A DFT study of asymmetric meso-substituted porphyrins and their zinc complexes

In the present work density functional theory (DFT) is applied to calculate geometries and electronic structures of 3,4-dimethyl-N-{2-[10,15,20-tris-(3,5-di-tert-butyl-phenyl)-porphyrin-5-y1]-phenyl}benzamide (H2P-O34) and its zinc complex (ZnP-O34). The influences of the substituents in the porphyrin ring on the energies of frontier molecular orbitals are evaluated. This is done by gradually increasing the amount of substituents in the investigated porphine and zinc porphine rings. The DFT framework used in this work is found to correctly describe the differences in electronic structures, which arise from differences in the location, number, and electronic effects of the substituents at the meso-positions of the porphyrin ring. In addition, the applicability of the ground state DFT method for evaluating the one-electron transition energies, which correspond to the near U-V-Vis optical absorptions of porphyrin molecules, is investigated. The transition energies and the orbitals involved in electronic transitions are well reproduced by this method, as shown by comparing the results to our time dependent density functional calculations. (C) 2004 Elsevier B.V. All rights reserved.