High-pressure studies of rotational dynamics for coumarin 153 in alcohols and alkanes

Subpicosecond fluorescence anisotropy measurements are used to characterize the rotational dynamics of coumarin 153 (C153) at high pressures in a series of alcohol and alkane solvents, Rotational correlation times (tau(R)) are determined as a function of solvent viscosity to reveal the effect of the frictional behavior of the solvent. The results of the viscosity dependence of tau(R) were compared with those predicted by the hydrodynamic model. Bimodal anisotropy decays of excited C 153 are observed only in alcohol solvents. The specific viscosity dependence of tau(R) in alcohols, which is observed when the solvent viscosity is varied by changing the pressure, is discussed on the basis of the pressure dependence on the solute-solvent and solvent-solvent interactions in alcohols.