The cyclic voltammetry of some sulphonated transition metal phthalocyanines in dimethylsulphoxide and in water

The aqueous voltammetry of Co, Ni, Cu and Zn sulphonated metallophthalocyanines has been examined and compared to the voltammetry in DMSO. In DMSO, Ni, Cu and Zn phthalocyanines exhibit two quasi-reversible, phthalocyanine ligand based, one-electron transfers. Two reduction waves were also observed for Co phthalocyanine. However, the first reduction wave appeared to involve both a metal based electron transfer and a change in the coordination of the metal. The aqueous voltammetry of the cobalt phthalocyanine was similar to its non-aqueous behaviour. The other three phthalocyanines did not show the quasi-reversible behaviour in aqueous solution. Reversibility was much diminished and the forms of the waves changed greatly, indicating the involvement of protons in the redox processes.