Attempted photoproduction of hydrogen using sulphophthalocyanines as chromophores for three-component systems

Abstract

Tetrasulphophthalocyanine and the Zn^II and Cu^II complexes have intense absorption in the near i.r. region but the compounds aggregate in aqueous solution. Aggregation is hindered by addition of organic solvents, such as pyridine, and here H₂PcS^4– and ZnPcS^4– show strong fluorescence. Photophysical data have been collected for both compounds and for the Cu^II complex and the observed values related to the ideal properties of a chromophore for a three-component [chromophore/donor/methyl viologen (MV²⁺)] H₂-producing system. The Zn^II complex appears as the most attractive chromophore but irradiation in the presence of EDTA, MV²⁺ and colloidal Pt gives no H₂ production due to efficient reverse electron-transfer. The yield of H₂ is increased in the absence of MV²⁺ but the sulphonated phthalocyanines compare unfavourably with metalloporphyrins.