Photoredox properties of tetra-2,3-pyridinoporphyrazines (29H,31H-tetrapyrido[2,3-b: 2′, 3′-g : 2″,3″-l:2‴,3‴-q]porphyrazine)

Tetra-2,3-pyridinoporphyrazines (29H,31H-tetrapyrido[2,3-b : 2′,3′-g : 2″,3″-l : 2‴,3‴-q]porphyrazine)(1) and the corresponding water-soluble NN′N″N‴-tetramethylated quaternized tetracationic forms (2) with different central metal atoms were prepared and their photoredox activities investigated. The synthesis of (2; M = Zn, Cu) leads to mixtures of different constitutional isomers, which were isolated and characterized. The photoredox activities of (1) upon irradiation with visible light in the presence of EDTA and methylviologen (MV2+) are comparable with those of phthalocyanines. The photochemical reaction of (2) with different donors works clearly through a reductive quenching mechanism. Reaction with EDTA proceeds by a two-step sensitization to the dicationic species of (2).