Electrochromic Materials Research Articles

Transparent-to-Brown-Black Patterned Electrochromic Metal-Organic Frameworks.

Metal-organic frameworks (MOFs) exhibit promising electrochromic (EC) performance owing to their porous structure, regular channel, and tunable component characteristics. However, few reports focus on MOF materials with the EC performance of a transparent to brown-black (neutral colored state) change that is more suitable for smart windows. In this work, we proposed a strategy for synthesizing MOF (named Ni-BPY) EC materials and corresponding films fabricated via a low-cost electrostatic spray deposition technique. The obtained film exhibits excellent EC performance with a neutral color change from transparent to brown-black, a large optical modulation of 70% at 430 nm, and a fast response within 10 s. Benefiting from good electrical and chemical stability, the Ni-BPY film can be cycled over 500 times. Notably, the Ni-BPY MOF film also delivers a stepwise-controlled process during the bleached state due to its porous characteristics. In addition, the unique color variation of the Ni-BPY film derives from the redox reaction of the Ni metal node between Ni2+ and Ni3+, which is verified by the in situ potential-dependent Raman and X-ray photoelectron spectroscopy (XPS) measurement. As a proof of application, the patterned Ni-BPY EC films and devices are additionally constructed to demonstrate their potential application in electronic tags and logo displays.

Nonconventional Symmetric Double-Side Electrochromic Devices Employing a Nafion Conductive Layer to Unlock Superior Durability.

In this work, we present a methodology to create an effective novel double-sided symmetric architecture of solid-state electrochromic devices. This principally new nonconventional configuration provides access to novel electrochromic systems that could be applicable for the creation of smart double-side signage, smart boards, nonemissive displays, and other smart interactive devices that change their color upon application of a voltage. The proposed configuration is based on the assembly of two identical electrochromic materials facing each other through an opaque optical separator. As a proof of concept, we use an electrochromic material based on bis(4'-(pyridin-4-yl)-2,2':6',2″-terpyridine) iron complex, covalently immobilized on screen-printed surface-extended ITO support. The symmetric configuration allows for a drastic enhancement of the overall stability of the device due to both attenuation of the counter electrode polarization and minimization of electrolyte decomposition. A nontransparent ion-permeable separator, in turn, allows observing the color change of only one of the electrodes by cutting off the optical contribution of the electrode located behind it. Further functionalization of the electrochromic material with a thin layer of Nafion is a beneficial strategy to significantly boost up long-term durability of the devices. Applying a layer of Nafion to the electrochromic material results in an increase in ionic conductivity within the device and ensures better retention of electrochromic molecules on the surface, thus minimizing device decomposition during long-term electrochemical cycling. An electrochromic device that bears Nafion-functionalized electrodes can operate (i) in the dual-side mode, where both sides demonstrate effective electrochromic performance; or (ii) in a one-side manner, where only one side of the device changes color. Notably, when operating in the one-side mode, the device withstands 70,000 cycles, after which the performance of the device can be resumed by simply turning the device to the other side (via switching the polarity of the electrodes).

Fine-tuning the color hue of the solution-processable electrochromic copolymers based on the diketopyrrolopyrrole, benzodithiophene and dithienosilole units

Electrochromic materials (ECMs) have attracted increasing attentions on account of their extensive prospects and numerous demands. Here, the classical donor-acceptor (D-A) alternative copolymerization strategy was used to synthesize three kinds of novel conjugated polymers PBPS-1, PBPS-2, and PBPS-3. The diketopyrrolopyrrole (M1) unit with a long alkyl side-chain was employed as the core acceptor while the dithienosilole (M2) used as the donor units. More importantly, the benzodithiophene (M3) units which have the high skeleton coplanarity was selected as the bridge units to enhance the charge transport. Variations of the feed ratios of monomers was used to regulate the energy level and spectral absorption range of the solid films. Three polymers exhibited the abundant color hues in the redox process, which including grape purple/brownness/aircraft ash color (PBPS-1), dark grey/red soap/dusty blue color (PBPS-2) and marine blue/grayish/celadon color (PBPS-3). Electrochromic performances demonstrated that PBPS-2 possessed the fast discoloration speed as low as 0.26 s and the outstanding coloration efficiency (550.1 cm2·C−1), which portended a valuable material for smart ECMs applications. Furthermore, the effect of different feed ratios for three polymer in electrochemical, optical and kinetic properties were investigated in detail, which showed the satisfactory optical contrasts (>70% in the NIR region) and good kinetic stability (>97% retention in 1000 s). In general, this exploration supplied a handy design strategy for fine tuning of polymer color and conducive to strengthen the understanding of EC behaviors of the ternary polymers, which deserve further researches to explore more promising ECMs.

Sensitive Recognition of Acetamiprid with a Unique Electrochromic Molecular Imprinted Polymer Sensor

The development of molecularly imprinted polymers (MIPs) and the applications for them have attracted a great deal of interest during the last two decades. MIPs are generally used in different fields, specially molecularly imprinted electrochemical sensors (MIECS), due to their particular design and specific detection abilities [1]. The advantages of an electrochemical MIP sensor include low cost, easy operation, rapid response time and excellent potential for miniaturization and construction for portable equipment applications [2]. In the scope of this work, we performed that electropolymerization of IrO2 as an electrochromic material on an indium tin oxide (ITO) glass substrate and electrosynthesis on this electrode using pyrrole as a functional monomer in the presence of acetamiprid as template were used to create the electrochromic molecular imprinted polymer sensor (MIP/IrO2/ITO). With the created electrochromic MIP sensor, it is intended to create a selective pesticide sensor by utilizing molecular imprinted polymer (MIP) technology, and to detect with the naked eye by color change depending on the acetamiprid concentration by using electrochromic material. The IrO2/ITO electrochromic film demonstrated magnificent cycle stability (100 cycles), high coloration efficiency (400 cm2 C-1 at 450 nm), and quick coloring/bleaching reaction time (8.60s/7.10s, respectively). By using in-situ spectroelectrochemical measurements, these optical properties of MIP/IrO2/ITO were obtained at various acetamiprid concentrations for quantitative analysis. By using differential pulse voltammetry between -0.2 V and +0.8 V (versus Ag/AgCl in 0.1 M PBS), the sensor performance of MIP/IrO2/ITO was assessed. In an acetamiprid concentration range of 4.29–38.6 nM, the MIP/IrO2/ITO electrode demonstrated linear response with a detection limit of 2.72 nM, sensitivity of 47.2 µA nM-1, and repeatability of 0.87%. Keywords: Electrochromism; Molecularly imprinted polymer (MIP); Pyrrole; IrO2;Acetamiprid; Electrochemical sensor; Spectroelectrochemistry. Acknowledgements This work was supported by The Scientific and Technological Research Council of Türkiye, TUBITAK (Project No:121Z784) as the financial.

Dynamically transflective multicolor modulation via single metal-dielectric inorganic electrochromic electrode

Transflective electrochromic (EC) materials with the ability to dynamically adjust color in both reflection and transmission mode are extremely attractive for tunable filter, smart windows, and ultralow-power displays due to their wide applicability in dark and bright environment and unique tunability of optical properties. However, simultaneously brilliant multicolor modulation of both reflection and transmission in one EC film is challenging. Here, integrated and metal/dielectric structured EC electrode composed of three-layered Cr/Ag/WO3 (CAW) films are demonstrated. Benefiting from the synergistic effect of the good conductivity, strong optical interference, and excellent substrate-film adhesion, these well-designed CAW films successfully demonstrate dynamic variegated modulation of both reflective and transmissive colors. This modulation encompasses a broad spectrum of hues, boasts high saturation, rapid response times, and exhibits impressive cycling stability. The flexible CAW film with superior bending stability is also achieved for the successful construction of the patterned flexible EC device.

Electrically Triggered Color‐Changing Materials: Mechanisms, Performances, and Applications

AbstractElectrically 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.

Stable WO3 electrochromic system based on NH4+ hydrogen bond chemistry

As the best-known and extensively-studied electrochromic material, tungsten trioxide (WO3) has drawn tremendous interest due to its low material cost, environmental benignity, dual band regulation, high optical modulation, and high chemical stability. However, these films always suffer from ion-trapping-induced degradation in electrochromic performance when cycled in alkali cation (such as Li+, Na+, K+, etc.) electrolytes. Herein, we report a stable WO3 electrochromic system enabled by a NH4CF3SO3-TEP (Triethyl phosphate) organic electrolyte. Based on comparative experiments and systematic characterizations, the prolonged cycling stability is mainly attributed to the formation of hydrogen bonds between the NH4+ ions and the WO3 lattice, which are much weaker than metallic coordination bonds. Furthermore, the bulky CF3SO3− anion and large TEP solvent molecule are also favorable to stabilize WO3, since they are more resistive to be co-inserted into the WO3 lattice along with the shuttling NH4+ cations. Thanks to these merits, this NH4CF3SO3-TEP electrolyte simultaneously enables great electrochromic activity (76.1 % transmittance modulating ability at 633 nm) and impressive cyclic color-switching stability (1000 times color change without any detectable electrochromic performance or mechanical degradation), overwhelmingly outperforming the conventional Li+/K+ electrolytes. Furthermore, as a demonstration of its application, a WO3/Zn electrochromic device is fabricated based on a NH4+/Zn2+-CF3SO3 dual-cation TEP electrolyte. These findings may shed light on the in-depth understanding of WO3′s “ion trapping” effect, as well as the electrolyte design of high-performance WO3-based electrochromic devices.

Mixed-valence system with near-infrared electrochromism of Fe(II)-based metal-organic coordination polymers

Near-infrared electrochromic materials have garnered great attention due to their potential applications in optical data storage and military camouflage. Herein, a networked metal-organic coordination polymer bearing multi-redox centra (Fe-MCP) was successfully prepared by coordination interaction of Fe ions with D-A-D-structure ligands through the liquid-liquid interface self-assembly strategy. The resultant uniform film exhibits improved NIR electrochromic attributed to the construction of mixed-valence system. Furthermore, a sandwich-structured electrochromic device was fabricated by combining Fe-MCP electrochromic layer, a gel composed of LiClO4, PMMA, and PC as the electrolyte layer, and anodically coloring PB as an ion storage layer. The resultant device illustrated an optical contrast of 31.4 % at 800 nm and 34.2 % at 1000 nm, a response speed of 4.0 s/8.3 s at 800 nm and 7.6 s/2.7 s at 1000 nm, and good cycling durability. The design principles proposed in this study provide a new insight for the preparation of high-performance NIR electrochromic materials.

Preparation and properties of electrochromic polyimide hybrid materials containing graphene oxide

The aminosylated graphene oxide was synthesized using the compound E3, three anhydrides (3,3′,4,4′ -diphenyl ether tetracarboxylic acid dianhydride, 3,3′,4,4′ -biphenyl tetracarboxylic acid di anhydride and 1,2,4, 5-phenyl tetracarboxylic acid di anhydride) is a series of electrochromic polyimide hybrid materials containing carbazole groups prepared by polypolymerization with aminated graphene oxide (F2). These PIs not only have good solubility and thermal properties,but also the introduction of 0.5 wt% GO increased the contact area between the film and electrolyte ions, which was beneficial to transport and diffusion of ions, thus improving the response speed of the electrochromic materials. Moreover, its excellent tensile properties make it an ideal material for manufacturing flexible devices. In addition, the polyimide hybrid materials exhibit excellent electrochemical and electrochromic properties as well as electrofluorescent properties. Therefore, the new material will be suitable for hole transmission, electrochromic, chemical sensing and other fields.

Structural Color Boosted Electrochromic Devices: Strategies and Applications

AbstractElectrochromic 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.

Dibenzofulvene Derivatives as Promising Materials for Photovoltaic and Organic Electronics

This review aimed to summarize the current knowledge regarding dibenzofulvene derivatives (DBF) investigated for photovoltaics and organic electronics applications. The work begins with a detailed analysis of the synthesis and modification methods for dibenzofulvene derivatives’ structure. Then, the physicochemical properties (thermal, electrochemical, and optical) of the selected compounds are discussed in detail. Moreover, this article also presents the DFT calculations performed so far. Finally, the review presents the latest research on the applications of dibenzofulvene derivatives as dyes for DSSC cells, hole transport materials (HTMs) for perovskite solar cells (PSCs), organic light-emitting diodes (OLEDs), and luminescent and electrochromic materials. Considering the above, this review may be helpful when designing new organic compounds for photovoltaic and organic electronic applications.

Smart Lipid Nanoparticle that Remodels Tumor Microenvironment for Activatable H2S Gas and Photodynamic Immunotherapy.

Hydrogen sulfide (H2S) has shown promise for gas therapy. However, it is still controversial whether H2S can remodel the tumor microenvironment (TME) and induce robust antitumor immunity. Here, a tumor-targeting and TME-responsive "smart" lipid nanoparticle (1-JK-PS-FA) is presented, which is capable of delivering and releasing H2S specifically in tumor tissues for on-demand H2S gas and photodynamic immunotherapy. 1-JK-PS-FA enables a burst release of H2S in the acidic TME, which promptly reduces the embedded organic electrochromic materials and consequently switches on near-infrared fluorescence and photodynamic activity. Furthermore, we found that high levels of H2S can reprogram the TME by reducing tumor interstitial fluid pressure, promoting angiogenesis, increasing vascular permeability, ameliorating hypoxia, and reducing immunosuppressive conditions. This leads to increased tumor uptake of 1-JK-PS-FA, thereby enhancing PDT efficacy and eliciting strong immunogenic cell death during 808 nm laser irradiation. Therefore, 1-JK-PS-FA permits synergistic H2S gas and photodynamic immunotherapy, effectively eradicating orthotopic breast tumors and preventing tumor metastasis and recurrence. This work showcases the capacity of H2S to reprogram the TME to enhance H2S gas and immunotherapy.

Approach to Significantly Enhancing the Electrochromic Performance of PANi by In Situ Electrodeposition of the PANi@MXene Composite Film.

Electrochromic materials (ECMs) are capable of reversibly adjusting their transmittance or reflectance properties in response to changes in the external biasing voltages. In this study, we enhanced the electrochromic and electrochemical properties of polyaniline (PANi) effectively through the incorporation of MXene Ti2CTx using an in situ composite strategy. This improvement in the electrochromic and electrochemical properties observed can be attributed to the intermolecular forces between the aniline group of PANi and the terminal groups of MXene Ti2CTx sheets. The presence of hydrogen bonds between the PANi monomers and the MXene sheets was confirmed through theoretical calculations and photoluminescence results, which effectively improved the composite interfaces. Additionally, the PANi@MXene composite films were successfully prepared through a simple one-step in situ polymerization process, as verified by SEM and XPS characterization. The electrochemical studies revealed enhanced electronic conductivity, a high ion diffusion coefficient, and a narrow energy redox gap, all contributing to the excellent electrochemical properties observed. Overall, our results demonstrate that the MXene Ti2CTx composition effectively enhances the electrochromic performance of PANi. The PANi@MXene composite films exhibited a high optical modulation range, rapid switching response time, good thermal radiation regulation, and excellent operational stability. This composite strategy significantly improves the performance and practical applicability of ECMs.

C-Rich Carbon Nitride Conjugated Polymer Enabling Ion-Migration-Induced Precise Electrochromic Display.

The development of electrochromic (EC) displays has been in the challenge of displaying precise patterns, such as characters or high-resolution images of small size. High-performance EC materials as well as efficient, precise-display strategies are still urgent. To enable a microfactor-guided strategy for highly precise display, I3-/I- ion-migration-induced localized electrochromism is developed in an EC device based on the C-rich polymeric carbon nitride (CPCN). The CPCN material with an extended conjugated backbone of individual aromatic nuclei and heptazine rings has been reported possessing remarkable photorechargeable performance. Owing to the self-charging behavior, the CPCN exhibits color switching by the interfacial charge recombination with I3- ions in electrolyte and serves as the EC material with a coloration efficiency of 210.2 cm2 C-1 and an optical contrast of 48.6%. Material synthesis, electrode preparation, device design and fabrication, mechanism analysis, and performance evaluation of the CPCN-based EC display device are described.

Dual-Functional Electrochromic Smart Window Using WO3·H2O-rGO Nanocomposite Ink Spray-Coated on a Low-Cost Hybrid Electrode.

Electrochromic windows have gained growing interest for their ability to change their optical state in the visible and NIR ranges with minimal input power, making them energy-efficient. However, material processing costs, fabrication complexity, and poor electrochromic properties can be barriers to the widespread adoption of this technology. To address these issues, electrochromic material and fabrication processes are designed to realize their potential as a cost-effective and energy-efficient technology. In this work, an electrochromic composite material-based ink is synthesized consisting of WO3·H2O nanoplates supported on rGO (reduced graphene oxide) nanosheets (WH-rGO), wherein an optimized amount of rGO (0.05 to 0.5 wt %) is introduced for providing a higher conduction pathway for efficient charge transport without sacrificing the electrochromic performance of WO3·H2O nanoplates. The stable ink dispersion prepared in the study is deposited by spray coating on transparent conducting electrodes over large areas (25 cm2). The WH-rGO nanocomposite (0.4 wt %) results in 43% optical modulation at 700 nm, with bleaching and coloration times of 6 and 8 s, respectively. Interestingly, the device also possesses an electrochemical energy storage capability with an areal capacitance of 16.3 mF/cm2. The electrochromic composite material is successfully translated on tin doped indium oxide (ITO)-coated Al metal mesh hybrid electrodes (T = 80%, Rs = 40 Ω/□) to replace ITO. Finally, an electrochromic device of 5 × 5 cm2 is fabricated by spray-coating the ink on cost-effective ITO/Al-mesh hybrid electrodes. The device displays blue to colorless modulation with an excellent bleaching time of 0.43 s and a coloration time of 2.16 s, making it one among the fast-operating devices fabricated by complete solution processing. This work showcases the economical production of a dual-function electrochromic device, which can be a feasible option as an alternative to existing ITO-based devices in both automotive and infrastructure applications.

High-contrast energy-efficient flexible electrochromic devices based on viologen derivatives and their application in smart windows and electrochromic displayers

Electrochromic materials and corresponding devices display reversible optical changes under applied voltage. While inorganic and organic electrochromic materials are extensively studied, enhancing their performance is crucial. This study presents a high-contrast energy-efficient flexible electrochromic device based on viologen derivatives and driven by film solar cell. The aims are to foster applications in smart windows, displays, and energy-efficient technologies. Two symmetric viologen derivatives of 1,1′-bis(4-(dimethylamino) phenyl)- [4,4′-bipyridine]dihexafluorophosphate (DNPV) and 1,1′-bis(4-acetamidophenyl)-[4,4′-bipyridine]dihexafluorophosphate (DAcPV) and two asymmetric viologen derivatives of 1-benzyl-1'-(4-(dimethylamino)phenyl)-[4,4′-bipyridine]dihexafluoro-phosphate (Bn-NPV) and 1-(4-acetamidophenyl)-1′-benzyl-[4,4′-bipyridine]dihexa-fluorophosphate (Bn-AcPV) were synthesized. These viologen derivatives as active materials were used to assemble both flexible and rigid electrochromic devices (ECDs). After applying voltage of 1.0 V, both of flexible and rigid ECDs based on DNPV and Bn-NPV exhibited reversible color change from purple to deep purple and red to deep viologen respectively, while ECDs based on DAcPV and Bn-AcPV exhibited a color change from yellow to black and pale yellow to green under applied voltage of 1.2 V, respectively. After 1000 cycles, flexible and rigid ECDs showed good stability. Especially, the flexible ECDs maintained good performance after 1000 bending cycles. In additional, the ECDs based on these viologen derivatives were prepared to displayer, which showed clear display function. And ECDs driven by solar cells demonstrated good stability after 100 cycles. Furthermore, it showed that the rigid ECD based on DAcPV with high solar irradiation modulation of 70.3 %, holds great potential in smart window applications.

Photochromic visual sensing chip for isothermal amplification detection of porcine transmissible gastroenteritis virus

The outbreak of transmissible gastroenteritis virus (TGEV) will cause huge economic losses to the whole pig industry. Hence, there is urgent need to develop a rapid and ultrasensitive method for detection of TGEV. As a nucleic acid detection technique, loop-mediated isothermal amplification (LAMP) can achieve quantitative detection of targeted nucleic acids with high sensitivity and selectivity. Nevertheless, the signal outputs of LAMP method must be acquired by complicated instruments. In this work, we firstly developed a LAMP photochromic sensing chip for porcine TGEV detection by combination of the photochromic sensing chip and nucleic acid amplification. The detection signal was based on color change of electrochromic material rather than electrical signal, and thus the detection signal can be obtained by visualization without relying on complicated instrument. The entire test was performed with small fluorinated indium tin oxide electrodes modified with zinc oxide (ZnO) (a photocatalytic material) and Prussian blue (PB) (an electrochromic material). When photoinduced electrons produced by ZnO were injected into PB under light, the PB was reduced to Prussian white. The higher the concentration of TGEV, the more double-stranded DNA was produced after amplification. The amplified product produced greater impedance, and fewer electron was transferred, which affect the corresponding color change of PB. The sensing chip also showed highly sensitive response to TGEV, with the minimum limit of detection was determined to be 2.5 fg/μL. The sensing chip developed herein will provide a new avenue for DNA amplification detection by visualization.

Niobium-Tungsten Bimetallic Oxide Electrodes with High Dual-Band Electrochromic Performance Prepared by Hydrothermal Method

Dual-band electrochromic (EC) smart windows, capable of selectively regulating visible (VIS) and near-infrared (NIR) light, are one of the most attractive candidates for significantly reducing the energy consumption of buildings. Niobium-tungsten bimetallic oxides exhibit a fast ion exchange rate and high cycle stability in the electrochemical field because of various structural chemistry in the pseudobinary system Nb2O5/WO3, showing excellent dual-band EC potential. Herein, we employ a facile hydrothermal technique to synthesize Nb18W16O93 (NWO) films with low temperature and facile procedure. The obtained NWO films exhibit impressive dual-band electrochromic performances, including high optical regulation (radiation blocking rates of 33.1% and 77.5% in the VIS and NIR band) and short coloring/bleaching time (12 s/2.6 s at 633 nm and 6.5 s/6.1 s at 1600 nm). These results demonstrate that NWO is a high-performance dual-band EC material and provide a practical strategy to synthesize the NWO electrodes with nanorod stacking architectures in a facile and low-cost way.

Amorphous/ordered porous crystalline stacked WO3 films fabricated by electrodeposition-assisted sol–gel and its application to electrochromic devices

WO3 is currently the most widely used and promising electrochromic material, but the preparation of WO3 thin films with excellent optoelectronic properties is a formidable challenge. The amorphous WO3/ordered porous crystalline WO3 stacked films (a-WO3/OP-c-WO3) were prepared by electrodeposition-assisted sol–gel method with polystyrene (PS) spheres as the templates. The microstructure and properties of a-WO3/OP-c-WO3 films were significantly influenced by electrodeposition time (150 s ∼ 300 s). The optimized a-WO3/OP-c-WO3 films exhibited even better electrochromic properties (at 633 nm) with high cycling stability, superior optical modulation (53.9 %), fast response time (3.9 s/6.1 s for bleaching /coloration), and especially high coloration efficiency (51.3 cm2/C), compared with OP-c-WO3 film (25.1 cm2/C) and a-WO3 film (35.2 cm2/C), which is unique synergistic effect between the top layer of a-WO3 and the bottom layer of OP-c-WO3 film. The ordered porous structure allows the film to fully contact with the electrolyte, thereby providing a greater specific surface area and more active sites for the electrochemical reaction. The electrochromic device (EDC) prototype assembled with a-WO3/OP-c-WO3 laminated film as the electrochromic layer has better electrochromic properties.

Synthesis, characterization, electrochemistry and spectroelectrochemistry of new non-peripherally substituted lutetium bis phthalocyanines

The synthesis, characterization, spectral, and electrochemical properties of bis-(phthalocyanine)lutetium (III) (LuPc2) bearing halogenated (F (F-LuPc2), Cl (Cl-LuPc2) and Br (Br-LuPc2)) phenoxy groups were reported for the first time. To explore the possible application of the LuPc2 complexes, their detailed redox mechanisms were determined by voltammetric and spectroelectrochemical characterizations. One of the Pc rings exhibits radical characteristics as a result of the sandwich structures of the complexes, which led to the typical one electron reduction process between 0.20 and 0.40 V and the typical one electron oxidation process between 0.60 and 0.80 V.In addition to the characteristic Pc.-Lu3+Pc2-/Pc2-Lu3+Pc2-1- reduction and Pc.-Lu3+Pc2-/Pc.-Lu3+Pc.-1+ oxidation couple of the complexes, further two-electron reduction and oxidation processes were also observed due to the simultaneous electron transfer reactions of each Pc ring at very close potentials. Moreover, at more negative potentials sequential one electron reduction waves for each Pc ring were also observed. While the Cl-LuPc2 reduced at less positive potential and more negative potential, changing Br with Cl and F alters the ease of the electron transfer reactions of the complexes. In situ spectroelectrochemical results supported these voltammetric assignments. Moreover, distinct color changes of LuPc2 in the solution observed with in situ spectroelectrochemical measurements indicated their functionality as electrochromic materials.