Dispersive excitation transport at elevated temperatures (50-298 K) : experiments and theory

Time-resolved fluorescence depolarization has been used to measure electronic excitation transport among naphthyl chromophores in polymeric glasses. 2-ethylnaphthalene randomly distributed in PMMA and 2-vinylnaphthalene/methyl methacrylate copolymer in PMMA were studied. It was found that excitation transport is dispersive at all temperatures studied, from 50 K to room temperature, i.e., the extent of transfer depends on the excitation wavelength within the S0–S1 absorption band. A theory based on the nondispersive, Förster mechanism for excitation transfer has been developed to describe dispersive transport. Good agreement between the theoretical and experimental results are achieved without resorting to adjustable parameters. Both the theory and experiment show that, for the observable used here, excitation at a certain wavelength, called the ‘‘magic wavelength,’’ results in a time dependence that is identical to the Förster nondispersive result, i.e., dispersive transport appears to vanish.