Photoisomerization and Related Processes

A different type of environmental effect is manifested in the photoisomerization of trans-stilbene complexed to cyclodextrin. In picosecond laser studies a single decay in a-cyclodextrin shows binding occurs at one site, whilst in the (3-forra 

It has been deduced that the dimensionality of stilbene isomerization may not be one-dimensional, as commonly assumed, from an examination of the kinetics of isomerization of the meta-methyl substituted derivative of stilbene in decane as a function of 

Hochstrasser and his co-workers on both stilbene and diphenyl-butadiene. Their interpretation is based on measurements carried on the stiff diphenylbutadienes, where the phenyls are held rigid by saturated chains of 2-4 carbon atoms linked through the 2 positions of aromatic ring to the double band. The apparent energy barriers and the dependence on viscosity deviate from the Kramer s model but are consistent with the modified Kramers-Hubbard model 

Waldeck, on the other hand, conclude from their studies on 4,4 -dimethyl-stilbene in n-alkane solvents that the 1-dimensional hydrodynamic Kramers equation is not appropriate. In their view a 2-dimensional co-ordinate system with a reaction trajectory related to solvent viscosity is more appropriate. Further contributions to this subject are certain. 

Related studies have been carried out on isomeric stilbene 

3 Photoisomerization and Related Processes. - These rearrangements provide model systems for the examination of primary processes but are now showing increasing promise for exploitation 

Robinson have analysed the molecular dynamics of cis-trans isomerization and details of the influence of solvent structure. Excluded volume effects and the different sizes of cis and trans isomers have both been taken into account in this model. The 

Hynes and Kramers models for this type of process are compared with the experimental data. 

Schiff bases of various retinals and also have reported the 

The picosecond dynamics of barrier crossing in the conformational change of 1,1 -binapthyl in a series of alcohol 

A quantum chemical study of the mechanism of the cis-trans photochemical isomerization in retinal like protonated Schiff bases uses the model compound 1-imino-2.3-pentadiene23. The lowest excited state is B like but the second A like state is particularly labile photochemically. The photoisomerization of all trans-retinal has been studied in a variety of organic solvents and organized media232 The structure of the isomers involved in the photoisomerization of retinoic acid and photoprotective effects in model physiological solutions have been determined233. picosecond time-resolved absorption study of 

The influence of the counter anion on the excited state relaxation time of cationic polymethine dyes has also been reported . The fluorescence lifetime is dependent on the anion in weakly polar media but independent in polar media. The fluorescence behaviour of highly concentrated rhodamine GG solutions in methanol and water can be separated into monomer and dimer contributions2. Absorption emission and excitation spectral data support the view that the dye rose bengal forms H-type aggregates in water and polar protic solvents 1. The spectroscopic behaviour of rhodamine 6G in polar and nonpolar solvents as well as in thin glass and PMMA films shows dimer formation occurs and their stabilities have been compared under different conditions. The equilibrium between the neutral 

Aggregation of rose bengal units in synthesised dimeric systems has been used as a model for the medically interesting haematoporphyrin derivative dimer 1. 

The deactivation of the UV stabilizers of the 2-(hydroxyphenyl)—benzotriazole class which involve intramolecular hydrogen bonds has been researched in much detail in the 

Cis-trans photoisomerization of diarylethylene in ethanol glasses in the temperature range of 4.2 to 100K shows that structural nonequilibrium occurs in such matrices23S  

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Photoisomerization and Related Processes - The photoisomerization of stilbene and the related photophysics of this molecule must surely be the most thoroughly examined of all single photochemical systems. Nevertheless further investigations continue... 

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