Binding Orientation of a Ruthenium-Based Water Oxidation Catalyst on a CdS QD Surface Revealed by NMR Spectroscopy

We report on the binding of a Ru-based water oxidation catalyst (WOC) to CdS quantum dots (QDs) revealed by ¹H NMR spectroscopy. Spin centers within the WOC exhibit correlated trends in chemical shift and T₂ lifetime shortening upon QD binding. These effects are a highly directional function of proton position within the WOC, thus uncovering orientation information relative to the QD surface. The data suggest that the WOC interacts with the QD surface via the Ru terpyridine ligand, an unexpected orientation that has important implications for interfacial charge transfer and subsequent catalysis. This binding motif enables strong enough donor-acceptor electronic coupling for ultrafast photoinduced hole transfer while maintaining electronically distinct functional subunits.