CALCULATIONS OF ELECTRONIC EXCITATION TRANSFER - APPLICATIONS TO ORDERED PHASES IN POLYMERIC MATERIALS

A general treatment of electronic excitation transfer (EET) for any ra ndom or nonrandom chromophore distribution is applied to finite-volume systems which can be modeled as spherical shells of finite thickness, cylinders, and lamellae. These geometries were chosen because they oc cur in a wide variety of materials of interest in synthetic polymer re search, as well as in biological systems. The EET dynamics are describ ed by the function [G(s)(t)], the probability of finding the excitatio n on the originally excited chromophore. [G(s)(t)] is directly related to the observables in fluorescence anisotropy and lifetime experiment s, for donor-donor and donor-trap EET, respectively. The method is sho wn to be accurate in the limits for which analytical expressions in cl osed form are available. The model's usefulness in experimental design is demonstrated for the case of coronal swelling in spherical micelle s of diblock copolymers. It was found that random labeling of the bloc ks which form coronae is the preferred method for observation of this effect and that the sensitivity can be enhanced by selectively tagging the junction of the two blocks with trap chromophores. The influence of the shape of the chromophore distribution function on [G(s)(t)] was also investigated, to test the sensitivity of EET observables to the shape of the chromophore distribution at the A-B interface of a dibloc k copolymer material. The exact functional form of a symmetrical chrom ophore distribution was found not to appreciably affect the observable s, while the spatial extent of the chromophore distribution has a majo r effect.