Nanosecond timescale optical inhomogeneous broadening of dye molecules in liquids at and near room temperature

Time-resolved fluorescence depolarization measurements of the S& 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 dynamic Stokes shift about an excited chromophore.