Colored State Research Articles

Three‐Dimensional Electrochromic Soft Photonic Crystals Based on MXene‐Integrated Blue Phase Liquid Crystals for Bioinspired Visible and Infrared Camouflage

AbstractDeveloping bioinspired camouflage materials that can adaptively change color in the visible and infrared (IR) regions is an intriguing but challenging task. Herein, we report an emerging strategy for fabricating dynamic visible and IR camouflage materials by the controlled in situ growth of novel photopolymerizable blue phase liquid crystals with cubic nanoarchitectures onto highly aligned MXene nanostructured thin films. The resulting MXene‐integrated 3D soft photonic crystals exhibit vivid structural colors and reversible switching between a bright colored state and a dark black state under a low DC electric field. As an illustration, proof‐of‐concept pixelated devices that allow for pixel‐controllable electrochromism are demonstrated. Furthermore, a free‐standing electrochromic flexible film of such 3D soft photonic crystals is fabricated, where visible electrochromism and thermal camouflage are enabled by leveraging the superior electrothermal conversion and low mid‐IR emissivity of MXene nanomaterials.

ITO/Cu multilayer electrodes for high-brightness electrochromic displays

Fabry–Perot (F–P) nanocavity-type electrochromic devices with multicolor tunability have attracted significant interest in the past two years for their potential uses in a wide variety of applications, such as electronic display, military camouflage, and dynamic decoration. However, challenges such as insufficient brightness, lengthy switching times, and poor cycling stability have yet to be overcome. Herein, we demonstrate electrochromic electrodes based on ITO/Cu as both the current collector and the reflective layer, with WO3 as the electrochromic material, forming a unique three-layered structure. The constituted WO3/ITO/Cu films present a high brightness value of about 84% before coloration, and a decent brightness value of 48% after coloration at −0.8 ​V. Moreover, a fast switching time between different coloration states (tc ​= ​2.2 ​s; tb ​= ​1 ​s) is recorded, attributed to the extremely low sheet resistivity of the ITO/Cu current collector. The films also reveal excellent electrochemical cycling stability across 2000 cycles.

Colorimetric and coulometric dual-mode sensing based on electrochromic Prussian blue device for solid-contact ion-selective electrodes

The colorimetric and coulometric dual-mode sensing strategies based on electrochromic Prussian blue (PB) device are proposed for reading out the potentiometric responses of the solid-contact ion-selective electrodes (ISEs). The mechanism is that the transformation between the bleached state and the colored state for the PB-based electrochromic device is modulated by using the solid-contact Ca2+-ISE with changing the ion activities under the control of a constant potential, and a transient current related to the oxidation-reduction reaction of PB is also obtained. Results show that the concentration range of 1.0 × 10−6-1.0 × 10−2 Ca2+ can be qualitatively and semi-quantitatively detected through observing the color change via the naked eye or analyzing the red-green-blue (RGB) values by a smartphone and the corresponding integrated charges of the PB-based electrochromic device under the control of the applied potential. These proposed readout strategies are not only free from the influences of colored and turbid samples, but also can keep the inherent selectivity for the solid-contact Ca2+-ISE, since the signal detection based on the PB-based electrochromic device and the ion recognition based on the solid-contact Ca2+-ISE are separately placed. This work provides a simple, fast, and visual readout strategy for solid-contact ISEs, and expands the sensing concepts for reading out the potentiometric responses.

Ester decorated 1,2,4,5-tetraphenylbenzene electrochromic materials with AEE activity, high optical contrast, fast response, and good cycling stability

Multifunctional electrochromic materials are ideal candidates for applications in various commercial fields. In this work, a series of dual-functional materials, 1,2,4,5-tetrakis (4-carboxyphenyl)benzene esters (TCPBEs), were synthesized by decorating 1,2,4,5-tetraphenylbenzene with tetra-esters. TCPBEs exhibited aggregation-induced emission and distinct phenomenon of aggregation-enhanced emission in water/N-methyl pyrrolidone due to their polyphenyl substituted structures and electrochromic properties due to surrounding esters. TCPBEs underwent a two-step one-electron reduction process in the electrochemical behavior. The electrochromic devices based on TCPBEs showed good long-term cycling stability (i.e., Hex-TCPBE remained 90% of the initial optical contrast after 2350 cycles), high optical contrast (i.e., Et-TCPBE up to 64.5%) and coloration efficiency (i.e., Hex-TCPBE up to 261 cm2/C), rapid response (<3 s), and dual colored state. Significant changes in color from colorless bleached state to orange and brown colored states were observed. Each TCPBE demonstrated distinct electrochromic properties because of the electronic effects of different R-substituted ester groups. In general, Et-TCPBE, Hex-TCPBE, and CH3Ph-TCPBE performed better than Bn-TCPBE and CF3Ph-TCPBE. In summary, this study provides a strategy for the design of novel dual-functional electrochromic materials, which have broad application prospects in the field of multifunctional devices.

Coercion and non‐consent during birth and newborn care in the United States

In a subset analysis of the full sample of 2700, we examined survey responses for participants who described the experience of pressure or nonconsented procedures or intervention during perinatal care. We conducted multivariable logistic regression analyses by racial and ethnic identity for the outcomes: pressure to have perinatal procedures (eg, induction, epidurals, episiotomy, fetal monitoring), nonconsented procedures performed during perinatal care, pressure to have a cesarean birth, and nonconsented procedures during vaginal births. Among participants (n=2490), 34% self-identified as BIPOC, and 37% had a planned hospital birth. Overall, we found significant differences in pressure and nonconsented perinatal procedures by racial and ethnic identity. These inequities persisted even after controlling for contextual factors, such as birthplace, practitioner type, and prenatal care context. For example, more participants with Black racial identity experienced nonconsented procedures during perinatal care (AOR 1.89, 95% CI 1.35-2.64) and vaginal births (AOR 1.87, 95% CI 1.23-2.83) than those identifying as white. In addition, people who identified as other minoritized racial and ethnic identities reported experiencing more pressure to accept perinatal procedures (AOR 1.55, 95% CI 1.08-2.20) than those who were white. There is a need to address human rights violations in perinatal care for all birthing people with particular attention to the needs of those identifying as BIPOC. By eliminating mistreatment in perinatal care, such as pressure to accept services and nonconsented procedures, we can help mitigate long-standing inequities.

Lithium-plasmon-based low-powered dynamic color display.

Display and power supply have been two essential and independent cornerstones of modern electronics. Here, we report a lithium-plasmon-based low-powered dynamic color display with intrinsic dual functionality (plasmonic display and energy recycling unit) which is a result of the electric-field-driven transformation of nanostructured lithium metals. Dynamic color displays are enabled by plasmonic transformation through electrodeposition (electrostripping) of lithium metals during the charging (discharging) process, while the consumed energy for coloring can be retrieved in the inverse process respectively. Energy recycling of lithium metals brings energy consumption down to 0.390mW cm-2 (0.105mW cm-2) for the active (static) coloration state of a proof-of-concept display/battery device, which approaches nearly-zero-energy-consumption in the near-100%-energy-efficiency limit of commercial lithium batteries. Combining the subwavelength feature of plasmonics with effective energy recycling, the lithium-plasmon-based dynamic display offers a promising route towards next-generation integrated photonic devices, with the intriguing advantages of low energy consumption, a small footprint and high resolution.

Isomeric effects of poly-viologens on electrochromic performance and applications in low-power electrochemical devices

Electrochromic (EC) behaviors of poly-viologens are tuned by selecting positions ( ortho ( o ) , meta ( m ), and para ( p )) of the benzene rings linked to 4,4′-bipyridine. All-in-one type EC devices (ECDs) are conveniently fabricated by adding poly-viologens to highly conductive solid-state polymeric gel electrolytes. The maximum transmittance contrast (Δ T ) of the o -poly-viologen based ECD is much lower than that of the other isomers, and its bleaching is not reversible, whereas a large Δ T and high stability are achieved with the m - and p -poly-viologens. Considering the high solubility of the m -poly-viologen in ion gels, it is anticipated to have a larger hydrodynamic size, leading to low diffusivity (∼1.1 × 10 −12 cm 2 /s for cationic and ∼2.7 × 10 −12 cm 2 /s for anionic current). As a result, the m -poly-viologen ECD shows a superior memory effect and long-lasting colored state without voltage supply. This feature allows us to demonstrate a low-power ECD based on the m -poly-viologen, which only requires ∼3.54 μW/cm 2 to maintain the transmittance below 30%. The results indicate that adjusting the isomeric molecular structure of poly-viologen EC chromophores is an effective way to control their EC performance. • Three isomeric poly-viologens are designed and synthesized for electrochromic (EC) chromophores. • Poly-viologens with a larger hydrodynamic size exhibit a lower diffusivity and a higher memory effect. • EC devices with meta -poly-viologens consume very low power of ∼3.54 μW/cm 2 to maintain colored state.

A facile synthesis of porous amorphous/crystalline TiO2 hybrids for enhanced electrochromic performances

Porous crystalline/amorphous TiO2 (c/a-TiO2) hybrid films have been successfully grown on FTO substrates via a solvothermal reaction followed by a simple air annealing treatment. By adjusting reaction temperature, the porous structure and the proportion of amorphous TiO2 phase can be feasibly modulated. The in-situ transformation of crystalline TiO2 from amorphous phase could ensure the optimal crystalline/amorphous interface contact. The obtained c/a-TiO2 hybrid films shows excellent electrochromic properties which can switch between green color and transparent state with large optical contrast (59.3%) at 700 nm, high coloration efficiency (24.3 cm2 C−1) and short switching time (bleaching time of 2.0 s and coloration time of 12.1 s). Due to the desired porous structure for short Li+ ions diffusion paths and crystalline/amorphous interface enables low energy barrier and fast ion migration during the insertion/extraction of Li+ ions, the c/a-TiO2 hybrid film not only exhibits lower threshold voltage (+0.2 ∼ −1.5 V vs Ag/AgCl) and faster response than single crystalline anatase TiO2 (c-TiO2) counterpart, but also owns higher coloration efficiency and better durability than single amorphous TiO2 (a-TiO2). Compared to the commonly blue color of c-TiO2, the success to gain green color by using the prepared c/a-TiO2 hybrid film makes it very attractive for constructing electrochromic devices. Our study here also offers an alternative way of designing TiO2-based nanostructures for high-efficiency electrochromic applications.

Electrochromic Performance Fading and Restoration in Amorphous TiO2 Thin Films

AbstractElectrochromic performance fading is inevitable upon extended cycling, and the limited lifetime greatly prevents large‐scale commercialization of electrochromism‐based devices. Here the origin of the performance degradation is uncovered and the performance restoration in TiO2 thin films is explored. It is shown that, depending on the applied potential windows, the inserted ions are immobilized in α‐traps resulting in a monotonous degradation of colored state, or immobilized in b‐ and modified α‐traps leading to mutual degradation of colored and bleached state of the films. It is found by releasing the resided ions in various traps, the initial performance can be restored accordingly. Moreover, reversible sites and all traps are demonstrated to be interconvertible through an ion trapping and detrapping process. These results provide a general scope in understanding the electrochromism in oxide thin films and offer the scheme for potential traps control or even elimination, aiming at superior electrochromic devices.

Electrochemical polymerization of D-A-D type monomers consisting of triphenylamine and benzo[1,2-b:4,5-b′]dipyrazine units for multicolor electrochromism

We developed four donor-acceptor-donor (D-A-D) type monomers (YQ1 ∼ YQ4) with Y-shape configuration consisting of triphenylamine and benzo[1,2-b:4,5-b′]dipyrazine moities, which were further polymerized via electrochemical polymerization for electrochromic applications. The monomers were synthesized facilely from benzene-1,2,4,5-tetraamine tetrahydrochloride by sequential condensation reactions with diketones. The optical properties of these polymers in neutral states can be tuned by variation of the additional substituents on the electron acceptor parts. All these polymers (PYQ1 ∼ PYQ4) exhibited multicolor electrochromism, and appeared similar green color at their second coloration states. Moreover, polymers PYQ1 and PYQ2 with two twisted substituents on the acceptor part showed superior electrochromic performance than the anologues PYQ3 and PYQ4 consisting fused electron acceptor moities with high coplanarity, involving faster response speed, and higher coloration efficiency, which demonstrated that the molecular configuration of monomer was crucial for efficient electrochromic performance.

Invasive chameleons released from predation display more conspicuous colors.

Conspicuous social and sexual signals are predicted to experience pronounced character release when natural selection via predation is relaxed. However, we have few good examples of this phenomenon in the wild and none in species with dynamic color change. Here, we show that Jackson’s chameleons inadvertently introduced from Kenya to Hawaii (Oahu), where there are no coevolved, native lizard predators, experienced pronounced character release of color signals. Hawaiian chameleons displayed more conspicuous social color signals than Kenyan chameleons during male contests and courtship, were less cryptic in response to bird and snake predators, and showed greater change between display and antipredator color states. Hawaiian chameleon display colors were also more conspicuous in their local than ancestral habitats, consistent with local adaptation of social signals. These results demonstrate that relaxed predation pressure can result in character release of dynamic social signals in introduced species experiencing strong sexual selection.

Detection of Beef Type Dark, Firm, and Dry (DFD) and Pale, Soft, and Exudative (PSE) for Sale at Peunayong Market Banda Aceh

This study aims to determine beef types Dark, Firm, and Dry (DFD) and Pale, Soft, and Exudative (PSE) that are sold at the Peunayong Market, Banda Aceh. A total of nine samples of beef from different sellers will be used as extracts and the pH is measured three times every 1 hour for 12 hours to determine the trend of decreasing pH. Organoleptic observations were carried out to determine the visual differences shown by the meat samples. Parameters observed were meat color, meat aroma, meat texture and surface state of the meat. The data obtained from pH measurements and organoleptic tests were analyzed descriptively. Based on the results of pH measurements seen from the decreasing trend of pH in nine samples of beef, seven of them were PSE type beef with a pH value of 5.2 and the other two samples were of good quality meat with a pH value ranging from 5.6 to 5.4. From the results of organoleptic tests for color parameters, four samples were pale, one sample was very pale and the rest were red. All the meat samples tasted normal. Meat texture and surface condition for soft-textured meat has a wet surface, while hard-textured meat has a dry surface.

Electrically induced coloration of polymer-stabilized cholesteric liquid crystal films with broadband reflection capability for smart windows

In this work, a novel approach to realizing the electrically induced coloration of polymer-stabilized cholesteric liquid crystal (LC) films with broadband reflection capability for smart windows was reported. Only starting common materials and an established preparation method were used. The polymer-stabilized cholesteric LC films with broadband reflection capability were prepared via the method of polymerization-induced pitch gradient. After doping with a commercial ionic liquid which served as the supporting electrolyte in the system, the initial broadband reflection capability of the polymer-stabilized cholesteric LCs film was not damaged, and the film can change into a colored state from a colorless state under a low direct current (DC) voltage. The color of the polymer-stabilized cholesteric LCs also can gradually disappear after the removal of the field despite the slow response rate. The as-prepared polymer-stabilized cholesteric LCs in this work not only can be applied in the energy-saving smart windows and thermal management for buildings, but also presented the performance of electrically induced coloration under a low voltage. This work is expected to provide a creative approach for the preparation of electrochromic energy-saving smart windows.

Study of a Novel Electrochromic Device with Crystalline WO3 and Gel Electrolyte.

Most ECDs are coated with an electrochromic material on the transparent conductive oxide (TCO) substrate. A novel electrochromic device (ECD), having a variable optical performance, was prepared by using tungsten foil as a substrate in this study. It was found that the WO3 discoloration layer, having a monoclinic phase crystalline structure made of 600 °C calcined, had optimum charge transmission performance with PADA gel polymer electrolyte. Ionic conductivity of PADA gel polymer electrolyte was 2.3 × 10−3 S cm−1 at −20 °C, and it was possible to help Li+ to implement embedding and extraction from WO3 even in low-temperature conditions. The colored time (tc) and the bleached time (tb) of the electrochromic device were 15 s and 26 s, and it showed yellowish-brown in the colored state and navy blue in the bleached state. The ECD (WO3-600) exhibited good cycle stability reach at least 150 times.

Multi-responsive, flexible, and structurally colored film based on a 1D diffraction grating structure

SummaryIn nature, many organisms (e.g., chameleons) protect themselves by changing their colors in response to environmental changes. Inspired by these organisms, we present a multi-responsive, flexible, and structurally colored hydrogel film with a one-dimensional (1D) ordered periodic groove structure. The groove structure endows the film with bright, highly angle-dependent structural colors, which can be reversibly tuned by stretching and releasing. In addition, because of the thermosensitive properties of the hydrogel, the film can be switched between colored state and opaque white state with temperature. In addition, the optical state of the film is sensitive to solvent and can be reversibly changed between colored state and transparent state with soaking and evaporation of the solvent. This reversible, multi-responsive, flexible, and structurally colored hydrogel film has great potential to be used in the fields of color display, sensors, anti-counterfeiting, and so on because of its flexible and diverse tuning methods, excellent optical performance, and convenient preparation process.

Water rewriteable double-inverse opal photonic crystal films with ultrafast response time and robust writing capability

Photonic paper, as a crucial branch of the research of structural color materials, has attracted considerable attention. Herein, innovative large-area water rewriteable double-inverse opal (WRDIO) film with ultrafast response time (∼0.8 s) and robust writing capability is fabricated by introducing polyacrylamide gel into the double-inverse opal. The hydrophilic nature of the polyacrylamide gel can induce water to quickly penetrate the internal pores of the inverted opal backbone. Simultaneously, the randomly distributed polystyrene microspheres within the pores become ordered under the action of liquid buoyancy, which eliminates the scattering disturbance and makes the film switch to the structural color state. Importantly, the as-prepared WRDIO film can be erased and rewritten over 500 cycles without significantly reducing the color quality. Besides, the retention time of the written marks can be controlled by writing using water pens with different water outputs. Interestingly, responsive spatio-temporal colorful patterns could be achieved based on the different volatilities of written marks. Furthermore, advanced optical anti-counterfeiting material with multistate switching for information security is prepared based on controlled wettability. Given these superior properties, this novel WRDIO film provides a new solution for future applications of rewriteable paper.

Targeted enhancement of electrochromic memory in Fe(II) based metallo-supramolecular polymer using molybdenum disulfide quantum dots

Bistable electrochromic (EC) display with long EC memory has been a much-anticipated goal owing to its zero-energy consumption when maintaining the colored or bleached state when used in smart windows. However, it is very challenging to engineer the structure of the materials to accomplish a long EC memory along with high optical contrast, durability, switching fastness, and coloration efficiency which are of significance for fabricating the electrochromic devices with essentially power efficiency. Herein, we have judiciously incorporated the charge trapping MoS2 quantum dots (QDs) to prepare an electrochromic nanocomposite (polyFe-QD-10) of an Fe2+-based metallo-supramolecular EC polymer (polyFe) for the targeted enhancement of EC memory than the pristine polyFe polymer. The polyFe-QD-10 based electrochromic device (ECD) exhibits more cycle durability as it produced no loss in ΔT after the measurement of 100 cycle, while pristine polyFe-based ECD produced 14% loss in similar 100 cycle. The prototype ECD with polyFe-QD-10 film is also demonstrated with fast switching time (3.3 s for bleaching and 0.78 s for coloring), and good coloration efficiency (242.2 cm2 C−1). Remarkably, the ECD based on polyFe-QD-10 composite displays higher EC memory in open circuit condition as it takes 32 min for 90% reappearance of the original purple color after complete bleaching, while the pristine polyFe based ECD regains 90% of the transmittance of the color state only in 15 min. The strategy reported here presents the polyFe-MoS2 QD composite thin film an encouraging candidate for developing power efficient electrochromic information displays and smart windows.

Stable and reversible electrochromic behaviors in anodic NiO thin films

We report the synthesis and electrochromic behavior of nickel oxide (NiO) nanostructures deposited over conducting glass substrates by hot-filament metal vapor deposition (HFMVD). The NiO crystallized into rhombohedra structure with R3-m space group without any post-treatment. The cyclic voltammogram (CV) revealed the coloration and bleaching effect of NiO nanostructures with forward and reverse scans, respectively. The 85.05% reversibility for NiO films from the coloration state back to its bleached state was calculated from Chronocoulometry (CC) measurements. The highest optical transmittance difference obtained at 420 nm has resulted in a corresponding optical density of 1.016. The switching time between the coloration and bleaching cycles calculated from transmittance spectra unfolded the lowest coloration time of 4.96 sec at 354 nm, which increased up to 6.32 sec at 590 nm, whereas the bleaching time at all the wavelengths was estimated to be less than 0.5 sec.

Disordered Low Molecular Weight Spiropyran Exhibiting Photoregulated Adhesion Ability.

The functions of the materials composed of small molecules are highly dependent on their ordered molecular arrangements in both natural and artificial systems. Without ordered structure, small molecules hardly gain complicated functions, due to the absence of intermolecular covalent bond connection or strong network. Here, a low molecular weight spiropyran that could exhibit attractive photochromism and powerful adhesion property in disordered solid state is demonstrated. With maximum up to ∼8 MPa, the adhesion strength could be photoregulated in multiple levels, which also shows one-to-one correspondence to the specific color state. The working mechanism analysis on the photoregulated adhesion reveals that the isomer ratio of merocyanine form and the molecular packing density of spiropyran are the determining factors for the adhesion ability. The discovery of photoregulated adhesion from pure spiropyran provides a new strategy for developing functional materials by employing low molecular weight compounds.

Achieving transmissive-to-black chromism via engineered dual electro-thermoresponsive single-molecule for full modulation of solar transmittance

Pursuit of complete and null transmissive optical material in smart windows for full control of the intensity and spectrum of incoming solar light has led to the advancement of transmissive-to-black chromism. While most reported transmissive-to-black devices are electrically stimulated, we report here an alternative approach based on dual stimulation of a new dual responsive molecule. By integrating asymmetric viologen onto a newly engineered poly(2-isopropyl-2-oxazoline)-based molecule, one can achieve transmissive-to-black chromism. The synergistic effect of its thermochromic and electrochromic response when stimulated simultaneously shows full absorption of the entire visible solar spectrum resulting to a truly black state that is ideal for building facades requiring absolute privacy. Autonomous chromic switchability function is also possible by independently stimulating the material either electrically or thermally where it displays unique colored state of vibrant magenta and a hazy state, respectively. Tunability of the material’s overall performance in terms of optical contrast, switching kinetics, coloration efficiency and cyclic stability based on the lattice water concentration was elucidated in this work. Furthermore, the fabricated device displays self-bleaching property and has a short-term “memory” effect that may broaden its potential for other applications.