Electronic dephasing, vibrational relaxation, and solvent friction in molecular nonlinear optical line shapes

The role of solvation dynamics in molecular nonlinear optical line shapes is analyzed using a reduced description based on the time evolution of the density matrix in Liouville space. Langevin equations are used to treat the coupling of the solvent to the molecular electronic and nuclear degrees of freedom. Electronic dephasing is calculated using a solvation coordinate which satisfies a generalized Fokker-Planck equation, and vibrational relaxation is related to the solvent viscosity and friction. The combined effect of both processes is incorporated into appropriate multitime correlation functions which are evaluated using a Liouville-space generating function. The present eigenstate-free approach is particularly suitable for calculating spectral line shapes as well as rate processes (isomerization, electron transfer) of large polyatomic molecules in condensed phases.