Photoinduced Bending of Self-Assembled Azobenzene–Siloxane Hybrid

Dynamic Transformation of High-Architectural Nanocrystal Superlattices upon Solvent Molecule Exposure

The cluster-based body-centered-cubic superlattice (cBCC SL) represents one of the most complicated structures among reported nanocrystal assemblies, comprised of 72 truncated tetrahedral quantum dots per unit cell. Our previous report revealed that truncated tetrahedral quantum dots within cBCC SLs possessed highly controlled translational and orientational order owing to an unusual energetic landscape based on the balancing of entropic and enthalpic contributions during the assembly process. However, the cBCC SL's structural transformability and mechanical properties, uniquely originating from such complicated nanostructures, have yet to be investigated. Herein, we report that cBCC SLs can undergo dynamic transformation to face-centered-cubic SLs in response to post-assembly molecular exposure. We monitored the dynamic transformation process using in situ synchrotron-based small-angle X-ray scattering, revealing a dynamic transformation involving multiple steps underpinned by interactions between incoming molecules and TTQDs' surface ligands. Furthermore, our mechanistic study demonstrated that the precise configuration of TTQDs' ligand molecules in cBCC SLs was key to their high structural transformability and unique jelly-like soft mechanical properties. While ligand molecular configurations in nanocrystal SLs are often considered minor features, our findings emphasize their significance in controlling weak van der Waals interactions between nanocrystals within assembled SLs, leading to previously unremarked superstructural transformability and unique mechanical properties. Our findings promote a facile route toward further creation of soft materials, nanorobotics, and out-of-equilibrium assemblies based on nanocrystal building blocks.

Insight into Multiphase Interlayer Molecular Packing and Stepwise Phase Transition in 4-(Phenylazo)benzoate Anion-Intercalated Layered Zinc Hydroxide

The properties of layered intercalation hybrids are closely related to interlayer molecular packing. To develop functional intercalation hybrids, it is essential to gain deep insights into interlayer molecular packing. This work reports a new comprehensive insight into the controllable multiphase interlayer molecular packing in 4-(phenylazo)benzoate anion-intercalated layered zinc hydroxide (LZH-4-PAB intercalation hybrids). The new insight breaks up the general understanding that the interlayer molecular packing of anions is usually single-phase, lacking diversity and controllability. Furthermore, it uncovers an interesting stepwise rather than the generally expected continuous phase transition of the interlayer molecular packing. The intercalated 4-PAB anions initially organize into the horizontal monolayer packing (θ = 0°, Phase I), which stepwise transforms to the tilted interdigitated antiparallel bilayer packing (θ ≈ 50°, Phase II) along with an increased intercalation loading and eventually to the vertical interdigitated antiparallel bilayer packing (θ = 90°, Phase III). The LZH-4-PAB hybrids exhibited a greatly enhanced interlayer molecular packing-dependent UV-vis absorption. This study provides helpful guidance for developing property-tailored intercalation hybrids. It may attract new interest in more layered intercalation hybrids. New and rich intercalation chemistry might be discovered in more functional intercalation hybrids beyond the 4-PAB anion-intercalated layered zinc hydroxide.

Boosting Ion Conductivities: Light-Modulated Azobenzene-Based Ionic Liquids in Vertical Nanochannels

Exploring stimuli-responsive ion-conductive materials is a challenging task, but it has gained increasing attention because of their enormous potential applications in actuators, sensors, and smart electronics. Here, we demonstrate a distinctive photoresponsive ion-conductive device that utilizes azobenzene-based ionic liquids ([AzoCnMIM][Br], where n = 2, 6, and 10), confined in nanochannels of anodic aluminum oxide (AAO) templates for photoisomerization. The structure of [AzoCnMIM][Br] comprises photoresponsive and hydrophobic azobenzene moieties, hydrophilic imidazolium cations, and negatively charged bromide ions. Therefore, [AzoCnMIM][Br] can form micelles and exhibit photoresponsive ion conductivities. The nanochannels of AAO templates exhibit a confinement effect on the formation of azobenzene-based ionic liquid micelles due to the pore size, thereby preventing the formation of larger micelles that could lead to a decrease in conductivity. Consequently, the ion conductivities of the azobenzene-based ionic liquids are higher in the nanochannels of the AAO templates. The effects of the length of carbon chains on the azobezene-based ionic liquids and the pore size of the AAO templates have also been investigated. Additionally, through irradiation with UV/vis light, [AzoCnMIM][Br] can undergo reversible isomerization, thereby reversibly changing the sizes of the micelles and subsequently altering the ion conductivities.

Facile Photoresponsive Actuators Based on Ferrocene-Doped Poly(butyl methacrylate)

This paper presents facile photoresponsive actuators comprising ferrocene as a guest chromophore and poly(butyl methacrylate) (PBMA) as a host matrix. The ferrocene-doped PBMA film exhibits mechanical expansion and contraction when a 445 nm laser is turned on and off, respectively. The photoresponsive film is attached by a commercially available acetylcellulose adhesive tape, which exhibits a bending motion that is controlled by turning the laser on and off. Thereafter, the double-layer film is employed to fabricate a table-shaped lifting machine (0.7 mg) that lifts a 10.5 mg object up and down by turning the laser on and off, respectively, and the mechanical force offered by the double-layer film is recorded. Additionally, the film is coated with gold and applied to an electric circuit that serves as a reversible photoresponsive switch. This film preparation technique is applied to other chromophores (e.g., Coumarin 343, Rhodamine 6G, Sudan Blue II, and Solvent Green 3) to independently control the motions of the films with 445, 520, and 655 nm lasers. The ferrocene-containing films also exhibit photoinduced healing from mechanical damage. Finally, the photoirradiation-accompanied morphological changes in the film are observed via small-angle X-ray scattering.

Reentrant 2D Nanostructured Liquid Crystals by Competition between Molecular Packing and Conformation: Potential Design for Multistep Switching of Ionic Conductivity

Reentrant phenomena in soft matter and biosystems have attracted considerable attention because their properties are closely related to high functionality. Here, we report a combined experimental and computational study on the self-assembly and reentrant behavior of a single-component thermotropic smectic liquid crystal toward the realization of dynamically functional materials. We have designed and synthesized a mesogenic molecule consisting of an alicyclic trans,trans-bicyclohexyl mesogen and a polar cyclic carbonate group connected by a flexible tetra(oxyethylene) spacer. The molecule exhibits an unprecedented sequence of layered smectic phases, in the order: smectic A-smectic B-reentrant smectic A. Electron density profiles and large-scale molecular dynamics simulations indicate that competition between the stacking of bicyclohexyl mesogens and the conformational flexibility of tetra(oxyethylene) chains induces this unusual reentrant behavior. Ion-conductive reentrant liquid-crystalline materials have been developed, which undergo the multistep conductivity changes in response to temperature. The reentrant liquid crystals have potential as new mesogenic materials exhibiting switching functions.

Photoinduced movement: how photoirradiation induced the movements of matter

Pioneered by the success on active transport of ions across membranes in 1980 using the regulation of the binding properties of crown ethers with covalently linked photoisomerizable units, extensive studies on the movements by using varied interactions between moving objects and environments have been reported. Photoinduced movements of various objects ranging from molecules, polymers to microscopic particles were discussed from the aspects of the driving for the movements, materials design to achieve the movements and systems design to see and to utilize the movements are summarized in this review.

Coatable 2D Conjugated Polymers Containing Bulky Macromolecular Guests for Thermal Imaging

Dynamic properties are derived from the structural flexibility of 2D polymers. Softening layered structures has the potential for tuning and enhancing the dynamic properties. In the present work, the flexibility of layered polydiacetylene (PDA) is tuned by the interlayer polymeric guests with different branching structures. PDA shows thermoresponsive color-change properties through shortening the effective conjugation length with molecular motion. Whereas the blue-to-red color transition is observed at certain threshold temperatures for the layered PDA without the interlayer guest, the intercalation of the bulky polymer guests lowers the starting temperature and widens the temperature range for the thermoresponsive color changes. The resultant layered composite of PDA and bulky polymer affords the homogeneous coating on substrates on the centimeter scale. The thermoresponsive color-change coating is applied to temperature-distribution imaging. The specific heat of liquids is colorimetrically estimated using the coating on the bottle. The coating on a silk cloth visualizes the temperature distribution on a simulated tissue during surgical operation using an ultrasonic coagulation cutting device. The coating can be applied to thermal imaging in a variety of fields. Moreover, the softening strategy contributes to explore dynamic properties of soft 2D materials.

Jammed Microgel-Based Inks for 3D Printing of Complex Structures Transformable via pH/Temperature Variations

Structure changes mediated by anisotropic volume changes of stimuli-responsive hydrogels are useful for many research fields, yet relatively simple structured objects are mostly used due to limitation in fabrication methods. To fabricate complex 3 dimensional (3D) structures that undergo structure changes in response to external stimuli, jammed microgel-based inks containing precursors of stimuli-responsive hydrogels are developed for extrusion-based 3D printing. Specifically, the jammed microgel-based inks are prepared by absorbing precursors of poly(acrylic acid) or poly(N-isopropylacrylamide) in poly(acrylamide) (PAAm) microgels, and jamming them. The inks exhibit shear-thinning and self-healing properties that allow extrusion of the inks through a nozzle and rapid stabilization after printing. Stimuli-mediated volume changes are observed for the extruded structures when they are post-crosslinked by UV light to form interpenetrating networks of PAAm microgels and stimuli-responsive hydrogels. Using this method, a dumbbell-shaped object that can transform to a biconvex shape, and a gripper that can grasp and lift an object in response to stimuli are 3D-printed. The jammed microgel-based 3D printing strategy is a versatile method useful for variety of applications as diverse types of monomers absorbable in the microgels can be used to fabricate complex 3D objects transformable by external stimuli.

Colloidal Self-Assembly Approaches to Smart Nanostructured Materials

Colloidal self-assembly refers to a solution-processed assembly of nanometer-/micrometer-sized, well-dispersed particles into secondary structures, whose collective properties are controlled by not only nanoparticle property but also the superstructure symmetry, orientation, phase, and dimension. This combination of characteristics makes colloidal superstructures highly susceptible to remote stimuli or local environmental changes, representing a prominent platform for developing stimuli-responsive materials and smart devices. Chemists are achieving even more delicate control over their active responses to various practical stimuli, setting the stage ready for fully exploiting the potential of this unique set of materials. This review addresses the assembly of colloids into stimuli-responsive or smart nanostructured materials. We first delineate the colloidal self-assembly driven by forces of different length scales. A set of concepts and equations are outlined for controlling the colloidal crystal growth, appreciating the importance of particle connectivity in creating responsive superstructures. We then present working mechanisms and practical strategies for engineering smart colloidal assemblies. The concepts underpinning separation and connectivity control are systematically introduced, allowing active tuning and precise prediction of the colloidal crystal properties in response to external stimuli. Various exciting applications of these unique materials are summarized with a specific focus on the structure-property correlation in smart materials and functional devices. We conclude this review with a summary of existing challenges in colloidal self-assembly of smart materials and provide a perspective on their further advances to the next generation.

Stimuli-Responsive AIEgens

The unique advantages and the exciting application prospects of AIEgens have triggered booming developments in this area in recent years. Among them, stimuli-responsive AIEgens have received particular attention and impressive progress, and they have been demonstrated to show tremendous potential in many fields from physical chemistry to materials science and to biology and medicine. Here, the recent achievements of stimuli-responsive AIEgens in terms of seven most representative types of stimuli including force, light, polarity, temperature, electricity, ion, and pH, are summarized. Based on typical examples, it is illustrated how each type of systems realize the desired stimuli-responsive performance for various applications. The key work principles behind them are ultimately deciphered and figured out to offer new insights and guidelines for the design and engineering of the next-generation stimuli-responsive luminescent materials for more broad applications.

Photo-Responsive Behavior of Azobenzene Based Polar Hockey-Stick-Shaped Liquid Crystals

A study on the photoswitching behavior of azobenzene-based polar hockey-stick-shaped liquid crystals (HSLCs) has been presented. Two new series of five phenyl rings based polar HSLCs have been designed and synthesized. Solution state photoisomerization of the synthesized materials was investigated thoroughly via UV-visible and ¹ H NMR spectroscopic techniques, whereas solid-state photochromic behavior was elucidated via physical color change of the materials, solid-state UV-visible study, powder XRD, and FE-SEM techniques. The materials exhibited decent photochromic behavior for different potential applications. The thermal phase behavior of the superstructural assembly has been characterized via polarizing optical microscopy (POM), differential scanning calorimetry (DSC), and temperature-dependent small and wide-angle X-ray scattering (SAXS/WAXS) studies. Depending upon the length of the terminal alkyl chain, nematic (N) and partially bilayer smectic A (SmA_d ) phases were observed. DFT calculations revealed the favorable anti-parallel arrangement of the polar molecules that substantiate the formation of SmA_d phase.

Self-Assembly of Bolaamphiphiles into 2D Nanosheets via Synergistic and Meticulous Tailoring of Multiple Noncovalent Interactions

A bolaamphiphile possessing a hydrophobic skeleton and two hydrophilic groups at both ends represents an important class of building blocks toward a rich variety of self-assembled materials for use in ion transport, optoelectronic devices, and drug and gene delivery. Herein, we report a one-step synthesis of an array of rationally designed anionic bolaamphiphiles and unravel the correlation between molecular structure of anionic bolaamphiphiles and their disparate self-assemblies via synergistic and meticulous tailoring of a set of interactions. Intriguingly, by delicately regulating the interactions among these supramolecular interactions, two-dimensional (2D) nanosheets are crafted via self-assembly of anionic bolaamphiphiles. Particularly, single-layered 2D nanosheets are formed through the synergy of aromatic π-π stacking, hydrophobic, hydrogen-bonding, and electrostatic repulsion interactions. In contrast, the selective converting of anionic headgroups of bolaamphiphiles into nonpolar alkyl chain screens the electrostatic repulsion between neighboring bolaamphiphiles while keeping the other segments of bolaamphiphiles intact, thereby allowing them to self-assemble into multilayered 2D nanosheets. Interestingly, the intrinsically charged 2D nanosheets could anchor oppositely charged metal nanoparticles via electrostatic attraction. Conceptually, anionic bolaamphiphile-derived 2D nanosheets may function as a substrate to position a diversity of nanocrystals and conjugated polymers for a broad range of applications in catalysis, optical devices, and photothermal therapy.

Unprecedentedly Ultrafast Dynamics of Excited States of C═C Photoswitching Molecules in Nanocrystals and Microcrystals

The C═C photoswitching molecules [1,2-di(4-pyridyl)ethylene (DPE), 4-styrylpyridine (SP), and trans-1,2-stilbene (TS)] show favorable photoisomerization characteristics. Although the solid states of photoswitching molecules are usually used in optical devices, their excited state's evolution has been little explored. Here, the excited state's relaxation of DPE, SP, and TS in nanocrystal/microcrystal suspensions as well as in solution phase was studied to uncover the early events of their excited states. The dynamics of nanocrystal/microcrystal suspensions was tremendously accelerated in comparison to the kinetics obtained in the solution for these molecules under excitation. DPE exhibits the slowest decay rate, while SP shows the fastest decay rate in nanocrystal suspensions or solution, suggesting SP may be the best candidate for the photoswitching device. The intermolecular interactions and space restriction of the crystal lead to the acceleration of the excited state's evolution for DPE, SP, and TS. This provides new insight into the design of optical materials.

Azobenzene-modified Ag/Ag2O/CN photocatalysts with photoresponsive performance for controllable photodegradation of tetracyclines

In this work, an Azo@Ag/Ag₂O/CN composite photocatalyst with light-responsive performance was successfully prepared by precipitation and emulsion polymerization. Azo@Ag/Ag₂O/CN exhibits cis-trans isomerism under different light exposures.

Intercalation and flexibility chemistries of soft layered materials

Layered materials, alternate stackings of two or more components, are found in a wide range of scales. Chemists can design and synthesize layered structures containing functional units. The soft-type layered materials exhibit characteristic dynamic functions originating from two-dimensional (2D) anisotropy and structure flexibility. This feature article focuses on "intercalation" and "flexibility" as two new perspectives for designing soft layered materials. Intercalation of guests is a characteristic approach for design of layered structures. Flexibility is an important factor to control the dynamic functions of the layered structures. As a model case, the intercalation-induced tunable stimuli-responsive color-change properties of layered polydiacetylene (PDA) are introduced to study the impact of the intercalation and flexibility on the dynamic functions. Recently, layered materials have drastically expanded the research area from conventional rigid inorganic compounds to new self-assembled nanostructures consisting of organic components, such as polymers, metal-organic frameworks, and covalent-organic frameworks. These new layered architectures have potentials for exhibiting dynamic functions originating from the structure flexibility beyond the static properties originating from classical intercalation and host-guest chemistries. Therefore, intercalation and flexibility chemistries of soft layered materials are regarded as new perspectives for design of advanced dynamic functional materials.

Photoinduced Mechanical Motions of Pseudorotaxane Crystals Composed of Azobenzene and Ferrocenyl Groups on an Axle and a Crown Ether Ring

This work describes the design and characterization of photoresponsive dynamic pseudorotaxane crystals composed of azobenzene and ferrocenyl groups in an ammonium cation axle component threaded through dibenzo[24]crown-8 ether rings. Pseudorotaxanes provide flexibility for cis and trans isomerization of azobenzene groups in a crystal state, enabling reversible bending motions under alternating 360 and 445 nm laser irradiation. For such bending motions, strained azobenzene structures were essential; these motifs were obtained by increasing the bulkiness of the substituents on the axle and ring molecules. In addition, the crystals showed photosalient effects, such as jumping motions, under 445 nm laser irradiation. These motions were assisted by the photoabsorption of the ferrocenyl group, which converted 445 nm laser light into heat. The maximum lifting weight accompanied by the photoinduced mechanical motion of a particular crystal was estimated to be 9600 times the crystal weight. These pseudorotaxane crystals exhibit promising features for applications in micro-nanometer-sized miniature mechanical devices.

Dual-emission fluorescent silicon nanoparticle-based nanothermometer for ratiometric detection of intracellular temperature in living cells

In this article, we present a kind of dual-emission fluorescent nanothermometer, which is made of europium (Eu3+)-doped silicon nanoparticles (Eu@SiNPs), allowing the detection of intracellular temperature in living cells with high accuracy. In particular, the presented SiNP-based thermometer features dual-emission fluorescence (blue (455 nm) and red (620 nm) emission), negligible toxicity (cell viability of treated cells remains above 90% during 24 h of treatment) and robust photostability in living cells (i.e., preserving >90% of fluorescence intensity after 45 min of continuous UV irradiation). More significantly, the fluorescence intensity of the Eu@SiNPs exhibits a linear ratiometric temperature response in a broad range from 25 to 70 °C. Taking advantage of these attractive merits, the Eu@SiNP-based nanothermometer is able to accurately (∼4.5% change per °C) determine dynamic changes in intracellular temperature in a quantitative and long-term (i.e., 30 min) manner.

R-Silsesquioxane-Based Network Polymers by Fluoride Catalyzed Synthesis: An Investigation of Cross-Linker Structure and Its Influence on Porosity

Silsesquioxane-based networks are an important class of materials that have many applications where high thermal/oxidative stability and porosity are needed simultaneously. However, there is a great desire to be able to design these materials for specialized applications in environmental remediation and medicine. To do so requires a simple synthesis method to make materials with expanded functionalities. In this article, we explore the synthesis of R-silsesquioxane-based porous networks by fluoride catalysis containing methyl, phenyl and vinyl corners (R-Si(OEt)₃) combined with four different bis-triethoxysilyl cross-linkers (ethyl, ethylene, acetylene and hexyl). Synthesized materials were then analyzed for their porosity, surface area, thermal stability and general structure. We found that when a specified cage corner (i.e., methyl) is compared across all cross-linkers in two different solvent systems (dichloromethane and acetonitrile), pore size distributions are consistent with cross-linker length, pore sizes tended to be larger and π-bond-containing cross-linkers reduced overall microporosity. Changing to larger cage corners for each of the cross-linkers tended to show decreases in overall surface area, except when both corners and cross-linkers contained π-bonds. These studies will enable further understanding of post-synthesis modifiable silsesquioxane networks.

Polymorph induced diversity of photomechanical motions of molecular crystals

Photomechanical motions of the polymorphs of trans-4,4′-azopyridine are distinct under the influence of different molecular packing and intermolecular interactions.

Molecular engineering of stimuli-responsive, functional, side-chain liquid crystalline copolymers: synthesis, properties and applications

This review describes recent progress made in designing stimuli-responsive, functional, side-chain, end-on mesogen attached liquid crystalline polymers (LCPs).

Design of Collective Motions from Synthetic Molecular Switches, Rotors, and Motors

Precise control over molecular movement is of fundamental and practical importance in physics, biology, and chemistry. At nanoscale, the peculiar functioning principles and the synthesis of individual molecular actuators and machines has been the subject of intense investigations and debates over the past 60 years. In this review, we focus on the design of collective motions that are achieved by integrating, in space and time, several or many of these individual mechanical units together. In particular, we provide an in-depth look at the intermolecular couplings used to physically connect a number of artificial mechanically active molecular units such as photochromic molecular switches, nanomachines based on mechanical bonds, molecular rotors, and light-powered rotary motors. We highlight the various functioning principles that can lead to their collective motion at various length scales. We also emphasize how their synchronized, or desynchronized, mechanical behavior can lead to emerging functional properties and to their implementation into new active devices and materials.

Independent Multi-states of Photo-responsive Polymer/Quantum Dot Nanocomposite Induced via Different Wavelengths of Light

Stimuli-responsive systems are attractive since their properties can be controlled by external stimuli and/or surrounding environment. Recently, more than one stimulus is utilized in order to enhance the performance of systems, or to bypass undesired effects. However, most of previous research on multi-stimuli has been focused on enhancing or inducing changes in one type of response. Herein, we developed a nanocomposite material with independent multi-states composed of photo-responsive polymer and quantum dots (QDs), in which its properties can independently be controlled by different wavelengths of light. More specifically, azobenzene-incorporated poly(dimethylsiloxane) (AzoPDMS) triggers photobending (PB) by 365 nm light and uniformly dispersed methylammonium lead bromide perovskite (MAPbBr₃) QDs show photoluminescence (PL) by light below 500 nm. The PB and PL could be simultaneously and independently controlled by the wavelength of applied light creating multi-states. Our approach is novel in that it creates multiple independent states which can further be used to transfer information such as logic gates (00₍₂₎, 01₍₂₎, 10₍₂₎, 11₍₂₎) and possibly widen its application to flexible and transparent opto-electric devices.

Shape-memory effects in molecular crystals

Molecular crystals can be bent elastically by expansion or plastically by delamination into slabs that glide along slip planes. Here we report that upon bending, terephthalic acid crystals can undergo a mechanically induced phase transition without delamination and their overall crystal integrity is retained. Such plastically bent crystals act as bimorphs and their phase uniformity can be recovered thermally by taking the crystal over the phase transition temperature. This recovers the original straight shape and the crystal can be bent by a reverse thermal treatment, resulting in shape memory effects akin of those observed with some metal alloys and polymers. We anticipate that similar memory and restorative effects are common for other molecular crystals having metastable polymorphs. The results demonstrate the advantage of using intermolecular interactions to accomplish mechanically adaptive properties with organic solids that bridge the gap between mesophasic and inorganic materials in the materials property space.

Molecular crystals can be bent elastically by expansion or contraction on opposite faces, or plastically by delamination into slabs that glide along slip planes. Here the authors report crystals that can be bent plastically while undergoing a mechanically induced phase transition without delamination.

Synthesis and Photoinduced Anisotropy of Polymers Containing Nunchaku-Like Unit with an Azobenzene and a Mesogen

A series of polymers containing nunchaku-like unit with an azo chromophore and a mesogen group was successfully prepared and photoinduced anisotropy of the obtained polymers was minutely investigated. Firstly, monomers containing nunchaku-like unit with an azo chromophore and a mesogen group linked by flexible group were synthesized. The structure of the monomers was confirmed via NMR COSY spectra. Subsequently, the obtained monomers were polymerized into corresponding polymers through RAFT polymerization. The prepared polymer samples were characterized through NMR, FTIR, gel permeation chromatography (GPC), and UV-vis testing while the thermal properties of the samples were investigated through differential scanning calorimeter (DSC) and thermogravimetric analysis (TGA) measurements. The photoinduced isomerization of the polymers, which was researched in situ via measuring UV-vis spectra of the polymer solutions and spin-coated films under irradiation with 450 nm light or putting in darkness, demonstrated the rapid trans-cis-trans isomerization of the polymers. When irradiated with a linearly polarized light, significant photoinduced birefringence and dichroism were observed, suggesting photoinduced isomerization of azobenzene can drive orientation of mesogen in the system. This study blazes a way to design the optical materials with light-controllable birefringence and dichroism.

Configuration-Controllable E/Z Isomers Based on Tetraphenylethene: Synthesis, Characterization, and Applications

Configuration-controllable E/Z isomers based on tetraphenylethene were prepared with a facile and effective method. First, compounds 1 and 2, configuration-controllable precursors of E/Z isomers, were synthesized. Then, pure E/Z isomers were obtained via Suzuki reaction, avoiding the difficulties of separation. The conformational changes of E/Z isomers can occur through photoactivation. Importantly, red-shifts of 66 nm from 6 (E-) to 3 (Z-) and 58 nm from 7 (E-) to 4 (Z-) were observed remarkably on the photoluminescence (PL) emission spectra. The Z isomer showed a longer fluorescence lifetime compared with the E isomer. The Z isomers 3 and 4 exhibited piezofluorochromism under grinding, whereas the E isomers 6 and 7 showed no such behaviors. The E isomer has better thermal stability than the Z isomer. Lastly, graphene-like molecules were synthesized with the FeCl₃/CH₃NO₂ system. The E and Z isomers after oxidation showed negligible differences in the PL emission spectra because the effective conjugated lengths of oxidized E and Z isomers were both extended. Furthermore, the fabricated field-effect transistors showed nice performance with mobilities of 0.92 and 1.14 cm^-2 V^-1 s^-1 at low operating voltages, respectively.

Light-Responsive Size of Self-Assembled Spiropyran-Lysozyme Nanoparticles with Enzymatic Function

Novel light-responsive nanoassemblies with switchable size and enzymatic activity are built from a protein and a water-soluble spiropyran. Assemblies are created by electrostatic self-assembly in aqueous solution such that the photochromic property of the spiropyran enables light responsiveness. Upon visible light exposure, the aggregate size increases from 200 to 400 nm. The enzyme retains its activity upon aggregation into the assembly, while it decreases through visible light irradiation. Fundamentally, we show how the two different spiropyran isomers, the open-ring merocyanine form and the closed-ring spiropyran form, bind differently to the protein, which triggers the assembly size and use of thermodynamic data to understand the binding process and the size response. Thus, as a proof of concept, a self-assembly driven light-tunable enzyme activity in conjunction with a triggerable assembly size is demonstrated for a model system. The concept bears future potential for various possible biological applications ranging from genetic control over vaccine applications to the detection of certain proteins.

Reversibly photoswitchable alkoxy azobenzenes connected benzenetricarboxamide discotic liquid crystals with perpetual long range columnar assembly

Reversibly photoswitchable discotic liquid crystals (DLCs) with no change in columnar assembly.

Dependence of the photo-response behavior of self-assembled 2D Azo-derivatives on the functional groups on a solid surface

Here, by means of scanning tunneling microscopy, we found that 2D self-assembled monolayers of four azobenzene derivatives exhibited different isomerization behaviors when taken from dark to irradiation conditions.

Photoswitchable Self-Assembly/Disassembly of Near-Infrared Fluorophores

A new photoswitchable near-infrared fluorophore (TDI-4DTE) with a symmetric structure exhibited reversible photo-controllable self-assembly and disassembly. The modification of π-conjugated terrylenediimide with four dithienylethene groups not only induced photoswitchable near-infrared fluorescence, but also photoregulated reversible precipitation-dissolution with microscopic and macroscopic polymorphism. Upon 302 nm UV-light irradiation, a noticeable precipitation was observed within seconds. The precipitate was gradually dissolved again in half an hour upon visible light irradiation. Different microscopic morphologies of the precipitates, including nanoparticles, nanofibrils and nanosheets, were observed when altering the intensity of the 302 nm light irradiation, indicating the dynamic control process of self-assembly. Upon UV-light irradiation, TDI-4DTE nanosheets were also obtained as a solid polymeric film, whereas well-defined nanoribbons with molecular monolayer thickness formed at the oil/water interface with slower assembly dynamics.

Visualization and Quantitative Detection of Friction Force by Self-Organized Organic Layered Composites

Visualization and quantitative detection of external stimuli are significant challenges in materials science. Quantitative detection of friction force, a mechanical stress, is not easily achieved using conventional stimuli-responsive materials. Here, the quantitative detection of friction force is reported, such as the strength and accumulated ammount, from the visible color of organic layered composites consisting of polydiacetylene (PDA) and organic amines without an excitation light source. The composites of the layered diacetylene monomer crystal and interlayer organic amine are synthesized through self-organization from the precursor solution. After topochemical polymerization, the layered composites based on PDA show tunable temperature-responsive and mechanoresponsive color-change properties depending on the types of interlayer amines. The layered composites are homogeneously coated on a filter paper. The change in color of the paper is quantitatively used to visualize the strength and accumulated amount of the applied friction force. Furthermore, writing pressure is measured by friction force using the paper device.

A self-healing photoinduced-deformable material fabricated by liquid crystalline elastomers using multivalent hydrogen bonds as cross-linkers

Liquid crystalline elastomers (LCEs) using multivalent hydrogen bonds as cross-linkers were successfully fabricated, which showed both self-healing and photoinduced-deformable properties. More interestingly, this LCE could be readily molded into different shapes through a versatile and efficient procedure, and the fibrous and filmy samples showed different photoinduced-deformable behavior originating from the difference in molecular orientations.

Self-Assembly-Triggered Cis-to-Trans Conversion of Azobenzene Compounds

Cis-to-trans transition of azobenzene compounds usually occurs under appropriate light irradiation or slow thermal relaxation, and one can hardly obtain complete cis-to-trans transition of azos due to the overlap of the n-π* transition of the trans and the cis isomers. We show that by viewing the photostationary state as a chemical equilibrium between the cis and trans isomers, triggered self-assembly of the trans isomers can promote the cis-to-trans transition, and trans azos with spectrum-grade purity can even be achieved using an elegantly designed coordinating azo. This work establishes a new paradigm for manipulating the cis-to-trans transition of azo compounds, which may inspire designs for various azo-based advanced materials.

Thermosalient effect of two polymorphs of a diketopyrrolopyrrole dye with different crystal systems and molecular arrangements

Two polymorphs of a diketopyrrolopyrrole dye, one yellow and the other orange, were obtained.