ELECTRONIC-ENERGY TRANSFER IN LIQUIDS - THE EFFECT OF MOLECULAR-DYNAMICS

A Liouville formalism has been developed for treating energy transfer processes within the same conceptual framework as other relaxation pro cesses. The theory of Forster, describing energy transfer between a pa ir of immobile fluorescent molecules has been generalized to include t he effects of molecular dynamics the static, intermediate and fast dyn amic regimes. Forster's master equation of the excitation populations is derived from the Liouville formalism and we arrive at the proper cr iteria for its validity within the physical model. A closed form expre ssion is derived for the fluorescence anisotropy of a macromolecular s ystem containing pair of pairwise interacting chromophores where one o f the chromophores undergoes a two state conformational change. The ex pression derived is valid without assuming that the nonradiative state and the conformation dynamic is uncoupled. It is shown that when ener gy transfer and conformational changes occur on the same time scale, t he decay times of the fluorescence anisotropy depend in a complex way on the molecular relaxation.