A novel panchromatic shutter based on an ambipolar electrochromic system without supporting electrolyte

A solvent-controlled photoresponsive ionic hydrogen-bonded organic framework for encryption applications

Two novel ionic hydrogen-bonded organic frameworks (iHOF-17 and iHOF-18) were obtained by integrating organosulfonic acids with amidine salts. Among them, iHOF-18 exhibits fast, reversible, and high-contrast UV-induced photochromic properties, and this property is solvent-controlled. This work provides valuable insights for designing advanced anti-counterfeiting techniques and encryption applications.

Black electrochromic ink with a straightforward method using copper oxide nanoparticle suspension

Electrochromic (EC) materials for smart windows must exhibit a dark colour and block visible light (wavelength = 380-780 nm) to reduce environmental impact. In particular, black tones are also desired, and there are many reports of attempts to create these dark tones using organic materials such as polymers. However, their fabrication methods are complicated, expensive, and may even use hazardous substances; moreover, they are often not sufficiently durable, such as upon exposure to ultraviolet light. There are some reported cases of black materials using the CuO system as an inorganic material, but the synthesis method was complicated and the functionality was not stable. We have found a method to synthesize CuO nanoparticles by simply heating basic copper carbonate and adjusting the pH with citric acid to easily obtain a suspension. The formation and functionality of CuO thin films were also demonstrated using the developed suspension. This research will enable the creation of EC smart windows using existing inorganic materials and methods, such as printing technology, and is the first step towards developing environment-friendly, cost-effective, and functional dark inorganic materials.

Heteroacene-Based Polymer with Fast-Switching Visible-Near Infrared Electrochromic Behavior

The electrochromic properties and application of electronically conducting polymers (ECPs) (PTRPZ-EDOT) consisting of a 3,4-ethylenedioxythiophene (EDOT) and the heteroacene-based molecular scaffold, 6H-pyrrolo[3,2-b:4,5-b'] bis [1,4] benzothiazine (TRPZ), are reported. Known for its high electron mobility and conducting properties, the novel TRPZ scaffold was synthesized to possess two EDOT molecules termini affording TRPZ-EDOT. Electropolymerization of TRPZ-EDOT resulted in remarkable spectroscopic and conductive properties suitable for electrochromic device fabrication. Using atomic force microscopy (AFM), the average surface roughness and surface topography of PTRPZ-EDOT polymer thin films were determined. Spectroelectrochemical data showed that the polymer achieved switching times of 4.07 (coloration) and 0.47 s (bleaching) at 539 nm. The PTRPZ-EDOT film exhibits an optical contrast of 36-44% at 539 nm between its neutral and colored states, respectively. The NIR region from 1000 to 1700 nm shows the appearance of charge carrier bands with a 0-1 V potential range. An electrochromic device was successfully fabricated from PTRPZ-EDOT, showcasing the potential and applicability of the polymer material for advanced technologies such as smart windows, flexible electrochromic screens, and energy storage devices.

Synthesis and electrochromic properties of polyamines containing a 4,4′-diaminotriphenylamine-N,N′-diyl unit in the polymer backbone: Ru-catalyzed N–H insertion polycondensation of 1,4-phenylenebis(diazoacetate) with 4,4′-diaminotriphenylamine derivatives

Polycondensation of a bis(diazocarbonyl) compound and diaminotriphenylamine derivatization via Ru-catalyzed N–H insertion to afford electroactive polyamine.

Colorless to Multicolored, Fast Switching, and Highly Stable Electrochromic Devices Based on Thermally Cross-Linking Copolymer

Transparent-to-colored electrochromic devices exhibit promising application prospects and have gained popularity. Herein, two triphenylamine derivatives TPA-OCH₃ and TPA-CN with styryl moieties and different donor or acceptor units were designed and synthesized to further prepare solvent-resistant thermally cross-linking polymer P(TPA-OCH₃) and P(TPA-CN) without any additional initiator. P(TPA-OCH₃) and P(TPA-CN) possess two pairs of redox peaks, and P(TPA-OCH₃) shows a lower onset oxidation potential compared to P(TPA-CN) because of the pendent donor unit. Correspondingly, both polymers exhibit multicolored changes from the neutral colorless state to noticeable oxidized colors under different potentials. Furthermore, the thermally cross-linking copolymer P(TPA-OCH₃-co-TPA-CN) was obtained by TPA-OCH₃ and TPA-CN (the molar ratio is 2:1) and presents outstanding electrochromism with four color changes (colorless-orange-blue-purple) due to the multistep redox process of TPA-OCH₃ and TPA-CN units. It is more intriguing that the electrochromic device based on the copolymer films possesses a high optical contrast of 57.8% at 680 nm, fast switching time (0.52 and 0.66 s), and robust cyclic stability over 30 000 cycles with very little decay. Therefore, the thermally cross-linking copolymer is a promising candidate material for high-performance transmittive electrochromic devices, such as smart windows, sunglasses, and E-papers.

Colorless-to-Black Electrochromism from Binary Electrochromes toward Multifunctional Displays

Cyclohexane-1,2,4,5-tetracarboxylic diimide with a nonconjugated core has been incorporated to bridge two conventional triphenylamine units. The obtained monomer has successfully hypsochromically shifted the maximum absorption wavelength by 10 nm in comparison to the one with a pyromellitic diimide bridge. Consequently, a colorless electrochromic (EC) polymer poly(bis(N,N-diphenyl-4-aminophenyl)cyclohexane-1,2,4,5-tetracarboxylic diimide) (PTPA-HDI) was electropolymerized on indium tin oxide (ITO)-coated glass. The morphology, absorption, and spectroelectrochemistry properties of polymer PTPA-HDI films electropolymerized by different scan cycles have been systematically investigated. It is found that comprehensive properties, such as color contrast and initial transparence, can be achieved for the polymer film electropolymerized by 15 scan cycles. Moreover, to realize colorless-to-black electrochromism, an asymmetric viologen derivative 1-(4-cyanophenyl)-1'-hexyl-4,4'-bipyridinium dihexafluorophosphate (HVCN) has been designed and straightforward synthesized. With the introduction of a cyanophenyl group and a hexyl chain on the two pyridinium units, colorless-to-green electrochromism can be realized for this processible viologen derivative. The absorption band at 495 nm of colorated PTPA-HDI compensates well for the valley in the absorption spectrum of colorated HVCN. Therefore, different types of colorless-to-black electrochromic devices (ECDs) are fabricated using polymer PTPA-HDI-deposited ITO electrode and HVCN-based gel electrolyte. Such a supporting electrolyte-free ECD with binary electrochromes exhibits fast coloration, high color contrast, and excellent reversibility. Furthermore, an encryption ECD is demonstrated by switching a black two-dimensional code. In addition, an autodigital display is integrated on a smart window and hence different functions can be realized in a single ECD. Overall, this study may facilitate the understanding of the EC behaviors of binary electrochromes and present a new path to design multifunctional displays.

Facile Approach of Porous Electrochromic Polyamide/ZrO2 Films for Enhancing Redox Switching Behavior

Porous redox-active polyamide hybrid films have been successfully prepared to enhance the electrochromic (EC) properties in this report comparing with salt-caused porous films and hybrid films obtained via in situ sol-gel reaction of hydroxyl groups and zirconium dioxide (ZrO₂). With the assistance of porous and hybrid structures, the diffusion rate of counterions between electrolyte and EC species could be effectively increased, and the charges could be delivered and stored between the donor-acceptor system constructed by the organic-inorganic hybrid during the electrochemical process. Furthermore, there would be a synergistic effect while combining the porous structure and hybrid system together, which can improve the EC behaviors much more obviously; that is, the enhancement of porous hybrid films is more than that of porous films and hybrid films individually. For further application, the porous hybrid films were fabricated into devices, which exhibit a lower oxidation potential (from 1.07 to 0.94 V) and shorter switching response time (from 81.3 to 9.7 s for coloring time and from 44.7 to 20.8 s for bleaching time) with good electrochemical stability. Consequently, these results indicate that the EC properties could be enhanced and improved dramatically by the facile approach of merging the porous structure and hybrid system.

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).

Substituent effects of AIE-active α-cyanostilbene-containing triphenylamine derivatives on electrofluorochromic behavior

Four aggregation-induced emission (AIE)- and electro-active cyanostilbene-based triphenylamine-containing derivatives with different substituents were synthesized to investigate their effects on the photoluminescence properties and electrochromic (EC) and electrofluorochromic (EFC) behavior of gel-type electrochromic devices (ECDs). The optical and photoluminescence properties of the obtained materials were influenced by the substituents, and revealed AIE-active characteristics, exhibiting stronger fluorescence intensity in the aggregated state than in solution. Consequently, the EFC devices could be fabricated by combining these AIE- and electro-active materials with cathodic EC heptyl viologen HV into the gel-type electrolyte system to enhance the emission intensity, on/off contrast ratio, and response capability.

Synthesis and Characterization of Novel Triarylamine Derivatives with Dimethylamino Substituents for Application in Optoelectronic Devices

Two novel triphenylamine-based derivatives with dimethylamino substituents, N, N'-bis(4-dimethylaminophenyl)- N, N'-bis(4-methoxyphenyl)-1,4-phenylenediamine (NTPPA) and N, N'-bis(4-dimethylaminophenyl)- N, N'-bis(4-methoxyphenyl)-1,1'-biphenyl-4,4'-diamine (NTPB), were readily prepared for investigating the optical and electrochromic behaviors. These two obtained materials were introduced into electrochromic devices accompanied with heptyl viologen (HV), and the devices demonstrate a high average coloration efficiency of 287 cm²/C and electrochemical stability. Besides, NTPB/HV was further used to fabricate electrofluorochromic devices with a gel type electrolyte, and exhibit a controllable and high photoluminescence contrast ratio ( I_off/ I_on) of 32.12 from strong emission to truly dark by tuning the applied potential in addition to a short switching time of 4.9 s and high reversibility of 99% after 500 cycles.

Design, Synthesis, and Electrofluorochromism of New Triphenylamine Derivatives with AIE-Active Pendent Groups

Triphenylamine (TPA) and 4,4'-dimethoxy-triphenylamine (TPAOMe) derivatives were successfully linked with two high-performance AIEgens, triphenylethylene (TPE) and benzo[ b]thiophene-1,1-dioxide (BTO), to obtain four aggregation-induced emission and electro-active materials, TPETPA, BTOTPA, TPETPAOMe, and BTOTPAOMe. The effects on photoluminescence characteristics and electrochromic (EC) and electrofluorochromic (EFC) behaviors in cross-linking gel-type devices derived from the prepared materials were systematically investigated. Furthermore, heptyl viologen was introduced into the EFC devices to enhance EC performance including lower working potential, faster switching time, and superior stability.

Multifunctional polyurethanes synthesized from different triarylamine units with electrochromic, photogeneration, memory storage and sensing properties

Herein, we report three multifunctional polyurethane materials, which exhibit excellent electrochromic, photoelectric, memory and sensing properties, and also have good mechanical properties.

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.

Soluble Electrochromic Polymers Incorporating Benzoselenadiazole and Electron Donor Units (Carbazole or Fluorene): Synthesis and Electronic-Optical Properties

A series of π-conjugated polymers containing alternating benzoselenadiazole (BSe)-bi(thiophene derivative)-carbazole or benzoththiadiazole (BSe)-bi(thiophene derivative)-fluorene units were designed and synthesized. Thiophene derivatives, namely 3-hexylthiophene, 3,4-bihexyloxythiophene, and 3,4-bioctyloxythiophene, were used as the π-bridges of the polymers. The polymers were characterized in detail in terms of their thermal stabilities, cyclic voltammograms, UV-Vis absorption, spectroelectrochemistry, dynamic switching property and so forth. The alkoxy thiophene π-bridged polymers have lower onset oxidation potentials and bandgaps than that of their corresponding alkyl thiophene π-bridged polymers. The selection of the donor units between the carbazole and the fluorene units has nearly no effect on the bandgaps and colors as well as the onset oxidation potentials of the polymers. The increase in the length of the side alkyl chains on the thiophene ring caused a slight increase in the polymer bandgap, which may be caused by the space hindrance effect. The dynamic switching abilities of the polymers were obtained by the chronoabsorptometry method, and the results also suggested that the alkoxy thiophene-containing polymers (as π-bridges) have higher contrast ratios than the corresponding alkyl thiophene-containing polymers. Furthermore, the increase in the length of the side alkyl chain might have a detrimental effect on the optical contrast ratios of the polymers.

Electrochromism of alkylene-linked discrete chromophore polymers with broad radical cation light absorption

This paper details the theoretical calculations, synthesis, and electrochromism of polymeric materials consisting of conjugated chromophores separated by nonconjugated linkers.