Thionine sensitised photochemistry of manganese gluconate

Abstract

The photoredox properties of the manganese gluconate system sensitised by thionine have been investigated in aqueous solution by flash photolysis techniques. With manganese (II) gluconate, the main reactions are between the ligand and triplet thionine, the former being a good reductant. Only at high manganese (II) to gluconate ratios did the manganese react with thionine but this photo-reaction did not lead to oxidation of the metal. With manganese (III) gluconate, the thionine sensitised reaction leads to oxidation to the mixed valence binuclear manganese (III, IV) gluconate complex. Reduction of this product does not involve water oxidation and there is no observed formation of molecular oxygen.