Role of Solvent Dynamics in Photoinduced Proton-Coupled Electron Transfer in a Phenol-Amine Complex in Solution.

Photoinduced proton-coupled electron transfer (PCET) plays an essential role in a wide range of energy conversion processes. Previous experiments on a phenol-amine complex in solution provided evidence of an electron-proton transfer (EPT) excited state characterized by both intramolecular charge transfer and proton transfer from the phenol to the amine. Herein we analyze hundreds of surface hopping trajectories to investigate the role of solvent dynamics following photoexcitation to the EPT state. This solvent dynamics leads to a significant decrease in the energy gap between the ground and EPT states, thereby facilitating decay to the ground state, and generates an electrostatic environment conducive to proton transfer on the EPT state. In addition to solvent reorganization, the geometrical properties at the hydrogen-bonding interface must be suitable to allow proton transfer. These mechanistic insights elucidate the underlying fundamental physical principles of photoinduced PCET processes.