Designing Rewritable Dual-Mode Patterns using a Stretchable Photoresponsive Polymer via Orthogonal Photopatterning

Visualizing the Sliding Motion of Dynamic Rotaxanes by Surface Wrinkles

Visualizing the sliding dynamics of a topological network can provide critical insight into determining the design and properties of mechanically interlocked materials. Although several auxiliary techniques have been proposed to infer the microscopic motion of rotaxanes, employing intuitive and convenient methods to explore the microscopic dynamics of a mechanically interlocked polymer remains a significant challenge. Herein, this work introduces a mechanically interlocked network (MIN) into the patterned surfaces for visualizing and regulating the sliding process of [2]rotaxane units through the evolution of surface wrinkles. Upon the photodimerization of the anthracene-functionalized polymer chain, the surface wrinkle can be formed after thermal treatment and subsequent cooling to room temperature. Specifically, the cross-linked films exhibit visible changes in wrinkle topography through the disruption of host-guest recognition by alkaline stimuli. Moreover, by leveraging the unique mechanical properties of surface wrinkles, we prolonged and amplified the originally extremely transient and difficult-to-detect sliding motion of rotaxane units in terms of time scale. Through statistical analysis of the changes in wrinkle morphology, we were able to correspondingly deconstruct the three processes of the rotaxane sliding motion: (I) unrestricted rapid sliding following host-guest dissociation; (II) restricted sliding; and (III) termination of sliding. The novel approach we propose opens a new avenue for studying the microscopic molecular motion of mechanically interlocked materials, facilitating the advancement and application of mechanically interlocked structures. In addition to using macroscopic surface patterns to visualize and explore microscopic molecular motion, the motion of microscopic molecules can also be used to regulate macroscopic surface patterns.

Dual-Responsive Ultrathin Peptoid Nanofibers Assembled from Amphiphilic Alternating Peptoids with an Integration of Azobenzene and Histamine Moieties

Ultrathin organic nanofibers (UTONFs) have favorable potential as emerging nanomaterials due to their large aspect ratio, lightweight nature, and mechanical flexibility. Achieving dual stimuli-responsive UTONFs is necessary to satisfy the on-demand requirements of smart and miniature devices but remains challenging. Herein, amphiphilic alternating peptoids (AAPs) modified with azobenzene and histamine groups were successfully synthesized using the solid-phase submonomer synthesis technique. Following subsequent solution self-assembly, photo/CO2 dual-responsive ultrathin peptoid nanofibers (UTPNFs) with a diameter of ∼1.8 nm and a length of up to several micrometers were generated based on the pendant hydrophobic conjugate stacking mechanism. The photoisomerization of azobenzene was accountable for the reversible transformation from UTPNFs to spherical micelles (∼60 nm) under recyclable light irradiation. Owing to the protonation and the resulting electrostatic repulsion interaction, both UTPNFs and spherical micelles displayed a reversible variation in shape and physicochemical properties, including the size, diameter, zeta potential, and pH. Our work offers prospective guidance on the construction of dual-responsive ultrathin organic nanofibers with controllable shape transformation and performance transition.

"All-in-One Functionalization and Synergic Ordering" Strategy Enables Multimode Anti-Counterfeiting Patterns

Conventional multimode anticounterfeiting systems usually suffer high cost, complicated structures, and different optical channel interferences. In this study, we demonstrate a simple strategy named "all-in-one functionalization and synergic ordering" to prepare quadruple mode patterns on a photoresponsive alternating copolymer P(DPA-alt-BP) film. Herein, a 9,10-diphenylanthracene (DPA) nonanoate unit serves as the multipurpose moiety with photoresponse and fluorescence, performing photodimerization upon 365 nm UV irradiation. The liquid crystal mesogen biphenyl (BP) caproate units can orderly align along strain for polarized sight and improve the microphase separation. Upon UV irradiation through a photomask followed by solvent annealing, the P(DPA-alt-BP) film is first gradient-cross-linked and then undergoes stress relief and microphase separation, giving rise to a synergic ordering effect that enables fabrication of an anticounterfeiting pattern with quadruple modes, i.e., wrinkled pattern, substructure on a wrinkled surface, distinguishable fluorescent emission, and polarized sight on the film. This strategy is promising for high-level anticounterfeiting applications and provides helpful inspiration to the development of innovative photoresponsive materials.

Dynamic multimodal information encryption combining programmable structural coloration and switchable circularly polarized luminescence

Multimodal optical-materials are highly desirable due to their advantages in enhancing information security, though independent modulation is challenging, especially accurately controlling the orthogonal relationship between the structural coloration (SC) and fluorescence (FL) pattern. Herein, we report a strategy which combines programmable structural coloration and switchable circularly polarized luminescence (CPL) for multimodal information encryption. Using photomask with aligned grating, programmable periodic patterns are fabricated on a polydiacetylene (PDA) gel film, which produces image in tunable structural colors. Introducing a chiral fluorescence layer containing perovskite nanocrystals and twisted-stacking Ag nanowires (NWs) bilayers, which provides stimuli-responsive FL and CPL with high dissymmetry factor (glum, up to 1.3). Importantly, the structural coloration information and FL patterns (including CPL pattern) can be independently modulated without mutual interference, even selectively concealed or exposed by varying microstructure design of the cross-linked PDA gel or by acetonitrile treatment.

High-Security Plastic with Integrated Holographic and Phosphorescent Images

Organic room temperature phosphorescence (ORTP) polymer materials have sparked considerable research interests in recent years, but their optical function is still limited for multi-mode optical imaging. Herein, a feasible and universal approach is proposed to endow ORTP polymer materials with periodic refractive index modulation functions by holographic patterning. The key to this approach is to design a two-stage stepwise crosslinking. Stage-1, with low crosslinking density (≤0.75 mol L-1), is phosphorescence-silent but can provide greater free volume for monomer diffusion and thus facilitate the patterning of refractive index modulated holograms via photopolymerization-induced phase separation. The dense crosslinking at stage-2 can turn on phosphorescence with the intensity rising by 144% when the crosslinking density increases from 3.77 to 4.12 mol L-1. The enhanced phosphorescence is primarily ascribed to the increase of conformational distortion and spin-orbit coupling of organic phosphors based on theoretical calculations. Eventually, the first example is demonstrated of holographic plastic with the unique capability of independently displaying holographic andphosphorescent images. This work not only provides a novel paradigm to impart added optical functions to ORTP polymer materials but also paves the way for the development of high-security optical materials to combat counterfeiting.

Stimuli-Responsive Polymers for Tubal Actuators

Stimuli-responsive polymers for tubal actuators have garnered significant attention due to their potential applications in soft robotics, artificial blood vessels, controlled liquid transportation, and microchemical reactors. This perspective emphasizes the advantages, response mechanisms, and fundamental design principles of stimuli-responsive polymers for tubal actuators. It also addresses the biological and engineering applications, current challenges, and future prospects of stimuli-responsive polymers for tubal actuators. The discussion categorizes stimuli-responsive polymers for tubal actuators based on various properties, including liquid crystal elastomer actuators, hydrogel actuators, and shape memory polymer actuators. The subsequent sections focuses on the structural features, design principles, and biological applications of stimuli-responsive polymers for tubal actuator, elucidating their potential interrelationships. The molecular architectures and design principles are intricately linked to the stimuli-responsive mechanisms. Finally, this perspective outlines the challenges faced by stimuli-responsive polymers for tubal actuators. This article aims to facilitate broader applications of stimuli-responsive polymers for tubal actuators, thereby promoting progress across multiple fields.

Phase-transition-induced dynamic surface wrinkle pattern on gradient photo-crosslinking liquid crystal elastomer

Liquid crystal elastomers (LCEs) with various deformation properties based on phase transition were widely used as actuators and provided potential to fabricate functional surfaces with tunable microstructure. Herein, we demonstrate a strategy to fabricate dynamic micro wrinkles on LCE surfaces based on LC phase transition. Stable micron-sized surface wrinkles on the anthracene-containing LCE film (AnLCE) are fabricated by ultraviolet exposure induced gradient cross-linking and subsequently stretching-releasing (UV-SR). The surface wrinkle is stabilized by the orientation of liquid crystal mesogens in the crosslinked top layer, while it can be erased by heating due to the isotropic phase-transition and recovered by stretching-releasing again. The dynamic natures cooperated with multi display modes under natural light, UV light and polarized light enable wrinkled AnLCE as a dynamic and multi-mode display platform. This strategy provide a path for modifying LCEs and regulating surface polarized images via wrinkling, which may be potential in soft sensors and optics, smart windows and anti-counterfeiting.

Functional Semi-Interpenetrating Polymer Networks

Semi-interpenetrating polymer networks (SIPNs) have garnered significant interest due to their potential applications in self-healing materials, drug delivery systems, electrolytes, functional membranes, smart gels and, toughing. SIPNs combine the characteristics of physical cross-linking with advantageous chemical properties, offering broad application prospects in materials science and engineering. This perspective introduces the history of semi-interpenetrating polymer networks and their diverse applications. Additionally, the ongoing challenges associated with traditional semi-interpenetrating polymer materials are discussed and provide an outlook on future advancements in novel functional SIPNs.

Dynamic metal-ligand coordination enables a hydrogel with rewritable dual-mode pattern display

The realization of dual-mode information display in the same material is of great significance to the expansion of information capacity and the improvement of information security. However, the existing systems lose the ability to re-encode information once they are constructed. Here, dynamic metal-ligand coordination is introduced into a novel hydrogel-based optical platform that allows rewritable dual-mode information display. The hydrogel system consists of a hard lamellar structure of poly(dodecylglyceryl itaconate) (pDGI) and soft double networks of poly(acrylamide)/poly(acrylic acid) (PAAm/PAAc) containing fluorescent carbon dots (CDs). As the carboxylic acid groups can coordinate with metal ions such as Al3+, the layer spacing of the lamellar structure is reduced while CDs aggregate, leading to the blue shift of the structural color and the red shift of the fluorescent color. Additionally, the metal chelating agent, ethylenediaminetetraacetic acid (EDTA), is able to strip away Al3+ ions and restore the two colors, realizing an erasable dual-mode information display. This study opens up a path for the development of new materials and technologies for rewritable dual-mode information protection.

Illuminating Biomimetic Nanochannels: Unveiling Macroscopic Anticounterfeiting and Photoswitchable Ion Conductivity via Polymer Tailoring

Artificial photomodulated channels represent a significant advancement toward practical photogated systems because of their remote noncontact stimulation. Ion transport behaviors in artificial photomodulated channels, however, still require further investigation, especially in multiple nanochannels that closely resemble biological structures. Herein, we present the design and development of photoswitchable ion nanochannels inspired by natural channelrhodopsins (ChRs), utilizing photoresponsive polymers grafted anodic aluminum oxide (AAO) membranes. Our approach integrates spiropyran (SP) as photoresponsive molecules into nanochannels through surface-initiated atom transfer radical polymerization (SI-ATRP), creating a responsive system that modulates ionic conductivity and hydrophilicity in response to light stimuli. A key design feature is the reversible ring-opening photoisomerization of spiropyran groups under UV irradiation. This transformation, observable at the molecular level and macroscopically, allows the surface inside the nanochannels to switch between hydrophobic and hydrophilic states, thus efficiently modulating ion transport via changing water wetting behaviors. The patternable and erasable polySP-grafted AAO, based on a controllable and reversible photochromic effect, also shows potential applications in anticounterfeiting. This study pioneers achieving macroscopic anticounterfeiting and photoinduced photoswitching through reversible surface chemistry and expands the application of polymer-grafted structures in multiple nanochannels.

Photocontrolled Reversible Solid-Fluid Transitions of Azopolymer Nanocomposites for Intelligent Nanomaterials

Intelligent polymer nanocomposites are multicomponent and multifunctional materials that show immense potential across diverse applications. However, to exhibit intelligent traits such as adaptability, reconfigurability and dynamic properties, these materials often require a solvent or heating environment to facilitate the mobility of polymer chains and nanoparticles, rendering their applications in everyday settings impractical. Here intelligent azopolymer nanocomposites that function effectively in a solvent-free, room-temperature environment based on photocontrolled reversible solid-fluid transitions via switching flow temperatures (Tfs) are shown. A range of nanocomposites is synthesized through the grafting of Au nanoparticles, Au nanorods, quantum dots, or superparamagnetic nanoparticles with photoresponsive azopolymers. Leveraging the reversible cis-trans photoisomerization of azo groups, the azopolymer nanocomposites transition between solid (Tf above room temperature) and fluid (Tf below room temperature) states. Such photocontrolled reversible solid-fluid transitions empower the rewriting of nanopatterns, correction of nanoscale defects, reconfiguration of complex multiscale structures, and design of intelligent optical devices. These findings highlight Tf-switchable polymer nanocomposites as promising candidates for the development of intelligent nanomaterials operative in solvent-free, room-temperature conditions.

Angle-Multiplexed 3D Photonic Superstructures with Multi-Directional Switchable Structural Color for Information Transformation, Storage, and Encryption

Creating photonic crystals that can integrate and switch between multiple structural color images will greatly advance their utility in dynamic information transformation, high-capacity storage, and advanced encryption, but has proven to be highly challenging. Here, it is reported that by programmably integrating newly developed 1D quasi-periodic folding structures into a 3D photonic crystal, the generated photonic superstructure exhibits distinctive optical effects that combine independently manipulatable specular and anisotropic diffuse reflections within a versatile protein-based platform, thus creating different optical channels for structural color imaging. The polymorphic transition of the protein format allows for the facile modulation of both folding patterns and photonic lattices and, therefore, the superstructure's spectral response within each channel. The capacity to manipulate the structural assembly of the superstructure enables the programmable encoding of multiple independent patterns into a single system, which can be decoded by the simple adjustment of lighting directions. The multifunctional utility of the photonic platform is demonstrated in information processing, showcasing its ability to achieve multimode transformation of information codes, multi-code high-capacity storage, and high-level numerical information encryption. The present strategy opens new pathways for achieving multichannel transformable imaging, thereby facilitating the development of emerging information conversion, storage, and encryption media using photonic crystals.

Dual-Mode Patterns Enabled by Photofluidization of an Azobenzene-Containing Linear Liquid Crystal Copolymer

Creating dual-mode patterns in the same area of the material is an advanced method to increase the dimension of information storage, improve the level of encryption security, and promote the development of encoding technology. However, in situ, different patterns may lead to serious mutual interference in the process of manufacturing and usage. New materials and patterning techniques are essential for the advancement of noninterfering dual-mode patterns. Herein, noninterfering dual-mode patterns are demonstrated by combining the structural color and chromatic polarization, which is designed with an azobenzene-containing linear liquid crystal copolymer featuring a photofluidization effect. On the one hand, structural color patterns are imprinted via silicon templates with periodic microstructures after a UV-light-induced local transition of the polymer surface from a glassy to rubbery state. On the other hand, different polarization patterns based on the local photoinduced orientation of mesogens are created within the photofluidized region by the Weigert effect. Especially, the secondary imprinting is used to eliminate the partial damage to the structural color patterns during writing of the polarization patterns, thus obtaining dual-mode patterns without interference. This study provides a blueprint for the creation of advanced materials and sophisticated photopatterning techniques with potential cross-industry applications.

Photochemical Design for Diverse Controllable Patterns in Self-Wrinkling Films

Harnessing the spontaneous surface instability of pliable substances to create intricate, well-ordered, and on-demand controlled surface patterns holds great potential for advancing applications in optical, electrical, and biological processes. However, the current limitations stem from challenges in modulating multidirectional stress fields and diverse boundary environments. Herein, this work proposes a universal strategy to achieve arbitrarily controllable wrinkle patterns via the spatiotemporal photochemical boundaries. Utilizing constraints and inductive effects of the photochemical boundaries, the multiple coupling relationship is accomplished among the light fields, stress fields, and morphology of wrinkles in photosensitive polyurethane (PSPU) film. Moreover, employing sequential light-irradiation with photomask enables the attainment of a diverse array of controllable patterns, ranging from highly ordered 2D patterns to periodic or intricate designs. The fundamental mechanics of underlying buckling and the formation of surface features are comprehensively elucidated through theoretical stimulation and finite element analysis. The results reveal the evolution laws of wrinkles under photochemical boundaries and represent a new effective toolkit for fabricating intricate and captivating patterns in single-layer films.

Designable Photo-Responsive Micron-Scale Ultrathin Peptoid Nanobelts for Enhanced Performance on Hydrogen Evolution Reaction

The development of high-reactive single-atom catalysts (SACs) based on long-range-ordered ultrathin organic nanomaterials (UTONMs) (i.e., below 3 nm) provides a significant tactic for the advancement in hydrogen evolution reactions (HER) but remains challenging. Herein, photo-responsive ultrathin peptoid nanobelts (UTPNBs) with a thickness of ≈2.2 nm and micron-scaled length are generated using the self-assembly of azobenzene-containing amphiphilic ternary alternating peptoids. The pendants hydrophobic conjugate stacking mechanism reveals the formation of 1D ultralong UTPNBs, whose thickness is dictated by the length of side groups that are linked to peptoid backbones. The photo-responsive feature is demonstrated by a reversible morphological transformation from UTPNBs to nanospheres (21.5 nm) upon alternative irradiation with UV and visible lights. Furthermore, the electrocatalyst performance of these aggregates co-decorated with nitrogen-rich ligand of terpyridine (TE) and uniformly-distributed atomic platinum (Pt) is evaluated toward HER, with a photo-controllable electrocatalyst activity that highly depended on both the presence of Pt element and structural characteristic of substrates. The Pt-based SACs using TE-modified UTPNBs as support exhibit a favorable electrocatalytic capacity with an overpotential of ≈28 mV at a current density of 10 mA cm-2. This work presents a promising strategy to fabricate stimuli-responsive UTONMs-based catalysts with controllable HER catalytic performance.

Steerable mass transport in a photoresponsive system for advanced anticounterfeiting

Numerous anticounterfeiting platforms using photoresponsive materials have been designed to improve information security, enabling applications in anticounterfeiting technology. However, fabricating sophisticated micro/nanostructures using bidirectional mass transport to achieve advanced anticounterfeiting remains challenging. Here, we propose one strategy to achieve steerable mass transport in a photoresponsive system with the assistance of solvent vapor at room temperature. Upon optimizing the host-guest ratio and the width of photoisomerized areas, wettability gradient is acquired just photo-patterning once, then bidirectional mass transport is realized due to the competition of mass transport induced by surface energy gradient of the material itself and flow of the solvent on the film surface with wettability gradient. Taking advantage of the interaction between solvent and film surface with wettability gradient, this bidirectional polymer flow has been successfully applied in multi-mode anticounterfeiting. This work paves a promising avenue toward high-level information storage in soft materials, demonstrating the potential applications in anticounterfeiting.

Light-Responsive Supramolecular Liquid-Crystalline Metallacycle for Orthogonal Multimode Photopatterning

The development of multimode photopatterning systems based on supramolecular coordination complexes (SCCs) is considerably attractive in supramolecular chemistry and materials science, because SCCs can serve as promising platforms for the incorporation of multiple functional building blocks. Herein, we report a light-responsive liquid-crystalline metallacycle that is constructed by coordination-driven self-assembly. By exploiting its fascinating liquid crystal features, bright emission properties, and facile photocyclization capability, a unique system with spatially-controlled fluorescence-resonance energy transfer (FRET) is built through the introduction of a photochromic spiropyran derivative, which led to the realization of the first example of a liquid-crystalline metallacycle for orthogonal photopatterning in three-modes, namely holography, fluorescence, and photochromism.

Stimulus-responsive polymer materials toward multi-mode and multi-level information anti-counterfeiting: recent advances and future challenges

Information storage and security is one of the perennial hot issues in society, while the further advancements of related chemical anti-counterfeiting systems remain a formidable challenge. As emerging anti-counterfeiting materials, stimulus-responsive polymers (SRPs) have attracted extensive attention due to their unique stimulus-responsiveness and charming discoloration performance. At the same time, single-channel decryption technology with low-security levels has been unable to effectively prevent information from being stolen or mimicked. As a result, it would be of great significance to develop SRPs with multi-mode and multi-level anti-counterfeiting characteristics. This study summarizes the latest achievements in advance anti-counterfeiting strategies based on SRPs, including multi-mode anti-counterfeiting (static information) and multi-level anti-counterfeiting (dynamic information). In addition, the promising applications of such materials in anti-counterfeiting labels, identification platforms, intelligent displays, and others are briefly reviewed. Finally, the challenges and opportunities in this emerging field are discussed. This review serves as a useful resource for manipulating SRP-based anti-counterfeiting materials and creating cutting-edge information security and encryption systems.

Manipulation of photoresponsive liquid-crystalline polymers and their applications: from nanoscale to macroscale

We summarize the molecular design of photoresponsive liquid-crystalline polymers, manipulation at multiple scales and various applications based on their intrinsic properties, providing an opportunity for future development in this field.

Digital Laser Direct Writing of Internal Stress in Shape Memory Polymer for Anticounterfeiting and 4D Printing

Shape memory polymers (SMPs) are a type of smart shape-shifting material that can respond to various stimuli. Their shape recovery pathway is determined by the internal stress stored in the temporary shapes. Thus, manipulating the internal stress is key to the potential applications of SMPs. This is commonly achieved by the types of deformation forces applied during the programming stage. In contrast, we present here a digital laser direct writing method to selectively induce thermal relaxation of internal stress stored in the two-dimensional (2D) shape of a thermoplastic SMP. The internal stress field, while invisible under natural light, can be visualized under polarized light. Consequently, the digital stress pattern can be used for anticounterfeiting. In addition, further uniform heating induces the release of the programmed internal stress within the 2D film. This triggers its transformation into a three-dimensional (3D) shape, enabling 4D printing. The simplicity and versatility of our approach in manipulating internal stress and shape-shifting make it attractive for potential applications.

Customizable High-Contrast Optical Responses: Dual Photosensitive Colors for Smart Textiles

Smart textiles demonstrating optical responses to external light stimuli hold great promise as functional materials with a wide range of applications in personalized decoration and information visualization. The incorporation of high-contrast, vivid, and real-time optical signals, such as color change or fluorescence emission, to indicate light on/off states is both crucial and challenging. In this study, we have developed a dual output photosensitive dye system possessing photochromic and photofluorescent properties, which was successfully applied to the dyeing and finishing processes of cotton fabrics. The design and fabrication of this dye system were based on the unique photoinduced proton transfer (PPT) principle exhibited by the water-soluble spiropyran (trans-MCH) molecule. The dual output response relies on the open-/closed-loop mechanism, wherein light regulates the trans-MCH molecule. Upon excitation by UV or visible light, the dye system and dyed fabrics display significant color changes and fluorescence switching in a real-time and highly reversible manner. Moreover, diverse photosensitive color systems can be tailored by direct blending with commercially available water-soluble dyes. By integrating high-contrast dual optical outputs into this scalable, versatile, and reversible dye system, we envisage the development and design of smart textiles capable of producing high-end products.

A Photopatternable Conjugated Polymer with Thermal-Annealing-Promoted Interchain Stacking for Highly Stable Anti-Counterfeiting Materials

Photoresponsive polymers can be conveniently used to fabricate anti-counterfeiting materials through photopatterning. However, an unsolved problem is that ambient light and heat can damage anti-counterfeiting patterns on photoresponsive polymers. Herein, photo- and thermostable anti-counterfeiting materials are developed by photopatterning and thermal annealing of a photoresponsive conjugated polymer (MC-Azo). MC-Azo contains alternating azobenzene and fluorene units in the polymer backbone. To prepare an anti-counterfeiting material, an MC-Azo film is irradiated with polarized blue light through a photomask, and then thermally annealed under the pressure of a photonic stamp. This strategy generates a highly secure anti-counterfeiting material with dual patterns, which is stable to sunlight and heat over 200 °C. A key for the stability is that thermal annealing promotes interchain stacking, which converts photoresponsive MC-Azo to a photostable material. Another key for the stability is that the conjugated structure endows MC-Azo with desirable thermal properties. This study shows that the design of photopatternable conjugated polymers with thermal-annealing-promoted interchain stacking provides a new strategy for the development of highly stable and secure anti-counterfeiting materials.

Bio-Inspired Electro-Thermal-Hygro Responsive Rewritable Systems with Temporal/Spatial Control for Environment-Interactive Information Display

Utilization of rewritable luminescent materials for secure information storage and delivery has long been envisaged to reduce the cost and environmental wastes. However, it remains challenging to realize a temporally/spatially controlled display of the written information, which is crucial for secure information encryption. Here, inspired by bioelectricity-triggered skin pattern switching in cephalopods, an ideal rewritable system consisting of conductive graphene film and carbon dots (CDs) gel with blue-to-red fluorescence-color changes via water-triggered CDs aggregation and re-dispersion is presented. Its rewritability is guaranteed by using water ink to write on the CDs-gel and employing Joule heat of graphene film to evaporate water. Due to the highly controlled electrical stimulus, temporally/spatially controlled display is achieved, enabling on-demand delivery and duration time regulation of the written information. Furthermore, new-concept environment-interactive rewritable system is obtained by integrating sensitive acoustic/optical sensors and multichannel electronic time-delay devices. This work opens unprecedented avenues of rewritable systems and expands potential uses for information encryption/delivery.

Photoresponsive Diarylethene-Containing Polymers: Recent Advances and Future Challenges

Photoresponsive polymers have attracted increasing interest owing to their potential applications in anticounterfeiting, information encryption, adhesives, etc. Among them, diarylethene (DAE)-containing polymers are one of the most promising photoresponsive polymers and have unique thermal stability and fatigue resistance compared to azobenzene- and spiropyran-containing polymers. Herein, the design of DAE-containing polymers based on different types of structures, including main chain polymers, side-chain polymers, and crosslinked polymers, is introduced. The mechanism and applications of DAE-containing polymers in anti-counterfeiting, information encryption, light-controllable adhesives, and photoinduced healable materials are reviewed. In addition, the remaining challenges of DAE-containing polymers are also discussed.

CO2-responsive gels

CO₂-responsive materials undergo a change in chemical or physical properties in response to the introduction or removal of CO₂. The use of CO₂ as a stimulus is advantageous as it is abundant, benign, inexpensive, and it does not accumulate in a system. Many CO₂-responsive materials have already been explored including polymers, latexes, surfactants, and catalysts. As a sub-set of CO₂-responsive polymers, the study of CO₂-responsive gels (insoluble, cross-linked polymers) is a unique discipline due to the unique set of changes in the gels brought about by CO₂ such as swelling or a transformed morphology. In the past 15 years, CO₂-responsive gels and self-assembled gels have been investigated for a variety of emerging potential applications, reported in 90 peer-reviewed publications. The two most widely exploited properties include the control of flow (fluids) via CO₂-triggered aggregation and their capacity for reversible CO₂ absorption-desorption, leading to applications in Enhanced Oil Recovery (EOR) and CO₂ sequestration, respectively. In this paper, we review the preparation, properties, and applications of these CO₂-responsive gels, broadly classified by particle size as nanogels, microgels, aerogels, and macrogels. We have included a section on CO₂-induced self-assembled gels (including poly(ionic liquid) gels).

Orthogonal Photochemistry toward Direct Encryption of a 3D-Printed Hydrogel

Encryption technologies are essential for information security and product anti-counterfeiting, but they are typically restricted to planar surfaces. Encryption on complex 3D objects offers great potential to further improve security. However, it is rarely achieved owing to the lack of encoding strategies for nonplanar surfaces. Here, an approach is reported to directly encrypt on a 3D-printed object employing orthogonal photochemistry. In this system, visible light photochemistry is used for 3D printing of a hydrogel, and ultraviolet light is subsequently employed to activate its geometrically complex surface through the dissociation of ortho-nitrobenzyl ester units in a spatioselective manner for information coding. This approach offers a new way for more reliable encryption, and the underlying orthogonal photochemistry can be extended toward functional modification of 3D-printed products beyond information protection.

Organic‒inorganic semi-interpenetrating networks with orthogonal light- and magnetic-responsiveness for smart photonic gels

Living matter has the ability to perceive multiple stimuli and respond accordingly. However, the integration of multiple stimuli-responsiveness in artificial materials usually causes mutual interference, which makes artificial materials work improperly. Herein, we design composite gels with organic‒inorganic semi-interpenetrating network structures, which are orthogonally responsive to light and magnetic fields. The composite gels are prepared by the co-assembly of a photoswitchable organogelator (Azo-Ch) and superparamagnetic inorganic nanoparticles (Fe₃O₄@SiO₂). Azo-Ch assembles into an organogel network, which shows photoinduced reversible sol-gel transitions. In gel or sol state, Fe₃O₄@SiO₂ nanoparticles reversibly form photonic nanochains via magnetic control. Light and magnetic fields can orthogonally control the composite gel because Azo-Ch and Fe₃O₄@SiO₂ form a unique semi-interpenetrating network, which allows them to work independently. The orthogonal photo- and magnetic-responsiveness enables the fabrication of smart windows, anti-counterfeiting labels, and reconfigurable materials using the composite gel. Our work presents a method to design orthogonally stimuli-responsive materials.

Highly efficient light-induced self-assembly of gold nanoparticles promoted by photoexcitation-induced aggregatable ligands

There are numerous ways to achieve light-induced self-assembly of gold nanoparticles, but most of them are through chemical reaction and slow. Ligands that can perform photoexcitation-induced aggregation were synthesized and modified onto gold nanoparticles. The leading functionalized nanoparticles exhibit highly efficient light-induced self-assembly properties and show high-contrast color fading in tens of seconds.

Photo-Rewritable Glaring Patterns Composed of Stripe Domains in Nematic Elastomers

Dynamic ordered micropatterns in polymeric materials provide an effective approach for the on-demand tuning of optical properties toward a smart optical material. In this study, we show that glaring patterns exhibiting strong anisotropic light diffusion can be developed at specific locations in nematic liquid-crystal elastomers with light-sensitive azobenzene units. Glaring originates from the stripe domains of the nematic directors that self-organize in light-irradiated regions after a simple uniaxial stretching and releasing process without any complicated lithographic technique. The nematic order transiently reduced by the photo-induced cis azobenzene isomers unlocks entropic elasticity, which induces local uniaxial shrinkage that causes buckling of the directors forming stripe domains. The written pattern on the film is tangibly visible with the backlight owing to the difference in anisotropic light diffusion. Furthermore, this pattern can be erased by light irradiation or thermal annealing. These films can be applied to optical elements for achieving augmented luminaries, security labeling, and sign-sheeting applications. This article is protected by copyright. All rights reserved.