Synthesis and Characterization of Polythiophenes Bearing Diphenyl Groups in the Conjugated Chain

4,4'-dibromo-2-nitro-biphenyl and 4,4'-dibromo-2,3'-dinitro-biphenyl have been synthesized via nitration reaction with 4,4'-dibromobiphenyl as the raw material. Three novel thiophene derivatives, 4, 4'-di(4-hexyl-thiophen-2-yl)biphenyl, 4,4'-di(4-hexyl-thiophen-2-yl)-2-nitro-biphenyl and 4,4'-di(4-hexyl- thiophen-2-yl)-2,3'-dinitrobiphenyl were synthesized through Stille coupling reaction, followed by polymerization in the presence of FeCl3, respectively. UV-vis absorption spectra, fluorescence spectra, photoluminescence spectra and electrochemical properties of the polymers were investigated. And the band-gap (E-g), HOMO orbital energy (E-HOMO), and LUMO orbital energy (E-LUMO) of the polymers were calculated. Among the polymers, polymer PBTN and PBTD show lower band-gap (2.67 and 2.63 eV), lower HOMO energy level (-5.38 and -5.4 eV) and broader wavelength (432 and 438 nm) than that of polymer PBTB (2.69 eV, -5.36 eV and 424 nm) with incorporation of one nitro group or two nitro groups in the main chain, respectively.