Dynamics of Solvation and Charge Transfer Reactions in Dipolar Liquids

Abstract

The effects of solvent and solvent dynamics on chemical reactions, especially on charge transfer processes, have long been a subject of great importance in physical chemistry. In the past, attention was focused pri­ marily on equilibrium solvent effects, such as the effect of solvent polarity on the reaction potential surface. Tn recent years it has become clear that in many fast reactions solvent dynamics can play a direct role and can affect both the rate and the outcome of a reaction profoundly. Thus, an understanding of the time-dependent response of a polar solvent to a changing charge distribution in a polar solute molecule is essential to understand the role of solvent in many important chemical and biological processes in liquids. Such understanding can be achieved by studying the dynamics of solvation of a newly created ion or of an instantaneously changed dipole in a polar liquid. This subject has undergone a renaissance in recent years because of the availability of ultra-short laser pulses that make it possible to study solvation dynamics directly with a time resolution hitherto impossible. An understanding of the details of solvent response to a sudden change in the charge distribution of a polar solute probe molecule is beginning to emerge. Experimental studies on the dynamics of solvation are usually carried out by instantaneously creating a charged species inside a polar solvent and subsequently monitoring the emission/absorption spectrum of this