Solvent Effects on the Non-equilibrium Dynamics of Excited-state Proton Transfer

Morgan Hammer, University of Illinois at Urbana-Champaign

Storing energy from light in the form of chemical bonds is a key goal in the development of technologies for solar fuels. A key class of photochemical reactions involves the transfer of both electrons and protons. As these reactions occur under non-equilibrium conditions, explicit molecular dynamics simulations are required to gain insight into the factors driving them. Through computation we investigate excited-state proton transfer in an experimentally studied dye molecule to better explain the effects of varied solvents on the measured rate for ultrafast proton transfer following photoexcitation. This is accomplished through a mixed quantum mechanics/molecular mechanics (QM/MM) approach with a classical force field describing the solvent and on-the-fly production of the excited state potential energy surface using a reparametrized semi-empirical Hamiltonian. We have accomplished this by reparameterizing the AM1/FOMO-CASCI method to reproduce key features of the excited state potential energy surface as calculated by ab initio results obtained at the CASSCF/CASPT2 level of theory. The goal is that providing a better understanding of charge transfer processes on ultrafast timescales will better inform the development of systems for generating solar fuels.

Abstract Author(s): M. Hammer, P. Goyal, S. Hammes-Schiffer