Kinetics of Photocatalytic Water Oxidation at Liposomes: Membrane Anchoring Stabilizes the Photosensitizer

Abstract

A tris(bipyridine)ruthenium(II) photosensitizer (PS) was anchored to the lipid bilayer of liposomes together with Ru-, Co-, or Ir-based water-oxidation catalysts in order to study the effect of liposomes on photocatalytic water oxidation in the presence of Na2S2O8. The Ru-based and Co-based systems both showed O2 production upon light irradiation, whereas the Ir-based system did not. Membrane anchoring caused a large shift in the quantum yield of oxidative quenching of the photosensitizer excited state by peroxodisulfate, which decreased from 180% in homogeneous solution to 7.3% at the surface of liposomes. For the Ru-based system the electron-transfer rate between the photosensitizer PS+ and the water-oxidation catalyst was increased relative to oxidative quenching. Consequently, the rate-limiting step of the photocatalytic water oxidation reaction at liposomes was oxidative quenching, whereas previous work showed that in homogeneous solution it is the reduction of the oxidized photosensitizer PS+ by the...