ABSORPTION AND MAGNETIC CIRCULAR-DICHROISM SPECTRA OF NITROGEN HOMOLOGS OF MAGNESIUM AND ZINC PHTHALOCYANINE

Absorption and magnetic circular dichroism (MCD) spectra are reported for the metallophthalocyanine-N-isologs: magnesium-3,4-pyridinoporphra zine (MgPcN4(-2)), zinc-3,4-pyridinoporphyrazine (ZnPcN4(-2)), and zin c-3,4-pyridazinoporphyrazine (ZnPcN8(-2)). Band deconvolution calculat ions, which couple both the absorption and the MCD spectra, are report ed for each complex. The presence of the peripherally fused pyridine r ings in MgPN4(-2) and ZnPcN4(-2) reduces the molecular symmetry and sp lits the degenerate Q band into its x and y components with zero field splitting parameters (DELTAQ(xy)) of 224 and 279 cm-1, respectively. Band fitting results for ZnPcN8(-2) show that with the fused pyridazin e rings the degeneracy in the 1E(g) excited state is retained and the MCD envelope in the region of the Q00 transition can be described by a n 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 a s the number of nitrogens substituted increases from 0 to 8, the Q ban d blue shifts from 671 nm in ZnPc(-2) to 664 nm in ZnPcN4(-2) (midpoin t between the x and y components) to 654 nm in ZnPcN8(-2) and from 672 nm in MgPc(-2) to 666 nm in MgPcN4(-2) (midpoint). These results demo nstrate that chemical modification (symmetric and asymmetric) of the p eripherally fused benzene rings influences both the energy and the sym metry of the states that form the inner 18-pi-electron system.