PHOTOCHEMISTRY OF ANIONIC POLYMETHINE DYES

Spectral and kinetic properties of photoisomers and triplet molecules of a number of anionic polymethine dyes, namely, differential absorpti on spectra, rate constants (k(i)) and activation parameters of reverse cis-trans-isomerization, and triplet-state-decay rate constants k(T), are studied by flash photolysis. CINDP/2 calculations of electron den sity in anionic dyes show that k(i) and k(T) in polar solvents are det ermined primarily by the electronic effect of the substituents in the meso-position of the polymethine chain of a dye. The increase in k(i) due to the formation of ion pairs consisting of a dye with a counterio n is observed in nonpolar solvents.