Solvent dynamic effects in electron transfer reactions in slow liquids: interplay between ultra-fast solvation and vibronic coupling in betaines

Abstract

Recent experimental and theoretical studies have indicated that for many electron transfer reactions in slow liquids, like alcohols, the dynamics solvent effects are remarkably absent. This particularly evident in betaines which, according to the classical Marcus picture, is in the inverted regime. An analysis based on the hybrid model indicates that the absence of the solvent dynamic effects may arise due to the presence of an ultra-fast component in the solvation dynamics which allows the system to probe efficient vibronic channels from the product surface. Detailed calculations on the betaine charge transfer behavior in alcohols have been carried out by using a newly developped technic which allows us to include the biphasic solvation dynamics consistently. However, the results indicate that for alcohols, solvent relaxation effects continue to play a role, though weakened due to the vibronic channels, in electron transfer. This seems to indicate that further generalization of the hybrid-model may be necessary in order to explain the experimental results.