Journal of the American Chemical Society, Vol.116, No.21, 9730-9732, 1994
Electronic-Structures of Halogenated Porphyrins - Spectroscopic Properties of Zntfppx(8) (Tfppx(8)=octa-Beta-Halotetrakis(Pentafluorophenyl)Porphyrin X=cl, Br)
We report here spectroscopic and theoretical (AM1) studies on zinc(II) octa-beta-halotetrakis(pentafluorophenyl)-porphyrins (ZnTFPPX(8); X = Cl, Br) that show a red shift in the Soret and Q absorption bands attributable to substituent-induced saddling of the macrocycle. The electronic effect of the halogens is to reduce the energies of both the HOMOs and LUMOs; however, this stabilization of orbital energies is counteracted by the distortion of the macrocycle, which results in a large destabilization of the porphyrin HOMOs and a smaller destabilization of the LUMOs. The net result is a slight increase in stability of the HOMOs and a greater stabilization of the LUMOs. Lowering the energies of the porphyrin HOMOs is an important factor to consider in the development of robust porphyrin catalysts.