Some properties and molecular orbitals of planar heterodinuclear phthalocyanines

The electronic absorption and magnetic circular dichroism (MCD) spectra, and differential pulse (DP) voltammograms of planar heterodinuclear phthalocyanine (Pc) dimers consisting of Pc and pyrazinoporphyrazine (PyZ), [Mt₂PcPyZ (Mt = H₂ and Zn)] and of Pc and naphthalocyanine (Nc), [Mt₂PcNc (Mt = H₂ and Co)] have been recorded. These dimers commonly show broad absorption bands between ca. 500 and 1000 nm, while the DP voltammograms suggest that the dimers are unstable towards oxidation, and that the two relatively independent chromophore units interact with one another. Molecular orbital (MO) calculations using the ZINDO/S Hamiltonian were performed in order to enhance the interpretation of the experimental results. Dimer orbitals were expressed by coupling the orbitals of the same symmetry, of the constituting mononucleates. It was suggested that for the HOMO of the dimers, the contribution of the more electron-rich moiety is large, while conversely for the LUMO, the contribution of the more electron-deficient moiety is large. The calculations suggested that there are three prominent transitions in the Q band region of the heterodimers. The intensity and position of these bands were suggested to be affected by the constituting mononucleates.