SUBPICOSECOND SOLVATION RELAXATION OF DASPI IN POLAR LIQUIDS

The solvation dynamics of 2-(p-dimethylaminostyryl)pyridylmethyl iodid e (DASPI) dissolved in the solvents methanol, ethylene glycol, ethanol and acetonitrile, has been studied using the fluorescent up-conversio n technique with a time resolution of about 100 fs. A bimodal solvent response function is obtained for DASPI dissolved in the polar solvent s. In the bimodal response function the ultrafast initial decay compon ent, a Gaussian term with a characteristic frequency of omega(G) congr uent to 10 ps(-1), is attributed to inertial free streaming motions of the solvent molecules. In addition, for all solutions slower decay co mponents with time constants of several picoseconds typical of rotatio nal and translational diffusional motions of the solvent molecules hav e been found.