Electron transfer reaction of porphyrin and porphycene complexes of Cu(II) and Zn(II) in acetonitrile

The outer-sphere one-electron oxidation reaction of the Cu(ii) and Zn(ii) complexes of nonplanar 2,3,7,8,12,13,17,18-octaethyl-5,10,15,20- tetraphenylporphyrin and planar porphycenes as well as those of 2,3,7,8,12,13,17,18-octaethylporphyrin and 5,10,15,20-tetraphenylporphyrin by Cu²⁺ giving corresponding π-cation radicals was investigated spectrophotometrically in acetonitrile. The electron self-exchange rate constants between the parent porphyrin and porphycene complexes and their π-cation radicals were determined using the Marcus cross relation for the electron transfer reaction. The obtained rate constants are in the order of 10⁹ to 10¹¹ M^-1 s^-1 for the planar porphyrin and porphycene complexes and 10⁴ to 10⁶ M ^-1 s^-1 for the nonplanar OETPP complexes at T = 25.0 °C. The relatively slow self-exchange reaction of the distorted porphyrin complexes, as compared with those for the planar porphyrin and porphycene complexes, was ascribed to the significant deformation of the complex associated with the oxidation reaction from the parent complex to the corresponding π-cation radical.