NONEXPONENTIAL SOLVATION DYNAMICS OF SIMPLE LIQUIDS AND MIXTURES

Novel measurements on the microscopic solvation dynamics of coumarin probes in several simple polar solvents and solvent mixtures have been made using the time dependent fluorescence Stokes shift technique. The microscopic solvent relaxation function, C(t), is observed to be poorly modeled by a single exponential decay in many cases. The average experimental solvation times, <tau-s>, for pure solvents and binary solvent mixtures are close to values predicted by dielectric continuum theory, but in many cases, the observed C(t) shape does not agree with that predicted by dielectric continuum theory. The results suggest that molecular motion of solvent molecules near the solute can be responsible for microscopic solvation components of C(t) that are not predicted using bulk dielectric data of the neat solvent and the dielectric continuum theory. In addition to the solvation dynamics results, some potential sources of probe molecule non-ideality are examined, and it is shown that these effects are not significant contributors to experimental error for these C(t) measurements.