Electronic Structures of Halogenated Porphyrins: Spectroscopic Properties of ZnTFPPX8 (TFPPX8 = 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[sub 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. 25 refs., 1 fig., 3 tabs.