Photogeneration of hydrogen sensitised by a water-soluble 9-oxothioxanthene

Abstract

The photophysical properties of a water-soluble 9-oxothioxanthene have been determined in dilute aqueous solution. The first excited singlet state, which is of charge-transfer character, is strongly fluorescent and possesses a relatively long lifetime. Inefficient triplet-state formation occurs, but the triplet state, which is also of charge-transfer character, has a very long lifetime in the absence of oxygen. Neither excited state is able to abstract hydrogen atoms from organic materials, but both oxidative and reductive electron-transfer reactions can be observed following irradiation in the presence of viologens, iron(III) ions or amines. Irradiation at 400 nm in the presence of triethylamine and colloidal Pt produces H₂ with an optimised quantum yield of 1.02. The total yield of H₂ obtained upon exhaustive photolysis and the rate of H₂ formation compare favourably with any photosystem reported previously.