Femtosecond X-ray Spectroscopy Directly Quantifies Transient Excited-State Mixed Valency
Chelsea Liekhus-Schmaltz, Zachary W. Fox, Amity Andersen, Kasper S. Kjær, Roberto Alonso‐Mori, Elisa Biasin, Julia Carlstad, Matthieu Chollet, James D. Gaynor, James M. Glownia, Kiryong Hong, Thomas Kröll, Jae Hyuk Lee, Benjamin I. Poulter, Marco Reinhard, Dimosthenis Sokaras, Yu Zhang, Gilles Doumy, Anne Marie March, S. H. Southworth, Shaul Mukamel, Amy A. Cordones, R. W. Schoenlein, Niranjan Govind, Munira Khalil
Abstract
Quantifying charge delocalization associated with short-lived photoexcited states of molecular complexes in solution remains experimentally challenging, requiring local element specific femtosecond experimental probes of time-evolving electron transfer. In this study, we quantify the evolving valence hole charge distribution in the photoexcited charge transfer state of a prototypical mixed valence bimetallic iron–ruthenium complex, [(CN)5FeIICNRuIII(NH3)5]−, in water by combining femtosecond X-ray spectroscopy measurements with time-dependent density functional theory calculations of the excited-state dynamics. We estimate the valence hole charge that accumulated at the Fe atom to be 0.6 ± 0.2, resulting from excited-state metal-to-metal charge transfer, on an ∼60 fs time scale. Our combined experimental and computational approach provides a spectroscopic ruler for quantifying excited-state valency in solvated complexes.