Photo-Oxidation of Methanol in Complexes with Pyrido[2,3-b]pyrazine: a Nonadiabatic Molecular Dynamics Study

Excited-state Proton-Coupled Electron Transfer (PCET) constitutes a key step in the photooxidation of small, electron-rich systems possessing acidic hydrogen atoms, such as water or alcohols, which can play a vital role in green hydrogen production. In this contribution, we employ ab initio quantum-chemical methods and on-the-fly nonadiabatic molecular dynamics simulations to study the mechanism and the photodynamics of PCET in 1:1 pyrido[2,3-b]pyrazine complexes with methanol. We find the process to be ultrafast and efficient when the intramolecular hydrogen bond is formed with one of the β-positioned nitrogen atoms. The complex exhibiting a hydrogen bond with an isolated nitrogen site, on the contrary, shows much lower reactivity. We explain this effect with the stabilization of the reactive ππ∗ charge-transfer electronic state in the former case.