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.

Especially, CPs-based electrochromic materials, such as polyanilines [13], polycarbazoles [14], polypyrroles [15], polyindoles [16], polythiophenes [17][18][19], poly(3,4-ethylenedioxythiophene)(PEDOT) [20], and polytriphenylamine [21], have been extensively investigated for using as anodic (or cathodic) layers in ECDs. Among these materials, polytriphenylamine possesses hole conducting properties and can be easily oxidized to form polarons, the redox process exhibits obvious color variations. Hsiao et al. reported that triphenylaime-containing polyamides displayed good electrochemical stability and multicolor electrochromic behaviors upon applying potentials [22], the percent transmittance change and coloration efficiency of triphenylamine-containing polyamides are 58% and 209 cm 2¨C´1 at 929 nm, Potential (V) vs. Ag/AgCl  Copolymer films P(TTPA-co-DIT) and P(TTPA-co-BDTA) prepared by constant potential deposition at 1.0 V were scanned at different rates in the range from 25 to 200 mV·s −1 in 0.1 M LiClO4/ACN solution. As can be seen in Figures 3a,4a, the P(TTPA-co-DIT) and P(TTPA-co-BDTA) presented two well-defined redox peaks, the current density response increased with the increasing of the scan rate, indicating that the copolymer films had good electrochemical activity and were adhered well to the electrode. With the increasing scan rate, the anodic and cathodic peak current Copolymer films P(TTPA-co-DIT) and P(TTPA-co-BDTA) prepared by constant potential deposition at 1.0 V were scanned at different rates in the range from 25 to 200 mV·s −1 in 0.1 M LiClO4/ACN solution. As can be seen in Figures 3a,4a, the P(TTPA-co-DIT) and P(TTPA-co-BDTA) presented two well-defined redox peaks, the current density response increased with the increasing of the scan rate, indicating that the copolymer films had good electrochemical activity and were adhered well to the electrode. With the increasing scan rate, the anodic and cathodic peak current Copolymer films P(TTPA-co-DIT) and P(TTPA-co-BDTA) prepared by constant potential deposition at 1.0 V were scanned at different rates in the range from 25 to 200 mV¨s´1 in 0.1 M LiClO 4 /ACN solution. As can be seen in Figures 3a and 4a, the P(TTPA-co-DIT) and P(TTPA-co-BDTA) presented two well-defined redox peaks, the current density response increased with the increasing of the scan rate, indicating that the copolymer films had good electrochemical activity and were adhered well to the electrode. With the increasing scan rate, the anodic and cathodic peak current densities showed a linear dependence on the scan rate as illustrated in Figures 3b and 4b, demonstrating that the redox process of the copolymers were not limited by diffusion control [33].
Polymers 2016, 8, 206 5 of 16 densities showed a linear dependence on the scan rate as illustrated in Figures 3b,4b, demonstrating that the redox process of the copolymers were not limited by diffusion control [33].

Electrochromic Properties of the Copolymer Films
Spectroelectrochemistry combines electrochemical and spectroscopic methods for investigating the changes in the absorption spectra upon applying of an external electrical potential. Spectroelectrochemistry of P(TTPA-co-DIT) and P(TTPA-co-BDTA) copolymer films coated on ITO electrode was studied in an ionic liquid solution. Figure 5 displayed the spectroelectrochemical spectra of P(TTPA-co-DIT) film at various potentials in EPIDIL solution. The copolymer films were prepared potentiostatically at 1.0 V, 1.1 V, and 1.2 V (see Figure 5a-c, respectively). As shown in Figure 5a and Table 1, the peak of P(TTPA-co-DIT) film in the neutral state was found at 388 nm, which corresponded to the π-π * transition of P(TTPA-co-DIT) in EPIDIL solution. Upon applying more than 0.8 V, the absorbance of π-π * transition peak of P(TTPA-co-DIT) decreased gradually and charge carrier bands appeared in higher wavelength region, which corresponded to the development of polaron and bipolaron bands [34]. When the P(TTPA-co-DIT) film was prepared potentiostatically at 1.1 V and 1.2 V, the π-π * transition of P(TTPA-co-DIT) film did not shift significantly. However, the position of polaron peak with maximal absorbance changes shifted densities showed a linear dependence on the scan rate as illustrated in Figures 3b,4b, demonstrating that the redox process of the copolymers were not limited by diffusion control [33].

Electrochromic Properties of the Copolymer Films
Spectroelectrochemistry combines electrochemical and spectroscopic methods for investigating the changes in the absorption spectra upon applying of an external electrical potential. Spectroelectrochemistry of P(TTPA-co-DIT) and P(TTPA-co-BDTA) copolymer films coated on ITO electrode was studied in an ionic liquid solution. Figure 5 displayed the spectroelectrochemical spectra of P(TTPA-co-DIT) film at various potentials in EPIDIL solution. The copolymer films were prepared potentiostatically at 1.0 V, 1.1 V, and 1.2 V (see Figure 5a-c, respectively). As shown in Figure 5a and Table 1, the peak of P(TTPA-co-DIT) film in the neutral state was found at 388 nm, which corresponded to the π-π * transition of P(TTPA-co-DIT) in EPIDIL solution. Upon applying more than 0.8 V, the absorbance of π-π * transition peak of P(TTPA-co-DIT) decreased gradually and charge carrier bands appeared in higher wavelength region, which corresponded to the development of polaron and bipolaron bands [34]. When the P(TTPA-co-DIT) film was prepared potentiostatically at 1.1 V and 1.2 V, the π-π * transition of P(TTPA-co-DIT) film did not shift significantly. However, the position of polaron peak with maximal absorbance changes shifted

Electrochromic Properties of the Copolymer Films
Spectroelectrochemistry combines electrochemical and spectroscopic methods for investigating the changes in the absorption spectra upon applying of an external electrical potential. Spectroelectrochemistry of P(TTPA-co-DIT) and P(TTPA-co-BDTA) copolymer films coated on ITO electrode was studied in an ionic liquid solution. Figure 5 displayed the spectroelectrochemical spectra of P(TTPA-co-DIT) film at various potentials in EPIDIL solution. The copolymer films were prepared potentiostatically at 1.0 V, 1.1 V, and 1.2 V (see Figure 5a-c, respectively). As shown in Figure 5a and Table 1, the peak of P(TTPA-co-DIT) film in the neutral state was found at 388 nm, which corresponded to the π-π * transition of P(TTPA-co-DIT) in EPIDIL solution. Upon applying more than 0.8 V, the absorbance of π-π * transition peak of P(TTPA-co-DIT) decreased gradually and charge carrier bands appeared in higher wavelength region, which corresponded to the development of polaron and bipolaron bands [34]. When the P(TTPA-co-DIT) film was prepared potentiostatically at 1.1 V and 1.2 V, the π-π * transition of P(TTPA-co-DIT) film did not shift significantly. However, the position of polaron peak with maximal absorbance changes shifted conspicuously upon applying various potentials, this can be ascribed to adherent polymer films undergo configuration changes during electrochemical overoxidation [35]. The π-π * transition of P(TTPA-co-BDTA) film in EPIDIL solution located at similar position with P(TTPA-co-DIT) film, whereas the polaron peak positions of P(TTPA-co-BDTA) film with maximal absorbance shifted bathochromically relative to those of P(TTPA-co-DIT) film upon applying various potentials ( Figure 6), which could be attributed to an electron-withdrawing 1,2,5-thiadiazole unit in BDTA unit showed narrower band gap in EPIDIL solution than that of DIT unit. conspicuously upon applying various potentials, this can be ascribed to adherent polymer films undergo configuration changes during electrochemical overoxidation [35]. The π-π * transition of P(TTPA-co-BDTA) film in EPIDIL solution located at similar position with P(TTPA-co-DIT) film, whereas the polaron peak positions of P(TTPA-co-BDTA) film with maximal absorbance shifted bathochromically relative to those of P(TTPA-co-DIT) film upon applying various potentials ( Figure  6), which could be attributed to an electron-withdrawing 1,2,5-thiadiazole unit in BDTA unit showed narrower band gap in EPIDIL solution than that of DIT unit.   Polymer films λ(π-π* peak)/nm λ(polaron peak)/nm P(TTPA-co-DIT)-1.0 V 388 1,042 P(TTPA-co-DIT)-1.1 V 388 1,046 P(TTPA-co-DIT)-1.2 V 394 1,220 P(TTPA-co-BDTA)-1.0 V 394 1,096 P(TTPA-co-BDTA)-1.1 V 392 1,194 P(TTPA-co-BDTA)-1.2 V 388 1,304 Table 2 shows the photographs and colorimetric values (L*, a*, b*) of the copolymer films at various potentials in EPIDIL solution. The P(TTPA-co-DIT) film was yellow (0.2 V) in the neutral state, yellowish-green (0.8 V) and green (1.0 V) in the intermediate state, and blue (1.2 V) in highly oxidized state. The P(TTPA-co-BDTA) film showed less color changes than those of P(TTPA-co-DIT) film, P(TTPA-co-BDTA) film was yellow (0.2 V) in the neutral state, bluish-green (1.0 V) in the intermediate state, and blue (1.2 V) in highly oxidized state, indicating the incorporation of DIT unit into copolymer backbone gives rise to more color changes than that of BDTA unit.

Polymer films
λ (π-π* peak) /nm λ (polaron peak) /nm P(TTPA-co-DIT)-1.0 V 388 1,042 P(TTPA-co-DIT)-1.1 V 388 1,046 P(TTPA-co-DIT)-1.2 V 394 1,220 P(TTPA-co-BDTA)-1.0 V 394 1,096 P(TTPA-co-BDTA)-1.1 V 392 1,194 P(TTPA-co-BDTA)-1.2 V 388 1,304 Table 2 shows the photographs and colorimetric values (L*, a*, b*) of the copolymer films at various potentials in EPIDIL solution. The P(TTPA-co-DIT) film was yellow (0.2 V) in the neutral state, yellowish-green (0.8 V) and green (1.0 V) in the intermediate state, and blue (1.2 V) in highly oxidized state. The P(TTPA-co-BDTA) film showed less color changes than those of P(TTPA-co-DIT) film, P(TTPA-co-BDTA) film was yellow (0.2 V) in the neutral state, bluish-green (1.0 V) in the intermediate state, and blue (1.2 V) in highly oxidized state, indicating the incorporation of DIT unit into copolymer backbone gives rise to more color changes than that of BDTA unit.   A square-wave potential step technology coupled with a UV-Visible spectrophotometer was used for analysis of switching kinetics and optical contrast of the copolymer films [36]. The P(TTPA-co-DIT) and P(TTPA-co-BDTA) films were stepped by repeated potential between neutral state (0.2 V) and oxidized state (+1.2 V) with a time interval of 5 s in an ionic liquid solution. The in    A square-wave potential step technology coupled with a UV-Visible spectrophotometer was used for analysis of switching kinetics and optical contrast of the copolymer films [36]. The P(TTPA-co-DIT) and P(TTPA-co-BDTA) films were stepped by repeated potential between neutral state (0.2 V) and oxidized state (+1.2 V) with a time interval of 5 s in an ionic liquid solution.   A square-wave potential step technology coupled with a UV-Visible spectrophotometer was used for analysis of switching kinetics and optical contrast of the copolymer films [36]. The P(TTPA-co-DIT) and P(TTPA-co-BDTA) films were stepped by repeated potential between neutral state (0.2 V) and oxidized state (+1.2 V) with a time interval of 5 s in an ionic liquid solution.   A square-wave potential step technology coupled with a UV-Visible spectrophotometer was used for analysis of switching kinetics and optical contrast of the copolymer films [36]. The P(TTPA-co-DIT) and P(TTPA-co-BDTA) films were stepped by repeated potential between neutral state (0.2 V) and oxidized state (+1.2 V) with a time interval of 5 s in an ionic liquid solution.   A square-wave potential step technology coupled with a UV-Visible spectrophotometer was used for analysis of switching kinetics and optical contrast of the copolymer films [36]. The P(TTPA-co-DIT) and P(TTPA-co-BDTA) films were stepped by repeated potential between neutral state (0.2 V) and oxidized state (+1.  A square-wave potential step technology coupled with a UV-Visible spectrophotometer was used for analysis of switching kinetics and optical contrast of the copolymer films [36]. The P(TTPA-co-DIT) and P(TTPA-co-BDTA) films were stepped by repeated potential between neutral state (0.2 V) and oxidized state (+1.2 V) with a time interval of 5 s in an ionic liquid solution. Absorbance (a.u)  A square-wave potential step technology coupled with a UV-Visible spectrophotometer was used for analysis of switching kinetics and optical contrast of the copolymer films [36]. The P(TTPA-co-DIT) and P(TTPA-co-BDTA) films were stepped by repeated potential between neutral state (0.2 V) and oxidized state (+1.2 V) with a time interval of 5 s in an ionic liquid solution. Absorbance (a.u)  A square-wave potential step technology coupled with a UV-Visible spectrophotometer was used for analysis of switching kinetics and optical contrast of the copolymer films [36]. The P(TTPA-co-DIT) and P(TTPA-co-BDTA) films were stepped by repeated potential between neutral state (0.2 V) and oxidized state (+1.2 V) with a time interval of 5 s in an ionic liquid solution.   A square-wave potential step technology coupled with a UV-Visible spectrophotometer was used for analysis of switching kinetics and optical contrast of the copolymer films [36]. The P(TTPA-co-DIT) and P(TTPA-co-BDTA) films were stepped by repeated potential between neutral state (0.2 V) and oxidized state (+1.2 V) with a time interval of 5 s in an ionic liquid solution. The in 54. 12 2.65 1.14 A square-wave potential step technology coupled with a UV-Visible spectrophotometer was used for analysis of switching kinetics and optical contrast of the copolymer films [36]. The P(TTPA-co-DIT) and P(TTPA-co-BDTA) films were stepped by repeated potential between neutral state (0.2 V) and oxidized state (+1.2 V) with a time interval of 5 s in an ionic liquid solution. The in situ transmittance-time profiles of P(TTPA-co-DIT) and P(TTPA-co-BDTA) films in EPIDIL solution are displayed in Figure 7, and the optical contrast (∆T) estimated at 1st, 50th, and 100th cycles are summarized in Table 3. For P(TTPA-co-DIT) film prepared potentiostatically at 1.0 V, 1.1 V, and 1.2 V, the ∆T of P(TTPA-co-DIT)-1.0 V, P(TTPA-co-DIT)-1.1 V, and P(TTPA-co-DIT)-1.2 V films at first cycle are 60.3, 55.6, and 49.4%, respectively, and P(TTPA-co-DIT) film prepared potentiostatically at 1.0 V shows the highest ∆T. For the ∆T of copolymer films at different switching cycles, the ∆T of P(TTPA-co-DIT)-1.0 V film from the bleaching state to the coloration state in EPIDIL solution was 60.3, 58.8 and 57.1%, respectively, at 1st, 50th, and 100th cycle. However, the ∆T of P(TTPA-co-DIT)-1.2 V film from the bleaching state to the coloration state in EPIDIL solution was 49.4, 43.2 and 42.6%, respectively, at 1st, 50th, and 100th cycle. The stability of P(TTPA-co-DIT)-1.0 V and P(TTPA-co-DIT)-1.2 V films at the 100th cycle was 94.7 and 86.2%, respectively, and the P(TTPA-co-DIT)-1.0 V film shows higher stability than that of P(TTPA-co-DIT)-1.2 V film at high switching cycles, which can be attributed to an overoxidation of the copolymer takes place when electropolymerization at high potential (i.e., in highly oxidized state). The ∆T of P(TTPA-co-DIT)-1.0 V and P(TTPA-co-BDTA)-1.0 V films from the bleaching state to the coloration state in EPIDIL solution were 60.3 and 47.1%, respectively, at the first cycle, implying P(TTPA-co-DIT) film shows higher ∆T than that of P(TTPA-co-BDTA) film. The stability of P(TTPA-co-DIT)-1.0 V and P(TTPA-co-BDTA)-1.0 V films at the 100 th cycle was 94.7 and 85.6%, respectively, revealing the P(TTPA-co-DIT) film shows higher stability than that of P(TTPA-co-BDTA) film at high switching cycles. situ transmittance-time profiles of P(TTPA-co-DIT) and P(TTPA-co-BDTA) films in EPIDIL solution are displayed in Figure 7, and the optical contrast (∆T) estimated at 1st, 50th, and 100th cycles are summarized in Table 3. For P(TTPA-co-DIT) film prepared potentiostatically at 1.0 V, 1.1 V, and 1.2 V, the ∆T of P(TTPA-co-DIT)-1.0 V, P(TTPA-co-DIT)-1.1 V, and P(TTPA-co-DIT)-1.2 V films at first cycle are 60.3, 55.6, and 49.4%, respectively, and P(TTPA-co-DIT) film prepared potentiostatically at 1.0 V shows the highest ∆T. For the ΔT of copolymer films at different switching cycles, the ΔT of P(TTPA-co-DIT)-1.0 V film from the bleaching state to the coloration state in EPIDIL solution was 60.3, 58.8 and 57.1%, respectively, at 1st, 50th, and 100th cycle. However, the ΔT of P(TTPA-co-DIT)-1.2 V film from the bleaching state to the coloration state in EPIDIL solution was 49.4, 43.2 and 42.6%, respectively, at 1st, 50th, and 100th cycle. The stability of P(TTPA-co-DIT)-1.0 V and P(TTPA-co-DIT)-1.2 V films at the 100th cycle was 94.7 and 86.2%, respectively, and the P(TTPA-co-DIT)-1.0 V film shows higher stability than that of P(TTPA-co-DIT)-1.2 V film at high switching cycles, which can be attributed to an overoxidation of the copolymer takes place when electropolymerization at high potential (i.e., in highly oxidized state). The ΔT of P(TTPA-co-DIT)-1.0 V and P(TTPA-co-BDTA)-1.0 V films from the bleaching state to the coloration state in EPIDIL solution were 60.3 and 47.1%, respectively, at the first cycle, implying P(TTPA-co-DIT) film shows higher ΔT than that of P(TTPA-co-BDTA) film. The stability of P(TTPA-co-DIT)-1.0 V and P(TTPA-co-BDTA)-1.0 V films at the 100 th cycle was 94.7 and 85.6%, respectively, revealing the P(TTPA-co-DIT) film shows higher stability than that of P(TTPA-co-BDTA) film at high switching cycles. The coloration switching time (τc) and the bleaching switching time (τb) of copolymer films estimated at 1st, 50th, and 100th cycles are also summarized in Table 3. The switching time was estimated at 90% of the full-transmittance variation. P(TTPA-co-BDTA) film shows shorter τc and τb than those of P(TTPA-co-DIT) film, revealing that P(TTPA-co-BDTA) film exhibits fast switching speeds from the dedoped to the doped state and from the doped to the dedoped state when we employ EPIDIL as a supporting electrolyte. The ΔTmax of P(TTPA-co-DIT)-1.0 V and P(TTPA-co-BDTA)-1.0 V films are higher than that reported for PTTPA derivative (P(TTPA-co-EDOT)) [37], and higher than those reported for PSNS derivatives (PTEPA [38], PSNS-1-NAPH [39], and P(SNS-Fc-co-EDOT) [40]). This could be ascribed to the fact that ΔTmax of P(TTPA-co-DIT)-1.0 V and P(TTPA-co-BDTA)-1.0 V films were estimated in long wavelength region (1042-1096 nm) when we employed EPIDIL as a supporting electrolyte. The coloration switching time (τ c ) and the bleaching switching time (τ b ) of copolymer films estimated at 1st, 50th, and 100th cycles are also summarized in Table 3. The switching time was estimated at 90% of the full-transmittance variation. P(TTPA-co-BDTA) film shows shorter τ c and τ b than those of P(TTPA-co-DIT) film, revealing that P(TTPA-co-BDTA) film exhibits fast switching speeds from the dedoped to the doped state and from the doped to the dedoped state when we employ EPIDIL as a supporting electrolyte. The ∆T max of P(TTPA-co-DIT)-1.0 V and P(TTPA-co-BDTA)-1.0 V films are higher than that reported for PTTPA derivative (P(TTPA-co-EDOT)) [37], and higher than those reported for PSNS derivatives (PTEPA [38], PSNS-1-NAPH [39], and P(SNS-Fc-co-EDOT) [40]). This could be ascribed to the fact that ∆T max of P(TTPA-co-DIT)-1.0 V and P(TTPA-co-BDTA)-1.0 V films were estimated in long wavelength region (1042-1096 nm) when we employed EPIDIL as a supporting electrolyte. ∆OD is the discrepancy of optical density, which can be estimated using the transmittance of the oxidation state (T ox ) and neutral state (T neu ) using the following equation:
The coloration efficiency (η) at a specific wavelength can be defined as the ∆OD for the charge (q) consumed per unit electrode area (A): As shown in Table 4, the η max of P(TTPA-co-DIT)-1.0 V film at 1042 nm and P(TTPA-co-BDTA)-1.0 V film at 1096 nm in EPIDIL solution are 181.9 and 217.8 cm¨C´1, respectively, which were higher than those reported for PTEPA [38] at 448 nm and PSNS-1-NAPH [39] at 423 nm.

Spectroelectrochemistry of ECDs
Dual type ECDs consisting of electrochemically deposited P(TTPA-co-DIT)-1.0 V/PProDOT-Et 2 and P(TTPA-co-BDTA)-1.0 V/PProDOT-Et 2 were constructed and their spectroelectrochemical behaviors were studied by recording the optical absorbance spectra at various potentials. ECDs showed a reversible response in a potential range of´0.4 V and 1.2 V, as depicted in Figure 8. At´0.4 V, P(TTPA-co-DIT)-1.0 V/PProDOT-Et 2 and P(TTPA-co-BDTA)-1.0 V/PProDOT-Et 2 ECDs revealed well defined transitions at ca. 382 and 424 nm, respectively, which are in accordance with the spectral behaviors of P(TTPA-co-DIT)-1.0 V and P(TTPA-co-BDTA)-1.0 V films in reduced state. However, in this situation, the complementary PProDOT-Et 2 layer is expected to be in oxidized state and it does not show significant transition in UV spectrum. Upon increasing the potential gradually, P(TTPA-co-DIT)-1.0 V and P(TTPA-co-BDTA)-1.0 V films begin to oxidize and a new absorption band at 588 nm appeared due to neutralization of the PProDOT-Et 2 layer, and the ECDs were blue in the potential range of +0.8 and 1.2 V for P(TTPA-co-DIT)-1.0 V/PProDOT-Et 2 ECD and in the potential range of +1.0 and 1.4 V for P(TTPA-co-BDTA)-1.0 V/PProDOT-Et 2 ECD (Table 5). Table 5. Electrochromic photographs and colorimetric values (L*, a*, and b*) of the ECDs. The P(TTPA-co-DIT) and P(TTPA-co-BDTA) films were prepared potentiostatically at 1.0 V on ITO glass electrodes.

Spectroelectrochemistry of ECDs
Dual type ECDs consisting of electrochemically deposited P(TTPA-co-DIT)-1.0 V/PProDOT-Et2 and P(TTPA-co-BDTA)-1.0 V/PProDOT-Et2 were constructed and their spectroelectrochemical behaviors were studied by recording the optical absorbance spectra at various potentials. ECDs showed a reversible response in a potential range of −0.4 V and 1.2 V, as depicted in Figure 8. At −0.4 V, P(TTPA-co-DIT)-1.0 V/PProDOT-Et2 and P(TTPA-co-BDTA)-1.0 V/PProDOT-Et2 ECDs revealed well defined transitions at ca. 382 and 424 nm, respectively, which are in accordance with the spectral behaviors of P(TTPA-co-DIT)-1.0 V and P(TTPA-co-BDTA)-1.0 V films in reduced state. However, in this situation, the complementary PProDOT-Et2 layer is expected to be in oxidized state and it does not show significant transition in UV spectrum. Upon increasing the potential gradually, P(TTPA-co-DIT)-1.0 V and P(TTPA-co-BDTA)-1.0 V films begin to oxidize and a new absorption band at 588 nm appeared due to neutralization of the PProDOT-Et2 layer, and the ECDs were blue in the potential range of +0.8 and 1.2 V for P(TTPA-co-DIT)-1.0 V/PProDOT-Et2 ECD and in the potential range of +1.0 and 1.4 V for P(TTPA-co-BDTA)-1.0 V/PProDOT-Et2 ECD (Table 5). Table 5. Electrochromic photographs and colorimetric values (L*, a*, and b*) of the ECDs. The P(TTPA-co-DIT) and P(TTPA-co-BDTA) films were prepared potentiostatically at 1.0 V on ITO glass electrodes. The transmittance-time profiles of P(TTPA-co-DIT)-1.0 V/PProDOT-Et2 and P(TTPA-co-BDTA)-1.0 V/PProDOT-Et2 ECDs were shown in Figure 9, which were stepped by repeated potential in the range of neutral (− 0.2 V) and oxidized states (+1.2 V) with a time interval of 5 s, and the ΔT, τc, and τb estimated at different double-step potential cycles are summarized in Table 6. The ΔT of P(TTPA-co-DIT)-1.0 V/PProDOT-Et2 and P(TTPA-co-BDTA)-1.0 V/PProDOT-Et2 ECDs is 43.5 and 48.1% at the first cycle, respectively, implying P(TTPA-co-BDTA) film is a promising electrochromic material to increase the ΔT when we employ P(TTPA-co-BDTA) film as anodic copolymer layer in ECDs. For P(TTPA-co-BDTA) film was prepared potentiostatically at 1.

Spectroelectrochemistry of ECDs
Dual type ECDs consisting of electrochemically deposited P(TTPA-co-DIT)-1.0 V/PProDOT-Et2 and P(TTPA-co-BDTA)-1.0 V/PProDOT-Et2 were constructed and their spectroelectrochemical behaviors were studied by recording the optical absorbance spectra at various potentials. ECDs showed a reversible response in a potential range of −0.4 V and 1.2 V, as depicted in Figure 8. At −0.4 V, P(TTPA-co-DIT)-1.0 V/PProDOT-Et2 and P(TTPA-co-BDTA)-1.0 V/PProDOT-Et2 ECDs revealed well defined transitions at ca. 382 and 424 nm, respectively, which are in accordance with the spectral behaviors of P(TTPA-co-DIT)-1.0 V and P(TTPA-co-BDTA)-1.0 V films in reduced state. However, in this situation, the complementary PProDOT-Et2 layer is expected to be in oxidized state and it does not show significant transition in UV spectrum. Upon increasing the potential gradually, P(TTPA-co-DIT)-1.0 V and P(TTPA-co-BDTA)-1.0 V films begin to oxidize and a new absorption band at 588 nm appeared due to neutralization of the PProDOT-Et2 layer, and the ECDs were blue in the potential range of +0.8 and 1.2 V for P(TTPA-co-DIT)-1.0 V/PProDOT-Et2 ECD and in the potential range of +1.0 and 1.4 V for P(TTPA-co-BDTA)-1.0 V/PProDOT-Et2 ECD (Table 5). Table 5. Electrochromic photographs and colorimetric values (L*, a*, and b*) of the ECDs. The P(TTPA-co-DIT) and P(TTPA-co-BDTA) films were prepared potentiostatically at 1.0 V on ITO glass electrodes. The transmittance-time profiles of P(TTPA-co-DIT)-1.0 V/PProDOT-Et2 and P(TTPA-co-BDTA)-1.0 V/PProDOT-Et2 ECDs were shown in Figure 9, which were stepped by repeated potential in the range of neutral (− 0.2 V) and oxidized states (+1.2 V) with a time interval of 5 s, and the ΔT, τc, and τb estimated at different double-step potential cycles are summarized in Table 6. The ΔT of P(TTPA-co-DIT)-1.0 V/PProDOT-Et2 and P(TTPA-co-BDTA)-1.0 V/PProDOT-Et2 ECDs is 43.5 and 48.1% at the first cycle, respectively, implying P(TTPA-co-BDTA) film is a promising electrochromic material to increase the ΔT when we employ P(TTPA-co-BDTA) film as anodic copolymer layer in ECDs. For P(TTPA-co-BDTA) film was prepared potentiostatically at 1.

Spectroelectrochemistry of ECDs
Dual type ECDs consisting of electrochemically deposited P(TTPA-co-DIT)-1.0 V/PProDOT-Et2 and P(TTPA-co-BDTA)-1.0 V/PProDOT-Et2 were constructed and their spectroelectrochemical behaviors were studied by recording the optical absorbance spectra at various potentials. ECDs showed a reversible response in a potential range of −0.4 V and 1.2 V, as depicted in Figure 8. At −0.4 V, P(TTPA-co-DIT)-1.0 V/PProDOT-Et2 and P(TTPA-co-BDTA)-1.0 V/PProDOT-Et2 ECDs revealed well defined transitions at ca. 382 and 424 nm, respectively, which are in accordance with the spectral behaviors of P(TTPA-co-DIT)-1.0 V and P(TTPA-co-BDTA)-1.0 V films in reduced state. However, in this situation, the complementary PProDOT-Et2 layer is expected to be in oxidized state and it does not show significant transition in UV spectrum. Upon increasing the potential gradually, P(TTPA-co-DIT)-1.0 V and P(TTPA-co-BDTA)-1.0 V films begin to oxidize and a new absorption band at 588 nm appeared due to neutralization of the PProDOT-Et2 layer, and the ECDs were blue in the potential range of +0.8 and 1.2 V for P(TTPA-co-DIT)-1.0 V/PProDOT-Et2 ECD and in the potential range of +1.0 and 1.4 V for P(TTPA-co-BDTA)-1.0 V/PProDOT-Et2 ECD (Table 5). Table 5. Electrochromic photographs and colorimetric values (L*, a*, and b*) of the ECDs. The P(TTPA-co-DIT) and P(TTPA-co-BDTA) films were prepared potentiostatically at 1.0 V on ITO glass electrodes. The transmittance-time profiles of P(TTPA-co-DIT)-1.0 V/PProDOT-Et2 and P(TTPA-co-BDTA)-1.0 V/PProDOT-Et2 ECDs were shown in Figure 9, which were stepped by repeated potential in the range of neutral (− 0.2 V) and oxidized states (+1.2 V) with a time interval of 5 s, and the ΔT, τc, and τb estimated at different double-step potential cycles are summarized in Table 6. The ΔT of P(TTPA-co-DIT)-1.0 V/PProDOT-Et2 and P(TTPA-co-BDTA)-1.0 V/PProDOT-Et2 ECDs is 43.5 and 48.1% at the first cycle, respectively, implying P(TTPA-co-BDTA) film is a promising electrochromic material to increase the ΔT when we employ P(TTPA-co-BDTA) film as anodic copolymer layer in ECDs. For P(TTPA-co-BDTA) film was prepared potentiostatically at 1.

Spectroelectrochemistry of ECDs
Dual type ECDs consisting of electrochemically deposited P(TTPA-co-DIT)-1.0 V/PProDOT-Et2 and P(TTPA-co-BDTA)-1.0 V/PProDOT-Et2 were constructed and their spectroelectrochemical behaviors were studied by recording the optical absorbance spectra at various potentials. ECDs showed a reversible response in a potential range of −0.4 V and 1.2 V, as depicted in Figure 8. At −0.4 V, P(TTPA-co-DIT)-1.0 V/PProDOT-Et2 and P(TTPA-co-BDTA)-1.0 V/PProDOT-Et2 ECDs revealed well defined transitions at ca. 382 and 424 nm, respectively, which are in accordance with the spectral behaviors of P(TTPA-co-DIT)-1.0 V and P(TTPA-co-BDTA)-1.0 V films in reduced state. However, in this situation, the complementary PProDOT-Et2 layer is expected to be in oxidized state and it does not show significant transition in UV spectrum. Upon increasing the potential gradually, P(TTPA-co-DIT)-1.0 V and P(TTPA-co-BDTA)-1.0 V films begin to oxidize and a new absorption band at 588 nm appeared due to neutralization of the PProDOT-Et2 layer, and the ECDs were blue in the potential range of +0.8 and 1.2 V for P(TTPA-co-DIT)-1.0 V/PProDOT-Et2 ECD and in the potential range of +1.0 and 1.4 V for P(TTPA-co-BDTA)-1.0 V/PProDOT-Et2 ECD (Table 5). Table 5. Electrochromic photographs and colorimetric values (L*, a*, and b*) of the ECDs. The P(TTPA-co-DIT) and P(TTPA-co-BDTA) films were prepared potentiostatically at 1.0 V on ITO glass electrodes. The transmittance-time profiles of P(TTPA-co-DIT)-1.0 V/PProDOT-Et2 and P(TTPA-co-BDTA)-1.0 V/PProDOT-Et2 ECDs were shown in Figure 9, which were stepped by repeated potential in the range of neutral (− 0.2 V) and oxidized states (+1.2 V) with a time interval of 5 s, and the ΔT, τc, and τb estimated at different double-step potential cycles are summarized in Table 6. The ΔT of P(TTPA-co-DIT)-1.0 V/PProDOT-Et2 and P(TTPA-co-BDTA)-1.0 V/PProDOT-Et2 ECDs is 43.5 and 48.1% at the first cycle, respectively, implying P(TTPA-co-BDTA) film is a promising electrochromic material to increase the ΔT when we employ P(TTPA-co-BDTA) film as anodic copolymer layer in ECDs. For P(TTPA-co-BDTA) film was prepared potentiostatically at 1.

Spectroelectrochemistry of ECDs
Dual type ECDs consisting of electrochemically deposited P(TTPA-co-DIT)-1.0 V/PProDOT-Et2 and P(TTPA-co-BDTA)-1.0 V/PProDOT-Et2 were constructed and their spectroelectrochemical behaviors were studied by recording the optical absorbance spectra at various potentials. ECDs showed a reversible response in a potential range of −0.4 V and 1.2 V, as depicted in Figure 8. At −0.4 V, P(TTPA-co-DIT)-1.0 V/PProDOT-Et2 and P(TTPA-co-BDTA)-1.0 V/PProDOT-Et2 ECDs revealed well defined transitions at ca. 382 and 424 nm, respectively, which are in accordance with the spectral behaviors of P(TTPA-co-DIT)-1.0 V and P(TTPA-co-BDTA)-1.0 V films in reduced state. However, in this situation, the complementary PProDOT-Et2 layer is expected to be in oxidized state and it does not show significant transition in UV spectrum. Upon increasing the potential gradually, P(TTPA-co-DIT)-1.0 V and P(TTPA-co-BDTA)-1.0 V films begin to oxidize and a new absorption band at 588 nm appeared due to neutralization of the PProDOT-Et2 layer, and the ECDs were blue in the potential range of +0.8 and 1.2 V for P(TTPA-co-DIT)-1.0 V/PProDOT-Et2 ECD and in the potential range of +1.0 and 1.4 V for P(TTPA-co-BDTA)-1.0 V/PProDOT-Et2 ECD (Table 5). Table 5. Electrochromic photographs and colorimetric values (L*, a*, and b*) of the ECDs. The P(TTPA-co-DIT) and P(TTPA-co-BDTA) films were prepared potentiostatically at 1.0 V on ITO glass electrodes. The transmittance-time profiles of P(TTPA-co-DIT)-1.0 V/PProDOT-Et2 and P(TTPA-co-BDTA)-1.0 V/PProDOT-Et2 ECDs were shown in Figure 9, which were stepped by repeated potential in the range of neutral (− 0.2 V) and oxidized states (+1.2 V) with a time interval of 5 s, and the ΔT, τc, and τb estimated at different double-step potential cycles are summarized in Table 6. The ΔT of P(TTPA-co-DIT)-1.0 V/PProDOT-Et2 and P(TTPA-co-BDTA)-1.0 V/PProDOT-Et2 ECDs is 43.5 and 48.1% at the first cycle, respectively, implying P(TTPA-co-BDTA) film is a promising electrochromic material to increase the ΔT when we employ P(TTPA-co-BDTA) film as anodic copolymer layer in ECDs. For P(TTPA-co-BDTA) film was prepared potentiostatically at 1.

Open Circuit Memory of ECDs
The open circuit memory test of P(TTPA-co-DIT)-1.0 V/PProDOT-Et 2 and P(TTPA-co-BDTA)-1.0 V/ PProDOT-Et 2 ECDs were monitored at 590 and 588 nm, respectively, as a function of time by applying potential for 1 s for each 200 s time interval. The test potentials for P(TTPA-co-DIT)-1.0 V/PProDOT-Et 2 ECD were´0.4 and 1.2 V in neutral and oxidized states, respectively, for P(TTPA-co-BDTA)-1.0 V/ PProDOT-Et 2 ECD were´0.2 and 1.2 V in neutral and oxidized states, respectively. It can be seen in Figure 10a,b that these ECDs show less than 5% transmittance change in oxidized state and less than 2% transmittance change in neutral state, indicating the presence of good optical memories for the ECDs.