DECAY ASSOCIATED FLUORESCENCE-SPECTRA OF COUMARIN-1 AND COUMARIN-102 - EVIDENCE FOR A 2-STATE SOLVATION KINETICS IN ORGANIC-SOLVENTS

Bi- and triexponential and emission-wavelength-independent fluorescence decays have been observed for the 7-aminocoumarins C1 and C102 in several polar solvents. An analysis of the lifetimes of the short-lived components and of the decay-associated spectra of the decay components demonstrates that the solvation dynamics of the excited states fit an irreversible two-state kinetic model. Clear differences in the fluorescence decay kinetics were found between the coumarin dyes in 1-octanol on one hand and in methanol or 1-butanol, on the other, which may indicate subtle differences in the solvation process in the two cases.