Light-responsive Materials Research Articles

A multi-stage single photochrome system for controlled photoswitching responses.

The ability of molecular photoswitches to convert on/off responses into large macroscale property change is fundamental to light-responsive materials. However, moving beyond simple binary responses necessitates the introduction of new elements that control the chemistry of the photoswitching process at the molecular scale. To achieve this goal, we designed, synthesized and developed a single photochrome, based on a modified donor-acceptor Stenhouse adduct (DASA), capable of independently addressing multiple molecular states. The multi-stage photoswitch enables complex switching phenomena. To demonstrate this, we show spatial control of the transformation of a three-stage photoswitch by tuning the population of intermediates along the multi-step reaction pathway of the DASAs without interfering with either the first or final stage. This allows for a photonic three-stage logic gate where the secondary wavelength solely negates the input of the primary wavelength. These results provide a new strategy to move beyond traditional on/off binary photochromic systems and enable the design of future molecular logic systems.

Cyclodextrin-Confined Supramolecular Lanthanide Photoswitch.

The utilization of azobenzene-based photoisomerization cannot only control the morphology of supramolecular assemblies, but can also regulate many biological processes. However, the design of azobenzene-involved nanoconstructs with switchable photoluminescence remains challenging because of the light-quenching ability of azobenzene. Herein, an azobenzene-derived multicomponent nanosystem is reported and its function as a supramolecular lanthanide photoswitch is explored. The metal chelation between lanthanide ions (Ln3+ = Eu3+ and Tb3+ ) and 2,6-pyridinedicarboxylic acid is utilized as the light-emitting center but its inherent fluorescence emission is completely suppressed via the disordered motion of the adjoining azophenyl unit. Interestingly, the hydrophobic cavity of α-cyclodextrin can provide a confined microenvironment to immobilize the molecular conformation of trans-azobenzene, thus leading to the recovery of characteristic lanthanide luminescence both in aqueous solution and the hydrogel state. Also, the luminescence can be reversibly turned off when the cis-azobenzene is expelled from the cavity of α-cyclodextrin upon alternating light irradiation. This mutual cooperation arising from host-guest complexation and metal-ligand coordination confers the desired photoswitchable luminescence abilities on the commonly used azobenzenes, which may hold great promise in the creation of more advanced light-responsive smart materials.

Cooperative light-induced breathing of soft porous crystals via azobenzene buckling

Although light is a prominent stimulus for smart materials, the application of photoswitches as light-responsive triggers for phase transitions of porous materials remains poorly explored. Here we incorporate an azobenzene photoswitch in the backbone of a metal-organic framework producing light-induced structural contraction of the porous network in parallel to gas adsorption. Light-stimulation enables non-invasive spatiotemporal control over the mechanical properties of the framework, which ultimately leads to pore contraction and subsequent guest release via negative gas adsorption. The complex mechanism of light-gated breathing is established by a series of in situ diffraction and spectroscopic experiments, supported by quantum mechanical and molecular dynamic simulations. Unexpectedly, this study identifies a novel light-induced deformation mechanism of constrained azobenzene photoswitches relevant to the future design of light-responsive materials.

Fabrication of Laponite-Reinforced Dextran-Based Hydrogels for NIR-Responsive Controlled Drug Release.

Natural polymer gels with sensitivity to near-infrared (NIR) light have attracted the attention of scientists working on intelligent drug delivery systems. Compared to ultraviolet or visible light, NIR light has the advantages of strong trigger levels, deep penetration through affected tissues, and fewer side effects. Herein, we present a topical photothermal hydrogel for NIR-controlled drug delivery. The proposed DexIEM-GM-Laponite hydrogel was prepared through free radical polymerization of vinyl-functionalized dextran (DexIEM), vinyl-modified graphene oxide (GM), and Laponite; thereafter, the hydrogel was loaded with ciprofloxacin (CIP, an antibacterial drug) as a model drug. With the Laponite content increased, the density of crosslinking in the hydrogel increased, and its mechanical properties improved noticeably. Under NIR irradiation, the DexIEM-GM-Laponite hydrogel exhibited a photothermal property, where the surface temperature increased from 26.8 to 55.5 °C. The simulation of subcutaneous drug delivery experiments ex vivo showed that under the specified pork tissue thickness (2, 4, and 6 mm), the CIP release remained NIR-controllable. Additionally, the results of the antibacterial performance tests indicated the excellent antibacterial effect of the hydrogel, and the blood hemolysis ratio of the hydrogel was less than 5%, signifying good blood compatibility. This work will provide an avenue for the application of NIR light-responsive materials in antimicrobial therapy.

Wide-Range Time-Dependent Color-Tunable Light-Response Afterglow Materials via Absorption Compensation for Advanced Information Encryption.

Stimuli-responsive luminescent materials with time-dependent color are highly desirable in optical information encryption. In this study, multiple time-dependent color processes are achieved by light-responsive afterglow materials through the strategy of absorption compensation. Based on the single-emission band of light-responsive afterglow materials, the color of samples could show a time-dependent change from colored to colorless over several seconds. The strategy possesses high flexibility such that the stimulus light and emission color of light-responsive afterglow materials can be adjusted conveniently to adapt to various scenes. It is also beneficial to expand the capacity and complexity of information encryption. A three-color, time-resolved anticounterfeiting, and data encryption mode is demonstrated. This facile absorption compensation method based on light-response afterglow materials may promote the development of advanced dynamic information encryption.

Metallophilicity versus π-π Interactions: Argentophilicity in Porphyrin Dimer

The interaction between two unsupported Ag(III)porphyrins, which exist as a metalloporphyrin dimer has been studied. The UV-visible spectrum shows only slight change in Soret band position indicative of Ag(III) formation. Optimized structure of the complexes has clearly revealed that only metal-centered oxidation results in short Ag-N (porphyrin) distance with large distortion in the porphyrin macrocycle. The dispersion effect brings two rings more closer to form an unprecedented Ag(III)···Ag(III) interaction and cancel out the π-π repulsion. The interaction energy was found to be 55.34 Kcal/mol and was further supported by electron localization function, AIM analysis. The Ag(III) dimer also gives pink emission at low temperature. This type of interaction can be exploited to design several light responsive materials and molecular semiconductors.

Light-responsive polyurethanes: classification of light-responsive moieties, light-responsive reactions, and their applications.

Stimuli responsiveness has been an attractive feature of smart material design, wherein the chemical and physical properties of the material can be varied in response to small environmental change. Polyurethane (PU), a widely used synthetic polymer can be upgraded into a light-responsive smart polymer by introducing a light-sensitive moiety into the polymer matrix. For instance, azobenzene, spiropyran, and coumarin result in reversible light-induced reactions, while o-nitrobenzyl can result in irreversible light-induced reactions. These variations of light-stimulus properties endow PU with wide ranges of physical, mechanical, and chemical changes upon exposure to different wavelengths of light. PU responsiveness has rarely been reviewed even though it is known to be one of the most versatile polymers with diverse ranges of applications in household, automotive, electronic, construction, medical, and biomedical industries. This review focuses on the classes of light-responsive moieties used in PU systems, their synthesis, and the response mechanism of light-responsive PU-based materials, which also include dual- or multi-responsive light-responsive PU systems. The advantages and limitations of light-responsive PU are reviewed and challenges in the development of light-responsive PU are discussed.

Synergistically enhanced photothermal transition of a polyoxometalate/peptide assembly improved the antibiofilm and antibacterial activities.

We successfully developed an antimicrobial assembly (Mo154/TK-14) using molybdenum-polyoxometalate and a positively charged peptide of TK-14. It was characterized and assayed using zeta-potential, dynamic light scattering (DLS), and TEM measurements. The Mo154/TK-14 assembly showed an enhanced 808 nm absorption and, therefore, improved the photothermal conversion efficiency of Mo154 (30.3%) to 38.6%. Consequently, in comparison to 5 μM Mo154 without irradiation, both the biofilm formation and bacterial viability of S. aureus were 24.6% and 20.2%, respectively, for the Mo154/TK-14 assembly; the biofilm formation and bacterial viability were further decreased to 7.7% and 4.4% under 808 nm irradiation, respectively. Therefore, the Mo154/TK-14 assembly reflects convincing antibacterial properties compared to Mo154. This is due to the synergistic effect between the peptide-binding enhanced 808 nm absorption and the improved PTT properties. The antimicrobial assembly offers a novel strategy for the rational design of light-responsive antibacterial materials.

CxNy: New Carbon Nitride Organic Photocatalysts

The search for metal-free and visible light-responsive materials for photocatalytic applications has attracted the interest of not only academics but also the industry in the last decades. Since graphitic carbon nitride (g-C3N4) was first reported as a metal-free photocatalyst, this has been widely investigated in different light-driven reactions. However, the high recombination rate, low electrical conductivity, and lack of photoresponse in most of the visible range have elicited the search for alternatives. In this regard, a broad family of carbon nitride (CxNy) materials was anticipated several decades ago. However, the attention of the researchers in these materials has just been awakened in the last years due to the recent success in the syntheses of some of these materials (i.e., C3N3, C2N, C3N, and C3N5, among others), together with theoretical simulations pointing at the excellent physico-chemical properties (i.e., crystalline structure and chemical morphology, electronic configuration and semiconducting nature, or high refractive index and hardness, among others) and optoelectronic applications of these materials. The performance of CxNy, beyond C3N4, has been barely evaluated in real applications, including energy conversion, storage, and adsorption technologies, and further work must be carried out, especially experimentally, in order to confirm the high expectations raised by simulations and theoretical calculations. Herein, we have summarized the scarce literature related to recent results reporting the synthetic routes, structures, and performance of these materials as photocatalysts. Moreover, the challenges and perspectives at the forefront of this field using CxNy materials are disclosed. We aim to stimulate the research of this new generation of CxNy-based photocatalysts, beyond C3N4, with improved photocatalytic efficiencies by harnessing the striking structural, electronic, and optical properties of this new family of materials.

Multi-Component Collaborative Step-by-Step Coloring Strategy to Achieve High-Performance Light-Responsive Color-Switching.

Light‐responsive color‐switching materials (LCMs) are long‐lasting hot fields. However, non‐ideal comprehensive performance (such as color contrast and retention time cannot be combined, unsatisfactory repeatability, and non‐automated coloring mode) significantly hinder their development toward high‐end products. Herein, the development of LCMs that exhibit long retention time, good color contrast, repeatability, and the property of automatic coloring is reported. The realization of this goal stems from the adoption of a bio‐inspired multi‐component collaborative step‐by‐step coloring strategy. Under this strategy, a conventional one‐step photochromic process is divided into a “light+heat” controlled multi‐step process for the fabrication of the desired LCMs. The obtained LCMs can effectively resist the long‐troubled ambient‐light interference and avoid its inherent yellow background, thereby achieving the longest retention time and good repeatability. Multiple colors are generated and ultra‐fast imaging compatible with the laser‐printing technology is also realized. The application potential of the materials in short‐term reusable identity cards, absorptive readers, billboards, and shelf labels is demonstrated. The results reported herein can potentially help in developing and designing various high‐performance, switchable materials that can be used for the production of high‐end products.

Advances and opportunities in the exciting world of azobenzenes.

Azobenzenes are archetypal molecules that have a central role in fundamental and applied research. Over the course of almost two centuries, the area of azobenzenes has witnessed great achievements; azobenzenes have evolved from simple dyes to 'little engines' and have become ubiquitous in many aspects of our lives, ranging from textiles, cosmetics, food and medicine to energy and photonics. Despite their long history, azobenzenes continue to arouse academic interest, while being intensively produced for industrial purposes, owing to their rich chemistry, versatile and straightforward design, robust photoswitching process and biodegradability. The development of azobenzenes has stimulated the production of new coloured and light-responsive materials with various applications, and their use continues to expand towards new high-tech applications. In this Review, we highlight the latest achievements in the synthesis of red-light-responsive azobenzenes and the emerging application areas of photopharmacology, photoswitchable adhesives and biodegradable materials for drug delivery. We show how the synthetic versatility and adaptive properties of azobenzenes continue to inspire new research directions, with limits imposed only by one's imagination.

Light-Responsive Soft Actuators: Mechanism, Materials, Fabrication, and Applications

Soft robots are those that can move like living organisms and adapt to the surrounding environment. Compared with traditional rigid robots, the advantages of soft robots, in terms of material flexibility, human–computer interaction, and biological adaptability, have received extensive attention. Flexible actuators based on light response are one of the most promising ways to promote the field of cordless soft robots, and they have attracted the attention of scientists in bionic design, actuation implementation, and application. First, the three working principles and the commonly used light-responsive materials for light-responsive actuators are introduced. Then, the characteristics of light-responsive soft actuators are sequentially presented, emphasizing the structure strategy, actuation performance, and emerging applications. Finally, this review is concluded with a perspective on the existing challenges and future opportunities in this nascent research frontier.

Bioinspired light-responsive materials for on-demand drug delivery

Bioinspired light-responsive materials for on-demand drug delivery

Low-power photo-carving of dye-volatile co-crystals: the sublime cutting edge of light-responsive materials

Low-power photo-carving of dye-volatile co-crystals: the sublime cutting edge of light-responsive materials

Flexible light-responsive self-healing polymeric composite film based on two-dimensional MoS2 - organic halide perovskite longitudinal heterostructure

Organic hybrid perovskite (OHP) is one of the most attractive optical absorbable and reactive materials. However, excellent light-responsive self-healing polymeric composite film based on OHP is difficult to obtain. Here, four two-dimensional (2D) OHP with different typical sizes and morphologies were prepared by regulating with four different typical diamines, and the novel scale-like plate-stack 2D MoS2-OHP longitudinal heterostructure was fabricated. Then, a valid structure strategy, utilizing 2D MoS2-OHP as the light-responsive material and self-healing polyurethane (PU) as polymer matrix, is firstly developed to realize high performance light response. Among these light responsive self-healing polymer materials, the MoS2-OHP-3/PU composite film exhibited excellent figures of merit, including high light stimulation response (ΔR value was 70.0589 MΩ), strong tensile strength value (8.06 ± 0.05 MPa), high maximum elongation (467 ± 13.82%), high self-healing efficiency (80% for mechanical properties, 95% for light-response) and ultra-high humidity stability (86% for light response, 81.89% mechanical properties). This work provided a novel method and a feasible substrate for the development of self-healing, flexible and scalable intelligent response soft materials.

Spiropyran dyes

Abstract This article furnishes an introduction to one of the most well-known classes of photochromic colorant. While the properties of spiropyran dyes inspired pioneering efforts to exploit photochromism for industrial applications, their lack of robustness held them back from commercialization. Nevertheless, this type of dye remains at the heart of much of the work to develop light-responsive materials upon which many potential applications in different fields of scientific and technological endeavor depend. The article describes the photochromism, synthesis, and applications of spiropyran colorants with an emphasis on the structural subtype that has attracted the greatest scrutiny. It also acts as a springboard to sources of more detail on these aspects.

Tetraphenylethylene based amphiphilic derivatives: The self-assembly, photo-responsiveness and their application for erasable fluorescent ink

Since the discovery of aggregation induced emission (AIE) phenomenon, various stimuli-responsive materials have been rapidly developed. However, the development of self-assembled amphiphilic light-responsive materials in aqueous solution needs to be solved urgently. In this work, three new amphiphilic tetraphenylethylene (TPE) derivatives (TPE-1, TPE-2 and TPE-3) with AIE properties and photochromism were synthesized and investigated. Owing to the different electron-donating abilities of the three groups attached to TPE units, the TPE-1, TPE-2 and TPE-3 displayed blue-green, yellow-green, and orange fluorescence emission in the aggregation state respectively. Furthermore, ordered nanoparticles formed via self-assembly in aqueous solution showed interesting photocyclization behaviors, which lead to fluorescence quenching under ultraviolet light irradiation (λ = 365 nm). Therefore, the compounds can be used as anti-counterfeiting ink in the information encryption due to their amphiphilicity and photo-responsiveness. This work contributes new members to the amphiphilic light-responsive materials family and demonstrates the potential for applications in the fields of optical information storage, information security protection, and erase/rewrite systems.

Heat- and Light-Responsive Materials Through Pairing Dynamic Thiol-Michael and Coumarin Chemistry.

Covalent adaptable networks (CANs) based on the thiol-Michael (TM) linkages can be thermal and pH responsive. Here, a new vinyl-sulfone-based thiol-Michael crosslinker is synthesized and incorporated into acrylate-based CANs to achieve stable materials with dynamic properties. Because of the reversible TM linkages, excellent temperature-responsive re-healing and malleability properties are achieved. In addition, for the first time, a photoresponsive coumarin moiety is incorporated with TM-based CANs to introduce light-mediated reconfigureability and postpolymerization crosslinking. Overall, these materials can be on demand dynamic in response to heat and light but can retain mechanical stability at ambient condition.

Light-Responsive Luminescent Materials for Information Encryption Against Burst Force Attack.

Optical encryption with easy operation, multichannel and high security has been one of the most significant technologies for information security. Stimuli-responsive luminescent materials have emerged as an ideal candidate for optical encryption, owing to its smart responsive property and high security. Herein, a type of light-responsive multicolor luminescent materials for high-security information encryption, which are fabricated by combining sensitizer, consumption unit, and emitter is developed. Different types of sensitizers to achieve different stimulus light responses, and multicolor light-responsive luminescent can be obtained by varying the composition of perovskite nanocrystals emitter can be selected. Both stimulus light and emission color can be used as distinguishable encoding dimensions, which enable multiplexed encoding with high capacity and complexity. Importantly, the controllable consumption can be manipulated by varying the concentration of consumption unit, so the programmed information encoded in different channels can be selectively read and erased simultaneously by varying stimulus light. The method makes the encryption information highly resistive to brute force trial-and-error attacks, which achieves high security level of information protection.

Light‐Powered Microrobots: Challenges and Opportunities for Hard and Soft Responsive Microswimmers

Microrobots In article number 2000256, Ada-Ioana Bunea and co-workers provide a critical overview of how microrobots can be manufactured and manipulated using light. The cover image shows blue structures printed in hard polymer and precisely manipulated by optical trapping with focused near-infrared light, together with orange structures printed using soft, light-responsive materials, which change shape in response to green light. Cover image drawn by Alexandre Wetzel.