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Micro-sized chiral-nematic liquid crystal (N* LC) polymer particles have attracted considerable interest as versatile reflective colorants with selective circularly polarized light (CPL) properties. However, challenges in achieving the desired size distribution of N* LC particles have led to an incomplete understanding of their reflective characteristics. In this study, we successfully synthesized N* LC particles via dispersion polymerization, enabling precise control over size polydispersity by manipulating the composition of the polymerization solvent. Our investigation revealed that monodisperse N* LC particles displayed distinct reflection bands with high CPL selectivity, while polydisperse particles exhibited broader reflection with lower CPL selectivity. These findings underscore the potential to synthesize N* LC particles with tailored reflective properties using identical monomeric compounds. Furthermore, we demonstrated the production of multifunctional reflective colorants by blending N* LC particles with varying reflection colors. These discoveries hold significant promise for advancing the development of reflective colorants and anti-counterfeiting printing techniques utilizing micro-sized N* LC particles. [ABSTRACT FROM AUTHOR]

The development of multifunctional optical elements capable of controlling polarization, wavelength, and propagation direction is pivotal for the miniaturization of optical devices. However, designing the spatial distribution of the refractive index for the fabrication of such elements remains challenging. This study demonstrates the spectroscopic function of microparticles composed of chiral-nematic liquid crystals (N* LC), which inherently selectively reflect circularly polarized light. The measurement of the reflection spectra with fiber probes revealed angular-dependent back-reflection of the single layer of the N* LC particles. These results indicate that our N* LC microparticles possess multiple optical functions, enabling the separation of incident light polarization and wavelength within a single material. This suggests broad applications of N* LC particles as compact optical elements. [ABSTRACT FROM AUTHOR]

Organometallic materials that exhibit white luminescence in condensed phases are of considerable interest for lighting and display applications. Herein, new carbazole-based Au(I) complexes containing an isocyanide group and a long pentyl chain were synthesized. The complex with an unsubstituted carbazole moiety exhibited a white emission at room temperature as well as nematic liquid crystalline behavior. Color tunability from white to blue was achieved when bulkier substituents were introduced at the 3 and 6 positions of the carbazole moiety. Furthermore, all complexes possessed long phosphorescence lifetimes in the crystal state. The proposed design framework provides new opportunities for practical applications using luminescent organometallic molecules. [ABSTRACT FROM AUTHOR]

Advances in tuning the mechanoresponsive behavior of liquid crystal elastomers have facilitated the development of next‐generation applications such as reconfigurable photonic/electronic materials, energy‐harvesting devices, and flexible sensors. However, the molecular‐level control of mechanical responses remains difficult, with limited tunability achieved for recovery processes after stimulus removal. Herein, a design concept is proposed for facilely tuning the recovery of both the macroscopic deformation and molecular orientation change of liquid crystal elastomers using layered materials that exhibit the desired mechanoresponsive behavior. Changing the layering materials (a polydimethylsiloxane film with elastic response to a polymethylpenten film with plastic response) alters the relaxation time from <1 s to >6 months. To demonstrate this concept, highly sensitive, stretchable mechano‐optical sensors with fast and ultraslow recovery times are developed that enable an applied strain to be quantitatively detected in real time or memorized with high spatial resolution, even with a conventional camera. This material design concept for arbitrarily controlling the recovery response can provide a platform for stimuli‐responsive applications. [ABSTRACT FROM AUTHOR]

Chiral-nematic liquid crystal (N* LC) elastomers exhibit mechano-optical responsive behavior. However, practical sensor applications have been limited by the intrinsic sensitivity of N* LC elastomers to environmental conditions, such as temperature. Although densely cross-linked LC network polymers exhibit high thermal stability, they are not proper for the mechanical sensor due to high glass transition temperatures and low flexibility. To overcome these issues, we focused on enhancing thermal stability by introducing noncovalent cross-linking sites via intermolecular interactions between LC molecules bonded to the polymer network. N* LC elastomers with a cyanobiphenyl derivative as a side-chain mesogen exhibited mechano-optical responsive behavior, with a hypsochromic shift of the reflection peak wavelength under an applied tensile strain and quick shape and color recovery owing to high elasticity. Notably, the N* LC elastomers showed high resistance to harsh environments, including high temperatures and various solvents. Interactions, such as π–π stacking and dipole–dipole interactions, between the cyanobiphenyl units can act as weak cross-links, thus improving the thermal stability of the LC phase without affecting the mechano-optical response. Thus, these N* LC elastomers have great potential for the realization of practical mechano-optical sensors. [ABSTRACT FROM AUTHOR]

Photoinduced reorientation (photon-mode process) and thermal effects in an oligothiophene-doped liquid crystal (LC) system were investigated by self-diffraction measurements in different experimental configurations. The results obtained in homeotropic sample cells were compared with those obtained in homogeneous cells. Optical Freedericksz transition could be induced by low-intensity light in the homeotropic cell, and the induced birefringence was affected by the thermal effect. No photoinduced reorientation effect was observed in the homogeneous cell in the present experimental configuration; however, due to the thermal modulation of the refractive index of the LC, which arises from light absorption, self-diffraction phenomena could also be observed. © 2002 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Luminescent liquid-crystalline (LC) Au complexes with various aromatic cores and flexible terminal chains were synthesized. The aromatic core aspect ratio crucially affected the LC temperature range and melting point of the complexes. Moreover, branched flexible chains reduced the melting point, thus expanding the LC temperature range. In the crystalline and LC phases of the complexes, fluorescence was quenched by the aggregation-caused quenching effect, but phosphorescence was enhanced by the crystallization-induced phosphorescence effect. However, no phosphorescence was observed in the isotropic phase. Thus, not only aggregation but also regularity of molecular aggregates is necessary for the observed crystallization-induced phosphorescence effect. [ABSTRACT FROM AUTHOR]

A highly ordered nanochannel array consisting of giant-ring-shaped polyoxomolybdate (POMo) was prepared via self-assembly of the oxomolybdate monomers. Concentration and pH optimization of the reaction solution favored the self-assembly; the nanochannel structure spontaneously self-constructed during the crystallization process. The obtained crystal showed a highly ordered nanochannel with a diameter of 2.0 nm and no distribution in the channel size. In addition, the material was found to be very stable at ambient temperature in atmospheric air due to the formation of three-dimensional crosslinks via Mo–O–Mo covalent bonds between neighboring molecules in the crystal. [ABSTRACT FROM AUTHOR]

Rod-like gold(I) complexes with phenyl, biphenyl, or naphthyl rings in a mesogenic core were synthesized by complexation of ethynyl-substituted aromatic derivatives with (tetrahydrothiophene)AuCl, followed by ligand exchange with alkyl isocyanide, to investigate the effects of molecular and molecular-aggregated structures on their liquid-crystalline (LC) behavior and photoluminescence properties. The gold complexes exhibited enantiotropic liquid crystallinity. Introduction of multi-ring systems into the mesogenic core effectively expanded the LC temperature range. A comparison of the photoluminescence properties in the crystalline phase showed that the molecular-aggregated structure plays a crucial role in the luminescence of these gold complexes. [ABSTRACT FROM AUTHOR]

Gold nanoparticles having a monolayer of azobenzene liquid crystals (LCs) were synthesized and their aggregation structures on solid surfaces were observed. The gold nanoparticles formed a single-particle layer on bare mica and mica with a polyimide layer. We demonstrated that the morphology of the gold nanoparticle aggregates could be controlled by UV light irradiation at 366 nm; the mass transfer of gold nanoparticles from the exposed area to the nonexposed area was induced by the isomerization of azobenzene LC molecules. [ABSTRACT FROM PUBLISHER]

A gold nanoparticle having a monolayer of azobenzene liquid crystal (LC) was synthesized. The size of the gold nanoparticle obtained was 4.7 nm in average diameter, and it was soluble in common non-polar organic solvents such as toluene and dichloromethane. We confirmed that the reversible photochemical and thermal isomerization of the azobenzene could take place on the surface of the gold nanoparticles in analogy with free azobenzenes in solutions. Furthermore, a 1-dimensional self-organization of the nanoparticle was observed by transmission electron microscopy. However, a gold nanoparticle without LC molecules never showed such self-organization. Therefore, we conclude that the self-organization of the gold nanoparticle is based on the liquid crystallinity of the organic ligands attached on their surface. [ABSTRACT FROM PUBLISHER]

Gold(I) complexes, enabling to form linear coordination geometry, are promising materials for manifesting both aggregation-induced emission (AIE) behavior due to strong intermolecular Au–Au (aurophilic) interactions and liquid crystalline (LC) nature depending on molecular geometry. In this study, we synthesized several gold(I) complexes with rod-like molecular skeletons where we employed a mesogenic biphenylethynyl ligand and an isocyanide ligand with flexible alkoxyl or alkyl chains. The AIE behavior and LC nature were investigated experimentally and computationally. All synthesized gold(I) complexes exhibited AIE properties and, in crystal, room-temperature phosphorescence (RTP) with a relatively high quantum yields of greater than 23% even in air. We have demonstrated that such strong RTP are drastically changed depending on the crystal-size and/or crystal growth process that changes quality of crystals as well as the aggregate structure, of e.g., Au–Au distance. Moreover, the complex with longer flexible chains showed LC nature where RTP can be observed. We expect these rod-like gold(I) complexes to have great potential in AIE-active LC phosphorescent applications such as linearly/circularly polarizing phosphorescence materials. [ABSTRACT FROM AUTHOR]

Abstract: One- and two-photon induced phase transition behavior of low-molecular-weight and polymer liquid crystals (LCs) was observed. When a photochemical reaction of a two-photon absorbing dye was induced in a nematic (N) LC, N-to-isotropic (I) phase transition was induced with high spatial resolution. As a result of the phase transition, the refractive index of the materials was changed by two-photon processes. Furthermore, the I phase induced in the polymer LC was thermally stable and it still appeared after heating above N–I phase transition temperature. The results reported here are the first observation of the photochemical phase transition of the LCs induced by a two-photon process. [Copyright &y& Elsevier]

The change in transmittance of a 1.55- μ m laser beam was investigated by a photochemical phase transition of an azobenzene liquid-crystalline polymer. Effects of the intensity of actinic light and temperature on the photoresponsive behavior were explored using laser beams at 633 nm and 1.55 μ m. It was found that the intensity of the actinic light or temperature affected on the response, regardless of the wavelength of the probe beam. [ABSTRACT FROM AUTHOR]

Optical switching of a 1.55-μm laser beam was explored by means of photochemical phase transition of polymer and low-molecular-weight azobenzene liquid crystals (LCs). It was observed that the 1.55-μm laser beam could be repeatedly switched by turning on and off the actinic light, and a large change in refractive index was induced in the azobenzene LCs at the near infrared region. It was also found that controlling the thickness of LCs could enhance the change in the transmittance of the 1.55-μm laser. [ABSTRACT FROM AUTHOR]

The recent highlights in the photoinduced modulation of the liquid-crystalline (LC) alignment and their applications to photonics are reviewed. The molecular alignment of LCs can be controlled by either the photochemical process or the photophysical process and we can change the birefringence as well as refractive index of the material by the modulation of the LC alignment. The photoresponsive LCs show very quick response to stimulus light: the response time is ∼200 ns. Furthermore, the extremely large refractive index modulation (Δn=∼10−1) can be also induced. The photoresponsive LCs, therefore, are potential materials for holographic recording and other photonic device. [Copyright &y& Elsevier]

Chiral nematic (N*) liquid crystal elastomers (LCEs) are suitable for fabricating stimuli-responsive materials. As crosslinkers considerably affect the N*LCE network, we investigated the effects of crosslinking units on the physical properties of N*LCEs. The N*LCEs were synthesized with different types of crosslinkers, and the relationship between the N*LC polymeric system and the crosslinking unit was investigated. The N*LCEs emit color by selective reflection, in which the color changes in response to mechanical deformation. The LC-type crosslinker decreases the helical twisting power of the N*LCE by increasing the total molar ratio of the mesogenic compound. The N*LCE exhibits mechano-responsive color changes by coupling the N*LC orientation and the polymer network, where the N*LCEs exhibit different degrees of pitch variation depending on the crosslinker. Moreover, the LC-type crosslinker increases the Young's modulus of N*LCEs, and the long methylene chains increase the breaking strain. An analysis of experimental results verified the effect of the crosslinkers, providing a design rationale for N*LCE materials in mechano-optical sensor applications. [ABSTRACT FROM AUTHOR]

Explores the optical switching behavior of low-molecular-weight and polymer azobenzene liquid crystals (LCs). Phase transition behavior of azobenzene LCs; Application of reflection-mode analysis; Observation of a slower decay for the polymer LCs.

Studies novel thermotropic liquid crystals without a rigid core formed by amphiphiles having phosphonium ions. Proposal of a concept for the mode of action of the cationic biocides; Assumptions that the phosphonium salts possess a high ability of molecular organization; Examination of the thermotropic liquid-crystalline behavior of phosphonium salts.

The influence of the spacer structure on the photochemical phase transition behaviour was explored for azobenzene polymer liquid crystals (azo-PLCs) possessing siloxane spacers in the polymer side chain, and for analogue without the siloxane spacer. The photochemical phase transition of the azo-PLC with the siloxane spacer was found to proceed less effectively than that of the azo-PLC without the siloxane spacer. It was also confirmed that the spacer structure does not affect the trans-cis photoisomerization behaviour of the azobenzene moieties. These results were interpreted in terms of stabilization of the alignment of the mesogens in the liquid crystalline phase by the siloxane spacer, since the siloxane chain is one of the most flexible spacers and decouples the motion of the polymer backbone from that of the aligned mesogens. Furthermore, the response of the azo-PLCs in the photochemical phase transition was evaluated by means of a laser pulse. The phase transition occurred in 300 mus for both samples. [ABSTRACT FROM AUTHOR]

Pure organic luminescent materials with high efficiency in the solid state are of great importance for potential applications. Unlike blending two or three dyes, getting white-light emission from a single component is a hot research topic for its advantages in practical applications. Although thermo/mechanochromic materials are a smart class of stimuli-responsive systems, using these materials to manipulate the luminescence spectrum to achieve full-color emission from one component is rarely reported. In this work, we have designed two novel liquid crystal copolymers containing different monomer ratios of ethynylbiphenyl and biphenylcarbonitrile skeletons in the side chains. The polymers are free of rare or precious metals and exhibited thermochromism, mechanochromism, white emission from a single component, and high emission efficiency in the solid state. Ethynylbiphenyl skeleton is the key structure as a luminescent group that emits white light upon heating to the liquid crystal phase. However, controlling the ratio between ethynylbiphenyl and biphenylcarbonitrile side chains is essential to get high emission efficiency along with good purity of the white luminescence. The thermochromism and mechanochromism primarily due to the transition between creating and breaking down π-π interactions with different modes of molecular packing. This transition switches the emission color from blue to white (thermochromism) and vice versa (mechanochromism). The developed polymers showed a smart stimuli-responsive behavior and provided a simple strategy to get single-component white-light luminescent materials in the solid state. • We designed smart stimuli-responsive copolymers with numerous merits: • Simple structure, pure organic, liquid crystallinity, and strong emission in the solid state. • Color tuning by a combination of luminescence thermo- and mechanochromism. • White emission from a single chromophore upon heating to the liquid crystal phase. • Phenylacetylene skeleton is a key structure to switch the emission color upon heating. [ABSTRACT FROM AUTHOR]

Gold(I) complexes are some of the most attractive materials for generating aggregation-induced emission (AIE), enabling the realization of novel light-emitting applications such as chemo-sensors, bio-sensors, cell imaging, and organic light-emitting diodes (OLEDs). In this study, we propose a rational design of luminescent gold complexes to achieve both high thermochemical stability and intense room temperature phosphorescence, which are desirable features in practical luminescent applications. Here, a series of gold(I) complexes with ligands of N-heterocyclic carbene (NHC) derivatives and/or acetylide were synthesized. Detailed characterization revealed that the incorporation of NHC ligands could increase the molecular thermochemical stability, as the decomposition temperature was increased to ~300 °C. We demonstrate that incorporation of both NHC and acetylide ligands enables us to generate gold(I) complexes exhibiting both high thermochemical stability and high room-temperature phosphorescence quantum yield (>40%) under ambient conditions. Furthermore, we modified the length of alkoxy chains at ligands, and succeeded in synthesizing a liquid crystalline gold(I) complex while maintaining the relatively high thermochemical stability and quantum yield. [ABSTRACT FROM AUTHOR]

This research focuses on the characterization of a simple organic molecule incorporating biphenyl, methacrylate, trimethylsilyl acetylene, and liquid crystal compounds. Extensive analysis of the molecule's physical and optical properties, including refractive index, extinction coefficient, dielectric constant, and conductivity, was conducted. Complementary TD-DFT computations validated the experimental findings. The molecule exhibited intriguing behavior in terms of extinction coefficient and refractive index, showing an initial increase followed by a decrease with increasing photon energy. CASTEP/DFT simulations confirmed these results. The molecule demonstrated surfactant properties, indicated by its increasing dielectric constant and optical conductivity, suggesting enhanced charge transfer and energy storage potential. Additionally, the study investigated the impact of flexible spacer length on organic compounds, revealing that shorter spacers improve refractive index, extinction coefficient, and optical conductivity, indicating enhanced light absorption and bending capabilities. The observed differences in optical values between compounds with different spacer lengths can be attributed to factors such as molecular packing, dipole moment, molecular orientation, and light interactions. Furthermore, the removal of the TMS group from the main compound impacted the optical properties by influencing molecular arrangement, electronic states, and energy levels. These findings provide valuable insights for the design of materials with tailored optical properties. • A simple organic molecule combined four different groups, each with its potential optical applications. • The results revealed a significant resemblance between the DFT simulated and observed values. • The dielectric constant behavior indicates the surfactant properties of this material. • The optical conductivity pattern provides additional evidence for the surfactant properties. • The flexible spacer length has a direct impact on the optical properties. [ABSTRACT FROM AUTHOR]

Developing broad spectrum white-light emitting materials was always considered a challenge in terms of color stability and reproducibility. Here, we report the design and optical properties of two materials bearing an ethynylbiphenyl group. The two materials exhibited excellent thermal stability and showed liquid crystal (LC) behavior. Promisingly, temperature-dependent photoluminescence results demonstrated distinct thermochromic behavior which switches the emission color from deep blue in the crystal phase to white in the LC phase. It was revealed that the overall effect of the intermolecular interactions forming a new excited state in the LC phase of the ethynylbiphenyl moiety is the main cause for the white-light emission. The emission behavior of the studied materials was tuned by thermal stimuli, and the emission color was regulated by changing the aggregate structure. These present findings open a door to develop more appealing single-molecule white-light emitters. • Liquid-crystalline luminogens with thermal stimuli-responsiveness were designed. • The materials are simple, easy to synthesize, and show deep-blue emission in the crystal. • Blue-to-white emission was realized by a phase transition to the smectic phase. • White color emission from a single chromophore has been achieved. • Formation of a new excited state in the smectic phase lies behind the white emission. [ABSTRACT FROM AUTHOR]