Ground- and excited-state spectral and redox properties of cadmium(II) texaphyrin

Cadmium texaphyrin, [(TXP)Cd]⁺, a representative of a new family of expanded porphyrins, has an absorption maximum around 760 nm in acetonitrile solution. The first excited triplet state, which is formed with a quantum yield of 0.9, is quenched by O₂, via an energy-transfer process, and by aromatic amines, via an electron-transfer reaction. This latter process produces [(TXP)Cd]⁰, the neutral radical, as characterized by flash photolysis methods, with an overall quantum efficiency of about 60%. The potential of the texaphyrin family as photosensitizers for photodynamic therapy is highlighted.