WATER PHOTOOXIDATION SENSITIZED BY ZINC(II) MESO-TETRAKIS(N-METHYL-4-PYRIDYL) PORPHINE

The irradiation (lambda > 520 nm) of a weakly acidic solution containing zinc(II) meso-tetrakis(N-methyl-4-pyridyl)porphine (ZnTMPyP4+), Fe(bpy)3(2+) (bpy = 2,2'-bipyridine) and S2O8(2-) leads to the formation of the strong one-electron oxidant Fe(bpy)3(3+) with a quantum yield of about 0.2. The reaction mechanism established by means of flash and steady state photolysis includes photochemical generation of zinc porphyrin radical cation ZnTMPyP.5+, which rapidly oxidizes Fe(bpy)3(2+) to give Fe(bpy)3(3+) and ZnTMPyP4+. After the accumulation of Fe(bpy)3(3+) in the presence of Co2+ (oxygen evolution catalyst precursor) an oxygen formation reaction was initiated by means of the addition of KOH (to pH 12) to the solution. O2 was detected in the gas phase by gas chromatography.