Liquid crystals (LCs) are omnipresent in living matter, whose chirality is an elegant and distinct feature in certain plant tissues, the cuticles of crabs, beetles, arthropods, and beyond. Taking ...inspiration from nature, researchers have recently devoted extensive efforts toward developing chiral liquid crystalline materials with self‐organized nanostructures and exploring their potential applications in diverse fields ranging from dynamic photonics to energy and safety issues. In this review, an account on the state of the art of emerging chiral liquid crystalline nanostructured materials and their technological applications is provided. First, an overview on the significance of chiral liquid crystalline architectures in various living systems is given. Then, the recent significant progress in different chiral liquid crystalline systems including thermotropic LCs (cholesteric LCs, cubic blue phases, achiral bent‐core LCs, etc.) and lyotropic LCs (DNA LCs, nanocellulose LCs, and graphene oxide LCs) is showcased. The review concludes with a perspective on the future scope, opportunities, and challenges in these truly advanced functional soft materials and their promising applications.
Chiral liquid crystal nanostructures are omnipresent in living systems. A state‐of‐the‐art account of emerging chiral liquid crystalline nanostructured materials and their potential applications is provided. The perspectives for future scope, challenges, and opportunities on such a multidisciplinary topic are outlined.
The ability to control light direction with tailored precision via facile means is long‐desired in science and industry. With the advances in optics, a periodic structure called diffraction grating ...gains prominence and renders a more flexible control over light propagation when compared to prisms. Today, diffraction gratings are common components in wavelength division multiplexing devices, monochromators, lasers, spectrometers, media storage, beam steering, and many other applications. Next‐generation optical devices, however, demand nonmechanical, full and remote control, besides generating higher than 1D diffraction patterns with as few optical elements as possible. Liquid crystals (LCs) are great candidates for light control since they can form various patterns under different stimuli, including periodic structures capable of behaving as diffraction gratings. The characteristics of such gratings depend on several physical properties of the LCs such as film thickness, periodicity, and molecular orientation, all resulting from the internal constraints of the sample, and all of these are easily controllable. In this review, the authors summarize the research and development on stimuli‐controllable diffraction gratings and beam steering using LCs as the active optical materials. Dynamic gratings fabricated by applying external field forces or surface treatments and made of chiral and nonchiral LCs with and without polymer networks are described. LC gratings capable of switching under external stimuli such as light, electric and magnetic fields, heat, and chemical composition are discussed. The focus is on the materials, designs, applications, and future prospects of diffraction gratings using LC materials as active layers.
Control of light is of fundamental importance across all fields of science and technology. Next‐generation devices require nonmechanical capabilities and easy tuning for adapting to fastchanging situations. How, over the last 50 years, liquid crystals have been used as switchable diffraction gratings, along with fabrication, designs, challenges, and the future of liquid crystal gratings are discussed.
Supramolecular approaches toward the fabrication of functional materials and systems have been an enabling endeavor. Recently, halogen bonding has been harnessed as a promising supramolecular tool. ...Herein we report the synthesis and characterization of a novel halogen‐bonded light‐driven axially chiral molecular switch. The photoactive halogen‐bonded chiral switch is able to induce a self‐organized, tunable helical superstructure, that is, cholesteric liquid crystal (CLC), when doped into an achiral liquid crystal (LC) host. The halogen‐bonded switch as a chiral dopant has a high helical twisting power (HTP) and shows a large change of its HTP upon photoisomerization. This light‐driven dynamic modulation enables reversible selective reflection color tuning across the entire visible spectrum. The chiral switch also displays a temperature‐dependent HTP change that enables thermally driven red, green, and blue (RGB) reflection colors in the self‐organized helical superstructure.
Color switch: A novel halogen‐bonded light‐driven axially chiral molecular switch is able to induce a self‐organized, tunable helical superstructure when doped into an achiral liquid‐crystal host. Both light‐ and temperature‐driven dynamic modulation of the helical superstructure has enabled red, green and blue reflections to be achieved for the first time employing the halogen‐bonded chiral molecular switch.
Development of light-driven functional materials capable of displaying reversible properties is currently a vibrant frontier from both scientific and technological points of view. Here a new ...visible-light-driven chiral molecular switch is synthesized and characterized. To the best of our knowledge, this is the first example of a chiral molecular switch in which the visible-light-driven azobenzene motif is directly linked to an axially chiral scaffold through a C–C bond. The chiral molecular switch exhibits trans-to-cis photoisomerization upon 530 nm irradiation and cis-to-trans isomerization upon 450 nm irradiation. The switch can thus be photoisomerized in both directions using visible light of different wavelengths, a promising attribute for device applications. It was found that this relatively rigid molecular switch exhibited a high helical twisting power (HTP) in liquid crystal hosts and a large change of HTP value upon photoisomerization. We achieved dynamic reflection tuning across the visible spectrum through incorporation into a self-organized helical superstructure, i.e., a cholesteric liquid crystal. We also demonstrated patterned photodisplays reflecting red, green, and blue circularly polarized light using these cholesteric films. Phototunable color displays were fabricated by selective light irradiation where the information can be reversibly hidden by applying an electric field and restored by applying either a mechanical force or an electric field of higher voltage.
Owing to their dynamic attributes, non‐covalent supramolecular interactions have enabled a new paradigm in the design and fabrication of multifunctional material systems with programmable properties, ...performances, and reconfigurable traits. Recently, the “halogen bond” has become an enticing supramolecular synthetic tool that displays a plethora of promising and advantageous characteristics. Consequently, this versatile and dynamic non‐covalent interaction has been extensively harnessed in various fields such as crystal engineering, self‐assembly, materials science, polymer chemistry, biochemistry, medicinal chemistry and nanotechnology. In recent years, halogen bonding has emerged as a tunable supramolecular synthetic tool in the design of functional liquid‐crystalline materials with adjustable phases and properties. In this Concept article, the use of halogen bond in the field of stimuli‐responsive smart soft materials, that is, liquid crystals is discussed. The design, synthesis and characterization of molecular and macromolecular liquid crystalline materials are described and the modulation of their properties has been emphasized. The power of halogen bonding in offering a large variety of functional liquid crystalline materials from readily accessible mesomorphic and non‐mesomorphic complementary building blocks is highlighted. The article concludes with a perspective on the challenges and opportunities in this emerging endeavor towards the realization of enabling and elegant dynamic functional materials.
Holy halogens: The halogen bond is increasingly used in the realization of advanced functional materials. In this Concept article, we discuss the usage of halogen bond as an enabling supramolecular tool in the preparation of different kinds of functional liquid crystalline materials towards the understanding of their structure–property and structure–function relationships.
Remote driving of functional hybrid soft materials for various applications is emerging as an enabling pursuit. Toward this end, soft materials driven by photothermal agents have been attracting ...tremendous attention from both fundamental science and technological applications points of view. These stimuli‐responsive materials combine the beneficial attributes of both classes of promising materials, i.e., soft materials and photothermal agents. Both inorganic and organic photothermal agents have been incorporated into the matrices of soft materials. Metal nanoparticles, carbon nanomaterials, and organic photothermal agents have been impregnated into the matrices of liquid crystals, polymers, and gels that can be remotely driven by light irradiation. In this review, the remote driving of functional hybrid soft materials and their various applications are discussed. Photothermal functional nanocomposites are demonstrated to act as actuators, therapeutic agents, drug delivery systems, microvalves, etc. Smart and adaptive systems are realized by dispersing photothermal agents into soft matter matrices. Challenges and opportunities in this fascinating frontier are outlined.
Functional stimuli‐responsive hybrid materials that can be driven by remote control have been attracting tremendous attention both from fundamental science and technological applications points of view. In this review, soft materials driven by photothermal effect are discussed. Metal nanoparticles, carbon nanomaterials, and organic photothermal agents are used to remotely drive liquid crystals, polymers, and gels for different applications.
Mechanochromic Photonic Gels Chan, Edwin P.; Walish, Joseph J.; Urbas, Augustine M. ...
Advanced materials (Weinheim),
August 7, 2013, Letnik:
25, Številka:
29
Journal Article
Recenzirano
Odprti dostop
Polymer gels are remarkable materials with physical structures that can adapt significantly and quite rapidly with changes in the local environment, such as temperature, light intensity, ...electrochemistry, and mechanical force. An interesting phenomenon observed in certain polymer gel systems is mechanochromism – a change in color due to a mechanical deformation. Mechanochromic photonic gels are periodically structured gels engineered with a photonic stopband that can be tuned by mechanical forces to reflect specific colors. These materials have potential as mechanochromic sensors because both the mechanical and optical properties are highly tailorable via incorporation of diluents, solvents, nanoparticles, or polymers, or the application of stimuli such as temperature, pH, or electric or strain fields. Recent advances in photonic gels that display strain‐dependent optical properties are discussed. In particular, this discussion focuses primarily on polymer‐based photonic gels that are directly or indirectly fabricated via self‐assembly, as these materials are promising soft material platforms for scalable mechanochromic sensors.
Mechanochromic photonic gels are polymer gels that display mechanical strain‐responsive structural color. These gels are interesting materials for mechanochromic sensing applications due to their highly tunable mechanical and optical properties. In this progress report, recent advances in developing mechanochromic photonic gels that display strain‐responsive optical properties for scalable sensors are highlighted.
Light‐induced phenomena occurring in nature and in synthetic materials are fascinating and have been exploited for technological applications. Here visible‐light‐induced formation of a helical ...superstructure is reported, i.e., a cholesteric liquid crystal phase, in orientationally ordered fluids, i.e., nematic liquid crystals, enabled by a visible‐light‐driven chiral molecular switch. The cyclic‐azobenzene‐based chiral molecular switch exhibits reversible photoisomerization in response to visible light of different wavelengths due to the band separation of n–π* transitions of its trans‐ and cis‐isomers. Green light (530 nm) drives the trans‐to‐cis photoisomerization whereas the cis‐to‐trans isomerization process of the chiral molecular switch can be caused by blue light (440 nm). It is observed that the helical twisting power of this chiral molecular switch increases upon irradiation with green light, which enables reversible induction of helical superstructure in nematic liquid crystals containing a very small quantity of the molecular switch. The occurrence of the light‐induced helical superstructure enables the formation of diffraction gratings in cholesteric films.
Light‐induced phenomena abound in nature and have served as inspiration in the development of light‐driven materials for device applications. In this work, visible‐light‐induced formation of a helical superstructure is accomplished in orientationally ordered fluids, i.e., nematic liquid crystals, enabled by a visible‐light‐driven chiral molecular switch.
Light in biological media is known as freely diffusing because interference is negligible. Here, we show Anderson light localization in quasi-two-dimensional protein nanostructures produced by ...silkworms (Bombyx mori). For transmission channels in native silk, the light flux is governed by a few localized modes. Relative spatial fluctuations in transmission quantities are proximal to the Anderson regime. The sizes of passive cavities (smaller than a single fibre) and the statistics of modes (decomposed from excitation at the gain-loss equilibrium) differentiate silk from other diffusive structures sharing microscopic morphological similarity. Because the strong reflectivity from Anderson localization is combined with the high emissivity of the biomolecules in infra-red radiation, silk radiates heat more than it absorbs for passive cooling. This collective evidence explains how a silkworm designs a nanoarchitectured optical window of resonant tunnelling in the physically closed structures, while suppressing most of transmission in the visible spectrum and emitting thermal radiation.
Chiral media exhibit optical phenomena that provide distinctive responses from opposite circular polarizations. The disparity between these responses can be optimized by structurally engineering ...absorptive materials into chiral nanopatterns to form metamaterials that provide gigantic chiroptical resonances. To fully leverage the innate duality of chiral metamaterials for future optical technologies, it is essential to make such chiroptical responses tunable via external means. Here we report an optical metamaterial with tailored chiroptical effects in the nonlinear regime, which exhibits a pronounced shift in its circular dichroism spectrum under a modest level of excitation power. Strong nonlinear optical rotation is observed at key spectral locations, with an intensity-induced change of 14° in the polarization rotation from a metamaterial thickness of less than λ/7. The modulation of chiroptical responses by manipulation of input powers incident on chiral metamaterials offers potential for active optics such as all-optical switching and light modulation.
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