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 pi electron delocalization effect. The counterion is indispensable in a theoretical study of electronic and spectral structure of porphyrin diacids. (C) 2011 Elsevier B.V. All rights reserved.