ULTRAFAST MEASUREMENTS OF THE DYNAMICS OF SOLVATION IN POLAR AND NONDIPOLAR SOLVENTS

The dynamics of solvation of the probe solute coumarin 153 has been measured with similar to 100 fs time resolution using the fluorescence upconversion technique. A wide variety of solvents, including polar aprotic solvents, hydrogen bonding solvents, and non-dipolar solvents have been examined. For all solvents of even moderate polarity (epsilon(0)>5), the solvation dynamics observed follows the predictions simple models based on the solvent's bulk dielectric response. For a number of ''non-dipolar'' solvents such as dioxane and benzene, for which epsilon(0)<5, we observe surprisingly large time-dependent shifts, which seem to reflect the solute interacting with the large quadrupole (and higher multipole) moments of the solvent molecules. These dynamics represent a solvation distinct from the dipolar solvation dynamics previously studied and they cannot be modeled in terms of any currently available theory.