Electronic structures and spectra of symmetric meso‐substituted porphyrin: DFT and TDDFT—PCM investigations

DFT and TDDFT calculations at the level of PBE0/6‐31G(d)/6‐31+G(d) were performed systematically on seven porphyrins with symmetrical meso‐substitutents. Our results show that the planarity of the free base porphyrin (BP) are affected by the introduction of substitutents at the meso‐position of the ring. Geometrical studies show that the introduction of electron‐withdrawing groups brings about in‐plane deformation in the porphyrin ring, whereas the bulky substitutents make an out‐of‐plane deformation. However, FMO's diagram shows that electron‐withdrawing groups alter the degeneracy of the HOMO and HOMO ?1 orbtial. Up on introduction of substituents at the meso‐position, the Q band FMOs transitions were the same as in the case of free BP; however, the oscillator strength is changed. Electron releasing substituted at the meso‐position shows bathochromic shift in the Q band region. However, the intensity or the hyperchromic shift is higher for the electron withdrawing groups. Solvation studies show that Q bands are blue shifted and B bands are red shifted, whereas the intensity of the B bands was highly enhanced compared with the Q bands. These theoretical studies would be helpful in designing new porphyrins for the photodynamic therapy and dye‐sensitized solar cell applications. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2011