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Spectral diffusion of an electronic transition of solute chromophores in liquid solutions is investigated experimentally and theoretically through its influence on electronic excited‐state transfer (EET). Observation of dispersive EET in liquids (the EET rate depends on the excitation wavelength) demonstrates that absorption lines are inhomogeneously broadened on a nanosecond time scale in the systems studied although the time scale for homogeneous dephasing is tens of femtoseconds. A theory is developed that relates the rate of spectral diffusion to the wavelength dependence and temperature dependence of EET. Time‐resolved fluorescence depolarization measurements are used to measure EET in the systems rhodamine B (RB) in glycerol and propylene glycol as a function of wavelength and temperature from room temperature (298 K) to 200 K. Comparison with theory permits the rates of the solvent fluctuations responsible for spectral diffusion to be determined for the two solvents at several temperatures. Measure...

Time-resolved fluorescence depolarization measurements of the S 0 S 1 electronic absorption band of rhodamine B in glycerol and propylene glycol have been made at different excitation wavelengths. It was found that electronic excitation transport between the rhodamine B chromophores is dispersive in glycerol at room temperature and in propylene glycol below 250 K. This demonstrates inhomogeneous broadening of the dye absorption spectrum which persists for the time scale of the fluorescence lifetime (nanoseconds) or longer. Measurements of time-resolved emission spectra at a number of different excitation wavelengths and temperatures support this conclusion and suggest that the chromophore—solvent microenvironments causing inhomogeneous broadening are the same as those responsible for the dynamics Stokes shift about an excited chromophore.

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, Forster 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 Forster nondispersive result, i.e., dispersive transport appears to vanish.

Time-resolved fluorescence depolarization is used to examine electronic excitation transport among naphthalene chromophores in a polymeric solid as a function of excitation wavelength between 300 and 50 K. The characteristics of the wavelength and temperature dependences reveal, for the first time, that dispersive transport occurs at and near room temperature. The rate of excitation transport depends on the wavelength of excitation. A theoretical treatment is able to reproduce the essential features of the wavelength and temperature dependences without recourse to adjustable parameters by avoiding the complexities of the relationship between the difference in energy of a pair of molecules and the pairwise transfer rate.