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 photosensitizers
(Rubpy and Ru4dend) 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.