β to β Terpyridylene–bridged porphyrin nanorings

Abstract

6,6″-Terpyridylene bridged cyclic porphyrin dimer 2Ni, trimer 3Ni, tetramer 4Ni and pentamer 5Ni were obtained through Suzuki-Miyaura coupling reaction of β,β′-diboryl Ni(II) porphyrin with 6,6″-dibromo-2,2′:6′,2″-terpyridine. Free base porphyrin nanorings 2H-5H were obtained by demetallation of 2Ni-5Ni with sulfuric acid in CHCl3 and then were converted into 2Zn-5Zn upon treatment with Zn(OAc)2 in quantitative yields, respectively. All of these newly synthesized porphyrin nanorings were characterized by high-resolution mass spectrometry and 1H NMR spectroscopy. The photophysical properties of porphyrin nanoring were examined by UV–vis and fluorescence spectra. The electrochemical properties of 2Ni–5Ni were investigated by cyclic voltammetry and differential pulse voltammetry. The UV–vis absorption spectra and fluorescence spectra of these cyclic porphyrin arrays indicate that there exist unique electronic interactions between the constituent porphyrin units in each ring. Electrochemical analysis shows that the trimer 3Ni exhibit different redox behavior, which indicate that the porphyrin units in 3Ni are presumably more coplanar than in other cyclic porphyrin arrays.