Assignment of the optical spectra of metal phthalocyanines through spectral band deconvolution analysis and ZINDO calculations

The optical spectra of the porphyrins and phthalocyanines are dominated by the φ → φ* bands associated with the heteroaromatic, 16 atom, 18 φ-electron inner perimeter cyclic polyene. Despite experimental measurements spanning over 60 years, no model exists that completely accounts for all bands in the UV-vis-near IR regions in each of the accessible redox states of many of these ring compounds. Spectral data for many neutral porphyrin and phthalocyanine compounds with a range of metals, axial and peripheral substituents have been reported from absorption and magnetic circular dichroism (MCD) techniques. Spectroscopic measurements during electrochemical, photochemical and chemical oxidation and reduction experiments have yielded high quality spectral data for the ring-oxidized radical cation and a range of ring-reduced species. As more data become available, the need for quantitative interpretation becomes more important. We describe in this review, progress towards understanding the optical spectrum of the phthalocyanines based on the spectral deconvolution analyses of absorption and magnetic circular dichroism data (MCD) and the use of ZINDO calculations to provide the theoretical model required to fully analyze these results.