Photochromism into nanosystems: towards lighting up the future nanoworld

Photoswitchable WO3-x QD/Cu NC composite films for efficient UV detection and dual-mode anticounterfeiting

Photoswitchable fluorescent materials (PFMs) have attracted considerable attention owing to their intrinsic advantages of non-contact operation, cleanliness, and non-invasiveness. Conventional PFMs always require complicated preparation processes with poor fluorescence switching properties, which are affected by the Föster resonance energy transfer (FRET) or photoinduced electron transfer (PET) mechanism. Herein, WO3-x QD/Cu NC composite films were prepared on different substrates via a solution casting method and display outstanding fluorescence switching properties owing to the super photochromic performance of WO3-x QDs and aggregation-induced fluorescence of Cu NCs. The composite film exhibits reversible on/off switchable fluorescence under UV light irradiation and heat treatment based on the inner filter effect (IFE) mechanism. The composite film shows dynamic variations in dual-mode signals, and the applications of UV sensing and anti-counterfeiting are analyzed. Sensitive dual-mode detection is achieved in UV sensing, particularly for UVB. The composite film exhibits a dual-modal imaging capability with good reproducibility and high resolution for security information encryption and anti-counterfeiting. This work provides a novel strategy for fabricating advanced PFMs for multiple optical applications.

Chiral alkynyl Au(I) complexes: Enhancing chiroptical amplification of circularly polarized luminescence through supramolecular helices

The construction of helical structures through self-assembly and the exploration of their formation mechanisms not only amplify chiroptical properties but also provide profound insights into the structures and functions of natural helices. In this study, we developed a chiral Au(I) system based on BINAP and alkynyl ligands. The modification of the length or number of alkyl chains at the terminal positions of the alkynyl ligands significantly impacted the self-assembly behavior of the complexes. Complexes (S)/(R)-2, (S)/(R)-3, (S)/(R)-5, and (S)/(R)-6 demonstrated aggregation-induced circularly polarized luminescence (AICPL). Notably, complexes (S)-6 and (R)-6 were capable of self-assembling into highly ordered helical aggregates, resulting in amplified glum values reaching an order of magnitude of 10-2. The unique double-helix stacking observed in the crystal structure of (R)-6 provided a plausible explanation for the formation of such helical aggregates. This research offers a strategy for achieving amplified CPL through artificial helices, providing new insights and guidance for the development of Au(I) complexes with CPL activity.

Smart Polydimethylsiloxane Materials: Versatility for Electrical and Electronic Devices Applications

Bio-inspired autonomous smart polydimethylsiloxane (PDMS) and its composite materials hold immense promise for a wide range of applications in electrical and electronic devices. These materials mimic natural protective mechanisms with self-healing, self-reporting, and self-cleaning properties, enabling innovative and efficient device design. Smart PDMS materials autonomously activate repair mechanisms in response to mechanical or electrical damage, achieving rapid structural and functional recovery and preventing failure due to the accumulation of minor damage. These materials can intuitively report their status through striking color changes, fluorescence, or luminescence when exposed to external stimuli, providing efficient and practical visual feedback for device health monitoring and fault warning. They also have the capacity to effectively eliminate contaminants and ice deposits from their surfaces, thereby ensuring stable device operation. This review aims to introduce the current research progress in self-healing, self-cleaning, and self-reporting PDMS materials. The review systematically discusses the principles, methodological innovations, mechanistic analysis, and applications of these materials, highlighting their significant potential for applications in the field of electrical and electronic devices. Moreover, the review provides an in-depth analysis of the key challenges facing current research and offers insights into future research directions and strategies.

Soft Matter Photonics: Interplay of Soft Matter and Light

The light-soft matter interaction and its applications form the foundation of Soft Matter Photonics, here termed "Soft Mattonics", positioning it as fertile ground for developing next-generation photonic technologies. Over the past few decades, this rapidly evolving field has achieved significant advancements, leading to successful applications across a wide range of disciplines, including optoelectronics, photonics, information technology, material science, robotics, biomedicine, and astronomy. In this Perspective, we provide an overview of Soft Mattonics, highlighting recent developments in light-controlled soft matter and their applications in light field manipulating. Additionally, we offer insights into future research directions for Soft Mattonics, with an emphasis on both foundational research and practical applications that will drive continued growth and innovation in this field.

Manipulation of Chemistry and Biology with Visible Light Using Tetra-ortho-Substituted Azobenzenes and Azonium Ions

Molecular photoswitches are used for precise and reversible control over the properties and function of chemical, biological and material systems, offering exceptional spatiotemporal control. Their current development focuses on enabling operation with non-damaging and deep tissue penetrating visible/near-IR light. In this context, tetra-ortho-substituted azobenzenes and azonium ions play a leading role, thanks to their unique photophysical properties and easily modifiable structure. However, it is only recently that synthetic approaches to those sterically demanding systems have been established and their structure-photochemistry relations have been understood to provide general rules for their tuning to a given application. In this review, we provide a comprehensive overview of this family of molecular photoswitches, providing an analysis of their photophysical properties, followed by a discussion of the available synthetic methodologies. Finally, we showcase the versatility of tetra-ortho-substituted azobenzenes and azonium ions for enabling light-control in biological and material sciences, providing multiple insights for future applications.

Visible-Light Switchable Rings and Chains in Dynamic Covalent Imine Chemistry

The self-assembliy of red-light switchable, functionalised ortho-difluoroazobenzene isomers E-/Z-A with aliphatic diamines exhibits an alternating match/mismatch behaviour depending on the diamine's chain length. While even-numbered diamines exclusively form imine macrocycles with the Z-configured azobenzene isomer, odd-numbered diamines form photoswitchable, defined macrocycles. The formation of Z,Z-A2X2-type macrocycles was demonstrated with butane-1,4- (B) and hexane-1,6-diamine (H), while additionally E,E-A2X2-type macrocycles were obtained with propane-1,3- (Pr), pentane-1,5-diamine (Pe), and diethylene glycol bisamine (O), validated by single-crystal X-ray structures of E,E-A2Pr2 and E,E-A2O2. The observed reactivity differences arise from the preferred conformations of the flexible diamines in solution, which alternate predictably with odd and even numbers of methylene groups, investigated by 19F-DOSY NMR experiments, MALDI-MS measurements, and UV/Vis spectroscopy. These findings provide detailed insight into photoresponsive self-assembled systems and highlight the potential of azobenzenes in dynamic covalent chemistry, offering new opportunities for controlling structure and function in adaptive materials.

Blue-/near-infrared light-triggered photochromism in a reinforced acceptor-acceptor type dithienylethene with aggregation-induced emission

The development of photochromic dithienylethene (DTE) derivatives activated by visible light, particularly those exhibiting aggregation-induced emission (AIE) properties, is highly sought after for applications in photoelectric functional materials and biological systems. In this study, we rationally designed and successfully synthesized a novel cyanostilbene- and nitro-functionalized DTE derivative (6) featuring a reinforced acceptor (A)-DTE-acceptor (A) structural motif. Each of the two cyanostilbene fragments bearing nitrobenzene groups imparts both electron-withdrawing effects and AIE characteristics, thereby ensuring efficient visible light-driven photochromic performance. The chemical structure of compound 6 was characterized using standard techniques, including 1H NMR, 13C NMR, and HRMS. As anticipated, the resulting DTE (6) demonstrates efficient photochromism in various solvents when alternately irradiated with blue light (λ = 460-470 nm) and near-infrared (NIR) light (λ = 730-740 nm). Prior to blue light irradiation, the AIE performance and solid-state luminescence behavior were assessed. Furthermore, DTE (6) exhibits enhanced photoswitching behavior within a poly(methyl methacrylate) (PMMA) film. The experimental findings are corroborated by density functional theory (DFT) calculations. Ultimately, this derivative has been successfully employed for information recording and erasing, thereby demonstrating its potential for information storage and encryption.

Self-Assembled Metal Complexes in Biomedical Research

Cisplatin is widely used in clinical cancer treatment; however, its application is often hindered by severe side effects, particularly inherent or acquired resistance of target cells. To address these challenges, an effective strategy is to modify the metal core of the complex and introduce alternative coordination modes or valence states, leading to the development of a series of metal complexes, such as platinum (IV) prodrugs and cyclometalated complexes. Recent advances in nanotechnology have facilitated the development of multifunctional nanomaterials that can selectively deliver drugs to tumor cells, thereby overcoming the pharmacological limitations of metal-based drugs. This review first explores the self-assembly of metal complexes into spherical, linear, and irregular nanoparticles in the context of biomedical applications. The mechanisms underlying the self-assembly of metal complexes into nanoparticles are subsequently analyzed, followed by a discussion of their applications in biomedical fields, including detection, imaging, and antitumor research.

Visible-Light-Driven Fluorescence Turn-on Photoswitches With Near Quantitative Photocyclization Yield

Photoswitchable fluorescent materials have gained significant attention for their potential in advanced information encryption and anti-counterfeiting applications. However, the common use of UV light to trigger the isomerization processes leads to photobleaching and poor fatigue resistance. Visible-light-driven fluorescent photoswitches are highly desirable, but achieving high cyclization yield remains challenging. Herein, it is reported that all visible-light-driven turn-on fluorescence in dimethoxyphenyl functionalized diarylethene isomers. The open-ring form of o-DMPB and p-DMPB exhibits near quantitative conversion yields (up to 94%) under 405 nm visible light, attributed to the strong electron-donating character. In contrast, the meta isomer m-DMPB shows limited response to visible light, with a ring-closing yield of 22%. Furthermore, all photoswitches display good thermal stability, photostability, and fatigue resistance. Notably, o-DMPB demonstrates promising applications in anti-counterfeiting, information encryption, and photorewritable patterns. This work provides a valuable strategy for the development of high-performance fluorescent photoswitches.

Solvent-Free Artificial Light-Harvesting System in a Fluid Donor with Highly Efficient Förster Resonance Energy Transfer

Multi-step Förster resonance energy transfer (FRET) plays a vital role in photosynthesis. While the energy transfer efficiency (ΦET) of a naturally occurring system can reach 95%, that of most artificial light-harvesting systems (ALHSs) is still limited. Herein, we propose a strategy to construct highly efficient ALHSs using a blue-emitting, supercooled ionic compound of naphthalimide (NPI) as the donor, a green-emitting BODIPY derivate as a relay acceptor, and a commercially available, red-emitting dye [rhodamine B (RhB)] as the final acceptor. The broad emission of the fluid donor can overlap simultaneously with the absorption of BODIPY and RhB, enabling the occurrence of a sequential FRET from NPI to BODIPY to RhB as well as a parallel FRET directly from NPI to RhB. These two complementary energy transfer routes lead to an overall ΦET up to 97.4%, which is the champion among all of the reported ALHSs and is also higher than that found in plants and photosynthetic bacteria. This strategy is universal, and ΦET of the system could be further improved by optimizing the structures of the fluid donor and relay acceptor.

Advanced Design for Stimuli-Reversible Chromic Wearables With Customizable Functionalities

Smart wearable devices with dynamically reversible color displays are crucial for the next generation of smart textiles, and promising for bio-robots, adaptive camouflage, and visual health monitoring. The rapid advancement of technology brings out different categories that feature fundamentally different color-reversing mechanisms, including thermochromic, mechanochromic, electrochromic, and photochromic smart wearables. Although some reviews have showcased relevant developments from unique perspectives, reviews focusing on the advanced design of flexible chromic wearable devices within each category have not been reported. In this review, the development history and recent progress in smart chromic wearables across each category are systematically examined. The design strategies for each chromic wearable device are outlined with a focus on functional materials, synthesis processes, and advanced applications. Furthermore, integrated devices based on dual-stimuli and multi-stimuli responsive chromics with customizable functionalities are summarized. Finally, challenges and perspectives on the future development of smart chromic wearables are proposed. Such a systematic summary will serve as a valuable insight for researchers in this field.

Peptide-based nanomaterials and their diverse applications

The supramolecular self-assembly of peptides offers a promising avenue for both materials science and biological applications. Peptides have garnered significant attention in molecular self-assembly, forming diverse nanostructures with α-helix, β-sheet, and random coil conformations. These self-assembly processes are primarily driven by the amphiphilic nature of peptides and stabilized by non-covalent interactions, leading to complex nanoarchitectures responsive to environmental stimuli. While extensively studied in biomedical applications, including drug delivery and tissue engineering, their potential applications in the fields of piezoresponsive materials, conducting materials, catalysis and energy harvesting remain underexplored. This review comprehensively elucidates the diverse material characteristics and applications of self-assembled peptides. We discuss the multi-stimuli-responsiveness of peptide self-assemblies and their roles as energy harvesters, catalysts, liquid crystalline materials, glass materials and contributors to electrical conductivity. Additionally, we address the challenges and present future perspectives associated with peptide nanomaterials. This review aims to provide insights into the versatile applications of peptide self-assemblies while concisely summarizing their well-established biomedical roles that have previously been extensively reviewed by various research groups, including our group.

570 nm/770 nm light-excited deep-red fluorescence switch based on dithienylethene derived from BF2-curcuminoid

Developing dithienylethene (DTE)-based fluorescence switches triggered by biocompatible visible light has always been a long-term goal in view of their potential in numerous biological scenarios. However, their practical availability is severely limited by the short visible light (generally less than 500 nm) required for photocyclization, their inability to achieve red or near-infrared emission, and their short fluorescence lifetimes. Herein, we present a novel DTE derivative featuring a dimethylamine-functionalized BF2-curcuminoid moiety (NBDC) by using an "acceptor synergistic conjugation system" strategy. The dimethylamine group not only enables a red shift in the absorption and emission wavelengths of the open isomer but also endows NBDC with unique acid/base-gated photochromism. As expected, as-prepared NBDC presents 570 nm/770 nm light-driven photochromic properties, red-emissive fluorescence, and thermally activated delayed fluorescence (TADF) switching in toluene. To our knowledge, this represents the first instance of a yellow-green- and NIR light-controlled red fluorescence DTE switch with the longer fluorescence lifetime. Specifically, NBDC, which shows weak photochromic activity in CHCl3, demonstrates enhanced photochromic performance when gated by TFA/TEA. Ultimately, this non-toxic deep-red fluorescence switch has been successfully applied for photoswitchable imaging in vivo of living cells and zebrafish, further proving its versatility in life sciences.

The Role of Light Irradiation and Dendrimer Generation in Directing Electrostatic Self-Assembly

pH-responsive polyamidoamine (PAMAM) dendrimers are used as well-defined building blocks to design light-switchable nano-assemblies in solution. The complex interplay between the photoresponsive di-anionic azo dye Acid Yellow 38 (AY38) and the cationic PAMAM dendrimers of different generations is presented in this study. Electrostatic self-assembly involving secondary dipole-dipole interactions provides well-defined assemblies within a broad size range (10 nm-1 μm) with various shapes. The size and shape of these assemblies were determined using dynamic and static light scattering (DLS/SLS) and small-angle neutron scattering (SANS); ζ-potential measurements were performed to elucidate the charge characteristics, revealing the effective surface charge density of the nano-objects as an important parameter in the size and shape control. UV-vis spectroscopy and isothermal titration calorimetry (ITC) were employed to investigate the interaction on a molecular level and from a thermodynamic point of view. The results show that the amount of isomerized cis dye depends on the dendrimer generation because of a photoprotective effect through electrostatics for lower generations and through dipole-dipole interactions for higher generations; as the cis dye and trans dye bind with different strength, the amount of cis dye then again encodes the charge density and thereby the particle size and shape.

Diazocines as Guests of Cucurbituril Macrocycles: Light-Responsive Binding and Supramolecular Catalysis of Thermal Isomerization

The photoswitching of supramolecular host-guest complexes is the basis of numerous molecularly controlled macroscopic functions, such as sol-gel transition, photopharmacology, the active transport of ions or molecules, light-powered molecular machines, and much more. The most commonly used systems employ photoactive azobenzene guests and synthetic host molecules, which bind as the stable E isomers and dissociate as the Z forms after exposure to UV light. We present a new, extraordinarily efficient cucurbit[7]uril (CB7)/diazocine host/guest complex with inverted stability that self-assembles under UV irradiation and dissociates in the dark. The association constants of the Z and E isomers in water differ by more than 104-fold. We also show that the thermally activated E → Z isomerization is significantly accelerated by CB7, which is a rare case of enzyme-like catalysis by transition state stabilization without product inhibition. In contrast to CB7, cucurbit[8]uril (CB8) binds both isomers with high affinity, showing good selectivity (∼1000-fold) toward the Z isomer. Notably, this isomer preferentially binds CB8 relative to CB7 by a factor greater than 1 × 106. We also use the system to introduce a supramolecular photoacid that builds on the increased basicity of a guest bound to CB7 and on the extremely high affinity of the E isomer, which is utilized to displace the acid from CB7, thereby switching the pH of the solution.

Main-chain stiff-stilbene photoswitches in solution, in bulk, and at surfaces

Molecular photoswitches have been incorporated into polymer backbones to control the macromolecular conformations by structural changes of the main-chain photoswitches. However, previous photoswitches installed in the main chains are thermolabile, which precludes deep understanding, precise regulation, and practical applications of the macromolecular conformational changes. Herein, we focus on sterically hindered stiff stilbene (HSS), an emerging photoswitch offering large structural changes in isomerization between the thermally bistable E and Z isomers, and disclose the chemistry of main-chain HSS photoswitches in solution, in bulk, and at thin film surfaces. We synthesize and investigate three types of linear polymers with different chemical linkages between HSS repeating units, polyurethane, polyester, and polyene. The polymer conformations in solution, i.e., hydrodynamic volume, are reversibly photocontrollable in a precise manner by the E/Z ratio. Furthermore, the nanoscopic conformational transformations are amplified to macroscopic photoswitching of the solution transmittance and the surface wettability synergistically with changes between interchain and intrachain hydrogen bonding in the polyurethanes. Additionally, the Z-to-E photoisomerization yields in the glassy state are above 70%, comparable to those in solution, and extraordinarily high despite the restricted molecular mobility. The findings of this study will pave the way for practical and unconventional applications of smart polymer systems based on photoswitches.

Light-Operated Diverse Logic Gates Enabled by Modulating Time-Dependent Fluorescence of Dissipative Self-Assemblies

Light-fueled dissipative self-assembly possesses enormous potential in the field of optical information due to controllable time-dependent optical signals, but remains a great challenge for constructing intelligent light-operated logic circuits due to the limited availability of optical signal inputs and outputs. Herein, a series of light-fueled dissipative self-assembly systems with variable optical signals are reported to realize diverse logic gates by modulating time-dependent fluorescence variations of the loaded fluorophores. Three kinds of alkyl trimethylammonium homologs are employed to co-assemble with a merocyanine-based photoinduced amphiphile separately to construct a series of dissipative self-assemblies, showing unexpectedly different fluorescence control behaviors of loaded fluorophores during light irradiation and thermal relaxation processes. The opposite monotonicity of time-dependent emission intensity is achieved just by changing the excitation wavelength. Furthermore, by varying the types of trimethylammoniums and excitation wavelengths, a robust logic system is accomplished, integrating AND, XNOR, and XOR functions, which provides an effective pathway for advancing information transmission applications.

Diverse Self-assembly Pathways in Nematic Compartment Network: Topological Percolation and Pathfinding

The self-assembly of nematic molecules in microcompartments with unambiguously defined surface anchoring is well predictable and is likely to have a single stable topological structure. Here, in contrast, a confined nematic system comprising an array of microcompartments interconnected by channels is demonstrated, exhibiting diverse molecular assembly pathways leading to the formation of four types of topological structures and twelve different patterns randomly distributed. Intercompartment communication via channels plays a crucial role in the diversity of patterns and distributions. It determines the sizes and structures of domains separated by channel defects. The domain structure, which features a pathfinding algorithm and reverse tree structure, can be modelled by an isotropically directed bond percolation with additional restrictions. This system serves as a model for controlled randomness and restricted growth of networks, with potential applications in anticounterfeit protection as a physically unclonable function (PUF) with multiple-level communication protocols.

Robust, intelligent photochromic cotton fabrics with superamphiphobicity and expedient UV detection ability

Multifunctional photochromic cotton fabrics have enormous application potential in our daily lives, but still suffer from poor durability, slow coloration, tedious fabrication process, and short service life. The hydrophilic and polysaccharide characteristics of cotton fabrics make them vulnerable to bacteria adhesion and proliferation. Herein, intelligent photochromic cotton fabrics featured with durable superamphiphobicity are fabricated by in situ growth of ZIF-8 nanoparticles encapsulating spirooxazine (SP) photochromic dyes on the fabric surface, followed by low surface energy treatment using a fluorocarbon resin (FR) via a dip-coating method. The resultant SP@ZIF-8/FR cotton fabrics exhibit superamphiphobicity with contact angles of over 150° to both water and oils (surface tension ≥30 mN/m). When exposed to UV light, the fabric rapidly changes its color from white to blue within 10 s and fades in 2 min under visible room light. The developed SP@ZIF-8/FR coating is durable against numerous damages in daily usage, such as machine laundry, abrasion and UV irradiation, without losing photochromic and superamphiphobic properties. The high durability and excellent reversible color response allow the coated fabric to intuitively and quantitatively monitor outdoor UV intensity. Owing to the presence of ZIF-8, the treated fabrics also show excellent antibacterial property with antibacterial rates of over 99 % against both E. coli and S. aureus. The developed fabric coating can be engineered to visually assess the UV intensity in the outdoor environment.

Expanding the Color Range of Photoresponsive Multicolor Luminescent System Through Host-Guest Interaction

Photoresponsive multicolor luminescent systems offer interesting functions, which have led to applications in anticounterfeiting and biological imaging. However, expanding the color range of these materials remains a challenging task. Herein, a carbazole-modified dithienylethene derivative (DTE-CZ) that exhibits modulated fluorescence color changes through the photocyclization reaction and photolysis reaction is synthesized. DTE-CZ emits orange fluorescence, and it can release a fluorophore which emits blue fluorescence by the photolysis reaction, resulting in the color change. Upon complexation of DTE-CZ with cucurbit[10]uril (CB[10]), the fluorescence wavelength will have a blue shift and the photolysis reaction will be inhibited. Benefiting from the influence of CB[10] and the photolysis reaction of free guests, the color range of the photoresponsive system which is composed of free guests and host-guest complexes is further extended. White light emission along with a color shift from yellow-green to blue was achieved by adjusting the ratio of free guests to host-guest complexes. Finally, the photoresponsive multicolor systems are utilized to construct a photostimulated PVA film and an information encryption system. This work provides an alternative strategy for the preparing of photoresponsive multicolor luminescent system and modulation of its color range.

Aggregation-Induced Emissive Feringa-Type Motor: Toward the Dual-Functional Motor in a Single Molecular Aggregation System

Aggregation-induced emission (AIE)allows tunable photoluminescence via the simple regulation of molecular aggregation. The research spurt along this vein has also offered tremendous opportunities for light-responsive artificial molecular machines that are to be fully explored for performing versatile functions. Herein, the study reports a light-driven Feringa-type motor, when in the appropriate aggregation state, not only demonstrates the light-activated rotary motion but emits photons with good quantum yield. A semi-quantitative TD-DFT calculation is also conducted to aid the understanding of the competitive photoluminescence and photoisomerization processes of the motor. Cytotoxicity test shows this motor possesses good biocompatibility, laying a solid foundation for applying it in the bio-environment. The results demonstrated that the engagement of the aggregation-induced emission concept and light-driven Feringa-motor can lead to the discovery of the novel motorized AIEgen, which will further stimulate the rise of more advanced molecular motors capable of executing multi-functionalities.

A reversible photochromic covalent organic framework

Covalent organic frameworks are a type of crystalline porous materials that linked through covalent bond, and they have numerous potential applications in adsorption, separation, catalysis, and more. However, there are rarely relevant reported on photochromism. Fortunately, a hydrazone-linked DBTB-DETH-COF is rapidly generated through ultrasound method. The DBTB-DETH-COF is found to exhibit reversible photochromism (at least 50 cycles) from yellow to olive in the presence of light and air, and subsequently back to the original color upon heating. In addition, the structure of DBTB-DETH-COF remains unchanged after 15 days of light illumination. Furthermore, the reason of photochromic process is discussed by electron paramagnetic resonance, X-ray photoelectron spectroscopy, electrochemistry characterizations and transient absorption measurements. The reversible photochromic DBTB-DETH-COF can be used as anti-counterfeiting ink and optical switch in the presence of air. This work expands a stable organic photochromic material and broadens the applications of COFs.

Ionic Liquid Crystals as Chromogenic Materials

Ionic liquid crystals (ILCs), a class of soft matter materials whose properties can be tuned by the wise pairing of the cation and anion, have recently emerged as promising candidates for different applications, combining the characteristics of ionic liquids and liquid crystals. Among those potential uses, this review aims to cover chromogenic ILCs. In this context, examples of photo-, electro- and thermochromism based on ILCs are provided. Furthermore, thermotropic and lyotropic ionic liquid crystals are also summarised, including the most common chemical and phase structures, as well as the advantages of confining these materials. This manuscript also comprises the following main experimental techniques used to characterise ILCs: Differential Scanning Calorimetry (DSC), Polarised Optical Microscopy (POM) and X-Ray Powder Diffraction (XRD). Chromogenic ILCs can be interesting smart materials for energy and health purposes.

Recent Advances of Light/Hypoxia-Responsive Azobenzene in Nanomedicine Design

Azobenzene (Azo) and its derivatives are versatile stimuli-responsive molecules. Their reversible photoisomerization and susceptibility to reduction-mediated cleavage make them valuable for various biomedical applications. Upon exposure to the UV light, Azo units undergo a thermodynamically stable trans-to-cis transition, which can be reversed by heating in the dark or irradiation with visible light. Additionally, the N=N bonds in azobenzenes can be cleaved under hypoxic conditions by azoreductase, making azobenzenes useful as hypoxia-responsive linkers. The integration of azobenzenes into nanomedicines holds promise for enhancing therapeutic efficacy, particularly in tumor targeting and controllable drug release. In this Concept paper, recent advances in the design and applications of azobenzene-based nanomedicines are updated, and future development opportunities are also summarized.

Tuning the Properties of Hydrazone/Isosorbide-Based Switchable Chiral Dopants

The long-range supramolecular interactions in liquid crystals (LCs) can be used to amplify and subsequently propagate microscopic structural changes into macroscopic events. Here, we report on a systematic structure-property analysis using 16 chiral photoswitchable dopants composed of bistable hydrazones and chiral isosorbide moieties. Our findings showcase the relationship between the dopant's structure and its helical twisting power (β), and hence, the photophysical properties of the host LC. We show that an increase in the hydrazone CNNH dihedral angle results in an increase in the β value, while alkoxy chains do not lead to such an increase. These results contradict established rules of thumb, stating that structural rigidity and long alky chains are needed for high β values. We also found that the position of the substitution, whether at the 2' or 5' positions of the isosorbide unit, or the attachment of the chiral unit to the rotor or stator phenyl units can have negative or positive additive effects that can either increase or decrease the β values. These results made us hypothesize that unsymmetrically functionalized dopants should result in large Δβ values, which we corroborated experimentally. Moreover, a fluorine-functionalized dopant resulted in higher overall β values, most likely because of π-π interactions. Finally, the dopants were used in modulating and locking in the reflective properties of LC films, yielding multicolor LC canvases that can reflect light from the ultraviolet to the infrared range (i.e., a manipulation of up to ca. 1500 nm of reflected light).

Reversible Photochromism of 4,4'-Disubstituted 2,2'-Bipyridine in the Presence of SO3

We report an unusual photochromic behavior of 4,4'-disubstituted-2,2'-bipyridine. It was found that in the presence of a SO3 source and HCl, 2,2'-bipyridine-4,4'-dibutyl ester undergoes a color change from yellow to magenta in solution with maximum absorbance at 545 nm upon irradiation with 395 nm light. The photochromism is thermally reversible in solution. Different from the known bipyridine-based photoswitching pathways, the photo response does not involve any metal which form colored complexes or the formation of colored free radical cations like the photo-reduction of viologens. A combination of experimental and computational analysis was used to probe the mechanism. The results suggest the colored species to be a complex formed between N-oxide of the 2,2'-bipyridine-4,4'-dibutyl ester and SO2; the N-oxide and SO2 are formed from photoactivated oxidation of the bipyridine with SO3 serving as the oxygen source. This complex represents a new addition to the library of photoswitches that is easy to synthesize, reversible in solution, and of high fatigue resistance, making it a promising candidate for applications in photo-switchable materials and SO3 detection. We also demonstrated experimentally similar photochromic behaviors with 2,2'-bipyridine-containing polymers.

Aqueous Supramolecular Transformations of Motor Bola-Amphiphiles at Multiple Length-Scale

Molecular motor amphiphiles have already been widely attempted for dynamic nanosystems across multiple length-scale for developments of small functional materials, including controlling macroscopic foam properties, amplifying motion as artificial molecular muscles, and serving as extracellular matrix mimicking cell scaffolds. However, limiting examples of bola-type molecular motor amphiphiles are considered for constructing macroscopic biomaterials. Herein, this work presents the designed two second generation molecular motor amphiphiles, motor bola-amphiphiles (MBAs). Aside from the photoinduced motor rotation of MBAs achieved in both organic and aqueous media, the rate of recovering thermal helix inversion step can be controlled by the rotor part with different steric hindrances. Dynamic assembled structures of MBAs are observed under (cryo)-transmission electron microscopy (TEM). This dynamicity assists MBAs in further assembling as macroscopic soft scaffolds by applying a shear-flow method. Upon photoirradiation, the phototropic bending function of MBA scaffolds is observed, demonstrating the amplification of molecular motion into macroscopic phototropic bending functions at the macroscopic length-scale. Since MBAs are confirmed with low cytotoxicity, human bone marrow-derived mesenchymal stem cells (hBM-MSCs) can grow on the surface of MBA scaffolds. These results clearly demonstrate the concept of designing MBAs for developing photoresponsive dynamic functional materials to create new-generation soft robotic systems and cell-material interfaces.

Determining Chemical Microheterogeneity from the Analysis of Absorption and Luminescence Transient Signals

The characterization of chemical microheterogeneity is compelling due to its relevant role in soft materials, high-entropy materials, and systems chemistry, to cite just a few instances. This work investigates the microheterogeneity of photochromic samples and metal oxide solid solutions by fitting time-resolved absorption and luminesce signals recorded after photoexcitation. The transient spectroscopic signals have been analyzed using polyexponential functions determined through the Maximum Entropy Method (MEM) and discrete exponential, Kohlrausch, and Becquerel functions through the Levenberg-Marquardt algorithm. The outputs of the different fitting functions and algorithms are compared and exploited to characterize chemical microheterogeneity quantitatively. The practical relevance of chemical microheterogeneity is supported by the demonstration that photochromic samples are transformed from binary to multistate systems, capable of encoding much more information, and that microheterogeneous photocatalysts are provided with several structural defects that guarantee the coexistence of many active sites and higher catalytic activity.

"On-the-Fly" Nonadiabatic Dynamics Simulation on the Ultrafast Photoisomerization of a Molecular Photoswitch Iminothioindoxyl: An RMS-CASPT2 Investigation

Iminothioindoxyl (ITI) is a new class of photoswitch that exhibits many excellent properties including well-separated absorption bands in the visible region for both conformers, ultrafast Z to E photoisomerization as well as the millisecond reisomerization at room temperature for the E isomer, and switchable ability in both solids and various solvents. However, the underlying ultrafast photoisomerization mechanism at the atomic level remains unclear. In this work, we have employed a combination of high-level RMS-CASPT2-based static electronic structure calculations and nonadiabatic dynamics simulations to investigate the ultrafast photoisomerization dynamics of ITI. Based on the minimum-energy structures, minimum-energy conical intersections, linear interpolation internal coordinate paths, and nonadiabatic dynamics simulations, the overall photoisomerization scenario of ITI upon excitation is established. Upon excitation around 416 nm, the molecule will be excited to the S2 state considering its close energy to the experimentally measured absorption maximum and larger oscillator strength, from which ultrafast decay of S2 to S1 state can take place efficiently with a time constant of 62 fs. However, the photoisomerization is not likely to complete in the S2 state since the dihedral associated with the Z to E isomerization changes little during the relaxation. Upon relaxing to the S1 state, the molecule will decay to the S0 state ultrafast with a time constant of 232 fs. In contrast, the decay of the S1 state is important for the isomerization considering that the dihedral related to the isomerization of the hopping structures is close to 90°. Therefore, the S1/S0 intersection region should be important for the isomerization of ITI. Arriving at the S0 state, the molecule can either go back to the original Z reactant or isomerize to the E products. At the end of the 500 fs simulation time, the E configuration accounts for nearly 37% of the final structures. Moreover, the photoisomerization mechanism is different from the isomerization mechanism in the ground state; i.e., instead of the inversion mechanism in the ground state, the photoisomerization prefers the rotation mechanism. Our results not only agree well with previous experimental studies but also provide some novel insights that could be helpful for future improvements in the performance of the ITI photoswitches.

Multiexcitation Peaks and Multicolor Emission Nanoassemblies for Transmembrane Cell Imaging and Photoresponsivity Antibacterial

Nanomaterials with photoresponsivity have garnered attention due to their fluorescence imaging, photodynamic, and photothermal therapeutic properties. In this study, a photoresponsivity nanoassembly was developed by using photosensitizers and carbon dots (CDs). Due to their multiple excitation peaks and multicolor fluorescence emission, especially their membrane-permeating properties, these nanoassemblies can label cells with multiple colors and track cell imaging in real time. Additionally, the incorporation of photosensitizers and CDs provides the nanoassemblies with the potential for photodynamic therapy (PDT) and photothermal therapy (PTT). The nanoassemblies effectively suppressed the activity of Escherichia coli and Staphylococcus aureus through PDT and PTT. Moreover, the nanoassemblies exhibited a high affinity for E. coli and S. aureus. These distinct features confer broad-spectrum antibacterial properties to the nanoassemblies. As a photoresponsivity nanoplatform, these nanoassemblies have demonstrated potential applications in the fields of bioimaging and antimicrobial.

Environmental permittivity-asymmetric BIC metasurfaces with electrical reconfigurability

Achieving precise spectral and temporal light manipulation at the nanoscale remains a critical challenge in nanophotonics. While photonic bound states in the continuum (BICs) have emerged as a powerful means of controlling light, their reliance on geometrical symmetry breaking for obtaining tailored resonances makes them highly susceptible to fabrication imperfections, and their generally fixed asymmetry factor fundamentally limits applications in reconfigurable metasurfaces. Here, we introduce the concept of environmental symmetry breaking by embedding identical resonators into a surrounding medium with carefully placed regions of contrasting refractive indexes, activating permittivity-driven quasi-BIC resonances (ε-qBICs) without altering the underlying resonator geometry and unlocking an additional degree of freedom for light manipulation through active tuning of the surrounding dielectric environment. We demonstrate this concept by integrating polyaniline (PANI), an electro-optically active polymer, to achieve electrically reconfigurable ε-qBICs. This integration not only demonstrates rapid switching speeds and exceptional durability but also boosts the system's optical response to environmental perturbations. Our strategy significantly expands the capabilities of resonant light manipulation through permittivity modulation, opening avenues for on-chip optical devices, advanced sensing, and beyond.

Accessing a Diverse Set of Functional Red-Light Photoswitches by Selective Copper-Catalyzed Indigo N-Arylation

The ability to correlate the structure of a molecule with its properties is the key to the rational and accelerated design of new functional compounds and materials. Taking photoswitches as an example, the thermal stability of the metastable state is a crucial property that dictates their application in molecular systems. Indigos have recently emerged as an attractive motif for designing photoswitchable molecules due to their red-light addressability, which can be advantageous in biomedical and material applications. The lack of synthetic techniques to derivatize the abundant parent dye and a thorough understanding of the impact of structural factors on the photochemical and thermal properties hinder broad applications of this emerging photoswitch class. Herein, we report an efficient copper-catalyzed indigo N-arylation that enables the installation of a wide variety of aryl moieties carrying useful functional groups. The exclusive selectivity for monoarylation likely originates from a bimetallic cooperative mechanism through a binuclear copper-indigo intermediate. Functional N-aryl-N'-alkylindigos were prepared and shown to photoisomerize efficiently under red light. Moreover, this design allows for the modulation of thermal half-lives through N-aryl substituents, while the N'-alkyl groups enable the independent attachment of functional moieties without affecting the photochromic properties. A strong correlation between the structure of the N-aryl moiety and the thermal stability of the photogenerated Z-isomers was achieved by multivariate linear regression models obtained through a data-science workflow. This work thus builds an avenue leading to versatile red-light photoswitches and a general method for structure-property correlation that is expected to be broadly applicable to the design of photoresponsive molecules.

Photochromic Carbon Nanomaterials: An Emerging Class of Light-Driven Hybrid Functional Materials

Photochromic molecules have remarkable potential in memory and optical devices, as well as in driving and manipulating molecular motors or actuators and many other systems using light. When photochromic molecules are introduced into carbon nanomaterials (CNMs), the resulting hybrids provide unique advantages and create new functions that can be employed in specific applications and devices. This review highlights the recent developments in diverse photochromic CNMs. Photochromic molecules and CNMs are also introduced. The fundamentals of different photochromic CNMs are discussed, including design principles and the types of interactions between CNMs and photochromic molecules via covalent interactions and non-covalent bonding such as π-π stacking, amphiphilic, electrostatic, and hydrogen bonding. Then the properties of photochromic CNMs, e.g., in photopatterning, fluorescence modulation, actuation, and photoinduced surface-relief gratings, and their applications in energy storage (solar thermal fuels, photothermal batteries, and supercapacitors), nanoelectronics (transistors, molecular junctions, photo-switchable conductance, and photoinduced electron transfer), sensors, and bioimaging are highlighted. Finally, an outlook on the challenges and opportunities in the future of photochromic CNMs is presented. This review discusses a vibrant interdisciplinary research field and is expected to stimulate further developments in nanoscience, advanced nanotechnology, intelligently responsive materials, and devices.

Photo-switching operation of MoS2field effect transistor by photoisomerization of azobenzene in solution delivered on a microfluidic platform

Combining the photoisomerization of molecules with an electrical device is important for developing optoelectronic devices. Field effect transistors (FETs) with atomically thin channels are suitable for this purpose because the FET properties respond to chemical changes in molecules. Since the photoisomerization wavelength of the switching molecules can be tuned, complex logic operations can be realized if a specific molecule is delivered to the target FET of an integrated circuit. However, conventional techniques for transferring molecules, such as drop casting and sublimation, cannot efficiently realize this goal. In this study, we fabricated a MoS2FET device combined with a microfluidic platform, wherein the MoS2channel was in contact with the flow of an azobenzene solution in isopropyl alcohol as the solvent. UV radiation (365 nm) and thermal relaxation realize the cycle of trans- and cis-azobenzene states and the switching of the substantial FET properties. This study demonstrated the feasibility of using the solution for optical switching of the MoS2-FET, which can realize quick phase changes in the molecule and the delivery of the molecule to the target FET by a microfluidic platform.

Transforming patterned defects into dynamic poly-regional topographies in liquid crystal oligomers

We create high-aspect-ratio dynamic poly-regional surface topographies in a coating of a main-chain liquid crystal oligomer network (LCON). The topographies form at the topological defects in the director pattern organized in an array which are controlled by photopatterning of the alignment layer. The defect regions are activated by heat and/or light irradiation to form reversible topographic structures. Intrinsically, the LCON is rubbery and sensitive to temperature changes, resulting in shape transformations. We further advanced such system to make it light-responsive by incorporating azobenzene moieties. Actuation reduces the molecular order of the LCON coating that remains firmly adhered to the substrate which gives directional shear stresses around the topological defects. The stresses relax by deforming the surfaces by forming elevations or indents, depending on the type of defects. The formed topographies exhibit various features, including two types of protrusions, ridges and valleys. These poly-regional structures exhibit a large modulation amplitude of close to 60%, which is 6 times larger than the ones formed in liquid crystal networks (LCNs). After cooling or by blue light irradiation, the topographies are erased to the initial flat surface. A finite element method (FEM) model is adopted to simulate structures of surface topographies. These dynamic surface topographies with multilevel textures and large amplitude expand the application range, from haptics, controlled cell growth, to intelligent surfaces with adjustable adhesion and tribology.

Dual-Mode Hydrogels with Structural and Fluorescent Colors toward Multistage Secure Information Encryption

Constructing an anti-counterfeiting material with non-interference dual optical modes is an effective way to improve information security. However, it remains challenging to achieve multistage secure information encryption due to the limited stimulus responsiveness and color tunability of the current dual-mode materials. Herein, a dual-mode hydrogel with both independently tunable structural and fluorescent colors toward multistage information encryption, is reported. In this hydrogel system, the rigid lamellar structure of poly(dodecylglyceryl itaconate) (pDGI) formed by shear flow-induced self-assembly provides the restricted domains wherein monomers undergo polymerization to form a hydrogel network, producing structural color. The introduction of fluorescent monomer 6-acrylamidopicolinate (6APA) as a complexation site provides the possibility of fluorescent color formation. The hydrogel's angle-dependent structural color can be controlled by adjusting the crosslinking density and water content. Additionally, the fluorescence color can be modulated by adjusting the ratio of lanthanide ions. Information of dual-mode can be displayed separately in different channels and synergistically overlayed to read the ultimate message. Thus, a multistage information encryption system based on this hydrogel is devised through the programed decryption process. This strategy holds tremendous potential as a platform for encrypting and safeguarding valuable and authentic information in the field of anti-counterfeiting.

Synthesis and Reactivity of an X-Shaped Molecule: Reversible Formation and Cleavage of a Four-Membered Ring in Response to External Stimuli

We herein report the synthesis and reactivity of an X-shaped molecule featuring three four-membered rings (4MRs) arranged in a ladder configuration. This molecule exhibits a reversible opening and closure of the central 4MR upon exposure to light irradiation and thermal treatment. The central 4MR of this molecule is also cleaved via electrochemical and chemical reductions. The stimuli-responsiveness of the X-shaped molecule is attributed to the small energy gap difference between its open and closed states, stemming from the antiaromatic character of its precursor.

Multiple photofluorochromic luminogens via catalyst-free alkene oxidative cleavage photoreaction for dynamic 4D codes encryption

Controllable photofluorochromic systems with high contrast and multicolor in both solutions and solid states are ideal candidates for the development of dynamic artificial intelligence. However, it is still challenging to realize multiple photochromism within one single molecule, not to mention good controllability. Herein, we report an aggregation-induced emission luminogen TPE-2MO2NT that undergoes oxidation cleavage upon light irradiation and is accompanied by tunable multicolor emission from orange to blue with time-dependence. The photocleavage mechanism revealed that the self-generation of reactive oxidants driving the catalyst-free oxidative cleavage process. A comprehensive analysis of TPE-2MO2NT and other comparative molecules demonstrates that the TPE-2MO2NT molecular scaffold can be easily modified and extended. Further, the multicolor microenvironmental controllability of TPE-2MO2NT photoreaction within polymer matrices enables the fabrication of dynamic fluorescence images and 4D information codes, providing strategies for advanced controllable information encryption.

Light switching for product selectivity control in photocatalysis

Artificial switchable catalysis is a new, rapidly expanding field that offers great potential advantages for both homogeneous and heterogeneous catalytic systems. Light irradiation is widely accepted as the best stimulus to artificial switchable chemical systems. In recent years, tremendous progress has been made in the synthesis and application of photo-switchable catalysts that can control when and where bond formation and dissociation take place in reactant molecules. Photo-switchable catalysis is a niche area in current catalysis, on which systematic analysis and reviews are still lacking in the scientific literature, yet it offers many intriguing and versatile applications, particularly in organic synthesis. This review aims to highlight the recent advances in photo-switchable catalyst systems that can result in two different chemical product outcomes and thus achieve a degree of control over organic synthetic reactions. Furthermore, this review evaluates different approaches that have been employed to achieve dynamic control over both the catalytic function and the selectivity of several different types of synthesis reactions, along with the remaining challenges and potential opportunities. Owing to the great diversity of the types of reactions and conditions adopted, a quantitative comparison of efficiencies between considered systems is not the focus of this review, instead the review showcases how insights from successful adopted strategies can help better harness and channel the power of photoswitchability in this new and promising area of catalysis research.

Photoresponsive Biomimetic Functions by Light-Driven Molecular Motors in Three Dimensionally Printed Liquid Crystal Elastomers

Despite the fascinating developments in design and synthesis of artificial molecular machines operating at the nanoscales, translating molecular motion along multiple length scales and inducing mechanical motion of a three-dimensional macroscopic entity remains an important challenge. The key to addressing this amplification of motion relies on the effective organization of molecular machines in a well-defined environment. By taking advantage of long-range orientational order and hierarchical structures of liquid crystals and unidirectional rotation of light-driven molecular motors, we report here photoresponsive biomimetic functions of liquid crystal elastomers (LCEs) by the repetitive unidirectional rotation of molecular motors using 3D printing. Molecular motors were built in the main chain of liquid crystals oligomers to serve as photoactuators. The oligomers were then used as the ink, and liquid crystal elastomers with different morphologies were printed. The obtained LCEs are able to conduct multiple types of motions including bending, helical coiling, closing of petals, and flipping of wings of a butterfly upon UV illumination, which paves the way for future design of responsive materials with enhanced complex actuating functions.

Optical Phenomena in Molecule-Based Magnetic Materials

Since the last century, we have witnessed the development of molecular magnetism which deals with magnetic materials based on molecular species, i.e., organic radicals and metal complexes. Among them, the broadest attention was devoted to molecule-based ferro-/ferrimagnets, spin transition materials, including those exploring electron transfer, molecular nanomagnets, such as single-molecule magnets (SMMs), molecular qubits, and stimuli-responsive magnetic materials. Their physical properties open the application horizons in sensors, data storage, spintronics, and quantum computation. It was found that various optical phenomena, such as thermochromism, photoswitching of magnetic and optical characteristics, luminescence, nonlinear optical and chiroptical effects, as well as optical responsivity to external stimuli, can be implemented into molecule-based magnetic materials. Moreover, the fruitful interactions of these optical effects with magnetism in molecule-based materials can provide new physical cross-effects and multifunctionality, enriching the applications in optical, electronic, and magnetic devices. This Review aims to show the scope of optical phenomena generated in molecule-based magnetic materials, including the recent advances in such areas as high-temperature photomagnetism, optical thermometry utilizing SMMs, optical addressability of molecular qubits, magneto-chiral dichroism, and opto-magneto-electric multifunctionality. These findings are discussed in the context of the types of optical phenomena accessible for various classes of molecule-based magnetic materials.

All-visible-light-driven stiff-stilbene photoswitches

Molecular photoswitches are potent tools to construct dynamic functional systems and responsive materials that can be controlled in a non-invasive manner. As P-type photoswitches, stiff-stilbenes attract increasing interest, owing to their superiority in quantum yield, significant geometric differences between isomers, excellent thermostability and robust switching behavior. Nevertheless, the UV-light-triggered photoisomerization of stiff-stilbenes has been a main drawback for decades as UV light is potentially harmful and has low penetration depth. Here, we provided a series of para-formylated stiff-stilbenes by Rieche ortho-formylation to achieve all-visible-light-responsiveness. Additional phenolic groups provide access to late-stage chemical modification facilitating design of molecules responsive to visible light. Remarkably, the photoisomerization of aldehyde-appended stiff-stilbenes could be fully manipulated using visible light, accompanied by a high photostationary state (PSS) distribution. These features render them excellent candidates for future visible-light-controllable smart materials and dynamic systems.

Photoswitching the fluorescence of nanoparticles for advanced optical applications

The dynamic optical response properties and the distinct features of nanomaterials make photoswitchable fluorescent nanoparticles (PF NPs) attractive candidates for advanced optical applications. Over the past few decades, the design of PF NPs by coupling photochromic and fluorescent motifs at the nanoscale has been actively pursued, and substantial efforts have been made to exploit their potential applications. In this perspective, we critically summarize various design principles for fabricating these PF NPs. Then, we discuss their distinct optical properties from different aspects by highlighting the capability of NPs in fabricating new, robust photoswitch systems. Afterwards, we introduce the pivotal role of PF NPs in advanced optical applications, including sensing, anti-counterfeiting and imaging. Finally, current challenges and future development of PF NPs are briefly discussed.

Robust, Ultrafast and Reversible Photoswitching in Bulk Polymers Enabled by Octupolar Molecule Design

Improving the photoswitching rate and robustness of photochromic molecules in bulk solids is paramount for practical applications but remains an on-going challenge. Here, we introduce an octupolar design paradigm to develop a new family of visible light organic photoswitches, namely multi-branched octupolar Stenhouse Adducts (MOPSAs) featuring a C3-symmetrical A3-(D-core) architecture with a dipolar donor-acceptor (D-A) photochrome in each branch. Our design couples multi-dimensional geometric and electronic effects of MOPSAs to enable robust ultrafast reversible photoswitching in bulk polymers. Specifically, the optimal MOPSA (4 wt %) in commercial polyurethane films accomplishes nearly 100 % discoloration in 6 s under visible light with ∼ 100 % thermal-recovery in 17.4 s at 60 °C, while the acquired kinetics constants are 3∼7 times that of dipolar DASA counterpart and 1∼2 orders of magnitude higher than those of reported DASAs in polymers. Importantly, the MOPSA-doped polymer films sustain 500 discoloration/recovery cycles with slow degradation, superior to the existing DASAs in polymers (≤30 cycles). We discover that multi-dipolar coupling in MOPSA enables enhanced polarization and electron delocalization, promoting the rate-determining thermal cyclization, while the branched and non-planar geometry of MOPSA induces large free volume to facilitate the isomerization. This design can be extended to develop spiropyran or azobenzene-based ultrafast photochromic films. The superior photoswitching performance of MOPSAs together with their high-yield and scalable synthesis and facile film processing inspires us to explore their versatile uses as smart inks or labels for time-temperature indicators, optical logic encryption and multi-levelled data encryption.

Photoswitchable Cascades for Allosteric and Bidirectional Control over Covalent Bonds and Assemblies

Studies of complex systems and emerging properties to mimic biosystems are at the forefront of chemical research. Dynamic multistep cascades, especially those exhibiting allosteric regulation, are challenging. Herein, we demonstrate a versatile platform of photoswitchable covalent cascades toward remote and bidirectional control of reversible covalent bonds and ensuing assemblies. The relay of a photochromic switch, keto-enol equilibrium, and ring-chain equilibrium allows light-mediated reversible allosteric structural changes. The accompanying distinct reactivity further enables photoswitchable dynamic covalent bonding and release of substrates bidirectionally through alternating two wavelengths of light, essentially realizing light-mediated signaling cycles. The downfall of energy by covalent bond formation/scission upon photochemical reactions offers the driving force for the controlled direction of the cascade. To show the molecular diversity, photoswitchable on-demand assembly/disassembly of covalent polymers, including structurally reconfigurable polymers, was realized. This work achieves photoswitchable allosteric regulation of covalent architectures within dynamic multistep cascades, which has rarely been reported before. The results resemble allosteric control within biological signaling networks and should set the stage for many endeavors, such as dynamic assemblies, molecular motors, responsive polymers, and intelligent materials.

Photoswitchable Temperature Nanosensors Based on the Chemical Kinetics of Photochromic Naphthopyran for Live Cell Imaging

Microscopic temperature imaging holds significant importance in various fields, particularly in the development of nanomaterials for photothermal therapy (PTT). In this study, we present an analytical method to probe cellular temperature based on chemical kinetics and additional luminescence quenching by photoswitchable naphthopyrans. Taking advantage of the rapid ring-closing reaction of naphthopyran, temperature sensing was realized with a linear relationship between the logarithmic decay time constant (ln τ) and the reciprocal temperature (T-1). To create luminescent temperature nanosensors, we harnessed the ability of ring-opened naphthopyran to quench the luminescence of a semiconducting polymer, resulting in a diverse array of probes. Structural modifications on the naphthopyran also provided a way to fine-tune the sensitivity and response window of the nanosensors. The method allowed cellular temperature imaging on a cost-effective fluorescence microscopic setup. As an application, the temperature increase induced by gold nanorods (AuNRs) in cell lysosomes was successfully monitored, laying the foundation for a new class of photoswitchable nanosensors with promising biological applications.

Conductance Evolution of Photoisomeric Single-Molecule Junctions under Ultraviolet Irradiation and Mechanical Stretching

A comprehensive understanding of carrier transport in photoisomeric molecular junctions is crucial for the rational design and delicate fabrication of single-molecule functional devices. It has been widely recognized that the conductance of azobenzene (a class of photoisomeric molecules) based molecular junctions is mainly determined by photoinduced conformational changes. In this study, it is demonstrated that the most probable conductance of amine-anchored azobenzene-based molecular junctions increases continuously upon UV irradiation. In contrast, the conductance of pyridyl-anchored molecular junctions with an identical azobenzene core exhibits a contrasting trend, highlighting the pivotal role that anchoring groups play, potentially overriding (even reversing) the effects of photoinduced conformational changes. It is further demonstrated that the molecule with cis-conformation cannot be fully mechanically stretched into the trans-conformation, clarifying that it is a great challenge to realize a reversible molecular switch by purely mechanical operation. Additionally, it is revealed that the coupling strength of pyridyl-anchored molecules is dramatically weakened when the UV irradiation time is prolonged, whereas it is not observed for amine-anchored molecules. The mechanisms for these observations are elucidated with the assistance of density functional theory calculations and UV-Vis spectra combined with flicker noise measurements which confirm the photoinduced conformational changes, providing insight into understanding the charge transport in photoisomeric molecular junctions and offering a routine for logical designing synchro opto-mechanical molecular switches.

Photochromic biomaterials: Synthesis and fluorescence properties of spiroxanthenes-grafted alginate derivatives

Herein, we reported a general and green synthetic strategy for photochromic functional alginate derivatives grafting with isoindolinone spiroxanthenes. Under mild condition, diverse 2-aminoalkyl isoindolinone spiroxanthene derivatives have been prepared from organic photochromic isobenzofuranone spiroxanthenes (including rhodamine B, rhodamine 6G and fluorescein), and grafted on alginate chains through amidation reaction using diamine as a linkage with water as a green solvent at room temperature. The photochromic properties of the fluorophores-modified polymers and the effect of pH value have been explored. Under acid conditions, the spiroisoindolinone rings of alginate derivatives are opened resulting in showing absorption bands and fluorescence with orange to green emission, while the alginate derivatives turned to colourless under basic conditions which is reversibly. In addition to biodegradability and biocompatibility, the polymers exhibit good film-forming properties simultaneously. The films and fibers produced from the alginate derivatives also project good fluorescence properties.

Chelating Coordination Regulated Photochromic Electrospun Nanofibers for Waterproof and Long-Color-Retention Rewritable Wearables

Photochromic materials with rapid color-switching, long color retention times, and rewritability are crucial for meeting the requirements of future rewritable ink-free media. However, these requirements are challenging to satisfy simultaneously due to the inherent constraints among these features. Herein, a novel photochromic nanofiber nonwoven fabric was designed and constructed based on a conjugated organic-inorganic hybrid structure through electrospinning and hot-pressing techniques. The as-prepared fabric can change color in merely 5 s under UV irradiation and can reach saturation within 2 min. In addition, upon the introduction of a potent metal chelator, its color retention time exceeds 14 days under ambient conditions, significantly longer than that of most rewritable materials recently reported (several hours to 5 days). Moreover, the fabric exhibits high writing resolution and can be photoprinted and heat-erased for over 100 cycles while still retaining 96% of its initial reflectivity. Hydrophobic thermoplastic polyurethane provides the fabric with excellent waterproof and antifouling properties, thus preventing the composite from swelling or collecting graffiti due to moisture or dust. This work exploits a competitive approach for designing flexible, rewritable, and superior functional wearables with practical applications.

Ultrafast Response Organic Photoswitch Materials and Their Application in Volumetric 3D Display

Volumetric three-dimensional (3D) display technology based on static screens is a crucial branch of 3D displays. The essential component in volumetric 3D displays is selectively excitable display media that can generate voxels at any position. Here, we synthesized a series of organic photoswitch materials to meet the specific requirements of 3D display mediums. In these photoswitch solutions, voxels are activated ultrafast within tens of picoseconds at the intersection of two control lasers and faded rapidly within tens of milliseconds when switching light is turned off. An experimental volumetric 3D display system utilizing an organic photoswitch solution as a screen is demonstrated. The system not only achieves a dynamic 3D display but also enables 360° viewing. The volumetric 3D display system can display true 3D images without auxiliary glasses and is expected to be applicable in fields as diverse as virtual reality, medical imaging, architectural design, and military visualization.