What it is
Researchers combine three time-resolved techniques (femtosecond optical spectroscopy, N K-edge X-ray absorption spectroscopy, and X-ray solution scattering) to follow a sequential proton-coupled electron transfer in water with atomic-site specificity. Using a ruthenium polypyridyl model complex, they resolve the electron redistribution that follows photoinduced metal-to-ligand charge transfer, then protonation at a ligand nitrogen at ~460 ps, together with rearrangement of the first solvation shell. The excited-state electron density localizes markedly at the protonated nitrogen site, and the hydrogen bonding switches from N···HO to NH···O.
Why it matters
Directly observing how electronic redistribution, protonation, and solvent reorganization interplay during proton-coupled electron transfer has remained challenging, so the individual steps were not resolved with atomic-site specificity. Tracking them together on a ruthenium model, down to the ~460 ps protonation event, ties each change to a specific atomic site.
How to read this
It establishes a multimodal X-ray framework for mechanistic insight into proton-coupled electron transfer and its control in catalysis, artificial photosynthesis, and biological energy flow.
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