Tracking Electron, Proton, and Solvent Motion in Proton-Coupled Electron Transfer with Ultrafast X-rays
Abdullah Kahraman, Michael Sachs, Soumen Ghosh, Benjamin I. Poulter, Estefanía Sucre-Rosales, Elizabeth S. Ryland, Douglas Garratt, Sumana L. Raj, Natalia Powers-Riggs, Subhradip Kundu, Christina Y. Hampton, David J. Hoffman, Giacomo Coslovich, Georgi L. Dakovski, Patrick L. Kramer, Matthieu Chollet, Roberto A. Mori, Tim B. van Driel, Sang-Jun Lee, Kristjan Kunnus, Amy A. Cordones, Robert W. Schoenlein, Eric Vauthey, Amity Andersen, Niranjan Govind, Christopher Larsen, Elisa Biasin
公開日: 2025/10/4
Abstract
Proton-coupled electron transfer (PCET) is foundational to catalysis, bioenergetics, and energy conversion, yet capturing and disentangling the coupled motions of electrons, protons, and solvent has remained a major experimental challenge. We combine femtosecond optical spectroscopy, site-specific ultrafast soft X-ray absorption spectroscopy, and time-resolved X-ray scattering with advanced calculations to disentangle the elementary steps of PCET in solution. Using a ruthenium polypyridyl model complex, we directly resolve photoinduced electron redistribution, ligand-site protonation within 100 ps, and the accompanying solvent reorganization. This unified multi-modal approach provides an orbital-level, atomistic picture of PCET, showing how electronic, nuclear, and solvation degrees of freedom can be separated experimentally. Our results establish a general X-ray framework for understanding and ultimately controlling PCET in catalysis, artificial photosynthesis, and biological energy flow.