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Viologen-based organic electrochromic materials have been extensively studied due to their excellent electrochromic performance. Nevertheless, the dimerization of the radical cation state will destroy the reversibility of viologens and result in poor stability of the electrochromic device (ECD). Herein, two π-extended viologen derivatives (Spr-MPTT and Sbu-MPTT) are synthesized by inserting a thiazolo[5,4-d]thiazole unit between bipyridine moieties and N-bisubstituted with alkyl sulfonate groups. All-in-one hydrogel ECDs are assembled using Spr-MPTT or Sbu-MPTT and ferrocene modified by a water-soluble group. The Spr-MPTT-based ECD exhibited alternating color change between yellow-green and violet, while the Sbu-MPTT-based ECD displayed alternating color change between yellow-green and purple at 1.0/0 V pulse voltage. The extended conjugation of the viologen chromophore confers these devices with visible-NIR absorption and good cyclic stability. Their optical contrasts at 535 nm are 54.85% and 60.17%, respectively, for Spr-MPTT or Sbu-MPTT based ECD. These results demonstrate their potential application in electrochromic hydrogel smart windows. [ABSTRACT FROM AUTHOR]

Viologens, with their unique redox‐active properties, have garnered increasing attention in the development of electrochromic devices. This review focuses on key strategies in molecular design, synthesis methodologies, and tailored functionalities that have propelled the field forward from 2019 to the present. The convergence of these approaches has led to the construction of viologen‐based electrochromic materials with enhanced performance, stability, and responsiveness. The review not only examines the current state of the field but also explores promising outlooks and opportunities, including tailored applications, environmental sustainability, and integration with emerging technologies. The synergy between molecular engineering and viologen‐based electrochromic materials holds significant promise, shaping the future of dynamic, responsive materials in diverse technological domains. This review serves as a valuable resource for researchers, offering insights into recent breakthroughs and inspiring further advancements in this rapidly evolving field. [ABSTRACT FROM AUTHOR]

Electrochromic materials enable the precise control of their optical properties, making them essential for energy-saving applications such as smart windows. This study focuses on the synthesis of molybdenum-doped niobium oxide (Mo-Nb2O5) thin films using a one-step hydrothermal method to investigate the effect of Mo doping on the material's electrochromic performance. Mo incorporation led to distinct morphological changes and a transition from a compact granular structure to an anisotropic rod-like feature. Notably, the MN-3 (0.3% Mo) sample displayed an optimal electrochromic performance, achieving 77% optical modulation at 600 nm, a near-perfect reversibility of 99%, and a high coloration efficiency of 89 cm2/C. Additionally, MN-3 exhibited excellent cycling stability, with only 0.8% degradation over 5000 s. The MN-3 device also displayed impressive control over color switching, underscoring its potential for practical applications. These results highlight the significant impact of Mo doping on improving the structural and electrochromic properties of Nb2O5 thin films, offering improved ion intercalation and charge transport. This study underscores the potential of Mo-Nb2O5 for practical applications in energy-efficient technologies. [ABSTRACT FROM AUTHOR]

The interface mismatch between electrochromic materials and conductive layer seriously affects the cycle stability of electrochromic smart windows (ESW). However, it is difficult to improve the interface matching at the same time because of the different physical and chemical properties of anode and cathode materials. In this work, SnO 2 nanosheets are used as the interface modification layer between electrochromic materials and conductive layer. SnO 2 interface engineering significantly can improve the cycle stability of WO 3 film and Prussian blue (PB) film. The WO 3 /SnO 2 -PB/SnO 2 complementary ESW exhibits a high optical modulation of 60.2 % at 633 nm, fast response time (bleached/colored time = 8.5/2.5 s), and coloration efficiency of 91.7 cm2 C−1. The WO 3 /SnO 2 -PB/SnO 2 device can still maintain an optical modulation of 45.2 % after 2000 cycles, suggesting excellent long cycle stability. And the device shows the energy storage of 5.06 mF cm−2 at 0.1 mA cm−2, which can improve energy efficiency. The excellent electrochromic properties and energy storage suggests that SnO 2 interface engineering has a good application prospect in multi-functional ESW with excellent cycle stability. [ABSTRACT FROM AUTHOR]

Organic‐hybrid particle‐based materials are increasingly important in (opto)electronics, sensing, and catalysis due to their printability and stretchability as well as their potential for unique synergistic functional effects. However, these functional properties are often limited due to poor electronic coupling between the organic shell and the nanoparticle. N‐heterocyclic carbenes (NHCs) belong to the most promising anchors to achieve electronic delocalization across the interface, as they form robust and highly conductive bonds with metals and offer a plethora of functionalization possibilities. Despite the outstanding potential of the conductive NHC‐metal bond, synthetic challenges have so far limited its application to the improvement of colloidal stabilities, disregarding the potential of the conductive anchor. Here, NHC anchors are used to modify redox‐active gold nanoparticles (AuNPs) with conjugated triphenylamines (TPA). The resulting AuNPs exhibit excellent thermal and redox stability benefiting from the robust NHC‐gold bond. As electrochromic materials, the hybrid materials show pronounced color changes from red to dark green, a highly stable cycling stability (1000 cycles), and a fast response speed (5.6 s/2.1 s). Furthermore, TPA‐NHC@AuNP exhibits an ionization potential of 5.3 eV and a distinct out‐of‐plane conductivity, making them a promising candidate for application as hole transport layers in optoelectronic devices. [ABSTRACT FROM AUTHOR]

NiO, an anodic electrochromic material, has applications in energy‐saving windows, intelligent displays, and military camouflage. However, its electrochromic mechanism and reasons for its performance degradation in alkaline aqueous electrolytes are complex and poorly understood, making it challenging to improve NiO thin films. We studied the phases and electrochemical characteristics of NiO films in different states (initial, colored, bleached and after 8000 cycles) and identified three main reasons for performance degradation. First, Ni(OH)2 is generated during electrochromic cycling and deposited on the NiO film surface, gradually yielding a NiO@Ni(OH)2 core–shell structure, isolating the internal NiO film from the electrolyte, and preventing ion transfer. Second, the core–shell structure causes the mode of electrical conduction to change from first‐ to second‐order conduction, reducing the efficiency of ion transfer to the surface Ni(OH)2 layer. Third, Ni(OH)2 and NiOOH, which have similar crystal structures but different b‐axis lattice parameters, are formed during electrochromic cycling, and large volume changes in the unit cell reduce the structural stability of the thin film. Finally, we clarified the mechanism of electrochromic performance degradation of NiO films in alkaline aqueous electrolytes and provide a route to activation of NiO films, which will promote the development of electrochromic technology. [ABSTRACT FROM AUTHOR]

Recent years have shown many advances in the development of tunable structural colors by combining nanostructures with electrochromic materials. One main goal is to develop energy saving color displays that rely on ambient light instead of being emissive. However, all displays need to be pixelated to show arbitrary images and few studies have addressed the challenge of preparing and controlling individual electrochromic pixels. Herein, a very simple method to reach this milestone by using passive matrix addressing is presented, which requires no additional electronic components in the pixels. It is shown that the common transparent conductor indium tin oxide (ITO) in non‐aqueous electrolytes exhibits the diode‐like behavior (threshold in voltage in relation to current and coloration) necessary to prevent significant cross‐talk between pixels. The chemical nature of the redox activity that enables this behavior is attributed to omnipresent oxygen and the formation of superoxide ions. Additionally, it is shown that a gel‐like electrolyte can be prepared by optical lithography, which makes the concept compatible with patterning of pixels at high resolution. This method for preparing pixelated displays should be compatible with practically any type of electrochromic surface in both reflective and transmissive configurations. Also, the counter electrode maintains excellent transparency since it simply consists of ITO. The results should prove very useful as the research field of tunable structural colors moves from proof‐of‐concept to real devices. [ABSTRACT FROM AUTHOR]

Electrically triggered color‐changing materials, termed as electrochromic materials, offer precise and programmable color transistions through the manipulation of electric field frequency and amplitude. They are used as displays, sensors, military camouflage, wearable devices, and anticounterfeiting materials. Their future advancements depend on clear understanding of the color change mechanisms and pros/cons between different electrochromic materials. To this end, we starts by categorizing electrochromism into two classes according to color production mechanism: chemical color‐based and physical color‐based. Within the former, color emerges from chemical molecules selectively absorbing specific wavelengths of light and color changes stem from electrochemical redox reactions. The latter, meanwhile, hinges upon electrically induced alterations in the geometries, dimensions, or arrangements of nano/micro structures, such as photonic crystals and plasmonic nanostructures. The principles of color changes in both categories are detailed, and compare their differences in terms of response time, operating voltage, degree of color change, and stability. At the end, their applications will be discussed spanning from smart windows to color display, dynamic camouflage, energy storage, and thermal management. This critical review is aimed to provide multidisciplinary insights that will benefit both novices and seasoned experts engaged in fundamental exploration or practical investigations of electrochromic materials. [ABSTRACT FROM AUTHOR]

Phenazine-based redox-active centers are capable of averting chemical bond rearrangements by coupling during the reaction process, leading to enhanced stabilization of the material. When introduced into a high-performance polymer with excellent physicochemical properties, they can be endowed with electrochemical properties and related prospective applications while maintaining the capabilities of the materials. In this study, a facile C-N coupling method was chosen for the synthesis of serial poly(aryl ether sulfone) materials containing phenazine-based redox-active centers and to explore their electrochemical properties. As expected, the cyclic voltammetry curves of PAS-DPPZ-60, which basically overlap after thousands of cycles, indicate the stability of the electrochemical properties. As an electrochromic material, the transmittance change in PAS-DPPZ-60 exhibits only a slight attenuation after as long as 600 cycles. Meanwhile, as an organic battery cathode material, PAS-DPPZ has a theoretical specific capacity of 126 mAh g−1, and the capacity retention rate is 82.6% after 100 cycles at a 0.1 C current density. The perfect combination of advantageous features between phenazine and poly(aryl ether sulfone) is considered to be the reason for the favorable electrochemical performance of the material series. [ABSTRACT FROM AUTHOR]

Electrochromic devices (ECDs) have been extensively investigated as promising candidates in broad cutting-edge applications, such as smart windows, electronic labels, adaptive camouflage, etc. However, they have suffered from either inadequate color variations or poor cycling stability for a long time. Herein, we developed a general strategy to boost the cyclic stability and enrich the color variations of ECDs by scrupulous design of the composition and nanostructure of electrodes, in which porous tin oxide (SnO2) nanosheets serve as the scaffold and typical metal oxides or conducting polymers as the active electrochromic materials. Various electrochromic composite materials, including polyaniline (PANI)@SnO2, V2O5@SnO2, and WO3@SnO2 heterostructured nanoarrays were prepared by the facile wet-chemical method. These composite electrodes exhibit remarkable electrochromic performances, e.g., superior cycling stability (more than 2000 cycles), rich color variations (more than 5 colors for PANI@SnO2), and enlarged optical modulation. These excellent performances account for the heterogenous porous nanoarrays, which not only facilitate the intercalation/extraction of ions but also relieve the stress generated during the electrochemical process. In addition, diverse prototypes of complementary multicolor ECD with excellent cycling stability (over thousands of cycles) and rich color variations (8 colors) were realized for the first time. We believe that our work put forward a general strategy for developing high-quality multicolor complementary electrochromic devices. [ABSTRACT FROM AUTHOR]

Electrochromic devices (ECDs) have attracted substantial attention on account of their unique characteristics and prosperous applications. However, their monotonous color modification remains a momentous challenge that significantly restricts their application scope. Integrating structural colors that arise from the interaction between light and periodic micro/nanostructures with electrochromic materials (ECMs) turns out to be an effective approach to enhancing the comprehensive performance of ECDs more than the coloration effectiveness. This review provides an overview on the recent burgeoning development of structural color ECDs regarding strategies and applications. The performance parameters of ECDs and physical principles regarding the generation of structural colors are introduced. Then, strategies that introduce structural colors into ECDs are discussed according to the category of chromogenic micro/nanostructures, namely, gratings, (single‐layer and multilayer) thin films, photonic crystals, plasmonic metasurfaces, and composite structures. The current state‐of‐the‐art research activities of structural color ECDs for display application including segmented and pixelated devices are also presented. Additionally, the future perspective of structural color ECDs with respect of major challenges and potential solutions is proposed. [ABSTRACT FROM AUTHOR]

Electrochromic materials allow for precise control of their optical properties by applying an electric field, which has led to recent developments in energy-saving and indoor temperature control systems like smart windows. The selective incorporation of metal dopants is an effective technique for generating highly advanced semiconducting metal oxides with precisely customized physicochemical characteristics. In this report, we employed a one-step electrodeposition process to fabricate nickel-doped tungsten oxide (W–Ni) thin films, systematically probing the impact of nickel (Ni) doping on the collective material characteristics. Comprehensive X-ray diffraction research revealed significant changes in diffraction patterns, suggesting slight modifications in the structure caused by Ni doping. The scanning electron microscopy showed complex differences in the microstructure of the film, such as a dense surface, porosity, and clustering of nanogranules. The WNi-3% thin film doped at 3 wt. % exhibited excellent electrochromic performance by efficiently handling lithium ions and displaying favorable electrochromic properties. The improved electrode, WNi-3%, showed a maximum optical modulation of 81.90%, exceptional reversibility of 99.4%, and a high coloration efficiency of 75.12 cm2/C. These findings underscore the efficacy of Ni-doping in tailoring the electrochromic properties of nickel-doped tungsten oxide thin films, thereby advancing the frontiers of high-performance electrochromic materials for energy-efficient applications. [ABSTRACT FROM AUTHOR]

Viologens, a typical group of electrochromic materials, show rich color changes under the external electrical stimulus. Recently, some of the viologen derivatives are reported to exhibit good luminescent performance. However, their luminescence colors are difficult to adjust owing to the strong electron‐accepting properties of viologens, which seriously hinders their applications in smart light‐emitting devices. In this work, the color/emission dual‐switchable viologen derivative Phen‐vio is designed and synthesized by introducing fluorophore 1,10‐phenanthroline into 4,4′‐bipyridine, for multicolor large‐area and patterned electrochromic/electrofluorochromic devices. Under voltage driving of −2.3 and −2.8 V, the devices exhibited reversible color and fluorescence color changes from light yellow to dark orange to dark blue, and from yellow to orange to green, respectively. Moreover, the devices displayed a high color contrast ratio of up to 77% at 600 nm. More importantly, the driving voltages of the devices do not vary with the change of the device area, which is huge application potential in smart windows and tags. [ABSTRACT FROM AUTHOR]

Localized surface plasmon resonance (LSPR) is attractive to fabricate visible (VIS) and near‐infrared (NIR) dual‐band electrochromic materials. However, the introduction of the LSPR effect in the available dual‐band electrochromic materials can only be manifested to the spectral enhancement in the NIR region, and difficult issues of electrochromic materials such as low coloration efficiency and unsatisfactory long‐term cycling durability still remain. Here, a dual‐band electrochromic thin film consisting of a 2D ordered macroporous (2DOM) Au LSPR layer and a poly(3,4‐(2,2‐dimethylpropylenedioxy)thiophene) (PProDot‐Me2) electrochromic layer is presented, where LSPR and electrochromism interact in a complementary fashion. The 2DOM Au exhibits LSPR effect at wavelengths of 550 and 1700 nm, leading to a unique electrochromic performance improvement of the film in both of the VIS and NIR spectral regions. Large optical modulation, rapid switching speed, high coloration efficiency, and long‐term durability are achieved due to the collective effect of the near‐field enhancement of the 2DOM Au and the reduced bandgap of PProDot‐Me2. These advantages can be well retained in the dual‐band electrochromic device using the 2DOM Au/PProDot‐Me2 films as the electrochromic layers. This work provides new ideas for designing LSPR‐based devices, especially dual‐band electrochromic materials and devices, both experimentally and theoretically. [ABSTRACT FROM AUTHOR]

The 4‐[5‐(undecylthio)‐1,3,4‐oxadiazol‐2‐yl)phenol (3)and 4‐(4‐(5‐(undecylthio)‐1,3,4‐oxadiazol‐2‐yl)phenoxy)phthalonitrile (5)were prepared viasubstitution reactions. Metallo‐phthalocyanines (6–9) were obtained by the cyclotetramerization of the phthalonitrile (5). The structures of novel compounds were verified using IR, 1H‐NMR, mass, UV‐Vis methods. Electrochemical characterization of synthesized MPcs (6–9)was carried out by the CV and SWV techniques in DCM/TBAP electrolyte. While MnClPc and CoPc complexes exhibited metal‐based and ring‐based reduction redox couples, CuPc and NiPc gave two ring‐based reduction redox couples. Spectroelectrochemical measurements were performed to observe the color transition during the reduction and oxidation reactions. Thus, the potentials of using the complexes as electrochromic materials were investigated. The CoPc gave the Q band at 667 nm with a shoulder at 663 nm. When the potential was applied to the cell, the intensity of Q band decreased with a shift in wavelength (from 667 nm to 663 nm). In addition, the natural turquoise color (x=0.2720, y=0.3366) of CoPc turned to greenish blue color (x=0.3080, y=0.3461). During the oxidation reactions, CuPc and NiPc gave ring‐based oxidation species. The intensity of Q bands decreased without shift. As a result of the in‐situ spectroelectrochemical measurements, it was observed that CuPc and NiPc, have sharper color transitions and have the potential to be used as electrochromic materials. [ABSTRACT FROM AUTHOR]

The electrochromic detection of latent fingermarks on polished or unpolished, flat or curved metal surfaces is described using electrochromic material, 1,1'‐dibenzyl‐4,4'‐bipyridinium dichloride. The surface area covered by fingermarks acts as an insulating mask, causing 1,1'‐dibenzyl‐4,4'‐bipyridinium dichloride to change color and produce inversed images of the fingermark. By changing the applied potential, the optical properties of 1,1'‐dibenzyl‐4,4'‐bipyridinium dichloride can be continuously and reversibly adjusted to optimize the visual contrast of fingermarks, so as to realize the detection of latent fingermarks on stainless steel surface. It is demonstrated that the fabricated electrochromic devices can detect the fingermarks on these types of surfaces within twenty seconds at −1.0∼−2.0 V. This work can qualify as a tangible improvement in fingermark detection of the natural fingermarks on the never‐cleaned (more than 3 years) and curved surfaces of daily‐used container, e. g. cup, and the handle of cleaning tool, mop. [ABSTRACT FROM AUTHOR]

Electrochromic materials (ECMs) have received attention owing to its huge potential applications, such as smart dimming windows, static displays, and electrochromic capacitors. High optical contrast and long cyclic life of ECMs are extremely critical for practical applications. In this work, the WO 3 and rare earth Sm-doped WO 3 (WSm x , x = 2.0, 3.0, 4.0, 5.0) films were constructed by hydrothermal system, and then their morphology and electrochromic performance were explored. The morphology of the WO 3 film was transformed from an urchin-like to a nest-like porous structure by adding 4.0%Sm into the hydrothermal system. In comparison with the WO 3 film, the WSm4.0 film displayed higher optical contrast and cyclic life, which was resulting from its crystalline and amorphous mix phases, and nest-like porous structure with high Li + diffusion coefficient and strong structure stability. The optical contrasts of the WO 3 and WSm4.0 films were 57.9% and 61.4% at 633 nm wavelength, respectively. Furthermore, WSm4.0 film exhibited optical contrast of around 70% range from 700 to 1100 nm wavelength. Remarkably, WSm4.0 film still retained 91.7% and 73.6% of primitive optical contrast after 6000 and 10000 cycles, respectively. The nest-like porous WSm4.0 film are promising for assembling electrochromic smart windows with long cyclic life and high optical contrast. [Display omitted] [ABSTRACT FROM AUTHOR]

Electrochromism of organic compounds is a well-known phenomenon; however, nowadays, most research is focused on anodic coloring materials. Development of efficient, cathodic electrochromic materials is challenging due to the worse stability of electron accepting materials compared with electron donating ones. Nevertheless, designing stable cathodic coloring organic materials is highly desired—among other reasons—to increase the coloration performance. Hence, four phthalimide derivatives named 1,5-PhDI, 1,4-PhDI, 2,6-PhDI and 3,3′-PhDI were synthesized and analyzed in depth. In all cases, two imide groups were connected via naphthalene (1,5-PhDI, 1,4-PhDI, 2,6-PhDI) or 3,3′-dimethylnaphtidin (3,3′-PhDI) bridge. To observe the effect of chemical structure on physicochemical properties, various positions of imide bond were considered, namely, 1,5- 1,4- and 2,6-. Additionally, a compound with the pyromellitic diimide unit capped with two 1-naphtalene substituents was obtained. All compounds were studied in terms of their thermal behavior, using differential calorimetry (DSC) and thermogravimetric analysis (TGA). Moreover, electrochemical (CV, DPV) and spectroelectrochemical (UV–Vis and EPR) analyses were performed to evaluate the obtained materials in terms of their application as cathodic electrochromic materials. All obtained materials undergo reversible electrochemical reduction which leads to changes in their optical properties. In the case of imide derivatives, absorption bands related to both reduced and neutral forms are located in the UV region. However, importantly, the introduction of the 3,3′-dimethylnaphtidine bridge leads to a noticeable bathochromic shift of the reduced form absorption band of 3,3′-PhDI. This indicates that optimization of the phthalimide structure allows us to obtain stable, cathodic electrochromic materials. [ABSTRACT FROM AUTHOR]

Electrochromic effect has been discovered in many materials with a wide range of applications from visible to infrared, such as smart windows, electronic displays, infrared camouflage, and color‐changeable tactile sensor. However, conventional electrochromic materials cannot meet the growing demand for electrochromic performance in terms of optical contrast, response time, durability, color diversity, and flexibility, which slows down developments in this area. This is mainly due to the limited number and variety of electrochromic materials. In strong contrast, nanoarchitectonics of 2D materials with atomically thin thickness, large lateral size, and diversified series can be an effective way to address these issues and improve the electrochromic performances. This review highlights the recent achievements of emerging 2D electrochromic materials, namely covalent organic frameworks, coordination nanosheets, and transition metal carbides/nitrides/carbonitrides (MXenes). The structures, electrochromic performances and their structure–performance relationship, and future challenges of these materials have been systematically explored. This review can pave a new avenue for the promotion of the nanoarchitectonic 2D materials for the up‐scaled practical electrochromic applications. [ABSTRACT FROM AUTHOR]

Two reported D‐A‐D monomers based on 3,4‐ethylenedioxythiophene (EDOT) were selected for electrochemical copolymerization to obtain copolymer film, named pRG. Then, a soluble polymer poly[3,4‐ethylenedioxythiophene‐alt‐3,4‐bis([2‐ethylhexyl]oxy)thiophene] (pEA) based on the EDOT derivative was screened out, which is complementary to the absorption trough of the pRG film in visible region and matched with its working potential. The bilayer composite film pRG/pEA was obtained by spinning pEA basement membrane on fluorine doped tin oxide (FTO) coated glass surface, and then in situ electrochemical polymerization of pRG film. Compared to the pRG monolayer film, the bilayer composite film shows a more saturated black color in the neutral state and significant improvement on cyclic stability (only decreased by 1.7% after 250 cycles, while pRG film decreased by 17.1%). The introduction of pEA buffer layer not only achieves the full spectral absorption of the composite film in the visible region, but also significantly improves the cyclic stability of the bilayer composite film. The assembled EC prototype device based on the pRG/pEA composite film exhibits a "black to high transmission" reversible switch. Finally, this method combining electrochemical copolymerization, spin‐coating, lamination and other methods provides a new research idea for designing and preparing black to transmissive electrochromic materials. [ABSTRACT FROM AUTHOR]

Zirconium (Zr)-doped NiO films with different contents were successfully synthesized via the chemical spray pyrolysis technique. The structure, morphology, optical and electrochemical behaviors of these films were investigated by X-ray diffraction (XRD), Raman spectrometer, scanning electron microscopy (SEM), energy dispersive spectrometer (EDS), UV–Vis-NIR spectrophotometry, cyclic voltammetry (CV), and chronoamperometry (CA). XRD results suggested that the synthesized samples have the cubic crystal structure and a preferred orientation along the plane (111). Raman spectra further confirmed the successful incorporation of zirconium ions into the NiO films. SEM images explained that the surfaces of the doped films were composed of uniform and dense nanoparticles. EDS analysis suggested that Zr, Ni and O elements were uniformly distributed on the films. The optical results showed that the band gap decreases from 3.53 eV to 3.47 eV as the increase of zirconium doping content. The electrochemical analysis suggested that zirconium doping improved the specific capacitance of the NiO films (the NiO film with the Zr amount of 7 %, 59 F/g at 6 mV/s). In addition, the NiO film with 5 % Zr doped amount exhibited the largest Δ OD (81 %), the largest CE (60.37 cm2/C), and the fastest coloring time (t c =2.1 s) and bleaching time (t b = 2.4 s). These results showed that this film had the excellent electrochromic properties, suggesting that the optimal Zr doped amount of NiO films is 5 %. As a novel kind of electrochromic material, the Zr-doped NiO film has broad application prospects in smart windows, green buildings and energy efficient utilization fields. [ABSTRACT FROM AUTHOR]

Electrochromic materials have been widely applied in smart windows due to their color conversion and adjusting indoor solar radiation abilities. The researches on electrochromic properties of tungsten bronzes with near-infrared light absorbing abilities are important to obtain multifunctional smart windows. Here, nano potassium tungsten bronze K x WO 3 with space group P 6 3 / mcm has been synthesized to study the effects of crystal structures and valence states of W ions on its electrochromic properties. By altering the composition of reaction solution in solvothermal method, the K content x of samples can be controlled together with the adjustments in sizes of hexagonal and trigonal channels in the crystal structure and valence states of W ions. The maximum optical modulation and coloration efficiency are achieved for the maximum x. The enhanced electrochromic performance mainly benefits from the synergistic size effects of hexagonal and trigonal channels. [Display omitted] • The potassium tungsten bronze K x WO 3 has been synthesized by a solvothermal method. • The crystal structure and x are controlled by varying the molar ratio of starting materials. • Changing the channel size and ionic valence state can optimize the electrochromic properties. [ABSTRACT FROM AUTHOR]

A novel type of triphenylamine derivatives, phenyl-bridged N , N , N ′, N ′-tetrasubstituted bis(2-amino-5-thiazolyl) diamine (4) and its cationic form (5) were synthesized via the Hantzsch reaction. The UV–Vis spectroscopy, cyclic voltammetry (CV) and density functional theory (DFT) calculation results showed that the diamine possesses excellent redox properties and a narrow optical energy gap (∼1.85 eV). As an electrochromic material, compound 4 exhibits a notable color change from colorless to blue. It maintains stable cycling performance for up to 175 cycles, even within a higher voltage range of −2.4 to 2.4 V. In addition, as a catalyst, compound 5 exhibits good substrate compatibility and an aniline conversion rate of up to 89 % during the photocatalytic reduction of nitrobenzene. These results would contribute to understand the synthesis of triphenylamine electrochromic materials and expand their applications in the field of photocatalysis. • A new type of triphenylamine derivatives phenyl-bridged N,N,N′,N′ -tetrasubstituted bis(2-amino-5-thiazolyl) diamine (4) and its cationic form (5) were synthesized through hantzsch reaction. • 4 exhibited good electrochemical stability, even at the higher voltage range of −2.4 to 2.4 V, it can still cycle stably for 175 cycles. • 5 exhibited good substrate compatibility and an aniline conversion rate of up to 89 % during the photocatalytic reduction of nitrobenzene. [ABSTRACT FROM AUTHOR]

Electrochromism is a reversible color change triggered by the external electrical field, which can be utilized in smart windows, displays, etc. The ability to display multiple colors in a single electrochromic device is highly beneficial for the versatile applications of the electrochromic technique. Yet, achieving the ability to adopt multiple colors in one electrochromic device has proven to be a challenging task by merely using the conventional chemical structure engineering of the electrochromic materials. In this study, a thermochromic electrolyte is introduced. A multicolor electrochromic prototype device is produced by integrating the thermochromic engineered electrolyte together with electrochromic material in which both can independently contribute to the coloring of the device. This "color palette" strategy gives an additional degree of freedom and extensive flexibility to the design of multicolor electrochromic devices. It introduces a new pathway for producing multicolor electrochromic devices and removes a bottleneck imposed by conventional strategies merely depending on the electrochromic material structure engineering. Moreover, it inspires further development of electrolytes, that share the responsibility of tuning the optical properties of electrochromic devices together with the electrochromic materials, thereby accelerating and diversifying the applications of electrochromics in industry. [ABSTRACT FROM AUTHOR]

Electrochromic materials can tune the illumination and heat exchange of a building with the environment and thereby save energy in lighting, heating, and air conditioning in a cost‐effective way, which is vital in realizing carbon neutrality. 2D frameworks such as coordination nanosheets (CONASHs) that are widely explored for a wide range of applications in energy storage and conversion can be a cluster of novel electrochromic materials. In this work, a series of transition metal benzenehexathiol (TM‐BHT) CONASHs are theoretically investigated via first‐principles simulations. During ion intercalation and deintercalation in TM‐BHTs, changes in lattice structures, lithium diffusion barriers, atomic charges, bond strength, and electronic properties are explored in‐depth. The incurred changes are then correlated with critical electrochromic properties, including the transmittance adjustment ranges in the visible light, near‐infrared, solar spectrum, and mid‐infrared. Among the various TM‐BHT systems, Cu‐BHT and Ag‐BHT are the most promising broadband electrochromic materials for optical and thermal management in the wavelength range from visible to mid‐infrared. The theoretical guidance from this work paves a new path toward electrochromic applications of CONASHs that exploit the versatility of these 2D materials. [ABSTRACT FROM AUTHOR]

A comparative analysis of electrochromic properties of composites CuWO4.WO3, Bi2WO6.WO3 and WO3 films obtained by electrochemical and chemical methods was carried out. The study into the kinetics of light transmission and spectral characteristics of electrochromic coloration revealed some differences in electrochromic processes. It found that in the WO3, Bi2WO6.WO3, CuWO4.WO3 series, lithium intercalation in the film is slowed down, which is due to diffusion limitations in the process of coloring of the Bi and Cu oxides. Spectral characteristics of light transmission Bi2WO6.WO3 and CuWO4.WO3 also differ from WO3 in that the contribution to light absorption is also made by Bi and Cu oxides, which are partially reduced by lithium in the process of their coloring. It is shown that the metal tungstates can be effective electrochromic materials with an additional absorption band in the visible region. [ABSTRACT FROM AUTHOR]

Electrochemical switching of luminescence color between magenta and blue using two types of luminescent materials and electrochromic molecules was demonstrated based on the control of excited energy transfer through an electrochromic reaction. The magenta photoluminescence, due to the integration of red luminescence from the Eu(III) complex and blue fluorescence from the anthracene derivative, was reversibly modulated to a pure-blue luminescence color by an electrochemical redox reaction. Electrofluorochromism is induced by effective excited energy transfer from the Eu(III) complex to the electrochromic molecule under a redox reaction. [ABSTRACT FROM AUTHOR]

Previous work has reported the synthesis of donor–acceptor–donor molecules based on dibenzophenazine acceptor group, presenting thermally activated delayed fluorescent (TADF) properties and their application in the assembly of highly efficient electroluminescent devices. Herein, we focus on the characterisation of charge carrier species through UV‐Vis‐NIR spectroelectrochemical and potentiostatic EPR techniques, in addition to the investigation of electropolymerisation properties of some compounds depicted in this study. The promising electrochromic features of both small molecules and conjugated polymers led to the assembly and investigation of electrochromic devices, evidencing the materials' versatility, applied in such different approaches as electrochromic windows and electroluminescent devices. Furthermore, the assembled OLEDs provided high efficiencies, with small roll‐off, EQEs up to 20.5 % and luminance values up to 85 000 cd/m2. [ABSTRACT FROM AUTHOR]

In this study, a new copolymer, which is a combination of two chemical structure (9,10-di(furan-2-yl)anthracene and 3,4-ethylenedioxythiophene was synthesized via electrochemical synthesis methods in the electrolyte medium of 0.1 M TBAPF6/ACN solution. PEDOT homopolymer was also electrosynthesized for comparator experiments of the polymer formations in the same medium. The characterizations of polymers were achieved with general optical and electrochemical characterization techniques. The corresponding electrochromic copolymer shows blue and lilac color in its neutral and oxidized states, respectively. The copolymer has an optical band gap of 1.65 eV and 24% optical contrast at 500 nm with a high coloration efficiency (170 cm2/C) and a fast switching time (1.0 s). [ABSTRACT FROM AUTHOR]

Color is a property directly discernible by our eyes, making it perceptually conspicuous. Changes in color, whether achromatic (from white to black) or chromatic (from colorless to colored or between different colors), are easily detectable by people with normal vision or through simple spectrophotometric instruments. The categorization of chromogenic systems reveals various mechanisms of chromism. Applications photochromic, thermochromic, and electrochromic materials have been extensively discussed, including their behavior, mechanisms, and limitations. In the landscape of future energy storage systems, the significance of chromisms transcends conventional boundaries, promising transformative impacts on energy efficiency, management strategies, and sustainability. Chromic materials, endowed with their dynamic color-changing attributes, emerge as catalysts for innovation across diverse applications such as batteries, supercapacitors, and smart windows. This review aspires to offer a comprehensive exposition on the intrinsic chromism phenomena within energy storage systems. Commencing with a succinct overview of chromism phenomena and their nuanced formation mechanisms, the narrative seamlessly transitions to an exhaustive scrutiny of recent strides. This exploration encompasses a thorough examination of the components, intricate structures, and diverse properties characterizing chromism phenomena. [ABSTRACT FROM AUTHOR]

Pursuing to develop novel polymer-based electrode materials and explore their performance in electrochromic capacitive windows (ECWs), three polyamides containing propylenedioxythiophene (ProDOT) units were synthesized. The polymers were processed into thin coatings and subjected to rigorous structural and photophysical characterization, with focus on the electrochromic response and energy storage capability. One of the polymers showed electrochromic response with ultrafast color change (0.8 s for coloring) from highly transmissive yellow to deep green, opposite to most ProDOT-based materials that exhibit bleaching trends during oxidation, which is more convenient for smart glazing. A coloration efficiency of 358 cm2 × C−1, a maximum CE decay of 2.6 % after 100 cycles, and an excellent electrochromic stability, even up to 500 cycles was achieved for this material. In three-electrode cell configuration, this polymer revealed practical energy storage properties, including a wide voltage window, a good capacitance, of 5.63 mF × cm−2, and an outstanding electrochemical cycling durability. Therefore, a prototype polyamide based-ECW device was built and its overall performance was explored. Due to the well capability of this polymer to simultaneously operate as a smart color changing and energy storage electrode, it can be considered as promising material for use in energy storage smart windows with potential applications in green-enabling technologies. • Three polyamides containing propylenedioxythiophene (ProDOT) units are synthesized. • The polymers display thermal stability up to 270 °C and CT blue/green fluorescence. • The polymers containing only ProDOT provide low capacitance and no electrochromism. • TPA- and ProDOT-based polyamide undergoes ultrafast color switch while stores energy. • An ECW is realized enabling smart monitoring of the energy level stored in the device. [ABSTRACT FROM AUTHOR]

The covalent organic frameworks (COFs) possess high designability, which provides a platform for synthesizing novel optoelectric materials, including electrochromic materials. In this work, N,N,N′,N′-tetra-(4-aminophenyl)-1,4-phenylenediamine (TPDA) with π-electron conjugate system and redox active centers was used as the main building block. The 4,4′-biphenyl diformaldehyde (BDA) and the 2,2′-thiophene-5,5′-diformaldehyde (TDA) were used as the aldehyde building units. Two imine-based COF electrochromic active materials (COF TPDA-BDA and COF TPDA-TDA) were prepared by Schiff base reaction. The test results reveal that COF TPDA-TDA has superior electrochromic properties than COF TPDA-BDA. Their contrasts are 0.46 and 0.40, and the coloring/fading times are 3.1/10.6 s and 10.9/14.3 s, respectively. The COF TPDA-TDA material possessing a bifunctional group structure was synthesized by replacing the biphenyl group with the bithiophene group with redox activity, which can enhance the optical properties and inter-layer π-π conjugation. Besides the electrochromic properties, the morphology and crystal lattice parameters are different. Therefore, it is expected to develop COFs-based electrochromic materials with rich colors, excellent performance, and wide application by introducing construction units with different redox active centers. [ABSTRACT FROM AUTHOR]

Electrochromic materials represent a class of highly promising smart materials in contemporary research. Viologen, as a prevalent organic small molecule in smart chromic materials, has garnered extensive attention due to its tunable intermediate structure involving pyridine units and diverse nitrogen atom substituents. In this investigation, the molecular structure of dinaphthoviologen (DNV2+) were modified, and various groups were introduced to ionize nitrogen atoms. This structural modification aimed to decrease the molecular energy gap and enhance the electron acceptability of nitrogen atoms. The results demonstrate robust redox ability in DNV2+. To explore the practical applications, a straightforward DNV2+-based electrochromic device was fabricated, incorporating ferrocene as an electronic supplement. This device exhibited commendable cycling performance (exceeding 1000 cycles) and rapid response times (8 s for coloring and 10 s for fading) without the need for additional electrolytes. Additionally, the transmittance changes by more than 45 %. Moreover, owing to the presence of conjugated structures, DNV2+ exhibited noteworthy fluorescence properties. In fluorescence-based picric acid detection experiments, the synthesized molecules exhibited high selectivity and sensitivity, as evidenced by the determined Stern–Volmer constants (K 6b = 2.17 × 104 L/mol, K 6c = 3.87 × 104 L/mol). The findings highlight the potential of the developed dinaphthoviologen derivatives for advanced applications in electrochromic devices and sensitive detection of picric acid. • A series of dinaphthoviologen derivatives were synthesized, and their photoelectric properties were investigated. • Simple electrochromic devices (ECDs) were fabricated, demonstrating excellent transmittance and cycle stability. • The derivatives were utilized as fluorescent probes for picric acid detection with remarkable selectivity and sensitivity. [ABSTRACT FROM AUTHOR]

[Display omitted] • WO 3 /EuMOF assembly was firstly prepared by an electrodeposition method. • The assembly was applied as a fluorescence switch. • The "on" and "off" states can be modulated by changing the voltage. • The assembled fluorescence switch exhibits good reversibility. In recent years, lanthanide metal organic frameworks have been widely used in various fields because of their excellent fluorescence properties. Fluorescence switch has also been considered as a research hot spot and widely applied in many fields. The combination of fluorescent material and electrochromic material has emerged in the preparation of fluorescence switch. Herein, a simple and rapid electrodeposition method is proposed for the preparation of amorphous EuMOF film. The whole process takes only half an hour under room temperature. The prepared amorphous EuMOF film exhibits significant emission peaks characteristic of Eu3+ when excited by 277 nm UV lamp. In addition, the prepared EuMOF is also applied in an electrochromic device to construct WO 3 /EuMOF fluorescence switch by stepwise electrodeposition using polystyrene microsphere as template. By changing the voltage, the coloring and fading of the device color, and the quenching and recovery of fluorescence can be reversibly regulated, in order to achieve the control of the "on" and "off" states of the fluorescence switch. [ABSTRACT FROM AUTHOR]

Electroactive asymmetric bis-carbazole small molecules bearing cyano functional group(s) were conveniently synthesized and fully characterized by physicochemical and electrochemical methods. These carbazole-based small molecules are colorless in the neutral states and possess reversible redox processes and outstanding thermal stability. The utilization of these bis-carbazole small molecules as the electrochromic materials for the fabrication of electrochromic devices (ECDs) provided high-performance ECDs of high optical contrast up to 99% switching between colorless bleaching state and dark-red colored state and excellent coloration efficiencies of 412 cm2/C. The present work illuminates the excellent qualification of functionalized carbazole-based small molecules in developing efficient ECDs. • Cyano-modified bis-carbazole molecules show high thermal stability, colorless neutral state, and excellent redox properties. • The bis-carbazoles based electrochromic devices (ECDs) exhibit striking color change from colorless neutral states to red. • The ECDs show high optical contrast up to 94−99% and coloration efficiencies of 225−412 cm2/C. • The performances of ECDs were markedly improved by increasing of the number of cyano groups incorporated in carbazole unit. [ABSTRACT FROM AUTHOR]

In the era of intelligent automation, smart energy storage devices are highly sought after due to their capability to reveal their state of charge by a visual color change. In principle, this is typically obtained by integrating electrochromic materials which demonstrate a change in optical band gap during redox reactions as electrodes in batteries/supercapacitors. Among various electrochromic materials, transition metal oxides have received significant interests because of their natural abundance, good cycling stability and high electrochemical response. In this work, metal organic framework (MOF) derived carbon embedded NiO (NiO@C) demonstrates very fast switching speeds of ∼1.4 s for coloration and ∼3.5 s for bleaching with high coloration efficiency of ∼135.16 cm2/C. These aspects make MOF‐derived NiO@C a potential candidate to be integrated as a smart positive electrode in an alkaline zinc (Zn) battery to construct a rechargeable Zn−NiO electrochromic (EC) battery. The Zn−NiO EC battery delivers an average voltage of ∼1.84 V and demonstrates a specific capacity of ∼85.3 mAh/m2 at 0.1 mA/cm2 current density. It visually displays its energy storage level by changing its color from dark brown (charged state) to colorless (discharged state), making it a potential candidate in smart windows and energy storage displays. [ABSTRACT FROM AUTHOR]

The rapidly expanding field of intelligent ion‐based devices has increased interest in the use of anodically‐coloring electrochromic nickel oxide thin films. The degradation and coloration mechanisms of nickel oxide, especially in Li+‐based electrolytes, are yet to be well understood. Herein we demonstrate that high potentials have a positive effect on the electrochromic performance of nickel oxide thin films. Our studies show that Cl− ions involved in the electrochromic process have been accumulated on the surface of the films upon extended electrochemical cycling, as confirmed by the X‐ray Photoelectron Spectroscopy. X‐ray Absorption Spectroscopy results indicate that the formation of Ni−Cl bonds influence the structural distortion and that the hybridization between Ni 3d and O 2p orbitals has been enhanced. Density functional theory calculations provide further insights for the band structures and how they change when Li+ and Cl− are adsorbed. Our results have revealed the underlying physical and chemical origins associated with the coloration mechanism and the degradation of nickel oxide thin films and highlighted the key role of Cl−. These new understandings will advance the development of superior electrochromic materials and the designing of efficient and durable electrochromic devices, both experimentally and theoretically. [ABSTRACT FROM AUTHOR]

Comprehensive Summary: Doping plays an essential role in the properties of conducting polymers. Film thickness not only has a direct influence on their photoelectric properties, but also affects the doping ability, which may lead to the decline of capacitance and electrochromic properties caused by incomplete doping. Therefore, it is essential to study the quantitative relationship between doping level and film thickness in application. Herein, empirical formula between doping level and thickness was obtained by studying the spectroelectrochemistry behaviors of two different electrochromic materials, poly(N,N'‐bis(3,5‐(2‐thienyl)‐phenyl)‐1,6,7,12‐tetrachloroperylene‐3,4,9,10‐perylenetetracarboxylic diimide) (poly(Th‐Cl‐PBI)) and poly(3,4‐ethylenedioxythiophene) (PEDOT). The doping level is verified to be correlated to the reciprocal of the 3rd power of film thickness. Experimental results fit these formulas very well, giving correlation coefficient R2 higher than 0.99. The optical contrast prediction of these two electrochromic materials is also used to verify this relationship formula. For the first time, we quantitatively connect these two important parameters of conducting polymers, doping level and thickness. [ABSTRACT FROM AUTHOR]

The development of electrochromic materials has opened the door to the development of numerous devices including smart windows, color displays, optical filters, wearable camouflages, among others. Although the current electrochromic devices do not consume energy while maintaining their colored or colorless states, their bistable operation requires external electrical energy to be consumed during switching. To reduce the energy consumption of an electrochromic device, an emerging Zn anode‐based electrochromic device concept was recently introduced to partially retrieve the consumed electrical energy. In this Review, key technological developments and scientific challenges are presented for a broad range of Zn anode‐based electrochromic device configurations with emphasis on the inherent distinctions between the Zn anode‐based and conventional electrochromic devices. Specifically, a comprehensive comparison of the two classes of electrochromic devices in the high‐performance device design is provided. For the electrochromic layer, the methods for obtaining high‐quality electrochromic materials and thin films are reviewed. For the electrolytes, the effect of the dual ion system on the electrochromic performance is discussed. Also, some critical but unresolved issues in the device design and fabrication are discussed. The perspectives and outlook at the end of this Review provide recommendations to improve performance for future electrochromic studies. [ABSTRACT FROM AUTHOR]

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Electrochromism has attracted wide attention as futuristic adaptive camouflage technologies due to its reversible and sustainable optical modulation with low energy consumption. However, limited color control of the electrochromic materials has hampered its applications. Inspired by the remarkable dynamic camouflage capabilities of cephalopods, polyaniline (PANI) and polystyrene‐block‐poly (2‐vinyl pyridine) (PS‐b‐P2VP) thin films are integrated to simulate chromatophores and iridophores in the skin of cephalopods, respectively. Herein, it is demonstrated that the adaptive lamellar PANI/PS‐b‐P2VP thin film exhibits a wide range of color control, switchable vivid coloration, and excellent durability. It serves as an ideal multicolored electrochromic platform due to the combined effect of electrochromism from PANI and structural coloration from PS‐b‐P2VP. Unambiguous evidence shows that optical properties of the PANI/PS‐b‐P2VP thin film are related to the thickness of each layer and nanostructure of PANI, pronounced color changes mainly depend on electronic states of PANI and transition of hydrated SO42− ions between PANI and P2VP. The coloration mechanism is discussed using quantitative analysis via RGB color specification and optical transmittance and reflectance simulations. The new insights will advance the design of reflection‐contributed superior multicolored electrochromic materials, and have great potential in the fields of displays and camouflage. [ABSTRACT FROM AUTHOR]

The electrochromic materials have received immense attention for the fabrication of smart optoelectronic devices. The alteration of the redox states of the electroactive functionalities results in the color change in response to electrochemical potential. Even though transition metal oxides, redox‐active small organic molecules, conducting polymers, and metallopolymers are known for electrochromism, advanced materials demonstrating multicolor switching with fast response time and high durability are of increasing demand. Recently, two‐dimensional covalent organic frameworks (2D COFs) have been demonstrated as electrochromic materials due to their tunable redox functionalities with highly ordered structure and large specific surface area facilitating fast ion transport. Herein, we have discussed the mechanistic insights of electrochromism in 2D COFs and their structure‐property relationship in electrochromic performance. Furthermore, the state‐of‐the‐art knowledge for developing the electrochromic 2D COFs and their potential application in next‐generation display devices are highlighted. [ABSTRACT FROM AUTHOR]

Electrochromic materials that integrate structural colors and dielectric elastomer actuators (DEAs) can simultaneously change colors and shapes upon voltages. Typically, operation voltages for these materials are high, reaching several kilovolts. To achieve color changes at lower voltages, we reduce the modulus by lowering silica nanoparticle volume fraction and adding a secondary acrylate monomer, while also ensuring that photonic elastomers maintain recognizable colors. We utilize binary silica nanoparticles to make photonic glass elastomers that show angle-independent structural colors. The photonic glass DEA shows color changes of 85 nm at 800 V with color change sensitivity of 0.11 nm/V, surpassing previous reports. By making a double-layered DEA, we can not only control the shape changes, but also increase the color contrast. This solid-state elastic electrochromic material, offering programmable color change and shape morphing, holds broad applications in wearable devices, camouflage, and flexible displays. [Display omitted] • Photonic elastomers with low angle dependence and low modulus have been prepared. • Novel photonic DEAs shifts wavelengths up to 85 nm at 800 V with a sensitivity of 0.11 nm/V. • Two-layered DEAs enable control in shape changes with increasing color contrast. [ABSTRACT FROM AUTHOR]

Three novel triphenylamine-based compounds with arylene-vinylene, or mixed arylene (cyano)vinylene-ethynylene moieties in a star-shaped configuration, have been synthesized and used to electrogenerate smart polymers coatings able to sense harmful nitroaromatic derivatives and to provide chromic response to an applied voltage. The introduction of different π-spacers between triphenylamine units led to oligomers with variable structures, which were validated by NMR, FT-IR, and MALDI-TOF analyses. The detailed study of their photophysical and electrochemical characteristics revealed some intriguing structure-properties correlations. Due to the presence of the peripheral TPA units, the electropolymerization of oligomers generated thin films exhibiting distinct colours and morphologies. Their supramolecular arrangements in granular or tubular assemblies were notably influenced by the initial oligomeric structures. The donor-acceptor polymer containing arylene-(cyano)vinylene-ethynylene moieties displayed reversible and stable multicolour switches, and a very good coloration efficiency, while the polymer containing only arylene-vinylene π-spacers behaved as an efficient sensor towards trinitrophenol, with a highest detection limit of 25 μM. Overall data obtained in this study demonstrates the potential of electrogenerated polymers derived from TPA-based star-shaped oligomers to behave not only as intelligent electrochromic materials but also as promising receptors for nitroaromatic derivatives through electrochemical detection, indicating their perspective applications in nowadays fields. [Display omitted] • Three novel triphenylamine-based star-shaped oligomers were synthesized through a convergent approach. • The influence of the internal π-spacer on the photophysical and morphological characteristics was assessed. • Electrogenerated polymer coatings displayed efficient electrochromic responses. • Polymers derived from star-shaped oligomers showed promise for TNP derivative detection. [ABSTRACT FROM AUTHOR]

Thiadiazolobenzotriazole (TBZ)‐containing donor‐acceptor (D–A) type polymers are rarely investigated as electrochromic materials, although they have made important progress in the fields of organic transistors and solar cells. In this work, a new class of soluble D–A type electrochromic polymer is designed using the alkyl substituted TBZ units as the acceptor, the alkyl substituted 3,4‐propylenedioxythiophene (ProDOT) units as the donor, and benzene (B) units as the π‐bridge. Through altering the molar ratio of ProDOT/B/TBZ, three polymers named PPBT‐1, PPBT‐2 and PPBT‐3 are chemically synthesized. After various characterizations, it is found that all the polymers display saturated green in their neutral states and switch to transparent gray upon oxidation with narrow optical bandgaps, and moreover, they demonstrate high optical contrast, rapid switching speed, and excellent coloration efficiency particularly in the near infrared region. The impacts of different donor‐acceptor feed ratios on electrochromic performances are mainly reflected in the optical, electrochemical and kinetic properties. In contrast to PPBT‐1 and PPBT‐3, PPBT‐2 show the best performances with the most appropriate ProDOT/B/TBZ ratio of 2/3/1 in its backbone. These positive results provide a theoretical basis for the research of electrochromic polymers based on TBZ units. [ABSTRACT FROM AUTHOR]

An imidazolium-based ionic liquid (IL) modified triphenylamine derivative, namely 1-(4-((4-(diphenylamino)benzoyl) oxy)butyl)-3-methyl imidazole tetrafluoroborate (TPAC6IL-BF4), was designed and synthesized, and further applied with 3,4-ethylene dioxythiophene (EDOT) to prepare conjugated copolymer P(EDOT:TPAC6IL-BF4) via electrochemical polymerization. The cyclic voltammetry curves show that the copolymer P(EDOT:TPAC6IL-BF4) possesses two pairs of redox peaks, which should be ascribed to the redox behaviors of EDOT and triphenylamine. The ultraviolet-visible (UV-Vis) absorption spectrum of P(EDOT:TPAC6IL-BF4) exhibits one maximum absorption peak at 580 nm and a small shoulder characteristic peak at 385 nm under neutral state which are assigned to π-π* conjugated structure of EDOT and triphenylamine. After being applied at the positive voltage, the copolymer color changes from dark blue to light blue, which is close to the color of poly(3,4-ethylenedioxythiophene) (PEDOT). Surprisingly, the copolymer P(EDOT:TPAC6IL-BF4) shows shorter switching time of 0.37 s, 0.30 s at 580 nm and 0.38 s, 0.45 s at 1100 nm compared with PEDOT. It is more intriguing that the copolymer P(EDOT:TPAC6IL-BF4) exhibits electrochromism even in free supporting electrolyte. The results confirm that the existence of imidazolium-based ionic liquid has an improvement on the ion diffusion properties and the switching time of conjugated polymer, which may provide a potential direction for the preparation of high-performance electrochromic materials. [ABSTRACT FROM AUTHOR]

A multi-shelled NiO hollow sphere was synthesized by a facile glucose-mediated hydrothermal route. The carbonaceous microsphere was utilized as a sacrificial template for the formation of multi-shells. All the shells were formed by a single pyrolysis step. The multi-shelled hollow sphere can provide enhanced active surface area and additional reactive sites, which facilitate faster ion intercalation and deintercalation, and play key roles in electrochromic devices and sensing application, including glucose sensing. Herein, we employed the as-synthesized material for electrochromic devices. As expected, NiO multi-shelled hollow microspheres exhibit a superior transmission modulation (ΔT = 47%) and yield a coloration efficiency of ~ 85.3 cm2 C−1, which is ~ 2.37 times higher than that of NiO microflakes which was synthesized in the absence of glucose. The geometry of the self-supported multi-shelled architecture ensures that the active faradaic sites can be in intimate contact with the electrolyte to enhance ionic diffusion. The observed colored and bleached switching time of multi-shelled hollow sphere is 6.7 s and 2.7 s respectively. A quasi-solid-state electrochromic device is also displayed with the aid of gel electrolyte with reversible color change from dark brown to transparent. Furthermore, the multi-shelled NiO displayed excellent catalytic activity towards non-enzymatic glucose sensing with a high sensitivity of 1646 ± 5 μA cm−2 mM−1 over a linear range of 2 μM–2.6 mM with a lowest detection limit of 1.5 ± 0.2 μM. Analysis on blood serum as a real biological sample reflects the practicability of the fabricated sensor. Developing hollow structured multi-shelled materials based on metal oxides will pave the way to design advanced electrode materials for electrochromic smart windows and non-enzymatic glucose sensors. [ABSTRACT FROM AUTHOR]

Printable organic electrochromic materials are the key component of flexible low power and low weight displays and dynamic shading systems. A vast number of more or less well‐performing materials is reported in the literature, but only a very limited number of them have been tested in an industrially‐relevant environment so far. Upscaling requires simplicity of synthesis, overall sustainability, low cost and compatibility with simple and high throughput wet‐chemical deposition techniques, such as slot‐die coating or inkjet printing. In the present paper, an original process is described that enables the controlled oxidative polymerization of a water insoluble, functionalized 3,4‐ethylene dioxythiophene (EDOT) derivative. This process leads to the formation of an ink that consists solely of active polymeric material (no dispersing agents) and has suitable rheological properties for use in roll‐to‐roll slot‐die coating or ink‐jet printing. The straightforward deposition, followed by a simple thermal treatment, directly yields stable and homogeneous thin films with state‐of‐the‐art electrochromic performance. [ABSTRACT FROM AUTHOR]

Electrochromism, an emerging energy conversion technology, has attracted immense interest due to its various applications including bistable displays, optical filters, variable optical attenuators, optical switches, and energy-efficient smart windows. Currently, the major drawback for the development of electrochromism is the slow switching speed, especially in inorganic electrochromic materials. The slow switching speed is mainly attributed to slow reaction kinetics of the dense inorganic electrochromic films. As such, an efficient design of nanostructured electrochromic materials is a key strategy to attain a rapid switching speed for their real-world applications. In this review article, we summarize the classifications of electrochromic materials, including inorganic materials (e.g., transition metal oxides, Prussian blue, and polyoxometalates), organic materials (e.g., polymers, covalent organic frameworks, and viologens), inorganic-organic hybrids, and plasmonic materials. We also discuss the electrochromic properties and synthesis methods for various nanostructured inorganic electrochromic materials depending on structure/morphology engineering, doping techniques, and crystal phase design. Finally, we outline the major challenges to be solved and discuss the outlooks and our perspectives for the development of high-performance nanostructured electrochromic materials. [ABSTRACT FROM AUTHOR]

A series of electronic push–pull, pull–pull, and push fluorophores has been prepared from a benzoselenadiazole core so that their spectroscopic, electrochemical, spectro‐electrochemical, and spectro‐electrofluorescence properties could be examined. The emission wavelengths and fluorescence quantum yields (Φfl) of the N,N‐dimethyl fluorophores were contingent on the solvent polarity and they ranged from 615 to 850 nm in aprotic solvents. The positive solvatochromism and the quenched Φfl in polar solvents were consistent with an intramolecular charge‐transfer state (ICT). Meanwhile, a locally excited state (LE) was assigned in nonpolar solvents from the blue‐shifted emission and high Φfl. The N,N‐dimethylamine fluorophores examined could be both electrochemically oxidized and reduced, whereas the symmetric dinitro pull–pull derivative could be only reversibly reduced. Courtesy of their electrochemical reversibility, the fluorophores could reversibly change color from yellow to blue with an applied potential in addition to switching off their emission. The absorption of the electrochemically generated intermediates of the N,N‐dimethyl derivatives spanned 500 nm over the visible and the NIR regions. The colors could be switched for upwards of two hours with applied potential, illustrating their potential use as electroactive materials in electrochromic devices. [ABSTRACT FROM AUTHOR]