Investigation of the solvation dynamics of an organic dye in polar solvents using the femtosecond transient grating technique

The solvation dynamics of an organic dye, IR140, in methanol, ethanol, and in a series of six alkanenitriles has been investigated using the transient grating technique. In all solvents, the dynamics exhibit ultrafast, almost solvent-independent, components ascribed to inertial solvation, and a slow er viscosity-dependent component, due to diffusive solvation. The relative amplitudes of these components depend on both the solvent and on the wavele ngth at which the experiment is performed. The contribution of inertial mot ion increases with decreasing size of the solvent molecules and with decrea sing wavelength. It appears that diffusive motion is associated with a loos e solvent shell, while inertial motion dominates when the solvation layer i s dense.