Bithiophene-EDOT Oligomers:Synthesis, Electrochemical Polymerization, And The Performances Of Their Polymers

Since the discovery of conductive polymer by Shirakawa, MacDiarmid and Heegerin in 1977, the development of new conductive polymer has attracted the wide attentions of scientists all over the world. Among them,poly(3,4-ethylenedioxythiophene) has found widely applications such as electrochromic and supercapacitor due to its high electrical conductivity (ca.500 S/cm), high electrochemical and thermal stability, low band gap, and low oxidation potential. The combination of 3,4-ethylenedioxythiophene unit with other units to synthesize various π-conjugated also madethe synthesizedconjugated oligomer/polymer owned some excellent properties. The bithiophene unit has been applied in various optoelectronic devices due to its simple synthesis and the copolymer based it shown some excellent-optical and electrical properties. In this thesis, five hybrid oligomers whichemployedalkyl functionalized bithiophene unit as the core and 3,4-ethylenedioxythiophene (EDOT) unit as the terminals we designed and synthesized.The structure, electronic, and optical properties of the oligomers were studied by UV-visspectra, fluorescencespectra, theoretical calculations, and two-photon fluorescence techniques, etc. The electrosynthesized polymers and its potential applications in the field of electrochromic and supercapacitor have been explored. Lastly, the electrochemical layer-by-layer (LbL) technique was used to prepare the multilayers (3-layer/ITOPEDOT/PBEDOT-BT/PEDOT) based on PEDOT films and PBEDOT-BT film alternately. By characterizing the properties of as-prepared polymers, we could conclude that the bithiophene-EDOT copolymers were excellent materials in the applications of electrochromic and supercapacitor.1. We designed and synthesized five oligomers based on alkylted bithiophene unit as the core and EDOT units as the terminal, and characterized its structure by means of NMR. The structure-property relationships of the oligomers were systematically studied by UV-vis, fluorescence, theoretical calculations, and two-photon fluorescence techniques. The synthetic route is realatively simple and the yield was about 60%. The oligomers show moderate fluorescence intensity (the fluorescence quantum yield was between 0.10-0.18) and weak two-photon fluorescence properties (the two-photon absorption cross-section was between 0.8 GM-7.76 GM) and the solvent effects is obvious. In the solutions, the alkyl chain length affected the photophysical properties of the oligomers seriouly due to the steric hindrance of the alkyl chain on the bithiophene backbonewould affect the torsion angle between bithiophene unit and the adjacent EDOT ring. These oligomers would found widerly applications in organic laser micro-optical device, optoelectronic transmitting apparatus, etc.2. We electopolymerized thecorrespondingcopolymers of the five oligomers by anodic oxidation method in CH2Cl2-Bu4NPF6 (0.10 mol L-1) electrotyle solution, and investigated its electrochemical and electrochromic performances in CH3CN-Bu4NPF6 solution. The structure, electrochemical properties, and surface morphology of the polymers were characterized by CV, FT-IR, SEM, TGA, UV and fluorescence technigues. The results show that the resulting polymer has excellent redox activity, excellent electrochemical stability and thermal stability, and its morphology is smooth and flat topography. As-prepared polymers also have good electrochromic properties:the optical contrast was reach up to 41.4%, the coloration efficiency was between 96.8 and 293.2 cm2 C-1, and the fastest response time was reach up to 0.2 s. These results indicated that the bithiophene-EDOT copolymers are potentially electrochromic device material.3. We taken the potential (0.7 V vs. Ag/AgCl) menthod to electropolymerize four bithiophen-EDOT-based copolymers. The capacitive properties of the copolymer investigated by cyclic voltammetry, galvanostatic charge-discharge, and AC impedance methods. The results showed that as-synthesized copolymer has good capacitive properties (138.2 F g-1--203.4 F g-1 (5 mV s-1)) and good rate capability (78.8%-91.0%), and excellent cycle stability (the maximum retention of the initival capacitance value was up to 84.6%). Symmetric supercapacitor based on them shown higher energy density (up to 11.6 Wh/kg) and power density (up to 13.9Wh /kg).The energy density of them was all higher than the commercial capacitor (typically 5-10 Wh/kg). These results indicated that these conductive polymers may be a promising supercapacitor electrode material.(4) Due to the good capacitance performance of PBEDOT-BT-based copolymers. In this chapter, we take a simple electrochemical deposition technique to prepare 3-layer/ITO PEDOT/PBEDOT-BT/PEDOT electrode. The capacitive performances of 3-layer/ITOPEDOT/PBEDOT-BT/PEDOT electrode in CH3CN-Bu4NPF6 solutionswere investigated by cyclic voltammetry, galvanostatic charge-discharge, and AC impedance methods.The mography of it were studied by AFM and SEM techniques. The results show that 3-layer/ITO PEDOT/PBEDOT-BT/PEDOT electrode is porous nanostructure, and having a high specific capacitance and good electrochemical stability. Symmetric supercapacitor based on it also shown a relatively high specific capacitance (96.8 F g-1) and a very high energy density (260. 1Wh kg-1).