Subpicosecond solvation relaxation of DASPI in polar liquids

The solvation dynamics of 2-(p-dimethylaminosotyryl)pyridylmethyl iodide (DASPI) dissolved in the solvents methanol, ethylene glycol, ethanol and acetonitrile, has been studied using the fluorescent up-conversion technique with a time resolution of about 100 fs. A bimodal solvent response function is obtained for DASPI dissolved in the polar solvents. In the bimodal response function the ultrafast initial decay component, a Gaussian term with a characteristic frequency of ωG ≊ 10 ps−1, is attributed to inertial free streaming motions of the solvent molecules. In addition, for all solutions slower decay components with time constants of several picoseconds typical of rotational and translational diffusional motions of the solvent molecules have been found.