Photoresponsive Materials Research Articles

Photoresponsive porous materials.

Molecular machines, switches, and motors enable control over nanoscale molecular motion with unprecedented precision in artificial systems. Integration of these compounds into robust material scaffolds, in particular nanostructured solids, is a fabrication strategy for smart materials with unique properties that can be controlled with external stimuli. Here, we describe a subclass of these structures, namely light-responsive porous materials metal–organic frameworks (MOFs), covalent–organic frameworks (COFs), and porous aromatic frameworks (PAFs) appended with molecular photoswitches. In this review, we provide an overview of a broad range of light-responsive porous materials focusing on potential applications.

Collective structural properties of embedded molecular motors in functionalized metal-organic frameworks.

Photo-responsive molecular motors incorporated in soft porous materials enable the amplification of the motion of individual motor units by employing their collective and cooperative behavior. Metal-organic frameworks (MOFs) provide in this regard, due to their structural diversity and modular assembly, a unique matrix to construct well-defined and systematically tunable molecular environments for the embedding of molecular motors. However, despite advances in the development of such photo-responsive functional materials, a thorough understanding of the governing interactions at the atomic scale has been missing so far, limiting the possibility of predicting and fully exploring the potential of these assembled machineries. Here, we present a conformational study to unravel the collective structural behavior and elucidate the impact of motor-motor interactions on the local and global properties of the scaffold. In particular, our work highlights the impact of full conversion of the embedded molecular motors on the overall network topology of the MotorMOF and thus acts as a benchmark for future studies to further explore the correlation of responsive building units with the resulting functionality of these hierarchical systems.

Sunlight-activated phase change materials for controlled heat storage and triggered release

Photo-responsive organic phase change materials that can absorb filtered solar radiation in the visible range to store both latent heat and photon energy are demonstrated.

The recent progress on metal-organic frameworks for phototherapy.

Some infectious or malignant diseases such as cancers are seriously threatening the health of human beings all over the world. The commonly used antibiotic therapy cannot effectively treat these diseases within a short time, and also bring about adverse effects such as drug resistance and immune system damage during long-term systemic treatment. Phototherapy is an emerging antibiotic-free strategy to treat these diseases. Upon light irradiation, phototherapeutic agents can generate cytotoxic reactive oxygen species (ROS) or induce a temperature increase, which leads to the death of targeted cells. These two kinds of killing strategies are referred to as photodynamic therapy (PDT) and photothermal therapy (PTT), respectively. So far, many photo-responsive agents have been developed. Among them, the metal-organic framework (MOF) is becoming one of the most promising photo-responsive materials because its structure and chemical compositions can be easily modulated to achieve specific functions. MOFs can have intrinsic photodynamic or photothermal ability under the rational design of MOF construction, or serve as the carrier of therapeutic agents, owing to its tunable porosity. MOFs also provide feasibility for various combined therapies and targeting methods, which improves the efficiency of phototherapy. In this review, we firstly investigated the principles of phototherapy, and comprehensively summarized recent advances of MOF in PDT, PTT and synergistic therapy, from construction to modification. We expect that our demonstration will shed light on the future development of this field, and bring it one step closer to clinical trials.

Spectral and kinetic manifestations of chain flexibility and polarity in the reversible photoisomerization of spironaphthoxazine-based acrylic copolymers

Future advances in photoresponsive materials essentially depend on our knowledge about how the substrates, and typically their Tg and polarity, affect their photochromic properties.

Synthesis, photochemical isomerization and photophysical properties of hydrazide–hydrazone derivatives

The structure–property relationships for the hydrazide–hydrazone derivatives were investigated to provide new insights into the design of photo-responsive materials.

Programmable photoresponsive materials based on a single molecule via distinct topochemical reactions.

Engineering the preorganization of photoactive units remains a big challenge in solid-state photochemistry research. It is of not only theoretical importance in the construction of topochemical reactions but also technological significance in the fabrication of advanced materials. Here, a cyanostilbene derivative, (Z)-2-(3,5-bis(trifluoromethyl)phenyl)-3-(naphthalen-2-yl) acrylonitrile (BNA), was crystallized into two polymorphs under different conditions. The two crystals, BNA-α and BNA-β, have totally different intra-π-dimer and inter-π-dimer hierarchical architectures on the basis of a very simple monomer, which provides them with distinct reactivities, functions and photoresponsive properties. Firstly, two different types of solid-state [2 + 2] photocycloaddition reaction: (i) a typical olefin–olefin cycloaddition reaction within the symmetric π-dimers of BNA-α and (ii) an unusual olefin-aromatic ring cycloaddition reaction within the offset π-dimers of BNA-β have been observed, respectively. Secondly, the crystal of BNA-α can be bent to 90° without any fracture, exhibiting outstanding flexibility upon UV irradiation, while the reversible photocycloaddition/thermal cleavage process (below 100 °C) accompanied by unique fluorescence changes can be achieved in the crystal of BNA-β. Finally, micro-scale photoactuators and light-writable anti-counterfeiting materials have been successfully fabricated. This work paves a simple way to construct smart materials through a bottom-up way that is realized by manipulating hierarchical architectures in the solid state.

Melanin-loaded CpG DNA hydrogel for modulation of tumor immune microenvironment

Photothermal immunotherapy has emerged as one of the most potent approaches for cancer treatment, but this strategy has suffered from the lack of biodegradability of the photoresponsive materials. In this study, we aimed to develop biodegradable materials for photothermal immunotherapy. To this end, we designed a DNA CpG hydrogel (DH, generated by rolling-circle amplification), loaded it with bis-(3′-5′)-cyclic dimeric guanosine monophosphate (G/DH), and coated the formulation with melanin (Mel/G/DH). Mel/G/DH exhibited a temperature increase upon near infrared (NIR) illumination. In vitro, Mel/G/DH plus NIR (808 nm) irradiation, induced the exposure of calreticulin on CT26 cancer cells, and significantly activated the maturation of dendritic cells (DC). In vivo, local administration of Mel/G/DH (+NIR) exerted photothermal killing of primary tumors and induced maturation of DC in lymph nodes. Treatment of primary tumors with Mel/G/DH(+NIR) prevented the growth of rechallenged tumors at a distant site. Survival was 100% in mice treated with Mel/G/DH(+NIR), 5-fold higher than the group treated with Mel/G(+NIR). Mel/G/DH(+NIR) treatment remodeled the immune microenvironment of distant tumors, increasing cytotoxic T cells and decreasing Treg cells. Taken together, the results of this study suggest the potential of Mel/G/DH as a platform for modulating tumor immune microenvironment aimed at preventing the recurrence of distant tumors.

Semi-convertible Hydrogel Enabled Photoresponsive Lubrication

Summary A semi-convertible hydrogel with reversible photoresponsive supramolecular lubricating ability is demonstrated by integrating a responsive supramolecular system of α-cyclodextrins/polyethylene glycol (α-CD/PEG) and competitive guest 1-[p-(phenylazo)benzyl]pyridinium bromide (AzoPB) within a poly(vinyl alcohol) (PVA) and polyacrylamide (PAAm) framework. The competitive host-guest interaction between α-CD/PEG supramolecular network and AzoPB after UV and visible-light irradiation enables the appearance and disappearance of the sol-state layer on the hydrogel surface while the PVA and PAAm consistently keeps the framework. This semi-convertible process realizes the reversible photoresponsive lubricating ability and variable toughness. We envision that this finding will offer a possible way for fabricating novel smart devices far beyond lubrication, leading to an emerging branch of interdisciplinary materials science that integrates supramolecular chemistry, hydrogel, and surface science.

Sequential and Diverse Synthesis of BN-Heterocycles and Investigation of Their Photoreactivity.

Substituents modification of BN-heterocycles on the boron atom has proven important to the photoreactivity and optoelectronic properties of BN-heterocycles. We developed a sequential and diverse synthetic strategy toward BN-heterocycles, in which the boron building block can be introduced with fully pre-functionalized substituents (Route A) or the substituents can be partially (Route B) or fully (Route C) modified after borylation. These three routes are complementary to provide more diverse BN-heterocycles, which will find broad applications in manipulating/controlling molecular transformations and the development of new photoresponsive materials.

Organic photoresponsive materials for information storage: a review

Organic photoresponsive materials can undergo various reversible variations in certain physical and chemical properties, such as optical properties, electrochemical properties, conformation, and conductivity, upon photoirradiation. They have been widely applied in various optoelectronic fields, especially in information storage. We summarize research progress on organic photoresponsive materials for information storage. First, the design strategies and photoswitching mechanisms for various kinds of organic photoresponsive materials, including small organic molecules, metal complexes, polymers, supramolecules, and cholesteric liquid crystals, are systematically summarized. These materials exhibit reversible changes of absorption and/or emission properties in response to different wavelengths of light. Subsequently, the applications of these organic materials in information storage, such as data (re)writing and erasing, encryption and decryption, and anticounterfeiting, are introduced in detail. Finally, the current challenges and future directions in this rapidly growing research field are discussed. The review will provide important guidance on the future works about the design of excellent organic photoresponsive materials for optoelectronic applications.

Dynamic azopolymeric interfaces for photoactive cell instruction.

The ability to affect a wide range of biophysical properties through the use of light has led to the development of dynamic cell instructive materials. Using photoresponsive materials such as azopolymers, smart systems that use external, minimally damaging, light irradiation can be used to trigger specific surface morpho-physical properties in the presence of living cells. The interaction of light with an azopolymer film induces a mass migration phenomenon, allowing a variety of topographic patterns to be embossed on the polymeric film. Photoisomerization induces conformational changes at the molecular and macroscopic scale, resulting in light-induced variations of substrate morphological, physical, and mechanical properties. In this review, we discuss the photoactuation of azopolymeric interfaces to provide guidelines for the engineering and design of azopolymer films. Laser micropatterning for the modulation of azopolymer surfaces is examined as a way to diversify the capabilities of these polymers in cellular systems. Mass migration effects induced by azopolymer switching provides a foundation for performing a broad range of cellular manipulation techniques. Applications of azopolymers are explored in the context of dynamic culture systems, gaining insight into the complex processes involved in dynamic cell-material interactions. The review highlights azopolymers as a candidate for various applications in cellular control, including cell alignment, migration, gene expression, and others. Recent advances have underlined the importance of these systems in applications regarding three-dimensional cell culture and stem cell morphology. Azopolymers can be used not only to manipulate cells but also to probe for mechanistic studies of cellular crosstalk in response to chemical and mechanical stimuli.

Development of photoresponsive coumarin-modified ethylene-co-vinyl alcohol copolymers with antifouling behavior

In this work, the modification of ethylene-co-vinyl alcohol (EVOH) copolymer with a coumarin derivative, 7-(hydroxyethoxy)-4-methyl coumarin (HEOMC), has been performed through the incorporation of different reactive groups, p-nitrophenyl chloroformate, succinic anhydride and phthalic anhydride as different linkers between coumarin and EVOH with the aim to obtain photo-responsive materials with improved protein absorption resistance. After purification, the modification degree was calculated by nuclear magnetic resonance and ultraviolet-visible spectroscopy. The thermal properties revealed the crystallinity loss and higher maximum degradation temperatures when EVOH is modified with coumarin derivative. Copolymers were successfully photo-crosslinked through the photo-responsive behavior of coumarin moieties. The micro-hardness test shown an increase of the mechanical performance due to the coumarin presence. The water contact angle measurements revealed that while coumarin-modified EVOH copolymers present a higher hydrophilic behavior than EVOH, the photo-dimerization process mainly leads to slightly deviations on the surface wettability of neat EVOH. Finally, the absorption of bovine serum albumin onto the surface of the coumarin-modified materials revealed enhanced antifouling properties, particularly after the photo-crosslinked process. Therefore, the introduction of coumarin through different chain extenders leads to functional materials with tunable photo-responsive performance and protein absorption resistance.

Azobenzene Based Photo-responsive Mechanical Actuator Fabricated by Intermolecular H-bond Interaction

Photo-responsive mechanical actuator is a class of stimuli-responsive materials transferring light to mechanical energy through macroscopic transformation. To fabricate photo-responsive mechanical actuator, soft polymeric materials crosslinked with functional bridging structures are desired. Supramolecular interaction is a relatively common way to fabricate crosslinked materials due to its excellent self-assembly performance. And azobenzene and derivatives are ideal candidates of photo-responsive materials because of the unique photo-induced trans-cis isomerization. Here, a new kind of crosslinked materials based on supramolecular interaction between 4,4′-dihydroxyazobenzene and chitosan is reported. Under 355 nm irradiation, the macroscopic bending of polymeric materials occurs rapidly due to the photo-isomerization of 4,4′-dihydroxyazobenzene. Meanwhile, the photo-responsive mechanical actuator can also lift weight which is up to 200 times that of the actuator itself, and convert energy from light to mechanical work efficiently. This report suggests a new kind of photo-responsive actuator based on supramolecular interaction and may be helpful to contribute a theoretical basis to the design and synthesis of photo-responsive mechanical actuator suitable for large-scale manufacturing industrialization in future.

Advanced multifunctional composite phase change materials based on photo-responsive materials

Phase change materials (PCMs) with excellent energy storage capacity and approximately constant temperature during the phase transition process can absorb and store thermal energy from their surroundings and release it when needed, thereby improving the energy utilization efficiency. However, thermal energy storage requires the temperature of PCMs above their melting points by passive heat absorption, which lacks of proactive control and has great limitations in actual applications. Emerging photo-responsive materials bring some new potentials to the PCM field owing to their distinct response to light and other special features, which can meet the specific requirements such as photothermal conversion in extreme environments. Meanwhile, photo-responsive materials have integrated some new functions into PCMs other than thermal energy storage. However, a comprehensive overview of multifunctional photo-responsive composite PCMs is still missing. Herein, we provide a comprehensive review of the state-of-the-art applications of photo-responsive PCMs. The mechanisms, current developments and further perspectives concerning multifunctional photo-responsive composite PCMs are also highlighted. Photothermal, photoluminescent and photocatalytic materials used in PCMs. • A comprehensive review of the recent advances in the application of photo-responsive materials in PCMs is reviewed. • This review provides in-depth insights into multifunctional composite PCMs based on photo-responsive materials. • Mechanism and perspectives on multifunctional photo-responsive composite PCMs are highlighted.

Mechanistic Process Understanding of the Biomimetic Construction of Porphyrin-Based Light-Capturing Antennas from Self-Assembled Fmoc-Blocked Peptide Templates

Natural photosynthesis provides a perfect example of solar energy utilization that converts CO₂ to carbohydrates at high efficiency. Herein, an innovative approach was developed to construct light-harvesting antennas via the precise control of porphyrin aggregation and platinum organization on the surface of the self-assembled structures of Fmoc-blocked peptides (Fmoc-ChaChaGK-NH₂ and Fmoc-FFGK-NH₂). The photophysical properties and the photocatalytic activity of the antenna are dependent on the aggregating structure of porphyrin and arrangement of Pt nanoparticles, which are related closely to the molecular structure of peptides, as well as to the peptide/porphyrin molar ratio and their concentrations. The Fmoc-ChaChaGK/porphyrin complexes prepared at a peptide (Fmoc-ChaChaGK)/TPPS molar ratio of 2 and TPPS concentration of 500 μM possess the highest photo-to-electric conversion efficiency and photocatalytic ability in transforming light energy into chemical energy and storing in the energy-storage molecules (reduced nicotinamide adenine dinucleotide, NADH). The results demonstrate the correlation between the hierarchical structure and light-responsive properties of the antenna and highlight the mediating effect of noncovalent interactions in the construction and stabilization of the photoresponsive materials.

Fabrication of switchable surface wettability with UV-triggered on cotton fabric

A series of switchable wettability cotton fabrics were fabricated with inorganic oxide nanoparticles (TiO2 or Al2O3) modification of stearic acid (STA). By adjusting the additive amount of binary of inorganic oxide nanoparticles, five kinds of samples were obtained. These cotton fabrics were fully characterized, and all the samples possessed superhydrophobic surface. Under the UV irradiation, the photoresponsive materials TiO2 could alter the fabrics wetting state, but the STA modified UV inactive Al2O3 nanoparticles could remain the superhydrophobicity of samples. The changed wettability fabrics recovered the superhydrophobicity after heating, and the switchable wettability of the samples was maintained even after several UV irradiation/heating cycles.

Tuning the Optical Band Gap of Semiconductor Nanocomposites-A Case Study with ZnS/Carbon.

The linear photochemical response of materials depends on two critical parameters: the size of the optical band gap determines the onset of optical excitation, whereas the absolute energetic positions of the band edges define the reductive or oxidative character of photo-generated electrons and holes. Tuning these characteristics is necessary for many potential applications and can be achieved through changes in the bulk composition or particle size, adjustment of the surface chemistry or the application of electrostatic fields. In this contribution the influence of surface chemistry and fields is investigated systematically with the help of standard DFT calculations for a typical case, namely composites prepared from ZnS quantum dots and functionalized carbon nanotubes. After comparing results with existing qualitative and quantitative experimental data, it is shown conclusively, that the details of the surface chemistry (especially defects) in combination with electrostatic fields have the largest influence. In conclusion, the development of novel or improved photoresponsive materials therefore will have to integrate a careful analysis of the interplay between surface chemistry, surface charges and interaction with the material environment or substrate.

Dual‐Function HKUST‐1: Templating and Catalyzing Formation of Graphitic Carbon Nitride Quantum Dots Under Mild Conditions

AbstractGraphitic carbon nitride quantum dots (g‐CNQDs) are highly promising photoresponsive materials. However, synthesis of monodispersed g‐CNQDs remains challenging. Here we report the dual function of MOF [Cu3BTC2] (HKUST‐1) as a catalyst and template simultaneously to prepare g‐CNQDs under mild conditions. Cyanamide (CA), a graphitic carbon nitride precursor, catalytically dimerized inside the larger MOF cavities at 90 °C and condensed into g‐CNQDs at 120 °C in a controlled fashion. The HKUST‐1 template was stable under the reaction conditions, leading to uniform g‐CNQDs with a particle size of 2.22±0.68 nm. The as prepared g‐CNQDs showed photoluminescence emission with a quantum yield of 3.1 %. This concept (MOF dual functionality) for catalyzing CA polycondensation (open metal sites (OMSs) effect) and controlling the produced particle size (pore‐templating effect), together with the tunable MOF porosity, is expected to produce unique g‐CNQDs with controllable size, morphology, and surface functionality.

Dual-Function HKUST-1: Templating and Catalyzing Formation of Graphitic Carbon Nitride Quantum Dots Under Mild Conditions.

Graphitic carbon nitride quantum dots (g‐CNQDs) are highly promising photoresponsive materials. However, synthesis of monodispersed g‐CNQDs remains challenging. Here we report the dual function of MOF [Cu3BTC2] (HKUST‐1) as a catalyst and template simultaneously to prepare g‐CNQDs under mild conditions. Cyanamide (CA), a graphitic carbon nitride precursor, catalytically dimerized inside the larger MOF cavities at 90 °C and condensed into g‐CNQDs at 120 °C in a controlled fashion. The HKUST‐1 template was stable under the reaction conditions, leading to uniform g‐CNQDs with a particle size of 2.22±0.68 nm. The as prepared g‐CNQDs showed photoluminescence emission with a quantum yield of 3.1 %. This concept (MOF dual functionality) for catalyzing CA polycondensation (open metal sites (OMSs) effect) and controlling the produced particle size (pore‐templating effect), together with the tunable MOF porosity, is expected to produce unique g‐CNQDs with controllable size, morphology, and surface functionality.