Analysis of absorption spectra of zinc porphyrin, zinc meso-tetraphenylporphyrin, and halogenated derivatives

The absorption spectra of zinc porphyrin, zinc meso-tetraphenylporphyrin, and their beta-halogenated derivatives are calculated and analyzed using time-dependent density functional theory (TDDFT) and time-dependent Hartree-Fock theory based on the intermediate neglect differential overlap/spectroscopic approximation (TDHF-INDO/S) to obtain the origin of the spectral shifts in color and intensity. Analysis of the spectral shifts is carried out to account for the effects of phenyl, fluoro, chloro, and bromo substituents on the spectra. The spectroscopic trends predicted by TDHF-INDO/S compare well with the more accurate time-dependent density functional theory results and with available experimental data.