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Abstract

The photochemical reactions performed by supramolecular transition metal complexes have been identified as viable routes towards conversion and strorage of solar energy into other forms that can be conveniently used in our everyday applications. In order to develop efficient materials, it is necessary to identify, characterize and optimize the elementary steps of the entire process. To this end, we have studied the photoinduced electronic and structural dynamics in two heterobimetallic ruthenium-cobalt complexes, which belong to the large family of donor-bridge-acceptor supramolecular complexes. Using a combination of ultrafast optical and X-ray absorption spectroscopies, we can clock the light-driven electron transfer processes with element and spin sensitivity. In addition, the changes in local structure around the metal centers are monitored. These experiments show that the nature of the molecular bridge connecting the two metal centers is decisive in controlling the forward and backward electron transfer rates, a result supported by quantum chemistry calculations. Some implications for further improving bridged sensitizer-catalysts utilizing the presented methodology are outlined.