Substituent Effect on Electrochemical and Electrochromic Behaviors of Ambipolar Aromatic Polyimides Based on Aniline Derivatives

Research Progress in Special Engineering Plastic-Based Electrochromic Polymers

SPECPs are electrochromic polymers that contain special engineering plastic structural characteristic groups (SPECPs). Due to their high thermal stability, mechanical properties, and weather resistance, they are also known as high-performance electrochromic polymer (HPEP or HPP). Meanwhile, due to the structural characteristics of their long polymer chains, these materials have natural advantages in the application of flexible electrochromic devices. According to the structure of special engineering plastic groups, SPECPs are divided into five categories: polyamide, polyimide, polyamide imide, polyarylsulfone, and polyarylketone. This article mainly introduces the latest research on SPECPs. The structural design, electrochromic properties, and applications of these materials are also introduced in this article, and the challenges and future development trends of SPECPs are prospected.

Synthesis and Characterization of Novel Triphenylamine-Containing Electrochromic Polyimides with Benzimidazole Substituents

Two novel electrochromic aromatic polyimides (named as TPA-BIA-PI and TPA-BIB-PI, respectively) with pendent benzimidazole group were synthesized from 1,2-Diphenyl-N,N'-di-4-aminophenyl-5-amino-benzimidazole and 4-Amino-4'-aminophenyl-4″-1-phenyl-benzimidazolyl-phenyl-aniline with 4,4'-(hexafluoroisopropane) phthalic anhydride (6FDA) via two-step polymerization process, respectively. Then, polyimide films were prepared on ITO-conductive glass by electrostatic spraying, and their electrochromic properties were studied. The results showed that due to the π-π* transitions, the maximum UV-Vis absorption bands of TPA-BIA-PI and TPA-BIB-PI films were located at about 314 nm and 346 nm, respectively. A pair of reversible redox peaks of TPA-BIA-PI and TPA-BIB-PI films that were associated with noticeable color changed from original yellow to dark blue and green were observed in the cyclic voltammetry (CV) test. With increasing voltage, new absorption peaks of TPA-BIA-PI and TPA-BIB-PI films emerged at 755 nm and 762 nm, respectively. The switching/bleaching times of TPA-BIA-PI and TPA-BIB-PI films were 13 s/16 s and 13.9 s/9.5 s, respectively, showing that these polyimides can be used as novel electrochromic materials.

High-Performance Electrochromic Covalent Hybrid Framework Membranes via a Facile One-Pot Synthesis

Porous framework materials have sparked enormous interest in the electrochromic field, as they possess intrinsic high porosity and a large surface area that are beneficial for electron and ion transport. However, the fabrication of these porous framework materials often requires multiple processing steps or harsh reaction conditions, which significantly limit large-scale fabrication of such materials. In this work, we report a one-pot in situ polycondensation method to construct electrochromic covalent hybrid framework membranes via nucleophilic substitutions between hexachlorocyclotriphosphazene (HCCP) and triphenylamine (TPA) in an ambient environment. With the high transparency of polyphosphazene in a wide optical range, the constructed phosphazene-triphenylamine (PPTA) covalent hybrid framework membranes can be reversibly switched between light gray and dark blue, with a high transmittance change of up to 79.8%@668 nm and fast switching time (<4 s). Owing to the easy one-pot fabrication and good electrochromic properties, the PPTA covalent hybrid framework membrane has great potential in various fields such as displays and dynamic optical windows.

Linear and star-shaped π-conjugated oligoanilines: a review on molecular design in syntheses and properties

Molecular Design and Synthesis of Linear and Star-shaped π-conjugated Oligoanilines with reversible optoelectrochemical properties.

Toward Easy-to-Assemble, Large-Area Smart Windows: All-in-One Cross-Linked Electrochromic Material and Device

Conventional electrochromic devices with a sandwich structure consist of multiple interfaces, which enhance electron trapping on the interfaces. Furthermore, crack generation in the electrochromic layer is inevitable due to repeated ion insertion and extraction during the service process. These problems increase the fabrication complexity and lead to poor performance and stability, which are severely limiting and prime concerns for the future development of the electrochromism field. Here, a strategy of synthesizing an all-in-one self-healing electrochromic material, TAFPy-MA, is presented, which has been utilized for the fabrication of a high-reliability, large-scale, and easy-assembly smart electrochromic window. The all-in-one self-healing electrochromic material can undergo in situ redox reactions with Li⁺ ions to reduce resistance transfer and avoid interface obstacles, and the reversible Diels-Alder cross-linking network structure can heal the cracks to improve the reliability of the electrochromic layer. High ion diffusivity (1.13 × 10^-5 cm² s^-1), rapid color switching (3.9/3.7 s), high coloration efficiency (413 cm² C^-1), excellent stability (sustains 88.7% after 1000 cycles) and reliability (crack can be healed in 110 s), and large-scale smart windows (30 × 35 cm²) are achieved using the all-in-one electrochromic material, which exhibits fascinating and promising features for a wide range of applications in buildings, airplanes, etc.

Design Rules for Improving the Cycling Stability of High-Performance Donor-Acceptor-Type Electrochromic Polymers

Although high-performance donor-acceptor (D-A)-type polymers have received much attention as an important class of electrochromic (EC) materials, the related studies have mostly focused on the influence of D and A units on the band gap, onset potential, and switching time, leaving the effect of D-A structures on cycling lifetime underexplored. Herein, we design and synthesize a series of poly(aryl amino sulfone)s (PAASs) as D-A polymers with triphenylamine-based donor units and the sulfone moiety as the acceptor unit. As a result, we present new rules to design and develop D-A structure polymers with high EC cycling stability: (1) the electron-donating and -withdrawing abilities of the donor and acceptor should be balanced during the electrochemical cycle process, and this balance can be measured by the ratio of J_red/J_ox; (2) the D-A structure should benefit to generate lower E_onset. By these design rules, the best-performing polymer PAAS-TPPA-OMe exhibits an excellent long-term cycling stability (over 3,900 cycles), low onset potential (0.26 V), fast switching time (6.0/4.3 s for the EC process), high contrast (87% at 688 nm and 94% at 928 nm), and high coloration efficiency (500 cm² C^-1 at 688 nm and 1131 cm² C^-1 at 928 nm).

Synthesis, characterization and electrochromic properties of novel redox triarylamine-based aromatic polyethers with methoxy protecting groups

Two series of novel redox aromatic polyethers were synthesized successfully from disilyl ether-containing triphenylamine-based monomers and they display one to three stage electrochromism with interesting and multi-coloured changes.

Intelligent Biomimetic Chameleon Skin with Excellent Self-Healing and Electrochromic Properties

Animals such as chameleons possess a natural ability to adjust their skin color as a preventive measure to deter any potential threat and to self-heal damaged skin tissues. Inspired by this, we present here a copolymer film possessing biomimetic properties that simultaneously integrates electrochromic triphenylamine and self-healing Diels-Alder groups. The flexible and stretchable copolymer film acts like natural chameleon skin, which exhibits significant color variation and also possesses excellent self-healing properties. These remarkable features make it a promising material for overcoming the crack-generation issue inherited by conventional biomimetic chameleon skin. Moreover, a flexible and wearable skin device based on the copolymer film with silver fabric as a electrode has also been fabricated. The electrochromic and self-healing properties were verified for the copolymer film, and it has been elucidated that the intelligent biomimetic "chameleon skin" was a new step toward the development of highly advanced biomimetic materials and devices.

Recent advances in triphenylamine-based electrochromic derivatives and polymers

Triphenylamine-containing electrochromic materials with great potential applications in low energy-consumption displays, light-adapting mirrors in vehicles, and smart windows have experienced an exponential growth of research interests. In this review, the newly developed triphenylamine-based derivatives and polymers are reviewed and elaborated.

Synthesis and Electrochromism of Highly Organosoluble Polyamides and Polyimides with Bulky Trityl-Substituted Triphenylamine Units

Two series of polyamides and polyimides containing bulky trityl-substituted triphenylamine units were synthesized from condensation reactions of 4,4′-diamino-4′′-trityltriphenylamine with various dicarboxylic acids and tetracarboxylic dianhydrides, respectively. The polymers showed good solubility and film-forming ability. Flexible or robust films could be readily obtained via solution-casting. The use of aliphatic diacid or dianhydride reduces interchain charge transfer complexing and leads to colorless polyamide and polyimide films. These polymers showed glass-transition temperatures in the range of 206–336 °C. Cyclic voltammograms of the polyamide and polyimide films displayed reversible electrochemical oxidation processes in the range of 0–1.0 or 0–1.3 V. Upon oxidation, the color of polymer films changes from colorless to blue-green or blue. As compared to the polyimide counterparts, the polyamides showed lower oxidation potentials and thus a higher electrochromic stability and coloration efficiency. Simple electrochromic devices were also fabricated as a preliminary investigation for electrochromic applications of the prepared polymers.

A novel self-healing electrochromic film based on a triphenylamine cross-linked polymer

A novel electrochromic material with self-healing properties, which may hold great potential to overcome the scar generation in ECDs, has been synthesized and studied.

Synthesis and electrochemical properties of new redox-active polyimides with (1-piperidinyl)triphenylamine moieties

A series of new electroactive aromatic polyimides with (1-piperidinyl)triphenylamine moieties were prepared from 4,4′-diamino-4″-(1-piperidinyl)triphenylamine and aromatic tetracarboxylic dianhydrides via the conventional two-step polycondensation technique. Flexible and strong polyimide films could be obtained via the thermal curing of their precursor poly(amic acid) films. The polyimides showed high glass transition temperatures between 288°C and 318°C, and they did not show significant decomposition before 500°C in air or nitrogen atmosphere. Cyclic voltammograms of the polyimide films on the indium–tin oxide-coated glass substrate exhibited a pair of reversible oxidation waves with low onset oxidation potentials of 0.45–0.49 V (vs. silver/silver chloride) in acetonitrile solution. Upon oxidation, the color of the polyimide films changes from pale yellow to yellowish green and finally to blue.

A new electrochromic copolymer which switched between neutral black and oxidized transmissive

A new type of electrochromic donor–acceptor type copolymer was obtained by the electrodeposition method. The P(1-co-2) film exhibited a deep black color in the neutral state and a transmissive light gray color in the oxidized state.

Linkage and donor–acceptor effects on resistive switching memory devices of 4-(N-carbazolyl)triphenylamine-based polymers

In order to gain deeper insight about the linkage effect and donor–acceptor effect on memory behavior (from DRAM to WORM), 4-(N-carbazolyl)triphenylamine-based polyimides and polyamides were synthesized and their memory behaviours were investigated.

Electrochemically fabricated electrochromic films from 4-(N-carbazolyl)triphenylamine and its dimethoxy derivative

4-(N-Carbazolyl)triphenylamine (TPACz) and its methoxy derivative MeOTPACz could be facilely fabricated into redox-active and electrochromic PTPACz polymer and (MeOTPACz)2 dimer films via electrochemical polymerization.

Synthesis, structures, and electrochromic behaviors of poly(triarylamine)s based on 3-substituted thiophene derivatives

The sole difference in chemical structure plays a role in inflecting reactivity, probably through altering electron cloud density.

Polyurethanes prepared from isocyanates containing triphenylamine derivatives: synthesis and optical, electrochemical, electrochromic and memory properties

Electrochromic behaviors of a PU (M1)-b thin film (in CH₃CN with 0.1 M LiCO₄ as the supporting electrolyte) at 0.0 V to 1.40 V (insets are the pictures of oxidized PU (M1)-b).

Colorless triphenylamine-based aliphatic thermoset epoxy for multicolored and near-infrared electrochromic applications

In this study, two novel colorless thermoset epoxy resins with anodically electrochromism were prepared from the thermal curing of two triphenylamine-based diamine monomers, 4,4'-diamino-4″-methoxytriphenylamine (1) and N,N'-bis(4-aminophenyl)-N,N'-di(4-methoxylphenyl)-1,4-phenylenediamine (2) with aliphatic epoxy triglycidyl isocyanurate, respectively. The resulting thermoset epoxy resins showed excellent softening temperature (Ts, 270 and 280 °C) due to the rigid structure and highly crosslinking density. In addition, novel colorless epoxy resin films revealed good reversible electrochemical oxidation and interesting multi-electrochromic behavior with high contrast ratio both in visible and near-infrared regions. The aliphatic thermoset epoxy resins also exhibited high transparency in visible region as colorless and great potential for practical electrochromic applications.