Synthesis, spectral and electrochemical properties of a novel phosphorous(V)-phthalocyanine

A novel phosphorous(V)-phthalocyanine, [P(tppc)(OH)(O)], where tppc denotes tetrakis{(2′,6′-dimethyl)phenoxy}phthalocyaninate, has been synthesized and its spectral properties in non-aqueous and aqueous media have been investigated. This compound has been found free from aggregation in EtOH whereas forms J-aggregates in CH₂Cl₂ and acetonitrile, suggesting the presence of chemical interaction between the axial ligand and the surrounding solvent molecules. The most intense absorption band (Q-band) appears at 683 nm in EtOH, however, reaction with CF₃COOH has given rise to a large red shift of the Q-band without lowering of its C₄ symmetry (evidenced by magnetic circular dichroism spectroscopy), indicating protonation at the axial site. Its fluorescence quantum yield has been determined (0.49 in EtOH) and has been found much higher than those of the known Sb^V or As^V derivatives by more than one order of magnitude. The first reduction potential has been determined by cyclic voltammetry (-1.09 V vs. ferrocenium⁺/ferrocene) in CH ₂Cl₂. It is noteworthy that the Q-band maximum wavelength and the first reduction potential values are normal for conventional phthalocyanines despite the presence of pnictogen(V) in the cavity of the macrocyclic ligand.