Organic Photochromic and Thermochromic Compounds Volume 2: Physicochemical Studies, Biological Applications, and Thermochromism Edited by John C. Crano Late of PPG Industries, Inc. Monroeville, Pennsylvania and Robert J. Guglielmetti University of Aix-Marseille II Marseille, France Kluwer Academic / Plenum Publishers New York, Boston, Dordrecht, London, Moscow
Introduction 1. Aim and Organization of the Book 1 2. Brief Historical Survey of Photochromism 2 3. Definitions of Photochromism 2 4. Brief Overview of the Chapters in the Book 4 5. Conclusion and Future Developments 7 References 8 1. Photochromic Polymers Kunihuro Ichimura 1.1. Introduction 9 1.2. Photochromism in Polymer Matrices 11 1.2.1. Synthesis 11 1.2.2. Matrix Effect on Photochromism 15 1.2.2.1. Spiropyrans and Related Compounds 15 1.2.2.2. Azobenzenes 16 1.2.2.3. Viologens 18 1.2.2.4. Fulgides 20 1.2.2.5. Photochromism in Sol-Gel Inorganic Matrices... 21 1.2.3. Polarization Photochromism in Polymer Solids 24 1.2.3.1. Background 24 1.2.3.2. Polymers Doped with Photochromic Compounds... 24 1.2.3.3. Polymers with Covalently Bound Photochromic Units 26 1.3 Photochromic Liquid-Crystalline Polymers 31 1.3.1. Photochromism in Polymeric Mesophases 31 1.3.1.1. Nematic and Smectic Phases 31 1.3.1.2. Cholesteric Phases 34 1.3.2 Polarization Photochromism of Liquid-Crystalline Polymers 35 xv
xvi 1.4. Surface Photochromism for Regulation of Liquid-Crystal Alignment 39 1.4.1. Surface-Assisted Liquid-Crystal Alignment Control 39 1.4.2. Out-of-Plane Alignment Photocontrol 40 1.4.2.1. Spin-Coated Films 40 1.4.2.2. Polymeric Langmuir-Blodgett Films 44 1.4.3. In-Plane Alignment Photocontrol 47 1.5. Concluding Remarks 50 Appendix. Preparation of Photochromic Polymers 52 A.l. Polymethacrylates Substituted with Spiroindolinebenzothiopyrans (5) 52 A.2. Polymethacrylates with Spirofluorenylindolizines 53 A.3. Poly[4'-[[2-acryloyloxyethyl]ethylamino]-4-nitroazobenzene] (12) 53 A.4. An Ionene Polymer Incorporating Viologen Units (17) 53 References 54 2. Photodegradation of Organic Photochromes V. Malatesta 2.1. Introduction 65 2.2. Properties and Reaction Mechanism(s) of Spiropyrans and Spirooxazines 66 2.2.1. Multiplicity of the Photoreactive State 67 2.2.2. The cis-cisoid X Isomer 68 2.2.3. Nitro-Substituted Spiropyrans, SP N0 68 2.2.4. Unsubstituted Spiropyrans and Spirooxazines 70 2.3. Colorability and Photostability (Photocoloration Quantum Yields).. 74 2.4. Photo- and Thermal Degradation of Photochromes 75 2.4.1. Degradation of Spiropyrans: General Approach 75 2.4.2. Photodegradation: Dependence on the Nature and Position of the Substituent 77 2.4.3. Substituents on the Indoline Moiety of Spiropyrans: Inductive and Mesomeric Effects 81 2.4.4. Substituents on the Indoline Moiety 82 2.4.5. Substituents on the Chromene Moiety of Spirobenzopyrans.. 84 2.4.5.1. Monosubstituted Compounds 84 2.4.5.2. Disubstituted Compounds 84 2.4.5.3. C3-Substituted Spiropyrans 84 2.4.5.4. Substituents on N and C3' 89 2.5. Photodegradation of Benzothiazolinospiropyrans 93 2.6. Saturated Five-Membered Ring Azaheterocyclic Spiropyrans 96 2.6.1. Pyrrolidine Series (X=C(CH 3 ) 2 ) 97
XVÜ 2.6.2. Thiazolidine Series (X=S) 99 2.6.3. Oxazolidine Series (X=0) 99 2.7. Saturated Six-Membered Ring Azaheterocyclic Spiropyrans 99 2.8. Spiropyran Degradation: A Quantitative Approach 99 2.9. Non-Azaheterocyclic Spiropyrans 111 2.9.1. 6- and 8-Substituted Spirobenzodithiolane and Spirobenzoxathiolane Benzopyran Series Ill 2.9.2. Spiro[bibenzopyrans] 115 2.9.3 Dithiole Series 115 2.10. Photodegradation of Spirooxazines 115 2.10.1. Solvent Polarity and Photodegradation 119 2.10.2. Structure and Photodegradation 119 2.10.3. Mechanism of Photooxidation of Spirooxazines: Singlet-Oxygen Reactivity 124 2.10.4. Oxidation in Dark Reactions of Spirooxazines 136 2.10.5. Reaction of Merocyanines with Free Radicals 141 2.11. Photodegradation Measurements: Experimental Apparatus 143 2.11.1. Irradiation Source 143 2.11.2. Analysis Setup 147 2.11.3. Signal-Conditioning Circuits (SCC) 147 2.11.4. Operating Modes 148 2.12. Photostability of Fulgides 151 2.13. Commercial Spirooxazines and Chromenes: Relevant Properties and Behavior 153 References 164 3. Photokinetics under Continuous Irradiation M. H. Deniel, D. Lavabre, and J. C. Micheau 3.1. Introduction 167 3.2. Dynamic Analysis of the Isolated Photochemical Step: А-»-В(1ф) 170 3.2.1. Establishment of the Photochemical Rate Equation 170 3.2.2. Photochemical Reactor Uniformly Stirred and Equipped with a System for UV/Visible Spectroscopic Analysis 172 3.2.3. Experimental Verification of the Validity of the Photochemical Kinetic Equations under Continuous Irradiation 173 3.3. AB Systems Involving Two Species 174 3.3.1. Establishment of the General Kinetic Equation under Continuous Irradiation 175
XV111 3.3.2. Properties of the Photostationary State of the AB, 2ф, Ik System 175 3.3.2.1. AB, 1ф, Ik Systems 176 3.3.2.2. AB, 2ф, Systems 177 3.3.3. Photostationary Methods 177 3.3.4. Dynamical Method 177 3.4. ABC Photochromic Systems Involving Three Species 182 3.4.1. General Comments 182 3.4.2. Examples 183 3.4.2.1. Systems with Two Photoisomers 183 3.4.2.2. Photodegradation of a Spiro[indoline-benzopyran].. 186 3.5. ABC Systems Exhibiting Nonlinear Behavior 190 3.5.1. Ideal ABC System Giving Rise to Bistability 190 3.5.2. Photochromism and Photodegradation of TPID 191 3.6. Conclusion 194 Appendix 1. Flash Photolysis versus Continuous Irradiation: Influence on the Accumulation of Reaction Intermediates 195 Appendix 2. Photostationary Methods 195 A2.1. AB, 2ф, 1А: Systems 195 A2.2. AB, 1ф, ljt Systems 197 A2.3. AB, 2ф Systems 198 Appendix 3. Thermal Relaxation of an ABC System 199 Appendix 4. Localization of an Elementary Relaxation Process in ABC Systems 202 Appendix 5. Localization of a Photodegradation Process 203 References 205 4. EPR and Radical Processes Angela Alberti 4.1. Introduction 211 4.2. Viologens 212 4.2.1. Radical Cations from the Reduction of Viologens 212 4.2.2. Some Particular Viologens 219 4.2.3. EPR of Viologens in Micellar Systems 220 4.3. ß-Tetrachloro-oc-Ketonaphthalene 224 4.4. Spiroindolinic Photochromes 226 4.4.1. Paramagnetic Species in Photochromism and Photodegradation 226 4.4.2. Radical Ions from Spiro Compounds 229 4.4.3. Spin Probes and Spin Traps with a Spiroindolinic Structure.. 234 References 236
xix 5. Molecular Modeling Calculations Shinichiro Nakamura 5.1. Introduction 241 5.2. Absorption Wavelength and Intensity 241 5.3. Thermal Stability 247 5.3.1. Photon-Heat Mode 247 5.3.2. Photon-Photon Mode 249 5.4. Reaction Mechanism 251 5.4.1. Spiropyran Derivatives 251 5.4.2. Fulgide Derivatives 253 5.4.3. Other Photochromic Systems 253 5.5. Quantum Yield 255 References 256 6. The Enantiomers of 2-Donor-Substituted Benzopyrans and Benzo-l,4-oxazines and Their Thermal Racemization Albrecht Mannschreck, Klaus Lorenz, and Michael Schinabeck 6.1. Introduction 261 6.2. Methods of Investigation 263 6.2.1. Remarks Pertaining to All Methods 263 6.2.2. Preparative Enrichment of Enantiomers by Enantioselective Liquid Chromatography 263 6.2.3. Determination of Enantiomeric Purities 265 6.2.4. Assignment of Relative Configurations 267 6.2.5. Measurement of Barriers by Thermal Racemization 269 6.3. Results of the Thermal Racemizations 271 6.3.1. Transition State of C(sp3)-0 Bond Cleavage 271 6.3.2. Remarks Pertaining to All Types of Benzopyrans and Benzo-l,4-Oxazines 273 6.3.3. 2-Aryl-2-methylbenzopyrans 274 6.3.4. 2-Alkoxybenzopyrans 274 6.3.5. Spirobibenzopyrans 280 6.3.6. Spirofoxaindane-benzopyrans] 283 6.3.7. Spirofindoline-benzoxazines] 284 6.3.8. Spiro[indoline-benzopyrans] 288 6.4. Conclusion 290 References 292
XX 7. Structural Studies by X-Ray Diffraction Serguei Aldoshin 7.1. Introduction 297 7.2. Spiropyrans 298 7.2.1. Indolinospiropyrans 298 7.2.1.1. Structural Features of SP Molecules 298 7.2.1.2. The Nature of Structural Changes in SP Molecules upon Photoexcitation 303 7.2.1.3. Effect of the Nature and Position of Substiruents in SP Molecules on the Length of the C spiro -0 Bond 304 7.2.2. The Structure of Permanent Merocyanines Models of the Open Forms of Indolinospiropyrans 306 7.2.2.1. Molecular Structure of Merocyanines 307 7.2.2.2. Geometric Isomers of Merocyanine Forms 312 7.2.2.3. Nature of the Molecular Packing and Energy of Intermolecular Interactions in Merocyanine Crystals 314 7.2.3. Effect of the Nature of Heteroatoms in the Spiro Center on the Structure and Photochemical Properties of Spiropyrans 315 7.2.3.1. Structural Features of Indoline Spirothiopyrans Containing S and N Heteroatoms in the Spiro Center 315 7.2.3.2. Structure of "Symmetrical" Spiropyrans Consisting of Two Benzopyran Fragments 317 7.2.3.3. Structure of the First Representative of Spiro-2tf- Naphtho[l,8-6c]oxepins (SPNO) 318 7.2.4. 2-Oxaindan Spiropyrans with Polycondensed Chromene Fragments 320 7.2.4.1. Structure of 2-Oxaindan Spiropyrans 320 7.2.4.2. Thermal Valence Isomerization of SPs 323 7.2.4.3. Photochromism of 2-Oxaindan Spiropyrans 324 7.3. Spirooxazines 324 7.4. Photochromic [2#]-Chromenes 330 7.5. Spirans of the Perimidine Series 333 7.6. Fulgides 338 7.6.1. Arylidene Derivatives of Fulgides (ArF) 339 7.6.2. Fulgides of the Indole Series 343 7.7. Conclusion 350 References 350
xxi 8. New Trends in Raman Studies of Organic Photochromes Jean Aubard 8.1. Introduction 357 8.2. Survey of Vibrational Studies on Spiropyran and Spirooxazine Photochromes 359 8.3. Dynamics and Structure of Transient Species Involved in the Photochromic Process of Spiro Compounds as Probed by Time-Resolved Raman Techniques 366 8.3.1. Instrumentation 367 8.3.2. Survey of Recent Time-Resolved Raman Studies of Spiro Compounds 369 8.3.3. Time-Resolved Resonance Raman Spectroscopy of Indolinospironaphthoxazines: Experimental Evidence for a TTC Resonant transoid Open Form in Different Solvents... 372 8.4. Surface-Enhanced Raman Spectroscopy of Spiro Compounds: A Route for Direct Detection and Identification of Their Photodegradation Products 378 8.4.1. SERS Detection of Spirooxazines and Spiropyrans at Trace Levels in Silver Colloidal Solutions 378 8.4.1.1. Brief Description of the SERS Effect 378 8.4.1.2. Analysis of SERS Spectra of Some Spiro Compounds 380 8.4.2. Detection by SERS of Degradation Products from UV-Irradiated Solutions of 8-Methoxy-6-Nitro-BIPS 382 8.4.2.1. Assignments of SERS Spectra of 8-Methoxy-6- Nitro-BIPS 382 8.4.2.2. SERS Analysis of UV-Irradiated Solutions of Photochromes 386 References 389 9. Biological Applications Supramolecular Chemistry Masahiko Inouye 9.1. Introduction 393 9.2. Photocontrol of Peptide and Protein Characteristics by Spiropyrans 394 9.2.1. Photomodulation of Polypeptide Conformation 394 9.2.2. Photoregulation of Protein Characteristics 397 9.2.2.1. Photoregulated Binding of Spiropyran-Modified Receptor Proteins 397
XXÜ 9.2.2.2. Photoregulation of Enzyme Activity by Use of Spiropyrans 398 9.2.2.3. Photocontrol of Antigen-Antibody Reactions 401 9.3. Spiropyran Derivatives Possessing a Molecular Recognition Site... 402 9.3.1. Spiropyran Derivatives as Artificial Signaling Receptors... 402 9.3.1.1. Crowned Spiropyrans as Alkali (Alkaline-Earth) Metal Cation Receptors 402 9.3.1.2. Spiropyridopyrans as Nucleobase Receptors 406 9.3.2. Photoregulation of Polymer Characteristics by Crowned Spiropyrans 408 9.3.3. Other Applications Utilizing Spiropyran Derivatives 410 References 412 10. Thermochromism of Organic Compounds Andre Samat and Vladimir Lokshin 10.1. Introduction 415 10.2. Spiroheterocyclic and Related Compounds 416 10.2.1. Compound Families 416 10.2.1.1. Spiropyrans and Spirooxazines 416 10.2.1.2. [2//]-pyrans 421 10.2.1.3. Other Spiroheterocyclic Compounds 421 10.2.2. Mechanism of Thermal Isomerization 422 10.2.2.1. Theoretical Studies 422 10.2.2.2. Activation Parameters of the Isomerization Reactions 425 10.2.3. Evaluation of Equilibrium Constants 431 10.3. Schiff Bases and Related Nitrogen-Containing Compounds 436 10.3.1. Thermochromism of Salicyl-Schiff Bases 436 10.3.2. Structural, Spectroscopic, and Theoretical Studies of Intramolecular Hydrogen Bonding 445 10.4. Biathrones and Other Overcrowded Ethenes 451 10.5. Miscellaneous Compounds 457 10.6. Conclusion 459 References 460 Index 467