A Nonequilibrium Molecular Dynamics Study of Infrared Perturbed Electron Transfer.

Infrared (IR) excitation is known to change electron-transfer kinetics in molecules. We use nonequilibrium molecular dynamics (NEqMD) simulations to explore the molecular underpinnings of how vibrational excitation may influence nonadiabatic electron-transfer. NEqMD combines classical molecular dynamics simulations with nonequilibrium semiclassical initial conditions to simulate the dynamics of vibrationally excited molecules. We combine NEqMD with electronic structure computations to probe IR effects on electron transfer rates in two molecular species, dimethylaniline-guanosine-cytidine-anthracene (DMA-GC-Anth) and 4-(pyrrolidin-1-yl)phenyl-2,6,7-triazabicyclo[2.2.2]octatriene-10-cyanoanthracen-9-yl (PP-BCN-CA). In DMA-GC-Anth, the simulations find that IR excitation of the NH scissoring motion and the subsequent intramolecular vibrational energy redistribution (IVR) do not significantly alter the mean-squared donor-acceptor (DA) coupling interaction. This finding is consistent with earlier computational analysis of static systems. In PP-BCN-CA, IR excitation of the bridging C═N bond changes the bridge-mediated coupling for charge separation and recombination by ∼30-40%. The methods described here enable detailed explorations of how IR excitation may perturb charge-transfer processes at the molecular scale.