Dual-type Electrochromic Devices Research Articles

“Perfect match” of the carbazole-based conducting polymer and polyoxometalate nanocomposite components for enhanced optical and electrical properties

Conducting polymers (CPs) have been recognized as ideal matrices for electroactive species because of their ability to host them at the molecular level and can interact synergistically. One of the promising approaches is to make the optical and electrical properties of CPs easily tunable with nano-sized reactive inorganic species such as electroactive molecules, metal oxides, and polyoxometalates. In this study, organic–inorganic nanocomposites that include a triazine-centered carbazole and different types of polyoxometalate (Keggin and Dawson) derivatives have been electrochemically synthesized to obtain enhanced electrical and optical properties by determining the perfect match of the components. In situ incorporating POM clusters into cross-linked conducting polymers lead to organic–inorganic hybrid materials with not only value-adding properties but also synergistic effects. It has been observed that charge density and optical contrast values increased with the introduction of POM derivatives into the conductive polymer structure, while these values decreased when the feed ratio of POM derivatives increased. Furthermore, the highest optical contrast and charge density values were obtained in the molybdenum (POM4) based POM derivative when compared to all POM derivatives. Within the scope of technological application, dual-type electrochromic devices (ECDs) have been fabricated using poly(3,4-ethylenedioxythiophene) (PEDOT) and PCT3 or POM4/PCT3 and their characterization studies have been carried out.

Hunting black color via absorption engineering: EDOT and thiophene-benzothiadiazole based black-to-transmissive copolymer and its electrochromic device application

Neutral state black electrochromics are prominent materials for smart applications such as displays, car rear views, e-papers etc. This work has aimed to obtain a neutral state black electrochromic polymer, by tuning the optical absorbance to whole visible region. Two monomers, 4,7-bis(5-(thiophen-2-yl)thiophen-2-yl)benzo[c] [1,2,5]thiadiazole (TTBTT) and 3,4-ethylenedioxythiophene (EDOT), were selected according to their complementary absorbance behaviors, and they were combined in the same polymer backbone via electrochemical copolymerization technique. Copolymerization was performed using three different monomer feed ratios (2:1, 1:1 and 1:2 (EDOT: TTBTT)). Even though all the copolymers exhibited dark to transmissive colors from neutral to oxidized states, changing the monomer feed resulted in different optical contrast, switching response and color hues for each copolymer. The higher optical contrast (from 17% to 27%) and faster switching response (from 3.6 s to 1.8 s) were recorded as EDOT unit increase in the copolymer chain. A dual type electrochromic device was also constructed using the copolymer and the resulting device was successfully changed its color from black to transmissive.

Electrosynthesis of electrochromic polymers based on bis-(4-(N-carbazolyl)phenyl)-phenylphosphine oxide and 3,4-propylenedioxythiophene derivatives and studies of their applications in high contrast dual type electrochromic devices

Five phenylphosphine oxide-containing polymers (PBCPO (poly(bis-(4-(N-carbazolyl)phenyl)-phenylphosphine oxide)), P(BCPO-co-ProD-Me2), P(BCPO-co-ProD-Et2), P(BCPO-co-ProD-Bz2), and P(BCPO-co-ProD)) are electrodeposited on indium tin oxide (ITO) coated glass slide and their electrochromic performances are characterized. The optical band gap of PBCPO is 3.14 eV. P(BCPO-co-ProD-Bz2) attains a high transmittance change (ΔT = 55% at 740 nm) and shows multicolored electrochromism from light tan (0.0 V), grayish-green (0.4 V), greenish-gray (1.1 V) to deep gray (1.2 V). Electrochromic devices (ECDs) containing phenylphosphine oxide-based polycarbazoles and poly(3,4-ethylenedioxythiophene) (PEDOT) as active electrode layers are constructed. PBCPO/PEDOT ECD displays light gray, gray, and greenish-gray at 0.0, 0.8, and 1.9 V, respectively. P(BCPO-co-ProD-Bz2)/PEDOT ECD displays a high optical contrast (ΔT = 42.5% at 630 nm) and P(BCPO-co-ProD)/PEDOT ECD shows a high coloration efficiency (η = 454.1 cm2•C−1 at 630 nm). In addition, P(BCPO-co-ProD derivatives)/PEDOT ECDs have adequate optical memories and long-term redox cyclic stability.Background: Polycarbazoles can create considerably stable radical cations (polarons) and dications (bipolarons) when increasing potentials or doping chemicals. Moreover, carbazole and phenylphosphine oxide are donor (D) and acceptor (A) units in BCPO, respectively. The incorporation of phenylphosphine oxide in polycarbazoles gives rise to the improvement of charge balances and carrier mobilities. It is interesting to investigate the absorption spectra and multicolored electrochromisms of five phenylphosphine oxide-containing polycarbazoles and their corresponding ECDs upon undergoing a redox process.Methods: A series of phenylphosphine oxide-containing anodic polymers (PBCPO, P(BCPO-co-ProD-Me2), P(BCPO-co-ProD-Et2), P(BCPO-co-ProD-Bz2), and P(BCPO-co-ProD)) are electrodeposited on ITO coated glass. The absorption spectra, color variations, response time, and long-term electrochemical stability of PBCPO/PEDOT, P(BCPO-co-ProD-Me2)/PEDOT, P(BCPO-co-ProD-Et2)/PEDOT, P(BCPO-co-ProD-Bz2)/PEDOT, and P(BCPO-co-ProD)/PEDOT ECDs are investigated comprehensively.Significant findings: The as-prepared phenylphosphine oxide-containing polycarbazoles exhibit multicolored electrochromism and high transmittance change (ΔT = 55% at 740 nm), which provide new structural insights to develop new generation electrochromic electrodes.

Correction to: A Dual-Type Electrochromic Device Based on Complementary Silica/Conducting Polymers Nanocomposite Films for Excellent Cycling Stability

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Comparison of Machine Learning Models on Performance of Single- and Dual-Type Electrochromic Devices.

This study shows that the model fitting based on machine learning (ML) from experimental data can successfully predict the electrochromic characteristics of single- and dual-type flexible electrochromic devices (ECDs) by using tungsten trioxide (WO3) and WO3/vanadium pentoxide (V2O5), respectively. Seven different regression methods were used for experimental observations, which belong to single and dual ECDs where 80% percent was used as training data and the remaining was taken as testing data. Among the seven different regression methods, K-nearest neighbor (KNN) achieves the best results with higher coefficient of determination (R2) score and lower root-mean-squared error (RMSE) for the bleaching state of ECDs. Furthermore, higher R2 score and lower RMSE for the coloration state of ECDs were achieved with Gaussian process regressor. The robustness result of the ML modeling demonstrates the reliability of prediction outcomes. These results can be proposed as promising models for different energy-saving flexible electronic systems.

An electrochemically and optically stable electrochromic polymer film based on EDOT and 1,2,3,4-tetrahydrophenazine

Abstract In this work, 3,4-ethylenedioxythiophene (EDOT) and 1,2,3,4-tetrahydrophenazine based donor-acceptor-donor type monomer (EBE) was synthesized, electropolymerized and the resulting polymer film (P(EBE)) was investigated in terms of its electrochemical and spectroelectrochemical properties. The polymer film showed excellent electrochemical stability upon 1000 switchings by saving almost full of its electroactivity. Moreover, 95% of the optical contrast was maintained after 500 switchings. The optical band gap value was calculated using Tauc Plot method and found as 1.5 eV. P(EBE) film revealed multichromic behaviour between its fully neutral and oxidized states; dark cyanish-green at −0.8 V, more green at −0.5 V and transmissive green beyond 0.6 V potentials. Finally, a dual type electrochromic device (ECD) was constructed with P(EBE) and poly(3,4-ethylenedioxythiophene) (PEDOT) films and the spectroelectrochemical behaviour of ECD was depicted.

A Dual-Type Electrochromic Device Based on Complementary Silica/Conducting Polymers Nanocomposite Films for Excellent Cycling Stability

In this work, the silica/polyaniline (SiO2/PANI) and silica poly(3,4-ethylenedioxythiophene) (SiO2/PEDOT) core/shell composite nanoparticles were successfully synthesized by in situ chemical oxidative polymerization. The SiO2/PANI nanocomposite film was employed as the anodically coloring electrode, and the SiO2/PEDOT nanocomposite film was employed as the cathodically coloring electrode. A viscous gel electrolyte (GE) of polymethyl methacrylate (PMMA) and lithium perchlorate (LiClO4) dissolved in propylene carbonates was used in an electrochromic device (ECD). The architectural design of dual-type ECD was glass/indium tin oxide (ITO)/SiO2-PANI/GE/SiO2-PEDOT/ITO/glass. Compared with the single-type ECD based on SiO2/PANI and SiO2/PEDOT nanocomposite films, the dual-type ECD exhibited larger optical modulation, faster response speed, higher coloration efficiency and better cycling stability.

A multipurpose conjugated polymer: Electrochromic device and biosensor construction for glucose detection

Abstract First example of electrochemically polymerized thiazolothiazole containing electrochromic conducting polymer; Poly(2,5-di(furan-2-yl)thiazolo[5,4-d]thiazole) (PTTzFr) was obtained via cyclic voltammetry. The polymer structure bears furan unit as the donor and thiazolothiazole unit as the acceptor. PTTzFr film was obtained on an ITO coated glass slide and its electrochemical and optoelectronic properties were investigated. Polymeric film showed reversible redox behavior along with reversible electrochromic behavior from reddish orange to grey having a band gap value of 1.80 eV. It has fast switching times (0.3 s and 0.4 s) with high optical contrast values at visible and NIR regions (38% at 460 nm and 63% at 1225 nm). Optoelectronic device application was performed by constructing a dual type electrochromic device (ECD) with poly(3,4-ethylenedioxythiophene) (PEDOT). Resulting device showed a remarkable optical memory without changing its % transmittance value during 200 s at 450 nm. Additionally, to construct a sensing interface, in the present work, a conjugated polymer (PTTzFr) containing biosensor was constructed for the glucose analysis. The architecture showed a promising sensing system for biosensor application. For the preparation of the proposed sensor, polymer film was coated on graphite electrode surface and fabricated as a glucose biosensor with immobilization of glucose oxidase. The biosensor was successfully applied for the determination of glucose in beverage. Under optimized conditions, the proposed sensor served a low detection limit (12.8 × 10−3 mM), and high sensitivity (65.44 μAmM−1cm−2). To the best of our knowledge, a sensor design and ECD construction using electrochemically polymerized PTTzFr that shows superior properties for both systems were attempted for the first time, and this approach resulted in improved biosensor and ECD characteristics.

Carbazole based electrochromic polymers bearing ethylenedioxy and propylenedioxy scaffolds

In this study, synthesis of two new monomers; 2-(2,3-dihydrothieno[3,4-b][1,4]dioxin-5-yl)-7(2,3-dihydrothieno[3,4-b][1,4]dioxin-7-yl)-9H-carbazole (ECzE) and2-(3,3-dihexyl-3,4-dihydro2H-thieno[3,4-b][1,4]dioxepin-6-yl)-7-(3,3-dihexyl-3,4-dihydro-2H-thieno[3,4-b][1,4] dioxepin-8-yl)-9H-carbazole (PCzP), via Stille cross-coupling reaction and their electrochemical polymerization both by repetitive cycling and by constant potential electrolysis was reported. The electrochemical and optical properties of the monomers and their corresponding polymers, PECzE and PPCzP, were investigated and it was found that 3,4-ethylenedioxythiophene (EDOT) unit containing monomer and polymer (ECzE and PECzE) have lower oxidation potentials and lower band gap values as compared to dihexyl substituted 3,4-propylenedioxythiophene (PRODOT-6) unit containing monomer and polymer (PCzP and PPCzP). Spectroelectrochemical studies revealed that both of the polymer films exhibit multielectrochromic behavior as well as good electrochemical stability. Moreover, PPCzP was found to be soluble in some organic solvents and its solution in tetrahydrofuran can be reversibly oxidized and reduced using chemical reagents. A dual-type electrochromic device was also constructed using soluble PPCzP as the anodically coloring material and the optical studies were performed on the device. The electrochromic device showed good electrochromic response, such as reasonable coloration efficiency and redox stability.

Poly(tris(4-carbazoyl-9-ylphenyl)amine)/Three Poly(3,4-ethylenedioxythiophene) Derivatives in Complementary High-Contrast Electrochromic Devices.

A carbazole-based polymer (poly(tris(4-carbazoyl-9-ylphenyl)amine) (PtCz)) is electrosynthesized on an indium tin oxide (ITO) electrode. PtCz film displays light yellow at 0.0 V, earthy yellow at 1.3 V, grey at 1.5 V, and dark grey at 1.8 V in 0.2 M LiClO4/ACN/DCM (ACN/DCM = 1:3, by volume) solution. The ΔT and coloration efficiency (η) of PtCz film are 30.5% and 54.8 cm2∙C−1, respectively, in a solution state. Three dual-type electrochromic devices (ECDs) are fabricated using the PtCz as the anodic layer, poly(3,4-ethylenedioxythiophene) (PEDOT), poly(3,3-dimethyl-3,4-dihydro-thieno[3,4-b][1,4]dioxepine) (PProDOT-Me2), and poly(3,4-(2,2-diethylpropylenedioxy)thiophene) (PProDOT-Et2) as the cathodic layers. PtCz/PProDOT-Me2 ECD shows high ΔTmax (36%), high ηmax (343.4 cm2·C−1), and fast switching speed (0.2 s) at 572 nm. In addition, PtCz/PEDOT, PtCz/PProDOT-Me2, and PtCz/PProDOT-Et2 ECDs show satisfactory open circuit memory and long-term stability.

Three Carbazole-Based Polymers as Potential Anodically Coloring Materials for High-Contrast Electrochromic Devices.

Three carbazole-based conjugated polymers (poly(3,6-di(2-thienyl)carbazole) (PDTC), poly(2,7-bis(carbazol-9-yl)-9,9-spirobifluorene) (PS2CBP), and poly(3,6-bis(N-carbazole)-N-ethylcarbazole) (PCEC)) are synthesized using electrochemical polymerization. The spectroelectrochemical studies indicate that the PDTC, PS2CBP, and PCEC films show reversible electrochromic behaviors in their redox states, and the PS2CBP film shows a distinct color transition with four various colors (gray at 0 V, grayish-green at 1.0 V, moss green at 1.2 V, and foliage green at 1.4 V). The maximum optical contrast of the PS2CBP and PCEC films is 39.83% at 428 nm and 32.41% at 420 nm, respectively, in an ionic liquid solution. Dual-type electrochromic devices (ECDs) that employ PDTC, PS2CBP, or PCEC film as an anodic layer, and PProDOT-Et2 film as a cathodic layer, were constructed. The as-prepared PCEC/PProDOT-Et2 ECD shows high optical contrast (38.25% at 586 nm) and high coloration efficiency (369.85 cm2 C−1 at 586 nm), and the PS2CBP/PProDOT-Et2 ECD shows high optical contrast (34.45% at 590 nm), good optical memory, and good long-term cycling stability.

Electrochromic characterizations of copolymers based on 4,4′-bis(N-carbazolyl)-1,1′-biphenyl and indole-6-carboxylic acid and their applications in electrochromic devices

Two homopolymers (poly(4,4′-bis(N-carbazolyl)-1,1′-biphenyl) (PBCz) and poly(indole-6-carboxylic acid) (PInc)) and three copolymers (P(BCz1-co-Inc1), P(BCz1-co-Inc2), and P(BCz1-co-Inc4)) with various BCz/Inc feed molar ratios are electrochemical polymerized on indium tin oxide (ITO) electrode. Spectroelectrochemical properties of polymer films reveal that P(BCz1-co-Inc2) film is yellow in the reduced state, yellowish brown in the intermediate state, and greyish black in highly oxidized states, and it can be reversibly oxidized and reduced with obvious color changes. Five dual-type electrochromic devices (ECDs) are fabricated using the BCz- and Inc-based polymers as coloring layers, and poly(3,4-(2,2-diethylpropylenedioxy)thiophene) (PProDOT-Et2) as the complementary layer. The ECD fabricated using an anodic copolymer P(BCz1-co-Inc2) with a BCz/Inc feed molar ratio of 1/2 has the highest optical contrast (42.0%) and coloration efficiency (634cm2/C) at 587nm. In addition, this ECD has satisfactory optical memory effect and long-term cycling stability.

Applications of Tris(4-(thiophen-2-yl)phenyl)amine- and Dithienylpyrrole-based Conjugated Copolymers in High-Contrast Electrochromic Devices.

Tris(4-(thiophen-2-yl)phenyl)amine- and dithienylpyrrole-based copolymers (P(TTPA-co-DIT) and P(TTPA-co-BDTA)) were electropolymerized on ITO electrode by applying constant potentials of 1.0, 1.1, and 1.2 V. Spectroelectrochemical investigations revealed that P(TTPA-co-DIT) film displayed more color changes than P(TTPA-co-BDTA) film. The P(TTPA-co-DIT) film is yellow in the neutral state, yellowish-green and green in the intermediate state, and blue (1.2 V) in highly oxidized state. The ∆Tmax of the P(TTPA-co-DIT) and P(TTPA-co-BDTA) films were measured as 60.3% at 1042 nm and 47.1% at 1096 nm, respectively, and the maximum coloration efficiency (η) of P(TTPA-co-DIT) and P(TTPA-co-BDTA) films were calculated to be 181.9 cm2·C−1 at 1042 nm and 217.8 cm2·C−1 at 1096 nm, respectively, in an ionic liquid solution. Dual type electrochromic devices (ECDs) consisting of P(TTPA-co-DIT) (or P(TTPA-co-BDTA)) anodic copolymer, ionic liquid-based electrolyte, and poly(3,4-(2,2-diethylpropylenedioxy)thiophene) (PProDOT-Et2) cathodic polymer were constructed. P(TTPA-co-BDTA)/PProDOT-Et2 ECD showed high ΔTmax (48.1%) and high coloration efficiency (649.4 cm2·C−1) at 588 nm. Moreover, P(TTPA-co-DIT)/PProDOT-Et2 and P(TTPA-co-BDTA)/PProDOT-Et2 ECDs displayed satisfactory optical memory and long term switching stability.

SYNTHESıS OF A NEW ELECTROCHROMıC POLYMER BASED ON TETRAPHENYLETHYLENE CORED TETRAKıS CARBAZOLE COMPLEX AND ıTS ELECTROCHROMıC DEVıCE APPLıCATıON

Poly-1,1,2,2-tetrakis(4-9H-carbazol-9-yl)phenyl)ethene P(TCP) was successfully synthesized by electrochemical oxidation of corresponding monomer, namely, 1,1,2,2-tetrakis(4-9H-carbazol-9-yl)phenyl)ethene (TCP) using dichloromethane as the solvent and tetrabutylammonium hexafluorophosphate (TBAPF6) as supporting electrolyte. Spectroelectrochemical properties of P(TCP) were investigated in situ recording the electronic absorption spectra of the polymer film coated on indium-tin oxide (ITO) at various potentials. P(TCP) displayed transparent to military green color in 1.80 s with an optical contrast of 23.0% (at 770 nm) and an optical band gap of 3.1eV. The objective evaluation of the colors of P(TCP) at various potentials was performed through colorimetry studies on the basis of ⿿Commission Internationale de l⿲Eclairage⿿ (CIE) standards. The morphology of the polymer film was investigated by AFM analysis. A dual type electrochromic device based on P(TCP) was constructed and its spectroelectrochemical properties were investigated. The electrochromic device exhibits color change from transparent to dark blue with a good open circuit memory.

Syntheses and Electrochemical Characterization of Low Oxidation Potential Nitrogen Analogs of Pedot as Electrochromic Materials

In this study, the electropolymerization of ethyl and methyl substituted asymmetrical nitrogen analogs of 3,4-ethylenedioxythiophene (OEt and OMe) were synthesized, characterized and their electrochemical properties were investigated. Both polymers (POEt and POMe) were synthesized electrochemically and characterized using spectroelectrochemical technique to determine optical changes of the resulting polymer films. Electrochemical studies demonstrated that these polymers exhibited a significantly low oxidation potential compared to their analogs reported in the literature. These polymers also provided a low optical bandgap with good optical contrasts. Furthermore, multi-electrochromic properties upon different applied potentials revealed that these polymers have potential applications in electrochromic devices. As a further characterization, their dual type electrochromic devices were constructed with poly(2,2,6,6-tetramethylpiperidinyloxy-4-yl methacrylate) (PTMA) which is transmissive in its both redox states. Devices were characterized via electrochemical and spectroelectrochemical techniques.

Two New Near-Infrared Switchable Electrochromic Bithiophenes Derivatives Based on 4-Methoxytriphenylamine Unit and Their Application for Electrochromic Devices

Two novel triphenylamine-containing thiophene derivative monomers, 4-methoxy-4′,4″-di(thiophen-2-yl)triphenylamine (MTTPA) and 4-methoxy-4′,4″-di(2,3-dihydrothieno[3,4-b][1,4]dioxin-7-yl)triphenylamine (METPA), were successfully synthesized. The corresponding polymers including PMTTPA and PMETPA were electrochemically synthesized and characterized by cyclic voltammetry (CV), UV–vis–NIR spectroscopy and scanning electron microscopy (SEM). Electrochemical and spectroelectrochemical analysis showed that two polymers had reversible redox behavior and multi-electrochromic property. Dynamic electrochromic experiments suggested that both the polymers had rapid switching time, high coloration efficiency, and high contrast of optical transmittance changes (ΔT%) in the NIR region (55.5% at 1280 nm for PMTTPA, 77.6% at 1200 nm for PMETPA). The dual-type electrochromic device based on PMTTPA film (or PMETPA film) was constructed and characterized as well. Both of them revealed excellent properties.

Novel multicolored electrochromic polymers containing phenanthrene-9,10-quinone and thiophene derivatives moieties

Two novel monomers 2,7-bis(3-ethylthiophen-2-yl)-9,10-phenanthrenequinone (ETPQ) and 2,7-bis(2,3-dihydrothieno[3,4-b][1,4]dioxin-5-yl)-9,10-phenanthrenequinone (DDPQ) were successfully synthesized via Stille cross coupling reaction. Meanwhile, the corresponding polymers PETPQ and PDDPQ were synthesized electrochemically and characterized carefully. Both polymer films displayed multi-colored electrochromism. The PETPQ film showed a yellow color at neutral state, and with the increase of the applied potential, its color switched from yellowish green to green, and then light blue, finally a blue color in the oxidized state was observed. The color of the PDDPQ film was red in its neutral state, and turned to blue in the oxidized state, in intermediate states, violet red and purple colors were observed. Moreover, the parameters (coloration efficiency, optical contrast and response time) of the two interesting polymers were all reasonable and satisfactory. The dual-type electrochromic device based on PETPQ film (or PDDPQ film) and PEDOT film was constructed and characterized as well. Both of them revealed excellent properties.

Electrochemical Synthesis and Characterization of Imidazole-Containing Polymers, and Their Electrochromic Devices Application

Two novel monomers 5,10-bis(4-ethylthiophen-2-yl)-2-phenyl-1H-phenanthro[9,10-d] imidazole (M1) and 5,10-bis(4-butylthiophen-2-yl)-2-phenyl-1H-phenanthro [9,10-d] imidazole (M2) were synthesized and electropolymerized to give corresponding polymers P1 and P2, respectively. Cyclic voltammetry (CV), UV–vis spectroscopy and scanning electron microscopy (SEM) were used to investigate the behaviors of the two structure related polymer films. It was interesting to find that slight structural difference of the two polymers can result in the variation of the optical and electronic properties. The P1 film showed a light yellow color at neutral state, and a brown color in intermediate state. Further oxidation of P1, a bluish violet color was observed. The P2 film also displayed three colors which were light yellow, gray and blue. Moreover, high optical contrast and satisfactory coloration efficiency of P1 and P2 film were obtained (46.7% and 190 cm2 C−1 for P1, 45.3% and 352 cm2 C−1 for P2). The high stability of the two polymers can be observed through electrochromic switching studies. Simple dual-type electrochromic devices (ECDs) based on P1 (or P2) and PEDOT were fabricated and characterized as well.

Optoelectronic Properties and Electrochromic Device Application of Novel Pyrazole Based Conducting Polymers

Here we report on the synthesis and characterization of pyrazole based conducting polymers and utilization of these polymers in electrochromic devices. For this purpose, 3,5-di-thiophen-2-yl-1H-pyrazole (DThPz) was synthesized via a Knorr type reaction and it was electrochemically polymerized. The resultant homopolymer had a band gap of 2.6 eV and displayed yellow to mode beige coloration upon doping. In order to enhance the switching characteristic; electrochemical copolymerization of DThPz in the presence of 3-hexylthiophene (HTh) and N-methyl pyrrole (NMP) was performed. Spectroelectrochemistry analysis of poly(DThPz-HTh) reflected electronic transitions at 405 and 740 nm due to π– π* transition and charge carrier band formation, respectively. The polymer displayed color change from chrome yellow to blue upon doping. Poly(DThPz-NMP), on the other hand had a π– π* transition at 355 nm and formation of new transitions at around 750 nm was observed. Additionally, as an application, dual-type electrochromic devices based on both poly(DThPz-HTh) and poly(DThPz -NMP) were assembled and characterized via spectroelectrochemistry, kinetic and colorimetry studies.

Electrosynthesis and characterization of a donor–acceptor type electrochromic material from poly(4,7-dicarbazol-9-yl-2,1,3-benzothiadia-zole) and its application in electrochromic devices

A donor–acceptor type monomer 4,7-dicarbazol-9-yl-2,1,3-benzothiadiazole (CBTD) was synthesized by modified Ullmann coupling reaction and its corresponding polymer (PCBTD) was obtained via electrochemical polymerization. Characterizations of the resulting polymer PCBTD were performed by cyclic voltammetry, UV–vis spectroscopy, Fourier transform infrared spectroscopy and scanning electron microscopy. The polymer displayed multiple colors changed from yellow to yellowish green, green, and turquoise blue with the applied potential. The UV–vis spectra depicted that polymer film have two absorption bands as expected for this type of donor–acceptor polymer, at 320 and 467nm, which attributed to the π–π* transition and intrachain charge transfer transition, respectively. Further, electrochemical and optical band gaps were obtained by using their oxidation and reduction onset potentials and absorption edges, respectively. The optical contrasts of the PCBTD film were found to be 28.1% at 420nm and 49.9% at 800nm in the visible region. The dual type electrochromic device constructed utilizing PCBTD and poly(3,4-ethylenedioxythiophene) showed a maximum contrast (ΔT %) of 49.4% at 620nm with response time of 0.6s and exhibited high coloration efficiency (1728cm2C−1) and good stability. These properties make the polymer a suitable material for electrochromic applications.