Ground state electronic structures and spectra of zinc complexes of porphyrin, tetraazaporphyrin, tetrabenzoporphyrin, and phthalocyanine: A density functional theory study

Density functional theory (DFT) electronic structure calculations were carried out to predict the structures and ground-state spectra for zinc complexes of porphyrin (ZnP), tetraazaporphyrin (ZnTAP), tetrabenzoporphyrin (ZnTBP), and phthalocyanine (ZnPc). All four porphyrins are found to have stable D4h structures. Structurally, meso-tetraaza substitutions significantly reduce the central hole in ZnTAP and ZnPc compared to ZnP. The excitation energies and oscillator strengths, computed by time-dependent DFT, provide a good account of the observed spectra of all four compounds. The TDDFT spectrum of ZnPc has a number of bands in the Soret region, in agreement with the experimental spectra that have been determined through spectral deconvolution. The low energy n→π* transition (Q′) reported for ZnPc, however, was not found in the computed spectrum. The effects of meso-tetraaza substitutions and tetrabenzo annulations on the spectrum of ZnP are discussed.