Absorption and magnetic circular dichroism spectra of nitrogen homologues of magnesium and zinc phthalocyanine

Abstract

Absorption and magnetic circular dichroism (MCD) spectra are reported for the metallophthalocyanine-N-isologs: magnesium-3,4-pyridinoporphrazine (MgPcN 4 (−2)), zinc-3,4-pyridinoporphyrazine (ZnPcN 4 (−2)), and zinc-3,4-pyridazinoporphyrazine (ZnPcN 8 (−2)). Band deconvolution calculations, which couple both the absorption and the MCD spectra, are reported for each complex. The presence of the peripherally fused pyridine rings in MgPN 4 (−2) and ZnPcN 4 (−2) reduces the molecular symmetry and splits the degenerate Q band into its x and y components with zero field splitting parameters (ΔQ xy ) of 224 and 279 cm −1 , respectively. Band fitting results for ZnPcN 8 (−2) show that with the fused pyridazine rings the degeneracy in the 1 E g excited state is retained and the MCD envelope in the region of the Q 00 transition can be described by an MCD A term. Comparison of the fitted band energies with the results reported for ZnPc(−2) (T. Nyokong, Z. Gasyna, and M.J. Stillman. Inorg. Chem. 26, 1087 (1987)) and MgPc(−2) (E.A. Ough, T. Nyokong, K.A.M. Creber, and M.J. Stillman. Inorg. Chem. 27, 2725 (1988)) shows that as the number of nitrogens substituted increases from 0 to 8, the Q band blue shifts from 671 nm in ZnPc(−2) to 664 nm in ZnPcN 4 (−2) (midpoint between the x and y components) to 654 nm in ZnPcN 8 (−2) and from 672 nm in MgPc(−2) to 666 nm in MgPcN 4 (−2) (midpoint). These results demonstrate that chemical modification (symmetric and asymmetric) of the peripherally fused benzene rings influences both the energy and the symmetry of the states that form the inner 18-π-electron system.