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

The dynamics of solvation of the probe solute coumarin 153 has been me asured with similar to 100 fs time resolution using the fluorescence u pconversion technique. A wide variety of solvents, including polar apr otic solvents, hydrogen bonding solvents, and non-dipolar solvents hav e been examined. For all solvents of even moderate polarity (epsilon(0 )>5), the solvation dynamics observed follows the predictions simple m odels based on the solvent's bulk dielectric response. For a number of ''non-dipolar'' solvents such as dioxane and benzene, for which epsil on(0)<5, we observe surprisingly large time-dependent shifts, which se em to reflect the solute interacting with the large quadrupole (and hi gher multipole) moments of the solvent molecules. These dynamics repre sent a solvation distinct from the dipolar solvation dynamics previous ly studied and they cannot be modeled in terms of any currently availa ble theory.