Two new donor–acceptor (D–A) type organic conjugated random copolymers were successfully synthesized by three-component Stille coupling polymerization of indolo[3,2-b]carbazole (ICZ), isoindigo (IID) and thiophene units, namely PITID-X (X = 1 and 2), with the controlled monomer feed ratios of 3:1:4 and 1:1:2, respectively. The strategy of incorporating different alkyl-branched donor/acceptor units and raw material feed ratios facilitated the improvement of optical properties, solubility, conjugated structure, and electrochromic performance. Cyclic voltammetry, UV-vis-NIR absorption spectra, kinetic and colorimetric measurements of the spray-coated films were recorded in the fabricated three-electrode cells. The results showed that PITID-2, whose optical/electrical properties were better than that of PITID-1, was the candidate electrochromic material due to low band gap of 1.58 eV accompanying the color changing from cyan (neutral state) to gray (oxidized state). The copolymer also illustrated fast bleaching/coloration response time of 2.04/0.33 and 1.35/1.50 s in a 4 s time interval, high coloration efficiency of 171.52 and 153.08 cm² C⁻¹ and stable optical contrast of 18% and 58% at the wavelength of 675 and 1600 nm, respectively.

In this study, four novel donor–acceptor systems, 4-(2,3-dihydrothieno[3,4-b][1,4]dioxin -5-yl)-N-(4-(2,3-dihydrothieno[3,4-b][1,4]dioxin-5-yl)phenyl)-N-(4-nitrophenyl)aniline (NETPA), 4- (4-methoxythiophen-2-yl)-N-(4-(4-methoxythiophen-2-yl)phenyl)-N-(4-nitrophenyl)aniline (NMOTPA), 4-(4-methylthiophen-2-yl)-N-(4-(4-methylthiophen-2-yl)phenyl)-N-(4-nitrophenyl) aniline (NMTPA) and 4-nitro-N,N-bis(4-(thiophen-2-yl)phenyl)aniline (NTTPA), were successfully synthesized by Stille coupling reaction and electropolymerized to obtain highly stable conducting polymers, PNETPA, PNMOTPA, PNMTPA and PNTTPA, respectively. The polymers were characterized using cyclic voltammetry (CV), step profiling and UV–Vis–NIR spectroscopy. The band gaps (Eg values) were 1.34, 1.59, 2.26, and 2.34 eV, for PNETPA, PNMOTPA, PNMTPA and PNTTPA, respectively. In addition, electrochromic switching showed that all polymers exhibit outstanding optical contrasts, high coloration efficiencies and fast switching speeds in the near-infrared region (NIR). These properties make the polymers suitable materials for electrochromic applications in NIR region.

Two new donor–acceptor type electrochromic copolymers containing non-fluorinated and di-fluorinated benzothiadiazole analogues, namely P(TBT-TBTh) and P(TBT-F-TBTh), were synthesized successfully through chemical polymerization. Both polymers were measured by cyclic voltammetry, UV-vis spectroscopy, colorimetry and thermogravimetric analysis to study the influence of fluoro substitution on the electrochromic performance. The results demonstrated that the two polymer films displayed well-defined redox peaks in pairs during the p-type doping, and showed distinct color change from dark gray blue to light green for P(TBT-TBTh) with the band gap of 1.51 eV, and from gray blue to celandine green for P(TBT-F-TBTh) with the band gap of 1.58 eV. P(TBT-F-TBTh) presented lower highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energy levels, and better stability than P(TBT-TBTh). It was found that the two fluorine atoms participated in not only inductive effects but also mesomeric effects in the P(TBT-F-TBTh) backbone. In addition, the polymers exhibited high optical contrasts, short response time, and favorable coloration efficiency, especially in the near infrared region. The characterization results indicated that the two reported polymers can be the potential choice as electrochromic materials.

Large-fused-ring-based conjugated polymers possess wide application prospects in optoelectronic devices due to their high charge transport and wide optical absorption. In this paper, three low-bandgap donor–acceptor (D–A) type polymers PBIT-X (X = 1, 2, 3) based on alkylated benzodithiophene and tris(thienothiophene) as donors and thiadiazol–quinoxaline as an acceptor were synthesized via Stille coupling polymerization at different (donor/acceptor) D/A molar feed ratios. The band gaps of PBIT-1, PBIT-2, PBIT-3 were 1.10 eV, 1.04 eV and 1.02 eV, respectively. Spectroelectrochemistry studies showed that the three D–A type polymers have dual bands located in visible and near-infrared regions in the neutral state. The three D–A type polymers possess good electrochromic properties, such as an optical contrast of 56% and response time of 0.3 s. In particular, PBIT-3 could achieve three color changes from magenta to yellowish green to cyan during the oxidation process. The results indicate that these D–A type conjugated polymers based on large fused-ring units exhibit multiple color changes, endowing them with huge potential applications in visible and near-infrared electrochromic devices.

Three soluble conjugated polymers, named BEDPP, FLDPP, and CADPP, were prepared through the Suzuki polymerized reaction, and employed benzene (BE), fluorene (FL), and carbazole (CA) as the donor units, respectively. The electron-deficient molecule 2,5-bis-(2-octyldodecyl)-3,6-bis-(5-bromo-thiophene)-pyrrole[3-c]pyrrole-1,4-diketone(DPP) was introduced and used as the acceptor unit. The properties of these three copolymers were studied by a series of detailed characterization analysis, including X-ray photoelectron spectroscopy (XPS), colorimetry, electrochemical measurements, spectroelectrochemistry, kinetics, quantitative calculation, and thermogravimetric (TG) analysis, etc. The results revealed that BEDPP displayed a blue color in the neutral state and a light brown color in the oxidized state, FLDPP exhibited a cyan color in the neutral state and a gray color in the oxidized state, while CADPP displayed pure blue color in the neutral state and a light gray color in the oxidized state. All these polymers possess narrow optical band gaps lower than 1.80 eV and satisfactory thermal stability. The kinetic characterization showed that the optical contrasts (ΔT%) in the near-infrared region were superior to the visible region. The optical contrasts of BEDPP, FLDPP, and CADPP are 41.32%, 42.39%, and 45.95% in the near-infrared region, respectively, which made them a good application prospect in the near-infrared region. Amid the three polymers, CADPP has the highest coloration efficiency (around about 288 cm²·C⁻¹) and fast switching times (0.77 s in the coloring process and 0.52 s in the bleaching process) in the visible region, and the comprehensive performance of CADPP can be comparable to that of the reported D-A (Donor-Acceptor) type blue color polymers. In general, based on the good performances and the stable neutral blue color, the three polymers had profound theoretical significance for the development of electrochromic material and the completion of the RGB (Red, Green, Blue) color space.

Molecularly imprinted polymer (MIP) for vanillin was synthesized successfully by multi-step swelling suspension polymerization using polystyrene (PS) as the “seed”. The PS-MIP was characterized by sca