Force-induced cleavage of C–O bond in photochromic naphthopyrans

Force-induced cleavage of C–O bond in photochromic naphthopyrans in the pure microcrystalline solid state is described. The ring-closed isomers (colorless form) of naphthopyrans undergo cleavage of C–O bond under stress and are converted to ring-open isomers (colored form) in solid state. It is found that the threshold stress required to produce cleavage of C–O bond in naphthopyran derivatives in pure microcrystalline solid state is more than 2 MPa. Besides, the cleavage of C–O bond in photochromic naphthopyrans in the pure microcrystalline solid state can also be achieved by grinding.     

Surface Strain Redistribution on Structured Microfibers to Enhance Sensitivity of Fiber‐Shaped Stretchable Strain Sensors

Fiber‐shaped stretchable strain sensors with small testing areas can be directly woven into textiles. This paves the way for the design of integrated wearable devices capable of obtaining real‐time mechanical feedback for various applications. However, for a simple fiber that undergoes uniform strain distribution during deformation, it is still a big challenge to obtain high sensitivity. Herein, a new strategy, surface strain redistribution, is reported to significantly enhance the sensitivity of fiber‐shaped stretchable strain sensors. A new method of transient thermal curing is used to achieve the large‐scale fabrication of modified elastic microfibers with intrinsic microbeads. The proposed strategy is independent of the active materials utilized and can be universally applied for various active materials. The strategy used here will shift the vision of the sensitivity enhancement method from the active materials design to the mechanical design of the elastic substrate, and the proposed strategy can also be applied to nonfiber‐shaped stretchable strain sensors.     

Thermal Conductivity during Phase Transitions

Thermal conductivity is a very basic property that determines how fast a material conducts heat, which plays an important and sometimes a dominant role in many fields. However, because materials with phase transitions have been widely used recently, understanding and measuring temperature‐dependent thermal conductivity during phase transitions are important and sometimes even questionable. Here, the thermal transport equation is corrected by including heat absorption due to phase transitions to reveal how a phase transition affects the measured thermal conductivity. In addition to the enhanced heat capacity that is well known, it is found that thermal diffusivity can be abnormally lowered from the true value, which is also dependent on the speed of phase transitions. The extraction of the true thermal conductivity requires removing the contributions from both altered heat capacity and thermal diffusivity during phase transitions, which is well demonstrated in four selected kinds of phase transition materials (Cu₂Se, Cu₂S, Ag₂S, and Ag₂Se) in experiment. This study also explains the lowered abnormal thermal diffusivity during phase transitions in other materials and thus provides a novel strategy to engineer thermal conductivity for various applications.     

Functional Metallofullerene Materials and Their Applications in Nanomedicine,Magnetics, and Electronics

Endohedral metallofullerenes exhibit combined properties from carbon cages as well as internal metal moieties and have great potential in a wide range of applications as molecule materials. Along with the breakthrough of mass production of metallofullerenes, their applied research has been greatly developed with more and more new functions and practical applications. For gadolinium metallofullerenes, their water‐soluble derivatives have been demonstrated with antitumor activity and unprecedented tumor vascular‐targeting therapy. Metallofullerene water‐soluble derivatives also can be applied to treat reactive oxygen species (ROS)‐induced diseases due to their high antioxidative activity. For magnetic metallofullerenes, the internal electron spin and metal species bring about spin sensitivity, molecular magnets, and spin quantum qubits, which have many promising applications. Metallofullerenes are significant candidates for fabricating useful electronic devices because of their various electronic structures. This Review provides a summary of the metallofullerene studies reported recently, in the fields of tumor inhibition, tumor vascular‐targeting therapies, antioxidative activity, spin probes, single‐molecule magnets, spin qubits, and electronic devices. This is not an exhaustive summary and there are many other important study results regarding metallofullerenes. All of this research has revealed the irreplaceable role of metallofullerene materials.     

Thermal decoloration kinetics of spirooxazines in Ormocer coatings prepared via sol-gel processing

Two free and one silylated (silane-substituted) photochromic spirooxazines are doped into organically modified ceramics (Ormocer) coatings by sol-gel processing and the thermal decoloration kinetics of these coatings are investigated and compared with the corresponding ethanol solutions and PMMA coatings. The decoloration behaviour of the two free dyes (SO-1 and SO-2) in the Ormocer coatings is similar to that in ethanol solutions, obeying a first-order mechanism and possessing almost the same decoloration rates as in ethanol. This suggests that the dye molecules encapsulated within the pores of the solid matrix are as free as those in ethanol solutions. The silylated dye (SO-3) in the Ormocer coatings, however, exhibits a considerably lower decoloration rate than the corresponding free dye (SO-1) and evident deviation from the first-order mechanism. This indicates apparently that the degree of freedom of the dye molecules is reduced by the silylation. These results are discussed on the basis of solvent polarity, porous structure of the Ormocer coating, and the dye-to-matrix connectivity.     

光致变色材料的研究与应用

变色材料在变色眼镜、光学信息存储、光分子开关等方面具有广泛的应用.主要分析了螺吡喃、俘精酸酐、二芳基乙烯以及二氧化钛、卤化银等有机和无机光致变色材料的研究现状及其变色机理,最后介绍了光致变色材料在国防以及信息存储材料等方面的应用前景.     

The generic enhancement of photochromic dye switching speeds in a rigid polymer matrix

The switching or isomerization speed of photochromic dyes in a rigid polymeric matrix (such as an ophthalmic lens) is generally significantly slower than that observed in the mobile environment of a solution. Here we describe that the attachment of flexible oligomers having a low glass-transition temperature-such as poly(dimethylsiloxane)-to photochromic dyes greatly increases their switching speeds in a rigid polymer matrix. The greatest impact was observed in the thermal fade parameters T(1/2) and T(3/4)-the times it takes for the optical density to reduce by half and three quarters of the initial optical density of the coloured state-which were reduced by 40-95% and 60-99% respectively for spirooxazines, chromenes and an azo dye in a host polymer with a glass-transition temperature of 120 degrees C. The method does not alter the electronic nature of the dyes but simply protects them from the host matrix and provides greater molecular mobility for the switching process. In addition to ophthalmic lenses, the generic nature of the method may find further utility in data recording or optical switching.     

Economizing Production of Diverse 2D Layered Metal Hydroxides for Efficient Overall Water Splitting

2D layered metal hydroxides (LMH) are promising materials for electrochemical energy conversion and storage. Compared with exfoliation of bulk layered materials, wet chemistry synthesis of 2D LMH materials under mild conditions still remains a big challenge. Here, an “MgO‐mediated strategy” for mass production of various 2D LMH nanosheets is presented by hydrolyzing MgO in metal salt aqueous solutions at room temperature. Benefiting from this economical and scalable strategy, ultrathin LMH nanosheets (M = Ni, Fe, Co, NiFe, and NiCo) and their derivatives (e.g., metal oxides and sulfides) can be synthesized in high yields. More importantly, this strategy opens up opportunities to fabricate hierarchically structured LMH nanosheets, resulting in high‐performance electrocatalysts for the oxygen‐ and hydrogen‐evolution reactions to realize stable overall water splitting with a low cell voltage of 1.55 V at 10 mA cm⁻². This work provides a powerful platform for the synthesis and applications of 2D materials.     

Characterization of fatigue resistance in photochromic composite materials for 3D rewritable optical memory applications

Fatigue resistance of the photochromic diarylethene molecules 1,2-bis[2-methylbenzo[b]thyophen-3-yl]-3,3,4,4,5,5-hexafluoro-1-cyclopentene embedded in three different acrylic polymers is studied upon multiple coloration–decoloration cycles. The resistance to photofatigue is found to be different in the three polymeric materials when one-photon excitation was used for the reversible photoconversion experiment. In particular, the photochromic molecules lose their photoisomerization ability faster if they are embedded in poly(methyl methacrylate) (PMMA) with respect to poly(ethyl methacrylate-co-methyl acrylate) (PEMMA) and poly(ethyl methacrylate) (PEMA). We propose several explanations based on the physico-chemical properties of the matrix and of the photochromic molecules. In the case of two-photon excitation, which is necessary for 3D optical writing, the fatigue resistance is found to be poorer than in the one-photon case. The accelerated photodegradation can be assigned to the non-linear nature of interaction between the polymeric composite material and light.     

Tailorable Dynamics in Nonlinear Optical Metasurfaces

Controlling light with light is essential for all-optical switching, data processing in optical communications and computing. Until now, all-optical control of light has relied almost exclusively on nonlinear optical interactions in materials. Achieving giant nonlinearities under low light intensity is essential for weak-light nonlinear optics. In the past decades, such weak-light nonlinear phenomena have been demonstrated in photorefractive and photochromic materials. However, their bulky size and slow speed have hindered practical applications. Metasurfaces, which enhance light–matter interactions at the nanoscale, provide a new framework with tailorable nonlinearities for weak-light nonlinear dynamics. Current advances in nonlinear metasurfaces are introduced, with a special emphasis on all-optical light controls. The tuning of the nonlinearity values using metasurfaces, including enhancement and sign reversal is presented. The tailoring of the transient behaviors of nonlinearities in metasurfaces to achieve femtosecond switching speed is also discussed. Furthermore, the impact of quantum effects from the metasurface on the nonlinearities is introduced. Finally, an outlook on the future development of this energetic field is offered.     

Magnetron Sputtering Deposition of Ag/TiO2 Nanocomposite Thin Films for Repeatable and Multicolor Photochromic Applications on Flexible Substrates

It is reported on a reactive magnetron sputtering‐based deposition method to synthesize, at room temperature, photochromic nanocomposite thin films consisting of Ag nanoparticles sandwiched between nanoporous TiO₂ layers. The fabrication process is compatible with large‐scale production and functional flexible substrates. It is shown that when TiO₂ is deposited in the metallic mode, the formation of Ag metal nanoparticles induces localized surface plasmon resonances in the visible range and therefore the as‐deposited samples are colored. In contrast, when TiO₂ is deposited in the compound mode, the trilayer samples are colorless because silver oxidizes during TiO₂ deposition. It is demonstrated that the colorless samples can be colored under ultraviolet (UV) laser exposure at 244 nm due to the reduction of oxidized silver and the formation of metallic Ag nanoparticles. Moreover, irradiation at 647 nm wavelength of colored samples (as‐prepared or after UV exposure) gives rise to changes in the particle morphology that strongly modifies the film absorbance and results in a color transition from blue to orange. The choice of the irradiation wavelength allows controlling the color saturation of the sample up to the complete discoloration by using a visible laser at 488 nm. All these photochromic mechanisms are repeatable during cyclic processes.     

The Antibacterial Applications of Graphene and Its Derivatives

Graphene materials have unique structures and outstanding thermal, optical, mechanical and electronic properties. In the last decade, these materials have attracted substantial interest in the field of nanomaterials, with applications ranging from biosensors to biomedicine. Among these applications, great advances have been made in the field of antibacterial agents. Here, recent advancements in the use of graphene and its derivatives as antibacterial agents are reviewed. Graphene is used in three forms: the pristine form; mixed with other antibacterial agents, such as Ag and chitosan; or with a base material, such as poly (N‐vinylcarbazole) (PVK) and poly (lactic acid) (PLA). The main mechanisms proposed to explain the antibacterial behaviors of graphene and its derivatives are the membrane stress hypothesis, the oxidative stress hypothesis, the entrapment hypothesis, the electron transfer hypothesis and the photothermal hypothesis. This review describes contributions to improving these promising materials for antibacterial applications.     

Optical Properties of Functional Hybrid Organic–Inorganic Nanocomposites

Functional hybrids are nanocomposite materials lying at the interface of organic and inorganic realms, whose high versatility offers a wide range of possibilities to elaborate tailor‐made materials in terms of chemical and physical properties. Because they present several advantages for designing materials for optical applications (versatile and relatively facile chemistry, easy shaping and patterning, materials having good mechanical integrity and excellent optical quality), numerous silica or/and siloxane based hybrid organic–inorganic materials have been developed in the past few years. The most striking examples of functional hybrids exhibiting emission properties (solid‐state dye lasers, rare‐earth doped hybrids, electroluminescent devices), absorption properties (photochromic), nonlinear optical (NLO) properties (second‐order NLO properties, photochemical hole burning (PHB), photorefractivity), and sensing are summarized in this review.     

Progress in 3D Printing of Carbon Materials for Energy‐Related Applications

The additive‐manufacturing (AM) technique, known as three‐dimensional (3D) printing, has attracted much attention in industry and academia in recent years. 3D printing has been developed for a variety of applications. Printable inks are the most important component for 3D printing, and are related to the materials, the printing method, and the structures of the final 3D‐printed products. Carbon materials, due to their good chemical stability and versatile nanostructure, have been widely used in 3D printing for different applications. Good inks are mainly based on volatile solutions having carbon materials as fillers such as graphene oxide (GO), carbon nanotubes (CNT), carbon blacks, and solvent, as well as polymers and other additives. Studies of carbon materials in 3D printing, especially GO‐based materials, have been extensively reported for energy‐related applications. In these circumstances, understanding the very recent developments of 3D‐printed carbon materials and their extended applications to address energy‐related challenges and bring new concepts for material designs are becoming urgent and important. Here, recent developments in 3D printing of emerging devices for energy‐related applications are reviewed, including energy‐storage applications, electronic circuits, and thermal‐energy applications at high temperature. To close, a conclusion and outlook are provided, pointing out future designs and developments of 3D‐printing technology based on carbon materials for energy‐related applications and beyond.     

Synthesis,characterization, and photochromic behaviors of polythiophene derivatives in the solid state

Novel polythiophene derivatives with azobenzene chromophore side chains, poly[3-(6-((4-phenylazo)phenoxyl)hexyl)thienylacetate] (PATh-6), and the copolymers of 3-(6-((4-phenylazo)phenoxyl)hexyl)thienylacetate with 3-alkylthiophenes including 3-hexylthiophene and 3-dodecylthiophene (COP-66 and COP-612) were synthesized. The structure and the thermal property of these polythiophene derivatives were characterized by NMR, FT-IR, UV–vis, XRD, GPC, MDSC, and TGA. The differences in photochromic features and thermochromic behaviors between homopolymer and copolymers have been comparatively studied. The photochemical control of photoluminescence property was achieved with homopolymer PATh-6 both in solution and in the solid state. However, this photo-induced effect becomes less prominent for copolymers COP-66 and COP-612 due to the lower content of azobenzene chromophore in the side chain of copolymers. The photo-induced photochromic feature of homopolymer PATh-6 might be promising for the development of novel field-responsive materials.     

On the computation of the coupled thermo‐electromagnetic response of continua with particulate microstructure

Recently, several applications, primarily driven by micro‐technology, have emerged where the use of materials with tailored electromagnetic properties is necessary for a successful design. The ‘tailored’ properties are achieved by doping an easily moldable base matrix with particles having dielectric constants that are chosen to give overall desired properties. In many cases, the analysis of such materials requires the simulation of the macroscopic and microscopic electromagnetic response, as well as its resulting coupled thermal response, which can be important to determine possible failure in ‘hot spots’. In this study, a model and a solution strategy are developed to compute the response of a class of fully coupled electro‐magneto‐thermal systems composed of heterogeneous materials, involving the absorption of electromagnetic energy, its conversion to heat and changes in the electromagnetic material properties. The algorithm involves recursive staggering, whose convergence is dependent on the discretized time‐step size. The multifield system coupling can change, becoming weaker, stronger or alternating back and forth. Therefore, it is quite difficult to determine a priori the time‐step size needed to meet a prespecified tolerance on the staggering error, i.e. the incomplete resolution of the coupling between the fields. The presented solution process involves time‐step size adaptivity to control the contraction mapping constant of the multifield system operator in order to induce desired staggering rates of convergence within each time step and to control the staggering error. Three‐dimensional numerical experiments are performed to illustrate the behavior of the model and the solution strategy. Copyright © 2008 John Wiley & Sons, Ltd.     

Recent Advances in Transparent Electronics with Stretchable Forms

Advances in materials science and the desire for next‐generation electronics have driven the development of stretchable and transparent electronics in the past decade. Novel applications, such as smart contact lenses and wearable sensors, have been introduced with stretchable and transparent form factors, requiring a deeper and wider exploration of materials and fabrication processes. In this regard, many research efforts have been dedicated to the development of mechanically stretchable, optically transparent materials and devices. Recent advances in stretchable and transparent electronics are discussed herein, with special emphasis on the development of stretchable and transparent materials, including substrates and electrodes. Several representative examples of applications enabled by stretchable and transparent electronics are presented, including sensors, smart contact lenses, heaters, and neural interfaces. The current challenges and opportunities for each type of stretchable and transparent electronics are also discussed.     

The Optical Janus Effect: Asymmetric Structural Color Reflection Materials

Structurally colored materials are often used for their resistance to photobleaching and their complex viewing‐direction‐dependent optical properties. Frequently, absorption has been added to these types of materials in order to improve the color saturation by mitigating the effects of nonspecific scattering that is present in most samples due to imperfect manufacturing procedures. The combination of absorbing elements and structural coloration often yields emergent optical properties. Here, a new hybrid architecture is introduced that leads to an interesting, highly directional optical effect. By localizing absorption in a thin layer within a transparent, structurally colored multilayer material, an optical Janus effect is created, wherein the observed reflected color is different on one side of the sample than on the other. A systematic characterization of the optical properties of these structures as a function of their geometry and composition is performed. The experimental studies are coupled with a theoretical analysis that enables a precise, rational design of various optical Janus structures with highly controlled color, pattern, and fabrication approaches. These asymmetrically colored materials will open applications in art, architecture, semitransparent solar cells, and security features in anticounterfeiting materials.     

Eu掺杂KNN陶瓷的制备及可调性发光研究

稀土离子掺杂铁电陶瓷是一类新型光致变色材料, 在光开关、光信息存储等领域具有潜在应用价值。本研究采用水热法制备了(K_0.5 Na_0.5)_1-xEu_xNbO₃(KNN:xEu)前驱体粉体, 随后利用高温烧结得到对应陶瓷样品。在465 nm激发下, 观察到615 nm处有强的红色发光, 对应于Eu ³⁺的 ⁵D₀→ ⁷F₂跃迁。通过紫外光照射, KNN:Eu陶瓷从乳白色变为深灰色。随后经过200 ℃加热10 min, 着色陶瓷又变回到初始颜色, 显示出良好的光致变色行为。紫外照射和反复加热循环可以有效调控该陶瓷的发光强度。且经过多次循环之后, 发光强度没有明显衰减。在紫外光照射下, KNN:0.06Eu陶瓷发光强度的可调比(ΔR_t)高达83.9%, 说明发光具有良好的可调性。进而结合发光中心和色心之间的能量转移, 对KNN:Eu陶瓷的光致变色和发光机理进行了解释。     

Light‐Emitting Polythiophenes

Polythiophenes are one of the most important classes of conjugated polymers, with a wide range of applications, such as conducting films, electrochromics, and field‐effect transistors, which have been the subject of a number of older and more recent reviews. Much less attention has been paid to the light‐emitting properties of this class of materials, although their unique properties present a number of opportunities unavailable from more popular polymeric light emitters such as polyfluorene or poly(p‐phenylene vinylene). This article reviews achievements to date in applications of thiophene‐based polymers and oligomers as electroluminescent materials. We demonstrate the basic principles of controlling the optical properties of polythiophenes through structural modifications and review the most important light‐emitting materials created from thiophene derivatives. Special attention is paid to consequences of structural variations on the performance of light‐emitting diodes fabricated with these materials.