Synthesis And Electrochromic Properties Of Isoindigo-thiophenes Based Donor-acceptor-donor Type Polymers

Electrochromic materials as an important functional material change their optical properties in response to the alteration in applied potential,mainly in color and transmittance in appearance.As a special kind of electrochromic material,donor-accepter-donor type conjugated polymers exhibited high electrochromic properties,low bandgap though structure modification.Preliminary reports showed that the more electron-accepting nature of acceptor in donor-accepter-donor type conjugated polymer electrochromic materials could decrease the LUMO energy and red-shift,resulting low-energy and NIR electrochromic materials.However,comparing with the donor groups,the researches of acceptor units are relatively limited.And the relationship between acceptor structure and electrochromic performance remains to be further studied.Isoindigo(IDO)possesses electron-accepting nature and easy modification,which has tremendous development potential.Thus,seven IDO-based electrochromic polymers were synthesized employing IDOH and IDOD as acceptor and thiophene(Th),3-hexylthiophene(HTh),3,4-ethylenedioxythiophene(EDOT),2,2',3,3'-tetrahydro-5,5'-bithieno[3,4-b][1,4]dioxine(BisEDOT)as donors,and corresponding polymers were obtained through electropolymerization.In this thesis,the relationship between donor and property was systematically studied.The research contents and conclusions are as follows:1.In order to investigate the relationship of the structures and electrochromic properties,both precursors,IDOH-Th and IDOD-Th,were synthesized though Stille coupling raection employing IDOH/D as acceptors and thiophene as donors.Introduction of alkyl chain groups on acceptor can improve the solubility of precursors.Both polymers were obtained using electropolymerization method and exhibited grey color in neuture and oxidation state.The optical contrast of IDOH-Th and IDOD-Th are about 3?6%,and the CE are 30?90 cm2 C-1.The longer alkyl chains resulted to steric resistance,led to lower electrochemical and electrochromic properties for PIDOD-Th.2.3-Hexylthiophene as donor was applied to IDO-based D-A-D type conjugated polymers,which improved the electrochemical and electrochromic properties of IDO-based electrochromic materials and enriched the variety of electrochromic materials.Alkyl groups on ? site of thiophene can effectively avoid cross-coupling reaction in electropolymerization process,reduce the applied potential and lead to the polymer film with more regularity and higher degree of regularity.The results show that both polymers were high electrochemical and electrochromic properties,which improving with PIDOH/D-Th.What'more,both polymers have obvious color changes(from blue in neuture state to grey color in oxidation state)and the optical contrast was up to 50%.3.High performance of PEDOT as donors in IDO-based electrochromic materials widely improved the electrochromic properties and obtained low-badgap and neutral green electrochromic polymers.PEDOT with large electron cloud density and strong electronic properties could decrease the applied potential and improved electrochemical and electrochromic properties.The loss of the total charge for PIDOH-EDOT was less than 8%after 4000th cycles(>92%),which made it a possibility to apply to device.What's more,the bandgap of[olymers were obviously reduced(1.26 eV)and the optical contrast in NIR were reach 30?59%,the CE were up to 362 cm2 C-1,the respond time were lower than 0.4 s.4.PBisEDOT with strong donor property and long conjugated structure was used as donor group,which widely improved the IDO-based electrochromic properties,achieved a new breakthrough in electrochromic filed,and developed application of isoindigo material in NIR region.The electroactivity of PIDOH-BisEDOT remained above 95%after circulation of 5000 cycles.Importantly,BisEDOT as donor groups makes PIDOH-BisEDOT exhibite low bandgap about 1.02 eV and reversible color conversion from emerald green in neutral state to sky-blue in oxidation state,which illustrated that the necessary conditions for the preparation of low band gap and NIR electrochromic materials is longer conjugate structures and high donor group.PIDOH-BisEDOT shows excellent electrochromic performances in NIR region with high optical contrast(more than 80%),high CE(more than 200 cm2 C-1.The highest is up to 1025 cm2 C-1 at 1300 nm),which provides a strong theoretical basis for preparation of high performance,low bandgap and green electrochromic materials.