Photochromic Performance Research Articles

Scalable, Fast Light‐Responsive, and Excellent Color‐Retention Fiber‐Based Photochromic Wearables for Sustainable Photo‐Patterning and Information Security Encryption

AbstractFiber‐based photochromic wearables have attracted growing attention in sustainable photo‐patterning information displays, information security encryption, and optical data recording/storage. Molybdenum trioxide (MoO3) is one of the key photochromic materials that possesses good photochromic performance, nevertheless, it faces considerable challenges in preparing photochromic textiles with stable, scalable, and long color‐retention properties. In this work, a new kind of fiber‐based photochromic wearables is designed and developed by combining cotton fabric with a MoO3‐based self‐adhesive polymer network and long chain silyl group. The prepared photochromic wearable has exhibited excellent fatigue resistance and favorable reversibility (> 40 cycles), rapid light response (reach color saturation with a UV dose of 60 kJ m−2), outstanding color retention capability (> 90 days), and desirable biocompatibility (cell viability > 100%). In addition, the prepared photochromic textiles could maintain a fast light response and excellent color retention even after experiencing repeated washing (20 cycles). Moreover, the photo‐patterning photochromic wearables are verified by resisting the deterioration of acid solution, alkali solution, and sweat (pH 2.0–9.0) as well as keeping clear patterns under sunlight irradiation. As a demonstration of the application, fiber‐based photochromic wearables are made and employed for the sustainable applications of rewritable photo‐patterning and information security encryption.

All-Visible-Light-Activated Diarylethene Photoswitches.

Photochromic compounds have attracted much attention for their potential applications in photo-actuators, optoelectronic devices and optical recording techniques. This interest is driven by their key photochemical and photophysical properties, which can be reversibly modulated by light irradiation. Among them, diarylethene compounds have garnered extensive investigation due to their excellent thermal stability of both open- and closed-form isomers, robust fatigue resistance, high photocyclization quantum yield and good photochromic performance in both solution and solid phases. However, a notable limitation in expanding the utility of diarylethene compounds is the necessity for ultraviolet light to induce their photochromism. This requirement poses challenges, as ultraviolet light can be detrimental to biological tissues, and its penetration is often restricted in various media. This review provides an overview of design strategies employed in the development of visible-light-responsive diarylethene compounds. These design strategies serve as a guideline for molecular design, with the potential to significantly broaden the applications of all-visible-light-activated diarylethene compounds in the realms of materials science and biomedical science.

Acceleration Photochromic Performance in Tungsten Oxide

Tungsten oxide (WO3) photochromic films require external force to accelerate the return to their original state after being photoinduced to color under ultraviolet light; otherwise, the fading process is exceedingly slow. The research explores the effects of various metal ion dopants on WO3 photochromic performance, with a focus on Fe doping. Fe-WO3 composite films demonstrate rapid coloration (3 minutes) and bleaching (30 minutes) processes, significantly improving upon undoped WO3. The mechanism of Fe ion catalysis in electron transfer is elucidated through HRTEM, SEM, EDS, and XPS analyses. The practical application of Fe-WO3 composite films in smart windows is evaluated using Energy-plus software, showing substantial energy savings across diverse climate zones. Our findings render great opportunities for innovative photochromic designs that can help achieve energy-saving performance in windows.

High‐Entropy Perovskite Oxides Integrating Sunlight‐Driven Photochromic and Upconversion Manipulation for Power‐Independent Intrusion Detection Monitoring

AbstractThe security monitoring of valuables is a crucial concern to ensure the stable development of human social business activities, scientific research, production, and daily life. The implementation of security precautions has traditionally involved the mere placement of items in safes. However, the formidable task of ascertaining whether valuables have been compromised during storage remains a significant challenge. Photochromic materials are important intelligent substances that can be employed as a potential candidates for security monitoring. However, previous studies have predominantly focused on achieving prominent photochromism by utilizing specific light sources such as ultraviolet, laser, and X‐ray radiation. In light of these existing challenges, a design strategy engaging high entropy is proposed to improve the photochromic performance. By selecting a diverse range of volatile metal elements, the A‐site high entropy is realized within the ABO3 perovskite structure, enabling the construction of various defects. This results in the successful realization of the material's sensitive response to sunlight, thereby validating the feasibility of the photochromism boosted by a high entropy strategy. The developed photochromic materials for intrusion indication demonstrate the capability to operate autonomously, making it a crucial component in high‐level security monitoring systems and presenting a novel approach toward enhancing security protection in traditional domains.

Switching from Molecules to Functional Materials: Breakthroughs in Photochromism With MOFs.

Photochromic materials with properties that can be dynamically tailored as a function of external stimuli are a rapidly expanding field driven by applications in areas ranging from molecular computing, nanotechnology, or photopharmacology to programable heterogeneous catalysis. Challenges arise, however, when translating the rapid, solution-like response of stimuli-responsive moieties to solid-state materials due to the intermolecular interactions imposed through close molecular packing in bulk solids. As a result, the integration of photochromic compounds into synthetically programable porous matrices, such as metal-organic frameworks (MOFs), has come to the forefront as an emerging strategy for photochromic material development. This review highlights how the core principles of reticular chemistry (on the example of MOFs) play a critical role in the photochromic material performance, surpassing the limitations previously observed in solution or solid state. The symbiotic relationship between photoresponsive compounds and porous frameworks with a focus on how reticular synthesis creates avenues toward tailorable photoisomerization kinetics, directional energy and charge transfer, switchable gas sorption, and synergistic chromophore communication is discussed. This review not only focuses on the recent cutting-edge advancements in photochromic material development, but also highlights novel, vital-to-pursue pathways for multifaceted functional materials in the realms of energy, technology, and biomedicine.

Naphthalene-embedded spiropyran derivative-A type of conjugated expanded material with solid-state photochromic properties and tunable color switching range

Due to the limited free volume in the solid state, spiropyrans generally exhibit photochromic properties in solution or mixed thin films. However, few spiropyrans can display the photoisomerization process in the solid state. One conventional solution for solid-state photochromism is to embed the spiropyran on polymer chains or introduce bulky groups to create an efficient free volume in the solid state. In this article, we attempt to introduce large conjugated fragments on the spiropyran backbone to construct a donor-acceptor (D-A) building block that not only possesses an enlarged π-electron system with enhanced electronic delocalization capability but also exhibits an improved free volume for efficient solid-state photoisomerization. Through this strategy, we have successfully embedded the naphthalene ring on the spiropyran backbone to obtain a novel D-A type conjugated building block, SP-Naph, which exhibits excellent solid-state photochromic performance and reversibility. Furthermore, the D-A structure of SP-Naph significantly tuned its photochromic color-switching range to blue. Consequently, SP-Naph was successfully applied in optical printing and invisible inks. The excellent solid photochromic properties make it exhibit remarkable photochromic effects, indicating significant potential for optical printing and anti-counterfeiting applications.

Preparation and Printing Performance of Visible Light Photochromic Paper Based on PMoA-PWA/ZnO/PVP Composite

The recyclable paper based on photochromic materials not only reduces the pollution in the paper manufacture process, but also reduces the pollution caused by the use of ink, which receives wide attention. In this paper, a series of phosphomolybdic acid–phosphotungstic acid/ZnO/polyvinylpyrrolidone (PMoA-PWA/ZnO/PVP) hybrid films, which had different ratio of PMoA/PWA, was prepared by the ultrasonic composite method. The results indicated that the hybrid film prepared when the ratio of PMoA to PWA was 3 had the best photochromic performance. In this system, ZnO was the photosensitizer, while PMoA/PWA was the chromophore. The photochromic mechanism of the PMoA-PWA/ZnO/PVP hybrid film was based on the photogenerated electron transfer mechanism. ZnO generated photoelectron under the excitation of visible light, then PMoA and PWA obtained the photoelectron and produced photoreduction reaction to generate heteropolyblue. The visible light photochromic paper was prepared by loaded PMoA-PWA/ZnO/PVP hybrid film (A3) on A4 paper. Application tests showed that the prepared paper had extremely stable, excellent and reversible visible light photochromic properties, whether it was printing patterns or words, and could replace ordinary paper to realize the reuse of paper.

Amplifying Photochromic Response in Tungsten Oxide Films with Titanium Oxide and Polyvinylpyrrolidone.

Tungsten oxide (WO3) is known for its photochromic properties, making it useful for smart windows, displays, and sensors. However, its small bandgap leads to rapid recombination of electron-hole pairs, resulting in poor photochromic performance. This study aims to enhance the photochromic properties of WO3 by synthesizing hexagonal tungsten oxide via hydrothermal synthesis, which increases surface area and internal hydrates. Titanium oxide (TiO2) was adsorbed onto the tungsten oxide to inject additional charges and reduce electron-hole recombination. Additionally, polyvinylpyrrolidone (PVP) was used to improve dispersion in organic solvents, allowing for the fabrication of high-quality films using the doctor blade method. Characterization confirmed the enhanced surface area, crystal structure, and dispersion stability. Reflectance and transmittance measurements demonstrated significant improvements in photochromic properties due to the composite structure. These findings suggest that the introduction of TiO2 and PVP to tungsten oxide effectively enhances its photochromic performance, broadening its applicability in various advanced photochromic applications.

Advanced functional photochromic wearables with fast photo-responsivity, long color-retention, and multi-environmental stability

Smart photochromic wearables have demonstrated attractive prospects in many emerging fields. However, their lower functional performance limits their applications. Herein, we have fabricated a novel photochromic wearable fabric via covalent grafting and chemical isolation technique grafting WO3 nanoflowers onto cellulose. In the charming system, exceptional photochromic properties of WO3 serve as the color-changing material. Besides, incorporated potassium persulfate as a fast-fading reagent is capable of slow oxygen release upon heating. These combined components give the photochromic fabric a rapid response time of 2 s, a fading time of 5 min, and an unprecedented long color-retention (>7 days). Moreover, this photochromic fabric exhibits outstanding rewritability (100 cycles) and exceptional water resistance, maintaining superb photochromic performance even after undergoing standard washing (50 cycles). Moreover, the activation barriers to the photochromic mechanism for the minimum energy pathway were calculated, which provides a theoretical basis for hydrophobic design. The fabric not only imparts water and oil repellence and antifouling properties but also has chemical stability in multi-environments. Notably, the fabrication process is cost-effective, environmentally friendly, and amenable to large-scale production. Such fabrics hold tremendous promise in household products, public facilities and wearable healthcare technologies.

Visible‐Light Photochromism of Polyoxometallate H4PMo11VO40 Composite Film Based on Polyvinylpyrrolidone with a Fast Response

AbstractThe visible‐light photochromic composite films with a fast response were prepared by entrapping H4PMo11VO40 into polyvinylpyrrolidone (PVP) networks. PMo11V/PVP composite films’ structure and morphology were characterized by IR spectroscopy, XRD and TEM. The skeleton structure of PMo11V and PVP were still remained through IR spectroscopy analysis. The photochromism performance of PMo11V/PVP composite films were analyzed by UV‐vis absorption. The photochromic process showed a first‐order kinetics. Meanwhile, the mechanism of photochromism composite films was investigated by XPS. PMo11V/PVP composite films with excellent circulation ability of rising‐fading color which has good application potential.

Series of Viologen-Based Metal-Organic Polyhedra with Photo/Electrochromic Behavior for Inkless Printing and UV Detection.

The fabrication of molecular crystalline materials with fast, multistimuli-responsive behavior and the construction of the corresponding structure-activity relationship are of extraordinary significance for the development of smart materials. In this context, three multistimuli-responsive functional metal-organic polyhedra (MOP), {[Dy2(bcbp)3(NO3)1.5(H2O)7]·Cl4.2·(NO3)0.3·H2O}n (1), {[Dy2(bcbp)4(H2O)8]Cl6}n (2), and {[Eu2(bcbp)4(H2O)10]Cl6·H2O}n (3; bcbp = 1,1'-bis(4-carboxyphenyl)-4,4'-bipyridinium), were successfully prepared and characterized. All of the compounds exhibit rapid and reversible photochromic and electrochromic dual-responsive behaviors. Furthermore, benefiting from the well-defined crystal structure and different responsive behaviors, the photoinduced electron transfer (PIET) process and structure-activity relationship were explored. In addition, considering the excellent photochromic performance, function filter paper and smart organic glass were successfully prepared and used for ink-free printing and UV light detection.

Amorphous Tungsten Oxide Nanodots for Chromatic Applications

AbstractAmorphous tungsten oxide (WO3) is widely exploited in the fields of photochromism and electrochromism. Despite its widespread use, the tractable synthesis of amorphous WO3 nanodots is still on the drawing board, even though the WO3 nanodots possess superior chromatic performance owing to their large surface‐to‐volume ratio. Therefore, a new efficient strategy to synthesize amorphous WO3 nanodots, which exhibit both excellent electrochromic and photochromic properties, is reported. For the first time, the ligand effects of the amorphous WO3 nanodots on chromatic applications are elucidated. The presence of the ligand on amorphous WO3 nanodots inhibits the electrochromic color switching, while promoting photochromic performance. As a proof of concept, zinc‐WO3 electrochromic devices, WO3‐polyvinyl alcohol (PVA) transparent hydrogels, and PVA/WO3 textiles are prepared for diverse rapid‐switching chromatic applications. These results present a new strategy for the synthesis of widely used amorphous WO3 nanodots and open new opportunities for the development of WO3‐based chromatic applications.

Interlocking viologen-based lanthanide complexes for multifunctionality: Photochromism, electrochromism, photoluminescence, photomagnetism, and inkless printing and UV shielding applications

The construction of molecular crystal materials with physical properties that can be dynamically controllable through various stimuli such as light and electricity is of extraordinary significance, while this remains a tremendous challenge. In this context, we demonstrate two novel 2-D multi-function viologen complexes, {[Ln(bcbp)(BDC)(CH3OH)(H2O)2]·Cl·CH3OH·H2O}n (1-Eu, and 2-Dy; H2bcbp·2Cl = 1,1′-bis(4-carboxyphenyl)-(4,4′-bipyridinium) dichloride; BDC = p-phthalic acid, and Ln = Eu, Dy). Due to the strong π-π interaction between viologen and BDC in the interlocked structure, both compounds exhibit rapid and reversible responses under the stimuli of UV light and electricity. Furthermore, accompanying the photochromic process, photo-modulated luminescent and photomagnetic behavior have been observed. Considering the excellent photochromic performance, the function filter paper and smart organic glass were successfully prepared and used for ink-free printing and UV light filtering.

Dual-mode luminescence light intensity modulation characteristics and optical radiation dependence of stannate photochromic ceramics

Alkaline earth stannate is characterized by good physicochemical stability. It has been applied in the field of optical information storage by coupling photoluminescence intensity modulation and photochromic performance, which has attracted the attention of researchers. The development of alkaline earth stannate ceramics with high light intensity modulation properties and non-destructive reading of optical information is of great research value. In this study, Er3+-doped Ca2SnO4 photochromic ceramics were prepared by high-temperature solid-phase reaction method. Alternating UV light irradiation and thermal stimulation, the ceramics achieve a reversible transition between light and dark gray. Er3+ doping gives the ceramics dual-mode luminescence light intensity modulation performance. When the doping amount of Er3+ is 0.01 mol, there is a maximum down-conversion luminous intensity modulation ratio of 93%, which is higher than most of the same type of photochromic materials. The photochromic behavior is explained using the capture-release model of traps for carriers, and the dual-mode luminescence light-intensity modulation behavior is analyzed through the energy transfer mechanism. The optical radiation response properties were investigated and the optimum light response wavelength is found to be 290 nm, which is related to the optical band gap Eg. And the selection of the optimal light response wavelength can effectively improve the performance of photochromic and light intensity modulation. This study provides a promising strategy for performance enhancement of photochromic materials.

Enhancing solid-state photochromic performance of Stenhouse Adducts doped in bulk polymers by C3-Symmetric multipolar design

Here, we introduce a C3-symmetric molecular design strategy to develop a brand-new visible-light organic photoswitch, named tri-branched multipolar Stenhouse Adduct (TMSA). After doping TMSA into low glass transition polymers (i.e. thermoplastic urethane, TPU) via simple blending and solution casting, the resultant composite films exploit unique geometric and electronic effects of TMSA to afford markedly-improved photoswitching performance compared to those doped with dipolar donor-acceptor Stenhouse Adduct (DASA) counterparts with suppressed solid state photochromism. Importantly, they display good fatigue resistance over 50 photo-discoloration/thermal-recovery cycles with slow degradation, surpassing those literature-reported composites involving various DASAs (<30 cycles). As revealed by combined experiment and computation studies, the multi-dimensional electronic coupling in multipolar TMSA facilitates the thermal cyclization and non-planar branched structures of TMSA afford large free space in polymers for efficient molecular isomerization, while the promoting effect on TMSA isomerization induced by ester-rich polymer micro-environments is more pronounced relative to DASA counterpart.

Grafting photochromic spiropyran polymer brushes on graphene oxide surfaces via surface-initiated ring-opening metathesis polymerization.

A practical "grafting-from" strategy is described to grow photochromic polymer brushes bearing spiropyran (SP) functional groups on graphene oxide (GO) surfaces via surface-initiated ring-opening metathesis polymerization (SI-ROMP). The Grubbs II catalyst was fixed on the GO surface, and the norbornene derivatives functionalized using spiropyran were synthesized from this active site via the ROMP method. The results indicated that the spiropyran-modified polymer brushes were obtained on the GO surface in the form of thin films. The solubility of GO modified by spiropyran polymers (GO-SPs) in organic solvents was significantly improved. The GO-SPs exhibited excellent photochromic properties, including fast coloration/decoloration. The modified GO with an isomeric structure was colored in 90 s under ultraviolet irradiation and decolored in 360 s under white light. The fading kinetic rate in the dark was slow and the kinetic attenuation curve followed bi-exponential decay. The GO-SP composite materials took more than 2 h to return to thermodynamically stable forms. The reversible change in the water contact angle reached 8° after continuous cycling with ultraviolet and visible light. GO-SP maintained its photochromic performance and possessed excellent fatigue resistance after more than six successive UV/light cycles. This work describes a practical strategy for the preparation of photochromic polymer brush modified GO composite materials and extends the applications of GO in photochromic materials.

Enhanced photochromic performance of Zn-doped W18O49-based films for smart windows

4 at% Zn-doped W18O49-based bilayer films exhibited excellent photochromic performance in ultra-high luminescence transmittance of 85.33%, good solar modulation efficiency of 47.18%, excellent cycling stability and good recovery ability.

Doping and Pressure Effects on Yttrium Hydrogen Selenide

In this paper, the structural, electronic, phonon, and optical properties of lanthanum (La)‐doped yttrium hydrogen selenide (YHSe), along with the effects of pressure variations on its optical properties, are investigated using the density functional theory method. Both the La‐doped and YHSe systems are dynamically stable, as indicated by phonon calculations showing no imaginary frequencies in the Brillouin zone (BZ). The influence of pressure on optical properties is examined, revealing that increased pressure enhances these properties, particularly by improving the absorption coefficient in the ultraviolet (UV) range. Moreover, the bandgap energy of both La‐doped YHSe and YHSe compounds is explored. Increasing La concentration reduces the bandgap and enhances the density of states (DOS) at Fermi energy, inducing metallic characteristics in YHSe. Furthermore, the optical properties are examined at various La concentrations, most of which exhibit a nonlinear relationship as the La concentration increases. Doping under extreme conditions significantly enhances the optical properties of La‐doped YHSe, particularly in the UV‐light wavelength range. Specifically, the absorption coefficient reaches its maximum value in the energy range of 6.678 −13.023 eV within the UV region for all concentrations, indicating strong absorption in this range. This suggests the material’s effectiveness in absorbing electromagnetic radiation, particularly in the UV range, making it a promising candidate for photochromic applications. A thorough exploration of the optical properties under doping reveals prominent peaks, particularly in response to the UV spectrum, with a slight shift toward higher energies beyond the UV range. This suggests that the material under study holds promise as a candidate for sustained photochromic performance over time.

Photoswitchable imines: aryliminopyrazoles quantitatively convert to long-lived Z-isomers with visible light

Simple structural modifications significantly boost the photochromic performance of imine-based photoswitches. This work lays a foundation for exploring new motifs in light-addressable dynamic combinatorial chemistry.

Effect of cis/trans isomerization on the photochromic performances of triphenylethylene

Monohalogenated triphenylethylene derivatives exhibit different photocolorabilities and fatigue processes, which are closely related to their trans-isomers.