Ultrafast Charge Migration Dynamics in Enol Keto Tautomerization Monitored with a Local Soft-X-Ray Probe

TL;DR

This study uses femtosecond soft-X-ray spectroscopy simulations to reveal ultrafast charge migration mechanisms during photoinduced enol-keto tautomerization, providing insights into proton-coupled electron transfer processes.

Contribution

It demonstrates how local soft-X-ray spectral signatures can track charge migration stages in PCET reactions with a full quantum dynamics approach.

Findings

Spectral signatures reveal stages of charge migration.

Ultrafast dynamics occur on femtosecond timescales.

Soft-X-ray spectroscopy can probe electronic rearrangements.

Abstract

Proton-coupled electron transfer (PCET) is the underlying mechanism governing important reactions ranging from water splitting in photosynthesis to oxygen reduction in hydrogen fuel cells. The interplay of proton and electronic charge distribution motions can vary from sequential to concerted schemes, with elementary steps occurring on ultrafast time scales. We demonstrate with a simulation study that femtosecond soft-X-ray spectroscopy provides key insight into the PCET mechanism of a photoinduced intramolecular enol* $\rightarrow$ keto* tautomerization reaction. A full quantum treatment of electronic and nuclear dynamics of 2-(2-hydroxyphenyl-)benzothiazole upon electronic excitation reveals how spectral signatures of local excitations from core to frontier orbitals display the distinct stages of charge migration for the H atom, donating, and accepting sites. Our findings indicate UV/X-ray pump-probe spectroscopy provides a unique way to probe ultrafast electronic structure rearrangements in photoinduced chemical reactions essential to understanding the mechanism of PCET.