-hexahydro-2,6-methano-2aHindeno[5,6-b]oxirene-2a carboxylate undergoes photochemical dimerization on irradiation in solution.'6

'

1.1.2 Additions to Cyclopentenones and Related Systems. - A report has given details of the photochemical (2+2)-cycloaddition reactions of cyclopentenone with dichloroethylene.l7 The stereochemistry of the principal adducts was established as cis,anti,cis and cis,syn,cis. The acetone-sensitized addition of ethene to the lactam (27) can be brought in good yield by irradiation at O"C.'* Two products are obtained from this reaction and were identified as a mixture of the 1R,5S- adduct (28) and the lS,SR-isomer in a ratio of 11:l. Addition also occurs to the lactam (29) where the two products isolated were identified as (30) and (31). The addition to (29) occurs with lower stereoselectivity to give a 3:l ratio of products. The major product (28) from the initial addition to (27) was used as a starting material in a synthesis of ~-2-(2-carboxycyclobutyl)glycinederivatives.

A series of (2+2) photocycloaddition reactions have been carried out using (5R)5-menthyloxy-2(5H)-furanone (32) as the substrate." Photoaddition of cyciopentenone to this substrate gives the four products (33)-(36) with some level of regioselectivity but no facial selectivity. Interestingly, cyclohexenone, cycloheptenone and cyclooctenone fail to undergo the mixed addition. High facial selectivity is observed when more complex enones such as the 3,5,5-trimethylcyclohexenone and isophorone, (37) are used. The reaction affords adducts of the type illustrated

0

H

oow oow

RO

0

RO

83

I112: Enone Cycdoadditions and Rearrangements

in (38). (2+2)-Photocycloaddition reactions have been carried out between 4hydroxy-2,5-dimethyl-3(2H)-furanone and chloroethylenes.20 1.1.3 Additions to Cyclohexenones and Related Systems - A re-investigation of the photodimerization of isophorone (37) has been reported.21 The study examined the influence of solvent and of the concentration of the enone. Some of the results and the yields of dimers obtained are shown in Scheme 4. From this detailed study the authors suggest that supramolecular structures are involved in the dimerization. These apparently take part even at low concentrations of enone. The photocycloaddition of enones such as (39) to buckminsterfullerene(C,) has been studied.22The outcome of the addition is the formation of low yields of furanylfullerenes. This addition occurs to the exclusion of de Mayo type of addition. Photocycloaddition of the cyanocyciohexenone derivative (40) to alkenes has been reported.23 0

-K

(37)

0

divers (%) conversion (YO) HH : HT

[MI Cyclohexane Butanol H20 H20 H20 (under argon)

0.1 0.1

40 5 95 90 100

25 70

0.02 0.06

90

85 100 0.02 Scheme 4

R

30 : 70 70 : 30 95: 5 90: 10 99: 1

M cN *:

R

OH

(39) R = MeorH

(40)

Over the years (+)-grandis01 (41) has been a popular target molecule for photochemical syntheses. Another approach to this molecule using (-)-quinic acid as the starting material has been described.24The cycloaddition provided a route to the key intermediate (42). Further chemical transformation of this afforded the final product. 0

Photochemistry

84

1.2 Intramolecular Additions - A synthesis of modhephene (43) has been reported using a sequence of reactions based on the enone (44).25Irradiation of this in benzene solution through Corex resulted in an 89% yield of the adduct (45) which was used as the key intermediate for elaboration into the final product.

1.2.1 intramolecular Additions to Cyclopentenones - Irradiation (h > 350 nm in THF) of the enone (46) affords a single diastereoisomer identified as (47, The outcome of the reaction does not seem to be solvent dependent and the same degree of success is obtained with methylene chloride, acetonitrile or methanol as solvents. The corresponding amide also cyclizes efficiently. Crimmins and coworkers have demonstrated that irradiation ( h > 350 nm) of the eiione (48) results in cycloaddition and the formation of the diastereoisomeric adducts (49) and (50) in a ratio of 83:17.27A single product (51) is obtained on irradiation of the related enone (52). These adducts are key intermediates in a synthesis of some spirovetivanes. 0

C02Et Me

(%?=Me I,

I,

Et3Si07\/

OSiEt3

(47)

bmH C02Me

(50)

(51)

(49)

0

(52)

The photochemical reactivity of the diastereoisomeric compounds (53) and (54) has been studied.28The irradiation of the individual compounds, using perdeuterated acetone as the sensitizer, results in the conversion into the cycloadducts ( 5 5 ) and (56), respectively. Direct irradiation of (54), however, affords a mixture of the two cycloadducts while direct irradiation of (53) affords only the cycloadduct

IIl2: Enone Cycloadditionsand Rearrangements

85

(55). The authors reason that direct irradiation of (54) must induce bond fission to yield the radical pair (57) as well as yielding the cycioadduct. Rebonding within the radical pair (57) can yield (53) which would then undergo the photocycloaddition to yield the cycloadduct (55). Intramolecular cycioaddition is observed on irradiation of the enones (58).29 The reaction is both wavelength and temperature dependent. Irradiation through Pyrex brings about the formation of a cisltrans mixture of the alkene moiety as the main reaction. Low yields of the two adducts (59a) and (59b) are also formed under these conditions. When a quartz vessel is used the cycloaddition assumes major importance. From the results obtained it is clear that there is a preference for the formation of isomer (59a). Both the isomeric products arise from the biradical intermediate (60) which is formed by addition at the p carbon of the enone moiety and affords the more stable biradical.

Bo0 8 N - R

I

R

R

(59)

a: R1 = Ph, R2 = H b: R'

= H,

R2 = Ph

1.2.2 Additions to Cyclohexenones and Related Systems - Interest is still being shown in the minutiae of the mechanism of the photochemical addition of alkenes to cyclic enones. Recently reported work has examined the intramolecular addition observed on the irradiation of (61) in solution.30 Apparently both Ca and Cp bond formation can occur. The principal products formed from the reaction are the two (2+2)-photo-adducts (62) and (63) and the ene-product (64). An analysis of the reaction has shown for the E-isomer of (61) that there is no cleavage of the 1,4-biradical (65) or of the endo-biradicals (66) and (67). Intramolecular (2+2)-cycloaddition occurs when the enones (68) and (69) are irradiated in hexane solution with wavelengths > 350 nm (using a uranium glass filter).31The authors reason that bond formation can either arise by 2,7 or 1,8 closure. Good yields of products are obtained and it is interesting to note that with the irradiation of (68c and d) only one product is formed in each case. The exclusive formation of the products (7Oc and d) must arise by a path involving diastereoisomeric transition states. Changes in the substitution pattern close to the alkene moiety have an adverse effect on the yield of product. Thus,

86

Photochemistry

&,&

(65)

H

H

(67)

OBu'

0 R' R2 (68) a: R' = R2 = H b: R' = H, R2 = Me c: R' = Me, R2 = H d: R' = OSiBu'Ph2, R2 = H

0

Me (69)

(71) a: X = CH2, R ' = R2 = H b: X = 0, R' = Me, R2 = H (72) a: X = CH2, R' = H, R2 = Me c: 70% R' = Me, R2 = R3 = H b: X = 0, R' = R2 = Me d: 75% R' = OSiBu'Ph2, R2 = R3 = H e: 50% R' = Me, R2 = H, R3 = 061.1'

(70)a: 65% R' b: 78%

R'

= R2 = R3 = H

=

R3 = H, R2 = Me

(73)a: 52% b: 62%

the irradiation of (69) gives (70e) but only in 50% yield. Contrary to the foregoing, the main photochemical reaction of the esters (71) was dimerization of the enone system and no intramolecular cycloaddition was detected.32 This failure was attributed to conformational problems that can be overcome by the introduction of alkyl substituents into the side chain as in (72). These derivatives

IIl2: Enone Cycloadditions unci Reurrungements

87

smoothly undergo cycloaddition to yield the adducts (73) in the yields shown. Conformational problems were also reduced by the use of a longer side chain as in (74) when cycloaddition also occurred with reasonable yield. The yield of products in this system was temperature dependent with poor yields obtained at -55 "C. The products of intramolecular cycloaddition from this enone (74) were accompanied by a mixture of cyclodimers of the general structures (75) and (76). A study of the intramolecular (2+2)-addition in the enones (77) has been reported.33 The outcome of the addition is both temperature and substituent dependent. Thus irradiation of the enone (77a) at 0°C in acetonitrile with benzophenone as the sensitizer yields a single adduct (78) in 900/0yield after only 35 min. irradiation. The photocycloaddition of the enone (77b) at lower temperatures yields a mixture of (78) and (79) in a ratio of 1.8:l. The other derivatives (77c,d) afford only one product identified as (79). The products obtained from the cycloaddition can be cleaved to spiroacetals. The synthetic potential of the intramolecular (2+2)-cycloaddition reaction of enones continues to be exploited. In a recent example example the cycloaddition of the enone (80) affords the product (81) which is then subjected to ring-opening and further transformation to provide a path to the natural product (+)-ligudentatol (82).34

(78)

R1 a: Me b: H c: Me d: Me

OBn

E = CO2Et

(79)

R2 Yield I%) Me 90

Bu.' Prl Ph

90 80 73

9"

Intramolecular (2+2)-cycloaddition within the dioxenones (83) results in the formation of the adducts (84) and (85) in the ratios shown.35The adducts can be opened by thermal means to provide routes to tetrahydrofuran-3-ones and tetrahydropyran-4-ones. Intramolecular cycloaddition of the dioxenone (86) results in the formation of the diastereoisomeric mixture of (87) and (88) in a

Photochemistry

88 Me

Me

Me Me

(83)R

R

= Ph = PhCH2CH2

0

4%

fq0"&! H

H

(84)

(85)

77 : 23 73 : 27

I

Md

,

Me' 0

Me

Md

ci 0

0

OH

OMe

(89)

ratio of 2.5:1.36 These compounds are important in an approach to the total synthesis of Saudin. The regio- and stereo-selective (2+2)-photocycloadditions have been reviewed.37 2

Rearrangement Reactions

2.1 a,fi-Unsaturated Systems. 2.1.1 Hydrogen Abstraction Reactions - The photochemical behaviour of the unsaturated enone (89) has been investigated." Irradiation of (89) yields the demethylated ketone (90) by way of a Norrish Type I1 hydrogen abstraction reaction from the Me0 substituent by the excited carbonyl group. This product is accompanied by the aldehyde (91) which arises by a Norrish Type I fission. The fission of this bond affords both an acyl radical and a stabilized ally1 radical. The ketone (89) is also reactive in the di-x-methane mode and affords a bicyclopentene product. The enone (92) is reactive in its triplet state and when irradiated in methylene chloride solution is converted into the tetracyclic compound (93).39The reaction involves a step-wise process in which the biradical(94) is involved. This process is reminiscent of (2+2)-cycloaddition reactions where bonding occurs at the p-atom of the enone, and rather than completing the cyclization, hydrogen (or deuterium) abstraction occurs. A detailed stereochemical analysis of the system was carried out and proof of the stereochemistry of the final product (93) has been presented.

IIl2: Enone Cycloadditions and Rearrangements

89

Photoreduction of steroids ( 9 9 , (96) and (97) in zeolites has been studied. The results indicate that hydrogen abstraction by the enone system is enhanced in NaY zeolite^.^' 2.1.2 Radical Addition Reactions - The photochemistry of enones such as (98) has been reported!' Generally these enones are inert on irradiation in benzene, but in alcohol solution addition to the enone double bond results. Addition of In radicals is also a key feature in the reactivity of the enones (99) and this case, the radicals are generated from propan-2-01 by hydrogen abstraction using excited state benzophenone. The carbon centred radicals formed by this process undergo facile addition to the terminal carbon of the double bond of the enones resulting in the formation of a-keto radicals. intramolecular cyclization of these onto the pendant alkenyl groups results in the formation of cyclic products such as (101, 5oy0)from (99) and (102, 8Oy0) from (100). The intramolecular cyclizations of the furanone derivative (103) have been studied.43The outcome of the reaction is dependent upon the conditions under which the irradiations are carried out. Thus, with acetone sensitization or on irradiation at 254 nm in acetonitrile, cyclization affords the two spiro derivatives (1 04) and (105). This reaction path presumably involves the triplet state of the enone. Transfer of the aldehyde hydrogen to the P-carbon of the enone double bond results in a biradical that cyclizes to yield the products. With chemical sensitization using

90

Photochemistry

3°

TBDMSO

OH

TBDMSO

T B D M s : ~ :

TBDMSO%

0

*’

Scheme 6

O

0

(1 14) R = Bu’MepSi

91

1112: Enone Cycloudditions und Rearrangements

benzophenone the product obtained is (106). This route involves abstraction of the aldehyde hydrogen by the benzophenone to yield an acyl radical. This cyclizes by addition to the P-carbon of the enone double bond to yield ultimately (106). A further example of this type of cyclization has been published which involves the cyclization of the enone (107).44 Again irradiation uses benzophenone as the hydrogen abstracting agent. The resultant radical, with the radical centre adjacent to the nitrogen, again adds to the P-carbon of the enone. The reaction is carried out at -50°C in acetonitrile and the process affords the two products, (108) and (109), in an overall yield of 21% and a ratio of 1.6:l. Better yields are obtained using dicyanonaphthalene as the sensitizer. Use of single electron transfer photochemistry has been made in the synthesis of cyclic alkanols from the unsaturated esters (1 lo)-( 1 12).45Thus irradiation of the aldehydo or keto esters (Scheme 5 ) with DCA and a sacrificial electron donor such as triphenylphosphine or 1,5-dimethoxynaphthaleneleads to the formation of the cyclized products. As can be seen from Scheme 5, the method is diastereoselective and the yields are high. The method was extended to the cyclization of the ester (1 13) as a route to the optically pure C-furanoside (1 14) as outlined in Scheme 6. Single electron transfer-induced cyclizations of the esters (1 15) have also been described.46This process is readily brought about by the use of the DCA/Ph3P/ DMF/2-propanol/H20 system. The incident light is filtered through a copper solution to achieve incident wavelengths >380 nm. Some of the systems studied are shown for the conversion of (1 15) into (1 16). Again the yields are high. R

R

1 1

2

H

CH20TBDMS H

90

80

85

Some years ago Sat0 and his colleagues reported the use of silver trifluoromethanesulfonate (silver triflate) in the photochemical synthesis of cyclic ket0nes.4~~ A further study from the same group has shown that the chloroenones (1 17) and (1 18) also undergo photoreactions with alkenes in the presence of the silver salt.47b The yields and identities of the products range from low to good as can be seen in the samples cited in Scheme 7. The irradiations are carried out through Pyrex in benzene solution and, while the mechanism of the reaction is not completely understood, the possibility of electron transfer cannot be ruled out. The authors suggest that a radical intermediate (1 19) is involved and the best yields are obtained when thiophenol is added to the reaction mixture to suppress the formation of unwanted by-products. The search for different or specific electron transfer sensitizers continues. Tetramethyl pyromellitate has been shown to be a useful sensitizer for the photochemical reactions of a$-unsaturated ketones with tetraalkylstannanes?*

92

Photochemistry

a CI

+

R' R2 Yield !YO) Me Me H Me H H

45 77 21

Me Me H Me

77 22

(1 18)

-

Scheme 7

The triplet state of the mellitate brings about the cleavage to the stannanes by electron transfer and the resultant alkyl radicals add readily to the enones. Fission of a 0 - C ether linkage is the prime photochemical event on irradiation of pseudo-saccharin ethers.49 2.1.3 Miscellaneous Processes

- The results of a study of the rearrangement of flavanone and 3-chloroflavanone on irradiation in an alkaline medium have been rep~rted.~' The enone (120) is formed by a photochemical (2+2)-cycloaddition reaction within the benzene derivative (121) in benzene ~olution.~'Such cycloadditions have become of considerable interest as paths to molecules with complex skeleta. The intramolecular adduct (120) is also photochemically active and on further irradiation is converted into the pentacyclic derivative (122). This product is also formed directly if the irradiation of (121) is carried out in methanol. The rearrangement of (120) involves, in the first instance, the fission of the bond marked "a" in (120). Subsequent rearrangement within the resultant biradical affords the final product. Irradiation of the a$-unsaturated compounds (123) with a high pressure mercury lamp in benzene solution results in their efficient conversion into the 1,4-diketones ( 124).52The quantum yield of around 0.1 for the processes shows that the reactions are reasonably efficient. Cross-over experiments have demonstrated that the rearrangement is truly intramolecular and proof of the mechanism of the rearrangement was obtained by the conversion of (125) into (126). This cyclopropane derivative can be converted thermally into the final 1,4-dicarbonyl compound (127). This transformation suggests that the reaction path involves an unusual 1,4-hydrogen abstraction to yield an intermediate biradical such as (128). Cyclization of this species affords a cyclopropane and in the case of the keto alcohols (123) the cyclopropanol intermediates (129) are unstable to the reaction conditions readily undergoing ring opening to afford the 1,4-diketones (124). The cyclopropenone (130) undergoes decarbonylation on flash photolysis in water.s3 The resultant ynamine (13 1) is accompanied by the enamine (1 32). The enamine is formed from the carbene (133) and its trapping with water. The ynamine (13 1) is unstable and transforms into the ketenimine (134). The photo-

1112: Enone Cycloudditions und Rearrangements

93

Me H‘ @o Me

Me

( 123)

R’

( 124)

R2

Yield (YO)

dissociation of acrylonitrile brought about by irradiation at 193 nm has been studied.% A novel coupling reaction has been reported following the irradiation at h > 280 nm of mixed crystals of 1,2,4,5-tetracyanobenzene and benzyl cyanide.55The product isolated from this reaction was identified as the adduct (135). This compound is formed by a path that involves electron transfer and an intermolecular hydrogen abstraction process.

Photochemistry

94

P,y-Unsaturated Systems - As was mentioned earlier in this Chapter, Norrish Type I processes can occur with P,y-unsaturated enones. This process is also observed in the formation of a ketene on irradiation at h > 230 nm of cyclopenten-3-one in an argon matrix.56 The presence of the ketene intermediate was detected by IR spectroscopy, Irradiation at 300 nm of the enones (136) results in decarbonylation again by a Norrish Type I process.57 The resultant biradical undergoes ring closure and yields the cyclopropylpropenes (137). The propenonitrile product (137b) is formed as mixtures of 2 and E-isomers. The enones (138) and (139) undergo efficient conversion into (140) and (141), respectively, on direct irradiation through Pyrex in a benzene solution.58 The reaction is a good example of a 1,3-acyl migration in a P,y-unsaturated enone and is a route to the protoilludanoid skeleton. Irradiation using quartz filtered light affords a complex mixture of products.

2.2

LR

Me Me

Me (136) a: R = Me b:R=CN

(138)

(137) a: R = Me

b:R=CN

(139) R = H or OH

2.2.1 The Oxa Di-x-methane Reaction and Related Processes - Interest in the control of reactions in the constrained environment of zeolites continues to grow. A recent report describes the control exercised on the outcome of the photochemical reactions of the enones (142).59The conditions used involve the enones included in some M Y zeolites where M was Cs or T1. The usual acetonesensitized irradiation of (142, n = 1) and (142, n = 2) brings about the oxa-di-nmethane conversion to yield (143a) and (143b) in 41?4 and 37.3%, respectively. The zeolite/enone irradiations were carried out either as slurries in hexane or as dry powders. The best yields were obtained from the dry powder irradiations when up to a twofold enhancement in product formation was observed. TI+ Zeolites gave better results than the Cs materials and, for example, (143a) was formed in 61.1% from (142, n = 1) and (143b) from (142, n = 2) in 44.7% from the former systems. Clearly the presence of heavy atom cations enhances the intersystem crossing within the enones. The dienone (144a) undergoes the oxa-dix-methane rearrangement on irradiation in benzene solution using a tungsten

IIl2: Enone Cycloadditions and Reurrangements

95 OTBS

,

(142) n = 1 o r 2

(143) a: n = 1 b:n=2

(144) a: R = H b: R = OMe

OTBS

f\ I

0

H

(149)

R’ = R2 = H R1 = R2 = Me R’ = CH&H=CH2,

R2 = Me

lamp as the light source.6oThis treatment gives the tricyclic product (145) in 50% yield. The related compound (144b) does not follow this reaction path either on direct irradiation or on acetone-sensitized irradiation and under either of these conditions, only the 1,3-acyl migrated product (1 46) is formed in 52% yield. The oxa-di-n-methane reactivity of the tricyclic enones (147) and (148) has been described.6’ The reactions are carried out by irradiation in acetone as the solvent and sensitizer and this transforms the compounds (147) into the rearranged products (149) in the good yield. The reactions can be dependent upon the nature of the substituents on the skeleton and for example (148) also undergoes the oxadi-n-methane rearrangement but rather than forming a diketone it is transformed into the acetal (150) by reaction of the second carbonyl group with the hydroxymethyl substituent .

2.2.2 Miscellaneous Processes - Triplet sensitization by benzophenone of solutions of the lactone (151a) in benzene using a Pyrex filter brings about bond fission.62The product obtained from this reaction was identified as (152a) and was formed in 83% yield. The formation of this product occurs via the specific bond rupture of “a” in (151). This specific reactivity is to be contrasted with the direct irradiation of (151a) when (153) and (154) are formed in low yield. Specificity in the sensitized reactions is also displayed by the substituted derivatives (151b - d) when (152b - d) are formed in the yields shown.

96

Photochemistry

Phenylacetonitrile undergoes photochemical addition of amines via an electron transfer process.63 Such reactivity is typical for many systems and the SET process yields the radical anion/radical cation pair (155). Loss of cyanide from (1 55) affords a benzylic radical from which the products (1 56 - 158) are formed.

(151) X Yield ("0) 83 96 c: CI 80 d: Me0 40 e: Ph 69

a: H b: Me

I-\

DPSO' V (159) Z = R' = Me, R 2 = H E = R' = H, R2 = Me DPS = Me2PhSi

DPS0'(160) a: R'

b: R'

= Me, R2 = H = H, R2 = Me

Further interest has been shown in the transfer of energy along the rigid backbone of steroidal fystems. The steroidal system (159) has been chosen from among the many systems reported as an example of the processes encountered. The irradiation of (1 59) at 254 or 308 nm results in the isomerism of the alkene moiety from the 2 to the E isomer.@ The conditions chosen mean that the phenyldimethylsiloxy group is the initial absorber. Singlet energy is transferred from this moiety to give the ketone singlet which then undergoes ISC to afford the triplet keto group. Triplet energy is then transferred to the alkene that undergoes the isomerism. The keto group has clearly been shown to be involved. Thus, prolonged irradiation affords the Norrish Type I1 products (160) by hydrogen abstraction from the adjacent methyl group followed by bond formation in the l ,4-biradical.

IIl2: Enone Cycloudditions and Rearrangements

3

97

Photoreactions of Thymines and Related Compounds

3.1 Photoreactions of Pyridones - Irradiation of 1-benzyl-1,4-dihydronicotinamide (161) with the malonate derivative (162) affords a variety of products resulting from debromination and dirnerisati~n.~’ The dihydropyridine derivatives (163) are photochemically reactive in the solid phase.66The formation of the products by irradiation has been shown to be a two step process affording the (2+2)-cycloaddition product (164)in the first step. Secondary irradiation of (164) then gives the cage compounds (165) in yields greater than 900/.

(163)

(1 64) Yield (YO)

R’

R2

Ar

H H

Me Et Et Me Et

pMeOC6H4

CHZPh Me Me

65 40 60 60 52

( 165)

Yield (YO) 91

92 96 96 90

The photochemical addition of the pyridones (166) to the pentadienoate (167) does not occur on sensitized i r r a d i a t i ~ nDirect . ~ ~ irradiation is effective, however, and many cycloadducts, (1 68)-(173, were obtained. The results from these cycloadditions were compared with those obtained from the addition of the same pyridone (166) to methylpropenoate. Single crystals of the pyridones (176) were grown and examined by X-ray diffraction.68 Some of the systems crystallized to give a chiral space group which was particularly evident for the derivatives (1 76ac). Irradiation of these crystals resulted in the formation of the f3-lactams (1 77) in high yield with reasonably high ees. The study of the photodegradation of some antimicrobial quinolones has been reported.69 Irradiation of the enantiomerically pure bis-pyridone (178) in acetone solution results in almost quantitative conversion into the single cycloadduct (1 79).70 Several years ago Sieburth and co-workers reported that irradiation of (180) gave the adduct (181).7’aThis unstable cycloadduct could be reduced to the saturated derivative (182). Further study has shown that the derivative (182) can be ring opened using lithium in liquid ammonia and that this provides a reasonable synthetic route to the large ring compound (1 83).7’b

98

Photochemistry

(166) R’ = H or Me

(168) R’ = H or Me R2 = H or Me R3 = C02Me R2

---/

4

(167) R2 = H or Me

R2

H

0

R3\ R’/

0 (172)

(173)

&

0

H

(176) R =a: mCI b: mMe c: mMeO, d: mBr, H. CFCI,pCI, pBu’

p’

0

0 (174)

(175)

k

0

+NH 0 (177) a: ee 78% b:ee 71% c: ee 100%

3.2 Photoreactions of Thymines etc. - The uracil derivative (184) undergoes photochemical transformation when it is irradiated in frozen benzene with added triff uoroacetic acid.72 Cyclodimerization occurs yielding derivatives of diazapentacyclo[6.4.0.0’~3.02y6.04~8]dodecane derivatives such as (185). Other addition products (186) and (187) were also identified. The photoreduction of 5-bromouracil (1 88) has been studied.73 De Keukeleire and co-workers have reported a further example of the intramolecular addition of a pyrimidone to a pendant benzene ring.74 In this example. the cyclobutane adduct (189) formed from (190) on irradiation could not be isolated. Instead it underwent rearrangement on attempted isolation. Cyclodextrin is often used as a template upon which specific photochemical reactions

99

IIf2: Enone Cycloariditions and Rearrangements

b..,.

Ph

Me

Me0

(180)

Ph

'Ph

0

NCOPh Me0

\ H Me (189)

0

(191)

100

Photochemistry

F

HO (192) ( 193) R' = ribosyl, R2 = deoxyribosyl

(195)

0 (196) 0

0 (197) S

can be carried out. Another such example has been studied recently which involves the irradiation at 280 nm of the modified cyclodextrin (191).75 This procedure brings about reversible dimerization of the thymine moieties and the kinetic details of the forward and back reactions have been analysed. Irradiation at 366 nm in aqueous solution of the thiothymine (192) in the

IIl2: Enone Cycloadditions and Reurrangemenfs

101

presence of the adenine derivative (193) results in the formation of the adduct (194).76 Further studies on the photochemistry of the pyridone adducts (195) have been reported.77 Interest in photochemical reactions in constrained environments or on backbones has continued in the present year. The study by Clivio et al. has examined the photochemical reactions between the thymine units shown in (196).78 Irradiation at 366 nm in water results in the formation of the product (197) and similar treatment of related peptide nucleic acid dimers such as (198) leads to intramolecular hydrogen abstraction reactions yielding the three new products (199) - (201).79 The photochemical dimerization of some esters of urocanic acid has been described." 4

Photochemistry of Dienones

4.1 Cross-conjugated Dienones - The photochemical behaviour of several derivatives of the cyclohexadieneone (202) has been studied. The irradiation of these compounds in methanol follows the conventional ring contraction path to yield cyclopentenone derivatives.8' A study of intermolecular electron transfer in the dyads of the type illustrated in (203) has been examined.82

4.2 Linearly Conjugated Dienones - An extremely detailed study of the reactions of a variety of 6,6-disubstituted cyclohexa-2,4-dienones has been published.83Spectroscopic analysis of the intermediates at low temperatures was also carried out. The ketene intermediates obtained by the ring opening processes can be trapped by a variety of reagents. In this case methanol was favoured and, for example, ring opening and trapping of the ketene from (204) affords the large ring ester (205). Many other examples including the ring opening and trapping of the ketene from (206) affording (207) were also described. Further interest has been shown in the mechanistic steps of the photo-Fries reaction. Recent work has used the two-laser technique of irradiating intermediate^.^^ Thus the irradiation of the ether or the acetate (208) at h = 266 nm brings about the formation of the linearly conjugated cyclohexadienone derivatives (209). Irradiation of these

Photochemistry

102

OAc (204)

(209)R = Bn or COCH3

(210)

OR2

0r2

R20

/

~. -0.. . R’

&- I

R’

R’ H Me H H H

H H Me Ac Ts

11 19

-

46 74

5 7

-

22 17

5

-

39 7

-

8 10 12 6

-

Scheme 8

b i v

species at 308 nm causes ring opening to give the ketenes (210). Calculations relating to the photochemical isomerism of 5hydroxytropolone have been carried The irradiation of the pyranone derivatives (21 1) results in the products shown in Scheme 8.86 The reaction is of use for the synthesis of eight-membered rings and is the result of a (4+4)-cycloaddition. The best conditions for the reactions

IIl2: Enone Cycloadditionsand Rearrangements

103

are low temperature and aqueous methanol. The synthesis of the exdendo products (212)/(213) was studied further with the cyclization of (214) to yield the two adducts (215) and (216) in 20% and 58%, respectively. These compounds are of value as starting materials for the synthesis of the fusicoccane/ophiobolane skeleton. A review has highlighted the photochemical cycloaddition reactions and photocyclization reactions of 2- and 4-pyrone derivative^.'^ 5

1,2-, 1 , s and 1,4-Diketones

5.1 Reactions of 1,2-Diketones - A study of the ketoamides (217) has shown that their direct irradiation in benzene solution brings about efficient cycloaddition to give the bicyclic oxetanes (218).*' In the solid state, irradiation of (217) also affords these products. However, the syn:anti ratio is higher in the solid state than in solution. Furthermore, there is a temperature effect and the syn:anti ratio is greater at lower temperatures. The ee is also affected by changes of temperature.

Ph '0 (217) R' R2

(218) Yield (%) syn : anti Me Pr' 100 2.1 : 1 100 2.1 : 1 Me PhCH2 76 2.1 : 1 Ph Me 100 2.1 : 1 Me etolyl Me 2,6diMe& 100 2.1 : 1 H Pr' 96 H CH2Ph 99 H Ph 100 H 2,6diM&&i3 100 H 2.6diCICeH3 100

Studies aimed at measuring the lifetimes of the biradicals formed on irradiation of the keto esters (219) have been carried Particular interest was directed towards the 1,4-biradicals formed by Norrish Type I1 reactivity. Apparently the triplet reactivity is not influenced to any great extent by the presence of the halogen substituent. The alkenylphenyl glyoxalates (220) have been shown to be photochemically reactive.g0The outcome of the reactions is dependent upon the substitution pattern of the alkenyl moiety; hydrogen abstraction, oxetane formation [e.g. formation of (221)] and large-ring lactones result. A detailed study of the mechanism of the processes was also reported. Neckers and co-workers have also described the photochemical behaviour of the keto esters (222).91 Irradiation of (222d) and (222g) leads to the formation of the large ring lactones (223a) and (223b) in moderate yield. The path to these products involves long range hydrogen transfer at either the 1,lO-positions for (222d) or the 1,ll-positions for

104

Photochemistry

0 Ph+OMo\

0

(219) n R 2 CI 2 Br 2 1 2 PhS 2 PhS=O 3 Br 3 PhS

R

0

= R2 = H n= 1 R' = H, R2 = Pr" n- 1 R 1 = R 2 = M e n=l R1=R2=Me n=2

(220)R'

a

b

c d

e f g h

2 2 3 4 5 6

3 5

Me

Et

Et Me Me Me PhCH2 PhCH2

(223)a: R = H, n = 1 (25%) b: R = Ph, n = 2 (20%)

(222g). The resulting biradicals cyclize but the main reaction of all the compounds studied is either intermolecular hydrogen abstraction that leads to the pinacols (224), or Norrish Type I1 hydrogen abstraction to yield benzaldehyde via the biradical (225). The photochemical hydrogen transfer reactions of ethyl phenylglyoxalate derivatives attached to a polymer backbone have also been studied.92 The photochemical ring opening of the series of cyclobutene-1 ,2-diones (226)

R' But B u b Me3Si Ph Ph Ph Ph Ph Me But C1 CI But B u b PhS Me3Si Me3Si R2 Bu' B u b EtO H Ph Me CN Br Me But CI Me0 Pr'O Bu'O PhS EtO Me

H CHO

IIl2: Enone Cycloadditions and Rearrangements

105

to yield the corresponding bisketenes (227) has been reported.93 The diketone (228) affords the two cyclobutane derivatives (229) and (230) in a ratio of 7:l on irradiation in benzene solution using wavelengths > 340 nm.94 This cyclization involves a typical Norrish Type I1 process and the cis-cyclobutane (229) is also formed when crystals of (228) are irradiated. However, under these latter conditions the trans-isomer (230) is not formed and the other product from the irradiation in the solid state was identified as the keto-aldehyde (231). The formation of (231) is thought to involve a-fission of the bond between the two keto groups followed by carbene-type insertion into a C-H bond. The study showed that the cis-cyclobutane is formed by a Norrish Type I1 hydrogel, abstraction within the conformer (232). In this species either bowsprit hydrogen can be abstracted to afford the 1,3-biradical that is the precursor of the final product. High chemical but low quantum yields of the two products (233) and (234) are obtained on irradiation ( h > 500 nm) of the tetraketones (235).95 The primary photochemical step is the conversion of the tetraketones into carbon monoxide and the ketenes (236). The reaction process occurs from the singlet state and is thought to be concerted. The final products are formed by the addition of these ketenes (236) to ground state tetraketone. The ketene (236b) was studied in a little more detail and it was shown that irradiation in benzene or toluene at room temperature results in the formation of the dimer (237). Addition of the same ketene to diketones such as biacetyl was also reported.

'OAr

Ar&Ar

0

(233)a:Ar=Ph

b: Ar = 4-BrC6H4 c: Ar = 4-MeOCsH4

(236)

(234)

0

(235)

(237)Ar = 4-BrC6H4

5.2 Reactions of 1,3-Diketones - Irradiation of the 1,3-diketone (238) in ethanol or benzene results in the formation of 1-hydro~y-2-naphthaIdehyde.~~ The site of photochemical hydrogen abstraction reactions within the keto esters (239, X = S) is controlled by SET transfer reactions from the thio substituent to the excited carbonyl The usual reaction train following this event yields the biradical (240) which undergoes cyclization to yield (241) in modest to good yields. The involvement of an SET process is proven by the failure of the sulfone derivative (239, X = SO*) to undergo the same reaction.

Pho tuchemistry

106 0

(2411 R1 R2 X

Yield(%)

a: Ph

H S 65 b: Me Me S 44 c: Me H S 29 26 d: H H S 35 8: Ph H SO2 0

Reactions of I&Diketones - A photo electrodhole transfer process is involved in the alkylation of maleic acid catalysed by titanium dioxide in acetonitrile solution.98The reaction involves the silyl derivatives (242) or the corresponding arylacetic acids. The electron transfer leads to the corresponding benzyl radical either by fission of the C-Si bond in (242) or decarboxylation of the carboxylic acid. This benzylic radical adds to maleic acid to yield either the monoalkylation products (243) or the di-adduct (244). Rivas and co-workers have reported the photochemical (2+2)-cycloaddition of maleic anhydride to selenophene and tellurophene derivatives using benzophenone sensitization.w Irradiation of the dianhydride (245) in an argon matrix using a XeCI laser results in conversion into the aryne (246) by decarbonylation and decarboxylation.Iw Further irradiation at this wavelength brings about little change in the observed spectra but if (245) is irradiated using a KrF laser the bis aryne (247) is formed and further decomposition results in the formation of hexa-1,3,5triyne.

5.3

107

IIl2: Enone CycloacWitionsand Rearrangements

The triplet state of the 1,4-diketones (248) has been shown to undergo electron transfer in polar solvents.lo' Irradiation of the Diels-Alder adduct (249) results in the formation of the cage dione (250) by intramolecular (2+2)-cycloaddition.lo*

f--ygx

Me

X

0

Me%Br

(248) X = Br or CI

Br'

H0 (249)

5.3.I Phthafimides and Related Compounds - 4-Amino-N-methylphthalimide has been studied by laser flash photoly~is.'~~ The photophysical parameters have been established by this approach and this study has supported the results obtained from steady state irradiations. Intramolecular photoelectron transfer photochemistry of the N-[(N-acetyl-N-trimethylsilyl-methyl)amidoalkylJphthalimides has been demonstrated.'04The yields obtained on irradiation in methanol range from low to medium. 0

qL:g--J II

0

& 0

HO>

H

H H O x P h

Ph

A

HO

R' R2 (257) R' = CH20H. R2 = H R' = H, R2 = CH20H

I08

Photochemistry

The tetrahydrophthalimide derivative (25 1) undergoes intramolecular (2+2)photocycloaddition on irradiation in acetonitrile solution using Pyrex-filtered light.Io5This process gives reasonable yields of the cyclobutane adduct (252). The system was extended to use silicon tethers for the alkene (253) or the alkyne (254) side chains to the tetrahydrophthalimide. In addition a chiral group was incorporated adjacent to the nitrogen of the phthalimide. When these molecules are irradiated the diastereoisomeric diols (255) and (256) were obtained from (253), after ring opening of the initially formed photoadducts. A similar result was observed with (254) which gave (257). The yields in all the examples are in the range of good to excellent. Lactams such as (258) can be synthesized from the phthalimides (259) by irradiation.'06 Again the reactions are controlled by single electron transfer processes that are usually encountered in the photochemical reactions of phthalimides. The outcome of the reaction is a conventional proton transfer from the benzylic site within the zwitterionic biradical formed on irradiation. Cyclization within the resultant 1,5-biradicaI affords the final product. Griesbeck and his coworkers have studied the photochemical reactivity of the phthalimide derivatives (260).'07 These compounds on irradiation under triplet sensitized conditions undergo decarboxylation and cyclization. The reaction involves SET and the key intermediates are shown as (261) and (262). The biradical anion (262) is the species that either cyclizes to afford (263) or abstracts hydrogen to yield (264). The reaction is controlled by a variety of factors that have been reported in some detail. Some photochemical reactions of phthaloylcysteine derivatives have been described."' Typical of the processes are the decarboxylations of the derivative 0

(260)/I= 1-5, 10, 11

(259)

(263) n Yield (YO) 1

2 3 4 5

10 11

-

5 75 61 71 72 78

(264) n Yield (YO) 1

2 3

95

45 4

4 4 5 5 8 10 97% C

5.3.2 Fulgides and Fulgimides - A b initio calculations have been carried out to assess the photochemical properties of 3-furylfulgide. l o Photochromism of fulgides continues to be an area of considerable interest. The photochromic behaviour of fulgides with chiral properties has also attracted interest." The effects of constraining environments are also important and photochromic properties of the indolylfulgide (272) have been examined where the compound has been trapped in a hybrid matrix prepared by a sol gel process.I12 More complex systems continue to be devised within this family of molecules and (273) is a good example of further developments.'13 The photochromism of ( a - 2 isopropylidene-3-[ 1-(3,4-dimethoxyphenyl)ethylidene]-3-isopropylidene succinic anhydride has been reported.'14 Fulgides have also been studied as potentials for optical switches.' l 5

'

I10

Photochemistry

The influence of chiral substituents attached to the trienes (274) on the cyclization of these molecules has been examined.'I6 Irradiation at 450 nm leads to diastereoisomeric pairs in the closed form. The outcome of the reaction is solvent dependent and one of the best results is obtained on irradiation at low temperature in toluene. Under these conditions the diastereoenantiomeric excess was 86.6%.

(CN

(274) R = Cmenthyl or &menthy1

6

Quinones

6.1 o-Quinones - Quinone methides can be formed by the irradiation of 0benzoquinones in the presence of diphenylacetylene. This reaction is quite normal behaviour for quinones and involves (2+2)-cycloaddition to the carbonyl function to yield an oxetene. In this instance elimination of benzaldehyde affords the quinone methide. 6.2 p-Quinones - The 1,3-diketone (275) in its enol form undergoes cycloaddition to p-benzoquinone derivatives.I l 8 The cycloaddition is a typical (2+2)process of the de Mayo type to afford a cyclobutane. Ring opening of the fourmembered ring yields the 1,Sdiketo (276). Duroquinone also undergoes (2+2)cycloaddition to yield cyclobutane derivatives.'" This photochemical addition to stilbene yields the unstable adduct (277). The final product from the reaction is the cyclooctatriene (278) which is formed by oxidation and ring opening of (277). A study of the photochemical addition of diarylalkynes (279) to the quinone (280) has shown that the quinone methides (281) are formed.'20 As is well known, the addition involves the formation of an oxetene (282) that ring opens. There is some degree of selectivity when non-symmetric alkynes are used as indicated by results shown beside the appropriate structures. The photochemical reaction can be brought about either by irradiation at wavelengths > 410 nm or by irradiation into the charge transfer band at wavelengths > 530 nm. The outcome is the same P h q o

Ph

0

P

Ph

Ph

Ph

0

h

a

H Me

M

e

;

;

G

M

Me

Me 0

e

Me

0

111

IIl2: Enone Cycloadditionsand Rearrangements

YtC' 0

A?-Arl

cPc'cT 0

:'

o A? /

0

A?

(281) a: 60% yield b: Ar' = 3,5diMeCsH3, A? = Ph Ar' = Ph, A? = 3,5diMeC6H3 80% (ratio 10 : 1) c: Ar' = 3,5diMeC6H3, A? = pMeC6H4 Ar' = pMBCsH4, A? = 3,5diMeC6H3 82% (ratio 3 : 2)

0 0

Me Me

/

Me Me

M*

Me0

112

Photochemistry

under both conditions. The authors state that the reaction probably involves a single electron transfer process with the formation of radical catiodradical anion pair. Indeed, irradiation of the crystalline complexes of the same alkynes with the same quinone also gives adducts.I2l One example is shown when irradiation at h > 410 nm of the quinone with the alkyne (283) gives a 90% yield of the adducts (284a) and (284b) in a ratio of 4:l. Irradiation of the benzoin derivative (285) readily affords the free alcohol, 2-ubiquinol. 122 The photoenolization of the quinone (286) can be carried by irradiation at 3 13 or 365 nm in acid solution.'23The steady state irradiation has identified the product as the unstable hydroxylated compound (287) which is formed via the enol(288). The presence of this intermediate was detected in a laser flash study of the reaction. The quinones (289) undergo cyclization when irradiated with visible light.124The mechanism by which the compounds (289) are transformed into the derivatives (290) involves the production of an excited state that is either a zwitterion or a biradical. After the transfer of a hydrogen the intermediate (291) is formed. It is within this species that cyclization occurs to give the final products. (2+2)-Cycloadducts such as (292) and oxetanes can be obtained by the photochemical addition of quinones to homobenzvalene. Interest in the photo-SET in quinone systems has led to the synthesis of the pyropheophytin substituted ndphthoquinone dyads (293). 126 A pulse radiolysis study of vitamin K in solution has been reported. 127

@ 0

@ Me

OH

0

R'

yJ$J

O*

0

(290) R2 Yield (Yo) H 27 H Me 38 Me Me 83 PhCH2 H 80

R1 H

0

1112: Enone Cycloadditionsand Rearrangements

113

1-Alkylanthraquinones undergo Norrish Type I1 hydrogen transfer on irradiation. 12' The photochromism exhibited by anthraquinones (294) has been examined. 129 With the corresponding phenoxyquinones the reactions involve a phenyl migration which is a non-adiabatic process and yields a triplet biradical. A study of the photochemical electron transfer systems of the substituted anthraquinone derivatives (295) has been carried out.'30 The influence of the binding mode of quinones such as (296) and (297) to DNA has an effect on the light-induced cleavage of duplex DNA.13' 0

II

NH-(CH2),-O-P-O-[5'-OLI-3'] I 0-

Q \ y-$lfJ$ry 0

0

(294)R =aryl or alkyl

(295)n = 2 or5

QypR 0 (296)R = S02NH(CH2)4NH&I R = CONH(CH&NH&I

(297)

Crystal structures of triptycene-l,4-quinone and its photoproduct have been determined. 132A full account of the photochemical reactivity of azulene quinones has been pub1i~hed.I~~ This study has already been published in note form.134The authors note that the methoxy substituted azulene quinone (298) undergoes

Me0

Ll

O

g

$

l

0

OMe (301)

qo

0

114

Photochemistry

photochemical dimerization on irradiation using a 400 W mercury arc lamp in methylene chloride. Three main products were isolated from this and were identified as (299), (300) and (301) in 6, 10 and 24%, respectively. The head-tohead adducts are predominant when the reactions are carried out in polar solvents, The bromo derivative (302), in contrast, yields only the single dimer (303).

7 1. 2.

3. 4. 5. 6.

7. 8. 9. 10. 11. 12. 13. 14.

15.

16. 17. 18. 19. 20. 21. 22.

References T. Hatsui, M. Taga, A. Mori and H. Takeshita, Chem. Lett., 1998, 1 13. J. J. Wang, C. J. Yao, B. Z. Chen and G. J. Jiang, Chin. Chem. Lett., 1997, 8, 781 (Chem. Abstr., 1997,127,307501). J. J. Wang, C. J. Yue, J. Qiu and C. Y. Qian, Chin. Chem. Lett., 1997, 8, 957 (Chem. Abstr., 1998, 128, 89025). T. Nakamura, K. Takagi, M. Itoh, K. Fujita, H. Katsu, Y. Imae and Y. Sawaki, J. Chem. SOC.,Perkin Trans. 2, 1997,2751, I. Weissbuch, W. Bouwman, K. Kjaer, J. Als-Nielsen, M. Lahav and L. Leiserowitz, Chiraltiy, 1998,10,60 (Chem. Abstr. 1998, 128,85139). G . W. Coates, A. R. Dunn, L. M. Henling, J. W. Ziller, E. B. Lobovsky and R. H. Grubbs, J. Am. Chem. Soc., 1998,120,3641. M. D’Auria and R. Racioppi, Tetrahedron, 1997,51, 17307. T. Thiemann, C. Thiemann, S. Sasaki, V. Vill, S. Mataka and M. Tashiro, J. Chem. Res., Synop., 1997,248. G . S . Han and S. C. Shim, Photochem. Photobiol., 1998,67, 84 (Chem. Abstr., 1998, 128,217353). A. Zhu and S. Wu,Ganguang Kexue Yu Guang Huaxue, 1997,15, 15 1 (Chem. Abstr., 1997,127,480026). Y. L. Chow, X. N. Cheng, S. S. Wang and S. P. Wu,Ccm. J. Chem., 1997,75,720. J. Bethke, A. Jakobs and P. Margaretha, J. Photochem. Photobiol., A , 1997, 104, 83 (Chem. Abstr., 1997,127, 128589). N. Marubayahsi, T. Ogawa and N. Hirayama, Bull. Chem. SOC.Jpn., 1998,71,321. N. Marubayashi, T. Ogawa, T. Hamasaki and N. Hirayama, J. Chem. Soc., Perkin Trans. 2, 1997, 1309. C. Jeandon, R. Constien, V. Sinnwell and P. Margaretha, Helv. Chim. Acta, 1998, 81,303. A. A. Pinkerton, A. Martin, A. P. Marchand and A. Devasagayaraj, J. Chem. Crystallogr., 1997,27,701 (Chem. A bstr., 1998,128,243970). A. B. Brown, S. E. McKay and D. E. Meeroff, Synth. Commun., 1997, 27, 1989 (Chem. Abstr., 1997,127,33899). H. Tsujishima, K. Nakatani, K. Shimamoto, Y. Shigeri, N. Yumoto and Y. Ohfune, Tetrahedron Lett., 1998,39, 1 193. S. Bertrand, N. Hoffmann and J. P. Pete, Tetrahedron, 1998,54,4873. T. Shimo, H. Minamishin and K. Somekawa, J. Heterocycl. Chem., 1997, 34, 533 (Chem. Abstr., 1997, 127,34076). H. Goncalves, G. Robinet, M. Barthelat and A. Lattes, J. Phys. Chem. A , 1998,102, 1279. A. W. Jensen, A, Khong, M. Saunders, S. R. Wilson and D. I. Schuster, J. Am. Chem. Soc., 1997,119,7303.

IIf2: Enone Cycloadditions and Rearrangements 23. 24. 25. 26. 27. 28. 29. 30. 31. 32. 33. 34. 35. 36. 37. 38. 39.

40. 41. 42. 43. 44. 45. 46. 47.

48. 49. 50. 51. 52. 53. 54.

55.

115

S. Andresen and P. Margaretha, J. Photochem. Photobiol. A , 1998, 112, 135 (Chem. Absfr., 1998, 128,25051 7). K. Matsuo, M.Morita and K.4. Kawashima, Chem. Pharm. Bull., 1997,45, 1734. C. A. Dvorak and V. H. Rawal, J. Chem. SOC.,Chem. Commun., 1997,2381. M. T. Crimmins and A. L. Choy, J. Am. Chem. SOC.,1997,119,10237. M. T. Crimmins, Z. Wang and L. A. McKerlie, J. Am. Chem. SOC.,1998,120, 1747. M. N. Wrobel and P. Margaretha, J. Chem. SOC.,Chem. Commun.,1998,541. N. Braussaud, N. Hoffmann and H.-D. Scharf, Tetrahedron, 1997,53, 14701. N. Haddad and N. Galili, TetrahedronLett., 1997,38,6083. M.T. Crimmins, B. W.King, P. G. Watson and L. E. Guise, Tetrahedron, 1997,53,

8963. S . Piva-Le Blanc, J.-P. Pete and 0. Piva, J. Chem. SOC.,Chem. Commun., 1998,235. N. Haddad, I. Rukhman and Z. Abramovich, J. Org. Chem., 1997,62,7629. N. Haddad and H. Salman, TetrahedronLett., 1997,38,6087. J. H. Dritz and E. M. Carreira, TetrahedronLett., 1997,38, 5579. J. D. Winkler and E. M.Doherty, TetrahedronLett., 1998,39,2253. S . A. Fleming, C. L. Bradford and J. J. Gao, Mol. Supramol. Photochem., 1997, 1 (Organic Photochemistry), 187 (Chem. Abstr., 1998,128,204464). J. T. Moon, Y.-C. Kong, D. S. Ryu and D. J. Choo, Bull Korean Chem. SOC.,1997, 18,1236 (Chem. Abstr., 1998,128, 167076). C. A. Hastings, J. D. Riggenberg and E. M. Carreira, Tetrahedron Lett., 1997, 38, 8789. V. J. Rao, S. R. Uppili, D. R. Corbin, S. Schwarz, S. R. Lustig and V. Ramamurthy, J. Am. Chem. SOC.,1998,120,2480. R. A. Bunce, R. S. Childress and E. M.Holt, J. Photochem Photobiol., A , 1997,109, 125 (Chem. Abstr., 1997,126,3 12965). A. M. Gomez, S. Mantecon, S. Valverde and J. C. Lopez, J. Org. Chem., 1997, 62, 6612. D. Brown, M. G. B. Frew and J. Mann, J. Chem. SOC.,Perkin Trans. I , 1997,3651. E. Farrant and J. Mann, J. Chem. SOC.,Perkin Trans. I , 1997,1083. G. Pandey, S. Hajra, M. K. Ghorai and K. R. Kumar, J. Org. Chem., 1997, 62, 5966. G. Pandey, M. K. Ghorai and S. Hajra, TetrahedronLett., 1998,39, 1831 (a) S. H. Oh, K. Tamura and T. Sato, Tetrahedron, 1992, 48, 9687; T. Sat0 and K. Tamura, Tetrahedron Lett., 1984,25, 1821; S.-H. Oh and T. Sato, J. Org. Chem., 59,3744 (1994); (b) Y.Sawayanagi, T. Sat0 and I. Shimizu, Chem. Lett., 1997,843. M. Fagnoni, M. Mella and A. Albini, J. Phys. Org. Chem., 1997, 10, 777 (Chem. Absrr., 1998,128, 74996). U. C. Yoon, J. H. Kim, S. J. Lee, H. J. Kim, S. W. Oh and W. W. Park, J. Korean Chem. SOC.,1997,41,666 (Chem. Abstr., 1998,128,60093). S. Jain, Natl, Acad. Sci. Lett. (India), 1997, 20, 130 (Chem. Abstr., 1998, 128, 238053). G. P. Kalena, P. P. Pradhan, Y. Swaranlatha, T. P. Singh and A. Banerji, Tetrahedron Lett., 1997,38,555 1. S. Matsumoto, Y. Okubo and K. Mikami, J. Am. Chem. SOC.,1998,120,4015. Y . Chiang, A. S. Grant, H.-X. Guo, A. J. Kresge and S. W. Paine, J. Org. Chem., 1997,62,5363. D. A. Blank, A. G. Suits, Y. T. Lee, S.W. North and G. E. Hall, J. Chem. Phys., 1998,108,5784. Y. Ito, S. Endo and S. Ohba, J. Am. Chem. SOC.,1997,119,5974.

116 56. 57. 58. 59. 60. 61. 62. 63.

64. 65. 66. 67. 68. 69, 70. 71. 72. 73. 74. 75. 76. 77. 78. 79. 80. 81. 82. 83.

Photochemistry

J.-P. Aycard, D. Synaly and H. Bodot, Spectroscop. Lett., 1997, 30, 1325 (Chem. Abstr., 1997, 127, 749591). S. Andresen and P. Margaretha, J. Chem. Res., Synop., 1997,345. V. Singh and U. Sharma, J. Chem. Soc., Perkin Trans. I , 1998, 305. R. Sadeghpoor, M. Ghandi, H. M. Najafi and F. Faraneh, J. Chem. Suc., Chem. Commun., 1998,329. R. M. Corbett, C.-S. Lee, M. M. Sulikowski, J. Reibenspies and G. A. Sulikowski, Tetrahedron, 1997,53,11099. V. Singh and B. Thomas, J. Org. Chem., 1997,62,5310. S . Kohmoto, H. Yajima, S. Takami, K. Kishikawa, M. Yamamoto and K. Yamada, J. Chem. Soc., Chem. Commun., 1997, 1973. K. Homma and S. Yamada, Chem. Pharm. Bull., 1997,45,1198 (Chem. Abstr., 1997, 127,240777). J. K. Agyin, L. D. Timberlake and H. Morrison, J. Am. Chem. Soc., 1997,119,7945. B. Li, Y.-C. Liu and Q.-X. Guo, J. Photochem. Photobiol. A , 1997, 103, 101 (Chem. Abstr., 1997, 127, 72888). A. Hilgeroth, Chem. Lett., 1997, 1269. T. Suishi, S. Tsuru, T. Simo and K. Somekawa, J. Heterocycl. Chem., 1997,34, 1005 (Chem. Abstr., 1997, 127, 161382). L.-C. Wu, C. J. Cheer, G. Olovsson, J. R. Scheffer, J. Trotter, S.-L. Wang and F.-L. Liao, Tetrahedron Lett. , 1997,38, 3 135. K. Thoma and N. Kubler, Pharmuzie, 1997, 52, 519 (Chem. Abstr., 1997, 127, 499813). D. L. Comins, Y.S. Lee and P. D. Boyle, Tetrahedron Lett., 1998,39, 187. (a) S. McN. Sieburth and C.-H. Lin, J. Org. Chem., 1994, 59, 3597; (b) S. McN. Sieburth, T. H. Ai-Tel and D. Rucando, Tetrahedron Lett., 1997,38,8433. K. Ohkura, Y. Noguchi and K. Seki, Heterocycles, 1998, 47, 429 (Chem. Abstr., 1998,187271). K. Fujimoto, H. Sugiyama and I. Saito, Tetrahedron Lett., 1998,39,2137. W. Saeyens, D. De Keukeleire, P. Herdewijn and A. De Bruyn, Biomed. Chromutogr., 1997,11,79 (Chem. Abstr., 1997,126, 343426). T. Nozaki, M. Maeda, Y. Maeda and H. Kitano, J. Chem. Soc., Perkin Trans. 2, 1997, 1217. C. Saintome, P. Clivio, A. Favre and J. L. Fourrey, J. Org. Chem., 1997,62, 8125. P . Clivio and J. L. Fourrey, Tetrahedron Lett., 1998,39,275. P. Clivio, D. Guillaume, M. T. Adeline and J. L. Fourrey, J. Am. Chem. Soc., 1997, 119,5255. P. Clivio, D. Guillaume, M.-T. Adeline, J. Hamon, C. Riche and J.-L. Fourrey, J. Am. Chem. Soc., 1998,120,1157. M. D’Auria and R. Racioppi, J. Photochem. Photobiol. A , 1998, 112, 145 (Chem. Abstr., 1998,128,237102). F.-T. Hong, K . 3 . Lee, Y.-F. Tsai and C.-C. Liao, J. Chin. Chem. SOC.(Taipei), 1998,45, 1 (Chem. Abstr., 1998, 190888). H. Zhang, M.Zhang and T. Shen, Sci. China, Ser. B: Chem, 1997,40, 192 (Chern. Abstr., 1997, 126, 330394). G. Quinkert, S. Scherer, D. Reichert, H.-P. Nessler, H. Wennemers, A. Ebel, K. Urbahns, K. Wagner, K.-P. Michaelis, G. Wiech, G. Prescher, B. Bronstert, B.-J. Freitag, I. Wicke, D. Lisch, P. Belik, T. Crecelius, D. Hoerstermann, G. Zimmermann, J. W. Bats, G. Duerner and D. Rehm, Helv. Chim. Acta, 1997, 80, 1683.

IIl2: Enone Cycloudditions and Rearrangements 84. 85. 86. 87. 88. 89. 90. 91. 92. 93. 94. 95. 96. 97. 98. 99. 100. 101. 102. 103. 104. 105. 106. 107. 108. 109. 110. 111.

112. 113. 114.

117

M. C. Jimenez, M. A. Miranda, J. C. Scaiano and R. Tormos, J. Chem. Soc., Chem. Commun., 1997,1487. J. J. Paz, M. Moreno and J. M. Lluch, J. Chem. Phys., 1997,107,6275. C. E. Chase, J. A. Bender and F. G. West, Synlett, 1996, 1 173. F. G. West, Adv. Cycloaddit., 1997, 1 (Chem. Abstr., 1997,127, 148738). M. Sakamoto, M. Takahashi, T. Fujita, S. Watanabe, T. Nishio, I. Iida and H. Aoyama, J. Org. Chem., 1997,62,6298. S . K. Hu and D. C. Neckers, J. Org. Chem., 1997,62,7827. S . Hu and D. C. Neckers, J. Org. Chem., 1997,62,6820. S . K. Hu and D. C. Neckers, J. Chem. Soc., Perkin Trans. 2, 1997, 1751. S. Hu and D C. Neckers, Macromolecules, 1998, 31, 322 (Chem. Abstr., 1998, 128, 22129). A. D. Allen, J. D. Colomvakos, F. Diederich, I. Egle, X. K. Hao, R. H. Liu, J. Lusztyk, J, H. Ma, M. A. McAllister, Y. Rubin, K. Sung, T. T. Tidwell and B. D. Wagner, J. Am. Chem. Soc., 1997,119,12125. G. Olovsson, J. R. Scheffer, J. Trotter and C. H. Wu, Tetrahedron Lett., 1997,38,6549, M. B. Rubin, M. Etinger, M. Kapon, E. C. Krochmal, R. Monosov, S. Wieriacher and W. Sander, J. Org. Chem., 1998,63,480. S . Garg and J. C. Kohli, Asian J. Chem., 1997, 9, 845 (Chem. Abstr., 1998, 128, 88649). Y. Yamazaki, T. Miyagawa and T. Hasegawa, J. Chem. Soc., Perkin Trans. 1, 1997, 2979. L. Cermenati, M. Mella and A. Albini, Tetrahedron, 1998,54,2575. C. Rivas, F. Vargas, G. Aguiar, A. Torrealba and R. Machado, J. Photochem. Photobiol., A , 1997,104, 59(Chem. Abstr., 1997,127, 128585). M. Moriyama and A. Yabe, Chem. Lett., 1998,337. 1. Amada, M. Yamaji, M. Sase, H. Shizuka, T. Shimokage and S. Tero-Kabata, Res. Chem. Intermed, 1998,24,81 (Chem. Abstr., 1998,128,78152). X.-P. Guan, Z. Su, J.-G. Sun and Y.-Z. Yu, Molecules, 1996, 1, 46 (Chem. Abstr., 1997,127, 50315). S . Aich, C. Raha and S. Basu, J. Chem. Soc., Faraday Trans., 1997,93,2991. U. C. Yoon, J. W. Kim, J. Y. Ryu, S. J. Cho, S. W. Oh and P. S. Mariano, J. Photochem. Photobiol. A , 1997,106,45 (Chem. Abstr., 1997,127,197606). K. I. Booker-Milburn, S. Gulten and A. Sharpe, J. Chem. Soc., Chem. Commun., 1997,1385. M. Close, J. D. Coyle, E. J. Haws and C. J. Perry, J. Chem. Res. Synop., 1997, 1 1 5 (Chem. Abstr., 1997, 126, 330576). A. G. Griesbeck, A. Henz, W. Kramer, J. Lex, F. Nerowski, M. Oelgemoller, K. Peters and E. M. Peters, Helv. Chim. Acta,, 1997, 80, 912 (Chem. Abstr., 1997, 3662 14). A. G. Griesbeck, J. Hirt, W. Kramer and P. Dallakian, Tetrahedron, 1998,54, 3169. B. M. Aveline, S. Matsugo and R. W. Redmond, J. ,4m. Chem. Soc.. 1997,119,11785. Y. Yoshioka and M. Irie, Electron. J. Theor. Chem., 1996, 1, I (Chem. Abstr., 1997, 35 9890). L. Yu, D. Zhu and M. Fan, Mol. Cryst. Liq. Cryst. Sci. Technol., Sect. A , 1997,2W, 107 (Chem. Abstr., 1997,461738). J . Biteau, F. Chaput, Y.Yokoyama and J. P. Boilot, Chem. Lett., 1998,359. 2. X. Guo, G. J. Wang, Y. W. Tang and X. Q. Song, Liebigs AnnJRecl., 1997,941. 2. Gou, Y. Tang, F. Zhang, F. Zhao and X. Song, J. Photochem. Photobiol., A , 1997,110, 29 (Chem. Abstr., 1998, 128,8653).

Photochemistry

118

Y. Yokoyama, S. Uchida, Y. Shimizu and Y. Yokoyama, Mol. Cryst. Liq. Cryst. Sci. Technol., Sect. A, 1997,297,85 (Chem. Abstr., 1997,461730). 116. T. Yamaguchi, K. Uchida and M. Irie, J. Am. Chem. SOC.,1997,119,6066. 117. A. R. Kim, Y. J. Mah, S. C. Shim and S. S. Kim, J. Photosci., 1997,4, 49 (Chem. Abstr., 1997,644665). 118. A. R.Kim, K. J. Kim, S. C. Shim and S . S. Kim, Bull. Korean Chem. SOC., 1997,18, 1125 (Chem. Abstr., 1998,128,22683). 119. A. R. Kim, S. S. Kim, D. J. Yo0 and S. C. Shim, Bull. Korean Chem. SOC.,,1997,18, 665 (Chem. Abstr., 1997,127, 176240). 120. E. Bosch, S. M. Hubig and J. K. Kochi, J. Am. Chem. SOC.,1998,120,386. 121. E. Bosch, S . M. Hubig, S. V. Lindeman and J. K. Kochi, J. Am. Chem. SOC., 1998, 115.

120, 592. 122.

M. H. B. Stowell, G. Y. Wang, M. W. Day and S. I. Chan, J. Am. Chem. SOC.,1998,

123.

Y. Chiang, A. J. Krege, B. Hellrung, P. Schunemann and J. Wirz, Helv. Chim. Acta,

124.

T. J. Onofrey, D. Gomez, M. Winters and H. W. Moore, J. Org. Chem., 1997, 62,

120, 1657.

1997,80,1106.

5658. 125. 126.

M. Christ1 and M. Braun, Liebigs Ann./ R e d , 1997, 1135. P. K. Malinen, A. Y. Tauber, J. Helaja and P. H. Hynninen, Liebigs Ann.lRecl.,

127.

J.-F. Chen, S.-D. Yao, G.-S. Chu, Z.-C. Zhang, M.-W. Zhang, W.-F. Wang and N.-Y. Lin, Gaodeng Xuexiao Huaxue Xuebao, 1997, 18, 2004 (Chem. Abstr., 1998,

1997, 1801.

128,22259).

Z. Leonenko, L. Klimenko and N. Gritsan, Mol. Cryst. Liq. Cryst. Sci. Technol., Sect. A , 1997,297, 1 75 (Chem. Abstr., 1997,46 1767). 129. N. Gritsan, Mol. Crysf. Liq. Cryst. Sci. Technol., Sect. A, 1997, 297, 167 (Chem. Abstr., 1997,461766). 130. S. M . Gasper and G. B. Schuster, J. Am. Chem. SOC., 1997,119,12762. 131. D. T. Breslin, J. E. Coury, J. R. Anderson, L. McFaillsom, Y. Z. Kan, L. D. Williams, L. A. Bottomley and G. B. Schuster, J. Am. Chem. SOC.,1997,119,5043. 132. T . Y. Fu, J. N. Gamlin, G. Olovsson, J. R. Scheffer, J. Trotter and D. T. Young, Acta Crystallogr., Sect. C: Cryst. Struct. Commun., 1998, C54B, 1 16 (Chem. Abstr., 128.

1998,128, 86234). 133. 134.

H. Kawakami, Y. Z. Yan, N. Kato, A. Mori, H. Takeshita and T. Nozoe, Bull. Chem. SOC.Jpn., 1998,71,711. A. Mori, H. Kawakami, H. Takeshita and T. Nozoe, Chem. Lett., 1996,985.

Photochemistry of Alkenes, Alkynes and Related Compounds BY WILLIAM M. HORSPOOL

1

Reactions of Alkenes

1.1 &,trans-Isomerization - Considerable interest has been shown over the years in the cis-trans-isomerism of cyclo-octene. Much of this work has focused on the sensitized process in routes to obtain optically active forms. A recent account is concerned with the cyclo-octene derivative ( I ) where the sensitizer is linked to the alkene by means of an optically active side chain.' Irradiation of this (a-cyclo-octene results in diastereoisomeric excesses of 33% and a ZIE ratio of

MeYYMe

RaN c) ) onononoAo

\\//

0

wOwOwOP Photochemistry, Volume 30 0The Royal Society of Chemistry, 1999 119

120

Photochemistry

up to 0.8. Further studies have shown that better des are obtained using the terephthalate analogue of (1). The solvent, temperature and wavelength dependency of reversible cis,trans-isomerism of the donor acceptor alkenes (2), (3) and (4) has been studied in great detail.2 Irradiation of the coronand (5) using benzoquinone as the sensitizer brings about trans,cis-isomerism of the double bond. Both the cis- and the trans-compounds of (5) have been synthesized independently and their photochemical behaviour ~ t u d i e d .The ~ irradiation, however, does not give pure cis- or trans- but yields a photostationary state with cis:trans ratio of 2:3. The photochemical cis,trans isomerism of the crotonate ester (6) using 313 nm radiation has been ~ t u d i e d Isomerism .~ in poly(methacryloyloxyethyl-3N-n-butylaminocrotonate) was also examined under the same conditions.

1.1.I Stifbenes and Related Compounds - The photoisomerization of stilbene has been studied under collisional gas-phase condition^.^ The photophysical characteristics of a series of 4,4'-disubstituted stilbenes have been measured.6 The control exercised by the dextrins on photochemical processes within the cavities continues to produce interesting results. Thus irradiation ( h = 312 nm) of the Interest in the synthesis stilbene (7) in P-cyclodextrin results in E,Z-is~merism.~ of polyrotaxanes has grown considerably over the years. Recently reported work has examined the trans,cis-isomerism of the model stilbene (8) and of polymers based on the more complex derivative (9).* The isomerism within the polymer system occurs smoothly and without degradation of the polymer chain. Saltiel

1113: Photochemistry of Alkenes, A Ikynes and Related Compounds

121

and his co-workers have studied the photochemical processes encountered with the stilbene analogue (lo).' Among many features studied the temperature dependence of the isomerism was evaluated. The photoisomerization of the stilbene analogues, e.g. 1-(9-anthryl)-2-(pyridyl)ethenes has been examined in various solvents." Upper excited singlet states are proposed to be implicated in the fluorescent decay of some trans- 1,2-diarylethenes bearing naphthyl, phenanthryl, anthryl, pyrenyl and pyridyl groups." Arai et al. have studied the photochemical isomerization of 2-styrylazulene and 1,2-di(azulenyl)ethene.l 2 Both of these compounds undergo one-way cis, trans-isomerism on direct and sensitized irradiation. A further study on the photochemical rearrangement of alkenes of the type represented by (1 1) has demonstrated that in the open form the system can complex Cs+ specifically.'3 Irradiation at 313 nm brings about ring closure (a six electron cyclization) into a form where Cs+ is not complexed. Thus the authors suggest that the thienylalkene behaves as a pair of molecular tweezers. Other studies by the same group have examined photocyclizations of such molecules as the dithienylperfluorocyclopentene (12 ) in the crystalline phase.14" The quantum yield for the photocyclization of (12) is enhanced when it is irradiated in the cavity

R

R (12) R = S03Na

F2(3F2

NC

"

(13) n = 0 , 1 or2

CN

122

Photochemistry

of p- or y-cyclodextrin. Applications of such systems for liquid crystal displays have also been noted.’4b A review has highlighted the advances made in the study of photochemistry in organized or constrained systems.l 5 More data concerning the photochemical behaviour of alkenes such as (13) has been reported.16 In this case the photochromic compound has thiophene oligomers as the aryl groups. Photochromism of some iodothienylethenes in a sol-gel matrix has been reported. l7 The photochromic properties of 2-(1,2-dimethyl-3-indoly1)-3-(2,4,5-trimethyl3-thieny1)maleic anhydride in poly(vinylbutyra1) film have been examined.l 8 1.2 Miscellaneous Reactions. 2.2.2 Addition Reactions - A novel photochemical reaction of stilbene in carbon tetrachloride solution has been described.’’ Irradiation of this system populates the first excited singlet state of stilbene which then abstracts a halogen from the solvent. The resulting radical pair composed of a trichloromethyl radical and (14) yields the products.

CI

(14)

H

Fischer and Wan report that the phenol derivatives (19,(16) and (1 7) undergo addition of water to the double bond when they are irradiated in acetonitrile/water solution.20 The study has shown that the hydrogen transfer occurs with the participation of a so-called water trimer. This process yields the zwitterion (18) that is responsible for the formation of the products [e.g.(19) from (15)]. The reactions are efficient withquantum yieldsin the0.1-0.24 region. Thephotohydrationofthediynes (20)has been examined indetail. Quenchingstudiesindicatethat the photohydration occurs from the excited singlet state of the alkyne in preference to the triplet. Four products, (21), (22), (23) and (24), are obtained from these hydrations. The ratio of C4:Cl hydration appears to besubstituentdependent and thevaluesobtainedareO.84 from (20, X=p-C02Me), 3.6 from(20, X =p-OMe), 0.12 from(20, X =rn-CF3)and0.73 from (20, X = p-CF3). A review has highlighted the photochemical reactions of conjugated polyalkynes. 22 As well as cis, trans-isomerism, irradiation of the cinnamylnaphthols (25) brings about photochemical cyclisation to afford the two products (26) and (27).23 Cyclization also occurs with phenyl derivatives such as (28).24Again the cyclizations follow two paths to yield a mixture of the cyclized derivatives (29) and (30). The influence on the photochemistry of substituent groups attached to the styryl moiety has been evaluated and it is evident that a charge transfer (CT) is involved and that the outcome of the reactions is solvent dependent. The CT in the excited state brings about a proton transfer followed by cyclization to yield the products (29) and (30) where the latter is predominant. When acetone is used as sensitizer no reaction is observed. The competition between dehalogenation and cyclization within the derivatives (31) has been studied.25 With the chloro and bromo derivatives fission of the halogen bond occurs and addition of solvent to the aromatic ring takes place.

IIl3: Photochemistry of Alkenes, Alkynes and Related Compounds

123

Yh

Ph

OH

HO

Wh@ II CH=C=CHC--BU'

@CH2C=C-But

x -

(22)

W \

OH

(23)

/ P

h

\

(24)

\

/

,.: R (26) R = H (55%) R = COCH3

R (25) R = H or CH3CO

/

R

(27)R = H (44%)

R = COCH3 (92%)

UR flR \

\

\

(28) R = Ph, Me, OMe

R

(29)

\ (31) R = CI or Br

(30)

Ph

1.2.2 Electron Transfer Processes - The use of photochemical single electron transfer processes has been made in an approach to the synthesis of naphthalones. The reaction involves irradiation of the en01 ether of a ketone such as (32) which yields the radical cation (33) that cyclizes onto the aryl ring.26

Photochemistry

124

(35)

0-TBDMS

(36)

'0

Elimination of the silyl group affords the final products (34). The reaction has been extended to provide a path to larger ring ketones such as the cyclization of (35) to yield (36) and also to the synthesis of spiro ketones (37) from (38). Other studies have sought to establish the scope and limitations of the photoNOCAS process. Thus Arnold and co-workers have examined the reactions of alkenes with 1,4-dicyanobenzene (DCB).27 A typical result from this reaction is shown in Scheme 1. All of the products arise from the attack of the radical cation of the alkene on the DCB sensitizer with loss of the cyano function. A further study of photo-NOCAS reactivity has demonstrated that the radical cation of 2,3-dimethylbut-2-ene, formed by irradiation in the presence of DCB/biphenyl, can be trapped by fluoride ion.**The resultant radical (39) reacts with the radical anion of DCB to yield the adduct (40). The radical cation of methylenecyclopropane (41) can be formed by irradiation in the presence of DCB as the ~ensi t i zer. ~~ The products are illustrated in Scheme 2 and, as shown, in all cases the cyclopropane ring remains intact. The diene (42) undergoes SET to dicyanobenzene as the sensitizer with biphenyl as the co-~ensitizer.~'In the absence of nucleophiles many products are formed such as (43) and (44)by reaction with the solvent acetonitrile or the sensitizer, respectively. In the presence of alcohols low yields of (45) and (46) are formed by reaction of the alcohol with the radical cation of the diene (42). A study of the cyclization of (aminoa1kyl)styrylamides has been rep~rt ed. ~' Medium sized-ring lactams can be prepared by irradiation of some N-(aminoalkyl)-2-stilbenecarboxamides.32A review has discussed the use of immobilized photosensitizers in organic photo~hemistry.~~ 1.2.3 Other Processes - The unfiltered irradiation of (47) in acetonitrile solution results in isomerization into (48) in reasonable yield.34The reaction is an example of a concerted 1,3-alkyl migration on an ally1 moiety. The authors claim this to be the first example of a rearrangement from a cembrane to the pseudoterdne

Ul3: Photochemistry of Aikenes, Alkynes und Reluted Compounds

CN

CN

CN

42%

23%

125

CN trace

Scheme 1

(41)

CN 5%

1 1Yo

13% Scheme 2

21%

8%

12%

-5' 6Me CN

0 (42)

(43) 2Yo

(44) 2%

CN

/

(45) 3%

(46) 2%

skeleton. Bentrude and co-workers previously reported the 1,3-allylic rearrangement of phosphites under electron transfer conditions3' and they have used this methodology in a further study.36Thus irradiation of (49) in acetonitrile solution using DCN as the sensitizer brings about conversion, via the radical cation, into the isomeric product (50). The study of the photochemical reactions of 1,3-diaryl-1,2-dihydropentalenes (5 1) has shown that irradiation transforms them into the isomers (52).37 It is proposed that this process occurs by a photochemical 1,5-hydrogen shift but concerted 1,Shydrogen migrations are

Photochemistry

126

(47)

OP(OEt)* (49)

@ A?

A?

required to be antarafacial on the skeleton and this is unlikely in this system. The same outcome could arise from two suprafacial 1,3-hydrogen migrations. A study of the photodissociation of chloroethene on irradiation at 193 and 210 nm has been reported.38 The photochemical decomposition of 1,l- and 1,2difluoroethene has also been studied using 193 nm light.39 Two studies have examined the photochemical decomposition of tri~hloroethene.~'One of these has utilized in situ NMR studies for the analysis of the system.40b 2

Reactions Involving Cyclopropane Rings

2.1 The Di-lt-methane Rearrangement and Related Processes - The di-nmethane reactivity of the 1,4-dienes (53) has been reported.41 The rearrangement occurs in either methanol or acetone and affords the cyclopropane derivative (54) as the major product. Other products include (55) and (56) from both (53a) and (53b). Another minor product (57) is forrned from (53b). While the reaction of (53) is fairly selective the photorearrangement of (58) affords many products. The authors reason that the preference for the formation of (54) is a result of the orientation of the phenyl moiety. The axial orientation is the one in which the 1,2-phenyl migration occurs most readily. The cyclopropane derivatives (55) could well be formed by a second photochemical step involving the rearrangement of the principal product (54). Other studies on the rearrangement of such systems have been described.42 Thus both the dienolactones (59) and (60)

127

IIl3: Photochemistry of Alkenes, Alkynes und Related Compounds

R 0

Ph

(54) a: 43% b: 48%

(53) a : R = R = H

b: R-R = (CH&

0

(55) a: 4% b: 80/0

Ph

(56) a: 5% b: 9%

Ph

k0k0 I

Ph

(611

Ph 0

(62)

6h

&o

Ph

(63)

undergo the di-x-methane conversion on irradiation in methanol to yield the rearrangement products (61), as a 1:l mixture of the 6a and the 6p isomers, from (59) and (62) and (63) from (60). The question of conformational control was discussed. Some enantioselectivity in the product (64)has been reported following the irradiation of the norbornadiene (65) in a TIY zeolite.43(-)-Ephedrine was used as the chiral inductor and sensitisation brought about the reaction in 30 min. An ee of about 14% was achieved. A study of the influence of electron-donating and electron-withdrawing substituents on the outcome of the di-x-methane reaction of some benzobarrelenes has been evaluated.4 George and co-workers have been studying the photochemical reactivity of systems such as (66) for a number of years?’ Irradiation of these dibenzobarrelenes yields the corresponding semibullvalenes and the structures of these photo-products have now been determined by X-ray crystallographic analysis. Other studies by the same group have examined the photoreactivity of (67).46 Direct irradiation in acetonitrile, benzene or p-xylene solution of the dibenzonorbornadiene derivative (68) affords the cyclooctatetraene (69) in 48% yield.47The reaction only arises from the singlet state and sensitized irradiation fails to yield a clean product. When the bis hydrochloride salt of (68) is irradiated in methanol using xanthene as the sensitizer the semibullvalene (70) is obtained. The photochemistry of (68) in the solid phase is completely different and irradiation yields only the pyrrole derivative (71). The authors suggest that steric effects within the crystal direct the reaction along this path. The barrelene (72a) undergoes efficient photorearrangement to the semibullvalene (73a).48 The reaction is best carried out in cyclohexane with 254 nm radiation. The yield of product (73a) is 94% and the isomeric barrelene (72b) is

Photochemistry

I28 COPh

COPh

But

(72) a: R'

= H, R2 = Ph b: R' = Ph, R2 = H

(73)a: R ' = But, R2 = H

b: R' = H, R2 = Bu'

also photoreactive by the same di-x-methane rearrangement path and yields (73b). A detailed review of the family of reactions related to and including the di-rcmethane rearrangement has been published.49

2.2 Other Reactions Involving Cyclopropane Rings. 2.2.I SET Induced Reactions The radical cation of phenylcyclopropane can be obtained by irradiation in the presence of chloranil as the electron accepting ~ensitizer.~' Armesto and his co-workers have studied the photochemical reactivity of the Sensitized imine (74) under both sensitized and electron transfer conditi~ns.~' irradiation using acetophenone in methylene chloride brings about conversion to the three products shown in Scheme 3. The reaction is proposed to take place by energy transfer to the 1,l -diphenyl alkenyl moiety followed by bridging to yield

M3: Photochemistry of Alkenes, Alkynes and Related Compounds

129

the biradical (75). This radical is the source of the primary photoproduct (76) which is converted during chromatography into the isolated products (77) and (78). A further product (79) survives the isolation procedures. Direct irradiation follows the same path and yields (77) and (78) as the isolable products. Single electron transfer with DCA yields the zwitterion (80) that has two possible forms. Reaction within this radical cation gives the products (77), (79) and another compound identified as (81). This last compound arises from hydrolysis of the structurally rearranged imine (82). Several other examples of this novel photochemical behaviour were reported.

(77) 82%

(74)

Ph Ph$ N Ph

-

Ph

Ph

" PhA

N

Ph

Ph

(79) 3%

(78) 11%

Scheme 3 Ph Ph Ph/$NyPfh9Lph "Ph

Ph

Ph

Ph

(75)

PhPh X

P NH2h

ex

P Phh

x

L

II

2.2.2 Miscellaneous Reactions Involving Three-membered Ring Compounds - The dichlorocyclopropylarenes (83) undergo photochemical ring opening via the corresponding radical cation.52 The intermediate is formed by irradiation of (83) at 300 nm in the presence of DCB as the sensitizer. When methanol is used as a co-solvent, addition occurs at the benzylic site to yield the adducts (84). The outcome of the reaction is somewhat substituent dependent as can be seen from the isolated yields shown below (84). The regiochemistry observed within this system is different from that reported from the irradiation of phenylcyclopropane under similar conditions when 1-phenyl-3-methoxypropanewas formed.53 The authors suggest that the controlling feature is the dichloro substituents. A review lecture has focused on the electron transfer photochemistry of strained-ring and unsaturated systems.54 The cyclopropane derivative (85) undergoes photochemical reduction when

rcl Photochemistry

130

Me0

Q

I&"

A

(83) R = OMe, Pr', Me, H, F, CI or CN

A

(84) R Yield (%)

Me0 Pr' Me H F

CI

CN

18 21 71 85

22 88 17

irradiated in a mixture of ethanol and a~etone.~' The reduction proceeds by way of the cyclopropyl radical intermediate (86) which cyclizes to yield a diastereoisomeric mixture of (87). The irradiation through Pyrex of solutions of (88) in cyclohexane affords the two products (89, 29%) and (90, 10Y0).The formation of (89) is clearly a result of radical attack on the solvent and involves hydrogen abstraction and bonding. An analogous reaction is observed when (88) is irradiated in pentane. A low temperature study has identified the biradical(91) as the key intermediate in the photochemical reaction.56

3

Reactions of Dienes and Trienes

Laser irradiation at 266 nm of the 2,5-dimethylhexa-2,4-dienein aerated acetonitrile affords the corresponding radical cation.57 Other less heavily substituted dienes do not undergo this process on direct irradiation and electron transfer sensitization has to be used. Typical of this process is the generation of the radical cation of piperylene by irradiation with dicyanobenzene as the sensitizer and biphenyl as the co-sensitizer. The presence of the co-sensitizer permits cage escape of the radical cation of the diene. A study of the photochemical ring

131

IIl3: Photochemistry of Alkenes. Alkynes und Reluted Compounds

opening of cyclohexa-1,3-diene has shown that the process is very rapid and occurs within 250 fs.'* The azepines (92) undergo photoisomerization, a typical reaction of such trienes, into the bicyclic derivatives (93).'9 Substitution dependent reactivity has been observed on irradiation of the differently substituted dienes (94) and (9S).60 The diester (94) undergoes the more usual isomerization, as observed for (92), to yield the cyclobutene derivative (96). The mono-ester, as the optically active compound (+)-(99, however, affords a good yield (77%) of the bicyciobutane (+)-(97). In this case crossed addition occurs within the diene.

(92) (93) R = OEt, NH2 or NMQ

(94) R=C@Me (95) R = H

(96) R=C@Me

(97)

Okoyuma et al. have reported that the strained Dewar paracyclophanes (98) can be converted into the benzenoid parent compounds (99) by irradiation of the compounds in a diethylether-isopentane glass at 77 K using 365 nm light.6' Interestingly when (99, R' = CN, R2 = H) is allowed to thaw to room temperature there is a thermal reaction that converts it back into the Dewar form which provides the first observation of such a thermal cyclization. Irradiation at 254 nm of the tetraene (loo), a bis-Dewar benzene, at 77 K in a matrix results in its conversion into the paracyclophane (10 1).62Continued irradiation transforms (101) into the (4+4)-adduct (102). The products from this low temperature

(98) R'

= CN,

R2= H

R1 =CN, R2=Me

I32

Photochemistry

irradiation were not isolable. A theoretical study of the phototransformations of the radical cation of cyclooctatetraene has been published.63ab initio Calculations have been used to study the photochemical reactivity of the protonated Schiff's base, 4-cis-y-methyl-nona-2,4,6,8-tet raeniminium ion.64 The photocycloreversion of the cage compounds (103) and (104) affords the corresponding naphthalenes q~antitatively.~~ Noh et al. have described the photochemical dissociation of the adducts (105)? Benzophenone-sensitized irradiation of the cyclobutene derivative (106) in acetonitrile solution results in the formation of a diene.67The reaction mixture is subsequently heated in xylene at 150 "C whereby the dimer (107) was obtained. Irradiation of the silacyclobutene (108) at 193 nm brings about ring opening with the formation of the silene ( 109).68 Various studies were carried out including the effects of solvent on the lifetime of the siladiene (109) and also its reactivity with alcohols. Leigh and coworkers have also reported that the irradiation of the disilacyclobutane derivative (1 10) at -196 "C in methylcyclohexane affords the silene (1 11) as the principal product.69 The silene can be trapped when the irradiations are carried out in the presence of buta-l,3-diene when (1 12) and (1 13) can be isolated. 2,2'-Biadamantylidene is also formed under these conditions. Similar behaviour was observed for the analogous 1,2-digermacyclobutanederivative.

(104) R = H or CN

(105) R = C02Me or CN

C02R2 C02R2 (106) R' = CHMe2, R2 = Me

(Me3Si)2Si-SicSiMe&

(110)

(111)

(112)

(113)

A study of the photochemical behaviour of the diene (114) using DCA as the sensitizer has shown that a degenerate Cope process is ~perative.~' This treatment affords a mixture (52:48) of the two dienes (1 14) and (1 1 9 , and a detailed study of this reaction has been carried out. 1 , l -Diphenylhepta-l,6-diene(1 16) undergoes photocyclization to give the radical cation (1 17) which cyclizes via the sixmembered transition state shown in (1 18).7' This intermediate is trapped by attack of acetonitrile to yield ultimately the adduct (1 19) which is formed in

133

IIl3: Photochemistry of Alkenes, Alkynes and Reluted Compounds

competition with (120) formed by the addition of water. Nitriles other than acetonitrile can be used effectively as traps for the cyclized radical cation (I 18). The reaction fails when the chain linking the two alkene moieties is shortened. Thus with (121) only the alcohol (122) is formed. Further examples of the intramolecular electron transfer photochemistry of compounds sucF as (1 23) have been reported.72 The first examples of this type of reaction were described by Armesto, Horspool and co-workers some years The present report gives further examples of the conversion of (123) into the cyclobutene (124), the principal photochemical product, and the fragmentation products (125) and ( 126).72 Ph

-f>

Ph /

/

Ph

Ph$

Ph& Ph

NHCOMe

Ph

NC

CONH2 (124)

R' R2 R3 Pri Pr' Ph Ph Ph Ph

H H H H H H

(126) (yield YO) (124) (125) (126)

(125)

Ph Me Ph Me Ph H

X C02Et C02Et C02Et C02Et COPh CN

26 49 29 29 21 23

-

-

11 20 17 17

-

-

10 8 13 22

Yoon and Chae have examined the photochemical reactivity of the cyclopentadiene derivatives (127) under DCA sensitized condition^.^^ Irradiation brings about the formation of several products but only the anti-Bredt adduct (128) is different from those obtained by thermal reactions. The data suggest that the

I34

Photochemistry

(127) n = 2 O f 3

(128) n=2(12%) n = 3 (13%)

(132) Ar = pMeOC6H4

adducts (1 28) are formed via a triplex intermediate, such as that shown in (129), with interaction between the diene, the alkene and the sensitizer. While the irradiation involves a mixture of the cyclopentadienes it is likely that the anti-Bredt products are formed exclusively from the 2-isomer (130). Irradiation of the vinylbenzofuran (13 1) in the presence of I ,3-dienes such as cyclohexa-l,3-diene and the pyrilium salt (132) results in the formation of adducts such as (1 33).75As well as the formation of the Diels-Alder product, cycloaddition to afford cyclobutane derivatives is observed. The authors propose that the reactions involve electron transfer processes resulting in radical cations that undergo the addition to the dienes. Calculations have been carried out that support these findings. The deactivation of the excited singlet state of the triene (134) by charge transfer processes has been studied in The influence of substituents on the spectroscopic properties of the triene (134) has also been studied.77 Other workers have demonstrated substituent effects on the cis-trans isomerism of (1 35) to give (136).78The quantum yield for this isomerism was enhanced when the substituents were polar. Contrary to this effect the isomerism to (137) was

(134)

(135) R = CN, Me02C, CHO, CI, CH3, OCH3

IIl3: Photochemistry of Alkenes, Alkynes and Related Compounds

135

enhanced when the substituents were electron donating. Tsujimoto and coworkers have observed that 11-methylretinochrome can be photochemically converted into 1 1-cis-1 1-methylretinochrome in 90% yield.79 This product is accompanied by the 13-&isomer and the all-trans-isomer. Other accounts have reported calculations dealing with the photoisomerism of retinals and protonated Schiff's bases8' Evenzahav and Turro have studied in considerable detail the photochemical cyclizations encountered with the diynes (1 38) and (139) in propan-2-01.~' This work was originally published in note form.82Direct irradiation of the diyne (138) results in the formation of the products shown in Scheme 4. These products are obtained in ratios of 2:4:2: 1. Irradiation of (139) gives the cyclized product (140) exclusively. From a series of investigations using triplet sensitization and laser flash studies it was concluded that a biradical mechanism was involved.

PiOH

+

__c

Scheme 4

The distyrylbenzene derivative (1 4 1) is photochemically reactive on irradiation in solution.83The solvent of choice is acetonitrile/benzene/water(7:2: 1) saturated with ammonia. The reactions encountered with this system are derived from electron transfer initiated by pdicyanobenzene as the electron accepting sensitizer. This process yields the radical cation (142) of the starting material and also the cyclized radical cation (143). These species are trapped by ammonia to yield the final products (144) and (145) in the yields shown. The naphthyl system [141, R-R = (CH=CH)z] is also reactive and affords the analogous products (146) and (147). A study has examined the photochemically-induced cyclization of tetraenes such as (148) under SET conditions in aqueous acetonitrile solution.84 A variety of electron accepting sensitizers was used. In the example cited the sensitizer (149) was effective and the cascade cyclization yielded the product (150). 3.1 Vitamin D Analogues - The analogues (1 5 1) of pre-vitamin D3 have been synthesised and their irradiation in THF solution at wavelengths around 300 nm brings about cis,trans-is~merism.~~ Cyclization to (152) is also observed and in this process there is a wavelength and excited state dependence. Thus with

136

Photochemistry

500 nm results in the exclusive formation of the (2+2)-cycloadduct identified as (173). The quantum yield for the formation of this adduct is 4 x The reaction in the crystal is thought to involve an electron transfer process with the generation of a radical ion pair. Irradiation of acenaphthene on silica gel at the gel air interface results in the formation of l-a~enaphthenol.'~~

Photochemical cycloadditions of the alkyne (174) to the dienedione (175) occurs sequentially and affords the two adducts (1 76) and (1 77).Io6 The latter was chemically transformed into the [ 1 . 1 Jparacyclophane (1 78) which was then studied photochemically. The photochemical cycloaddition of ethyne to the dehydrodoanthracene (1 79) results in the formation of the (2+2)-cycloadduct (1 80). Io7 A study of unti-o,o'-dibenzene (1 81 a) has shown that on irradiation bond cleavage occurs with the formation of excited state benzene.'" The related compound (1 8 1 b) is also photoreactive and on irradiation through a Vycor filter gives benzene and phenyl acetate. 0

gR 4 gR "

(174)

R

R

(175)

/

/

0

R

0

X

Ul3: Photochemistry of Alkenes, Alkynes and Related Compounds

141

(181) a : R = H

b: R = AcO

6

Miscellaneous Reactions

6.1 Miscellaneous Rearrangements and Bond Fission Processes - Full details of the photochemical reactivity of 1,3-dichloro-1,3-diphenylpropane have been p~blished.'~'Nagahara et al. have reported several examples of the photochemical conversion of alkyl iodides into esters."' This reaction is achieved by irradiation for 15 hours through Pyrex of an alkyl iodide in an alcohol under a pressure of 20 atm of carbon monoxide. If the reaction is carried out in the presence of a base such as potassium carbonate then good yields of product are obtained. The conversion of 2-iodooctane, for example, gives the ester (182) in 72% yield. In the absence of a base the reaction fails. Several alcohols were used such as benzyl alcohol, cyclohexanol and chloroalcohols. An acyl radical is the key intermediate and is formed by the trapping of the alkyl radical by carbon monoxide. Sonoda and Yanagi have patented this process.'I The patent reports that the irradiation for 16 hours of 5-iodononane in ethanol under a pressure of 40 atmospheres of carbon monoxide affords ethyl 2-butylhexanoate. The photochemical dissociation at 304 nm of methylene iodide has been studied.'I2

'

The product (183) is formed on irradiation of acridine (184):phenothiazine (185) crystals in which the ratio of the reactants is 3:4.'13 This reactivity is different from the solution phase (in acetonitrile) process which affords both (183) and the dihydro dimer (186). The photoinduced electron transfer reactions of some a-silyl ethers has been investigated. I4 The sensitizing system uses DCA/ biphenyl and irradiation at h > 345 nm in acetonitrilelmethanol. The irradiation brings about the formation of the radical cation (187) of the ether which undergoes cleavage to yield the radical (1 88), a hydroxymethyl equivalent. When these are generated in the presence of a$-unsaturated esters such as (189) addition takes place affording the adducts (190). Additions to dimethyl maleate were also carried out successfully. l4 High yields of alcohols can be obtained on irradiation of the ether derivatives (19 l).' l 5 The ethers in acetonitrile/water solution are photo-cleavable on irradiation at 254 nm or 300 nm and the yields obtained are good to excellent. The multi-photon chemistry of the naphthalene derivative (192) has been studied

'

'

Photochemistry

142

R.oATMs

-

-

+* [.-,ATMS] R.

(1 87) R = Me, PhCH2, TIPS or TBDMS

HH::3

00. (1 88)

Me

(1 89)

= Me (46%), R = TIPS (25%) R = PhCHP (64%), R = TBDMS (42%)

(190) R

using laser-jet irradiation at 333, 351 and 364 nm.'I6 The naphthalene (193) is obtained in 26% in a two-photon process when (192) is irradiated in carbon tetrachloride. Irradiation of Mannich bases such as (193) in acetonitrile/water solution using h c 300 nm induces the formation of the o-quinomethide intermediate (195) which is then readily trapped in a Diels-Alder reaction by ethoxyethene to give the adduct (196) in 71% yield.Il7 The use of wavelengths ca. 300 nm is less aggressive than the 254 nm irradiation of diols such as (197) that has been reported in past by Wan and his co-workers. The influence of the position of the aryl substituent in (194) was also investigated and it was shown that the best yields were obtained when the phenyl group was in the meta-position to the hydroxyl substituent. Other systems such as (198) and (199) were also studied. Wan and co-workers have previousIy shown that it is possible to generate o-quinone methides photochemically. Their recent account described such a reaction where the resultant quinone methide has a suitable electron rich dienophile substituent and this leads to Diels-Alder trapping. ** Photosolvolysis, using irradiation from a ruby laser or a flashed xenon lamp, of the cycloheptatrienes (200) results in the formation of the aryltropylium ions (2Ol).Il9 The lifetime of these species is dependent upon the substituent in the aryl ring. A study of the reactivity induced by irradiation at 254 nm of the epoxides (202) has been carried out.'*' The aim was to study the formation of the ylides (203). The reactions were carried out in acetonitrile solution with ethyl vinyl ether as the addend and are reported to be dependent to some extent on the substitution pattern. Thus, irradiation of (202a) fails to yield an adduct and only the enone (204, 33"/0) is formed. Epoxides (202b) and (202c) do produce ylides that add to the alkene to yield mixtures of the adducts (205) regiospecifically with a preponderance of the exo-adduct. The epoxide (202d) is also reactive and gives a low yield of the adduct (206, 2%). In general the overall yields are moderate. The

IIl3: Photochemistry of Alkenes, Alkynes and Related Compounds

143

photochemical reactivity of the 3-( 1 -naphthyl)-2-(1 -naphthalenemethyl)oxaziridine has been studied by benzophenone sensitized irradiation in acetonitrile or benzene.12' Ph O-R

(191) R = PhCH2CH2, Ph,-

gMe2 H:&

\

OH

\

\

R'

(202) R2

Q 0

R3QR1

R2

/

Ar

(204) 33%

n

a:H H b: CN H c: CN Me d: CN H

1 1 1

2

NC

CN

R'

(205) R' = H, R2 = OEt, R3 = H 36% R' = H, R2 = H, R3 = OEt 8% R' = Me, R2 = OEt, R3 = H 25% R' = Me, R2 = H, R3 = OEt 7%

OEt

N&

(206)2%

144

Photochemistry

Suzuki and co-workers have examined the influence of substituents on the outcome of some photochemical ring opening reactions involving SET sensitiOne of the reactions studied is the photochemical ring opening of the acetal (207). Following the photochemical reaction the mixture is treated with HCVMeOH and separated to yield the two products shown in Scheme 5. The relative quantum yields shown under the reaction sequence illustrates the influence of increasing substitution by methyl groups of the viability of 1,4dicyanobenzene and derivatives as SET sensitizers in this reaction.

relative 6 l,.Q-DCB 1 2-MeDCB 2 2,CidiMeDCB 2.3 0.8 2,3,5-triMeDCB 2,3,5,6-tetraMeDCB 0

Scheme 5

7 1.

2. 3.

4. 5. 6.

7. 8.

9. 10. 11.

12. 13. 14.

References T. Sugimura, H. Shimizu, S. Umemoto, H. Tsuneishi, T. Hakushi, Y. Inoue and A. Tai, Chem. Lett., 1998, 323. R. E. Martin, J. Bartek, F. Diederich, R. R. Tykwinski, E. C. Meister, A. Hilger and H. P. Luthi, J. Chem. Soc., Perkin Trans. 2, 1998,233. D. Marquis, B. Henze, H. Bouas-Laurent and J. P. Desvergne, Tetrahedron Lett., 1998,39, 35. I. Lukac, Cs. Kosa, U. Salz and N. Moszner, J. Photochem. Photobiol., A , 1997,110, 23 (Chem. Abstr., 1998,128, 8652). A. Meyer, J. Schroeder, J. Troe and M. Votsmeier, J. Photochem. Photobiol. A, 1997, 105,345 (Chem. Abstr., 1997,127, 197600). V. Papper, D. Pines, G. Likhtenshtein and E. Pines, J. Photochem. Photobiol., A , 1997,111,87 (Chem. Abstr., 1998,128, 108252). W. Herrmann, S. Wehrle and G . Wenz, J. Chem. SOC.,Chem. Commun., 1997, 1709. W. Hermann, M. Schneider and G. Wenz, Angew. Chem. Int. Ed. Engl., 1997, 36, 2511. J. Saltief, Y. Zhang and D. F. Sears, Jr., J. Am. Chem. Suc., 1997, 119, 1 1202. E. J. Shin, E. Y. Bae, S. H. Kim, H. K. Kang and S. C. Shim, J. Photochem. Photobiol. A , 1997,103, 137 (Chem. Abstr., 1997,127,255092). G . G. Aloisi, F. Elisei, L. Latterini, G. Marconi and U. Mazzucato, J. Photochem. Photobiol., A, 1997,105,289 (Chem. Abstr., 1997,127,212339). T . Arai, Y. Hozumi, 0. Takahashi and K. Fujimori, J. Photochem. Photobiol., A , 1997, 104, 85 (Chem. Abstr., 1997, 127, 128590). M. Takeshita and M. Irie, Tetrahedron Letl., 1998,39,613. (a) M. Takeshita, C. N. Choi and M. Irie, J. Chem. Soc., Chem. Commun., 1997,

1113: Photochemistry of Alkenes, Alkynes and Reluted Compounds

15. 16. 17.

18. 19. 20. 21. 22. 23. 24. 25. 26. 27. 28. 29. 30. 31. 32. 33.

34. 35. 36. 37. 38. 39. 40 41. 42. 43. 44. 45.

I45

2265; (b) M. Irie, T. Lifka and K. Uchida, Mol. Cryst. Liq. Cryst. Sci. Technol., Sect. A, 1997,297,81 (Chem. Abstr., 1997,461728). S. Wu, Huaxue Jinzhan, 1997,9, 160 (Chem. Abstr., 1997,501188). M. hie, T. Eriguchi, T. Takada and K. Uchida, Tetrahedron, 1997,53, 12263. J. Biteau, G. Tsivgoulis, F. Chaput, J.-P. Boilot, S. Gilat, S. Kawai, J.-M. Lehn, B. Darracq, F. Martin and Y. Levy, Mol. Cryst. Liq. Cryst. Sci. Technol., Sect. A , 1997,297,65 (Chem. Abstr., 1997,461725). T. Tsujioka, M. Kume and M. hie, J. Photochem. Photobiol., A , 1997, 104, 203 (Chem. Abstr., 1997,127, 142664). K. Twata and H. 0. Hamaguchi, Bull. Chem. SOC.Jpn., 1997,70,2677. M. Fischer and P. Wan, J. Am. Chem. SOC.,1998,120,2680. S. C. Shim, Y. S. Chae and E. K. Baek, Bull. Korean Chem. SOC., 1997, 18, 364 (Chem. Abstr., 1997,127,63358). S. C. Shim, Mol. Supramol. Photochem., 1997, l(0rganic Photochemistry), 1 1 1 (Chem. Abstr., 1998, 128,204462). M. C. Jiminez, P. Leal, M.A. Miranda, J. C. Scaiano and R. Tormos, Tetrahedron, 1998,54,4337. M. C. Jimenez, M. A. Miranda and R. Tormos, Tetrahedron, 1997,53, 14729. M. C. Jiminez, M. A. Miranda and R. Tormos, J. Org. Chem., 1998,63,1323. G. Pandey, M. Karthikeyan and A. Murugan, J. Org. Chem., 1998,63,2867. D. R. Arnold, K. A. McManus and M. S. W. Chan, Can. J. Chem., 1997,75,1055. M. S. W. Chan and D. R. Arnold, Can. J. Chem., 1997,75,1810. H . J . P. De Lijser, T. S. Cameron and D. R. Arnold, Can. J. Chem., 1997,75, 1795. H. J. P. De Lijser and D. R. Arnold, J. Chem. SOC.,Perkin Trans. 2, 1997,1369. F . D. Lewis, J. Wagner-Brennan and J. M. Denari, J. Photochem. Photobiol. A , 1998,112, 139 (Chem. Abstr., 1998,128,237101). F. D. Lewis and S. G. Kultgen, J. Photochem. Photobiol. A , 1998, 112, 159 (Chem. Abstr., 1998,128,250519). M. Julliard, Photosci. Photoeng., 1997, 2 (Homogeneous ), 22 1 (Chem. Abstr., 1998, 128,167004). A. D. Rodriguez and J.-G. Shi, J. Org. Chem., 1998,63,420. S. Ganapathy, K. P. Dockery, A. E. Sopchik and W. G. Bentrude, J. Am. Chem. SOC.,1993, 115,8863. G. S. Jeon and W. G. Bentrude, Tetrahedron Lett., 1998,39,927. V . Nair, G. Anilkumar, C. N. Jayan and P. N. Rath, Tetrahedron Lett., 1998, 39, 2437, K. Tonokura, L. B. Daniels, T. Suzuki and K. Yamashita, J. Phys. Chem. A,, 1997, 101,7754. B. A. Balko, J. Zhang and Y. T. Lee, J. Phys. Chem., 1997,101,661. (a) K.-H. Wang, H.-H. Tsai and Y.-H. Hsieh, Chemosphere, 1998, 36, 2763 (Chem. Abstr., 1998, 238326); (b) S. J. Hwang, C. Petucci and D. Raferty, J. Am. Chem. SOC.,1997, 119,7877. 0.Muraoka, G. Tanabe and Y. Igaki, J. Chem. Soc., Perkin Trans. 1,1997,1669. 0. Muraoka, G. Tanabe, E. Yamamoto, M. Ono, T. Minematsu and T. Kimura, J. Chem. SOC.,Perkin Truns. 1, 1997,2879. A. Joy, R. J. Robbins, K. Pitchumani and V. Ramamurthy, Tetrahedron Lett., 1997, 38,8825. R. Altundas and M. Balci, Aust. J. Chem., 1997,50,787. M. Muneer, N. P. Rath and M. V. George, Acta Crystallogr., Sect. C: Cryst. Struct. Commun., 1997, C53, 1475 (Chem. Abstr., 1997,127,324685).

146 46. 47. 48. 49. 50. 51. 52. 53. 54. 55.

56. 57. 58. 59. 60. 61. 62. 63.

64. 65.

66. 67. 68. 69. 70.

71. 72. 73. 74.

Photochemistry

S. A. Kumar, D. Ramaiah, N. V. Eldho, S. Das, N. P. Rath and M. V. George, J. Photochem Photobiol. A, 1997,103,69 (Chem. Abstr., 1997,127,72886). J. R. Scheffer and H. Ihmels, Liebigs Ann.lRecl., 1997, 1925. V. Nair, G. Anilkumar, J. Prabhakaran, D. Maliakal, G. K. Eigendorfand P. G. Williard, J. Photochem. Photobiol. A, 1997, 111, 57 (Chem. Abstr., 1998, 128, 121515). H. E. Zimmerman and D. Armesto, Chem. Rev., 1996,96,3065. W. Bergmark, S. Hector, G. Jones, 11, C. Oh, T. Kumagi, S. Hara, T. Segawa, N. Tanaka and T. Mukai, J, Photochem. Photobiol., A , 1997,109, 119 (Chem. Abstr., 1997,312964). D. Armesto, 0.Caballero and U. Amador, J. Am. Chem. Soc., 1997,119,12659. J. Y. Wu, J, C. Mai, K. Pan and T. I. Ho, Tetrahedron Lett., 1998,39,647. V. R. Rao and S. S. Hixson, J. Am. Chem. SOC.,1979,101,4658. H. D. Roth, H. Weng, D. Zhou and T. Herbertz, Pure Appl. Chem., 1997, 69, 809 (Chem. Abstr., 1997,430018). L. V. Sydnes and H. H. Ovrebo, Acta Chem. Scand., 1997, 51, 889 (Chem. Abstr., 1997,127,247789). W. T. Pan, M. Jones, B.Esat and P. M. Lahti, Tetrahedron Lett., 1998,39, 1505. C . S. Q. Lew, J. R. Brisson and L. J. Johnston, J. Org. Chem., 1997,62,4047. S . H. Pullen, N. A. Anderson, L. A. Walker, I1 and R.J. Sension, J. Chem. Phys., 1998,108,556. R. A. Odum and B. Schmall. J. Chem. Res., Synop., 1997,276 (Chem. Absfr., 1997, 127,220537). W. Tochtermann, T. Panitzsch, M. Peschanel, C. Wolff, E. M. Peters, K. Peters and H. G. Von Schnering, Liebigs AnnJRecl., 1997, 1125. M. Okoyuma, M. Ohkita and T. Tusji, J. Chem. SOC.,Chem. Commun., 1997,1277. T. Tsuji, M. Ohkita, T. Konno and S. Nishida, J. Am. Chem. SOC.,1997,119,8425. T. Bally, L. Truttmann and F. Williams, THEOCHEM, 1997, 398-399,255 (Chem. Abstr., 1997, 127,292776). M. Garavelli, T. Vreven, P.Celani, F. Bernardi and M. A. Robb, J. Am. Chem. Soc., 1998,120, 1285. T. Noh, D. Kim and S. Jang, Bull. Korean Chem. SOC.,1997,18, 357 (Chem. Abstr., 1997,127,65371). T. Noh, H. Lim and D. Kim, Bull. Korean Chem. SOC.,1997,18,247 (Chem. Abstr., 1997,126,330354). Y. Nakajima, H. Watanabe, T. Adachi and H. Hotta, Jpn. Kokai Tokkyo Koho, JP 09,278,711 (Chem. Abstr., 1998,128,3483). C . Kerst, M. Byloos and W. J. Leigh, Can.J. Chem., 1997,75,975. Y . Apeloig, D. Bravo-Zhivotovskii, I. Zharov, V. Panov, W. J. Leigh and G. W. Sluggett, J. Am. Chem. Soc., 1998,120,1398. H. Ikeda, T. Minegishi, H. Abe, A. Konno, J. L. Goodman and T. Miyashi, J. Am. Chem. SOC.,1998,120,87. H. Ishii, T. Hirano, S. Maki, H. Niwa and M. Ohashi, Tetruhedron Lett., 1998, 39,2791 . D. Armesto, A. Albert, F. H. Cano, N. Martin, A. Ramos, M. Rodriguez, J. L. Segura and C. Seoane, J. Chem. SOC.,Perkin Trans. 1, 1997,3401. D. Armesto, W. M. Horspool, N. Martin, A. Ramos and C. Seoane, J. Chem. SOC., Chem. Commun., 1987, 1231; D. Armesto, W. M. Horspool, N. Martin, A. Ramos, C. Seoane, J. Org. Chem., 1989,54,3069. H. Yoon and W. Chae, Tetrahedron Lett., 1997,38,5169.

1113: Photochemistry of Alkenes, Alkynes and Related Compounds

147

77.

J. Botzem, U. Haberl, E. Steckhan and S. Blechert, Acta Chem. Scand, 1998,52, 175 (Chem. Abstr., 1998,128, 180292). F. Schael, J. Kuester and H.-G. Loehmannsroebben, Chem. Phys., 1997, 218, 175 (Chem. Abstr., 1997, 127, 101641). G. Pistolis and A. Malliaris, Chem. Phys., 1998, 226, 83 (Chem. Abstr., 1998, 128,

78. 79. 80.

Y. Sonada, H. Morii, M. Sakuragi and Y.Suzuki, Chem. Lett., 1998,349. K. Tsujimoto. Y. Shirasaka, T. Mizukami and M. Ohahsi, Chem. Lett., 1997,813. M. Garavelli, T. Vreven, P. Celani, F. Bernardi and M. A. Robb, J. Am. Chem. SOC.,

75. 76.

167113).

1998,120,1285. A. Evenzahav and N. J. TUKO,J. Am. Chem. SOC.,1998,120,1835. N. J. Turro and A. Evenzahav, TetrahedronLett., 1994,358089. R. Kojima, T. Shiragami, K. Shima, M. Yasuda and T. Majima, Chem. Lett., 1997, 1241. 84. H. Goerner, K.-D. Warzecha and M. Demuth, J. Phys. Chem. A , 1997,101,9964. 85. W. G . Dauben, B. L. Zhou and J. Y.L. Lam, J. Org. Chem., 1997,62,9005. 86. A. M. Muller, S. Lochbrunner, W. E. Schmid and W. Fuss, Angew. Chem. Int. Ed. Engl., 1998,37,505. 87. W. Fuss and S. Lochbrunner, J. Photochem. Photobiol., A , 1997, 105, 159 (Chem. Abstr., 1997,127,212325). 88. 0. G. Dmitrenko, I. P. Terenetskaya and W . Reischl, J. Photochem. Photobiol., A, 1997,104, 113 (Chem. Abstr., 1997,127, 128594). 89. M. Nowakovska and J. E. Guillet, J. Photochem. Photobiol. A, 1997, 103, 189 (Chem. Abstr., 1997,127,240810). 90. S. Brand and R. Gleiter, TetrahedronLett., 1997,38,2939. 91. C.-T. Lin, N.-J. Wang, H.-Z. Twng and T.-C. Chou, J. Org. Chem., 1997,62,4857. 92. S. Samajdar, D. Patra and S. Ghosh, Tetrahedron, 1998,54,1789. 93. A. Haque, A. Ghatak, S. Ghosh and N. Ghoshal, J. Org. Chem., 1997,62,5211. 94. S. McIlroy, H. Weng and H. D. Roth, J. Phys. Org. Chem., 1997, 10, 607 (Chem, Abstr., 1997,645863). 95. V. A. Chernoivanov, A. D. Dubonosov, V. A. Bren, V. I. Minkin, A. N. Suslov and G. S. Gennadii, Mol. Cryst. Liq. Cryst. Sci. Technol., Sect. A , 1997,297,239 (Chem. Abstr., 1997,127, 212365). 96. V. A. Bren, V. I. Minkin, A. D. Dubonosov, V. A. Chernoivanov, V. P. Rybalkin and G. S. Gennadii, Mol. Cryst. Liq. Cryst. Sci. Technol., Sect. A , 1997, 297, 247 (Chem. Abstr., 1997,127, 212366). 97. M. Maafi, J.-J. Aaron and C. Lion, J. faclusion Phenom. Mol. Recognit. Chem., 1998,30,227 (Chem. Abstr., 1998,166730). 98. C.-H. Tung, L.-P. Zhang, Y. Li, H. Cao and Y. Tanimoto, J. Am. Chem. SOC.,1997, 119,5348. 99. F. Franceschi, M. Guardigli, E. Solari, C. Floriani, A. Chiesi-Villa and C. Rizzoli, Inorg. Chem., 1997,36,4099. 100. 0.A. Luzina, L. E. Tatarova, D. V. Korchagina, N. F. Salakhutdinov and V. A. Barkhash, Russ. J. Org. Chem., 1997,33, 183 (Chem. Abstr., 1998,72521). 101. Y. Nakamura, Y. Hayashida, Y. Wada and J. Nishimura, Tetrahedron, 1997, 53, 4593. 102. Y. Okada, M. Hagihara, M. Mineo and J. Nishimura, Synlett, 1998,269. 103. N. Haga, H. Takayanagi and K. Tokumaru, J. Org. Chem., 1997,62,3734. 104. N. Haga, H. Nakajima, H. Takayanagi and K.Tokumaru, J. Chem. SOC.,Chem. Commun., 1997, I 17 1. 81. 82. 83.

148

Photochemistry

C. Reyes, M. E. Sigman, R. Arce, J. T. Barbas and R. Dabestani, J. Photochem. Photobiol. A , 1998,112,277 (Chem. Abstr., 1998,128,250534). 106. H. Kawai, T. Suzuki, M. OhkitaandT. Tsuji, Angew. Chem. Znt. Ed. Engl., 1998,37, 817. 107. S. Kammermeier, P. G. Jones and R. Herges, Angew. Chem. Int. Ed. Engl., 1997,36, 1757. 108. T. Noh, H. Gan, S. Halfon, B. Hrnjez and N. C. Yang, J. Am. Chem. SOC.,1997, 119,7470. 109. M. A. Miranda, J. Perez-Prieto, E. Font-Sanchis, K. Konya and J. C. Scaiano, J. Org. Chem., 1997,62, 5713. 110. K. Nagahara, I. Ryu, M. Komatsu and N. Sonoda, J. Am. Chem. SOC.,1997, 119, 5465. 111. N. Sonoda and N. Yanagi, Jpn. Kokai, Tokkyo Koho, JP 09,241,181 (Chem. Abstr., 1997,127,277815). 112. K.-W. Woo, T. S. Ahmadi and M. A. El-Sayed, Bull, Korean Chem. Soc.,, 1997, 18, 1274 (Chem. Abstr., 1998,47434). 113. H. Koshima, Y. Wang, T. Matsuura, I. Miyahara, H. Mizutani, K. Hirotsu, T. Asahi and H. Masuhara, J. Chem. SOC.,Perkin Trans. 2, 1997,2033. 114. G. Gutenberger, E. Steckhan and S. Blechert, Angew. Chem. Znt. Ed. Engl., 1998,37, 660. 115. A. Misetic and M.K. Boyd, Tetrahedron Lett., 1998,39,1653. 116. W. Adam, K. Schneider and S. Steenken, J. Org. Chem., 1997,62,3727. 117. K. Nakatani, N. Higashida and I. Saito, Tetrahedron Lett., 1997,38,5005. 118. B. Barker, L. Diao and P. Wan, J. Photochem. Photobiol., A , 1997, 104, 91 (Chem. Abstr., 1997, 127, 128591). 119. U. Pischel, W. Abraham, W. Schnabel and U. Mueller, J. Chem. Soc., Chem. Commun., 1997,1383. 120. M. Kotera, K. Ishii, 0. Tamura and M. Sakamoto, J. Chem. SOC.,Perkin Trans. I, 1998,313. 121. Y. Ohba, K. Kubo and T. Sakurai, J. Photochem. Photobiol. A , 1998,113,45 (Chem. Abstr., 1998,128,250541). 122. M. Suzuki, T. Ikeno, K. Osoda, K. Narasaka, T. Suenobu, S. Fukuzumi and A. Ishida, Bull. Chem. SOC.Jpn., 1997,70,2269. 105.

4

Photochemistry of Aromatic Compounds BYALAN COX

1

Introduction

Topics which have formed the subjects of reviews this year include photoinduced organic synthesis, photoisomerisations involving super-cyclophanes,2regioselective and stereoselective [2+2] photocy~loadditions,~ position- and stereoselective photocyclisation? the photochemistry of indoles,' five-membered heterocyclic compounds of the indigo group,6 pyrazoles and i~othiazoles,~ and heterocyclic Noxides,*photochromic reactions of naphthopyran derivatives,' photodegradation reactions of photochromic spirooxazines and 2H-chromenes,lo and chiral photochromic compounds. Fluorescent calix[4]arenes which respond to alkali metal ions have also been discussed. l 2

''

2

Isomerisation Reactions

A new procedure has been described which enables the quantum yields of a reversible photoisomerisation to be determined.I3 Wave packet motion on the cis-stilbene reactive surface has been detected by ultrafast time re~olution.'~ Kamers theory in its original form has been found to fail in the case of the photoisomerisation of trans-stilbene and the error has been traced to modifications of the excited state potential energy surface by the solvent.I5 This explanation is applicable over a wide range of physical conditions from jet-cooled isolated molecules to compressed liquid solution at very high viscosities. An assessment of the effects of substituents and media polarity on the photoinduced E -+ Z isomerisation in stilbene, azobenzene, and N-benzylideneaniline shows that both electron-donor and -acceptor substituents in the 4- and 4'-positions have a powerful influence on the efficiency of the reaction and are discussed in terms of the relaxation of the E-excited singlet state.16 Singlet (1) induces ultrafast intramoexcitation of trans-4-Me2NC6H4CH:CHC6H4CN-4 lecular charge transfer followed by photoisomerisation to the cis isomer.'7 A study of this photoisomerisation in various solvent classes as a function of temperature indicates that the process does not depend on solvent viscosity and that the Stokes-Einstein-Debye equation holds for overall rotation of (1). Examination of the aminostilbenes (2), (3), and (4) reveals that in their excited ~~~~

~

~~

~~

~

~

Photochemistry, Volume 30 0The Royal Society of Chemistry, 1999 149

150

Photochemistry

singlet state the mderivatives have greater charge-transfer character, longer lifetimes, and higher fluorescence quantum yields than the corresponding pderivatives, and that only the meta derivatives are subject to quenching by methanol. Is These observations have been attributed to the charge transfer states of the rn-derivatives being twisted, and those of the para derivatives being planar. Photoisomerisation of a stilbenesulfonate-containing amphiphile in which the chromophore is present in the hydrophilic head group is reported to be capable of control by complexation with alkaline earth metals, under which conditions the transformation apparently proceeds faster. l9 A study of the sensitized

photoisomerisation of cis-stilbazolium by [Ru(bpy)3I2' in saponite clay layers has revealed that the reaction occurs by static quenching, and it has been concluded that substrate and sensitizer are suitably arranged for effective photoelectron transfer and subsequent relay action.20 It has been reported that the result of irradiating (E)-4,4'-bis(dimethylamrnoniummethyl)stilbene in the presence of P-cyclodextrin is to induce photoisomerisation to the (Z)-isomer, whereas in the presence of y-cyclodextrin, [2+2]-cycloaddition products are obtained.21 These products are a molecular imprint of the cyclodextrin cavity. Diphenylamine seems to accelerate the photoisomerisation of trans-di(a-naphthy1)ethyleneand to retard the photocyclisation of the corresponding The same workers have also measured the kinetics and determined the effect of excitation intensity on the photocyclisation of di(a-naphthylbthylene to dihydropicene, and have suggested a novel adiabatic pathway for the trans-cis photoisomerisation of the same substrate.23 Novel photoresponsive molecular tweezers ( 5 ) having two 18crown-6 groups as recognition sites for Cs' and based upon dithienylethene have been described,24and an investigation of the reversible trans-cis photoisomerisation of (E)-hex-3-ene-l,5-diynesand 3,4-diethynylhex-3-ene-1,Sdiynes substituted with electron donating p-dialkylaminophenyl or electron accepting pnitrophenyl groups shows that the partial quantum yields of isomerisation are greatly influenced by the type and degree of f~nctionalisation.~~ It has been reported that on triplet sensitization and even on direct irradiation, the azulenylethenes, 2-styrylazulene and 1,2-di(azuIenyl)ethene, undergo one-way cis -+trans isomerisation as a quantum chain process in the excited triplet state after intersystem crossing.26Measurements of the quantum yields of photoisomerisation of trans- 1-(9-anthryl)-2-(n-pyridyl)ethenes(n = 2,3,4) and the corresponding cis-isomers in various solvents reveal that as the solvent polarity is increased, the fluorescence intensity falls and isomerisation to the cis isomer becomes efficient.*7

1114: Photochemistry of Aromutic Compounh

151

An intramolecular charge transfer excited state may be involved, and the inverse relationship between fluorescence and photoisomerisation suggests a singlet state mechanism. Irradiation of (2)-urocanic acid, 3 4 1H-imidazol-4-yl)prop-2-enoic acid, in the presence of nitro blue tetrazolium and sodium azide promotes its photoisomerisation in a process which involves reversible addition of the azidyl radical to the double bond.28

A study of the photoisomerisation of the E,E and E,Z-isomers of benzalcyclohexanone oxime shows that direct irradiation of the E, E-isomer primarily induces C=N photoisomerisation whereas sensitized irradiation causes isomerisation about the C=C bond.29 The E,Z-isomer undergoes C=C isomerisation under both sets of conditions. These results have been rationalised in terms of steric effects on the relative energies of the intermediates. The minimum energy path for photoisomerisation of the minimal retinal protonated Schiff base model tZtpenta-3,5-dieniminium cation (c~s-CSH~NH~+) has been computed using MCSCF and multi-reference Moller-Plesset methods.30 The results reveal that cisC&NH2+ is a satisfactory “ab initio” model for the sub-picosecond isomerisation dynamics of the retinal chromophore in rhodopsin. Counter ions may greatly affect the rate, specificity, and quantum yield of the photoisomerisation. A time-resolved investigation of the photoisomerisation of cis-azobenzene on the fs timescale suggests that excitation to the Sl(nn*) state induces inversion at one of the N atoms,31 and reversible cisltrans photoisomerisation of the newly reported amphiphilic f3-alanine derivatives of the type 4-RNMeC6H4N:NC6H4-4CONHCH2CH2C02H [R = H, Me(CH2)loCO, Me(CH2)&0] has been studied.32 trans-cis-Photoisomerisation of aqueous solutions of an azobenzene 4,4‘-disubstituted with two f3-cyclodextrinsunits has been described.33Anomalously large increases have been observed in the quantum yields of cis-trans photoisomerisation of (6; n = 1 , 2) when complexed by alkaline earth metal ions, and these have been attributed to interaction between the coordinated metal ions and the oxygen atoms on the 2,2’-positions andor nitrogen atoms of the azobenzene moiety.34 The same authors also describe the photoisomerisation of (7) and report that the cis-isomer shows complexation selectivity towards Cs+ and Rb+.35The cationic double azobenzene-chain lipid (8) is reported to undergo an efficient trans-cis photoisomerisation in MeCN, but in co-aggregates with bis ether lipid (9) of certain compositions, or in pure liposomes, the degree of photoisomerisation is very sensitive to t e m p e r a t ~ r e . ~ ~

152

Photochemistry

A study of the photochemical behaviour of calix[4]resorcinarenes and 0octaacetylated derivatives with 4-azobenzene residues at their lower rim has been carried out in solution and mono layer^,^^ and the crystal structures of some calix[4]crowns including a photoisomerisable azobenzene unit in the ether bridge has appeared, and the diazo cisltrans geometry seems to be dependent on both the bridge-length and the calixarene c o n f ~ r m a t i o nPhotoisomerisation .~~ of p,p’bis(ch1oromethy1)azobenzene in poly-(N, N-dimethyl-4-vin y lphene t hylamineblock-styrene) block polymer has been observed not to proceed by first order kinetics,39and the novel biphotochromic systems 2-[N-(3-phenylnorbornadiene2-carbonyl)]-N-arylaminomethylene-(2H)benzo[b]thiophenones undergo Z1E photoisomerisation, N - + Oacyl rearrangement, and also valence isomerisation in the norbornadiene fragment.40 The E/Z photoisomerisation of phosphaethenyl-

M4: Photochemistry of Aromatic Compounds

153

CMe3

I

benzenes possessing more than one phosphorus-carbon double bond have been prepared, and the structure of 1,2-bis[2-(2,4,6-tri-t-butylphenyl)-2-phosphaethenyllbenzene (10) has been determined ~rystallographically.~' irradiation of deoxygenated solutions of trans-lob, 1Oc-dimethyl-lob,l0c-dihydropyrene gives anti-8,16-dimethy1[2.2]metacyclophane1,9-diene (1 l), whereas in non-degassed solutions, there is successive formation of (1 1) and 5,8-epidioxyanti-8,16-dimethy1[2.2]metacyclophane-1,9-diene.42 A series of potassium sulfonate derivatives of (11) has also been reported and in some cases epidioxybridged products are formed. The kinetics of the photoisomerisation of some to 2-aryl-4-methyltetrasubstituted 4-aryl-4-methyl-2,6-diphenyl-4H-thiopyrans 3,6-diphenyl-2H-thiopyransvia 6-aryl-5-methyl- 1,3-diphenyl-2-thiabicyclo[3.1 .O]hex-3-enes have been measured.43The results along with the effects of substituents and consideration of solvent polarity have enabled a mechanism for the interconversion to be proposed. Among some 4-alkyl or 4-phenyl substituted 2,3dihydro-6H-l,3-thiazine-5-carboxylates investigated, the 4-methyl derivative rearranges to a thiazolidine, and the 4-ethyl derivative gives an acyclic thioamidodiene.44 The 4-phenyl derivative gives a 2,3-dihydro-6H-1,3-thiazine. Photochemical isomerisation of some 4H-imidazole N-oxides and N,N-dioxides to yield oxaziridines has been studied.45 Photolysis of a-chloroacetophenones induces an electron transfer process to give (12) followed by a medium-sensitive 1,2-phenyl migration to produce phenylacetic acids; the effects of substituents on this process have been investigated.46 Irradiation of N-(2-phenylprop-2-enyl)thiobenzamides induces double bond migration to give N-(2-phenylprop- 1-enyl)thiobenzamides by consecutive 1,4- and 1,&hydrogen and benzene solutions of 4-methoxy-ONNazoxybenzene containing trichloroacetic acid have been photoisomerised to 4methoxy-NNO-azoxybenzene.48However, in the absence of the acid catalyst the

154

Photochemistry

products are 5-methoxy-2-(phenylazo)phenol(2) and 2-(4-methoxyphenylazo)phenol(3). The major photorearrangement products of 1-phenylbenzo[b]thiophenium salts are reported to be 2-phenylbenzo[b]thiophenes and 3phenylbenzo[b]thiophenes together with some dephenylated products; by contrast thermal rearrangement induces ring opening.49 PM3-RHF-CI semiempirical calculations have been performed on derivatives of furan, thiophene and pyrr~le.~' These show that isomerisation products of furans and thiophene can arise from the excited singlet state derived from the Dewar form, and that the only pyrrole known to be capable of giving this intermediate is 2-cyanopyrrole. 1-one and 7Both 9-phenyl-1,3,4,5,6,7,8,9-0ctahydronaphtho[2,3-c]furanphenyl- 1,3,4,7-tetrahydroisobenzofuran-l -one undergo di-n-methane rearrangement in processes whose chemoselectivity can be rationalised in terms of the configuration of the phenyl group.51 The same authors also report that di-xmethane rearrangement of cis- and trans-4,7-diphenyl-l,3,4,7-tetrahydroisobenzofuran-1-one, cis- and trans-( 13) and the 4-methyl analogues cis- and trans-(14) give (15), (16) and (1 7), and MM2 calculations suggest that rearrangement of (1 3) and (14) occurs by a boat conformation having a pseudo phenyl substituent.s2 The photoproducts arising from the di-n-methane rearrangement of the benzobarrelenes (1 8;X = CN, CHO) are (19) and (20), indicating that vinyl-vinyl nitrile bridging does not occur.53These observations have been accounted for in terms of the stabilising effect of the substituents on the intermediate radical, and their destabilising effect on the formation of the cyclopropane ring. Di-n-methane rearrangement of the quinoxalinobarrelenes (21) and (22) gives the quinoxalinosemibullvalenes (23) and (24) re~pectively,'~and direct irradiation of (25) produces the singlet state product (26), whereas irradiation in the presence of xanthen-9-one as triplet sensitizer gives the dihydrochloride salt of the semibullvalene (27).55In the solid state, the outcome is influenced by steric interactions, and the pyrrole (28) is produced. Under triplet sensitized conditions which promote single electron transfer, the py-unsaturated oximes (29; R' = Ph, R2 = H) and hydrazones (30; R = Me, X = Ts) cyclise to the corresponding dihydroisoxazoles (31; R' = Ph, R2 = H) and dihydropyrazoles (32; R = Me) re~pectively.~~ However, oxime and hydrazine derivatives from aldehydes undergo an aza di-n-methane rearrangement. Photochemical isomerisation of [6]( 1,4)naphthalenophane (33) and [6](1,4)anthracenophane (34) produces the corresponding Dewar valence isomers (35) and (36) re~pectively,~~ and the efficiency of excited product formation in the adiabatic photocycloreversion of the bridged biplanemer (37) has been determined by the size of its side-chain substituents which influence the interchromophore distance in photoproduct (38).58 Irradiation of 4-hydroxybenzonitrile in deoxygenated water and other hydroxylic solvents causes isomerisation to 4-hydroxyisobenzonitrile and subsequent hydrolysis to 4-hydro~yformanilide.~~ Kinetic analysis reveals the involvement of a two-stage photoprocess, the first step of which occurs on the triplet manifold to give an intermediate which may be an azirine, and which following absorption of a second photon is transformed into the product. In the presence of DCA, 2,5diaryl-3,3,4,4-tetradeuteriohexa1,5-diene undergoes a photosensitized electron

155

M4: Photochemistry of Aromatic Compounds

Me Ph

Me

n

Ph CMe3

(23)

CMe3

transfer Cope rearrangement to generate the 1,1,6,6-tetradeuterioanalogue of the starting material via the 1,4-diaryl-2,2,3,3-tetradeuteriocyclohexane1,&diyI cation radical which has been captured.60If cerium(1V) ammonium nitrate is used, degenerate Cope rearrangement does not occur, and this change is ascribed

Photochemistry

156

(H2c0-$ Ph (34)

(33)

(35)

Ph

RCON

to the absence of a back electron transfer in the ground state process. Solutions of either trans- or cis-9,10-di-tert-butyl-9,lO-dihydro-9,lO-disilaanthracenes will undergo photointerconversion in the presence of di-tert-butyl peroxide to give a photostationary state comprised of 81% cis and 19% trans isomer.61 These observations indicate that the rare inversion of silyl radicals is occurring. Irradiation of the sulfide (39) in benzene gives the thiaphosphirane derivative (40).62

An investigation of the influence of methyl and methoxy substituents situated para relative to the hydroxyl group in salicylic acid has appeared.63 The results show the existence of an excited tautomer arising from intramolecular H+ transfer, and the observations are further taken to imply the existence of a modification of the excited potential energy surface along the tautomerisation coordinate without introducing an energy barrier in the proton-transfer reaction. The proton transfer rates in some crystalline N-salicylideneanilines have been examined by fs time-resolved spectroscopy and other methods, and it has been concluded that in the excited state photoinduced transfer occurs by quantum mechanical tunnelling.64In aqueous media and alkanes, the lack of fluorescence

IIl4: Photochemistry of Aromatic Compounh

157

from 8-hydroxyquinoline (8-HQ) has been attributed to the existence of the substrate in the tautomeric form, 8-HQ(T*).65 Intermolecular proton transfer may occur with the surrounding medium under these conditions, along with the possibility of intramolecular proton transfer betwGsn the hydroxyl and N functions, but in organic media a stable dimer is formed in the ground state within which biprotonic concerted proton transfers may occur upon excitation. A study of excited state intramolecular proton transfer in 2-(2'-hydoxypheny1)benzimidazole has been made using steady state and time-resolved emission spectroas well scopy in cyclodextrins such as p-, y-, and 2,6-di-O-methyl-~-cyclodextrins, as in solvents.66 These media weaken the 2-(2'-hydoxyphenyl)benzimidazole intramolecular H-bonds and promote strong intermolecular H-bond formation with the various cyclodextrins and solvent molecules, suggesting that in the presence of cyclodextrins, 2-(2'-hydoxyphenyl)benzimidazole adopts a zwitterionic structure. Molecular packing is observed to be a crucial factor in photoinduced proton-transfer in crystals of 2-(2,4-dinitrobenzyl)pyridine and some of its derivative^.^^ Experimental results suggest that the absence of nstacking between the chromophore and other aromatic rings leads to photoactive systems, and that it is an 0 atom of the nitro group which systematically interacts with the abstracted proton and results in photoinduced proton abstraction of the benzylic H atom. The role of the pyridine N atom is mainly inductive. Quantum mechanical calculations on the structure of the triplet intermediates in the photochromic reactions of phenoxy quinones show that photochemically induced phenyl migration occurs non-adiabatically with generation of the spiro form of the triplet biradical.68 Details of a range of new photochromic compounds have appeared in both the scientific and patent l i t e r a t ~ r e . ~ ~ - ' * ~

3

Addition Reactions

Photoaddition of methanol to 1-aryl-2,2-dichlorocyclopropanesusing 1,4-dicyanobenzene as sensitizer occurs with reverse regioselectivity to give 1-aryl- I-methoxy3,3-dichloropropanes. '27 Analogous results are found with both ethanol and ammonia, and a cation-radical mechanism may be involved. Irradiation of pentafluoroiodobenzene and alkenes produces adducts, but in the presence of electron scavengers the reaction is suppressed suggesting the participation of an electron transfer mechanism. Quenching studies indicate that the dominant state in the photohydration of XC6H4CCCCBut (X = p COzMe, p-OMe, rn-CF3,p-CF3) to XC6H4CCCOCH2Bu',XC6H4CHzCOCCBu', XC6f&CHCCHCOBut and XC6H4COCHCCHBu' is a singlet,129and the same authors also report that photohydration of 1-aryl-5,5-dimethyIhexa- 1,3-diynes in aqueous sulfuric acid gives two types of alkynyl and allenyl ketones through both S1 and TI excited states for substituents other than a nitro group.I3* Electronwithdrawing substituents promote C1 protonation leading to one type of allenyl ketone, but by contrast electron donating groups cause C4 protonation and give the second type of allenyl ketone; nitro-substituted diynes form only allenyl ketones via TI excited states.

158

Photochemistry

Irradiation of a mixture of tetracyanobenzene and benzyl cyanide in the solid state leads to the coupling product (41) which subsequently cyclises to the isoindole (42). 13' In alcoholic media, irradiation of (+)-3,4,4a,5,6,7-hexahydro4a-methyl-7,7-diphenyl-1(2H)-naph thalenone and ( & )-3,4,4a,5,6,7-hexahydro4a,7,7-trimethyl-l(2H)-naphthalenone,both of which incorporate a rigid s-cis enone, leads to solvent addition to the enone double bond with formation of hydrogen-bonded enols. * 32 However, in aqueous dioxan P-hydroxy ketones are produced. The mechanism of the transformation is thought to be stepwise addition of the solvent to a triplet-derived ground state trans enone. Formation of 1,5-diketones by photochemical addition of benzophenone derivatives to 1,3diphenylpropan- 1,3-dione has been reported, 133 and irradiation of 9-aryloxyI , 10-anthraquinones in the presence of nucleophiles such as water, alcohols, and primary amines induces 1,4-addition. This and other observations are in good agreement with the results of AM 1 calculation^.'^^ Irradiation of phenanthrenequinone in the presence of various cyclic organosilanes such as (43), (44), and (45) leads to silylene adducts (46; R = Me, 'Pr) which arise by attack of the triplet state of the ketone on the organosilane to give radical insertion products, and which themselves subsequently undergo a displacement reaction. 35 Me. Me

Ph'

(45)

A photoaddition-fragmentation-aromatic annulation sequence Las been used in the first synthesis of (+)-ligudentatol (47),'36 and a study of the photoaddition of amines to styrylthiophenes and its derivatives shows that the addition o f tertiary and secondary amines to 2-styrylthiophenes is non-regioselective; the addition of ammonia sensitized by dicyanobenzene is, by contrast, regioselective. '37 Examination of the photochemical reaction between CC14 and anthracene using time-resolved IR spectroscopy suggests that the trichloromethyl radical is

1114: Photochemistryof Aromatic Compounds

159

involved and that the final product is the 9-chloro-l0-trichloro adduct of anthracene.13*Photoaddition of pyrroles to give 1:l and 2:l adducts occurs with phenylethenes and phenylethynes in a process which proceeds with formation of an exciplex. 39 The ortho photocycloadducts formed on irradiating 3-tert-butyl-4-phenoxybut1-ene and 3-acetoxy-4-(4-methoxyphenoxy)but-l -ene are reported to be further photorearranged to tricyclic species.l4O Irradiation of the pyrazinopsoralen (48) in the presence of ethenes such as dimethyl fumarate, dimethyl maleate, and dimethyl ethylidenemalonate gives the corresponding C4-cycloadducts in a process which occurs by a singlet exciplex.14' The 1 ,haphthylene-bridged syncyclophanes (49) and (50) have been synthesised by intramolecular [2+2] photocycloaddition of 1,8-bis(4-vinylphenyl)naphthalene and 1,8-(3-~inylphenyl)naphthalenes re~pectively,'~~ and irradiation of a variety of ketones in the presence of homobenzvalene promotes the formation of Paterno-Buchi products which contain the tricyclo[4.I .0.02.7]heptane fragment. '43 Use of naphtho-l,4quinone leads to (51). Irradiation of 5-cinnamyloxy-4-methyl-2(5H)-furanonein acetone as sensitizer induces a [2+2] intramolecular photocycloaddition by a process whose photostationary state composition has been determined, 144 and it has been reported that irradiation of the photochromic percinnamoylated cyclomaltoheptaose (P-cyclodextrin) solid inclusion complexes with N-salicylideneaniline and N-5-chlorosalicylideneaniline as guests causes formation of cyclobutane bridges, effectively restraining the guests to a specific geometry.145

So far the reverse reaction has not been achieved. Photolysis of (52; R = H) produces the alkyne (53; R = H), and evidence is also provided to support the view that the mechanism is an enantioselective [2+2] photocycloaddition involving a 1,4-biradical intermediate. 146 Intramolecular photocycloaddition of the enantiopure bis-dihydropyridone (54) gives a high yield of a single cycloa d d ~ c t . ' ~The ' photocycloaddition of arylalkenes to c60 has been shown to occur by a two-step mechanism and to involve formation of a dipolar or diradical intermediate in the rate determining step.'48 These authors also report that photocycloaddition of cis- and trans- 1-(p-methoxypheny1)prop- 1-ene to C a gives the trans [2+2] adducts only, and present evidence to suggest that a two-step mechanism again operates. 14' 1,2- and 1,2,4,5-Paddlanes have been prepared by [2+2]photocycloaddition of o-divinylbenzene and 1,2,4,5-tetravinyIbenzene,and in particular, cyclisation of 1,2,4,5-tetravinylbenzene( 5 5 ) gives 1,2,4,5-paddlane

I60

Photochemislry

(56).lS0 Sensitized irradiation of the alkenylcyclopentadiene (57; n = 2,3) using 9,lO-dicyanoanthracene gives the anti-Bredt [2+4] tricyclic adducts (58).15' Such adducts are not obtained thermally and this observation may indicate the involvement of a triplex intermediate in the photochemical reaction.

y e 3 I

2-Methoxy-5-[3-(trifluoromethyl)phenyl]pent-l -ene will undergo 2,6- and 1,3meta-photocycloaddition to give products having the methoxy group endo, whereas by contrast, the analogous trifluoro ortho- and para-substituted substrates form products derived from ortho photocycloaddition. 152 These observations have been rationalised in terms of the free enthalpy of electron transfer. Photoaddition of duroquinone to trans-stilbene gives the eight-membered ring 2,3,5,8-tetramethyl-6,7-diphenyl-2,5,7-cyclooctatrien1,4-dione,I s3 compound, and irradiation of 4-(4-methoxyphenoxy)-3-(N3-benzoylthymin1-yl)but-1-ene induces a chemo-, regio-, and stereo-selective intramolecular 1,2-ortho photocycloaddition to the phenyl ring to give (59).lS4 Intramolecular meta photocycloaddition of 3-benzyl(dimethylsila)prop-1-enes is reported to be controlled by the presence of an electron donor substituent on the phenyl ring and also by the silicon atom in the tether.155 Benzene 1,4-endoperoxide (60) is formed by irradiating the monoperoxide (61) at low temperature and following a concerted and intramolecular photorearretrocycloaddition gives benzene and 02( to the rangement of 7-hydroxy-2-methyl-2-(4-methylpent-3-enyl)chroman-4-one 1,3-arene-aIkenephotocycloadduct, rel-( 1R,2S,5S, 7S,10R,13S)-6,6,10-trimethyl-

I114: Photochemistry of Aromatic Compounh

161

14-oxapentacyclo[8.3.1.0'97.023'3.057'3]tetradeca-3, 12-dione, is reported to occur by secondary photorearrangement of the 1,2-arene-aIkene photocycloadduct. '57 The photocycloaddition of 2-morpholinoacrylonitrile to substituted 1-acetonaphthone (62) has been found to be substituent-dependent. '51 For example, (62; R = MeO, R' = H) gives only the [4+2] cycloadduct whereas (62; R = H, R' = CN; R = H, R' = MeO) lead to the [2+2] cycloadduct. The calix[4]arene-based 2naphthoate (63) is reported to be photoconverted into the dimer and photocycloreversion of the cyclodimers (65 - 69) gives quantitative yields of the corresponding naphthalenes. 16*

(63) Np = naphthalene

CMe3 Me& CMe3 (64)

CMe3

Quenching of the exciplex formed in acetonitrile solution between the lowest excited state of 9,lO-dichloroanthracene ('DCA*) and the ground state of 2,sdimethylhexa-2,4-diene gives the DCA radical anion intermediate which suffers mono-dechlorination.'61 In heptane solution no exciplex is formed, but by contrast a [4+2] adduct of a dibenzobicyclo[2.2.2]octadiene-type is produced. A detailed study of the photodissociation of (70; X = C02Me, CN), the [4+4] cyclodimer of furan with 9-cyanoanthracene, has appeared, 162 and the same authors also report that irradiation of tert-butyl 9-anthroate and furan gives a mixture of the [4+4] (70; X = C02Bu-tert), 1,4-10,9 (71; same X), and 9,lO-10,Y (72; same X) c y c l~di m er s . Upon '~ ~ excitation, the [4+4] cyclodimers of tert-butyl 9-anthroate and the [4+4] cyclodimers of methyl 9-anthroate are quantitatively dissociated, but no adiabatic photoreversion of any of the cyclodimers is

162

Photochemistry

observed. 9-Anthrylmethyl phosphite gives the corresponding phosphonate by a photo-Arbusov rearrangement but prolonged irradiation produces the centrosymmetric head-to-tail, [4+4] pho tocycloadduct. X

Mono- and disubstituted N-alkyl and N-arylaziridines are reported to undergo a photoinduced electron transfer [3+2] cycloaddition to dipolarophiles to produce five-membered heterocycles, and it is suggested that in this process the radical cation intermediate behaves differently from the corresponding classical azomethine ylide. Intramolecular [4+4] photocycloaddition of the dipyridylpropane (73) followed by Li/NH3 reduction is a useful route to the elevenmembered ring system (74),16' and on irradiation of benzene solutions of 2,3dicyano-5,6-dimethylpyrazinein the presence of allylic silanes a [2+2] cyclisation is induced followed by rearrangement to give 2,8-diazatricyclo[3.2.1.0498]oct-2-ene (75; R = H, Me).'67

q Me

(73)

0

h-NMe

O

(74)

[4+2] Cycloaddition of heteroaromatic analogues of o-quinonedimethanes such as furan, thiophene, oxazole, thiazole, indole, and quinoxaline to [60]fullerenes gives the corresponding heterocyclic-linked [60]fullerenes which undergo selfsensitized photooxygenation to epoxy-y-lactones. 2-Vinylbenzofuran and 2isopropenylbenzofuran will participate in photoelectron transfer cycloaddition reactions with alkenes such as cyclohexa-l,3-dienes, styrenes, and acyclic 1,3dienes to form a range of products including [2+2]-cycloadducts such as (76),'69 and irradiation of solutions of methyl 1-naphthoate in the presence of furan leads to three products, a syn-[2+2] cycloadduct, an endo-[4+4] cyclodimer, and a cage cy~lodirner.'~~ 2,3-Dimethylmaleic anhydride and 2,3-dimethylmaleimide will undergo a [2+2] benzophenone sensitized photocycloaddition to selenophene and to a range of substituted selenophenes, as well as to tellurophene and benzo[bJtellurophene. I 7 l Irradiation of indoline-2-thiones in the presence of alkenes promotes [2+2] cycloaddition followed by cleavage of the intermediate spirocyclic thietane to give 2-alkylindoles.17* Under similar conditions but in the presence of

1114: Photochemistry of Aromatic Compounh

I63

the tertiary amines R3N (R = Me, Et, Pr, Bu, PhCH*), 3-alkylindoles are formed. Diarylfuroxans (77; Ar = Ph, 2-ClCsH4, 2,6-C12CsH3) can be photolysed in the presence of alkenes such as tetramethylethylene to give cyclobutaphenanthrenes (78) in a process which occurs by loss of (NO)z from a diazete-N,N-dioxide intermediate. '73

Solid state excitation of electron donor-acceptor complexes of various diarylacetylenes and dichlorobenzoquinone in either the acceptor or the 1:2 complex absorption bands induces [2+2] cycloaddition and produces identical mixtures of the quinone methides.'74 Evidence is presented for the participation of an ionradical pair as the reactive intermediate in both cases. Irradiation of an appropriately substituted o-hydroxybenzyl alcohol precursor generates the corresponding o-quinone methide which is reported to undergo an efficient [4+2] cycloaddition to form the hexahydrocannabinol system.175Time-resolved studies confirm the intermediacy of the o-quinone methide and show its lifetime to be > 2 ms. Laser photolysis of 1,2-bis(phenoxymethyl)benzene, 1,2-bis[(phenylthio)methyllbenzene, and 1,2-bis[(phenylseleno)methyl]benzene occurs by a twophoton process to produce o-quinodimethane which will cycloadd to various dienophiles including maleic anhydride, dimethyl maleate, dimethyl fumarate, fumaronitrile and dimethyl acetylenedicarboxylate. 76

'

4

SubstitutionReactions

In the presence of methanol as solvent and 1,4-dicyanobenzene as acceptor, photoinduced electron transfer from 1,4-bis(methylene)cyclohexane gives 4(methoxymethy1)-1-methylenecyclohexane and 4-(4-~yanophenyl)-4-(methoxymethyl)- 1-methylenecyclohexanewhich arise by nucleophilic attack of the solvent on the radical cations, followed either by reduction and protonation, or by combination with the radical anion of the electron acceptor.'77 These observations are in accordance with the proposed mechanism of the nucleophile-olefin combination, aromatic substitution (photo-NOCAS) reaction. The same group has also investigated the use of cyanide ion as nucleophile and report that irradiation of a mixture of 1,4-dicyanobenzene in the presence of biphenyl as donor, KCN, and 18-crown-6 gives a mixture of (79) and (80).'78 These workers have also extended the scope of NOCAS to fluoride ion.'79 In particular, use of 2,3-dimethylbut-2-ene and 2-methylbut-2-ene gives 4-cyanophenyl substituted

Photochemistry

164

CN

(79)

fluoroalkanes in a process whose selectivity has been explained in terms of the HSAB principle, and whose regiochemistry is anti-Markownikov. The relative stability of the intermediate P-fluoroalkyl radicals has been determined by ab initio calculations and the addition step is kinetically controlled. Irradiation of chlorobenzene solutions of [Pd(PPh&] produces trans[PdC12(PPh&] and a mixture of chlorobiphenyls, 180 and irradiation of 2-amino5-iodo-3-(N-methyl-N-tosylarnino)pyridine in benzene solution gives 2-amino-3methylamino-5-phenylpyridine by simultaneous phenylation and tosyl removal.'*' This reaction is a key step in the synthesis of the food-borne carcinogen 2-amino- I -methyl-6-phenylimidazo[4,5-b]pyridine.Substituted 1,2'biazulenes have been prepared by photolysis of 2-diazo- I ,3-dicyanoazulen-6(2H)one in the presence of azulene derivatives.'82 Calculations performed on transient radical intermediates derived from cleavage of the C-X bond following irradiation of halogenoheterocycles have been found to be useful tools with which to rationalise the behaviour of these substrates towards arylation and deha10genation.I~~ Irradiation of acetonitrile solutions of 4(5)-nitro-2-iodoimidazole containing benzene leads to phenyl substitution in the 2-position, and similar reactions are observed for rn-xylene and thienyl derivatives.184A study of the chain photosubstitution of the chlorine atom in 4-chloro-1-hydroxynaphthalene by sulfite using aqueous sodium sulfite has appeared. 185 Two mechanisms of photoinitiation are involved and two intermediates have been observed, namely a radical anion of 4-chloro- 1-hydroxynaphthoxide and the sulfite radical anion. The conclusions are drawn that there are two other competitive mechanisms, an SRNlmechanism and a mechanism which involves the participation of sulfite radical anions, and secondly that these are independent of the initiation processes. A range of 6-iodo derivatives of 2,3-diphenylbenzo[b]furans has been prepared and on irradiation in benzene solution these give the corresponding 6-phenylated products; on further irradiaIOtion, photocyclisation to the corresponding 1 1-phenylbenzo[b]phenanthro[9, dlfurans occurs.186 From an examination of the photoreactions of 4-fluorophenol, 4-bromophenol, and 4-iodophenol using both steady state and timeresolved photolysis it appears that, as in the case of 4-chlorophenol, the carbene 4-oxocyclohexa-2,5-dienylideneis formed by loss of HX, and that this species reacts with molecular oxygen to produce benzo- 1,4-quinone O-oxide followed by its rearrangement to benzo- 1,4-quinone.187 Time-resolved photolysis of 9,l O-dibromoanthracene (DBA) in cyclohexane-amine gives the (' DBA-amine) exciplex but this is not observed to decay by electron transfer even though the

IIl4: Photochemistry of Aromatic Compounds

165

presence of DBA'- is apparent from absorption measurements in acetonitrile solution.'88 It is concluded that DBA'- is the intermediate in the amine-assisted monodebromination of DBA to give 9-bromoanthracene, and that the dielectric constant of the solvent plays a n important role in the transformation. The photochemistry of some iodo substituted pyrroles has been d e ~ c r i b e d . 'Ethyl ~~ 3,4-dimethyl-5-iodopyrrole-2-carboxylategives a 1:1 mixture of ethyl 3,4-dirnethyl-5-phenylpyrrole-2-carboxylate and ethyl 3,4-dimethylpyrrole-2-carboxylate quantitatively, and in acetonitrile as solvent the single product is ethyl 3,4dimethylpyrrole-2-carboxylate.Under similar conditions, 4,5-diiodopyrrole-2carbaldehyde in benzene gives the corresponding 5-phenyl derivative. The effects of adding ethanol to a range of solvents used in the photolysis of some alkoxy- and dialkoxyarenes in the presence tetranitromethane have been shown to include a reduction in the tendency of the trinitromethyl derivative to form the ring-substituted nitroarene, a reduction in the nucleophilicity of the trinitromethanide ion, and a reduction in attack ips0 to the alkoxy substituent.I9' Irradiation of the charge transfer complex formed between 1,4-dimethoxynaphthalene and tetranitromethane is reported to give mainly 1,4-dimethoxy-2nitronaph thalene, 1,4-dimethoxy -2-t rini trometh y lnapht halene and 4-met hoxy-2(dinitromethylene)-l(2H)-naphthalenone, together with small amounts of other materials.'" Reaction has been shown to occur by attack of the trinitromethanide ion or nitrogen dioxide ips0 to a methoxy group. Charge transfer complexes formed by irradiating benzofuran and tetranitromethane give the epimeric pairs of adducts 3-nitro-2-trinitromethyl-2,3-dihydrobenzofurans, 2-nitro-3-trinitromethyl-2,3-dihydrobenzofurans, and 3-hydroxy-2-trinitromethyl-2,3-dihydrofurans, together with other products.'92 These adducts seem to arise by attack of the trinitromethanide ion on the benzofuran radical cation. The use of lower temperatures in the bromate-induced monobromopentahydroxylation of benzene by catalytic photoinduced charge transfer osmylation favours formation of the neo diastereoisomer of the deoxybromoinositol. 193 Photolysis of N-(diphenylamino)-2,4,6-trimethylpyridinium tetrafluoroborate salts induces nuand N-[bis(4-methylphenyI)amino]-2,4,6-trimethylpyridinium cleophilic addition of various n-nucleophiles such as electron rich alkenes to the 0-and p-positions of one of the phenyl rings.'94 These observations are thought to imply the presence of the diarylnitrenium ion (Ar2N+) as intermediate, but evidence is also presented for the involvement of radical species, as well as for the formation of indoles and indolinones. Some MO calculations are also reported. Irradiation of aqueous solutions of 4-thiothymin- 1-ylacetic acid (8 1) and adenosine (82), 4-thiothymidine (83) and adenin-9-ylacetic acid (84), or (81) and (84) gives 4,5-diamino-6-formamidopyrimidinederivatives as observed after irradiating a mixture of (82) and (83).'95 From these observations it has been concluded that replacement of the nucleoside sugar residues by a carboxymethyl group does not affect the regioselectivity of the reaction, Photolysis of methanolic 5-amino-3-phenyl- and 3,5-diphenyl-1,2,4-oxadiazole in the presence of sodium hydrogen sulfide or thiols causes a redox reaction of the ring 0 - N bond, and formation of the corresponding N-substituted ben~amidines.'~~ However, in the presence of thioureas or thiocarbonates 3-phenyl-substituted 1,2,4-thiadiazoles

166

Photochemistry

are produced suggesting N-S bond formation between the ring-photolytic species and the sulfur nucleophile. 5

Cyclisation Reactions

[ 1 . l]Paracyclophane and its bis(methoxycarbony1) derivative have been success-

fully generated for the first time by photoisomerisation of the corresponding bis(Dewar benzene) precursors (Scheme l),I9’ and in some related work by the same authors the [4]paracyclophane (85; R’ = H, CN; R2 = Me,H) has been thermally isomerised to the Dewar valence tautomer (86; same R’, R2) and subsequently reconverted photochemically to (85). ‘98 Irradiation of the 7-silanorbornadiene (87) produces the silacyclopentadienylidene (88) which has been trapped in a hydrocarbon matrix at 77 K.’99 Similarly, photolysis of benzene solutions of (87) in the presence of MeZSiEtH as trapping agent gives dole (89). The photocyclisation quantum yield of 2,2’-dimethyl-3,3’-(perfluorocyclopentene- 1,2-diyl)-bis(benzo[b]thiophene-6-sulfonate) is enhanced on irradiation within the cavity of 0- or y-cyclodextrin, in which the favourable photoreactive antiparallel conformation is preferentially included.2m Irradiation of substituted a-carbonylstyrenes promotes either cyclisation or dimer formation depending upon the substitution pattern of the Solvent and substituent effects on the photocyclisation of a-(2-acylphenoxy)toluenes and ethyl 2-acylphenoxyacetates in the synthesis of dihydrobenzofuranols R

g

R

R

Scheme 1

R’ R\‘

R’

\didMe

Me Et

IIl4: Photochemistry of Aromutic Compound

167

have been examined, and conformational, solvent, and substituent effects on the cyclisation of the 1,5-biradicals and reaction pathways have been discussed.202 The naphthoic acid component of kedarcidin has been synthesised by a route which includes a photochemical electrocyclisation as a key feature.203A theoretical analysis of the conformational stereoisomerism in the sterically hindered 4a,4b-dihydrophenanthrenesof C2 symmetry which arise as photointermediates, suggests the presence of two low energy structures C and T.*04The C conformation has been assigned to the primary photocyclisation product from which the T conformation arises spontaneously. S-Aryl 2-benzoylbenzothioates undergo photoinduced cyclisation to 3-aryl-3-arylthioisobenzofuranonesin a process which is followed by homolytic cleavage of the isobenzofuranone product to give the dihydroisobenzofuranone dimer.*” A study of the consequences of attaching substituents to the styrene ring of trans-2-cinnamylphenol (90) shows that a lowering of the singlet state energy occurs, and this is reflected in the marked regioselectivity towards 6-membered ring products (91) which occurs in excited state proton transfer.206Annulated quinones of the type (92; R’ = R2 = H; R’= Me, R2 = H; R’ = R2 = Me; R’ = CH2Ph, R2 = H) are reported to be obtained when alkoxynaphthoquinones (93; same R’, R2) are irradiated, and the stability of the radical or carbocation intermediate is thought to be important for the efficiency of the reaction.207

Diarylethenes having an optically active 1- or d-menthyl group at the 2-position of a benzo[b]thiophene ring such as (94; R = I-menthyl, d-menthyl) can be photocyclised to give diastereomeric pairs whose product ratio is both solvent polarity and temperature dependent, and under suitable conditions a diastereomeric excess of 86% has been obtained.208The regioselectivity of the intramolecular photocyclisation of macrocyclic stilbenes is strongly influenced by the length of the connecting alkanediyl chain.209In the presence of p-dicyanobenzene, photoamination of 1,2-distyrylbenzene proceeds with nucleophiiic addition of NH3 to the 1,2-distyrylbenzene radical cation and results in intramolecular and 1-aminocyclisation to give l-benzyl-3-phenyl-l,2,3,4-tetrahydroisoquinoline 3-benzyl-2-phenylindane.”’ Irradiation of the enediyne (95) in propan-2-01 leads to (96) in an analogue of the thermal Bergman cyclisation, together with addition

168

Photochemistry

It is suggested that a substituted 1,4-dehydronaphthalene biradical is the most likely intermediate. The photochemical behaviour of the bridged 4-benzoylcyclohexanones (97; X = (CH& NZCH2, NZ(CH2)2, CH2NZCHz; Z = PhCH202C; n = 2-4) depends upon both ring size and the possible presence of the nitrogen atom.212In compounds capable of forming 1,6-biradicals, the reactions are unselective, but the remaining substrates afford tricyclic hydroxyketones with high diastereoselectivity if a protected nitrogen atom is present. Regiocontrolled photocyclisation of the aryl enamide (98; R = 4-MeOC6H4CH2)gives the phenanthridone (99), and may be important in the synthesis of the antineoplastic alkaloid pancratistatin; it is suggested that the regioselectivity may arise from hydrogen bonding between the A-ring phenolic hydrogen and the enamide carbonyl Photocyclisation of dicarboxamide Mannich bases of the type (100) gives o-hydroxylactams (101) which on treatment with HCl form the imidazole derivatives (102),214and a study of the photocyclisation of 2-halopyridinium salts tethered to an arene shows that pyrido[2,1-a]-3H,4H-isoquinolinium salts are formed, and that transient intermediates such as the 2,3-dihydrocyclohexadienylradical and dibromide radical are produced.215The transformation appears to occur by a photohomolytic radical mechanism. Photolysis of the azidopyrimidine (103) gives a mixture of the isoxazolopyrimidine (104) and the azo compound (105),216and diastereoselectivephotocyclisation of some N-arylenaminolactams and esters to spiroindoline lactams and imides has been reported; such transformations may be of significance for the synthesis of ( k )-vindorosine and Aspidosperma alkaloid^.^'^ Single electron transfer induced photocyclisation of N-[(N-acetyl-N-trimethylsilylmethyl)amidoalkyl]phthalimide (alkyl = ethyl, Pr, n-pentyl, n-hexyl) and N[(N-mesyl-N-trimethylsilylmethyl)amidoethyl]phthalimideleads to the formation of products in which the phthalimide carbonyl carbon has become bonded to the carbon of the side chain in place of the trimethylsilyl group.*l* It is suggested that these transformations occur by intramolecular single electron transfer from the nitrogen of the a-silylamido group to the singlet excited state of the phthalimide, followed by de-silylation of the intermediate a-silylamido cation radical and cyclisation by radical coupling. One-electron photoinduced cycloreversion of stereoisomeric stilbazolium cyclodimers has been achieved by irradiating their iodide salts and occurs by a process which is highly sensitive to structure.219 Evidence has been presented to show that the structural dependence of the quantum efficiency is attributable to through-bond interaction of the two pyridinium rings. 2-Alkylbenzimidazoles have been produced in high yield by

IIl4: Photochemistry of Aromatic Compounrtr

169

OEt

photolysis of suitable dinitrobenzenes or nitroanilines in the presence of Ti.22oIn aqueous alcohol or in a polymer matrix, 4,4-bis(2-pyridylamino)-3,3'-dichlorobiphenyl photocyclises regioselectively at the nitrogen atom of the heterocycle into 8-[4-(2-pyridylamino)-3-chlorophenyl]pyrido[1,2-a]benzimidazole, and in alcoholic solution 2-(2-pyridylamino)-3-chloroanthracene cyclises by forming C-C and C-N bonds to pyrido[ 1,2-a]anthra[2',3'-d]imidazoleand naphtho[3,2-h]-acarboline.221Irradiation of the 4,5-disubstituted 1,2,4-triazole-3-thione(106; X = halo; R' = H, Me; R2 = H or R'R2 = CH:CHCH:CH; R3 = H, Me, MeO; R4 = H, Me) gives s-triazolo[3,4-b]benzothiazoles(107; same R', R2, R3,R4)in what is a general route to these compounds.222The transformation may proceed by an electron transfer mechanism. Solutions of methyl 3-cyano-2-diazo-6-0~0-2,6dihydroazulene-1-carboxylate in THF are reported to undergo photolysis to 1,3-dioligomeric crown ethers .223 Dimethy 1 2-diazo-6-0~0-2,6-dihydroazulenecarboxylate, however, is observed to give only small quantities of the crown ether, and this is regarded as evidence of a significant steric factor in the cyclisation process. Irradiation of spiro[fluorene-9,1'-pyrrol0[2,1 -a]quinolines]

I70

Photochemistry

(108; R' = R2 = H) and their styryl homologues (109; R2 of 108 replaced by CH:CHR', where R2 = (un)substituted Ph) under time-resolved conditions indicates the presence of transients in the ps and ms domains.224 These are thought to possess slightly tilted educt or product-like geometries, and an energy diagram has been proposed for reaction of (108) to give (I 10).

A study of solvent and substituent effects on the cyclisation of 1,Sbiradical intermediates generated on photolysis of 2-RCH20C6H4COPh (1 11; R = H, Me, Et, CHMe2, Ph, CH:CH2, CN) and 2-PhCOC6H40CHRC02Et (112) has appeared.225 For (1 1 l), decreases in stereoselectivity in some solvents are attributed to intermolecular H-bonding between the hydroxyl group of the 1,5biradicals and the solvents, whereas in the case of (112) photolysis leads to a mixture of cis- and trans-dihydrobenzofuranolsas a consequence of intermolecular hydrogen bonding between the hydroxyl group of the 1,5-biradicals and the solvents. Irradiation of the ubiquinol-benzoin adduct (1 13) cleanly produces (1 15).226 ubiquinol-2 (1 14) and the expected 5,7-dimethoxy-2-phenylbenzofuran

Q

1114: Photochemistry of Aromatic Compounds

171

This observation is significant for the study of rapid electron-transfer events in ubiquinol oxidising enzymes. Photodecarboxylation of N-acylisoxazol-5-ones affords iminocarbenes which give oxazoles following intramolecular cyclisation through the oxygen of the acyl group.227The same authors also report that N-thioacylisoxazol-5(2H)-ones will photoextrude carbon dioxide, and, after subsequent intramolecular cyclisation of the iminocarbene, produce thiazoles.228Photocyclisation of 3-chloro-N-(3-phenanthryl)thieno[2,3-b]thiophene-2-carboxamide gives thieno[3’,2’:4,5]thieno[2,3c]naphtho[1,2-f ]q~inoIin-6(5H)-one.~~~ 6

Dimensation Reactions

In non-polar solvents, phenyl- and 2,6-diphenyl-p-benzoquinonegive the corresponding cyclobutane-type dimers, but polar solvents promote intramolecular photocyclisation to the corresponding 2-hydroxydibenzof~rans.~~~ In the case of alkoxy-substituted 2,6-diphenyl-p-benzoquinone,cyclisation to the 6H-dibenzo[b,d]pyran system occurs. Arylacrylonitriles in which the aromatic group may be homo- or heterocyclic undergo regiochemically controlled photodimerisation in the presence of benzophenone as sensitizer, and this has been rationalised in terms of overlap of the frontier orbitals participating in the reaction.231The products show structural similarities to some antimicrobially active sponges. Irradiation of cinnamic acids involving a complex with surfactant amine N-oxides (C,DAO, n = 12, 14 and 16) as vesicles in water gives cyclodimers, and studies have shown that the dimerisation is controlled by a range of molecular assemblies such as rod-like micelles and homogeneous or heterogeneous vesicles,232 Solid state irradiation of 1H-[2]benzothiopyran-l-one (1 16) selectively gives 6au,6ba, 12ba,l2cu-tetrahydrocyclobuta[l,2-c:4,3-c’)bis([2]benzothiopyran)-5,8dione (1 17), the head-to-head cis-cisoid-cis-cyclodimer of (1 16); the same dimer is obtained in low yields in solution.233In the presence of tetrachloroethene, the [2+2] photocycloadduct is (1 18) formed.

A study of the photodimerisation of anthracene in supercritical C02 at different densities has revealed that the reaction is about an order of magnitude more efficient in C02 than in normal liquid solvents,234This is rationalised in terms of a reaction whose mechanism is diffusion-controlled even for those rate constants which are of the order of 10” M-’ 6’. An investigation of the influence

172

Photochemistry

of ester chain length (C4-CI2) on the photodimerisation of n-alkyl esters of 9anthracenecarboxylic acid to the head-to-tail and head-to-head products has been carried out in micellar and vesicular solution.235Increasing the chain length promotes formation of the head-to-head dimer in organic solvents as do temperature decreases. Photodimerisation of 6,7-benz[c]acephenanthrylene(1 19), an overlapping and repeating CZ0 subunit of [60]fullerene, produces the ciscyclobutane (120) which can be thought of as a simple molecular tweezer.236 Irradiation of azulenequinones in polar solvents gives mainly head-to-head dimers whereas in less polar solvents head-to-tail dimers are formed in greater abundance.237The results of related reactions are also reported.

18 /

In contrast to most bulky olefins, irradiation of (4RS, 1'RS)-methyl l-phenyl-2piperidinoethyl- 1,4-dihydro-2,6-dimethyl-4 - (2-thienyl)pyridine-3,5-dicarboxylate (121) in the crystalline state has been found to give the corresponding dimer, (4RS,8SR)-4a,8a-dimethoxycarbonyl-2,4b,6,8b-tetramethyl-3-[( 1RS)- 1-phenyl-2piperidinoethoxycarbonyl]-7-[(1SR)- 1-phenyl-2-pipidinoethoxycarbonyl]-4,8-di(2- thieny1)- 1,4,4a,4b,5,8,8a,8b-octahydro-truns-cyclobuta[ 1,2-b:3,4-b']dipyridine Inspection of the crystal structure of (122) quantitatively as a single (121) reveals a space between the reacting molecules, designated a buffer zone, which may be capable of modulating the steric hindrance from which the reacting molecules suffer on close approach, and whose presence may be a prerequisite before solid state dimerisation can occur. In some closely related work, the same authors show that in the solid state photodimerisation of the three polymorphic crystal forms of the bulky olefin methyl (RS)- 1-phenyl-2-piperidinoethyl (RS)1,4dihydro-2,6-dimethyl-4-(2-thiazolyl)pyridine-3,5-dicarboxylatehydrochloride, the buffer zone is an essential controlling factor.239 Irradiation of 3-amino-2-oxo-4-hydroxyquinoline leads to its photochemical condensation to a dimer,240and photodimerisation of acridizinium bromide in both solution and in the solid state forms four photodimers, two of which may be In anionic micelles, a different regioselectivity is observed as enanti~meric.~~' reflected in a higher yield of those dimers showing higher dipole moments. Radiative lifetimes, quantum yields, and substituent and solvent effects have been examined for the photodimerisation of trans- 1,2-bis[2-(5-phenyloxazolyI)]ethene, and it has been found that increases in solvent polarity promote photodimerisation, whereas heavy atom solvents cause its suppression.242These observations are thought to suggest that the dimerisation occurs by a singlet mechanism.

173

1114: Photochemistry of Aromatic Compouncis

7

Lateral Nuclear Shifts

ZSM-5 is a member of the pentasil family whose internal surface possesses two pore systems, one of which is sinusoidal and the other straight and perpendicular to the sinusoidal channels.243Organic molecules such as arylmethyl esters can be occluded within these ordered media, and under such conditions their photochemistry has been examined. The same group has also investigated the photoFries reaction of various aryl phenylacetates such as p-tolyl phenylacetate, o-tolyl phenylacetate, and phenyl o-tolylacetate in homogeneous solution and adsorbed on ZSM-5 and NaY zeolites.2a Different products are reported for the two catalysts, and these are accounted for in terms of their size and shape sorption selectivity on the zeolite, and by the restriction of their diffusional and rotational mobility. The photo-Fries reaction of 1- and 2-naphthyl acetates has been investigated using a range of techniques including steady state and time-resolved photolysis, and CIDNP.245Confirmation that the primary radical pair is a singlet has been obtained (triplet radical pairs are shown to proceed to disproportionation products) and a general kinetic scheme for the rearrangement has been proposed. The photochemical behaviour of N-acetyl- and N-benzoylcarbazole is reported to be dependent on the properties of the medium and may give photoFries or photoinduced single electron transfer.246 AGoEThas been determined using the Weller equation. Two photon chemistry has been successfully promoted using the two-laser two-colour technique in the cases of benzyl phenyl ether and phenyl acetate, and is based upon the photoconversion of transient cyclohexa2,4-dienone intermediates which occur in the photo-Claisen and photo-Fries rearrangements, to the dienic ketenes (Scheme 2).247

0 6OR

0-

hv )1=266

R = Benzyl, Ac

\

0

H@ /

& !dR -

Scheme 2

The photo-Claisen rearrangement of ally1 phenyl ether in water and in the presence of P-cyclodextrin gives a mixture of o- and p-ally1 phenols and Product quantum yields are modified by addition of P-cyclodextrin, and the total yields are reduced by molecular oxygen with inhibition being less marked when P-cyclodextrin is present. An investigation of the benzophenonesensitized rearrangement of N-( 1-naphthoy1)-N-phenyl-O-benzoylhydroxylamine in micelles suggests that the benzoyloxy migrated products arise from the amidylbenzoyloxy radical pair present at the micellar surface, and that the amidylphenyl radical pair which is located more deeply within the micelle, leads to the phenyl rearranged products.249

I74

8

Photochemistry

Miscellaneous Photochemistry

A laser flash photolysis and time-resolved resonance Raman study of competitive energy and electron transfer processes in 1-nitronaphthalene has shown that in polar solvents the substrate can act as an electron acceptor with nitrite ions and trans-stilbene, but that in non-polar solvents energy transfer is the dominant process.250It has been suggested that the transition between these processes is governed by electronic and nuclear factors. A study of the influence of cyclodextrins on the photophysics of 4H-1-benzopyran-4-thionein solution and in the solid state has revealed that complexes with the cyclodextrins may be involved.25' An examination of the influence of molecular structure on the light sensitivity of 1,2- and 2,l -naphthoquinonediazide-4-sulfonicacid shows that the position of the diazide group is Flash photolysis of lO-diazo-9( 10H)-phenanthrenone in aqueous media gives fluorenylideneketene and subsequently its hydrated product fluorene-9-carboxylic acid enol as transients.253This has enabled the rate of enolisation of fluorene-9-carboxylic acid to be determined. Photolysis of the diazaquinone (1 23) gives the corresponding fluorenylideneketene which has been detected using laser photolysis techniques, and which reacts with amines such as diethylamine to give ylides (124) and subsequently amides as final products.254

A temperature-dependent photodecomposition has been established for 1-(2azidophenyl)-3,5-dimethylpyrazole, which at temperatures >200 K gives 1,3dimethylpyrazolobenzotriazole by electrophilic cyclisation of the singlet nitrene, but which at lower temperatures leads to products derived from the dimerisation of the triplet nitrene along with products arising from intramolecular radical c y c l i s a t i ~ n Recent . ~ ~ ~ advances in the photochemistry of 2-pyridylazides (tetrazolo[1,5-a]pyridines) have appeared.2s6 On photolysis, these compounds form 2pyridylnitrenes which rearrange to 1,3-diazacycloheptatetraenes,and the initially formed nitrenes have now been observed. Some new chemistry involving the Wolff rearrangement of pyridine diazoketones and in which ketene-nucleophile ylid intermediates are thought to participate has been described. Photolysis of methanolic 4,6-diazido-3-methylisoxazolo-[4,5-c]pyridinepromotes loss of nitrogen and subsequent solvent addition to give 3-methylisoxazolo-I ,3-diazepine derivatives,257and the triplet states of 4-nitrophenylnitrene and 4-nitrene-4'nitrostilbene have been generated at low temperature by photolysis of the corresponding azides, and have been ~ h a r a c t e r i s e d .Their ~ ~ ~ photoinduced hydrogen abstraction reactions may be accounted for either in terms of a hot ground state or alternatively as an excited state process. The experimental observations are correlated with the results of quantum mechanical calculations.

IIt4: Photochemistry of Aromatic Compounh

175

Irradiation of the charge transfer band of [ArN2+,Ar’H] initiates a homolytic chain arylation whose kinetics have been determined and which have been now been verified by computer ~imulation.~’~ In an inert matrix, 2- and 3-(diazomethy1)furan can be photolysed to (Z)-pent-2-en-4-yn- 1-a1 and (s-2)-(a-formy1)methylenecyclopropene in transformations which respectively proceed through a carbene and an oxabicyclopropene species.260 Irradiation of solutions of p-chloroaniline produces both benzidine and aniline as secondary products, and this is taken to indicate the formation of 4-iminocyclohexa-2,5-dienylidene as a transient.26’ N-Propyl-o-sulfobenzoic imide (125) has been photolysed in ethanol and various monocyclic aromatic solvents, and although the S1 and TI states participate in both cases, the ensuing transformations are different.262In ethanol, the diradical produced following extrusion of sulfur dioxide abstracts hydrogen from the solvent to give (126) as the final product, whereas in aromatic solvents energy transfer occurs from the solvent to the substrate triggering addition of the resulting radicals to the aromatics with formation of (127). The photoactivatable dolichol analogue (128; R = H, P03H2,; R’ = (102,142,182,222,262,302, 34E,38E)-Me2C:CHCH2(CH2CMe:CHCH2)2(CH2CMe:CHCH2)6) has been prepared and is a substrate for dolichol kinase from yeast membranes, an essential enzyme involved in the N-linked glycosylation p a t h ~ a y . 2 ~ ~ 0

RO-,

,-,

,CH~R’

Irradiation of 2-[N-(pentafluorophenyl)amino]-3-phenylcyclopropenone promotes decarbonylation to give N-(pentafluoropheny1)phenylethynamine and 2-phenyl-3-[N-(pentafluorophenyl)amino]acrylic acid by a process for which there is no known precedent,264and the photoextrusion of carbon monoxide from 1,3-bis(ethylenedioxy)indan-2-0ne has been used as the first step in a new synthesis of 1,2-dioxobenzocyclobutene.265This represents an unusual example of the decarbonylation of a five-membered cyclic ketone in the preparation of a highly strained and functionalised cyclobutane derivative. The photolysis of a-naphthaleneacetic acid in aqueous solution proceeds by decarboxylation and oxidation of the aromatic ring, and has been carried out at a variety of different wavelengths.266The primary step occurs by pseudo-first order kinetics and the optimum photolysis rate has been observed using Ti02 as photocatalyst. Within the cavity of P-cyclodextrin, naproxene (129) has been photodecarboxylated to

176

Photochemistry

give products having ethyl, 1-hydroxyethyl, and acetyl side chains.267Irradiation of 2-( 1-naphthyl)ethyl 3-anilinoalkanoates produces tricyclic lactones containing the 2-azabicyclo[3.3.llnonane skeleton,268and photodecomposition of the fluorescent system (130; T = thymidine) is reported to give the N,-deprotected cyclised precursor (1 3 1) together with (132).269These observations may be of relevance to photolabile fluorescent protecting groups. Photosensitive fatty acid esters which may serve as useful biological precursors of several model &unsaturated fatty acids, including arachidonic acid, have been prepared using 1-(2'-nitropheny1)ethanedi01.~~'Photocleavage of some carboxylic acid esters of 3',5'-dimethoxybenzoin (133; R = CH3, CH2Ph, Ph, C(CH3)3) in acetonitrile and aqueous acetonitrile gives the corresponding benzofuran (134; same R) and the corresponding carboxylic acid.271 The primary photochemical step is heterolytic cleavage of the C-OCOR bond a to the acetophenone carbonyl in a process which is assisted by electronic interaction between the electron-rich dimethoxybenzene ring and the n,x* excited carbonyl group of the acetophenone fragment; in this latter process the cyclohexadienyl cation is formed. The sulfimides, TosN-S(R')CH2R2 (135; R' = Ph, 2-pyridinyl, Me; R2 = naphthyl, Ph; Tos = p-toluenesulfonyl) are reported to undergo the photoStevens rearrangement, and for example (1 35; R = 2-pyridinyl; R2 = naphthyl) is

'

0

OMe

IIl4: Photochemistry of Aromatic Compounds

177

converted into R I S N ( T O S ) C H ~ RIt~is. ~ also ~ ~claimed that photolysis of the 2,13dithia[3.3](1,3)naphthalenophanes (136) in trimethyl phosphite gives the corresponding tetrahydro-3,4:8,9-dibenzopyrene(1 37) and tetrahydro-3,4:9,1O-dibenzopyrene (138).273

Photoprotecting groups continue to be an active field of interest. A mechanistic investigation of the photolytic transformation of various phenacyl esters (PhCOCH2-OCOR) in the presence of electron donating sensitizers, and which leads to the formation of acetophenone and the corresponding carboxylic acid, has appeared.274These reactions, which occur in high yield, seem to be triggered by photoinduced electron transfer to the phenacyl ester to give an anion radical which suffers C - 0 bond scission forming the phenacyl radical and the corresponding carboxylate anion. The authors have also shown that photolysis of phenacyl phenylacetate gives acetophenone and phenylacetic acid in a triplet state process whose quantum yield is increased by the presence of H-atom donors.275The p-hydroxyphenacyl protecting group has been used as a phototrigger for excitatory amino acids such as L-Glu and y-aminobutyric Irradiation of buffered solutions of the esters brings about release of the amino acid or peptide and this is accompanied by rearrangement of the phenacyl group to p-hydroxyphenylacetic acid in a process which occurs through the phenacyl triplet state, A new photosensitive protecting group for amines incorporating o-hydroxy-trans-cinnamicacid has been described, and which is based upon High overall yields the facile lactonisation of o-hydroxy-cis-cinnamic have been obtained for the range of amines, HNRR’ (R = H, Et, R’ = n-Pr, CHZCH~OH, CH*Ph, cyclohexyl). o-Nitrobenzyloxycarbonyl and related groups have been examined as photolabile protecting groups for nucleoside 5’-hydroxyl functions.278Photodeprotection rates for a series of 5’-0-protected thymidine derivatives irradiated at 365 nm vary by a factor of 17, and rates are also found to be affected by substitutions on both the phenyl ring and the a-carbon atom. Nucleoside derivatives have been prepared using a photolabile protecting group for oligonucleoside synthesis.279For example, N6-[02N-4-C6H4CH2CH20CO-]5’-0-[2-(O2N-2-C6H4)CH2CH2SO2-]-2’-deoxyadenosine has been prepared from N6-protected adenosine and 2-(2-chloro-6-nitrophenyl)ethylsulfonyl chloride. Irradiation of polymer supports containing the new o-nitrobenzyl photocleavable linker (139) gives amino acid and sugar products in high yields, and its utility has been demonstrated by the synthesis and photocleavage of a branched trimannan from a polymer support.28o The caged L-leucyl-L-leucine methyl ester ( 140) will release L-leucyl-L-leucine

Photochemistry

178

Hovc methyl ester on irradiation in methanol and in liposomes suspended in PBS.28' These observations may have significance for investigating the mechanism of the induction of an apoptosis to NK cells and macrophage. The o-nitrobenzyl group appears to be a useful photosensitive protecting group for indoles, benzimidazoles and 6 - c h l o r o ~ r a c i lphotocleavable ;~~~ cyclic oligonucleotides (141; X' = X2 = 5'oligonucleotide-3' or 3'-oligonucleotide-5') having a base sequence capable of hybridising with a target DNA or RNA and a structure cyclised with a photocleavable linkage have been prepared,283and substituted desyl (2-0x0- 1,2diphenylethyl) groups have been explored as potential photolabile protecting groups to mask primary and secondary amines as photosensitive a-keto carbamates such as (142; R' = H, OMe, SMe; R2 = H, OMe; R3 = H, Me, Ph).284

References 1.

2. 3. 4.

5. 6.

B. Ohtani, Yuki Gosei Kagaku Kyokaishi, 1997,55,460. T. Inazu and H. Takemura, Kagaku (Kyoto), 1998,53,68. S. A. Fleming, C. L. Bradford, and J. J. Gao, Mol. Supramol. Photochem., 1997, 1, 187. A. Sugimoto and K. Mizuno, Kokagaku, 1997,2444. A. Weedon, Adv. Photochem., 1997,22,229. M. Sainsbury, RoMs Chem. Carbon Compd (2nd E d ) , 1997,4(Pt. B), 361.

1114: Photochemistryof Aromatic Compounds

7. 8. 9. 10. 11. 12. 13. 14.

15. 16. 17. 18. 19. 20. 21. 22. 23. 24. 25. 26. 27.

28. 29. 30. 31. 32. 33. 34. 35. 36. 37. 38. 39. 40.

179

3. W.Pavlik, Mol. Supramol. Photochem., 1997, I, 57. H. Ciurla, Pr. Nauk Akad. Ekon. im. Oskara Langego Wroclawiu,1996,728,83. M. Uchida and M. Irie, Senryo to Yakuhin, 1997,42, 155. R. Guglielmetti, Opt. Spektrosk., 1997,83,682. Y.Yokoyama, Gendai Kagaku, 1997,321,46. T. Jin, Senryo to Yakuhin, 1997,42,187. R. Gade and Th. Porada, J. Photochem. Photobiol., A, 1997,107,27. D. K. Palit, A. Z. Szarka, N. Pugliano, and R. B. Hochstrasser, Ultrufast Processes Spectrosc., [Proc. Int. ConJ], 9th, 1996,75. J. Schroeder, Ber. Bunsen-Ges., 1997,101,643. N. R. King, E. A. Whale, F. J. Davis, A. Gilbert, and G. R. Mitchell, J. Mater. Chem., 1997,7,625. Y. V. Il’ichev and K. A. Zachariasse, Ber. Bunsen-Ges., 1997,101,625. F. D. Lewis and J.-S. Yang, J. Am. Chem. Soc,, 1997,119,3834. 0.Karthaus, H. Hioki, and M. Shimomura, Colloids SurJ, A, 1997,126, 181. H . Usami, T. Nakamura, T. Makino, H. Fujimatsu, and 0. Shinji, J. Chem. SOC., Faraday Trans., 1998,94,83. W. Herrmann, S. Wehrle, and G. Wenz, Chem. Commun. (Cambridge), 1997,1709. M . F. Budyka, 0.D. Laukhina, and D. N. Dogadkin, Mendeleev Commun., 1997,107. M. F. Budyka, 0. D. Laukhina, and V. F. Razumov, Chem. Phys. Lett., 1997,279, 327. M. Takeshita and M. Irie, Tetrahedron Lett., 1998,39,613. R. E. Martin, J. Bartek, F. Diederich, R. R. Tykwinski, E. C. Meister, A. Hilger, and H.P. Luthi, J. Chem. SOC.,Perkin Trans. 2, 1998,233. T. Arai, Y. Hozumi, 0. Takahashi, and K. Fujimori, J. Photochem. Photobiol., A , 1997,104,85. E. J. Shin, E. Y.Bae, S. H. Kim, H. K. Kang, and S. C. Shim, J. Photochem. Photobiol., A, 1997,107, 137. A. Kpissay, C. N. Kuhl, T. Mohammad, K. Haber, and H. Morrison, Tetrahedron Lett., 1997,38, 8435. R. J. Olsen, J. Photochem. Photobiol., A, 1997,103,91. M. Garavelli, P. Celani, F. Bernardi, M. A. Robb, and M. Olivucci, J. Am. Chem. SOC.,1997,119,6891. T . Naegele, R. Hoche, W. Zinth, and J. Wachtveitl, Chem. Phys, Lett., 1997, 272, 489. E. Markava, G. Matisova, andI. Muzikante, Latv. Kim. Z., 1997,65. T . Aoyagi, A. Ueno, M. Fukushima, and T. Osa, Macromol. Rapid Commun., 1998, 19, 103. R. Tahara, T. Morozumi, H. Nakamura, and M. Shimomura, J. Phys. Chem. B, 1997,101,7736. M. Saadioui, N. Reynier, J.-F. Dozol, Z. Asfari, and J. Vicens, J. Inclusion Phenom. Mol. Recognit. Chem., 1997,29, 153. R. A. Moss and W. Jiang, Langmuir, 1997,13,4498. K. Ichimura, N. Fukushima, M. Fujimaki, S.Kawahara, Y. Matsuzawa, Y.Hayashi, and K. Kudo, tangmuir, 1997,13,6780. P. Thuery, M. Lance, M.Nierlich, N. Reynier, V. Lamare, J.-F.Dozol, M.Saadioui, 2. Asfari, and J. Vicens, An. Quim. Int. Ed., 1997,93, 324. K. Se, M. Kijima, and T. Fujimoto, Polymer, 1997,38,5755. V. A. Bren, V. I. Minkin, A. D. Dubonosov, V. A. Chernoivanov, V. P. Rybalkin, and G. S. Borodkin, Mol. Cryst. Liq. Cryst. Sci. Technol., Sect. A , 1997,297,247.

180 41.

42. 43. 44. 45.

46. 47. 48. 49. 50. 51. 52. 53. 54. 55.

56. 57. 58. 59. 60. 61. 62. 63. 64. 65. 66. 67. 68. 69. 70. 71. 72. 73. 74.

Photochemistry

H. Kawanami, K. Toyota, M. Yoshifuji, J. Organomet. Chem., 1997,535, 1. H. Cerfontain, A. Koeberg-Telder, B. H. Bakker, R. H. Mitchell, and M. Tashiro, Liebigs AnnSRecl., 1997, 873. H. Rahmani and H. Pirelahi, J. Pholochem. Photobiol., A, 1997,111, 15. S . H. Bhatia, D. M. Buckley, R. W. McCabe, A. Avent, R. G. Brown, and P. B. Hitchcock, J. Chem. Soc., Perkin Trans. 1,1998,569. I. V. Nechepurenko, 0. P. Petrenko, I. A. Grigor’ev, and L. B. Volodarskii, Russ. J. Org. Chem., 1997,33, 705. D. P. Dhavale, V. P. Mali, S. G. Sudrik, and H. R. Sonawane, Tetrahedron, 1997, 53, 16789. H. Aoyama, J. Chem. Soc., Perkin Trans. I , 1997, 1851. T. Isshiki, H. Miyagawa, H. Sasaki, and J. Yamamoto, Nippon Kagaku Kaishi, 1997, 532. T. Kitamura, K. Morizane, H. Taniguchi, and Y. Fujiwara, Tetrahedron Lett., 1997, 38, 5157. M. D. Auria, Internet J. Sci.: Biol. Chem., 1997,4. 0. Muraoko, G. Tanabe, and Y. Igaki, J. Chem. Soc., Perkin Trans. I , 1997,1669. 0. Muraoka, G. Tanabe, E. Yamamoto, M. Ono, T. Minematsu, and T. Kimura, J. Chem. Soc., Perkin Trans. I , 1997, 2879. R. Altundas and M. Balci, Aust. J. Chem., 1997,50,787. V. Nair, G. Anilkumar, J. Prabhakaran, D. Maliakal, G. K. Eigendorf, and P. G. Williard, J. Photochem. Photobiol., A, 1997,111, 57. J . R. Scheffer and H. Ihmels, Liebigs Ann. /Red., 1997,1925. D. Armesto, A. Ramos, M. J. Ortiz, W. M. Horspool, M.J. Mancheno, 0.Caballero, and E. P. Mayoral, J. Chem. SOC.,Perkin Trans. I , 1997,1535. Y. Tobe, S. Saiki, H. Minami, and K. Naemura, Bull. Chem. SOC.Jpn., 1997, 70, 1935. H. Okamoto, K. Satake, and M. Kimura, Chem. Lett., 1997,873. F. Scavarda, F. Bonnichon, C. Richard, and G. Grabner, New J. Chem., 1997, 21, 1119. H. Ikeda, T. Minegishi, H. Abe, A. Konno, J. L. Goodman, and T. Miyashi, J. Am. Chem. SOC.,1998,120,87. S . Kyushin, T. Shinnai, T. Kubota, and H. Matsumoto, Organometallics, 1997, 16, 3800. M. Yoshifuji, H. Takahashi, K. Shimura, K. Toyota, K. Hirotsu, and K. Okada, Heteroat. Chem., 1997,8,375. F. Lahmani and A. Zehnacker-Rentien, J. Phys. Chem. A , 1997,101,6141. T. Sekikawa, T. Kobayashi, andT. Inabe, J. Phys. Chem. B, 1997,101,10645. E. Bardez, I. Devol, B. Larry, and B. Valeur, J. Phys. Chem. B, 1997,101,7786. E. L. Roberts, J. Dey, and I. M. Warner, J. Phys. Chem. A, 1997,101,5296. S . Khatib, M. Botoshansky, and Y. Eichen, Acta Cystallogr., Sect, B: Struct. Sci., 1997,53, 306. N. Gritsan, Mol. Cryst. Liq. Cryst. Sci. Technol., Sect. A., 1997,297, 167. T. Schirmeister, Liebigs Ann.lRecl., 1997, 1895. S. P. Gromov and M.V. Alfimov, Russ. Chem. Bull., 1997,46,611. Z . X.Guo, G. J. Wang, Y. W. Tang, and X. Q. Song, Liebigs Ann. IRecl., 1997,941. V. P. Tsybyshev, V. A. Livshits, B. B. Meshkov, 0.A. Fedorova, S. P. Gromov, and M. V. Alfimov, Russ.Chem. Bull., 1997,46,1239. T. Nakai, M. Tani, S. Nishio, A. Matsuzaki, and H. Sato, Chem. Lett., 1997,795. T. Nagasaki, S. Tamagaki, and K. Ogino, Chem. Lett., 1997,717.

IIl4: Photochemistry of Aromatic Compounds

75. 76. 77. 78. 79. 80.

81. 82. 83. 84.

85. 86. 87.

88. 89. 90. 91. 92. 93. 94. 95. 96. 97. 98. 99. 100. 101. 102. 103. 104. 105.

181

M. Irie, T. Eriguchi, T. Takada, and K. Uchida, Tetrahedron, 1997,53, 12263. P. Y. Wang and C. J. Wu, Dyes Pigm., 1997,35,279. H. Laatsch, A. J. Schmidt, A. Kral, N. Heine, and G. Haucke, Indian J. Chem., Sect. A: Znorg., Bio-inorg., Phys., Theor. Anal. Chem., 1997,36A, 476. V. I. Minkin and V. N. Komisarov, Mol. Cryst. Liq. Cryst. Sci. Technol., Sect. A , 1997,297, 205. 0.Brede, L. Goebel, and T. Zimmermann, J. Phys. Chem., A , 1997,101,4103. A. C. Benniston, A. Harriman, and C. McAvoy, J. Chem. SOC.,Faraday Trans., 1997,93,3653. Yu. K. Mihailovskii, V. E. Agabekov, I. V. Astapovich, and V. A. Azarko, Vestsi Akad Navuk Belarusi, Ser. Khim. Navuk, 1996,30. K. Chamontin, V. Lokshin, A. Samat, and R. Guglielmetti, PCT Int. Appl. WO 98 04,563. M. Campredon, B. Luccioni-Houze, G. Giusti, R. Lauricella, A. Alberti, and D. Macciantelli, J. Chem. Soc., Perkin Trans. 2, 1997,2559. Z.-N. Huang, S. Jin, Y. Ming, and M. Fan, Mol. Cryst. Liq. Cryst. Sci. Technol., Sect. A, 1997,2!97,99. J.-W. Kim, K.-H. Ahn, H. Kim, and T. Chang, Pollimo, 1997,21,512. E. P. Ivakhnenko, N. I. Makarova, M. I. Knyazhansky, V. A. Bren, V. A. Chernoivanov, A. I. Shiff, and G. S. Borodkin, Mol. Cryst. Liq. Cryst. Sci. Technol., Sect. A, 1997,297,233. A. T. Hu and H.-J. Lee, Proc. Natl. Sci. Counc., Repub. China, Part A: Phys. Sci. Eng., 1997,21, 185. V. Lokshin, A. Samat, and R. Guglielmetti, Tetrahedron, 1997,53,9669. Y.-P. Chan, PCT Int. Appl. WO 97 10,241. V. S. Marevtsev and N. L. Zaichenko, J. Photochem. Photobiol., A , 1997, 104, 197. A. V. Metelitsa, 0. A. Kozina, S. M. Aldoshin, B. S. Lukyanov, M. I. Knyazhansky, and V. I. Minkin, Mol. Cryst. Liq. Cryst. Sci. Technol., Sect. A , 1997,297,227. S . Delbaere, C. Bochu, N. Azaroual, G. Buntinx, and G. Vermeersch, J. Chem. SOC., Perkin Trans. 2,1997, 1499. T. Horii, Y. Miyake, R. Nakao, and Y. Abe, Chem. Lett., 1997,655. P. Celani, F. Bernardi, M. Olivucci, and M. A. Robb, J. Am. Chem. SOC.,1997, 119, 10815. Y. Kawanishi, K. Seki, T. Tamaki, M. Sakuragi, and Y. Suzuki, J. Photochem,. Photobiol., A , 1997, 109,237. H. Goerner, Chem. Phys., 1997,222,315. J. Momoda, S. Imura, and T. Kobayakawa, U.S. US 5,693,830. T. Hori, H. Tagaya, T. Nagaoka, J. Kadokawa, and K. Chiba, Appl. Su$ Sci., 1997,121,530. S . Yoshimoto and Y. Onishi, Jpn. Kokai Tokkyo Koho JP 09,323,990. Y. Dong, G. Fan, J. Shi, Q. Gao, and Y. Jia, Xibei Daxue Xuebao Ziran Kexueban, 1997,27, 103. L. Zhijie, H. Yi, and J. Zhang, IS&Ts Annu. ConJ, Final Program. Proc., 49th, 1996, 529. J.-Q. Bai, X.-C. Han, Y.-M. Wang, and J.-B. Meng, Chin. J. Chem., 1997, 15, 553. K. Fukunaga and M. Fujimoto, Jpn. Kokai Tokkyo Koho JP 10 36,354 [98 36,3541. H. G. Heller, J. R. Levell, D. E. Hibbs, D. S. Hughes, and M. B. Hursthouse, Mol. Cryst. Liq. Cryst. Sci. Technol., Sect. A , 1997,297, 123. J. Momoda and T. Hara, Eur. Pat. Appl. EP 778,276.

182

Photochemistry

106.

J. L. Pozzo, A. Samat, R. Guglielmetti, R. Dubest, and J. Aubard, Helv. Chim. Acta, 1997,80, 725.

A. Kumar, D. B. Knowles, and B. Van Gemert, PCT Int. Appl. WO 97 21,698. A Kumar, U.S. US 5698141 A. H. G. Heller and J. R. Levell, PCT Int. Appl. WO 9748762. M. Melzig and H. Zinner, Ger. Offen. DE 19,65 1,286. M. Melzig and H. Zinner, Ger. Offen. DE 19540185 Al. J. J. Luthern, Mol. Cryst. Liq. Cryst. Sci. Technol., Sect. A , 1997,297, 155. F. J. Hughes, U.S. US 5679805A. H. Pirelahi, H. Rahmani, A. Mouradzadegun, A. Fathhi, and A. Moudjoodi, Phosphorus, Sulphur, Silicon Relat. Elem., 1997,120,403. 115. H. Nakashima and M. hie, Macromol. Rapid Commun., 1997, 18,625. 116. T. Tsujioka, M. Kume, and M. Irie, J. Photochem Photobiol., A, 1997,104,203. 117. F. J. Hughes and E. A. Travnicek, U.S. US 5628935 A 13 May 1997. 118. Y. Yoshioka and M. Irie, Electron J. Theor. Chem., 1996,1, 1. 119. L. Yu, D. Zhu, and M. Fan, Mol. Cryst. Liq. Cryst. Sci. Technol., Sect. A, 1997,297, 107. 108. 109. 110. 111. 112. 113. 114.

120. 121. 122. 123. 124.

107. Z. Gou, Y. Tang, F. Zhang, F. Zhao, and X . Song, J. Photochem. Photobiol., A , 1997, 110, 29. Y. Yokoyama, S. Uchida, Y.Shimizu, and Y. Yokoyama, Mol. Cryst. Liq. Cryst. Sci. Technol., Sect. A, 1997,2W, 85.

H. G. Heller, K. Koh, M. Kose, and N. Rowles, Mol. Cryst. Liq. Cryst. Sci. Technol., Sect. A , 1997,297,73. T. Watanabe, G. Yamakawa, S. Tokita. and H. Nakahara, J. Photopolym. Sci. Technol., 1997,10,255. J. Biteau, G. M. Tsivgoulis, F. Chaput, J.-P. Boilot, S. Gilat, S. Kawai, J.-M. Lehn, B. Darracq, F. Martin, and Y. Levy, Mol. Cryst. Liq. Cryst. Sci. Technol. Sect. A, 1997,297,65.

125.

M. Irie, T. Lifka, and K. Uchida, Mol. Cr-yst.Liq. Cryst. Sci. Technol. Sect. A , 1997, 297,81.

126.

F. Pina, M. J. Melo, M. Maestri, R. Ballardini, and V. Balzani, J. Am. Chem. Sue.,

127. 128. 129. 130.

J.-Y. Wu, J.-C. Mai, K. Pan, and T.4, Ho, Tetrahedron Lett., 1998,39, 647. P. Cao, Z.-Y. Long, and Q.-Y. Chen, Molecules, 1997,2, 11. S . C. Shim, Y. S. Chae, and E. K. Baek, Bull. Korean Chem. SOC.,1997,18,364. S. C. Shim, Y. S. Chae, E. K. Baek, and S. K. Park, J. Photochem. Photobiol., A ,

131. 132.

Y. Ito, S. Edo, and S. Ohba, J. Am. Chem. SOC.,1997,119,5974. R. A. Bunce, C. R. Shawn, and E. M. Holt, J. Photochem. Photobiul., A , 1997, 109,

133.

A. R. Kim, K. J. Kim, S. C. Sim, and S. S. Kim, Bull. Korean Chem. SOC.,1997,18,

134.

L. Klimenko, Z. Leonenko, and N. Gritsan, Mol. Cryst. Liq. Cryst. Sci. Technol., Sect. A, 1997,297, 181. M. Kako, M. Ninomiya, and Y. Nakadaira, Chem. Commun. (Cambridge), 1997,

1997,119,5556.

1997,106, 155. 125.

1125. 135. 136. 137. 138.

1373. N . Haddad and H. Salman, Tetrahedron Lett., 1997,38,6087. T. I. Ho, C. S. Ho, S. M. Shin, and K. Pa, Electron. Con$ Heterocycl. Chem., (Proc.], 1997, Eds, H. S. Rzepa, J. P.Snyder, and C. Leach. K. Iwata and H. Hamaguchi, J. Mol. Struct., 1997,413, 101.

IIl4: Photochemistry of Aromatic Compounds

139. 140. 141. 142. 143. 144. 145. 146. 147. 148. 149. 150.

151. 152. 153.

154. 155. 156.

157. 158. 159. 160. 161. 162. 163. 164. 165. 166. 167.

168. 169. 170. 171. 172.

183

M. Austin, C. Covell, A. Gilbert, and R. Hendricks, Liebigs Ann./Recl., 1997, 943. R. Busson, J. Schraml, W. Saeyens, E. Van der Eycken, P. Herdewijn, and D. De Keukeleire, Bull. SOC.Chim. Belg., 1997, 106,671. G. S. Han and S. C. Shim, Photochem. Photobiol., 1998,67,84. Y. Nakamura, M. Matsumoto, Y. Hayashida, and J. Nishimura, Tetrahedron Lett., 1997,38,1983. M. Christ1 and M. Braun, Liebigs AnnJRecl., 1997, 1135. N. Braussaud, N. Hoffmann, and H.-D. Scharf, Tetruhetiron, 1997,53, 14701. E. Hadjoudis, A. Botsi, G. Pistolis, and H. Galons, J. Carbohycir. Chem., 1997, 16, 549. C. A. Hastings, J. D. Riggenberg, and E. M. Carreira, Tetruhedron Lett., 1997, 38, 8789. D. L. Comins, Y. S. Lee, and P. D. Boyle, Tetrahedron Lett., 1998,39, 187. G. Vassilikogiannakis and M. Orfanopoulos, J. Am. Chem. Suc., 1997,119, 7394. G. Vassilikogiannakis and M. Orfanopoulos, Tetrahedron Lett., 1997,38,4323. Y. Nakamura, Y. Hayashida, Y. Wada, and J. Nishimura, Tetrahedron, 1997, 53, 4593. H. Yoon and W. Chae, Tetrahedron Lett., 1997,38,5169. R. de Haan, E. W. de Zwart, and J. Cornelisse, J. Photochem. Photobiol., A, 1997, 102, 179. A. R. Kim, S. S. Kim, D. J. Yoo, and S . C. Shim, Bull. Korean Chem. SOC.,1997,18, 665. W. Saeyens, R. Busson, J. Van der Eycken, P. Herdewijn, and D. De Keukeleire, Chem. Commun. {Cambridge), 1997,8 17. D. M. Amey, D. C. Blakemore, M. G. B. Drew, A. Gilbert, and P. Heath, J. Photochem. Photobiol., A, 1997,102, 173. H. Gan, S. Halfon, B. J. Hrnjez, and N. C. Yang, J. Am. Chem. SOC.,1997, 119, 7470. G. P. Kalena, P. P. Pradhan, Y. Swaranlatha, T. P. Singh, and A. Banerji, Tetrahedron Lett., 1997,38,555 1 . H. R. Memarian, M. Nasr-Esfahani, R. Boese, and D. Dopp, Liebigs Ann./Recl., 1997,1023. H. Ji, Z. Tong, and C. Tung, Ganguang Kexue Yu Guung Huaxue, 1996,14,289. T. Noh, D. Kim, and S. Jang, Bull. Korean Chem. SOC.,1997,18,357. T. Nakayama, Y. Amijima, S. Miki, and K. Hamanoue, Chem. Lett., 1997,223. T. Noh, H. Lim, and D. Kim, Bull. Korean Chem. Soc., 1997,18,247. T. Noh, H. Lim, D. Kim, and K. Jeon, Buff.Koreun Chem. Soc., 1997,18, 1002. W. Bhanthumnavin, S . Ganapathy, A. M. Arif, and W. G. Bentrude, Heteroat. Chem., 1998,9,155. C . Gaebert and J. Mattay, Tetrahedron, 1997,53, 14297. S . M. Sieburth, T. H. Ai-Tel, and D. Rucando, Tetrahedron Lett., 1997,38,8433. G. Konishi, K. Chiyonobu, A. Sugimoto, and K. Mizuno, Tetrahedron Lett., 1997, 38,5313. M. Ohno, N. Koide, H. Sato, and S. Eguchi, Tetrahedron, 1997,53,9075. J. Botzem, U. Haberl, E. Steckhan, and S. Blechert, Acta Chem. Scund., 1998, 52, 175. T. Noh, C. Kim, and D. Kim, Bull. Korean Chem. Soc., 1997,18,781. C . Rivas, F. Vargas, G. Aguiar, A. Torrealba, and R. Machado, J. Photochem. Photobiol., A, 1997, 104, 53. T. Nishio and M. Oka, Helv. Chim. Acta, 1997,80,388.

184

Photochemistry

173. 174.

S. Auricchio, A. Selva, and A. M. Truscello, Tetrahedron, 1997,53, 17407. E. Bosch, S. M. Hubig, S. V. Lindeman, and J. K. Kochi, J. Org. Chem., 1998, 63, 592. B. Barker, L. Diao, and P. Wan, J. Photochem. Photobiol., A , 1997, 104,91. A. Ouchi and Y. Koga, J. Org. Chem., 1997,62,7376. H. J. P. de Lijser and D. R. Arnold, J. Chem. Soc., Perkin Trans. 2 , 1997, 1369. D. R. Arnold, K. A. Mcmanus, and M. S . W. Chan, Can. J. Chem., 1997,75,1055. M. S. W. Chan and D. R. Arnold, Can. J. Chem., 1997,75,1810. T. Tsubomura, A. Ishikura, K. Hoshino, H. Narita, and K. Sakai, Chem. Lett., 1997, 1171. F. S. Bavetta, T. Caronna, M. Pregnolato, and M. Terreni, Tetrahedron Lett., 1997, 38, 7793. S.-J. Lin, S.-Y. Jiang, T.-C. Huang, C.3. Dai, P.-F. Tsai, H. Takeshita, Y.-S. Lin, and T. Nozoe, Bull. Chem. Soc. Jpn., 1997,70,3071. M. D’Auria, Heterocycles, 1997,45, 1775. M. D’Auria, E. De Luca, G. Mauriello, and R. Racioppi, J. Chem. Soc., Perkin Trans. I, 1998,271. V. L. Ivanov, S. Yu. Lyashkevich, and H. Lemmetyinen, J. Photochem. Photobiol., A , 1997,109,21. H. Ofenberg, L. Cires, A. Vlahovici, and A. Lablache-Combier, Rev. Roum. Chim., 1997,42, 137. A.-P. Durand, R. G. Brown, D. Worrall, and F. Wilkinson, J. Chem. Soc., Perkin Trans. 2,1998, 365. T. Nakayama, S. Akimoto, 1. Yamazaki, and K. Hamanoue, J. Photochem. Photob i d , A, 1997,104, 77. M. D’auria, E. De Luca, G. Mauriello, R. Racioppi, and G. Sleiter, J. Chem. Soc., Perkin Trans. I , 1997,2369. C. P. Butts, L. Eberson, M. P. Hartshorn, and 0. Peterson, Acta Chem. Scand., 1997, 51, 718. C. P. Butts, L. Eberson, M. P. Hartshorn, 0. Persson, R. S. Thompson, and W. T. Robinson, Acta Chem. Scand., 1997,51, 1066. C. P. Butts, L. Eberson, R. Gonzales-Luque, C. M. Hartshorn, M. P. Hartshorn, M. Merchan, W. T. Robinson, B. 0. Roos, C . Vallance, and B. R. Wood, Acta Chem. Scand., 1997,51,984. P. M. J. Jung, W. B. Motherwell, and A. S . Williams, Chem. Commun. (Cambridge), 1997, 1283. R . J. Moran, C. Cramer, and D. E. Falvey, J. Org. Chem., 1997,62,2742. C. Saintome, P. Clivio, A. Favre, and J.-L. Fourrey, J. Org. Chem., 1997,62, 8125. N. Vivona, S. Buscemi, S. Asta, and T. Caronna, Tetrahedron, 1997,53, 12629. T. Tsuji, M. Ohkita, T. Konno, and S . Nishida, J. Am. Chem. Sue., 1997,119, 8425. M. Okuyama, M. Ohkita, and T. Tsuji, Chem. Commun. (Cambridge), 1997, 1277. M. Kako, S. Oba, R. Uesugi, S. Sumiishi, Y, Nakadaira, K. Tanaka, and T. Takada, J. Chem. Soc., Perkin Trans. 2 , 1997, 125 1. M. Takeshita and M. Irie, Chem. Commun (Cambridge), 1997,2265. J. Buddrus, S. Boeckstegers, H. Hemetsberger, H. Mayer-Figge, A. Nowienski, K. F. Rammert, and W. S . Sheldrick, J. Photochem. Photobiol., A , 1997, 105, 39. E. M. Sharshira and T. Horaguchi, J. Heterocycl. Chem., 1997,34, 1837. A. G. Myers and Y. Horiguchi, Tetrahedron Lett., 1997,38,4363. K. A. Muszkat, M. Eisenstein, E. Fischer, A. Wagner, Y. Ittah, and W. Luettke, J. Am. Chem. Soc., 1997,119,9351.

175. 176. 177. 178. 179. 180. 181. 182. 183. 184. 185. 186. 187. 188. 189. 190. 191. 192. 193. 194. 195. 196. 197. 198. 199. 200. 201. 202. 203. 204.

IIl4: Photochemistry of Aromatic Compounds

185

M. Takahashi, T. Fujita, S. Watanabe, and M. Sakamoto, J. Chem. Soc., Perkin Trans. 2,1998,487. 206. M. C. Jimenez, M. A. Miranda, and R. Tormos, Tetrahedron, 1997,53, 14729. 207. T. J. Onofrey, D. Gomez, M. Winters, and H. W. Moore, J. Urg. Chem., 1997, 62, 5658. 208. T. Yamaguchi, K. Uchida, and M. Irie, J. Am. Chem. SOC.,1997,119,6066. 209. G. Dyker, J. Koerning, and W. Stirner, Eur. J. Org. Chem., 1998, 149. 210. R. Kojima, T. Shiragami, K. Shima, M. Yasuda, and T. Majima, Chem. Lett., 1997, 1241. 21 1. A. Evenzahav and N. J. Turro, J. Am. Chem. Soc., 1998,120, 1835. 212. P. Wessig, J. Schwarz, D. Wulff-Molder, and G. Reck, Monatsh. Chem., 1997, 128, 849. 213. J. H. Rigby and V. Gupta, Synlett, 1995, 547. 214. M. Close, J. D. Coyle, E. J. Haws, and C. J. Perry, J. Chem. Res. Synop., 1997, 1 15. 215. Y.-T. Park, C.-G. Hwang, K.-W. Kim, N. W. Song, and D. Kim, J. Am. Chem. SOC., 1997,119, 10677. 216. V. P. Vetchinov, E. B. Nikolaenkova, V. 1. Mamatyuk, and V. P. Krivopalov, Russ. Chem. Bull., 1997,46,607. 217. M. Ibrahim-Ouali, M.-E. Sinibaldi, Y. Troin, D. Guillaume, and J.-C. Gramain, Tetrahedron, 1997,53, 16083. 21 8. U. C. Yoon, J. W. Kim, J. Y. Ryu, S. J. Cho, S. W. Oh, and P. S. Mariano, J. Photochem. Photobiol., A , 1997,106, 145. 219. T. Nakamura, K. Takagi, and Y. Sawaki, Bull. Chem. SOC.Jpn., 1998,71,419. 220. H. Wang, R. E. Partch, and Y. Li, J. Org. Chem., 1997,62,5222. 221. A. N. Frolov and N. I. Rtishchev, Rum. J. Urg. Chem., 1997,33,246. 222. G. Jayanthi, S. Muthusamy, R. Paramasivam, V. T. Ramakrishnan, N. K. Ramasamy, and P. Ramamurthy, J. Org. Chem., 1997,62, 5766. 223. S.-J. Lin, S.-Y. Jiang, T.-C. Huang, P. Kao, P.-F. Tsai, H. Takeshita, Y-S. Lin, and T. Nozoe, Heterocycles, 1997,45, 1879. 224. C. Andreis, H. Durr, V. Wintgens, P. Valat, and J. Kossanyi, Chem. Eur. J., 1997, 3, 509. 225. E. M. Sharshira, M. Okamura, E. Hasegawa, and T. Horaguchi, J. Heterocycl. Chem., 1997,34,861. 226. M. H. B. Stowell, G. Wang, M. W. Day, and S. I. Sunney, J. Am. Chem. SOC.,1998, 120, 1657. 227. R. H. Prager, J. A. Smith, B. Weber, and C. M. WilIiams, J. Chem. Suc., Perkin Truns. I , 1997,2665. 228. R. H. Prager, M. R. Taylor, and C. M. Williams, J. Chem. Soc., Perkin Trans. I, 1997,2673. 229. J.-K. Luo, R. F. Federspiel, and R. N. Castle, J. Heterocycl. Chem., 1997, 34, 1597. 230. H. J. Hageman and J. W. Verhoeven, J. Photochem. Photobiol., A , 1997,103,75. 231. M. D’auria and R. Racioppi, Tetrahedron, 1997,53, 17307. 232. T. Nakamura, K. Takagi, M. Itoh, K. Fujita, H. Katsu, T. Tmae, and Y. Sawaki, J. Chem. Soc., Perkin Trans. 2,1997,275 I . 233. J. Bethke, J. Kopf, P. Margaretha, B. Pignon, L. Dupont, and L. E. Christiaens, Helv. Chim. Acta, 1997,80, 1865. 234. P. Ya, J. Org. Chem., 1997,62,7324. 235. A. Schuetz and T. Wolff, J. Photochem. Photobiol., A, 1997,109, 251. 236. P. Magnus, J. C. Morris, and V. Lynch, Synthesis, 1997,506. 205.

186 237. 238. 239. 240. 241. 242. 243. 244. 245. 246. 247. 248. 249. 250. 251.

252. 253. 254. 255. 256. 257. 258. 259. 260. 261. 262. 263. 264. 265. 266. 267. 268. 269.

Photochemistry

H. Kawakami, Y. Z. Yan, N. Kato, A. Mori, H. Takeshita, and T. Nozoe, Bull. Chem. SOC.Jpn., 1998,71,711. N. Marubayashi, T. Ogawa, T. Hamasaki, and N. Hirayama, J. Chem. SOC.,Perkin Truns. 2 , 1997, 1309. N. Marubayashi, T. Ogawa, and N. Hirayama, Bull. Chem. SOC.Jpn., 1998,71,321. I. V. Ukrainets, S. G. Taran, L. V. Sidorenko, 0. V. Gorokhova, A. V. Turov, and A. A. Ogirenko, Chem. Heterucycl. Cumpci. ( N . Y),1997,33,815. C. Lehnberger, D. Scheller, and T. Wolff, Heterocycles, 1997,45, 2033. W. Zhang and M. Wang, Ganguang Kexue Yu h a n g Huaxue, 1997,15,19. Z. Tong, Y.-M. Ying, and L. Yuan, Gunguung Kexue Yu Guung Huaxue, 1997, 15, 104. C.-H. Tung and Y .-M. Ying, J. Chem. Soc., Perkin Truns. 2, 1997, 1319. I. F. Molokov, Yu. P. Tsentalovich, A. V. Yurkovskaya, and R. Z. Sagdeev, J. Photochem. Photobiol., A , 1997,110, 159. S. M. Bonesi and R. Erra-Balsells, J. Phorochem. Photobiol. A, 1997, 110,271. M. C. Jimenez, M. A. Miranda, J. C. Scaiano, and R. Tormos, Chem. Cummun. (Cumbridge), 1997, 1487. A. M. Sanchez, A. V. Veglia, and R. H. De Rossi, Can. J. Chem., 1997,75, 1 151. T. Kaneko, K. Kubo, and T. Sakurai, Tetrahedron Lett., 1997,38,4779. T. Fournier, S. M. Tavender, A. W. Parker, G. D. Scholes, and D. Phillips, J. Phys. Chem., A , 1997,101,5320. M. Milewski, M. Sikorski, A. Maciejewski, M. Mir, and F. Wilkinson, J. Chem. Sac., Furaday Trans., 1997,93, 3029. T. H. Nguyen and N. B. Tran, Tup Chi Hoa Hoe, 1996,34,34. J. Andraos, Y. Chiang, A. J. Kresge, and V. V. Popik, J. Am. Chem. SOC.,1997, 119, 8417. N. C. de Lucas, J. C. Netto-Ferreira, A. J. Lusztyk, B. D. Wagner, and J. C. Scaiano, Tetrahedron Lett., 1997,38, 5147. A. Albini, G. Bettinetti, and G. Minoli, J. Am. Chem. SOC.,1997, 119, 7308. C. Wentrup, A. Reisinger, G. G. Qiao, and P. Visser, Pure Appl. Chem., 1997, 69, 847. D. Donati, S. Fusi, and F. Ponticelli, J. Chem. Rex, Synop., 1997, 170. T. Harder, R. Stosser, P. Wessig, and J. Bendig, J. Photochem. Photobiol., A , 1997, 103, 105. D. Kosynkin, T. M. Bockman, and J. K. Kochi, J. Am. Chem. Soc., 1997,119,4846. R . Albers and W. Sander, Liebigs Ann.lRecl., 1997,897. B. Szczepanik and T. Latowski, Pol, J. Chem., 1997,71,807. I. Ono, S. Sato, K. Fukuda, and T. Inayoshi, Bull. Chem. SOC.Jpn., 1997,70,2051. D. Grassi, V. Lippuner, M. Aebi, J. Brunner, and A. Vasella, J. Am. Chem. SOC., 1997,119, 10992. Y. Chiang, A. S. Grant, H.-X. Guo, A. J. Kresge, and S. W. Paine, J. Org. Chem., 199?, 62,5363. D. Leinweber, Tetrahedron Lett., 1997,38,6385. Z . Zhou, W. Jiang, and W. Liu, Huanjing Kexue, 1997,18, 35. M . C. Jimenez, M. A. Miranda, and R. Tormos, J. Photochem. Photobiol., A , 1997, 104,119. A. Sugimoto, C. Hayashi, Y. Omoto, and K. Mizuno, Tetrahedron Lett., 1997, 38, 3239. K. Burgess, S. E. Jacutin, D. Lim, and A. Shitangkoon, J. Org. Chem., 1997, 62, 5165.

IIl4: Photochemistry of Aromatic Compounds

187

J. Xia, X. Huang, R. Sreekumar, and J. W. Walker, Bioorg. hied Chem. Lett., 1997, 7 , 1243. 271. Y. Shi, J. E. T. Corrie, and P. Wan, J, Org. Chem., 1997,62, 8278. 272. H. Morita, H. Kamiyama, M. Kyotani, T. Fujii, T. Yoshimura, S. Ono, and C. Shimasaki, Chem. Commun. (Cambridge), 1997, 1347. 273. M. Ashram, D. 0. Miller, J. N. Bridson, and P. E. Georghiou, J. Org. Chem. 1997, 62,6476. 274. A. Banerjee and D. E. Falvey, J. Org. Chem., 1997,62,6245. 275. A. Banerjee and D. E. Falvey, J. Am. Chem. Soc., 1998,120,2965. 276. R. S . Givens, A. Jung, C.-H. Park, J. Weber, and W. Bartlett, J. Am. Chem. Soc., 1997,119,8369. 277. B. Wang and A. Zheng, Chem. Pharm. Bull., 1997,45,715. 278. A. Hasan, K.-P. Stengele, H. Giegrich, P.Cornwell, K. R. Isham, R. A. Sachleben, W. Pfleiderer, and R. S. Foote, Tetrahedron, 1997,53,4247. 279. W. Pfleiderer and S. Eisele, Ger. Offen. DE 19,620,170. 280. R. Rodebaugh, B. Fraser-Reid, and €1. M. Geysen, Tetrahedron Lett., 1997, 38, 7653. 281. S. Watanabe and M. Iwamura, J. Org. Chem., 1997,62,8616. 282. T. Voelker, T. Ewell, J. Joo, and E. D. Edstrom, Tetrahedron Lett., 1998,39,359. 283. H. Shiono, H. Kodama, and M. Kojima, PCT Int. Appl. WO 97 47,639. 284. J. F. Cameron, C. G. Willson, and J. M. J. Frechet, J. Chem. Soc., Perkin Trans. 1 , 1997,2429. 270.

5

Photo-reduction and -oxidation BYALAN COX

1

Introduction

Topics which have formed the subjects of reviews this year include excited state chemistry within zeolites, photoredox reactions in organic synthesis,2 selectivity control in one-electron r e d ~ c t i o n ,the ~ photochemistry of f~llerenes,~ photochemical P-450 oxygenation of cyclohexene with water sensitized by dihydroxybiocoordinated (tetraphenylporphyrinato)antimony(V) hexafl~orophosphate,~ mimetic radical polycyclisations of isoprenoid polyalkenes initiated by photoinduced electron transfer,6 photoinduced electron transfer involving C6dC70,~" comparisons between the photoinduced electron transfer reactions of C ~ and O aromatic carbonyl compound^,^ recent advances in the chemistry of pyrrolidinofullerenes, l o photoinduced electron transfer in donor-linked fullerenes, I supraphotoinduced molecular model systems, I 2 , l 3 and within dendrimer architect~re,'~ electron transfer reactions of homoquinones, amines, l 6 and azo compounds,l 7 photoinduced reactions of five-membered monoheterocyclic compounds of the indigo group," photochemical and polymerisation reactions in solid C60,19 photo- and redox-active [2]rotaxanes and [ 2 ] ~ a t e n a n e sreactions ,~~ of sulfides and photoprocesses of sulfoxides and related sulfenic acid derivatives with 0 2 ( compounds,22 semiconductor photo catalyst^,^^ chemical fixation and photoreduction of carbon dioxide by metal p h t h a l ~ c y a n i n e sand , ~ ~ multiporphyrins as photosynthetic models.25 The role of excitation lifetime in electron transfer reactions,26 and photoinduced electron transfer in isolated jet-cooled molecular have also been discussed.

'

'

2

Reduction of the Carbonyl Group

Some general rules for photochemical hydrogen abstractions by n,x*-excited states have appeared.28 Computer simulation of intramolecular hydrogen atom transfer to carbonyl oxygen has been achieved by a Monte Carlo method.29 In particular, the model has been found to give good agreement when applied to intramolecular p-, y-, 6-, E-, and 435 nm) into the 1,4-dimethoxybenzendtetranitromethane charge-transfer band in dichloromethane are 2-nitro-l,4dimethoxybenzene, 2-trinitromethyl-1,4-dimethoxybenzene and the naphthalenone (273). Smaller amounts of labile adducts are also formed.2o5Similar irradiation with benzofuran gives adducts arising from initial attack by trinitromethanide anion at C-2, C-3 or C-4 of the benzofuran radical cation.

Photochemistry

260 ArCR’=CHR2 + C(NQ)4 260 Ar = Ph, 4-MeoCsH4,

hv

+ -C(N02)3

NQ + [AtCR1=CHR2]t

R1,R2= H, Me

NO2 c265

Ar

268 A~CR’-CHR~N@ I C(No2)3 269

0-

AreR2 R1=H

R’ H 270

TI-

0

271

R’ H 272

Scheme 3

Products formed include the cis- and trans-isomers of 2-trinitromethyl-3-nitro2,3-dihydrobenzofuran, 2-trinitromethyl-3-hydroxy-2,3-dihydrobenzofuran (from hydrolysis of the nitrite ester), 2-nitro-3-t rinit romet hyl-2,3-dihydrobenzofuran, 4-trinitromethyl-7-nitro-4,7-dihydrobenzofuran and nitronic ester (274).206 OMe

273

274

The inclusion of ethanol (8% v/v) in the reaction solvent (dichloromethane or acetonitrile) used for photolysis of the charge transfer complexes of tetranitromethane with alkoxy or dialkoxyarenes leads to stabilisation of alkoxytrinitromethylarenes. Reduction in the nucleophilicity of the trinitromethanide ion as well as changes in the regioselectivity of trinitromethanide ion attack on the arene radical cations and stabilisation of the adducts also result.207 Strong interest continues in the use of the 2-nitrobenzyl group as a convenient and versatile photoremovable protecting group and a variety of systems have been patented.208 The steroid derivative (275) releases cytotoxic L-leucyl-Lleucine methyl ester on photolysis in liposomes, leaving the undesired by-product, 2-nitrosobenzaldehyde, attached to the liposome-soluble steroid nucleus.209The photoactive mustards (276) and (277) are potential prodrug candidates, releasing a phosphoric acid derivative which has been identified as an intermediate in cyclophosphamide cancer therapy.210The 2-nitrobenzyl quaternary ammonium derivative (278) photodecomposes with rapid release of nor-butyryl choline and is

M6: Photoreactions of Compounds Containing Heteroatoms other than Oxygen

26 1

a promising probe for mechanistic studies on butyrylcholinesterase activity.21 The a-carboxyl-2-nitrobenzylderivatives (279) degrade thermally within several hours and are therefore unsuitable for use in biological studies. The a-(hydroxymethyl)-2-nitrobenzyl derivatives (280), however, are chemically stable, undergo clean photolytic release of the fatty acids and suggest 1-(2'-nitropheny1)1,2-ethanediolas a useful derivatising agent for fatty acids.212

275 276 277 278 279 280

R' = OSteroid, R2 = H, X = Leu-Leu OMeR' = OCH2C@Na, R2 = allyl, X = OP(O)(NHP)N(CH~CH~CI)~ R' = OCH2CH2NH3C1, R2 = (CH2)30HI X = OP(O)(NH2)N(CH2CH2CI)2 R' = H, R2 = Me, X = +NMe&H2CH20COCH2Et R' H, R2 = C02H, X = arachidonate, deate, linoleate or linolenate R' = H, = CHzOH, X = arachidonate, oleate, linoleate or linolenate

-

A photolabile fluorescent 2-nitrobenzyl derivative that releases a 5'-silylated thymidine has been developed.213A series of N-(2-nitrobenzyl)substituted indoles, benzimidazoles, indolones and 6-chlorouracilundergo clean deprotection on i r r a d i a t i ~ n . ~A' ~nitrobenzyl linker which can be incorporated at different positions in a fraction of the oligomers during the split syntheses combinatorial approach has been used to permit photolytic cleavage of the oligomers on a bead at these positions. Subsequent MALDI-MS analysis can then be used for efficient sequence determination of the peptides generated.21 Amino-derivatised polymer supports incorporating 2-nitrobenzyl linkers have been prepared and used for the synthesis of reducing oligosaccharides2I6and oligonucleotides:217cleavage from the solid support is being cleanly achieved by photolysis. Derivatives of EGTA, a calcium selective chelator, have been synthesised, each having a 2-nitrophenyl group attached to a backbone carbon. Cleavage of a benzylic bond on irradiation disrupts the coordination sphere and concentrationjumps in intracellular calcium can be achieved.218On irradiation in benzene 1,2-bis(2-nitrophenyl)ethaneyields 2-nitrobenzoic acid, 2-nitrobenzyl 2'-nitrophenyl ketone, 2,2'-dinitrobenzil and dibenzo[c,g][ 1,2]diazocin-5,6-dione N,N'dio~ide.~I'The photochromism of 2(2',4'-dinitrobenzyl)pyridine arises from intramolecular proton transfer involving three different tautomeric species. In the presence of a macrobicyclic cryptand proton transfer occurs from two of the tautomers and back transfer is slow as the proton is shielded within the cryptate cavity.22oIn propan-2-01, triplet excited 4nitroacetophenone is reduced to 4-hydroxylaminoacetophenone which in turn is further photoreduced to 4-aminoacetophenone and 4,4'-diacetyla~obenzene.~~' The stable triplet species generated by irradiation of crystalline 2-nitrobiphenyl below 120 K may be formed by intramolecular abstraction of the 2'-hydrogen by the nitro group?22 Nanosecond laser photolysis and conductimetric detection have been used to show that the photoisomerisation of 4-nitrobenzaldehyde to 4-nitrosobenzoic acid in aqueous solution occurs via the mechanism in Scheme 4.223 The

Photochemistry

262

photogeneration of 1-nitroso-2-naphthoic acid from 1-nitro-2-naphthaldehyde using 355 nm light provides the proton source for transformation of colourless non-fluorescent Rhodamine B base to the coloured and strongly fluorescing dye Rhodamine B. In solid PMMA matrices the process has been used as the basis for a ROM memory Aminopolycarboxylic esters react with [60]fullerene on photolysis to produce fulleropyrrolidine multicarboxylates. For example, tetramethyl ethylenediaminetetraacetate (EDTA) gives (281) as well as the more symmetrical fulleropyrrolidine C60(CHC02Me)2NCH2CH2N(CH2C02Me)2. Analogous reactions occur for the methyl esters of (N-morpho1ino)acetic acid and (N-piperidino)acetic acid whereas the free carboxylic acids photoreact with C a by decarboxylation and formation of the 1,2-dihydrofullerenes Cm(H)[CH2N(CH2CH2)20] and C60(H)[CH2N(CH2),] respectively.225y226 The one-pot formation of (282) by photolysis of (283)in benzene/trifluoroaceticacid is the key step in the synthesis of a food-borne carcinogen.227Excitation of the isoindoline nitroxide (284) results in abstraction of primary, secondary and tertiary hydrogens from unactivated hydrocarbons such as cyclohexane, 2-methylpropane and butane. The resulting carbon-centred radicals are trapped by ground state nitroxide as the adducts (28S).228

281

282 R - P h , X - H 283 R = I , X=tOSyl

284

x=o’

285 X-Oalkyl

Triplet excited 3-( 1-naphthyl)-2-(1-naphthylmethyl)oxaziridine (286) gives N(1-naphthoxy)-1-(aminomethyl)naphthalene (289) by N-O bond cleavage and a hydrogen shift, and 1-naphthaldehyde(287)by N - 0 and C-N bond fissions in the three-membered ring with naphthylmethylnitrene (288) as an intermediate. The oxaziridine radical cation (290), obtained by 9,lO-DCA sensitisation, is proposed to form the ring-opened nitrone radical cation (291).This species is believed to be a source of oxygen atoms for oxidation of naphthylmethylnitrene (288) to 1(nitromethy1)naphthalene(292) and also to be a precursor to naphthaldehyde (287)and 1 -(aminomethyl)naphthalene (293).229 1,3-Diarylpyrazolinesfluoresce efficiently and are used as optical brighteners. Studies with a series of derivatives (294) has concluded that the presence of a

1116: Photoreactionsof Compounds Containing Heteroatoms other than Oxygen

0

/ \

ArCH-NCH2Ar

286

h

PkCO

hlDCA

0'

/ \

ArCHZCH2Ar 290

ArCH=r;?CHzAr 291

-

0'

I Ar-CH-kH2Ar

-

I

ArCHO 287

+

+

ArCH&

HN='CHAr

DCA'

288

t

:NCH2Ar ps8

ArCONHCH2Ar 289

ArCHO 287

263

ArCHO +ArCH$H2 287

ArCH2N 288

DCA:

AICH2N&

293

4'4ialkylamino group makes them good electron transfer quenchers of excited ketones and singlet oxygen, resulting in physical decay rather than photoreaction. They are liable to radical attack, which leads to aromatisation of the heterocyclic ring, though this process is operative only under particular conditions.230 Irradiation of a titanium dioxide suspension in ethanol containing o-dinitrobenzene gives 2-methylbenzimidazole in 96% yield. Reduction to 2-nitroaniline, formation of the corresponding imine by reaction with the acetaldehyde formed by oxidation of the solvent and subsequent reduction of the second nitro group to the corresponding hydroxylamine, intramolecular cyclisation and dehydration lead to the observed product. The synthesis is tolerant of methyl, ethoxy, chloro and ester substituents on the aromatic ring and propan-1-01 may replace ethanol in the reaction.231The kinetics of photoreduction of nitroaromatics and methyl viologen by titanium dioxide have been investigated,232and mechanistic details of the cadmium sulfide mediated oxidative carbon-carbon bond cleavage of the pyrrole ring in 2- and 3-methylindoles have been e l ~ d i c a t e d . ~ ~ ~ ~ ~ ~ Iodopyrrole (2wwand 4-nitro-2-iodoimidazole (297),236 when irradiated in the presence of aromatic compounds such as benzene, rn-xylene, thiophene, 2chlorothiophene or 2-methylthiophene, yield the corresponding arylpyrroles (2%) and the 4-nitro-2-arylimidles (298). Reaction appears to require population of a higher triplet excited state (A,o*, n,n* or qn*)mainly lacalised in the Me

294 X = H, NEt2, N(CH2CH&O

295 x-I 296 X = Avl

297 X = I 298 X=Ar

264

Photochemistry

carbon-iodine bond, followed by C-I homolysis and reaction between the resulting radical and the aromatic substrate. In certain cases, for example ethyl 3,4-dimethyl-5-iodopyrrole-2-carboxylate, dehalogenation rather than arylation is observed. Semiempirical calculations show that, where the difference between the heats of formation of the radical intermediate and its parent halogenoheterocycle is ~ 5 kcal 5 mol-I, arylation occurs. Where this difference is >55 kcal mol- dehalogenation is observed.237 The pseudosaccharin 2-,3- and 4-pyridylmethyl ethers (2W)undergo facile singlet excited state reaction in methanol. Homolysis of the 0-CH2 bond and radical recoupling yield the corresponding N-(pyridylmethy1)saccharin derivatives and hydrogen abstraction from the solvent yields saccharin. The nucleophilic photosubstitution product, pseudosaccharin methyl ether, is also formed as a minor product.238 Photoinduced SET from the electron-donatingtetraphenylborate counteranion to a series of electron-accepting chromophores in benzylic trialkylammonium cations in acetonitrile results in efficient cleavage of the benzylic C-N bond and generation of the corresponding trialkyamines. Laser flash photolysis and product studies have shown that, for N-(4-benzoylbenzyl)-N,N,N-tributylammonium and N-(4-acetylbenzyl)-N,N,N-trimethylammoniumtetraphenylborates, SET occurs to their triplet excited states. The resulting reduced quaternary ammonium cations cleave to release the tertiary amine and a benzylic radical, coupling of which results in formation of the corresponding dimers. For N,N,Ntributyl-N-(2-naphthyl)methylammonium and N,N,N-tributyl-N-(7-methoxycoumariny1)methylammoniumtetraphenylborates SET occurs to their singlet excited states. The C-N bond breaking process in each case seems to be coupled to the primary SET step and to occur so rapidly that back electron transfer to regenerate the salt cannot compete.239 The photochemical reduction of Methylene Blue by triethylamine in methanol has been investigated.240Photolysis of 3-(3,4-dichlorophenyl)-l,1-dimethylurea (diuron) in aqueous solution containing methanol gives 3-(3-chlorophenyl)-1,ldimethyl~rea.~~' The photostabilities of chloroquine d i p h ~ s p h a t eand ~ ~ meflo~ quine hydrochloride243have been reported and a commentary published on the

299

300

301

302 R

I

Ar

I M : Photoreactions of Compounds Containing Heteroatoms other than Oxygen

265

suitability of the quinine actinometry system for use in drug stability testing.244 Further aspects of the photodegradation of the herbicides metribuzin (4-amino-6t-butyl-3-methylthio-1,2,4-triazin-5-0ne)~~’ and metamitron (4-amino-6-phenyl3-methylthio-1,2,4-triazin-5-0ne)~~~ have been reported. The pH dependence of the photoreactivity of the antimalarial chloroquine [4-(4-N,Ndiethylamino-lmethylbutyl)amino-7-chloroquinoline]247 and the influence of oxygen on the light-induced reactions of the antimalarial primaquine [8-(4-amino-1-methylbutyl)amino-6-methoxyquinoline]248 have been investigated. The carboxylate form of the factor Xa inhibitor, (2S)-2-[4-[(3S)-l -acetimidoyl-3-pyrrolidinyl]phenyl]-3-(7-amidino-2-naphthyl)propanoic acid, undergoes essentially quantitative decarboxylation whereas the free carboxylic acid is p h ~ t o s t a b l e .The ~~~ primary photoproduct from the synthetic 7-piperazinyl fluoroquinoline antibiotic ciprofloxacin is the corresponding 7-[(2-aminoethyl)amino-1-cyclopropyl-6fluoro-l,4-dihydro-4-oxo-3-quinoline carboxylic acid.2M Conditions for the photosensitised preparation of green-yellow fluorescent 7-(fl-D-ribofuranosylamino)pyrido[2,1-h]pteridin-1 1-ium-5-olate, luminarosine, and its 2’-deoxy- and 2’0-methyl analogues, from N-[9-(2,3,5-tri-O-acetyl-~-D-ribofuranosyl)purin-6-y1]pyridinium chloride, have been ~ptimised.~’’ Further diverse systems have been developed and used in the investigation of intramolecular SET processes. These include styrene/amide-spacerlamine diad~?’~ 9-aminoacridindpolyether-spacer/benzoateester d i a d ~ , ~1-(4-cyano’~ phenyl)-4-(cyanomethylene)piperidine,2” n-donor/polyoxyethylene/Zn(II)porphyrin/N,N’-dimethyl4,4’-bipyridinium sy~tems,~’’ naphthalene/porphyrin/ quinone cy~lophanes~’~ and their anthracene analogues,257pyropheophytinnaphthoquinone d i a d ~ , ~rigid ’ ~ donor/bridge/acceptor systems,259anilide-substituted 10-methylacridinium ions,2M)viologerdfluoresceirdcarbazole triads,261an anthraquinone/fluorescein/carbazoletriad,262 a carotenoid/porphyrin/dinitronaphthalenedicarboximide triad?63 pyrene/peptide/dimethylaniline systems?64 9-dicyanomethylene-10-( 1,3-dithiol-2-ylidene)ant h r a c e n e ~ * ~ and ’ * ~ ~9-N-cyanoimine-lo-( 1,3-dithi01-2-ylidene)anthracenes.

3

sulfurcontaining compounds

Singlet excited cis- 1,2-di(2-thienyl)ethylene cyclises to give benzo[ 1,2-b:4,3bldithiophene as a reaction product.267Irradiation of a series of bicyclic and monocyclic thioketones, for example 3,3dimethylthiocamphor, in pentane with 254 nm light leads primarily to &insertion via excitation to the S2 manifold: this is in agreement with earlier findings for related systems and in contrast to the preferred 6-insertion for aryl alkyl thioketones. For the more flexible bicyclic thione (300), and for 2,2-diet hy1-5,5-dimethylcyclopentanethione and 242thy12,6,6-trimethylcyclohexanethione,though B-insertion dominates some y-insertion is also observed. In contrast, endo-5,6-trimethylene-2-norbornanethionegives only the 6-insertion product (301). Vapour phase photolysis (254 nm) of these thiones on the other hand yields equivalent amounts of thioenol products resulting from Norrish type I1 fragmentation. For example, the thione (300)

266

Photochemistry

yields the thioenol (302) as the major product, in addition to the fb and yinsertion products observed in the solution phase photolysis. This process constitutes a potentially useful synthetic method for preparation of alicyclic thioenols (tautomerically stable isomers of thioketones) uncontaminated by the corresponding thioketones. Photophysical studies suggest that a vibrationally excited 52 state leads to the Norrish type I1 fragmentation via intramolecular yhydrogen abstraction and cleavage of the intermediate 1,4-biradical whereas the f3-insertion products originate from the vibrationally relaxed S2 state.268When the thioketones (303) are irradiated into the n,n* absorption band (Lax 320 nm), either in the solid state or in benzene solution, y-insertion is observed and the cyclobutanes (304)are N-Allylthioamides on irradiation yield the corresponding N-vinylthioamides and pyrroles. For example (305)yields (307)and (309)by &hydrogen abstraction and the intermediate biradical (306). Irradiation of the N-vinylthioamides, for example the enethioamide (308), results in formation of the corresponding isoquinolinethione derivative (310).270 mt

S

CHM~ 305

310

Irradiation of the monothioimides (311) in moist benzene yields the thiobenzanilides (314) and 3-phenylpropanoic acid (315), whereas in anhydrous benzene no reaction occurs. The same photoconversion is found in the solid state in the presence of moisture, whereas when moisture is rigorously excluded no reaction occurs. The monothioimides adopt conformation (311) in the solid state and M M X calculations indicate thi! to be the most stable. The short intramolecular OC(S)distances observed (2.8 A) suggest that excited state nucleophilic attack on the C=S group by the carbonyl oxygen results in (312) and that subsequent reaction with moisture forms (313) which decomposes to (315) and the thioenol Ar'

A? 311

-

Arl

R

OH

Ar'C-NHA? II S

+ RC02H

312 313 314 315 Ar' = Ph, 4-MeOC6H4; A6 = Ph, 4-BrC6H4,443r-2,6-M%GH2; R = CH2CH2Ph

267

1116: Photoreactionsof Compounh Containing Heteroatoms other than Oxygen

of the thiobenzanilide (314). An alternative mechanism, involving y-hydrogen abstraction by the thione group from the carbon u to the carbonyl group, has been eliminated by studies with deuterated precursor^.^^' The 4-(2-haloaryl)-5-aryl-1,2,4-triazole-3-thiones (316) are converted into the s-triazolo[3,4-b]benzothiazoles(317) on irradiation. SET from sulfur to the aryl ring, followed by sulfur-aryl bond formation and loss of hydrogen halide, is proposed.272

P?

--

Ar \

RJ @ J X N Y H

316 X CI, BI; R = H,Me; Ar Ph, 4-MG3H4,2-MeC6H4,4-MeOGjH4,2-naphthyl

317

The ethylthioalkyl phenylglyoxylates (322) undergo regioselectivephotocyclisation to produce up to 13-membered ring thiacyclols (324) involving bonding between the benzoyl carbon and the carbon u to sulfur on the remote side. SET from sulfur to the excited carbonyl, followed by proton transfer and subsequent cyciisation of the resulting biradical, yields the thiacyclols. Rate constants for electron transfer increase as the chain connecting the donor and acceptor becomes longer and more flexible. This also favours back electron transfer and results in lower yields of cyclisation products (324) as competition from Norrish type I1 and reductive dimerisation processes becomes important.273In the cases of the 1,3-dithiolaneand 1,3dithiane derivatives (323) back electron transfer is so efficient that thiacyclol formation does not occur and only Norrish type I1 and reductive dimerisation products are reported.274 Vinyl phenylglyoxylate, the result of p-elimination from the 1,4-biradicals (318) formed by triplet excited state y-hydrogen abstraction, is the dominant photoproduct from the corresponding iodoethyl or phenylsulfinylethyl phenylglyoxylates. For the bromoethyl or phenylthioethyl substituted radicals (319), both p-elimination and Norrish type I1 products are observed, whereas for the chloroethyl, bromopropyl and phenylthiopropyl analogues (320) and (321) only Norrish type 11 processes result.275Photocyclisation of 2-(alky1thio)ethyl benzoylacetatesgives 8-membered thialactones (325), involving 1,9-proton transfer following SET from sulfur to the excited benzoyl group. Lack of donor electrons on the sulfur in 2-(benzylsulfony1)ethyl benzoylacetate results in loss of p h o t ~ r e a c t i v i t y . ~ ~ ~ Dithia[3.3]metacyclophanes (326) containing at least one intra-annular methoxy group, when photolysed in trimethyl or triethyl phosphite, form the corresponding tetrahydropyrenes (329) in a one-pot procedure. The mechanism in Scheme 5 is supported by the isolation of intermediates corresponding to (327) and (328) from interrupted photolyses. Intra-annularly substituted methoxydithia[3.3](1,3)-naphthalenophanes similarly produce the corresponding tetrahydrodibenzopyrenesin a single synthetic step?77 Solid state photodimerisation has been reported for a series of unsymmetrical

268

Photochemistry

Ph

0

318 319 320 321

n = 1, n = 1, n = 1, n = 2,

X = I, S(0)Ph X = Br, SPh X=CI X = Br, S f h

322 n=2-8, X=SEt

1

S

324 n = 2-8

323 n=3,4, X =Hx, rn=1,2

s

)m

325 R1,R2 = H,Me Ph

trans- 1,Zdiheteroaryl e t h y l e n e ~ .Phosphatidylcholine ~~~ derivatives (330) containing the trans-styrylthiophene chromophore aggregate in aqueous dispersions. Irradiation of these aggregates results in formation of the syn HH-dimer, suggestive of a topologically controlled reaction from a translational structure in which nearest-neighbur chromophores are aligned parallel. Codispersion of styrylthiophene- and saturated-phospholipids results in bilayer vesicles which entrap water-soluble carboxyfluorescein.Irradiation results in photodimerisation

269

IIl6: Pholoreactions of Compounds Containing Heteroatoms other than Oxygen

M~sN(CH~)~-P-O-

330

8‘c

of the styrylthiophenes and release of the entrapped carboxfluorescein in a manner suggestive of “catastrophic” destruction of the vesicles.279 Irradiation of 3-thioxoandrosta-l,4-dien-l7-one (331) with 589 nm light in the presence of dimethyl acetylenedicarboxylateyields the 1:2 adduct (334), possibly involving intermediates such as (332) and (333). The reaction also occurs thermally.280

331

332

333

334

Alkyl thiopheneglyoxylates have a lowest triplet x,n* state which exhibits low photoreactivity in benzene: only traces of Norrish type I1 products are detected on prolonged irradiation. However, the upper triplet n,x* state is reactive and, in the presence of electron-rich 2,3-dimethylbut-2-ene, [2+2] cycloaddition occurs to give the oxetane (335) in high yield from the methyl ester. The corresponding alkyl furanylglyoxylates behave analogously.281The photophysics of the thiocoumarin Sz state has been investigated.282Irradiation (>350 nm) of solid isothiocoumarin affords the [2+2] dimer (336), which is also obtained in low yields in ethanol or acetonitrile but not in benzene. In acetonitrile in the presence of tetrachloroethylene, the adduct (337) is obtained from the triplet excited state. No photoreaction occurs between isothiocoumarin and 2.3dimethylb~t-2-ene.~’~ In contrast thiocoumarin gives a [2+2] photoadduct with 2,3-dimethylbut-2ene,284and the [2+2]photoadduct (341) with tetrachlorocthylene. Similar irradiation of thioangelicin in benzene containing 2,3-dimethylbut-Zene gives a mixture of the trans-adduct (338) and the cis-adduct (339) in 25% and 75% yields respectively. Angelicin gives only the corresponding cis-adduct (340)under these conditions.28s Thiopsoralen photobinds to DNA via a triplet mechanism, following intercalation inside duplex DNA. The furan side monoadduct with thymine, isolated from

270

Photochemistry

335 Me

336

@

CI

\

0 H CI CI

0 4

339 340

338

% 337

x-s

341

x=o

DNA photomodified by thiopsoralen, has the cis-syn structure (342). Thiopsoralen may also exert photobiological activity by damaging membrane components such as unsaturated fatty acids. In ethanol solution addition of linolenic acid to thiopsoralen occurs at the enone double bond to give an adduct of the type (343).286

342

343

The repair mechanisms of UV-induced DNA damage, caused by DNA crosslinking resulting from excited state product formation, are of major interest. The sulfur analogue of a (6-4)-pyrimidine/pyrimidone“dimeric” photoproduct undergoes efficient conversion to its Dewar valence bond isomer (344)?87 Irradiation of (344)in water has yielded a new “tetramer” (349). Previously pyrimidinone (347) was isolated, presumably via the Dewar isomer (346). The tetramer (349) has been suggested to arise from (344) via the mechanism in Scheme 6. Disproportionation of radical (345) yields (M), the precursor to (347), and the enamide (348).Michael addition of (344)to (348)yields the tetramer (349).288 Irradiation (366 nm) of aqueous solutions of the 4-thiothymines (352) in the presence of the N-9-substituted adenines (351) yields the N-6-formamidopyrimidines (354), which have potential use in the field of DNA lesion studies. Similarly N-3-methyl-4-thiothymidine(353) in the presence of adenosine gives the N-3methylcytidine (350), involving attack by the adenine 6-amino group at the electrophilic C-4 position of the excited thiocarbonyl group with subsequent elimination of hydrogen sulfide. In the formation of the N-6-formamidopyrimidines (354), analogous nucleophilic attack by the adenine N-7 centre in (351) at C-4 of the excited thiocarbonyl group of (352), followed by elimination of

I M : Photoreactions of Compounds Containing Heteroatoms other than Oxygen

tiN

27 1

0

344

346

346

tiN o&

348 0

hydrogen sulfide and hydrolytic imidazole ring opening, results in the observed

transformation^.^^^

hvl H20

350

A3

352 R' = H, R2 = CH2C02H, deoxyribosyl 353 R1= Me, R2= deoxyribosyl

A3

3s

Irradiation of the benzothiazinyl vinylcyclopropanes (355) in the presence of one equivalent of thiophenol gives good to excellent yields of the corresponding thiyl adducts. Regioselectivity is determined by captodative stabilisation of the intermediate radicals (356)which subsequently abstract hydrogen to yield the adducts. Substituent control of the conformations of the vinylcyclopropanes (355) determines the stereochemistriesof the radicals (356) and hence that of the product ally1 sulfides.29o Singlet excited state cyclisation of S-aryl-2-benzoylbenzothioates occurs by bond formation between the thioester oxygen and the

272

Photochemistry

benzoyl carbon to yield the zwitterionic intermediates (357). Subsequent aryl migration from the benzoyl carbon to the thioester carbon results in the formation of the 3-aryl-3-(arylthio)isobenzofuranoneproduct. Irradiation of the isobenzofuranone causes homolytic loss of the thioaryl group and subsequent dimerisation of the resulting isobenzofuranone radical occurs.29' Me

Me

355 a; R1 = R2 = Me

b; R1 = R2 = H C; R ' = Ph, R 2 = H d; R'= H, R 2 = Ph

356 a; E : Z = 9 : 1 b; E : Z = 1 : 9

357 R - H, Me; At-' = Ph, 4-MeCsH4,4-CIC6H4; AP = Ph, 2-,3-,4-MeC&Id

E : Z = 1 :4 d; E : Z = 1 :2 C;

Photoreaction of the N-acylbenzoxazole-2-thiones(358) with alkenes yields iminothietanes (362) and 2-substituted benzoxazoles (363) by intramolecular trapping of the zwitterionic intermediates (361) and (360), respectively, derived from the spirocyclic aminothietanes (359) whose regiochemistry is in accord with formation of the more stable biradical intermediate in the [2+2] cycloaddition process.292

I

I COR

COR

COR 360

358

aN+ OCOR

362

'

S-

I

ROC4 363

361

When ethyl a-(methy1thio)acetate (MeSCH2C02Et) is irradiated in the presence of an alkene (RCH=CH2), the corresponding carboethoxymethylated product (RCH2CH2CH2C02Et)is obtained in moderate to good yields via sulfurmethylene bond homolysis and attack by 'CH2C02Et on the alkene. Hydrogen abstraction by the adduct radical completes the addition. The success of this tinfree radical addition to alkenes, which is compatible with the presence of polar/ protic functional groups and solvents, relies on the inefficiency of thiomethyl group transfer. The major by-products are those from addition of the thiomethyl

I M : Photoreactions of Compounds Containing Heteroatoms other than Oxygen

273

radical to the alkene: this wastage may be reduced by inclusion of trimethylphosphite as a radical scavenger. N,N-Dimethyl a-(methy1thio)acetamide (MeSCH2CONMe2) may be used in the analogous process to yield RCH2CH2CH2CONMe2.293 Naphtho[ 1,8de]-1,3-dithiin-1-N-tolylsulfilimines (364) undergo consecutive photoreactions to give quantitatively the corresponding N-tosylaldimines (368) and naphtho[1,8-cd]-1,Zdithiole (369). The intermediate (367)can be isolated. That the conversion of (364)into (367) is intramolecular is confirmed by the absence of crossover products when a mixture of (365) and (366)is irradiated.294 In an analogous reaction, S-naphthylmethyl-N-p-tosylsulfimides(370) undergo photoinduced Stevens rearrangement in dichloromethane or acetonitrile to give (371). Separate irradiation of (371) results in S-Nbond cleavage and formation of R'SSR' and R'CH~NHTS.~~' H

sxs' R H

Rj-yswr

&

NS02Ar

s

s

L&

364 Ar = 4-WG3H4, R = aryl, akyl 365 Ar = Ph, R = 4-MeC6H4 366 Ar = 4-MGH4, R = Ph

+

NqAr

+& s-s

,RKH NSQAr

368

367

369

S02Ar

I

R'SCH2R2 R'SNCH2R2 370 371 R' = Me, Ph, Ppyridyl; R2 = Ph, 1-naphthyl, 2-naphthyl

The photochromic properties of a series of 4-aryl- and 4-methyl-2,3,4,5,6pentaphenyl4H-thiopyrans and of 4-aryl- and 4-methyl-3,5-dimethyl-2,4,6-triphenyl4H-thiopyrans have been reported.296'H-NMR spectroscopy has been used to investigate the photoconversion of a series of 4-aryM-methyl-2,6diphenyl-4H-thiopyrans into the corresponding 6-aryl-5-methyl-l,3-diphenyl-2thiabicyclo[3.I .O]hex-3-enes and subsequently to the thermodynamically more stable 2-aryl-4-methyl-3,6-diphenyl-2H-thiopyrans in quantitative yield. Electron-donating or electron-withdrawing groups at the 4-position of the migrating aryl group increase the relative rates of migration in methanol and, for each migrating aryl group, the rearrangement is faster in methanol than in benzene. A Zimmerman di-n-methane rearrangement mechanism, involving aryl-vinyl bridging via polarised transition states (372) or (373), is proposed for the aryl migration step.2974-Alkyl-2,3-dihydro-6H-1,3-thiazine-5-carboxylateson irradiation in toluene undergo carbon-sulfur bond homolysis to form the diradicals (374)-(376). Diradical(374), from the 4methyldihydrothiazine derivative, results in the formation of the enamine (377) and the corresponding imino tautomer whereas the 4-ethyldihydrothiazine derived diradical (375) results in a single product, Z,Z-(378). In contrast, the 4-benzyldihydrothiazine precursor yields a

Photochemistry

274

372 XsEWG,

*=a+,

*'=r

373 X=EDG, *=&, * ' = S +

374 R = Me 375 R = Et 376 R=CH2Ph

377

378 R1 = I? = Me 379 R1 = Me, R2 = Ph

mixture of all four geometrical isomers of (379) via the intermediacy of diradical (376)?98 Singlet excited benzyl P-naphthyl sulfoxide undergoes a-cleavage to give the isomeric sulfenic ester (np-S-0-benzyl) as major product, in addition to deoxygenation to benzyl P-naphthyl sulfide. Acetone sensitisation leads to the "escape" dimers, np-S02-S-np and bibenzyl, which are absent from the direct irradiation. Benzyl P-naphthyl sulfide is not formed from the sensitised reaction, confirming sulfoxide deoxygenation to be a singlet-derived process.2wPhotolysis of unsymmetrical dibenzylsulfones results in loss of sulfur dioxide and formation of a radical pair which, in solution, normally results in combination to form all three possible products. The corresponding processes in zeolites are highly sensitive to zeolite structure. In NaZSM-5 zeolite, benzoyl p-tolyl sulfone yields 1-phenyl-2-ptolylethane as the main product whereas benzyl a-naphthylmethyl sulfone gives only bibenzyl and 1,2-dinaphthylethane. The differences can be understood in terms of the size and shape selectivity of the absorbed substrate molecules on the zeolite surfaces and restrictions imposed by the surfaces on the diffusional motion of the radicals.300The effects of reaction conditions on the photodegradation of dibenzylsulfone catalysed by Ti02 semiconductor particles have been inve~tigated.~"Photolysis of S-phenylbenzo[b]thiophenium triflates results in phenyl migration to the thiophene 2- or 3-positions. Homolytic cleavage of the Sphenyl bond to give (381), followed by recombination within the solvent cage to form (380) or (382) and subsequent deprotonation, may be the route leading to the products.302 Ph* Ph

H 386

R1=H 2-recombinatm

381

382

The radical EtOCOCMe,COO', generated by photolysis of the corresponding Barton (N-hydroxy-2-thiopyridone) ester, decarboxylates inefficiently unless generated in benzene under reflux. Under these conditions 2-pyridyl-SCMe2C02Et is obtained in 80% yield. Investigation of the reaction of the decarboxy-

IIl4: Photoreactions of Compounh Containing Heteroatoms other than Oxygen

275

lated radical with methyl acrylate shows that its nucleophilicity is less than that of a simple alkyl radical.303The nonsteroidal antiinflammatory drug tiaprofenic acid, 2-(5-benzoyl-2-thienyl)propionicacid, has an unusually high energy gap between the Tl('rr,n*)and T2(n,'rr*)excited states and has been associated with phototoxic and photoallergic side effects. The T2 state decarboxylates to give 2benzoyl-5-ethylthiophene.The T2 state of this photoproduct abstracts hydrogen from propan-2-01 to give the corresponding pinacol, whereas the TI state can act as an electron acceptor.304Direct thioepoxidation of strained cyclic alkenes such as norbornene and trans-cyclooctene occurs by concerted sulfur atom transfer from the labile three-membered heterocyclic oxathiiranes generated by photolysis of sulfines Ar2C=S=0.30SThe irradiation of 2-iodo-5-nitrothiophene in the presence of B-methylstyrenes in acetonitrile gives the corresponding cinnamaldehyde (72-76%) and benzaldehyde (15-23Y0) derivatives. Formation of the cinnamaldehyde derivatives may involve hydrogen abstraction from the P-methylstyrenes by the excited nitroarene, followed by radical coupling and elimination, whereas benzaldehyde formation may involve an SET process.3o6 The major primary photoprocess for 2-phenylthiobenzothiazole involves rupture of the sulfur-thiazole bond whereas for 2-alkylthiobenzothiales product formation results from both sulfur-alkyl and sulfur-benzothiazolebond cleavages.3o7 S-Benzoyl2-mercaptoimidazol-2-ene(383),on irradiation in the presence of an aliphatic or aromatic m i n e (RNH2), yields the corresponding benzamide derivative (PhCONHR) in high yield. The reaction does not occur thermally and provides a mild method for amide formation.308

SCOPh

383

The charge-transfer complex of dibenzothiophene and tetranitromethane in dichloromethane gives the dibenzothiophene radical cation, the trinitromethanide ion and NO2 on photolysis and subsequent conversions result in formation of dibenzothiophene sulfoxide (56%), with minor amounts of 2-nitrodibenzothiophene, r- 1-hydroxy-c4trinitrornethyl-1,44ihydrodibenzothiophene, t-2-nitro-r1-trinitromethyl-1,2-dihydrodibenzothiophene and c- 1-nitro-r-4-trinitromethyl1,4dihydrodiben~othiophene.~~ Oxidation andor fragmentation products are observed in the photoreactions of alkyl phenyl sulfides with tetranitromethane; the product distribution is dependent on the substrate structure. For methyl phenyl sulfide or benzyl phenyl sulfide (384)only the corresponding sulfoxides are formed and are produced by geminate coupling between the sulfide radical cations and NO2 followed by loss of nitroxyl cation. Diphenylmethyl phenyl sulfide (385) gives some sulfoxide but fragmentation of the sulfide radical cation and subsequent conversions of Phs' and Ph2CH+ gave the main products. For triphenylmethyl phenyl sulfide (386)only products from PhS' and Ph&+ are formed. "he ease of C-S bond scission in these sulfur-centred radical cations follows the ease of carbocation formation: Ph3C+> Ph2CH+ > PhCH2' > CH3+.310

276

Photochemistry

PhSR

384 R = Me,CH2Ph 385 R=CHPh2 386 R=CPh3

387 R = carbohydrate moiety

388

The photodissociation of sulfonate esters has been widely used for photoacid generation in chemically amplified photoresists. Product and laser flash photolysis studies with three phenolic sulfonate esters are consistent with s-0 bond homolysis yielding phenoxy and sulfonyl radicals. Those that escape from the solvent cage are converted into phenol and a sulfonic acid. Alternatively sulfur dioxide lost from the sulfonyl radicals undergoes oxidative and hydration processes to form sulfuric and sulfurous acids. Phenyl benzylsulfonate undergoes essentially quantitative sulfur dioxide extrusion whereas, in addition to formation of a large excess of phenol and the corresponding sulfonic acid, phenyl methanesulfonate and phenyl p-toluenesulfonate undergo photo-Fries reax~angement.~' Sulfonic esters of a-hydroxymethylbenzoin ethers PhCOCPh(OR)CH20SO*R' undergo a-cleavage on irradiation to give benzoyl and a-alkoxy-a-sulfonyloxymethylbenzyl radicals from a short-lived triplet excited state. The a,a-disubstituted benzyl radicals subsequently fragment to generate benzoylmethyl radicals and sulfonic The imidazyl (imidazole-1-sulfonyl) group is a useful and readily photoremovable protecting group for carbohydrates. For example, irradiation of a series of carbohydrate imidazylates (387) in methanol in the presence of added triethylamine gives essentially quantitative yields of the precursor carbohydrates. SET forms the imidazylate radical anion which fragments to give the imidazolesulfonyl radical and an alkoxide which, on protonation by the solvent, yields the deprotected ~arbohydrate.~'~ The photochemistry of N-propyl2-sulfobenzoic imide involves both S-N and S-Ar bond cleavages and results in loss of sulfur dioxide to yield the diradical(388). In ethanol N-propylbenzamide is subsequently formed whereas in benzene the product is N-propyl-2-phenylbenzamide. A Stern-Volmer plot, using biacetyl as triplet quencher, shows that product formation in ethanol involves both singlet and triplet pathways. In contrast, quenching and sensitisation studies in benzene show that in this solvent reaction occurs almost exclusively from the singlet excited state. In the presence of toluene or anisole irradiation results in formation of 2-(2-tolyl)-N-propylbenzamide and 2-(p-tolyl)-N-propylbenzamidefrom the former and 2-(2-anisyl)-Npropylbenzamide and 2-(p-anisyl)-N-propylbenzamidefrom the latter. Analogous products are obtained from p-xylene and mesitylene whereas no reaction occurs with benzonitrile or acet~phenone.~'~ Arylazo sulfides (389)behave as arylating agents in an SRN' photostimulated process involving the conjugate bases (390) of malononitrile, ethyl cyanoacetate, diethyl malonate and ethyl acetoacetate and provide access to synthetically strategic substrates (391). The effectiveness of the arylation depends on the electrophilicity of the aryl radicals (392) and on the HOMO energy of the

'

277

IIf6: Photoreactions of Compoundr Containing Heteroatoms other than Oxygen

stabilised carbanions (390) participating in the propagation cycle (eqs. 2-4). A complicating factor in the use of arylazo sulfides is competition from sulfide anions (393) generated from the radical anion of (389)(eq. 2). In many cases the formation of significant quantities of aryl sulfides (394) (eqs. 5, 6) may be suppressed by the use of a large excess of the stabilised ~ a r b a n i o n . ~ ' ~

i Z X Y Z 990 hv I DMSO

Ar-N=N-SR

389

-

ii HsO+

Ar-N=N-SR

-

3 :

P

Malononitrile Ethyl cyanoacetate Diethyl rnalonate Diethyl methylmalonate Ethyl acetoacetate

-389

Ar-NrN-SR'

hv

+e

48 75 72 59 70

Ar-N=N--SR'

Ar' 392

+

N2

+

(eq.1) R S 393

Ar' + -CXYZ 390 ArCXYZ-' ArCXYZ-' Ar-N=N-SR ArCXYZ 391 Ar' + A S ArSR-'

ArSFt' + Ar-N=N-SR

I % Yield of 391

HCXYZ

Ar = 2-NCGH4, R Ph Ar 3-NCGH4, R CMe3 Ar = 4-PhCGH4, R = CMe3 Ar = 4-(2-thien0yl)C6H4, R CM% Ar = 2-NCGH4, R = Ph Ar-N=N-SR

Ar-CXYZ 391

-

+

(eq.2) (eq.3) Ar-N=N-SR'

A6R 394 + Ar-N=N-SR-'

(eq.4)

(eq.5) (eq.6)

Further studies of the deoxygenation of alcohols by triplet sensitisation and SET to their S-methyl dithioearbonates under a variety of conditions have been reported.316The properties of 2,4,6-triphenylthiapyrilium tetrafluoroborate as an SET sensitiser have been disc~ssed.~"The triplet excited state of 6H-purine-6thione acts as an electron donor for pdinitrobenzene and as an electron acceptor for tetramethylben~idine.~'~ Photolysis of sulfuryl chloride in the presence of tetramethylsilane yields exclusively Me3SiCH2S02Cl. In the presence of added yttrium(II1) chloride or sulfur, the reaction is less selective and Me3SiCH2Cl is also obtained. In contrast the presence of these photocatalysts in the photoreaction of sulfuryl chloride with hexamethyldisiloxane yields solely Me3SiOSiMe2CH2S02C1, whereas in their absence Me3SiOSiMezCHzCl is also 4

Compounds Containing Other Heteroatoms

Silicon and Germanium - Tris(trimethylsily1)silyl (sisyl) ethers are readily prepared from primary and secondary alcohols and are stable to many of the reagents used in organic synthesis. When irradiated through Pyrex in methanol/ dichloromethane the deprotected alcohols can be recovered in high yield and are readily separated from the silicon-based products by flash chr~matography.~~' A series of a-silyl ethers (RO-CH2TMS) have been used as hydroxymethyl anion equivalents. Photoinduced SET to 9,lO-DCAhiphenyl yields the corresponding radical cation which fragments with loss of the electrofugal trimethylsilyl group. 4.1

278

Photochemistry

The resulting nucleophilic alkoxymethyl radical may be trapped by an electrondeficient alkene. Reduction of the adduct radical (395) by DCA radical anion and protonation of the resulting anion, confirmed by deuterium incorporation from methanol-OD, gives the final product (3%). The diastereoselectivity shown has its origin in a preference for protonation, under kinetic control, from the less hindered side. For acyclic alkenes such as methyl 2-cyanocrotonate or dimethyl maleate, free rotation within (3%) results in a low cis:truns ratio of 1.8-2.5:l whereas for cyclic alkenes such as N,3-dimethylmaleimide or 3-methylmaleimide the cis:trans ratio is considerably higher at 86:14.32'

EWG 'EWG

395

EWG 'EWG

396

A detailed study of the competition between C-C, C-H and C-Si bond fragmentation in a series of 4-methoxy-a-substituted toluene radical cations in acetonitrile has confirmed the trimethylsilyl cation as an excellent electrofugal group. The 2-methyl-I ,3-dioxolan-2-yl cation may also be an effective alternat i ~ e Solar . ~ ~light ~ irradiation has been used to drive titanium dioxide photocatalysis of the reaction between maleic anhydride and (4-methoxybenzy1)trimethylsilane to give 2-(4-methoxybenzyl)succinic anhydride. Electrodhole transfer from the semiconductor produces a pair of radical ions. The silane radical cation fragments to give the 4-methoxybenzyl radical which is trapped by maleic anhydride. Reduction of this adduct radical by the persistent maleic anhydride radical anion, or by SET to the semiconductor, and protonation by water present in the solvent, yield the product.323 Excitation of 3-(t-butyldimethylsilyloxy)phenylmethylenemalonodinitrile (397) in acetonitrile leads to C-Si bond homolysis via a polarised singlet excited state which involves internal charge transfer. The phenoxydimethylsilyl radical (398) loses dimethylsilylene and is subsequently converted into the phenol (399). The accompanying t-butyl radicals diffuse out of the solvent cage and react with (397) to form the photolkylated derivative (401). In contrast the analogous photoalkylation of benzylidenemalononitrile (400)by t-butyldimethylsilyloxybenzenedoes not occur on direct irradiation. Rather, phenanthrene sensitisation is required and formation of (402) involves prior generation of the t-butyldimethylsilyloxybenzene radical cation. In apolar cyclohexane, (397) undergoes slow [2+2] dimerisation to give predominantly a single cyclobutane product.324 BU'

I

X 3S7 X = OSiMe@u' 398 X=OSiM+' 399 X = O H 400 X = H

X 401 X=OSiMe&' 402 X = H

IIl6: Photoreactionsof Compounh Containing Heteroatoms other than Oxygen

279

403 R = H

404 R = 2’-Me, 2’-OM9,4’-F, 3’-F, 2‘-F

The regiochemistry of intramolecular rneru-photocycloaddition of 3-(benzyldimethylsila)propl-ene (403)is controlled by the silicon in the tether. However the capacity of silicon to stabilise a positive charge at the P-carbon does not compete with the 1’,3’-directing influence of 2-electron-donating substituents in the aromatic ring. Only the products from 1’,3’-addition are found, which is the result of asymmetry in the benzene-ethene orientation in the bichromophore conformation (404)preceding addition. For the rn-fluoro bichromophore, both 1’,S-and 2’,6‘-additions occur, the P-silicon effect competing to some extent with fluorine stabilisation of an adjacent negative charge.325Laser flash photolysis and trapping experiments with the 1,Zdisilacyclobutane (405) suggest that the sole primary photoproduct is the disilene (Me3Si)2Si=Si(SiMe3)2, together with 2,2’biadamantylidene, and that the disilene dissociates to the silylene (Me3Si)zSi: on further photolysis. The 1,2-digemacyclobutane (406) undergoes analogous photwonversions. The disilenebutadiene adduct (407)is converted into (408)on irradiation. Thermolysis of disilacyclobutane (405)results in the alternative [2+2] cycloreversion process and formation of bis(trimethylsilyl)adamantylidenesilene, whereas the digermacyclobutane(406)cleaves thermally to give (Me3Si)2Ge= Ge(SiMe3)2.326

Si(SiMe& 405 X = S i 406 X = G e

407 n = l 408 n = O

Absolute rate constants have been reported for the reaction of Me2Si=CHCH=CH2, generated from 1,l-dimethyl-(1-sila)cyclobut-Zene by irradiation with 193 nm light, with alcohols and oxygen and the potential and limitations of the use of far-UV radiation in such solution phase flash photolysis studies have been discussed.327 The method has also been applied to similar reactions of Me2Si=CH2,similarly generated from 1,l -dimethyl~iletane.~~~ 2,3,4,5-Tetraphenylsilacyclopentadienylidene,the first silylene incorporated in a silole ring, has been generated by photolysis of 7-silanorbornadiene and norbornene precursors, for example (409),and has been observed in a frozen 3-methylpentane matrix at 77 K and trapped as the adducts with efficient silylene traps, EtMe2SiH and 2,3dimethylbuta-1,3-diene.329 Photolysis (254 nm) of substituted phenylpolysilanes (RL3SiSiR22Ph)in the presence of [60]fullerenein benzene results in 1,16-addition to Cm to give (410) by

280

Photochemistry

Ph Ph

Ph

409

411

410

silyl radical addition and/or 1,Zaddition to give (411) (and the corresponding cisand trans-1,6cyclohexadiene isomers) involving attachment of the phenylsilyl radical to Cso via the silicon and 2-carbon atoms.330 Irradiation of the disilanylethyne (412)in methanol yields the adduct E-(416), formed by methanolysis of silacyclopropene(414),which is the product of singlet excited state rearrangement of (412).In dichloromethane containing acetone as the trapping agent, cyclopropene (414)is converted into adduct (417).Intramolecular trapping by the 2-allyloxy substituent was not observed. Under these conditions an additional product (421)is also obtained, which is believed to be In formed via the intermediacy of silaallene (415)and the acetone adduct (418).331 a complementary laser flash photolysis study of phenylethynylpentamethyldisilane (413)in hexane, dimethylsilylene, the corresponding silacyclopropene (414) and silaallene (415)were detected and characterised. Absolute rate constants for reaction of the silaallene with methanol, acetic acid and oxygen have been determined.332Photolysis of hexa-t-butylcyclotrisilane in the presence of Nmethylpyrrole results in formation of (419),possibly via rearrangement of the adduct formed by addition of di-t-butylsilylene across the 2,3-double bond. Cophotolysis of (419)with hexa-t-butylcyclotrisilanegives the seven-membered ring compound (420), which is the product of addition of di-t-butylsilylene to (419)followed by cleavage of the central four-membered ring in the initially-

Ar--8-SiMe

Me Me 1. I

I

t

SiMe3 ACH+ SiMe2 I OMe

416

419

-ArMSiMe3

z'r-

Me Me 412 Ar = 2-(CH2=CHCH20)C6H4 413 Ar= Ph

Si Me2

SiMe3

MeZ S i M e 2 Me

417

420

+

Me3si)=C=SiMe2 Ar

415

J Me2CO

Me&i

A rMe % r eMe 2

418 Me Ar*O-Si-SiM%

Me I

Me

I Me

421

IIi4: Photoreactions of Compounds Containing Heteroatoms other than Oxygen

28 1

formed a d d ~ c t .(Trimethylsilylmethy1)trimethyldisilene ~~~ (Me2Si = SiMeCH2SiMe3) has been generated photochemically from 1-phenyl-7-trimethylsilylmethyl-7,8,8-trimethyl-7,8-disilabicyclo[2.2.2]octa-2,5-diene and the regioselectivity of the addition of phenols to the disilene investigated.334 1,2-Disila-3,5-cyclohexadienes(422) have been reported to give 2,6-disilabicycl0[3.1.O]hex-3-enes and 5,6-disilabicyclo[2.l.l]hex-2-eneson direct irradiation, possibly via ring-opened 1,6-disila-l,3,5-hexatrienes(425), by analogy with 1,3cyclohexadienes and 1-sila-2,4-cyclohexadienes.335 In contrast SET sensit isation of 1,2-disila-3,5-cyclohexadienes(422) by methylene blue yields the corresponding five-membered siloles (428). Silicon-silicon bond cleavage within the radical cation of (422) is proposed to yield an open intermediate and subsequent cyclisation, elimination and back electron transfer steps lead to the observed 1,ZDigermacyclohexa-3,5-dienes (423) on irradiation in benzene yield germoles (429) quantitatively by extrusion of a dialkylgermylene, which may be trapped by 2,3-dimethylbuta-l,3-dieneas the corresponding 1,l -dialkyl-3,4dimethyl-1-germacyclopent-3-enes. Irradiation of a 1-germa-2-silacyclohexa-3,5diene (424) yields mainly silole (428) along with a small amount of germole (429). These ring contractions may possibly proceed via labile dimetallotrienes (425) and the biradicals (426) and (427); the regioselectivity in the case of (424) is consistent with the C-Si bond being stronger than the C-Ge bond and with germylenes being more thermodynamically stable then ~ i l y l e n e sIrradiation .~~~ of the tetraphenyl-1,2-disila- (422) and 1,2-digermacyclohexa-3,5-dienes(423) in benzenelbenzonitrile in the presence of Cm as electron acceptor similarly yields the corresponding siloles (428) and germoles (429), respectively, via the intermediacy of the corresponding radical cations. That from 1-germa-2-silacyclohexa-3,5-diene(424) yields only the silole (428).-

422 X = Y = S i 423 X - Y = G e 424 X=Si, Y = G e

425 X,Y

= Si, Ge

426 X Y P Si, Ge 427 X=Si, Y = G e P

428 X = Si 429 X = G e

1,l -Dimethyl-2,5-diphenylgermoleyields anti,trans-, anti@-, and syn,cis-[2+2] photodimers, whereas the more sterically crowded 1,l-dimethyl-2,3,4,5-tetraphenyl or lf1,2,3,4,5-hexamethyl derivatives do not photodimerise. Triplet excited 9,lO-phenanthraquinone reacts with cyclic organosilanes to give silylene insertion products via radical displacement at the silicon of the organosilanes. For example reaction with dodecamethylcyclohexasilane or 1-phenyl-7-trimethylsilylmethyl-7,8,8-trimethyl-7,8-disilabicyclo[2.2.2.]octa-2,5-diene yields the adduct (430), in the latter case YMthe intermediacy of the biradical (431).339 Substituent labelling has been employed to confirm that the photoisomerkdtion of hexakis(t-butyldimethy1silyl)tetrasilacyclobutene to the corresponding tetrasilabicyclo[1.1 .O]butane (or the reverse thermal transformation) proceeds by

Photochemistry

282

431

1,Zmigration of a I-butyldimethylsilyl group with formation (or cleavage) of the central Si-Si bond, rather than skeletal isomerisation requiring cleavage or formation of two Si-Si bonds.340Irradiation of the 1-(pentamethyldigermanyl)naphthalenes (432) yields mainly the isomeric rearranged compounds (433), accompanied by small amounts of the 1-trimethylgermyl compounds (434). Homoiysis of the Ge-Ge bond, recombination of the resulting trimethylgermyl 1naphthyldimethylgermyl radical pair at the 8-position of the latter and an intramolecular 1,4-hydrogen shift to give (433) is consistent with deuterium labelling studies. Extrusion of dimethylgermylene from (432) results in formation of (434). In contrast the corresponding 2-(pentamethy1digermanyl)naphthalenes are converted into high molecular weight polymers under similar conditions of irradiati~n.~~'

432 R1 = H, R2 = GeMq, R3 = H, Me 433 R1 +i GeMe3, R2 = H, R3 = H, Me 434 R1 = H, R2 = Me, R3 = H, Me

Photoinitbated SET from an electron rich aromatic such as 1,S-dimethoxynaphthalene (DMN) to t-butyldiphenyl(phenylse1eno)silane yields the corresponding radical anion (439, mesolysis of which generates the phenylselenyl anion (436) and the t-butyldiphenylsilyl radical (437).This Se-Si system has been utilised syntheticallyin bimolecular group transfer radical processes. For example irradiation of a solution containing t-butyldiphenyl(phenylseleno)silane, the bromo ester (439, DMN and ascorbic acid (added as sacrificial electron donor to regenerate DMN from its radical cation) results in formation of the cyclisation product (441) in 75% yield via the intermediacy of radicals (439) and (4U2)?42 4.2

Phosphorus - Photochemical SET from singlet excited 1,Cdicyanonaphthalene converts the nucleoside analogue-based ally1 phosphites (443) into the allylphosphonates (444).343The relative quantum efficiencies of the triplet sensitised photorearrangement of allylphosphites to allylphosphonates have been qualitatively correlated using the 1,2-biradical model for n,n* excited states and consideration of the effect on excited state eneregies and lifetimes of placing the

I M : Photoreactions of Compounds Containing Heteroatoms other than Oxygen

PhSe-SiPh2But-'

435

-

283

Br

PhSe- + Ph&iBut 436 437 I

439

PhSeSePh

ii

I

LSePh 441

c

442

=

n-bond in a small ring.344Irradiation of dimethyl 9-anthrylmethyl phosphite in benzene yields the corresponding dimethyl 9-anthrylmethylphosphonate which, on further irradiation either in solution or in the solid state, undergoes HT 9,lOanthracene-type ph~todimerisation.~~~ P

443

444

445 R = Me, OAr; Ar = Inaphthyl

9,lO-DCA sensitisation of tri- I-naphthyl phosphate or di- 1-naphthyl methylphosphonate results in formation of 1,l'-binaphthyl. The reaction occurs only in compounds with at least two naphthyl substituents linked by an 0-P(0)-0chain. Reaction involves intramolecular face-to-face dimerisation of the two naphthyl units within the radical cation (445), followed by elimination of the 1,l'binaphthyl radical cation, which is subsequently reduced by the DCA radical anion.346 In a related reaction DCA-sensitisation of bis(3,4-methylenedioxyphenyl) methylphosphonate in acetonitrile gives 2-(3,4methylenedioxyphenyl)4,5-methylenedioxyphenyl methylphosphonate whereas direct irradiation in methanol gives bis(3,4-methylenedioxy)biphenyl as an additional product.347 In contrast to product formation by thermal extrusion of molecular nitrogen from the 4-phosphapyrazolines (446),photoproduct formation results in deepseated skeletal rearrangements. Irradiation of the 5-alkylidene derivatives yields the azomethineimines (447),which are spectroscopicallydetectable and thermally stable in solution. Continued irradiation converts (447)into (449) which opens to give (451). In the case of the 5-arylidene derivative, the ring-contracted product (448)is converted to primary photoproduct (450) which aromatises on standing to give (452).348 31P NMR has been used to observe the E,Z-photoisomerisation of phosphaethenes having more than one C=P group attached to a benzene ring.

284

Photochemistry Ar

Ar

Ar Ph

-

Ph

OSiR3

N=N

,

O-

I SiR3 449

R3Si 447 R' = CMe3,l-adamantyl 448 Ri = 4-MeOC6H4

446 Ar = 2,4,6-Me3CsH2, R = CHMe2

I

Ph

I Ph

Ar

At'

I

Ph R&iO

Ar

0 450

1

R1

451

H-shift

Ph R3Si0 452

E,E- 1,4- (453) and E,E-1,3(454) disubstituted benzenes appear to isomerise directly to the Z,Z-isomers to yield a photostationary state with an E,E-: Z,Zratio of 1:2 in each case. In contrast the E,E- 1,2-isomer (455) appears to reach a photostationary state involving only the E,E- and E , Z - i s ~ m e r sBoth . ~ ~ ~(2,4,6trimethylbenzoy1)diphenylphosphine oxide and bis(2,6-dimethoxybenzoyl)-2,4,4trimethyl-pentylphosphine oxide undergo a-cleavage to produce benzoyl and P-centred radicals mainly from their triplet excited states. Investigations on the nanosecond and picosecond timescales reveal that the rate of a-cleavage is of the same order or faster than the rate of intersystem crossing, analogous to the well investigated photochemistry of dibenzyl ketone.350 I

HYp

Me I

Other Elements - Further investigations of the benzophenone sensitised reactions of methyl-substituted selenophenes and tellurophenes with a range of maleic anhydride derivatives have been reported.351Cleavage of the acyl-tellurium 4.3

IIl6: Photoreactions of Compounh Containing Heteroatoms other than Oxygen

285

bond on photolysis of PhTeCOOCH(C8H 17)CH2CH2SeCH2Ph followed by cyclisation of the resulting oxyacyl radical yields the 3-oxaselenan-2-one derivative (456) in high yield. Attempted cyclisations to form larger rings have been unsuccessful.352Cycloalkyl radicals, generated by photolysis of cycloalkyl aryl tellurides in the presence of N-acetoxy-2-thiopyridone, react with protonated electron-deficient heteroaromatic bases to give the corresponding cycloalkylated heteroaromatic derivatives. For example 3-(benzyloxymethyl)cyclobutyl 4-methoxyphenyltelluride and 4-methyquinolinium trifluoroacetate yield a 1:1 mixture of cis- and trans-(457) in 68% yield.353The 1,3-stannyl photorearrangements of E-cinnamyl(tripheny1)stannane and E-cinnamyl(trialky1)stannanes to the corresponding branched allylstannanes occur intramolecularly via cinnamyl n,n* excitation in competition with homolysis of the (cinnamy1)C-Sn bond. But-2enyl(tripheny1)stannane and but-2-enyl(dibutyl)phenylstannane undergo the 1,3rearrangement via excitation of a phenyl group on the tin.354 References 1. 2. 3. 4. 5. 6 7. 8. 9. 10. 11. 12. 13. 14.

A. Weedon, Adv. Photochem., 1997,22,229. W. S . Jencks, D. D. Gregory, Y. Guo, W. Lee and T. Tetzlaff, Mol. Supramol. Photochem , 1997, I, 1. J. W. Pavlik, Mol. Supramol. Photochem., 1997,1, 57. P. Margaretha, Mol. Supramol. Photochem., 1997,1,85. J. S . D. Kumar and S. Das, Res. Chem. Zntermed, 1997,23,755. A. Kitamura, N. Miyagawa and T. Karatsu, Yuki Gosei Kugaku Kyokaishi, 1997,55, 678 (Chem. Abstr., 1997,127,205 184a). S. Fukuzumi, Res. Chem. Intermed, 1997,23,519. 0.Pieroni, A. Fissi and G. Popova, Prog. Polym. Sci., 1998,23,81. M. Irie and K. Uchida, Bull. Chem. SOC.Jpn., 1998,71,985. M. Sisido, A h . Photochem, 1997,22, 197. M. D’Auria, Targets Heterocycl. Syst., 1997, I, 277. Y. Kubo, Kokagaku, 1998,27,10 (Chem. Abstr., 1998,128,3082482). H. Hiratsuka, Bunko Kenkyu, 1997,46,167 (Chem. Abstr., 1997,127,248138f). I. K. Lednev, T.-Q. Ye, R. E.Hester and J. N. Moore, J, Phys. Chem. A , 1997, 101,

4966.

15. 16. 17. 18. 19. 20. 21. 22. 23.

Y. Yang and T. Arai, Tetrahedron Lett., 1998,39,2617. E. J. Shin, E. Y.Bae, S. H. Kim, H. K. Kang and S. C. Shim, J. Photochem.

Photobiol. A: Chem., 1997,107, 137. E. J. Shin and S. W .Choi, J. Photochem. Photobiol. A: Chem., 1998,114,23. A. C . Benniston, A. Harriman and C. McAvoy, J. Chem. SOC.,Faraday Trans., 1997, 93,3653. W . Hu, C. Werner and M.Hesse, Helv. Chim. Acta, 1998,81,342.

R. E. Martin, J. Bartek, F. Diederich, R. R.Tykwinski, E. C. Meister, A. Hilger and H. P. Liithi, J. Chem. SOC.,Perkin Trans. 2,1998,233. A. Kpissay, C. N. Kuhl, T. Mohammad, K. Haber and H. Morrison, Tetrahedron

Lett., 1997,38,8435. H. Goerner, Ber. Bunsen-Ges,, 1998,102,726. M. Garavelli, P. Celani, F. Bernardi, M. A. Robb and M. Olivucci, J. Am. Chem. Soc., 1997,119,6891.

286

Photochemistry

24.

M. Garavelli, F. Bernardi, P. Celani, M.A. Robb and M. Olivucci, J. Photochem. Photobiol. A: Chem., 1998,114, 109. M. Garavelli, T. Vreven, P. Celani, F. Bernardi, M, A. Robb and M. Olivucci, J. Am. Chem. SOC.,1998,120,1285. T. Arai, Y. Furuya, H. Kawashima and K. Tokumaru, J. Photochem. Photobiol. A: Chem., 1997,103,85. C . J. Groenenboom, H. J. Hageman, P. Oosterhoff, T. Overeem and J. Verbeek, J. Photochem. Photobiol. A: Chem., 1997,107,26 1. R. J. Olsen, J. Photochem. Photobiol. A: Chem., 1997,103,91. S. Mukherjee and S. C. b r a , J. Photochem. Photobiol. A: Chem, 1998,113,23. J. Wachtveitl, T. NPgele, B. Puell, W. Zinth, M. Kruger, S. Rudolph-Whner, D. Oesterhelt and L. Moroder, J. Photochem. Photobiol. A: Chem., 1997,105,283. H. Shinmori, M. Takeuchi and S. Shinkai, J. Chem. SOC.,Perkin Trans. 2,1998,847. R. Tahara, T. Morozumi, H. Nakamura and M. Shimomura, J. Phys. Chem. B, 1997,101,7736. M . Saadioui, N. Reynier, J.-F. Dozol, Z. Asfari and J. Vicens, J. Inclusion Phenom. Mol. Recognit. Chem., 1997,29. 153. Y. Q. Wang, H. Z. Yu, Y. Luo, C. X. Zhao and Z. F. Liu, J. Electroanal. Chem., 1997,438, 127. L. M. Goldenberg, J. F. Biernat and M. C. Petty, Langmuir, 1998, 14, 1236. X. Song, J. Perlstein and D. G. Whitten, J. Am. Chem. SOC.,1997,119,9144. R. A. Moss and W. Jiang, Langmuir, 1997,13,4498. T. Nagasaki, A, Noguchi, T. Matsumoto, S. Tamagaki and K. Ogino, An. Quim. Int. Ed., 1997,93, 341. R. A. Odum and B. Schmall, J. Chem. Res. (S), 1997,276. C. J. Aucken, F. J. Leeper and A. R. Battersby, J. Chem. SOC.,Perkin Trans. I , 1997, 2099. Z.-N. Huang, S. Jin, Y. Ming and M. Fan, Mol. Cryst. Liq. Cryst., 1997,297,99. M. Irie, T. Lifia and K. Uchida, MoZ. Cryst. Liq. Cryst., 1997,297,81. K. Uchida, T. Ishikawa, M. Takeshita and M. hie, Tetrahedron, 1998,54,6627. M. Takeshita, C. N. Choi and M. Irie, Chem. Commun., 1997,2265. M. Takeshita and M. Irie, TetrahedronLett., 1998,39,613. S. H. Kawai, TetrahedronLett., 1998,39,4445. H.-G. Cho and B . 4 . Cheong, Bull. Korean Chem. SOC.,1998,19,308. A. V. Metelitsa, M. I. Knyazhansky, E. A. Medyantseva, 0. T. Liashik, S. M. Aldoshin and V. I. Minkin, Mol. Cryst. Liq. Cryst., 1997,297,93. Y. Yokoyama, S. Uchida, Y. Shimin! and Y. Yokoyama, Mol. C r y t . Liq. Cryst., 1997,297,85. H. G. Heller, D. Hughes, M. B. Hursthouse and K. S. V. Koh, Chem. Commun., 1994,27 13. H. G. Heller, K. Koh, M. Kose and N. Rowles, Mol. Cryst. Liq. Cryst., 1997, 297, 73. L. Yu, D. Zhiu and M. Fan, Mol. Cryst. Liq. Cryst., 1997,297, 107. F. J. Hughes, U. S. Patent, 1997, US 5679805 A; M. Melzig and H. Zinner, U. S. Patent, 1997, US 5645768 A; A. Kumar, D. B. Knowles and B. Van Gemert, 1997, PCT Int. Appl., WO 97 21,689; S. Yoshimoto and Y. Onishi, Jpn. Kokai Tokkyo Koho, 1997, JP 09,323,990; A. Kumar, U. S. Patent, 1997, US 5698141 A; M. Tanaka, T. Aono, M. Satomura and Y. Ichijima, Jpn. Kokai Tokkyo Koho, 1997, JP 09,241,263; K. Chamontin, V. Lokshin, A. Samat and R. Guglielmetti, PCT Int. Appl., WO 98 04,563.

25. 26. 27. 28. 29. 30. 31. 32. 33. 34. 35. 36. 37. 38. 39. 40. 41. 42. 43. 44. 45. 46. 47. 48.

49. 50.

51. 52. 53.

1116: Photoreactionsof Compoundr Containing Heteroatoms other than Oxygen

54. 55. 56. 57. 58. 59. 60.

61. 62. 63. 64. 65. 66. 67. 68. 69. 70. 71. 72. 73. 74. 75. 76. 77. 78. 79. 80. 81. 82.

287

(a) H. Gorner, Chem. Phys., 1997, 222, 315; (6) A. K. Chibisov and H. Gorner, J. Photochem. Photobiol, A: Chem., 1997,105,261; (c) A. K. Chibisov and H. Gorner, J. Phys. Chem. A , 1997,101,4305; (4 H. Giirner, Chem. Phys. Lett., 1998,282,381. Y. Kawanishi, K. Seki, T. Tamaki, M. Sakuragi and Y. Suzuki, J. Photochem. Photobiol. A: Chem., 1997,109,237. X . D. Sun, M. G. Fan, X.J. Meng and E. T. Knobbe, J. Photochem. Photobiol. A: Chem., 1997,102,213. T. Horii, Y. Miyake, R. Nakao and Y. Abe, Chem. Lett., 1997,655. S. Delbaere, C. Bochu, N.Azaroual, G. Buntinx and G. Vermeersch, J. Chem. Soc., Perkin Trans. 2, 1997, 1499. V. Marevtsev and N. L. Zaichenko, J. Photochem. Photobiol. A: Chem., 1997, 104, 197. K. Chamontin, V. Lokshin, G. Garros, A. Samat and R. Guglielmetti, Mol. Cryst. Liq. Cryst., 1997,298, 7. A. V. Metelitsa, 0.A. Kozina, S. M.Aldoshin, B. S. Lukyanov, M. I. Knyazhansky andV. I. Minkin, Mol. Cryst. Liq. Cryst., 1997,297,227. L. V. Natarajan, T. M. Cooper and D. Stitzel, Mol. Cryst. Liq. Cryst., 1997, 298, 205. R. Guglielmetti, Mol. Cryst. Liq. Cryst., 1997,298, 13. H. Heller, J. R. Levell, D. E. Hibbs, D. S. Hughes and M. B. Hursthouse, Mol. Cryst. Liq. Cryst., 1997,297, 123. V. I. Minkin and V. N. Komissarov, Mol. Cryst. Liq. Cryst., 1997,2W, 205. A. V. Metelitsa, V. N. Komissarov M. I. Knyazhansky, and V. I. Minkin, Mol. Cryst. Liq. Cryst., 1997,297,219. A. V. Metelitsa, M. I. Knyazhansky, A. V. Koblik, L. A. Muradyan, S. M. Lukyanov and V. I. Minkin, Mol. Cryst. Liq. Cryst., 1997,297,227. S. Anguille, P. Brun and R. Guglielmetti, Heterocycl. Commun.,4,63. C. Salemi-Delvaux, G. Giwti and R. Guglielmetti, Mol. Cryst. Liq. Cryst., 1997, 2w, 53. M. H. Deniel, J. Tixier, D. Lavabre, J. C. Micheau and H. Durr, Mol. Cryst. Liq. Cryst., 1997,298, 129. H. Blesinger, P. Scheidhauer, H. DOrr, V. Wintgens, P. Valat and J. Kossanyi, J. Org. Chem., 1998,63,990. N. Sertova, J.-M Nunzi, I. Petkov and T. Deligeorgiev, J. Photochem. Photobiol. A: Chem, 1998,112,187. I. Baraldi, S. Ghelli, Z. A. Krasnaya, F. Momicchioli, A. S. Tatikolov, D. Vanossi and G. Ponterini, J. Photochem. Photobiol. A: Chem., 1997,105,297. E. Ivakhnenko, N. I. Makarova, M. I. Knyazhansky, V. A. Bren, V. A. Chernoivanov, A. I. Shiff and G. S. Borodkin, Mol. Cryst. Liq. Cryst., 1997,297,233. K. Kobayashi, M. Iguchi, T. Imakubo, K. Iwata and H. Hamaguchi, Chem. Commun., 1998,763. J. H. Rigby and M. E. Mateo, J. Am. Chem. Soc., 1997,119, 12655. J.-K. Luo,R. F. Federspiel and R. N. Castle, J. Heterocycl. Chem., 1997,34, 1597. S . Arai, M. Ishikura and T. Yamagishi, J. Chem. Soc., Perkin Trans. I , 1998,1561. A. N. Frolov and N. I. Rtishchev, Russ. J. Org. Chem., 1997,33,246. M. Ibrahim-Ouali, M.-E. Sinbaldi, Y. Troin, D. Guillaume and J.-C. Gramain, Tetrahedron,1997,53, 16083, Y.-T. Park, N. W. Song, C.-G. Hwang, K.-W. Kim and D. Kim, J. Am. Gem. SOC., 1997,119,10677. G. Jones and X . Qian, J. Phys. Chem. A , 1998,102,2555.

288

Photochemistry

83.

U. Lindemann, G. Reck, D. Wulff-Molder and P. Wessig, Tetrahedron, 1998, 54,

84.

P. Wessig, J. Schwarz, D. Wulff-Molder and G. Reck, Monatsh. Chem., 1997, 128,

2529. 849.

85.

86. 87. 88. 89. 90. 91. 92. 93. 94. 95. 96. 97. 98. 99. 100.

(a) T. Hasegawa, Y. Yamazaki and M. Yoshioka, J. Photosci., 1997, 4, 7; (b) T. Hasegawa, T. Ogawa, K. Miyata, A. Karakizawa, M. Komiyama, K. Nishizawa and M. Yoshioka, J. Chem. Soc., Perkin Trans. I , 1990,901. S. B. Rollins and R. M. Williams, Tetrahedron Lett., 1997,38,4033. L.-C. Wu, C. J. Cheer, G. Olovsson, J. R. Scheffer, J. Trotter, S.-L. Wang and F.-L. Liao, Tetruhedron Lett., 1997,38, 3135. T. Okano, H. Ishihara, N. Takakura, H. Tsuge, S. Eguchi and H. Kimoto, J. Urg. Chem., 1997,62,7192. F. D. Lewis, J. M. Wagner-Brennan and J. M. Denari, J. Photochem. Photobiol. A: Chem., 1998,112, 139. F. D. Lewis and S. G. Kultgen, J. Photochem. Photobiol. A: Chem., 1998,112,159. A. Sugimoto, C. Hayashi, Y. Omoto and K. Mizuno, Tetrahedron Lett., 1997, 38, 3239. U. C. Yoon, J. W. Kim, J. Y. Ryu, S. J. Cho, S. W. Oh and P. S. Mariano, J. Photochem. Photobiol. A: Chem., 1997,106,145. A. G. Griesbeck, J. Hirt, W. Kramer and P. Dallakian, Tetrahedron, 1998,54, 3169. B. M. Aveline, S. Matsugo and R. W. Redmond, J. Am. Chem. Soc., 1997, 119, 1 1785. H. Gorner, K.-D. Warzecha and M. Demuth, J. Phys. Chem. A , 1997,101,9964.

M. Suzuki, T. Ikeno, K. Osoda, K. Narasaka, T. Suenobu, S. Fukuzumi and A. Ishida, Bull. Chem. Soc. Jpn., 1997,70,2269. T. Tamai, N. Ichinose, T. Tanaka, T. Sasuga, I. Hashida and K. Mizuno, J. Urg. Chem., 1998,63,3204. C.-K. Sha, K. C. Santhosh, C.-T. Tseng and C.-T. Lin, Chem. Commun., 1998,397. Y. Blache, M.-E. Sinbaldi-Troin, A. Voldoire, 0. Chavignon, J.-C. Gramain, J.-C. Teulade and J.-P. Chapat, J. Org. Chem., 1997,62,8553. S. P. Gromov, 0. A. Federova, E. N. Ushakov, I. I. Baskin, A. V. Lindeman, E. V. Malysheva, T. A. Balashova, A. S. Arsen’ev and M. V. Alfimov, Russ. Chem. Bull., 1998,47,97.

W. Herrmann, S. Wehrle and G. Wenz, Chem. Commun., 1997,1709. T. Nakamura, K. Takagi, M. Itoh, K. Fujita, H. Katsu, T. Imae and Y. Sawaki, J. Chem. Soc.. Perkin Trans. 2, 1997,2751. 103. T. Nakamura, K. Takagi and Y. Sawaki, Bull. Chem. SOC,Jpn., 1998,71,909. 104. T. Suishu, S. Tsuru, T. Shimo and K. Somekawa, J. Heterocycl. Chem., 1997, 34, 101. 102.

1005.

105. 106. 107. 108. 109. 110.

111.

P. R.Dave, R. Duddu, J. Li, R. Surapaneni and R. Gilardi, Tetrahedron Lett., 1998, 39,548 1. M. D’Auria and R. Racioppi, J. Photochcm. Photobiol. A: Chem., 1998,112, 145. H. R. Memarian, M. M. Sadeghi and H. Aliyan, Indian J. Chem., 1998,37B, 219. N. Marubayashi, T. Ogawa, T. Hamasaki and N. Hirayama, J. Chem. Soc., Perkin Trans. 2, 1997, 1309. G. M. J. Schmidt, Pure Appl. Chem., 1971,27,647. N. Marubayashi, T. Ogawa, T. Hamasaki and N. Hirayama, Bull. Chem. Soc. Jpn., 1998,71, 321. T. Nozaki, M. Maeda, Y. Maeda and H. Kitano, J. Chem. Soc., Perkin Trans. 2, 1997,1217.

IIl4: Photoreactions of Compouncls Contuining Heteroatoms other than Oxygen

289

112. K. I. Booker-Milburn, S. Gulten and A. Sharp, Chem. Commun., 1997, 1385. 113. M. N. Wrobel and P. Margaretha, Chem. Commun., 1998,541. 114. T. Noh, D. Kim and Y.-J. Kim, J. Org. Chem., 1998,63, 1212. 115. J. D. Winkler, J. E. Stelmach, M. G. Siegel, N. Haddad, J. Axten and W. P. Dailey, Israel J. Chem., 1997,37,47. 116. G. Konishi, K. Chiyonobu, A. Sugimoto and K. Mizuno, Tetrahedron Lett., 1997, 38,5313. 117. D. L. Comins, Y. S. Lee and P. D. Boyle, TetrahedronLett., 1998,39,187. 118. H. Tsujishima, K.Nakatani, K. Shimamoto, Y. Shigeri, N. Yumoto and Y. Ohfune, Tetrahedron Lett., 1998,39, 1 193. 119. M. N. Wrobel and P. Margaretha, J. Photochem. Photobiol. A: Chem., 1997,105,35. 120. A. Hilgeroth, Chem. Lett., 1997, 1269. 121. T. Nakamura, K. Takagi and Y.Sawaki, Bull. Chem. SOC.Jpn., 1998,71,419. 122. M. Yasuda, Y. Nishinaka, T. Nakazono, T. Hamasaki, N. Nakamura, T. Shiragami, C. Pac and K. Shima, Photochem. Photobiol., 1998,67,192. 123. C. Jeandon, R. Constien, V. Sinnwell and P. Margaretha, Helv. Chim. Actu, 1998, 81, 303. 124. M. Sakamoto, M. Takahashi, T. Fujita, S. Watanabe, T. Nishio, I. Iida and H. Aoyama, J. Org. Chem., 1997,62,6298. 125. G. S. Han and S . C. Shim, Photochem. Photobiol,, 1998,67,84. 126. A. G. Griesbeck, S. Buhr and J. Lex, TetrahedronLett., 1998,39,2535. 127. H. Koshima, T. Nakagawa and T. Matsuura, TetrahedronLett., 1997,38,6063. 128. H. Koshima, Y. Wang, T. Matsuura, I. Miyahara, H. Mizutani, K. Hirotsu, T. Asahi and H. Masuhara, J. Chem. Soc., Perkin Trans.2,1997,1217. 129. S . Lahlou, N. Bitit and J.-P.Desvergne, J. Chem. Res. ( S ) , 1998,302. 130. J. H. R. Tucker, H.Bouas-Laurent, P. Marsau, S. W.Riley and J.-P. Desvergne, Chem. Commun., 1997,1165. 131. R . N. Warrener, M.Golic and D. N. Butler, TetrahedronLett., 1998,39,4717. 132. C. Lehnberger, D. Scheller and T. Wolff, Heferocycles, 1997,45,2033. 133. S. Andresen and P. Margaretha, J. Photochem. Photobiol. A: Chem., 1998,112, 135. 134. Y. Ito and S. Endo, J. Am. Chem. Soc., 1997,119,5974. 135. P. Clivio, D. Guillaume, M.-T. Adeline, J. Hamon, C. Riche and J.-L. Fourrey, J. Am. Chem. Soc., 1998,120, 1 157. 136. I. Saito, M. Takayama, H. Sugiyama and T. Nakamura, J. Photochem. Photobiol. A: Chem., 1997,106,141. 137. D. N. Nikogosyan and H. Gorner, Biol. Chem., 1997,378,1349. 138. (a) K. Ohkura, Y. Noguchi and K.-I. Seki, Heterocycles, 1997, 45, 141; (6) K. Ohkura, Y. Noguchi and K.-I. Seki, Heterocycles, 1998,47,429. 139. M. Kotera, K. Ishii, 0. Tamura and M. Sakamoto, J. Chem. Soc., Perkin Trans. I , 1998,313. 140. C. Gaebert and J. Mattay, Tetrahedron, 1997,53, 14297. 141. E. Albrecht, J. Mattay and S . Steenken, J. Am. Chem. Soc., 1997,119, 11605. 142. M. Fagnoni, M. Mella and A. Albini, J. Phys. Org. Chem., 1997,10, 777. 143. Y. Ming, Z. Huang, M. Fan, B. Xu, S. Jin and S . Yao, Sci. in China (Ser. B ) , 1997, 40,373. 144. F. Wang, Y. Li, X.Li and J. Zhang, Res. Chem. Intermed, 1998,2467. 145. T. Goto and Y.Tashiro, J. Luminescence, 1997,72-74,921. 146. A. Elmali and Y. Elerman, J. Mol. Struct., 1998,442,31. 147. A. 0. Doroshenko, E. A. Posokhov, V. M. Shershukov, V. G. Mitina and 0 . A. Ponomarev, High Energy Chem., 1997,31,388.

290

Photochemistry

148. M. Moriyama, Y. Kawakami, S. Tobita and H. Shizuka, Chem. Phys., 1998,231,205. 149. S . Santra and S. K. Dogra, Chem. Phys., 1998,231,285. 150. M. E. Kletskii, A. A. Millov, A. V. Metelitsa and M. I. Knyazhansky, J. Photochem Photobiol. A: Chem., 1997,110,267. 151. G. Wenska, B. Skalski, M. Insinska, S. Paszyc and R. E. Verrall, J. Photochem. Photobiol. A: Chem., 1997,108, 135. 152. J . R. Scheffer and H. Ihmels, Liebigs AnnJRecueil, 1997, 1925. 153. V. Nair, G. Anilkumar, J. Prabhakaran, D. Maliakal, G. E. Eigendorf and P. G. Willard, J. Photochem. Photobiol. A: Chem., 1997,111,57. 154. D. Armesto, 0.Caballero and U. Amador, J. Am. Chem Soc., 1997,119,12659. 155. D. Armesto, A. Albert, F. H. Cano, N. Martin, A. Ramos, M. Rodriguez, J. L. Segura and C. Seoane, J. Chem. Soc., Perkin Trans. I , 1997,3401. 156. F. Scavarda, F. Bonnichon, C. Richard and G. Grabner, New J. Chem., 1997, 21, 1119. 157. 0. Cullmann, M. Vogtle, F, Stelzer and H. Prinzbach, Tetrahedron Lett., 1998, 39, 2303. 158. I. V. Nechepurenko, 0. P. Petrenko, I. A. Grigor'ev and L. B. Volodarskii, Russ. J. Org. Chem., 1997,33,705. 159. A. V. El'tsov, A. V. Selitrenikov and N. I. Rtishchev, Russ. J. Gen. Chem., 1997,67, 285. 160. K . Kubo, M. Koshiba, H. Hoshina and T. Sakurai, Heterocycles, 1998,48,25. 161. S. M. Bonesi and R. Erra-Balsells, J. Photochem. Photobiol. A: Chem., 1997, 110, 271. 162. J. W. Pavlik and N. Kebede, J. Org. Chem., 1997,62,8325. 163. 0.E. Edwards, G. Grue-Serensen and B. A. Blackwell, Can. J. Chem., 1997,75,857. 164. T. Kaneko, K. Kubo and T. Sakurai, TetrahedronLett., 1997,38,4779. 165. J. H. Hwu, C. S. Yau, S.-C. Tsay and T.4. Ho, TetrahedronLett., 1997,38,9001. 166. M. G. Siskos, A. K. Zarkadis, S. Steenken, N. Karakostas and S. K. Garas, J. Org. Chem., 1998,63,325 1. 167. N. Vivona, S. Buscemi, S. Asta and T. Caronna, Tetrahedron, 1997,53, 12629. 168. H. J. P. de Lijser and D. R.Arnold, J. Org. Chem., 1997,62,8432. 169. D. R. Arnold, K. A. McManus and M. S. W. Chan, Can.J. Chem., 1997,75,1055. 170. M. S . W. Chan and D. R. Arnold, Can. J. Chem., 1997,75,1810. 171. T. Herbertz, F. Blume and H. D. Roth, J. Am. Chem. SOC.,1998,120,4591. 172. H. Ishii, T. Hirano, S. Maki, H. Niwa and M. Ohashi, Tetrahedron Lett., 1998, 39, 2791. 173. K. Homma and S. Yamada, Chem. Pharm. Bull., 1997,45,1198. 174. K. Fujimoto, H. Sugiyama and I. Saito, TetrahedronLett., 1998,39,2137. 175. B. Li, Y.-C. Liu and Q.-X. Guo, J. Photochem. Photobiol. A: Chem., 1997,103, 101. 176. H. Weng and H. D. Roth, J. Phys. Org. Chem., 1998,11, 101. 177. J . Lee, J. S. U, S. C.Blackstock and J. K . Cha, J. Am. Chem. SOC.,1997,119, 10241. 178. L. Chen, L. Lucia and D. G. Whitten, J. Am. Chem. SOC.,1998,120,439. 179. W. Weigel and H.-G, Henning, Chem. Commun., 1997,1893. 180. K. Nakatani, N. Higashida and A. Saito, TetrahedronLett., 1997,38,5005. 181. G. Venkateshwarlu and A. K. Murthy, J. Indian Chem. SOC.,1997,74,648. 182. K. H. Ang and R. H. Prager, Aust. J. Chem., 1998,51,483. 183. R. H. Prager, J. A. Smith, B. Weber and C. M. Williams, J. Chem. Soc., Perkin Truns. I , 1997,2665. 184. R. H. Prager, M. R. Taylor and C. M. Williams, J. Chem. Soc., Perkin Trans. I , 1997,2673.

M6: Photoreactions of CompounciS Containing Heteroatoms other than Oxygen

29 1

H. J. Hageman, Macromol. Rapid Commun., 1997,18,442. P. S. Engel, S. L. He and W. B. Smith, J. Am. Chem SOC.,1997,119,6059. S. Auricchio, A. Selva and A. M. Truscello, Tetrahedron, 1997,53, 17407. W. M. Nau, G. Greiner, J. Wall, H. Rau, M. Olivucci and M. A. Robb, Angew. Chem., Int. Ed Engl., 1998,37,98. 189. W . Adam, J. N. Moorthy, W. M. Nau and J. C. Scaiano, J. Am. Chem. SOC.,1997, 185. 186. 187. 188.

119,6749.

W . Adam, J. Moorthy, W.M.Nau and J. C. Scaiano, J. Org. Chem., 1997,62,8082. N. Yamamoto, M.Olivucci, P. Celani, F. Bernardi and M. A. Robb, J. Am. Chem. SOC.,1998,120,239 1. 192, N. Miyagawa, T. Karatsu and A. Kitamura, Chem. Lert., 1997, 1005. 193. S.-J. Lin, S.-Y. Jiang, T.-C. Huang, P. Kao, P.-F. Tsai, H. Takeshita, Y . 4 . Lin and T. Nozoe, Heterocycles, 1997,45, 1879. 194. Y.-S. Lin, S.-Y. Jiang, T.-C. Huang, S.-J. Lin and Y.L. Chow, J. Org. Chem., 1998, 190. 191.

195. 196. 197. 198. 199. 200. 201. 202. 203. 204. 205. 206. 207.

63,3364.

D. Kosynkin, T. M. Bockman and J. K.Kochi, J. Am. Chem SOC.,1997,119,4846. A. Albini, G. Bettinetti and G. Minoli, J. Am. Chem. SOC.,1997, 119,7308. E. Leyva and R. Sagredo, Tetrahedron, 1998,54,7367. M. Cano, G. FabriAs, F. Camps and J. Joglar, TetrahedronLett., 1998,39, 1079. D. Donati, S. Fusi and F. Ponticelli, J. Chem. Research ( S ) , 1997, 170. D. Chiapperino and D. E. Falvey, J. Phys. Org. Chem., 1997,10,917. J. Kalvoda, J. Grob, M. BjelakoviC, L. Lorenc and M. Lj. MihailoviC, Helv. Chim. Acta, 1997,80, 1221. L. Eberson, M. P. Hartshorn and 0.Persson, Acta Chem Scand., 1998,52,745. L. Eberson, M. P. Hartshorn and 0.Persson, Acta Chem. Scand., 1998,52,751. U. Berg, C. P. Butts, L. Eberson, M. P. Hartshorn and 0. Persson, Acta Chem. Scand, 1998,52,761. C. P.Butts, L. Eberson, M. P. Hattshorn, 0. Persson, R. S. Thompson and W. T. Robinson, Acta Chem. Scand, 1997,51,1066. C. P. Butts, L. Eberson, R. Gonzhles-Luque, C. M. Hartshorn, M. P. Hartshorn, M. Merchan, W. T. Robinson, B. 0. Roos, C. Vallance and B. R. Wood, Acta Chem Scand., 1997,51,984. C. P. Butts, L. Eberson, M. P. Hartshorn and 0. Persson, Acta Chem. Scad., 1997, 51,718.

208.

209. 210. 21 1. 212.

W . Meiderer and S.Eisele, Ger. Offen., 1997, DE 19,620,170; R. P. Haugland and K. R. Gee, U. S. Patent, 1997, US 5,635,608; F. Yagihashi, A. Kiyomori, T. Iwasaki and J. Hatakeyama, Jpn. Kokai Tokkyo Koho, 1998, JP 10 77,264, C. P. Holmes, U. S. Patent, 1998, US 5,739,386; S. Watanabe and M. Iwamura, J. Org. Chem., 1997,62,8616. R. Reinhard and B. F. Schmidt, J. Org. Chem., 1998,63,2434. L. Peng, J. Win and M. Goeldner, TetrahedronLett., 1997,38,2961. J. Xia, X.Huang, R. Sreekumar and J. W. Walker, Bioorg. Med Chem. Lett., 1997,

213. 214. 215.

7, 1243. K.Burgess, S. E. Jacutin, D. Lim and A, Shitan, J. Org. Chem., 1997,62,5165. T. Voelker, T. Ewell, J. Joo and E. D. Edstrom, TetrahedronLett., 1998,39,359. K.Burgess, C. I. Martinez, D. H. Russell, H. Shin and A. J. Zhang, J. Org. Chem.,

216. 217. 218.

R. Rodebaugh, B. Fraser-Reid and H. M. Geysen, TetrahedronLett., 1997,38,7653. C. Dell’Aquila, J.-L. Imbach and B. Rayner, Tetrahedron Left.,1997,38,5289. G. C . R.Ellis-Davies, TetrahedronLett., 1998,39,953.

1997,62,5662.

292 219. 220. 221. 222. 223. 224. 225. 226. 227. 228. 229. 230. 231. 232. 233. 234. 235. 236. 237. 238. 239. 240. 241. 242. 243. 244. 245. 246. 247. 248. 249. 250. 251. 252. 253.

Photochemistry

K. N. Rajasekharan and A. Sulekha, Indian J. Chem., 1997,36B, 697. K. Kuldovk, A. Corval, H. P. Trommsdorff and J. M. Lehn, J. Phys. Chem. A, 1997, 101,6850. Y.-N. Lin, G.-Y. Jeng, T.-T. Chan, G.-F. Yen and Y.-G. Wong, J. Chin. Chem. SOC., 1998,45,313. A. Yoshida, K. Sato, T. Takui, K. Itoh, M. Fujisawa, M. Yagi and J. Higuchi, Mol. Cryst. Liq. Cryst., 1997,306, 373. H. Gorner, J. Photochem. Photobiol. A: Chem., 1998,112, 155. A. S. Dvornikov, I. V. Tomov, P. Chen and P. M. Rentzepis, Mol. Cryst. Liq. Cryst., 1997,298, 251. W. Zhang, Y. Su, L. Gan, J. Jiang and C. Huang, Chem. Lett., 1997,1007. L. Gan, J. Jiang, W. Zhang, Y. Su, Y. Shi, C. Huang, J. Pan, M. Lii and Y. Wu, J. Org. Chem., 1998,63,4240. F. S. Bavetta, T. Caronna, M. Pregnolato and M. Terreni, Tetrahedron Lett., 1997, 38,7793. S. E. Bottle, U. Chand and A. S. Micallef, Chem. Lett., 1997, 857. Y. Ohba, K. Kubo and T. Sakurai, J. Phorochem. Photobiol. A: Chem., 1998, 113, 45. M. Mella, M. Fagnoni, G. Viscardi, P. Savarino, E. Elisei and A. Albini, J. Photochem. Photobiol. A: Chem., 1997, 108, 143. H. Wang, R. E. Partch and Y. Li, J. Org. Chem., 1997,62,5222. J. L. Ferry and W. H. Glaze, J. Phys. Chem. B, 1998,102,2239. A. Kumar, S. Kumar and D. P. S. Negi, J. Chem. Res. ( S ) , 1998,54. A. Kumar and S. Kumar, J. Phys. Org. Chem., 1998,11,277. M. D’Auria, E. De Luca, G. Mauriello, R. Racioppi and G. Sleiter, J. Chem. Soc., Perkin Trans. I , 1997,2369. M. D’Auria, E. De Luca, G. Mauriello and R. Racioppi, J. Chem. SOC.,Perkin Trans. I , 1998,271. M. D’Auria, Heterocycles, 1997,45, 1775. U. C. Yoon, J. H. Kim, S. J. Lee, H. J. Kim, S. W. Oh and W. W. Park, J. Korean Chem. Soc., 1997,41,666. A. M. Sarker, Y. Kaneko, A. V. Nikolaitchik and D. C. Neckers, J. Phys. Chem. A, 1998,102,5375. F. Uddin, I. M. Adhami and M. A. Yousufzai, J. Saudi Chem. SOC.,1998,2,47. V. Faure and P. Boule, Toxicol. Environ. Chem., 1997,63, 171. K. Nord, H. Andersen and H. Hanne, Drug Stab., 1997,1,243. H. H. Tonneswen, G. Skrede and B. K. Martinsen, Drug Stab., 1997,1,249. S . W. Baertschi, Drug Stab., 1997, 1, 193. U. Raschke, G. Werner, H. Wilde and U. Stottmeister, Chemosphere, 1998,36,1745. W.-U. Palm, M. Millet and C. Zetzsch, Chemosphere, 1997,35, 11 17. K. Nord, A.-L. Orsteen, J. Karlsen and H. H. Tsnnesen, Pharmazie, 1997,52,598. S. Kristensen, K. Nord, A.-L. Orsteen and H. H. Tsnnesen, Pharmazie, 1998,53,98. Y. Kawai and K. Matsubayashi, Chem. Pharm. Bull., 1998,46, 13 1 . K. Torniainen, C.-P. Askolin and J. Mattinen, J. Pharm. Biomed. Anal., 1997, 16, 439. A. Burdzy, B. Skalski, S. Paszyc, Z. Gdaniec and R. W . Adamiak, Nucleosides and Nucleotides, 1998, 17, 143. F. D. Lewis, J. M. Wagner-Brennan and J. M. Denari, J. Phys. Chem. A , 1998,102, 519. S. Li,. H. Tian, Q. Zhou, Z. Li and H. Xu, Chin. Sci. Bull., 1997,42, 1619.

IIl4: Photoreactions of Compound Containing Heteroatoms other than Oxygen 254. 255. 256. 257. 258. 259. 260. 261. 262. 263. 264. 265. 266. 267. 268. 269. 270. 271. 272. 273. 274. 275. 276. 277. 278. 279. 280. 281. 282. 283. 284.

293

S. Depaemelaere, F. C. de Schryver and J. W. Verhoeven, J. Phys. Chem. A, 1998, 102,2109. E. Kaganer, E. Joselevich, I. Willner, Z. Chen, M. J. Gunter, T. P. Gayness and M. R . Johnson, J. Phys. Chem. B, 1998,102,1159. H. A. Staab, A. Feurer, C. Krieger and A. S. Kurnar, Liebigs AndRecueil, 1997, 232 1. H. A. Staab, R. Hauck and B. Popp, Eur. J. Org. Chem., 1998,631. P. K. Malinen, A. Y. Tauber, J. Helaja and P. H. Hynninen, Liebigs Ann.lRecuei1, 1997,1801. M. R. Roest, A. M. Oliver, M. N. Paddon-Row and J. W. Verhoeven, J. Phys. Chem. A, 1997,101,4867. G. Jones, D.-X. Yan, S. R. Greenfield, D. J. Gosztola and M. R. Wasielewski, J. Phys. Chem. A, 1997,101,4939. H. Zhang, M. Zhang, and T. Shen, Science in China (Ser. B), 1997,40,449. H. Zhang, M. Zhang and T. Shen, J. Photochem. Photobiol. A: Chem., 1997,103,63. Q. Tan, D. Kuciauskas, S. Lin, S. Stone, A. L. Moore, T. A. Moore and D. Gust, J. Phys. Chem. B, 1997,101,5214. A. Knorr, E. Galoppini and M. A. Fox, J. Phys. Org. Chem., 1997,10,484. M. R . Bryce, E. Chinarro, A. Green, N. Martin, A. J. Moore, L. Sanchez and C. Seoane, Synth. Met., 1997,86, 1857. A. S. Batsanov, M. R. Bryce, M. A. Coffin, A, Green, R. E. Hester, J. A. K. Howard, I. K. Lednev, N. Martin, A. J. Moore, J. N. Moore, E. Orti, L. Sinchez M. Saviron, P. M. Viruela, R. Viruela and T.-Q. Ye, Chem. Eur. J., 1998,4,2580. Y. Yamashita, M. Maehara and S. Hayashi, Kenkyu Kiyo - Nihon Duiguku Bunrigakubu Shizen Kagaku Kenkyusho, 1998, 33, 237 (Chem. Abstr., 1998, 129, 4345w). H. Morrison, Y. Lu and D. Carlson, J. Phys. Chem. A , 1998,102,5421. T . Y. Fu, J. R. Scheffer and J. Trotter, Acta Cryst., 1997, C53,1257. H. Aoyama, J. Chem Soc., Perkin Trans. I , 1997, 1851. T. Y.Fu, J. R. Scheffer and J. Trotter, Acta Cryst., 1998, C54, 103. G. Jayanthi, S. Muthusamy, R. Paramasivan, V. T. Ramakrishnan, N. K. Ramasamy and P. Ramamurthy, J. Org. Chem., 1997,62,5766. S . Hu and D. C. Neckers, Tetrahedron, 1997,53,7165. S. Hu and D. C. Neckers, J. Photochem. Photobiol. A: Chem., 1998,114,103. S. Hu and D. C. Neckers, J. Org. Chem., 1997,62,7827. Y. Yamazaki, T.Miyagawa and T. Hasegawa, J. Chem. Soc., Perkin Trans. 1, 1997, 2979. M. Ashram, D. 0. Miller, J. N. Bridson and P. E. Georghiou, J. Org. Chem., 1997, 62,6476. V. Baret, A. Gandini and E. Rousset, J. Photochem Photobiol. A: Chem., 1997,103, 169. X . Song, J. Perlstein and D. G. Whitten, J. Phys. Chem. A, 1998, 102,5440. S. Moller, D. WeiD and R. Beckert, Liebigs AnnJRecueil, 1997,2347. Y. Kaneko, S. Hu and D. C . Neckers, J. Photochem. Photobiol. A: Chem., 1998,114, 173. M. Szymanski, A. Maciejewski, J. Kozlowski and J. Koput, J. Phys. Chem. A, 1998, 102,677. J. Bethke, J. Kopf, P. Margaretha, B. Pignon, L. Dupont and L. E. Christiaens, Helv. Chim. Acta, 1997,80, 1865. C. P. Klaus and P. Margaretha, Liebigs Ann., 1996,291.

294

Photochemistry

285.

J. Bethke, A. Jakobs and P. Margaretha, J. Photochem. Photobiol. A: Chem., 1997, 104,83. D. Vedaldi, G. Piazza, S. Moro, S. Caffieri, G. Miolo, G. G. Aloisi, F. Elisei and F. Dall’Acqua, I! Farmaco, 1997,52,645. P. Clivio, J.-L. Fourrey and A. Favre, J. Am. Chem. Soc., 1991,113,5481. P. Clivio and J.-L. Fourrey, Tetrahedron Lett., 1998,39,275. C. Saintomk, P. Clivio, A. Favre and J.-L. Fourrey, J. Org. Chem., 1997,62,8125. T. Kataoka, T. Iwama and H. Matsumoto, Chem. Pharm. Bull., 1998,46, 151. M. Takahashi, T. Fujita, S. Watanabe and M. Sakamoto, J. Chem. Soc., Perkin Trans. 2,1998,487. T. Nishio, J. Chem. Soc., Perkin Trans. I , 1998,1007. L. X. Deng and A. G. Kutateladze, Tetrahedron Lett., 1997,38,7829. T. Fujii, E. Horn and N. Furukawa, Heteroatom Chem., 1998,9,29. H. Morita, H. Kamiyama, M. Kyotani, T. Fujii, T. Yoshimura, S. Ono and C. Shimasaki, Chem. Commun., 1997, 1347. H. Pirelahi, H. Rahmani, A. Mouradzadegun, A. Fathi and A. Moudjoodi, Phosphorus, Sulfur and Silicon, 1997,120 &121,403. H. Rahmani and H. Pirelahi, J. Photochem. Photobiol. A: Chem., 1997,111, 15. S. H. Bhatia, D. M. Buckley, R. W. McCabe, A. Avent, R. G. Brown and P. B. Hitchcock, J. Chem. Soc., Perkin Trans. I, 1998,569. Y . Guo, A. P. Darmanyan and W. S. Jenks, Tetrahedron Lett., 1997,38, 8619. C.-H. Tung and Y.-M. Ying, Res. Chem. Intermed, 1998,24,15. Z . Chi and Y. Wang, Jilin Daxue Ziran Kexue Xuebao, 1998, 100 (Chem. Abstr., 1998,12s,208451s). T. Kitamura, K. Morizane, H. Taniguchi and Y. Fujiwara, Tetrahedron Lett., 1997, 38,5157. R. Borah and J. C. Sarma, Indian J. Chem., 1997,36A&B, 533. S . Encinas, M. A. Miranda, G. Marconi and S. Monti, Photochem. Photobiol., 1998, 67,420. W. Adam, 0. Deeg and S. Weinkotz, J. Org. Chem., 1997,62,7084. M. D’Auria and V. Esposito, Gazz. Chim. Ital., 1997,127,471. A. Gaplovskjl, R. Hercek and P. Kurt%, Toxicol. Environ. Chem., 1997,64, 155. E. Purushothaman, Ind. J. Heterocyclic Chem., 1997,7,93. C. P. Butts, L. Eberson, M. P. Hartshorn, F. Radner, W. T. Robinson and B. R. Wood, Acta Chem. Scand., 1997,51,839. W. Adam, J. E. Argiiello and A. B. Pefiefiory, J. Org. Chem., 1998,63,3905. J. Andraos, G. G. Barclay, D. R. Medeiros, M. V. Baldovi, J. C. Scaiano and R. Sinta, Chem. Muter., 1998,10, 1694. H. A. Gaur, H. J. Hageman, P. Oosterhoff, T. Overeem, J. Verbeek and S. van der Werf, J. Photochem. Photobiol. A: Chem., 1997,104,53. S . Duan, E. R. Binkley and R. W. Binkley, J. Carbohydr. Chem., 1998,17, 391. I. Ono, S. Sato, K. Fukuda and T. Inayoshi, Bull. Chem. SOC.Jpn., 1997,70,2051. C. Dell’Erba, M. Novi, G. Petrillo and C. Tavani, Gazz. Chim. Ital., 1997,127,361. L. Rodriguez-Hahn, M. E. Manriquez, B. A. Frontana and J. Cardenas, An. Quim. Int. Ed., 1997,93,29 1. R. Akaba, M. Kamata, A. Koike, K.4. Mogi, Y. Kuriyama and H. Sakuragi, J. Phys. Org. Chem., 1997,10,861. M. Alam, M. Fujitsuka, A. Watanabe and 0. Ito, J. Phys. Chem. A , 1998,102, 1338. S. A. Bol’shakova, N. N. Vlasove, Y. N. Pozhidaev and M. G. Voronkov, Russ. J. Gen. Chem., 1997,67,712.

286. 287. 288. 289. 290. 291. 292. 293. 294. 295. 296. 297. 298. 299. 300. 301. 302. 303. 304. 305. 306. 307. 308. 309. 310. 31 1. 312. 313. 314. 315. 316. 317. 318. 319.

M6: Photoreactions of Compounds Containing Heteroatoms other than Oxygen

320. 321. 322. 323. 324. 325. 326. 327. 328. 329. 330. 331. 332. 333. 334. 335. 336. 337. 338. 339. 340. 341. 342. 343. 344. 345.

346. 347. 348. 349. 350. 351. 352. 353. 354.

295

M. A. Brook, C. Gottardo, S. Baldazzi and M. Mohamed, Tetrahedron Lett., 1997, 38,6997. G. Gutenberger, E. Steckhan and S. Blechert, Angew. Chem., Int. Ed. Engl., 1998,37, 660. M. Freccero, A. Pratt, A. Albini and C. Long, J. Am. Chem. SOC.,1998,120,284. L. Cermenati, C. Richter and A. Albini, Chem. Commun., 1998,805. M. C . Courtney, M. Mella and A. Albini, J. Chem. SOC.,Perkin Trans. 2,1997,1105. D. M. Amey, D. C. Blakemore, M. B. Drew, A. Gilbert and P. Heath, J. Photochem. Photobiol. A: Chem., 1997,102, 173. Y. Apeloig, D. Bravo-Zhivotovskii, H. Zharov, V. Panov, W. J. Leigh and G. W. Sluggett, J. Am. Chem. SOC.,1998, 120, 1398. C. Kerst, M. Byloos and W. J. Leigh, Can J. Chem., 1997,75,975. C. Kerst, R. Boukherroub and W. J. Leigh, J. Photochem Photobiol. A: Chem., 1997,110,243. M. Kato, S. Oba, R.Uesugi, S. Sumiishi, Y. Nakadaira, K. Tanaka and T. Takada, J. Chem. SOC.,Perkin Trans. 2,1997,1251. T. Kusukawa and W. Ando, J. Organometal. Chem., 1998,559,ll. S . C. Shim and S. K. Park, Bull. Korean Chem. SOC.,1998,19,686. C. Herst, R. Ruff010 and W.J. Leigh, Organometallics, 1997,16,5804. M. Weidenbruch, L. Kirmaier, H. Marsmann and P. G. Jones, Organometallics, 1997,16,3080. T. Hoshi, R. Shimada, C.Kabuto, T.Sanji and H. Sakurai, Chem. Lett., 1998,427. Y. Nakadaira, S. Kanouchi and H. Sakurai, J. Am. Chem. SOC.,1974,%, 5622. M. Kako, H. Takada and Y. Nakadaira, TetrahedronLett., 1997,38,3525. K. Mochida, M. Akazawa, M. Goto, A. Sekine, Y. Ohashi and Y. Nakadaira, Organometallics, 1998,17, 1782. K. Mochida, M. Akazawa, M.Goto, A. Sekine, Y. Ohashi and Y . Nakadaira, Bull. Chem SOC.Jpn., 1997,70,2249. M. Kako, M. Ninomiya and Y. Nakadaira, Chem. Commun., 1997,1373. T. Iwamoto and M. Kira, Chem. Lett., 1998,277. K . Mochida, H. Ginyama, M. Takahashi and M. Kira, J. Organometal. Chem., 1998,553, 163. G. Pandey, K. S. S. P.Rao, D. K. Palit and J. P. Mittal, J. Org. Chem, 1998,63,3968. G. S . Jeon and W.G. Bentrude, TetrahedronLett., 1998,39,927. Y. Huang and W.G. Bentrude, TetrahedronLett., 1997,38,6989. W. Bhanthumnavin, S. Ganapsthy, A. M. Arif and W . G. Bebtrude, Heteroatom Chem, 1998,9,155. M. Nakamura, R. Dohno and T. Majima, Chem. Commun., 1997,1291. Y . Okamoto, T. Tatsuno and S. Takamuku, Phosphorus, Sulfur and Silicon, 1996, 117, 129. B. Manz, J. Kerth and G. Maas, Chem. Eur. J. , 1998,4,903. H. Kawanami, K. Toyota and M. Yoshifuji, J, Organometal. Chem., 1997,535, 1. S. Jockusch, I. V. Koptyug, P. F. McGarry, G. W. Sluggett, N. J. Turro and D. M. Watkins, J. Am. Chem. Soc., 1997,119,11495. C . Rivas, F. Vargas, G. Aguiar, A. Torrealba and R. Machado, J. Photochem. Photobiol. A: Chem., 1997,104,53. M. A. Lucas and C.H. Schiesser, J. Org. Chem, 1998,63,3032. W . He, H. Togo, H. Ogawa and M.Yokoyama, Heteroatom Chem., 1997,8,411. A. Takuwa, T. Kanaue, K. Yamashita and Y. Nishigaichi, J. Chem. Soc., Perkin Trans. I , 1998, 1309.

7

Photoelimination BY IAN R. DUNKIN

1

Introduction

This chapter deals with photoinduced fragmentations of organic and selected organometallic compounds, in particular reactions accompanied by loss of small molecules such as nitrogen, carbon monoxide or carbon dioxide. Photodecompositions which produce two or more larger fragments and other miscellaneous photoeliminations are reviewed in the final section. Photofragmentations of carbonyl compounds, taking place by Norrish Type I and I1 processes, are discussed in Part 11, Chapter 1. A number of papers have appeared which are of general relevance to photoelimination chemistry. These include discussions of spin-orbit coupling in diradicals,' and theoretical models for the selectivity of triplet and singlet photoreactions.* 2

Elimination of Nitrogen from Azo Compounds and Analogues

The photofragmentation of azomethane has been studied theoretically by classical trajectories and surface hopping on ub initio potential energy surface^.^ There were two main conclusions. Firstly, internal conversion, SI+SO, is so efficient that fragmentation takes place almost exclusively on the ground state potential energy surface. It seems unlikely that intersystem crossing could compete with such fast internal conversion; thus there is probably no significant role for triplet states. Secondly, both C-N bonds are broken within a short time, of the order of 1 ps. The majority of trajectories show almost simultaneous bond breaking, but, even when the CH3NN' radical is formed, its lifetime is too short to permit experimental detection. This result is consistent with a concerted mechanism, which has already been deduced from molecular beam experiments. A comprehensive theoretical study has been made of the potential energy surfaces and reaction pathways of the singlet (SO, S1) and triplet (TI, T2) states associated with the photolysis of 2,3-diazabicyclo[2.2.l]hept-2-ene(1) (Scheme 1): The S1 (nn*), TI (nx*), and T2 (RX*) reaction paths for N2 elimination via CN cleavage to a diazenyl diradical(2), and for rearrangement to an azirane ( 5 ) by way of CC cleavage to a hydrazonyl diradical(4), have been investigated, as well as reaction pathways for cyclization and rearrangement of the I ,3cyclopentadienyldiradical Photochemistry, Volume 30 0The Royal Society of Chemistry, 1999

296

297

IIi7: Photoelimination

(3). The reactions evolve through a network of 18 ground and excited state intermediates, 17 transition structures and 10 'funnels', where internal conversion or intersystem crossing may occur. A stable excited state 3(n7t*)3(7m*) intermediate is proposed as the best candidate for the transient triplet intermediate observed experimentally.

0-@

(4)

Scheme 1

(5)

Photolysis of (E)-perfluoroazooctane with 185 nm light provides an efficient method for the perfluorooctylation of aromatic and heteroaromatic compounds, such as benzene, toluene, anisole, furan, thiophene and pyrr01e.~Reported yields are in the range 50-75%. Mechanistic studies based on measurements of quantum yield, dependence on light intensity and UV-visible absorption showed that (E)perfluoroazooctane is isomerized to the (&)-isomer by absorption of one photon, with subsequent extrusion of N2 on absorption of a second photon. Thermolysis of the y-azoperester, tBuN=NCMe2CH2CHzCO+Bu, produces the y-azoradical, t-BuN=NCMe2CH2CH2',which undergoes cyclization by attack of the radical centre on the azo linkage.6 In contrast, photolysis of this y-azoperester selectively cleaves the azo group, yielding the y-perester radical, * C M ~ ~ C H ~ C H ~ C O + B U , which undergoes intramolecular attack on the peroxide linkage to give tetrahydro-5,5-dimethyl-2-furanone. A number of annulated 5-alkylidene-4,5-dihydro1H-tetrazoles, such as (6, (R=H, Me) (Scheme 2), have been synthesized and a study made of their ph~tolyses.~ For example, photolysis of (6) in d8-toluene at -60°Cresults in extrusion of N2, giving annulated iminoaziridines (E- and 2-7)with exocyclic C=N- bonds. On thermolysis, the iminoaziridines undergo [2 + 11 cycloreversion into methyl isocyanide and cyclic imines (8, R = H, Me). Irradiation of the tricylic analogue (9) (Scheme 3) in 2-methyltetrahydrofuran or butyronitrile matrices at 77 K yields a triplet diradical, with a four-line ESR spectrum, which is assigned the structure (1 0), the first triplet diazatrimethylenemethaneto be reported. The chemistry of the photoactive diazosulfonate group (-N*SO