Analytical theory of time-resolved fluorescence anisotropy and dynamic stokes shift of polar solute molecules based on continuum model for solvent Original Research Article

Theoretical expressions for time-resolved fluorescence anisotropy and dynamic Stokes shift of solute molecules in polar solvent were worked out on the basis of continuum model for solvent. Distribution function of rotational angles of solute molecules was obtained by solving a rotational analogue of generalized Smoluchowski equation into which a frequency-dependent diffusion coefficient of the rotational motion was introduced according to Nee and Zwanzig. By this distribution function, which contained the effect of dielectric friction, expressions for the anisotropy decay and the dynamic Stokes shift were derived. Numerical calculations of both the correlation function of the Stokes shift and the anisotropy decay were made with common parameters for some model systems. The obtained results suggest that the simultaneous measurements of the time-resolved Stokes shift and anisotropy decay under solvation are useful to investigate the solvation mechanisms and dynamics of excited solutes.