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

arXiv · 2510.03693

Tracking Electron, Proton, and Solvent Motion in Proton-Coupled Electron Transfer with Ultrafast X-rays

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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.

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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. 2025-10-04. Tracking Electron, Proton, and Solvent Motion in Proton-Coupled Electron Transfer with Ultrafast X-rays. https://arxiv.org/abs/2510.03693

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