Transient solvation of polar dye molecules in polar aprotic solvents

Subpicosecond fluorescence spectroscopy of the polar dye molecules coumarin 311 and coumarin 102 has been used to measure the microscopic solvation dynamics of several polar aprotic solvents. The measured solvation times are significantly longer than the longitudinal relaxation times τ1 of the solvents. τ1 is the predicted time for solvation according to dielectric continuum theory. The experiments were made with a newly constructed subpicosecond ultraviolet emission apparatus that takes advantage of recent advances in ultrafast laser technology. The newly developed, time saving procedure [Nagarajan et al., J. Chem. Phys. 86, 3183 (1987)] for measuring the microscopic solvation response functions was used in this research.