The Complexation of Zinc Tetraphenylporphyrintrisulfonate by Viologen and Its Role in Photoredox Processes

The formation of the cation radicals of viologen dyes was established when an aqueous solution containing zinc tetraphenylporphyrintrisulfonate (Zn–TPPS3), viologen dye, and 2-mercaptoethanol was irradiated by visible light. The reduction of viologen has been studied kinetically; its reduction rate may be expressed as follows: v=[V+]dt=(3[Zn−TPPS3]01+K1[V2+]+K2[V+])(4[V2+]k−3+k4[V2+])(6[RSH]k5[V+]+k6[RSH]), where [V2+], [V+], and [RSH] are the concentrations of the oxidized form and the reduced form of viologen, and 2-mercaptoethanol respectively. On the basis of the rate expression, a reaction mechanism containing the complexation of Zn–TPPS3 by viologen was proposed. On the addition of hydrogenase to the above photoirradiation system, hydrogen evolution was observed by the irradiation of visible light.