Photoinduced reduction of water by tin(IV) and ruthenium(II) porphyrins

In the paper are presented new photoredox systems for the reduction of water in which water- soluble Sn(IV) and Ru(II) porphyrins have been used as photosensitizers It has been found that during the photolysis of water Sn(IV) porphyrin underwent photoreduction whereas Ru(II) porphyrin underwent photooxidation. The successive photo- products of Sn(IV) porphyrin in the reaction from EDTA were, first, Sn(IV) chlorin and, second, Sn(IV) bacteriochlorin. In the experiments on the photo- generation of hydrogen, a correlation between the rates of hydrogen evolution and the reduction potentials of the electron carriers has been observed. The highest rate of hydrogen generation by means of Sn(IV) and Ru(II) porphyrins has been found for those electron carriers whose values of reduction potentials were tau; 0.55 and tau; 0.45 V. In the case of Ru(II) porphyrin, the rate of hydrogen evolution additionally depended on the molecular structure of the electron carrier. It has been found that during the water photolysis, viologens show a tendency to form their respective complexes with Ru(II) porphyrin, but only when they occur in a one-electron reduced form in the solution.