Photochemistry and sensitized evolution of hydrogen from water using water-soluble cationic porphyrins. Tetrakis(trimethylaminophenyl)porphyrinatozinc and its free base

Photophysical properties (fluorescence spectra, lifetimes, triplet–triplet absorption spectra, triplet lifetimes and quantum yields) and redox potentials have been measured for the free-base, Zn2+ derivatives of a cationic water-soluble porphyrin, tetrakis(trimethyl-aminophenyl)porphyrin [TAPP(4+)]; the values are similar to those of tetrakis(sulphonatophenyl)porphyrin, TPPS(4 –). The zinc porphyrin ZnTAPP undergoes facile photoredox reactions and also sensitizes H2 evolution upon visible-light photolysis in ‘sacrificial’ systems, albeit with a lower efficiency in comparison with tetrakis(4-methylpyridyl)porphyrin, ZnTMPyP.