Synthesis and characterization of porphyrin-pyrene hybrids

Palladium-catalyzed Suzuki-Miyaura coupling of 5-functionalized Ni(II) porphyrins with 1,3,6,8-tetrafunctionalizedpyrenes was carried out to obtain two kinds of porphyrin-pyrene hybrids. These compounds were comprehensively characterized by nuclear magnetic resonance (NMR), high-resolution mass spectrometry and ultraviolet-visible (UV-vis) absorption spectrometry, and their electrochemical properties were studied by both cyclic voltammetry (CV) and differential pulse voltammetry (DPV). Fluorescence spectra for zinc compounds and free-base compounds were performed. In addition, the structure of 4Zn, a porphyrin tetramer, was determined by X-ray diffraction analysis, in which two planes formed by the porphyrin unit and the pyrene moiety adopt nearly perpendicular geometry with two sets of dihedral angles displaying 85.14 (4)degrees and 83.90 (4)degrees, respectively. In the UV-vis absorption spectra, the maximum wavelengths of Soret bands and Q bands for these hybrids were observed at 434 and 648 nm. As the number of porphyrin units increases, the corresponding molar extinction coefficient rises markedly, in which the maximal value is 7.4 x 10(5) M-1 center dot cm(-1) belonging to 4Zn. Moreover, the presence of energy transformation from the pyrene moiety to the porphyrin unit has been proved by emission spectra. Finally, the electrochemical properties of these porphyrin-pyrene hybrids were analyzed by using cyclic voltammetry and differential pulse voltammetry, which show that the nickel hybrids possessed the maximal electrochemical highest occupied molecular orbital (HOMO)lowest unoccupied molecular orbital (LUMO) gap and the zinc compounds displayed the minimum electrochemical HOMO-LUMO gap.