Synthesis And Performance Of Donor-Acceptor Electrochromic Materials Based On Thiophene Units

Donor-acceptor (D-A) electrochromic materials have attracted great interest for the past years due to the fact that their band gap can be tuned through intramolecular charge transfer (ICT) between the donor and acceptor units. In this dissertation, the D-A electrochromic materials based on the thiophene units were developed. The effects of different side-chain accepted groups, networked polymer state, asymmetric structure on the performance of electrochromic materials were investigated. The main purpose was to gain the materials with multicolor-showing、high optical contrast and fast switching time.For the first part, four new electrochromic materials,4-(9H-carbazol-9-yl)-phenyl-methanone (CPM) and4-(3,6-di(thiophen-2-yl)-9H-carbazol-9-yl)-phenyl-methanone (TCPM), ethyl4-(3,6-di(thiophen-2-yl)-9H-carbazol-9-yl)-benzoate (ETCB) and9-(4-nitrophenyl)-3,6-di(thio-phen-2-yl)-9H-carbazole (NDTC), were synthesized and characterized. All the compounds show good electroactivity, and their corresponding polymer could be synthesized by electrochemical route. Moreover, the copolymer based on ETCB and3,4-ethylenedioxythiophene (EDOT) was also obtained by electropolymerization. Compared with the PCPM, PTCPM film shows better performance due to the introduction of the thiophene units, which can show yellow、brown and blue under different potentials and display reasonable optical contrast (41%,1100nm) and faster switching time (2s,1100nm). Moreover, PETCB film displays the color change from yellow-green to blue-purple, while the color-change of PNDTC film is from yellow to gray. Both the polymer films exhibit simlimar optical contrast and switching time with PTCPM. However, the copolymer show better electrochromic properties, which could show five colors change (brick red, orange, yellow, green, blue) under different applied potentials and higher optical contrast (50%of1100nm), faster switching time (1.9s,1100nm) and higher coloration efficiency (356.88cm2C-1,1100nm). All the results show that the band gap of the polymer can be tuned by the acceptor group of the side-chain, which leads to the different colors showing under different applied potentials. The band gap can also be further changed by the introduction of the monomer with narrow bandgap in the main chain, which improve the performance of the polymer.In this second part, a novel material, Z-2,3-bis(4-(thiophen-3-yl)-phenyl)-acrylonitrile (Z-TPA), was synthesized and characterized. Its polymer and copolymer with EDOT were gained by electropolymerization. UV-vis absorption and fluorescence spectra show that this monomer possesses the properties of aggregation-induced emission (AIE) due to the introduction of acrylonitrile unit, which can show sky-blue emitting at the aggregation state and almost no emitting at the solution state. Both its polymer and copolymer displayed better redox activity. Spectroelectrochemical analyses show that the copolymer film exhibited multicolor (from deep red, gray to blue). Spectrochronoamperometry data reveal that the copolymer films have high chromatic contrast (38%in546nm,42%in1100nm) and faster switching time (1.8s of546nm,1.9s of1100nm) as compared to the homopolymer P(Z-TPA). What’s more, the copolymer film was used to construct a dual type polymer electrochromic device (ECDs) with PEDOT. The ECDs shows the reasonable optical contrast (18%in560nm,22%in640nm)、fast switching time (1.5s of560,2s of640nm) and good stability.For the last part, two novel asymmetric-structure compounds based on thiophene derivative and Benzo-2,1,3-thiadiazole,4-(funan-2-yl)-7-(thiophen-2-yl)benzo[c][1,2,5]thiadiazole (FTBT) and4-(2,3-dihydro thieno[3,4-b][1,4]dioxin-5-yl)-7-(furan-2-yl)benzo[c][1,2,5]thiadiazole (DFBT), were synthesized and characterized. Their polymer could be gained by electropolymerization. Spectroelectrochemical analyses show the absorption peaks of PDFBT move to the long-wavelength region due to the existence of EDOT units, the bandgap of PFTBT and PDFBT are1.63and1.42eV, respectively. PFTBT film shows color change from purple to light blue upon different applied potentials and PDFBT film changes from blue-green to black-purple. Spectrochronoamperometry data indicate that PFTBT film exhibits better performance than PDFBT film, which displays the better optical contrast (35%in760nm,45%in1100nm) and faster switching time(0.9s of760nm,1.6s of1100nm). Both the polymer films hold better stability.