First-principle computation of absorption and fluorescence spectra in solution accounting for vibronic structure, temperature effects and solvent inhomogenous broadening

Abstract

We compute the line shape of absorption and emission electronic spectra of two different dyes, Coumarin C153 and N-methyl-6-Quinolinium betaine accounting for the vibronic structure, temperature effects and polar solvent inhomogeneous broadening, without using any phenomenological parameter. We exploit a number of recent developments including a time-dependent (TD) approach to the computation of vibronic spectra that provides fully converged line shapes at finite temperature accounting for both Duschinsky and Herzberg–Teller effects, and the state-specific (SS) implementation of Polarizable Continuum Model (PCM). This latter is adopted to compute the solvent reorganization energy connected to inhomogenoeus broadening. We compute the absorption and fluorescence spectra in the gas-phase, non-polar and polar solvents analyzing the relative importance of different sources of broadening. To this end we investigate the performance of TD Density Functional Theory, Complete Active Space Self Consistent Field (CASSCF) and Complete Active Space second-order Perturbation Theory (CASPT2) methods in the computation of inhomogeneous broadening.