Solvation Dynamics in Ionic Liquids, Results from ps and fs Emission Spectroscopy

Abstract

This chapter summarizes much of the data currently available on solvation dynamics in ionic liquids. Data show that complete solvent equilibration is much slower in high-viscosity solvents than it is in most conventional solvents. Attempts to correlate solvation times with viscosities and ion diffusion constants suggest that translational diffusion over small distances is the likely mechanism of solvation in ionic liquids. Despite the slow overall response in these systems, femtosecond Kerr-gated emission spectroscopy measurements also reveal significant relaxation. In some cases, the response may be clearly bimodal, but, in most cases, solvation in ionic liquids is characterized by a remarkably broad distribution of relaxation times. This broad distribution of times together with a number of other experimental observations suggests the glassy character of dynamics in ionic liquids. Much more experimental work, together with help from computer simulations and theory, is needed before a satisfying understanding of the dynamics of these interesting new liquids is achieved.