Electrochromic Devices Based on Poly(2,6-di(9H-carbazol-9-yl)pyridine)-Type Polymer Films and PEDOT-PSS

2,6-Di(9H-carbazol-9-yl)pyridine (DiCP) was synthesized and its corresponding homopolymer (PDiCP) and copolymers (P(DiCP-co-CPDT), P(DiCP-co-CPDT2), P(DiCP-co-CPDTK), and P(DiCP-co-CPDTK2)) were synthesized electrochemically. The anodic copolymer with DiCP:cyclopentadithiophene ketone (CPDTK) = 1:1 feed molar ratio showed high transmittance change (ΔT%) and colouration efficiency (η), which were measured as 39.5% and 184.1 cm2 C−1 at 1037 nm, respectively. Electrochromic devices (ECDs) were composed of PDiCP, P(DiCP-co-CPDT), P(DiCP-co-CPDT2), P(DiCP-co-CPDTK), and P(DiCP-co-CPDTK2) as anodically-colouring polymers, and poly(3,4-ethylenedioxythiophene)-poly(styrene sulfonic acid) (PEDOT-PSS) as cathodically-colouring polymers. P(DiCP-co-CPDTK)/PEDOT-PSS ECD showed light silverish-yellow at 0.0 V, light grey at 0.7 V, grey at 1.3 V, light greyish blue at 1.7 V, and greyish blue at 2.0 V. Moreover, P(DiCP-co-CPDTK)/PEDOT-PSS ECD presented high ΔT (38.2%) and high η (633.8 cm2 C−1) at 635 nm.


Electrochemical and Electrochromic Characterization
The electrochemical characterizations of polymer films were carried out in three-component cells. An ITO coated glass, Pt wire, and Ag/AgCl (3 M KCl) electrode were used as working, counter, and reference electrodes, respectively. The electrochromic experiments and double potential chronoamperometry were implemented with a Hitachi spectrophotometer and a CHI627D (CH Instruments, Austin, TX, USA) electrochemical analyser.

Electrochemical and Electrochromic Characterization
The electrochemical characterizations of polymer films were carried out in three-component cells. An ITO coated glass, Pt wire, and Ag/AgCl (3 M KCl) electrode were used as working, counter, and reference electrodes, respectively. The electrochromic experiments and double potential chronoamperometry were implemented with a Hitachi spectrophotometer and a CHI627D (CH Instruments, Austin, TX, USA) electrochemical analyser.

Electrochemical and Electrochromic Characterization
The electrochemical characterizations of polymer films were carried out in three-component cells. An ITO coated glass, Pt wire, and Ag/AgCl (3 M KCl) electrode were used as working, counter, and reference electrodes, respectively. The electrochromic experiments and double potential chronoamperometry were implemented with a Hitachi spectrophotometer and a CHI627D (CH Instruments, Austin, TX, USA) electrochemical analyser.
The PDiCP film showed three kinds of colour variations from neutral to oxidation state, PDiCP film was light gray at 0.0 V, dark khaki at 1.0 V, and grey black at 1.2 V. For the copolymer films, P(DiCP-co-CPDT) and P(DiCP-co-CPDT2) films were light brown at 0.0 V, light cadet blue at 0.4 V, and navy blue at 1.1 (or 1.3 V), whereas P(DiCP-co-CPDTK) and P(DiCP-co-CPDTK2) films were light yellow at 0.0 V, grey at 0.8 V, and rock grey at 1.1 V. The colorimetric values (L*, a*, and b*) and CIE chromaticity diagrams of PDiCP, P(DiCP-co-CPDT2), and P(DiCP-co-CPDTK) films at various potentials are displayed in Table 2. Absorbance Wavelength (nm)

Spectroelectrochemical Characterizations of Homopolymer and Copolymer Films
The PDiCP film showed three kinds of colour variations from neutral to oxidation state, PDiCP film was light gray at 0.0 V, dark khaki at 1.0 V, and grey black at 1.2 V. For the copolymer films, P(DiCP-co-CPDT) and P(DiCP-co-CPDT2) films were light brown at 0.0 V, light cadet blue at 0.4 V, and navy blue at 1.1 (or 1.3 V), whereas P(DiCP-co-CPDTK) and P(DiCP-co-CPDTK2) films were light yellow at 0.0 V, grey at 0.8 V, and rock grey at 1.1 V. The colorimetric values (L*, a*, and b*) and CIE chromaticity diagrams of PDiCP, P(DiCP-co-CPDT2), and P(DiCP-co-CPDTK) films at various potentials are displayed in Table 2. Table 2. Colorimetric values (L*, a*, and b*), CIE chromaticity values (x, y), and CIE diagrams of (a) PDiCP, (b) P(DiCP-co-CPDT2), and (c) P(DiCP-co-CPDTK) films at various applied potentials.
The PDiCP film showed three kinds of colour variations from neutral to oxidation state, PDiCP film was light gray at 0.0 V, dark khaki at 1.0 V, and grey black at 1.2 V. For the copolymer films, P(DiCP-co-CPDT) and P(DiCP-co-CPDT2) films were light brown at 0.0 V, light cadet blue at 0.4 V, and navy blue at 1.1 (or 1.3 V), whereas P(DiCP-co-CPDTK) and P(DiCP-co-CPDTK2) films were light yellow at 0.0 V, grey at 0.8 V, and rock grey at 1.1 V. The colorimetric values (L*, a*, and b*) and CIE chromaticity diagrams of PDiCP, P(DiCP-co-CPDT2), and P(DiCP-co-CPDTK) films at various potentials are displayed in Table 2. Table 2. Colorimetric values (L*, a*, and b*), CIE chromaticity values (x, y), and CIE diagrams of (a) PDiCP, (b) P(DiCP-co-CPDT2), and (c) P(DiCP-co-CPDTK) films at various applied potentials.
The PDiCP film showed three kinds of colour variations from neutral to oxidation state, PDiCP film was light gray at 0.0 V, dark khaki at 1.0 V, and grey black at 1.2 V. For the copolymer films, P(DiCP-co-CPDT) and P(DiCP-co-CPDT2) films were light brown at 0.0 V, light cadet blue at 0.4 V, and navy blue at 1.1 (or 1.3 V), whereas P(DiCP-co-CPDTK) and P(DiCP-co-CPDTK2) films were light yellow at 0.0 V, grey at 0.8 V, and rock grey at 1.1 V. The colorimetric values (L*, a*, and b*) and CIE chromaticity diagrams of PDiCP, P(DiCP-co-CPDT2), and P(DiCP-co-CPDTK) films at various potentials are displayed in Table 2. Table 2. Colorimetric values (L*, a*, and b*), CIE chromaticity values (x, y), and CIE diagrams of (a) PDiCP, (b) P(DiCP-co-CPDT2), and (c) P(DiCP-co-CPDTK) films at various applied potentials.

Films
Potential ( The optical band gap (E g ) of PDiCP homopolymer film calculated using Planck equation was 2.58 eV: E g = 1241/λ onset (1) where the onset UV absorption wavelength (λ onset ) of the π-π* transition band of PDiCP was 481 nm [35,36]. The onset oxidation potential vs. Ag/AgCl (3 M KCl) was 0.82 V, the E FOC of ferrocene/ferrocenium vs. Ag/AgCl (3 M KCl) determined using cyclic voltammetry was 0.80 V, and the onset oxidation potential vs. E FOC was found to be 0.02 V. The HOMO and LUMO energy levels of PDiCP determined from the onset oxidation potential with respect to the energy level of ferrocene/ferrocenium couple (−4.8 eV less than vacuum energy level) [37,38] and E g were taken as −4.82 and −2.24 eV, respectively. Figure 6 showed the electrochromic switching profiles of PDiCP, P(DiCP-co-CPDT), P(DiCP-co-CPDT2), P(DiCP-co-CPDTK), and P(DiCP-co-CPDTK2) films in 0.2 M LiClO 4 /ACN/DCM solution, which were monitored using double potential-step chronoamperometry by repeating potentials between 0.0 and 1.  Table 3, the τc and τb are determined at 90% of the whole transmittance change.