Time resolved spectroscopy of nonlinear solvation with pulses longer than electronic dephasing Original Research Article

n this study we show that transient four-photon spectroscopy with pulses longer than the electronic transition dephasing, can be used for nonlinear solvation study, i.e., when the linear response for the solvation dynamics breaks down. We derive new equations describing the time evolution of the moments of the nonlinear optical spectra and in particular, time resolved fluorescence in the case of nonlinear solvation. The formulae allow to use stochastic models and the information concerning time resolved Stokes shift is preserved. For broad and featureless electronic molecular spectra they provide simple analytical expressions. We demonstrate how solvation dynamics in the ground electronic state is obtained by time resolved hole-burning spectroscopy. We apply our results to the Debye model of rotational diffusion for the case of nonlinear solvation and obtain a long-time solution for the corresponding density of the conditional probability in a strong electrical field.