Site selective real‐time observation of bimolecular electron transfer in a photocatalytic system using L‐edge X‐ray absorption spectroscopy

Time-resolved X-ray absorption spectroscopy has been uti- lized to monitor the bimolecular electron transfer in a pho- tocatalytic water splitting system. This has been possible by uniting the local probe and element specific character of X-ray transitions with insights from high-level ab initio calculations. The specific target has been a heteroleptic [Ir III (ppy) 2 (bpy)] + photosensitizer, in combination with tri- ethylamine as a sacrificial reductant and Fe 3 (CO) 12 as a wa- ter reduction catalyst. The relevant molecular transitions have been characterized via high-resolution Ir L-edge X- ray absorption spectroscopy on the picosecond time scale and restricted active space self-consistent field calculations . The presented methods and results will enhance our un- derstanding of functionally relevant bimolecular electron transfer reactions and thus will pave the road to rational optimization of photocatalytic performance.