Donor-Acceptor-Type Copolymers Based on 3,4-Propylenedioxy-thiophene and 5,6-Difluorobenzotriazole: Synthesis and Electrochromic Properties

Benzotriazole-EDOT electrochromic conjugated polymers perform sub-second response time and 774 cm2C-1 coloration efficiency

To investigate the effect of double fluorine substitution on the optical, electrochemical, thermodynamic, morphological and electrochromic properties of electrochromic polymers, two benzotriazole-EDOT electrochromic conjugated polymers of PBTz-E and P2F-BTz-E were...

Implementing the donor–acceptor approach in electronically conducting copolymers via electropolymerization

Electropolymerization has become a convenient method for synthesizing and characterizing complex organic copolymers having intrinsic electronic conductivity, including the donor (D)–acceptor (A) class of electronically conducting polymers (ECPs).

Electrosynthesis of Electrochromic Polymer Membranes Based on 3,6-Di(2-thienyl)carbazole and Thiophene Derivatives

Five carbazole-containing polymeric membranes (PDTC, P(DTC-co-BTP), P(DTC-co-BTP2), P(DTC-co-TF), and P(DTC-co-TF2)) were electrodeposited on transparent conductive electrodes. P(DTC-co-BTP2) shows a high ΔT (68.4%) at 855 nm. The multichromic properties of P(DTC-co-TF2) membrane range between dark yellow, yellowish-green, gunmetal gray, and dark gray in various reduced and oxidized states. Polymer-based organic electrochromic devices are assembled using 2,2'-bithiophene- and 2-(2-thienyl)furan-based copolymers as anodic membranes, and poly(3,4-ethylenedioxythiophene)-poly(styrene sulfonic acid) (PEDOT-PSS) as the cathodic membrane. P(DTC-co-TF)/PEDOT-PSS electrochromic device (ECD) displays a high transmittance change (ΔT%) (43.4%) at 627 nm as well as a rapid switching time (less than 0.6 s) from a colored to a bleached state. Moreover, P(DTC-co-TF2)/PEDOT-PSS ECD shows satisfactory optical memory (the transmittance change is less than 2.9% in the colored state) and high coloration efficiency (512.6 cm2 C-1) at 627 nm.

4-(Trifluoromethoxy)phenyl-Containing Polymers as Promising Anodic Materials for Electrochromic Devices

Three 4-(trifluoromethoxy)phenyl-based polydithienylpyrroles (PTTPP, P(TTPP-co-DTC), and P(TTPP-co-DTP)) were synthesized electrochemically and their electrochromic behaviors were characterized. The introduction of electron withdrawing trifluoromethoxy unit in the side chain of polydithienylpyrroles (PSNS) decreases the HOMO and LUMO energy levels of PSNS. PTTPP film displays three various colors (grayish-yellow at 0 V, grayish-blue at 1.0 V, and bluish-violet at 1.4 V) from reduced to oxidized states. The optical contrast of PTTPP, P(TTPP-co-DTC), and P(TTPP-co-DTP) electrodes are 24.5% at 1050 nm, 49.0% at 916 nm, and 53.8% at 1302 nm, respectively. The highest η of the PTTPP electrode is 379.64 cm2 C−1 at 1050 nm. Three ECDs based on PTTPP, P(TTPP-co-DTC), or P(TTPP-co-DTP) as anodic film and PProDOT-Et2 as cathodic film were fabricated. PTTPP/PProDOT-Et2 ECD showed high transmittance change (35.7% at 588 nm) and high η (890.96 cm2·C−1 at 588 nm). P(TTPP-co-DTC)/PProDOT-Et2 and P(TTPP-co-DTP)/PProDOT-Et2 ECDs showed high transmittance change, rapid response time, adequate open circuit memory, and good electrochemical redox stability. Based on these findings, this work provides novel insights for appropriate design of high transmittance change and high efficient multi-colored electrochromic polymers.

Applications of Copolymers Consisting of 2,6-di(9H-carbazol-9-yl)pyridine and 3,6-di(2-thienyl)carbazole Units as Electrodes in Electrochromic Devices

A series of carbazole-based polymers (PdCz, P(dCz2-co-dTC1), P(dCz2-co-dTC2), P(dCz1-co-dTC2), and PdTC) were deposited on indium tin oxide (ITO) conductive electrodes using electrochemical polymerization. The as-prepared P(dCz2-co-dTC2) displayed a high ΔT (57.0%) and multichromic behaviors ranging from yellowish green, greenish gray, gray to purplish gray in different redox states. Five organic electrochromic devices (ECDs) were built using dCz- and dTC-containing homopolymers and copolymers as anodic materials, and poly(3,4-(2,2-dimethylpropylenedioxy)thiophene) (PProdot-Me₂) as the cathodic material. The P(dCz2-co-dTC2)/PProdot-Me₂ ECD presented remarkable electrochromic behaviors from the bleached to colored states. Moreover, P(dCz2-co-dTC2)/PProdot-Me₂ ECD displayed a high optical contrast (ΔT, 45.8%), short switching time (ca. 0.3 s), high coloration efficiency (528.8 cm² C⁻¹) at 580 nm, and high redox cycling stability.

Light-Induced Conformational Change of Uracil-Anchored Polythiophene-Regulating Thermo-Responsiveness

Tuning the electronic structure of a π-conjugated polymer from the responsive side chains is generally done to get desired optoelectronic properties, and it would be very fruitful when light is used as an exciting tool that can also affect the backbone chain conformation. For this purpose, polythiophene- g-poly-[ N-(6-methyluracilyl)- N, N-dimethylamino chloride]ethyl methacrylate (PTDU) is synthesized. On exposure to diffuse sunlight, the uracil moieties of the grafted chains cause the absorption maximum of PTDU solution to show gradual blue shift of 87 nm and a gradual blue shift of 46 nm in the emission maximum, quenching its fluorescence with time. These effects occur specifically at the absorption range of polythiophene (PT) chromophore on direct exposure of light of different wavelengths, and the optimum wavelength is found to be 420 nm. Impedance study suggests a decrease in charge transfer resistance upon exposure because of conformational change of PTDU. Theoretical study indicates that on exposure to visible light, uracil moieties move toward the backbone to facilitate photoinduced electron transfer between the PT and the uracil, attributing to the variation in optoelectronic properties. Morphological and light-scattering studies exhibit a decrease in particle size because of coiling of the PT backbone and squeezing of the grafted chain on light exposure. The transparent orange-colored PTDU solution becomes hazy with a hike in emission intensity on addition of sodium halides and becomes reversibly transparent or hazy on heating or cooling. The screening of cationic centers of PTDU by varying halide anion concentration tunes the phase transition temperature. Thus, the light-induced variation in the backbone conformation is responsible for tuning the optoelectronic properties and regulates the thermos-responsiveness of the PTDU solution in the presence of halide ions.

Synthesis and characterization of novel donor-acceptor type electrochromic polymers containing diketopyrrolopyrrole as an acceptor and propylenedioxythiophene or indacenodithiophene as a donor

A range of low band gap donor-acceptor conjugated polymers (P1-P3) with backbones composed of diketopyrrolopyrrole (DPP), propylenedioxythiophene (ProDOT) and indacenodithiophene (IDT) units were designed and synthesized using the Stille coupling reaction. The optical, electrochemical and electrochromic properties of the resultant polymers were thoroughly characterized. These polymers showed exceptional solubility in common organic solvents and displayed thermal stability at a high temperature. The optical and electrochemical measurements revealed slight variations in the maximum absorptions and oxidation peaks depending on the intrinsic D-A ratio in each polymer, and narrow band gaps lower than 1.60 eV were found for these polymers. Upon oxidation, the polymer films exhibit distinct color changes (pale violet-red to dark gray for P1, rosy brown to silver for P2, atrovirens to light grey for P3) in the VIS and NIR regions. Moreover, the electrochromic switching studies indicated that these polymers have favorable switching properties, such as rapid response speed and high optical contrast and coloration efficiency, and are outstanding candidates for electrochromic applications.

Synthesis and characterization of novel donor–acceptor type neutral green electrochromic polymers containing an indolo[3,2-b]carbazole donor and diketopyrrolopyrrole acceptor

Indolocarbazole bearing donor–acceptor type polymers have rarely been reported in the electrochromic field despite them having considerable development in the applications of organic photoelectric devices. In this paper, two novel soluble electrochromic polymers, namely PDTCZ-1 and PDTCZ-2, were prepared by chemical polymerization including indolo[3,2-b]carbazole (IC) units as the donor, diketopyrrolopyrrole (DPP) units as the acceptor and bithiophene units as the bridging group. Through diverse characterization techniques such as cyclic voltammetry (CV), scanning electron microscopy (SEM), UV-vis spectroscopy and thermogravimetric analysis (TGA), it was found that PDTCZ-1 and PDTCZ-2 exhibited saturated green in the neutral state and pale green in the oxidized state with optical band gaps of 1.44 eV and 1.39 eV, respectively, as well as demonstrating fast switching speed, satisfactory coloration efficiency and favorable thermal stability. In addition, the proportion of donors to acceptors definitely exerted an influence on the electrochromic properties of the polymers. As the thiophene/IC/DPP ratio changed from 4/3/1 (PDTCZ-1) to 5/4/1 (PDTCZ-2), meaning an increase of the donor ratio, the polymer showed a reduced onset oxidation potential, decreased optical band gap and different dynamic parameters. The positive results suggest that PDTCZ-1 and PDTCZ-2 could be promising candidates as neutral green electrochromic materials and deserve more attention and penetrating research.

Two novel neutral green D–A type conjugated polymers were synthesized, illustrating satisfactory electrochromic properties, such as low band gaps, desirable color switches, excellent solubility and favorable thermal stability.