Unified Theory of Time-Resolved Fluorescence Anisotropy and Stokes Shift of Excited Polar Molecules

Expressions for time-resolved fluorescence anisotropy and dynamic Stokes shift of solute molecules in polar medium were obtained on the basis of continuum model. 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 of the anisotropy decay and dynamic Stokes shift were derived. Numerical calculations of the both correlation function of the Stokes shift and anisotropy decay were made with common parameters for a model system.