Picosecond solvation of electronically excited solutes in alcoholic solvents: non-debye behaviour of the time-dependent fluorescence shift related to h

Abstract

Time-dependent fluorescence shifts (TDFS) of polar compounds in a series of alcoholic solvents have been studied on a pico-second time scale. A non-exponential TDFS kinetic behaviour is observed, particularly at short times (0< t< 50 ps). It cannot be represented by a sum of decreasing exponentials. The effects of solute-solvent interactions on the kinetics of TDFS have been analysed. It is shown that the non-standard kinetics is due to hydrogen bonding in the solvent, particularly to the presence of alcoholic hydrogen-bonded aggregates. Following electronic excitation of the polar solute reorganization of solvent aggregates controls the TDFS time development. Our results show that a simple Debye model is inadequate to explain such a process.