Synthesis Of Thiophene-based Conjugated Polymers For Applications On Electrochromism

Electrochromic materials are defined as that a material can be electrochemically switched between different color states(including visible and infrared region) as a result of an electron-transfer or redox reactions. Combining easy control, low cost, fast response time, long-term optical stability, electrochromic materials are now strongly impacting the development of smart windows, smart sunglass, green displays, electronic papers, military camouflage. As one of the most important electrochrmic materials, significant synthetic effort has been dedicated to develop novel conducting polymers during the past decades. However, the laborious, costly synthesis and limited color are not desired. Obtaining multielectrochromic polymers through simple and economical way are still important. In addition, donor-acceptor polymers have been proved to present dual-band or broad absorption of electrochromic properties. However, the limited electron-rich units and insolubility of most current D-A electrochromic polymers are not good for commercial applications, and the interaction mechanism of donor and acceptor part in the polymer backbone are still not clear, the development of electrochromism need more novel and soluble D-A electrochromic polymers.In this article, we use BFEE as the polymerization system, the solvent effect on electrochromic properties of PEDOT has been investigated. And copolymers based on thiophenes and anthrancene have been electrochemically and successfully prepared in BFEE system. A series number of thiophene-anthracene monomers have been synthesized, preparation and characterizations of the corresponding copolymers have been done to investigate the effect of thiophene content. Nine soluble D-A polymers have been synthesized via Suzuki and Stille coupling reaction, using Carbzole(Cz), Benzodithiophene(BDT), Indacenodithiophene(IDT) as the donor part and benzothiadiazole(Tz) as the acceptor part.In the first part, the solvent effect on preparation and electrochromic properties of PEDOT has been investigate. The onset oxidation potentials of EDOT in acetonitrile, aqueous solution and BFEE-THF are 1.07, 0.92 and 0.82 V, respectively. The lowest oxidation potential of EDOT in BFEE-THF can be attributed to the weak interaction between the Lewis acid(BFEE) and EDOT monomer system. In addition, the polymerization rate of EDOT in BFEE-THF is as one tens as that in acetonitrile and aqueous solution. The low onset oxidation potential can produce more EDOT cation radicals, and low polymerization rate can induce the regular and short-chain polymer. Therefore, PEDOT film prepared in BFEE-THF presents different electrochromic properties, which display claret red at-0.8V, light grey at 0.2V and sea blue at 1.0V. The π-π* transition absorption peak in the neutral state is located at 512 nm, which is much shorter than PEDOT film prepared in acetonitrile or aqueous solution.As the onset oxidation potential of aromatic monomers can be lowered by BFEE, copolymers base on thiophene(or EDOT) and anthracene have been successfully prepared. The chemical structure properties of derived copolymers can be tuned through the feed ratio. Even through the feed ratio of anthracene and thiophene is as low as 1/4, anthracene units are still major part in the copolymer chain because of the low onset oxidation potential of anthrancene. Multielectrochromic properties can be achieved via these copolymers. The copolymer prepared by anthracene/EDOT feed ratio of 1/4 exhibits a maximum optical contrast of 82% at 503 nm which is much close to the highest optical contrast of electrochromic materials. The copolymer prepared by thiophene and anthracene can display six colors(yellowish red, yellow, yellow green, blue green, light blue and dark blue) under various applied potentials, and reasonable. All of these indicate the satisfactory electrochromic properties of the copolymer films prepared from thiophene(or EDOT) and thracene.A series of monomers based on thiophene, EDOT and anthracene have been synthesized via Stille coupling. These monomers are failed to electropolymerize homopolymers. An assembled electrochromic device based on An-EDOT-An has been fabricated by applying a potential of 2.5V, and the device can present remarkable electrochromic behavior under various external potentials, while the switching response and stability are not good. The monomers based on thiophene and anthracene are good comonomers to electrochemically copolymerize with thiophene, EDOT, 3-methylthiophene. All of the prepared copolymers present multicolor electrochromism, reasonable response and stability can be achieved. In addition, the electrochromic properties of these copolymers can be tuned by the comonomers. As the anthrance content decrease into a very small amount, no obvious tuning effect can be observed on the optical properties of the copolymers.A series of soluble donor-acceptor(D-A) polymers containing 2, 1, 3-benzothiadiazole as the electron-deficient building core have been designed and synthesized via Stille and Suzuki polycondensation, wherein the alternating electron-rich moieties along the same backbone have been systematically tuned. These polymers show good solubility and easily spin-coat in thin film. By tuning the donor section of the D-A polymer via incorporating indacenodithiophene(IDT), benzodithiophene(BDT) and carbazole(Cz) and the addition of thiophene units, the spectroelectrochemical properties of the D-A polymers can be broadly tuned. The absorption spectrum of the neutral polymers can changes from red to blue.