Subpicosecond solvation relaxation of 4-(dicyanomethylene)-2-methyl-6-(p-(dimethylamino)styryl)-4H-pyran in polar liquids

The solvation dynamics of 4-(dicyanomethylene)-2-methyl-6-(p-(dimethylamino)styryl)-4H-pyran (DCM), dissolved in a polar solvent methanol, ethylene glycol, ethyl acetate, or acetonitrile, has been studied using the fluorescent up-conversion technique with a time resolution of approximate to 100 fs. Typically a bimodal dynamic Stokes shift behavior is found, with time constants of about 100 fs and a few picoseconds, respectively. The initial component in the solvation relaxation is attributed to the effect of free streaming motions of the solvent molecules, whereas the second component is typical of the rotational diffusion motions of the solvent molecules. From the initial rapid rise in the integrated emission intensity it is concluded that electron transfer is preferably to a higher lying (less emissive) charge transfer state which is formed in less than 100 fs.