Electrochromic Polyimides Research Articles

A refreshing perspective on electrochromic materials: Phenoxazine as an opportune moiety towards stable and efficient electrochromic polyimides

In our attempt to develop appealing EC materials, here we address the electrochromic materials field by employing the aryl-substituted phenoxazine (POZ) as a new member of triarylamine family with excellent potential for electrochromic applications. Thus, a simple synthetic strategy was followed to build a novel POZ-based diamine that was further used in polycondensation reaction with commercially available aromatic dianhydrides to develop three novel polyimides (PIs). Complementarily, POZ-based model compounds were synthesized to get insights into the electrochemical and electrochromic behavior of the synthesized PIs. With the support of the computational quantum mechanical modeling methods (Density-Functional Theory – DFT and Time-Dependent (TD)–DFT), the mechanism responsible for the absence of the dimerization process upon POZ oxidation was established. Without resorting to any structural modification to block the para position of POZ, the present PIs demonstrated exquisite electrochemical and electrochromic performance, including high redox stability during 100 repetitive cyclic voltammetry scans, unique deep-purple coloration during oxidation, high optical contrast, up to 62%, response time below 6.5 s for coloring and 5.1 s for bleaching, excellent electrochromic efficiency, up to 193 cm2/C and a maximum 21% decay of the electrochromic efficiency after 500 cycles. The most efficient EC polyimide was used as an active layer in electrochromic prototype devices to survey the full applicative potential of these PIs. The devices rendered an optical contrast of 51%, 7.9 s for coloring, and 7.2 s for bleaching, electrochromic efficiency of 178 cm2/C, and decay of the electrochromic efficiency of 6.1% after 100 cycles, placing for the first time the POZ-based PIs among the perspective electrochromic materials.

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.

Colorless-to-colorful switching electrochromic polyimides with very high contrast ratio

Colorless-to-colorful switching electrochromic polymers with very high contrast ratio are unattainable and attractive for the applications of smart wearable electronics. Here we report a facile strategy in developing colorless-to-colorful switching electrochromic polyimides by incorporating with alicyclic nonlinear, twisted structures and adjusted conjugated electrochromophores, which minimize the charge transfer complex formation. It is noted that, by controlling the conjugation length of electrochromophore, the colorless-to-black switching electrochromic polymer film (PI-1a) exhibites an ultrahigh integrated contrast ratio up to 91.4% from 380 to 780 nm, especially up to 96.8% at 798 nm. In addition, PI-1a film with asymmetric structure also demonstrates fast electrochemical and electrochromic behaviors (a switching and bleaching time of 1.3 s and 1.1 s, respectively) due to the loose chain stacking, which provides more pathways for the penetration of counterion. Moreover, the colorless-to-black EC device based on PI-1a reveals an overall integrated contrast ratio up to 80%.

Synthesis and characterization of stable electrochromic polyimides with quinolin-8-yloxy-substituted triphenylamine units

Herein, three kinds of electrochromic aromatic polyimides (PIs) were synthesized from 4,4′-diamino-4″-(quinolin-8-yloxy) triphenylamine (DAQTPA) with different dianhydrides, respectively. These PIs showed good thermostability below 450°C even in air atmosphere. The maximum UV–vis absorption bands of PIs located at 321–338nm for solid films. The highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energy levels of the PIs were calculated from the cyclic voltammetry (CV) test as −5.42 to −5.44eV and −3.53 to −3.85eV, respectively. These PIs performed stable reversible electrochromic properties with optical transmittance change (ΔT) around 28–43% and coloration efficiency (η) around 74–117cm2C−1.

Electroactive and ambipolar electrochromic polyimides from arylene diimides with triphenylamine N-substituents

Three bis(triphenylamine) diimides, TPA-PMDI, TPA-NTDI and TPA-PTDI, were synthesized from condensation of 4-aminotriphenylamine with pyromellitic dianhydride (PMDA), 1,4,5,8-naphthalenetetracarboxylic dianhydride (NTDA) and 3,4,9,10-perylenetetracarboxylic dianhydride (PTDA), respectively. Redox-active poly(arylamine-imide) films coded with TPA-PMPI, TPA-NTPI, and TPA-PTPI could be electrodeposited robustly on the electrode surface in an electrolyte solution via the oxidative coupling reactions between TPA radical cations. The CVs of these elecrtrodeposited films showed an ambipolar redox behavior, with a reversible redox couple at E1/2 of 0.99–1.02 V during the anodic scanning and two pairs of redox waves during cathodic scanning. The polyimide films exhibited multicolored anodic and cathodic coloring. Electrochromic devices using the electropolymerized films as active layers were also fabricated as preliminary investigations for electrochromic applications.

Synthesis and characterization of new redox-active and electrochromic polyimides with (4-morpholinyl)triphenylamine units

A series of electroactive aromatic polyimides with (4-morpholinyl)triphenylamine units in the backbone were prepared from a newly synthesized diamine monomer, 4,4′-diamino-4″-(4-morpholinyl)triphenylamine, and aromatic tetracarboxylic dianhydrides via the conventional two-step polycondensation technique. Flexible and tough polyimide films could be obtained via the thermal curing of their precursor poly(amic acid) films. The polyimides showed high glass-transition temperatures (Tg) between 290–313°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 (ITO)-coated glass substrate exhibited a pair of reversible oxidation waves with low onset oxidation potentials of 0.43–0.53V (vs. Ag/AgCl) in acetonitrile solution. They also exhibited multicolor electrochromic behavior between their neutral and oxidized states changing from pale yellow to cyan and bluish purple.

Multicolored near-infrared electrochromic polyimides: Synthesis, electrochemical, and electrochromic properties

A novel series of multicolored near-infrared electrochromic aromatic polyimides have been synthesized by a conventional two-step polymerization process. All polymers displayed outstanding thermal stability, i.e. 20 wt% loss in excess of 593 °C in nitrogen and high char yields (higher than 68% at 750 °C). In addition, the polymer films showed reversible electrochemical oxidation, high coloration efficiency, low switching time, and anodic green electrochromic behaviors. The Highest Occupied Molecular Orbital (HOMO) and Lowest Unoccupied Molecular Orbital (LUMO) energy levels of these polymers were determined in the range of −4.759 to −4.801 and −1.758 to −2.002 eV (vs the vacuum level) by cyclic voltammetry method consisting with the results of quantum chemical calculation well, respectively. The polymer films revealed excellent stability of electrochromic characteristics for the radical cations generated, changing color from original yellowish to green and blue, with the absorption changing from ultraviolet to near-infrared.

Novel rapid switching and bleaching electrochromic polyimides containing triarylamine with 2-phenyl-2-isopropyl groups

A series of novel organosoluble polyimides and copolyimides with a propeller-shaped triarylamine unit were prepared from diamine and various aromatic dianhydrides via direct polycondensation. All of the polymers possessed tough, flexible, and strong films with high molecular weights. The polyimide and copolyimide films revealed electrochromic characteristics, with a color change from pale yellowish at its neutral state, to green, and finally to blue at its oxidized state, at applied potentials ranging from 0 to 1.50 V. The polyimide ( Ib) film exhibited switching times of 4.5 s at 1.08 V at 424 and 877 nm and 1.9 s for fast bleaching due to a pendent substituted 2-phenyl-2-isopropyl group. Cyclic voltammetry (CV) of the polymer films showed two reversible redox couples at potentials of 0.91–0.99 V and 1.30–1.38 V, respectively. The CV results of the model compound M1 and model polyimide M2, were not a match to the oxidation peaks of polyimide Ib, indicating that the contribution of the oxidation was not only from the electron removal of nitrogen atoms.

The synthesis and characterization of near-infrared absorbing, electrochromic polyimides containing a dinuclear ruthenium complex in the polymer mainchain

A redox-active, near-infrared absorbing dinuclear ruthenium complex was incorporated into the mainchain of polyimides using a two-stage polymerization method. The polyimides show high thermal stability with a decomposition temperature range from 172 to 248 °C and glass transition temperature of 97–180 °C, depending on the dianhydride monomer used. The polyimides are redox active, electrochromic at 1600 nm with the ruthenium complex being in the mixed-valence state and fluorescent at 790 nm.