The redox properties of octakis(hexylthio)-substituted phthalocyanines with 2H, Zn-II and Cu-II in the phthalocyanine core have been investigated by cyclic voltammetry in dichloromethane and the energies of photo-excitation and oxide-reduction processes have been compared. Two successive one-electron reduction and one-electron oxidation processes were observed for the complexes used in this work. The displacement of two protons in the inner core with metal ion was found to shift the first reduction potential of phthalocyanine ring to more negative values as a result of the pi-back donation of the filled d(pi) of metal ion into the empty pc-pi* orbitals. The evaluation of cyclic voltammetry data together with the absorption spectra showed that photoexcitation arises from the orbitals below the HOMO for all the complexes used in this work. (C) 1997 Elsevier Science Ltd.