Studies On The Synthesis And Properties Ofβ,β Directly Bridged Porphyrin Arrays

Porphyrin arrays show better properties in electron and energy transfer than porphyrin monomers due to their enhanced π-conjugation systems. Porphyrin arrays have extensive applications in the area of optoelectronic devices, sensors, nonlinear optical (NLO) materials, and pigments for photodynamic therapy and so on in light of their unique optical, photophysical and photoelectrical properties, thus the study of porphyrin arrays has been a hot point in chemistry perpetually. In this paper, a series of β-β directly bridged covalently porphyrin arrays have been synthesized via Pd-catalyzed Suzuki-Miyaura cross-coupling reaction of β-borylated and (3-brominated porphyrins. Further examination of the photophysical and electrochemical properties of these new porphyrin arrays provided relatively ideal results. The key studies are listed below.(1) According to literature procedures,3,5-di-tert-butylbenzaldhyde was prepared from toluene. Then two important porphyrin monomers:5,10,15-triarylporphyrin and5,15-bisarylporphyrin (aryl=3,5-di-tert-butylphenyl) were synthesized from aldehydes and pyrrole. Highly regioselective Ir-catalyzed [3-borylation via C-H bond activation provided β-borylated porphyrins in high yields. A new synthetic methodology of β-brominated porphyrins has been developed:facile treatment of β-borylated porphyrins with CuBr2in refluxing THF, MeOH and water could efficiently furnish β-brominated porphyrins in high yields.(2) A series of cyclic and non-cyclic β-β directly bridged porphyrin arrays were synthesized successfully through classic Pd-catalyzed Suzuki-Miyaura cross-coupling reaction of β-borylated and (3-brominated porphyrins. These new compounds were characterized by1H NMR spectra, mass spectra and X-ray single-crystal diffraction analysis.(3) The photophysical and electrochemical properties of these new porphyrin arrays have been examined by UV/vis absorption spetra, fluorescence emission spectra, fluorescence decay profiles, femtosecond transient absorption spetra and cyclic voltammetry. The cyclic porphyrin oligomers exhibit the optical and electrochemical properties different from those of the non-cyclic oligomers, such as non-split and broad Soret bands, red-shifted Q-bands, small electrochemical HOMO-LUMO gaps, and reduced fluorescence quantum yields and lifetimes. Those results reveal that the cyclic porphyrin arrays display larger electronic interactions and faster energy imitation rate along the rings than non-cyclic arrays. The energy imitation rate of cyclic porphyrin pentamer10Zn is about (400fs)-1...