Theoretical study of electronic structure and absorption spectra of diacid and zinc species of series of meso-phenylporphyrins

DFT and TDDFT calculations with density functionals (PBE1PBE, B3LYP, and PBEPBE) have been employed in a study of HCl-acidified diacids of a series of meso-phenylporphyrins. This study aims to clarify the influence of conformational distortion, meso-phenyl substituents, and counterion Cl− on absorption spectra of porphyrin derivatives. Calculations indicate that all three factors increase the MO's level and decrease the Gouterman HOMO–LUMO gap; this, further, brings about the redshift of absorption band. In comparison with experimental methods, the PBE1PBE method produces a more credible description of UV–vis spectra than other two methods. TDDFT calculation with the PBE1PBE method indicates that the electronic effect of the meso-phenyl group is dominant for the spectral redshift of porphyrin diacid series as observed in zinc porphyrins. The redshift of the B band of porphyrin diacids is primarily caused by an electron-donating effect of the meso-phenyl group, whereas the Q band is more sensitive to the π electron delocalization effect. The counterion is indispensable in a theoretical study of electronic and spectral structure of porphyrin diacids.

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► Electronic structure of meso-phenylporphyrin diacids was studied.
► Absorption spectra of meso-phenylporphyrin diacids were simulated.
► The absorption redshift of porphyrin diacids was analyzed.
► Electronic effect of substituent is the key cause to the absorption redshift.