Dithienylpyrrole-and Tris [ 4-( 2-thienyl ) phenyl ] amine-Containing Copolymers as Promising Anodic Layers in High-Contrast Electrochromic Devices

Abstract: Three dithienylpyrroleand tris[4-(2-thienyl)phenyl]amine-containing copolymers (P(MPS-co-TTPA), P(MPO-co-TTPA), and P(ANIL-co-TTPA)) were deposited on indium tin oxide (ITO) surfaces using electrochemical polymerization. Spectroelectrochemical characterizations of polymer films revealed that P(MPS-co-TTPA) film was light olive green, greyish-green, bluish grey, and grey in neutral state, intermediate state, oxidized state, and highly oxidized state, respectively, whereas P(MPO-co-TTPA) film was green moss, foliage green, dark greyish-green, and bluish-grey in neutral state, intermediate state, oxidized state, and highly oxidized state, respectively. The ∆Tmax of P(MPS-co-TTPA) film at 964 nm, P(MPO-co-TTPA) film at 914 nm, and P(ANIL-co-TTPA) film at 960 nm were 67.2%, 60.7%, and 67.1%, respectively, and the coloration efficiency (η) of P(MPS-co-TTPA) film at 964 nm, P(MPO-co-TTPA) film at 914 nm, and P(ANIL-co-TTPA) film at 960 nm were calculated to be 260.3, 176.6, and 230.8 cm2 C−1, respectively. Dual type complementary colored electrochromic devices (ECDs) were constructed using P(MPS-co-TTPA), P(MPO-co-TTPA), or P(ANIL-co-TTPA) as anodic copolymer layer and PProDOT-Et2 as cathodic polymer layer. P(MPO-co-TTPA)/PProDOT-Et2 ECD revealed high ∆T (55.1%) and high η (766.5 cm2 C−1) at 580 nm. Moreover, P(MPS-co-TTPA)/PProDOT-Et2, P(MPO-co-TTPA)/PProDOT-Et2, and P(ANIL-co-TTPA)/PProDOT-Et2 ECDs showed satisfactory long-term cycling stability and optical memory.


Introduction
Electrochromic materials have increasingly garnered attention due to their potential applications in low-energy consumption displays, antiglare mirrors, smart windows, and adaptive camouflages [1].Electrochromic materials are mainly classified as inorganic metal oxides, conjugated polymers, Prussian blue, metal metallohexacyanates, metal phthalocyanines, and viologens [2].Among these materials, conjugated polymers have been widely investigated due to their satisfactory optical contrast, high coloration efficiency, rapid electrochromic switching speed, multiple color exhibitions, and tunable optical band gap with chemical structure modifications.Recently, conjugated polymers such as polytriphenylamines [3], polycarbazoles [4], polyanilines [5,6], polybenzothiadiazoles [7], polyindoles [8], polythiophenes [9], and polybenzotriazoles [10] have been reported for particular electrochromic behaviors.Among these conjugated polymers, polytriphenylamines and polycarbazoles have hole transport properties and can be oxidized to form stable aminium radical cations, and the

Spectroelectrochemical Characterizations of Copolymer Films and ECDs
Spectroelectrochemical properties of copolymer films and ECDs were measured using a CHI660a electrochemical analyzer (CH Instruments, Austin, TX, USA) and a V-630 JASCO UV-Visible spectrophotometer (JASCO International Co., Ltd., Tokyo, Japan).Copolymer films were characterized in a three-component system, copolymer films coated on ITO glass plate were used as working electrodes, a platinum wire and an Ag/AgCl electrode were used as counter and reference electrodes, respectively.

Preparation of Copolymer Films
The CV curves of neat TTPA, MPS, MPO, and ANIL monomers, and the mixtures of two monomers (TTPA + MPS, TTPA + MPO, and TTPA + ANIL) in 0.1 M LiClO4/ACN solution are presented in Figure 2. The homopolymer and copolymer films can be clearly seen with continuously increasing cycles, indicating the formation of homopolymer and copolymer films on the ITO glass surface during the electrocoating process [23].

Spectroelectrochemical Characterizations of Copolymer Films and ECDs
Spectroelectrochemical properties of copolymer films and ECDs were measured using a CHI660a electrochemical analyzer (CH Instruments, Austin, TX, USA) and a V-630 JASCO UV-Visible spectrophotometer (JASCO International Co., Ltd., Tokyo, Japan).Copolymer films were characterized in a three-component system, copolymer films coated on ITO glass plate were used as working electrodes, a platinum wire and an Ag/AgCl electrode were used as counter and reference electrodes, respectively.

Coatings 2018, 8 , 17 Table 2 .
x FOR PEER REVIEW 8 of Electrochromic behaviors of copolymer films at various voltages.

Table 1 .
The onset potentials, oxidation potentials, and reduction potentials values of copolymer films.

Table 1 .
The onset potentials, oxidation potentials, and reduction potentials values of copolymer films.

Table 2 .
Electrochromic behaviors of copolymer films at various voltages.

Table 2 .
Electrochromic behaviors of copolymer films at various voltages.

Table 2 .
Electrochromic behaviors of copolymer films at various voltages.

Table 2 .
Electrochromic behaviors of copolymer films at various voltages.

Table 2 .
Electrochromic behaviors of copolymer films at various voltages.

Table 2 .
Electrochromic behaviors of copolymer films at various voltages.

Table 2 .
Electrochromic behaviors of copolymer films at various voltages.

Table 2 .
Electrochromic behaviors of copolymer films at various voltages.

Table 2 .
Electrochromic behaviors of copolymer films at various voltages.

Table 2 .
Electrochromic behaviors of copolymer films at various voltages.

Table 2 .
Electrochromic behaviors of copolymer films at various voltages.

Table 3 .
Color-bleach switching properties of copolymer films in solution state.

Table 4 .
Comparisons of transmittance changes and coloration efficiencies of polymer films., new absorption bands at ca. 580 nm emerge, and the ECDs are blue at +1.4V, as shown in Table5.The colorimetric values of ECDs at various potentials are summarized in TableS2(in Supplementary Information), and the CIE chromaticity diagrams of P(MPS-co-TTPA)/PProDOT-Et2, P(MPO-co-TTPA)/PProDOT-Et2, and P(ANIL-co-TTPA)/PProDOT-Et2 ECDs at various potentials are shown in Figure9. reduce

Table 5 .
Electrochromic behaviors of ECDs at various voltages.

Table 7 .
The transmittance changes and coloration efficiency of ECDs.