Quantum mechanical calculations coupled with a dynamical continuum model for the description of dielectric relaxation: Time dependent Stokes shift of coumarin C153 in polar solvents

Abstract

We present here a study of the time dependent Stokes shift, performing quantum-mechanical calculations on coumarin C153 in polar solvents. The electrostatic interaction between the solute and the solvent is treated within the Polarizable Continuum Model, which allows us to use a molecular shaped cavity for the solute. In order to take into account that the sudden change in the solute electronic density after the S 0 → S 1 excitation can be accompanied by a non instantaneous rearrangement of a component of the solvent polarization, we use a non-equilibrium representation of the solvent response. We have implemented a procedure to calculate the solvation time correlation function (the theoretical counterpart of the Stokes shift), including experimental data of the complex dielectric permittivity \\ ̂ ge(ω). The results that we have obtained are in good agreement with the experimental measurements. We will report the calculations for water, methanol, acetonitrile and dimethyl sulfoxide as solvents, showing that a correct treatment of dielectric relaxation generally needs a more detailed description of the solvent response than diffusive models.