Thermal and photoinduced electron transfer reactions of phthalocyanine complexes of Zn(ii) and Cu(ii) in acetonitrile

Phthalocyanine that has four peripheral 2-methoxyphenyl substituents at the alpha-position and its Zn(ii) and Cu(ii) complexes were synthesized. Chemical oxidation by the Cu(ii) ion and electrochemical oxidation of these metal complexes were investigated spectrophotometrically in acetonitrile. The UV-visible absorption spectra of these metal complexes and their one-electron oxidized pi-cation radicals showed no concentration dependence, indicating that these species exist as monomers in solution. Kinetics of the thermal electron transfer reaction from each phthalocyanine complex to Cu2+ and the photoinduced electron transfer reaction of the Zn(ii) phthalocyanine complex with V(v) and V(iv) Schiff base complexes were studied using conventional spectrophotometric and transient absorption techniques, and the electron transfer rate constants were analysed using the Marcus cross relationship. The obtained rate constants of the electron self-exchange reaction between the parent phthalocyanine complexes and their pi-cation radicals were in the order of 10(9) to 10(11) M-1 s(-1) at T = 298.2 K. These large electron self-exchange rate constants are consistent with the phthalocyanine-centred redox reactions where small reorganization energies are required with little structural change during the electron transfer process.