SOLVATION DYNAMICS IN MIXTURES OF POLAR AND NONPOLAR-SOLVENTS

Time-resolved Stokes shift measurements and steady-state absorption an d fluorescence measurements of Coumarin 153 (C153) at different temper atures were used to explore the solvation dynamics of binary mixtures of alcohols and alkanes at various alcohol concentrations. These solve nt mixtures show even at alcohol concentrations as low as 0.3% a stron g Stokes shift of about 1200 cm(-1). Depending on alcohol concentratio n, this Stokes shift takes place on a time scale ranging from 300 ps u p to several nanoseconds. These characteristic times are 2 orders of m agnitude longer than the relaxation times typically found in alcohols, which is attributed to rotational reorientation of the solvent molecu les. A monoexponential temporal behavior of the Stokes shift and a lin ear dependence of the time constants on the alkane viscosity are obser ved. These-results and temperature dependent static fluorescence measu rements strongly support a diffusion-controlled process of solvation i n these mixtures.