Research On Synthesis And Luminescent Properties Of Polythiophenes With Dioxane Group

Polythiophene and its derivatives have occupied prime position due to their advantages including high conducting efficiency, good redox reversibility, swift change of color with potential, and good stability in environment. They have promising applications in non-linear optical devices, polymer light-emitting diodes, gas sensors, organic transistors and electrochromic devices. Recently, many researches have been working at synthesis of polythiophenes in order to find and obtain novel polythiophenes with high stability, good processability and luminescent properties, and have made a great progress.Two novel polythiophenes with 1,3-dioxane group in the side chain named poly[3-(1,3-dioxane-2-ylethyl)thiophene] (PDT) and poly[3-(1,3-dioxane-2-ylethyl)-4-methylthiophene] (PDMT) were synthesized respectively in this paper. The specific process as below:firstly, poly(3-bromothiophene)(PBrT) and poly(3-bromo-4-methylthiophene)(PBrMT) were synthesized respectively from 3-bromothiophene and 3-bromo-4-methylthiophene using FeCl3 as oxidative catalyst; then in the presence of Ni(dppp)Cl2, PBrT and PBrMT could react with Grignard reagents to afford PDT and PDMT respectively. All the polymers were found to be soluble in common organic solvents such as chloroform, dichloromethane, tetrahydrofuran(THF) with no evidence of gel formation. The chemical structure, molecular weight, thermal properties of the polymers were characterized by 1H NMR method, GPC, and TGA respectively.1H NMR studies on PDT and PDMT confirmed that 80% of the total number bratoms in thiophene were replaced with the 1,3-dioxane-2-ylethyl; both of the two polymers had high molecular weight and ralatively low polydispersity index. They were able to be used at relative high temperatures.The absorption and emission properties of polymers were studied. The results were as follows:(1) the wavelengths of emission peaks for PDT and PDMT were blue shifted than that for PBrT and PBrMT, and emitted orange-yellow light and green light respectively; (2) the maximan emission wavelength of PDMT was blue shifted than that for PDT due to its methyl-substitution at 4-position.The redox property of PDT and PDMT was studied by cyclic voltammetry, and the energy levels and band gaps were calculated based on the UV-VIS absorption spectra and cyclic voltammetry curve, the conclusions were as follows:the EHOMO of PDT and PDMT were -5.34 eV,-5.98 eV, the ELUMO of PDT and PDMT were -3.15 eV,-3.61 eV, the band gaps were 2.19 eV,2.37 eV, respectively. The results showed that the band gaps of PDT and PDMT were able to be used as light-emitting materials in organic light emitting diodes.The absorption and emission properties of PDT and PDMT were compared to those of poly(3-cyclohexylthiophene) (PCHT) and poly(3-cyclohexyl-4-methylthiophene) (PCHMT) (quoted from literatures) due to their similar chemical structure. Because of the the interaction resulted from the steric hindrance effect of the group of 1,3-dioxane-2-ylethyl and the electronegativity of oxygen atoms in the side chain of PDT and PDMT, the absorption and emission wavelengths of PDT's solution were bule shifted than that for PCHT; however, the maximan absorption and emission wavelengths for PDMT's solution and film were red shifted than that for PCHMT's.