In this study we show that the transient four-photon spectroscopy with
pulses longer than the electronic transition dephasing can be used fo
r nonlinear solvation study, i.e., when the linear response for the so
lvation dynamics breaks down. We have obtained new formulae describing
the time evolution of the moments of the nonlinear optical spectra an
d, in particular, the time resolved fluorescence in the case of nonlin
ear solvation.