SUBPICOSECOND MEASUREMENTS OF POLAR SOLVATION DYNAMICS - COUMARIN-153REVISITED

Time-resolved emission measurements-of the solute coumarin 153 (C153) are used to probe the time dependence of solvation in 24 common solven ts at room temperature. Significant improvements in experimental time resolution (similar to 100 fs instrument response) as well as correspo nding improvements in analysis methods provide confidence that all of the spectral evolution (including both the inertial and the diffusive parts of the response) are observed in these measurements. Extensive d ata concerning the steady-state solvatochromism of C153, coupled to an examination of the effects of vibrational relaxation, further demonst rate that the spectral dynamics being observed accurately monitor the dynamics of nonspecific solvation. Comparisons to theoretical predicti ons show that models based on the dielectric response of the pure solv ent provide a semiquantitative understanding of the dynamics observed.