Two Ethynylene-linked Polymers Based On Benzodithiophene:Synthesis And Photoelectric Properties

N,N-Diethylthiophene-3-carboxamide was synthesized by chlorination and amination reaction from Thiophene-3-carboxylic acid. Then, the amide was dealt with n-BuLi to acquire4,8-Dihydrobenzo[1,2-b:4,5-b’]dithiophen-4,8-dione. Subsequently,4,8-dioctyloxybenzo[1,2-b:4,5-b’]dithiophene was prepared from the dione and1-bromooctane in the presence of Zinc powder and NaOH, then brominated with Br2to give2,6-dibromo-4,8-dioctyloxybenzo[1,2-b:4,5-b’]dithiophene, the latter truned to2,6-trimethylsilyl-4,8-dioctyloxybenzo[1,2-b:4,5-b’]dithiophene in the presence of trimethylsilylacetylene, then2,6-bisacetenyl-4,8-dioctyloxybenzo[1,2-b:4,5-b’]dithiophene was obtained by removing the tremethylsilyl with an overall yield of35.87%. Besides,3,6-dibromobenzothiadiazole and N-octyl-3,6-diiodocarbazole were prepared from o-phenylenediamine and carbazole with yields of52.25%and53.22%, respectively. All compounds were confirmed by1H NMR and13C NMR spectra.Pl(poly(2,6-bisacetenyl-4,8-dioctyloxybenzo[1,2-b:4,5-b’]dithiophene-alt-3,6-dibromob enzothiadiazole)) and P2(poly(2,6-bisacetenyl-4,8-dioctyloxybenzo [1,2-b:4,5-b’]dithiophene-alt-N-octyl-3,6-diiodocarbazole)) were synthesized by Pd(Ⅱ)-catalyzed Sonogashira coupling reaction. Their structures were characterized by1H NMR and FT-IR spectra. The Mn of P1and P2are4502and7369Da, respectively, and the degrees of polymerization are7and10, respectively. TGA test indicated that P1and P2were thermally stable with decomposition temperature of285and326℃. The UV-Vis spectra tests showed they had the absorption peaks at404and483nm for P1, and401and429nm for P2, respectively. The optical band gap of P1and P2estimated from the absorption onset were1.92and2.27eV, respectively. Combined with CV test, the HOMO and LUMO level were-5.64eV and-3.72eV for P1,-5.66eV and-3.39eV for P2, respectively. DFT calculations were performed at B3LYP/6-31G*level, the result indicated that the HOMOs were distributed over benzo[1,2-b:4,5-b’]dithiophene and acetylene bond, but the LUMOs were localized in benzothiadiazole and acetylene bond. However, for P2, the HOMOs and LUMOs did not have much difference. The conductivity of P1and P2transformed from insulator to semiconductor after doping with iodine.