TIME-RESOLVED SPECTROSCOPY OF PHOTOELECTRON TRANSFER-REACTIONS OF POLYMETHINE DYES

The temporal and spectral behaviour of transient radicals produced after excitation of the singlet excited states of polymethine dyes was investigated by means of time-resolved absorption spectroscopy in the picosecond and microsecond range. Our investigations of electron transfer processes of cationic carbocyanines in solution with electron donors as well as with electron acceptors have shown that the transient dye radical spectra of both species (dication radical as well as the neutral radical) are blue-shifted with respect to the spectrum of the cationic dye. Only slight differences have been found between both radical spectra in solution. The decay kinetics of these transients differ in solution considerably from each other. Whereas the dication radical has in methanolic solution a lifetime of some nanoseconds, the neutral radical which is build up inbetween 50 picoseconds decays with a lifetime of approximately 600 ps. © 1990.