Solvation Dynamics in Mixtures of Polar and Nonpolar Solvents

Abstract

Time-resolved Stokes shift measurements and steady-state absorption and fluorescence measurements of Coumarin 153 (C153) at different temperatures were used to explore the solvation dynamics of binary mixtures of alcohols and alkanes at various alcohol concentrations. These solvent mixtures show even at alcohol concentrations as low as 0.3% a strong Stokes shift of about 1200 cm-1. Depending on alcohol concentration, this Stokes shift takes place on a time scale ranging from 300 ps up to several nanoseconds. These characteristic times are 2 orders of magnitude longer than the relaxation times typically found in alcohols, which is attributed to rotational reorientation of the solvent molecules. A monoexponential temporal behavior of the Stokes shift and a linear dependence of the time constants on the alkane viscosity are observed. These results and temperature dependent static fluorescence measurements strongly support a diffusion-controlled process of solvation in these mixtures.