LDS-750 as a probe of solvation dynamics: a femtosecond time-resolved fluorescence study in liquid aniline

The dynamics of the fluorescence Stokes shift of the styryl dye LDS-750 have been measured in liquid aniline with sub-100 fs time resolution. The shape of the time-resolved spectra are time dependent, which is not consistent with the predictions of a solvation dynamics mechanism. However, the measured spectral shift correlation function is reasonably well described by the dynamical mean spherical approximation model of solvation dynamics. It is suggested that these observations are consistent if solvent dynamics is the rate controlling process in both solvation of the increased dipole moment of the excited state of LDS-750 and the stabilisation of a distribution of solute conformers in the excited state.