Theoretical-computational modeling of photo-induced charge separation spectra and charge recombination kinetics in solution

Abstract

In this study we propose a theoretical-computational method, essentially based on molecular dynamics simulations and quantum-chemical calculations, for modelling the photo-induced charge separation (CS) and the subsequent charge recombination (CR) processes in solution. In particular we have reproduced the low-energy UV-Vis spectra of systems composed by an aromatic species (Ar = benzene or indene) and tetracyanoethylene (TCNE) in chloroform solution, dominated by the formation of the Ar⁺–TCNE⁻ ion pair (IP) complex. The kinetics of the charge recombination process leading to the regeneration of Ar and TCNE has also been modelled. In both the cases the agreement with the experimental data is satisfactory. Although the presence of systematic deficiencies makes our approach unable to address some key aspects of the above processes (e.g. the ultrafast internal vibrational redistribution), it appears to be a rather promising tool for modelling the CS–CR process for atomic-molecular systems of very high complexity. The involvement of the triplet IP complex has also been discussed.