Site specific solvation statics and dynamics of coumarin dyes in hexane-methanol mixture

We have studied the solvation statics and dynamics of coumarin 153 and 102 dyes in hexane - methanol mixtures. The solvation of the coumarin dyes, both in the ground and in the excited electronic states, exhibits a nonlinear solvatochromic shift in the methanol mole fraction. The solvation dynamics of both dyes in their excited states are rather slow and depend on the mixture composition. The statics and dynamics of the spectroscopic data are attributed mainly to the formation of a hydrogen bond between methanol and the carbonyl group of the coumarin dye. IR spectra of the coumarin dyes in these binary mixtures confirm the formation of hydrogen bonding with the carbonyl group. We analyzed the statics and dynamics of the solvation of coumarin dyes in a hexane - methanol mixture using a model of two distinct solvates. The first solvate is a coumarin dye which is not hydrogen bonded at the carbonyl group. The second solvate has a specific hydrogen bond between the hydroxyl group of the methanol and the carbonyl group of the coumarin dye. The excited-state dynamics are followed by time-resolved emission, and the analysis is based on the irreversible diffusion-influenced chemical reaction formalism.