Photooxidation of Phthalocyanines

Porphyrins and phthalocyanines can act as highly efficient electron donor molecules in linked donor-acceptor complexes that may be used in molecular solar cells. This paper describes the photochemical reaction that occurs in a series of metallophthalocyanines following irradiation into the phthalocyanine's Q band in the presence of electron acceptors which are irreversibly reduced. The products of these photooxidation reactions were characterized by optical absorption, magnetic circular dichroism (MCD) and electron paramagnetic resonance (EPR) spectroscopies. The MCD spectra, in particular, provide a starting point in the theoretical analysis of the origin of the electronic transitions in the spectra of the oxidized porphyrin species. These studies show that for zinc phthalocyanine, ruthenium phthalocyanine and cobalt phthalocyanine, one-electron oxidation of the Π ring takes place. However, oxidation of the ferrous ion takes place before the Π ring in iron phthalocyanine. The spectral data from photochemical experiments are compared with data from controlled potential electrolysis experiments. Transition energies calculated from band shape deconvolution programs that use both the absorption and MCD spectra are compared with the energies calculated theoretically.