Ruthenium based photosensitizer/catalyst supramolecular architectures in light driven water oxidation

Light driven water oxidation is a key step in artificial photosynthesis, aimed at splitting water into hydrogen and oxygen with sunlight. In such process, the interactions between a photosensitizer (PS) and a water oxidation catalyst (WOC) play a crucial role in the rates of photoinduced electron transfers, determining the overall quantum efficiency of the system. In this work, by means of Small Angle X-ray Scattering (SAXS) we investigate the nature of the aggregates between ruthenium polypyridine photo sensitizers (Rubpy and Ru(4)dend) and a tetraruthenium polyoxometalate (Ru4POM) water oxidation catalyst. Aggregate scattering is confirmed by the strong intensity-increase in the low-q regime, whereas the power law-fit of this region show slopes between 3 and 4, suggesting globular and porous aggregates. Intermolecular PS/WOC distances lower than 3 nm support the observed fast photoinduced electron transfers (<120 ps), however the proximity of the two components in the hybrids is also responsible for fast charge recombination. Approaches for inhibiting such undesired process are discussed. (C) 2016 Elsevier B.V. All rights reserved.