Studies On The Synthesis And Properties Of Meso-meso Pyrrole Bridged Porphyrin Arrays

Both cyclic and acyclic porphyrin arrays have received much attention in light of imitation of natural photosynthesis, applications to molecular wires, and nonlinear optical devices. Porphyrin arrays bridged by various spacers have been synthesized as a fundamental structural motif to investigate the electronic interactions between the porphyrins,which will influence their electrochemical and photophysical properties.Due to a pyrrole moiety is quite attractive as a bridging spacer in view of the electron-rich property, effective conjugation, and potential use as a hydrogenbonding donor. Hence this approach, which circumvents functionalization of pyrroles, is useful from a synthetic point of view.Here we report the synthesis of meso-to-meso pyrrole-bridged porphyrin arrays through Suzuki-Miyaura cross-coupling of brominated porphyrin with diborylated pyrrole. These compounds were characterized by 1H NMR spectra, mass spectra and X-ray single-crystal diffraction analysis,and the porphyrin photophysical properties were studied, the results were satisfactory. The key studies are listed below.(1) According to literature, 3,5-di-tert-butylbenzaldhyde was prepared from toluene. The porphyrin monomers: 5,15-bisarylporphyrin(aryl=3,5-di-tert-butylphenyl) was synthesized from meso-free dipyrroleand 3,5-di-tert-butylbenzaldhyde. Meso-brominated porphyrins were obtained successfully by NBS with free radical substitution reaction. A series of meso-to-meso pyrrole-bridged porphyrin arrays were synthesized via classic Pd-catalyzed Suzuki-Miyaura cross-coupling reaction of brominated porphyrin with diborylated pyrrole. These target compounds were characterized by mass spectra, 1H NMR spectra and X-ray single-crystal diffraction analysis.(2) Further examination of the photophysical and electrochemical properties of these new porphyrin arrays were provided by fluorescence emission spectra, UV/vis absorption spetra and cyclic voltammetry. The chain porphyrin oligomers exhibit the optical and electrochemical properties, such as small electrochemical HOMO-LUMO gaps, reduced fluorescence quantum yields, broad Soret bands and red-shifted Q-bands.Those results show that the chain porphyrin arrays display larger electronic interactions with chain extension.