FEMTOSECOND TO NANOSECOND SOLVATION DYNAMICS IN PURE WATER AND INSIDE THE GAMMA-CYCLODEXTRIN CAVITY

The dynamics of solvation of an excited chromophore in pure water and in a restricted space with a limited number of water molecules have been studied. The time-dependent Stokes shift of Coumarin 480 (C480) and Coumarin 460 (C460) were measured using femtosecond fluorescence upconversion and time-correlated single-photon-counting techniques. The system with a limited number of water molecules was an inclusion complex of Coumarin dyes with gamma-cyclodextrin (gamma CD). The results of molecular dynamics simulations are compared with the observed solvent response in pure water and in the gamma CD cavity. The observed relaxation times range from < 100 fs to 1.2 ns. Solvation of C480 in pure water is observed to occur with time constants of <50 and 310 fs. In sharp contrast with the solvation response in pure water, in the case of the C480/gamma CD inclusion complex, additional long solvation time constants of 13, 109 and 1200 ps are observed. The stoichiometry, structure and dynamics of the Coumarin/gamma CD complexes are also discussed.