Functional Liquid Crystals towards the Next Generation of Materials

Building Functional Liquid-Based Interfaces: From Mechanism to Application

Functional liquid-based interfaces, with their inhomogeneous regions that emphasize the functionalized liquids, have attracted much interest as a versatile platform for a broad spectrum of applications, from chemical manufacturing to practical uses. These interfaces leverage the physicochemical characteristics of liquids, alongside dynamic behaviors induced by macroscopic wettability and microscopic molecular exchange balance, to allow for tailored properties within their functional structures. In this Minireview, we provide a foundational overview of these functional interfaces, based on the structural investigations and molecular mechanisms of interaction forces that directly modulate functionalities. Then, we discuss design strategies that have been employed in recent applications, and the crucial aspects that require focus. Finally, we highlight the current challenges in functional liquid-based interfaces and provide a perspective on future research directions.

Isothermal Phase Transitions in Liquid Crystals Driven by Dynamic Covalent Chemistry

The dynamic nature of calamitic liquid crystals is exploited to perform isothermal phase transitions driven by dynamic covalent chemistry. For this purpose, nematic (N) arrays based on aldehyde 1 were treated with different amines (A-E) in an on-surface process, which resulted in different isothermal phase transitions. These phase transformations were caused by in situ imination reactions and are dependent on the nature of the added amine. Transitions from the N to crystal (1A, 1E), isotropic (1B), and smectic (Sm) (1C, 1D) phases were achieved, while the resulting materials feature thermotropic liquid crystal behavior. A sequential transformation from the N 1 to the Sm 1C and then to the N 1B was achieved by coupling an imination to a transimination processes and adjusting the temperature. All of these processes were well characterized by microscopic, spectroscopic, and X-ray techniques, unlocking not only the constitutional but also the structural aspects of the phase transitions. This work provides new insights into designing constitutionally and structurally adaptable liquid crystal systems, paving the way toward the conception of programable evolutive pathways and adaptive materials.

High Electrical Conductivity and Hole Transport in an Insightfully Engineered Columnar Liquid Crystal for Solution-Processable Nanoelectronics

Discotic liquid crystals (DLCs) are widely acknowledged as a class of organic semiconductors that can harmonize charge carrier mobility and device processability through supramolecular self-assembly. In spite of circumventing such a major challenge in fabricating low-cost charge transport layers, DLC-based hole transport layers (HTLs) have remained elusive in modern organo-electronics. In this work, a minimalistic design strategy is envisioned to effectuate a cyanovinylene-integrated pyrene-based discotic liquid crystal (PY-DLC) with a room-temperature columnar hexagonal mesophase and narrow bandgap for efficient semiconducting behavior. Adequately combined photophysical, electrochemical, and theoretical studies investigate the structure-property relations, logically correlating them with efficient hole transport. With a low reorganization energy of 0.2 eV, PY-DLC exhibits superior charge extraction ability from the contact electrodes at low values of applied voltage, achieving an electrical conductivity of 3.22 × 10-4 S m-1, the highest reported value for any pristine DLC film in a vertical charge transport device. The columnar self-assembly, in conjunction with solution-processable self-healed films, results in commendably elevated values of hole mobility (≈10-3 cm2 V-1s-1). This study provides an unprecedented constructive outlook toward the development of DLC semiconductors as practical HTLs in organic electronics.

Ionic Liquid Crystal-Polymer Composite Electromechanical Actuators: Design of Two-Dimensional Molecular Assemblies for Efficient Ion Transport and Effect of Electrodes on Actuator Performance

We present the development of free-standing ionic liquid crystal-polymer composite electrolyte films aimed at achieving high-frequency response electromechanical actuators. Our approach entails designing novel layered ionic liquid-crystalline (LC) assemblies by complexing a mesomorphic dimethylphosphate with either a lithium salt or a room-temperature ionic liquid through the formation of ion-dipole interactions or hydrogen bonds. These electrolytes, exhibiting room-temperature ionic conductivities on the order of 10-4 S cm-1 and wide LC temperature ranges up to 77 °C, were successfully integrated into porous polymer networks. We systematically investigated the impact of ions and electrodes on the performance of ionic electroactive actuators. Specifically, the Li+-based liquid crystal-polymer composite actuator with PEDOT:PSS electrodes demonstrated the highest bending deformation, achieving a strain of 0.68% and exhibiting a broad frequency response up to 110 Hz, with a peak-to-peak displacement of 3 μm. In contrast, the ionic-liquid-based liquid crystal-polymer composite actuator with active carbon electrodes showcased a bending response at a maximum frequency of 50 Hz and a force generation of 0.48 mN, without exhibiting the back relaxation phenomenon. These findings offer valuable insights for advancing high-performance electromechanical systems with applications ranging from soft robotics to haptic interfaces.

Phenanthrothiophene-Triazine Star-Shaped Discotic Liquid Crystals: Synthesis, Self-Assembly, and Stimuli-Responsive Fluorescence Properties

Lipophilic biphenylthiophene- and phenanthrothiophene-triazine compounds, BPTTn and CPTTn, respectively, were prepared by a tandem procedure involving successive Suzuki-Miyaura coupling and Scholl cyclodehydrogenation reactions. These compounds display photoluminescence in solution and in thin film state, solvatochromism with increasing solvent's polarity, as well as acidochromism and metal ion recognition stimuli-responsive fluorescence. Protonation of BPTT10 and CPTT10 by trifluoroacetic acid results in fluorescence quenching, which is reversibly restored once treated with triethylamine (ON-OFF switch). DFT computational studies show that intramolecular charge transfer (ICT) phenomena occurs for both molecules, and reveal that protonation enhances the electron-withdrawing ability of the triazine core and reduces the band gap. This acidochromic behavior was applied to a prototype fluorescent anti-counterfeiting device. They also specifically recognize Fe3+ through coordination, and the recognition mechanism is closely related to the photoinduced electron transfer between Fe3+ and BPTT10/CPTT10. CPTTn self-assemble into columnar rectangular (Colrec) mesophase, which can be modulated by oleic acid via the formation of a hydrogen-bonded supramolecular liquid crystal hexagonal Colhex mesophase. Finally, CPTTn also form organic gels in alkanes at low critical gel concentration (3.0 mg/mL). Therefore, these star-shaped triazine molecules possess many interesting features and thus hold great promises for information processing, liquid crystal semiconductors and organogelators.

Magnetic Supramolecular Spherical Arrays: Direct Formation of Micellar Cubic Mesophase by Lanthanide Metallomesogens with 7-Coordination Geometry

Here, an unprecedented phenomenon in which 7-coordinate lanthanide metallomesogens, which align via hydrogen bonds mediated by coordinated H2O molecules, form micellar cubic mesophases at room temperature, creating body-centered cubic (BCC)-type supramolecular spherical arrays, is reported. The results of experiments and molecular dynamics simulations reveal that spherical assemblies of three complexes surrounded by an amorphous alkyl domain spontaneously align in an energetically stable orientation to form the BCC structure. This phenomenon differs greatly from the conventional self-assembling behavior of 6-coordinated metallomesogens, which form columnar assemblies due to strong intermolecular interactions. Since the magnetic and luminescent properties of different lanthanides vary, adding arbitrary functions to spherical arrays is possible by selecting suitable lanthanides to be used. The method developed in this study using 7-coordinate lanthanide metallomesogens as building blocks is expected to lead to the rational development of micellar cubic mesophases.

A novel B,O,N-doped mesogen with narrowband MR-TADF emission

Modification of an unsymmetric B,O,N-doped aromatic core with peripheral mesogenic units triggers self-assembly into a columnar hexagonal mesophase, which is stable between 22 and 144 °C. The columnar assembly is preserved in a glassy state below 22 °C. The B,O,N-doped mesogen displays narrowband sky-blue multiresonance thermally activated delayed fluorescence (MR-TADF) under diluted conditions and bright excimer emission in condensed phase. Our combined experimental and theoretical approach provides insight into the development of strongly aggregating liquid crystalline MR-TADF emitters.

Self-Assembled and Polymerized Hierarchical Nanostructure Films of Cyanostilbene-Based Reactive AIEgens for Smart Chemosensors

For the development of acid-responsive advanced fluorescent films with a 2D nanostructure, a pyridyl cyanostilbene-based AIEgen (PCRM) is newly synthesized. The synthesized PCRM exhibits aggregation-induced emission (AIE) and responds reversibly to acid and base stimuli. To fabricate the nanoporous polymer-stabilized film, PCRM and 4-(octyloxy)benzoic acid (8OB) are complexed in a 1:1 ratio through hydrogen bonding. The PCRM-8OB complex with a smectic mesophase is uniaxially oriented at first and photopolymerized with a crosslinker. By subsequently removing 8OB in an alkaline solution, nanopores are generated in the self-assembled and polymerized hierarchical 2D nanostructure film. The prepared nanoporous fluorescent films exhibit not only the reversible response to acid and base stimuli but also mechanical and chemical robustness. Since the nanoporous fluorescent films have different sensitivities to trifluoroacetic acid (TFA) depending on the molecular orientation in the film, advanced acid vapor sensors that can display the risk level according to the concentration of TFA are demonstrated. Reactive AIEgens-based hierarchical nanostructure films with nanopores fabricated by a subsequent process of self-assembly, polymerization, and etching can open a new door for the development of advanced chemosensors.

Columnar liquid crystals based on antiaromatic expanded porphyrins

Three naphthorosarins, antiaromatic expanded porphyrins bearing different meso substituents (NRos 1-3), designed to self-assemble into columnar liquid crystalline (LC) structures, were synthesized and characterized using polarized optical microscopy (POM), differential scanning calorimetry (DSC), X-ray diffraction (XRD), as well as supporting computational calculations. The substituents were found to play a crucial role in modulating the LC behaviour.

Water in liquid crystal emulsion-based sensing platform for colorimetric detection of organophosphorus pesticide

Development of a simple and convenient method for the rapid detection of organophosphorus pesticides (OPs) is particular important for the safety of environmental water and agriculture products. In this work, the water/liquid crystal (W/LC) emulsion is obtained via dispersing an aqueous solution of sodium dodecyl sulfate (SDS) and peroxidase from horseradish (HRP) into a water-immiscible nematic LC and employed as a sensing platform for the detection of dichlorvos (2, 2-dichlorovinyl dimethyl phosphate, DDVP) that is a typical OP with acute toxicity. Remarkably, the stepwise release of the encapsulated cargo HRP from the W/LC emulsion can be triggered upon the addition of the cationic surfactant myristoylcholine chloride (Myr) due to the strong interfacial charge interactions with the anionic surfactant SDS. The released HRP induces an obvious color change of the overlaying bulk aqueous solution via the H2O2-HRP-TMB reaction system. As Myr can be enzymatically cleaved by AChE, the detection of AChE is fulfilled successfully. This approach is also employed to detect DDVP that can irreversibly inhibit the activity of AChE. This assay shows a linear response between the absorbance of the oxidized TMB solution and the DDVP concentration in the range of 0.001-10 μg/mL (R2 = 0.99). The limit of detection (LOD) and the limit of quantity (LOQ) of DDVP are determined to be 1.9 ng/mL and 6.3 ng/mL, respectively. In addition, this strategy also demonstrates excellent performance for the DDVP detection in real samples, the detection recovery rate of DDVP in water samples (lake water and tap water) and vegetables (tomatoes and cole) by this method is 88.0 % ∼112.6 %, the relative standard deviation (RSD) ≤ 7.5 %. These results suggest the W/LC emulsion-based sensing platform shows great potential for visual detection of DDVP in real samples. In conclusion, the proposed approach is scalable for practical application in food safety as well as environmental monitoring fields, and will provide promising solutions for the assay of pesticide residues.

Chirality-induced supramolecular nanodishes: enantioselectivity and energy transfer

Self-assembly is one of the most important issues of fabricating materials with precise chiral nanostructures. Herein, we constructed a chiral assembly system from amphiphiles containing hydrophobic/hydrophilic chiral coils bonded to hexabiphenyl, exhibiting controllable enantioselectivity over various aggregation behaviors. The chiral coils aroused various steric hindrances affecting intrinsic stacking tendency and compactness, leading to different aggregating behaviors, as concluded from the self-assembly investigation. The strong π-π stacking interaction between the long hexabiphenyl groups gave rise to a relatively compact arrangement in the aqueous solution, whereas the methyl side groups on the coil segments raised steric hindrance at the rigid-flexible interface, resulting in loose stacking and formation of nanostructures with a larger curvature. Compared with the achiral molecule 1 that formed micron-sized large sheets, molecules 2-4 containing chiral coils aggregated into nanodishes, which looked exactly like mosquito-repellent incense, to overcome surface tension. The helical structures effectively amplified chirality and exhibited strong circular dichroism (CD) signals, which indicate enantioselectivity. In addition, the relatively loose packing behavior permitted their co-assembly with a dye and aided efficient energy transfer, providing a foundation for the chiral application of supramolecules. Thus, by introducing a simple methyl side group in amphiphilic molecules, asymmetric synthesis and energy transfer efficiency can be realized.

2D Materials Nanoarchitectonics for 3D Structures/Functions

It has become clear that superior material functions are derived from precisely controlled nanostructures. This has been greatly accelerated by the development of nanotechnology. The next step is to assemble materials with knowledge of their nano-level structures. This task is assigned to the post-nanotechnology concept of nanoarchitectonics. However, nanoarchitectonics, which creates intricate three-dimensional functional structures, is not always easy. Two-dimensional nanoarchitectonics based on reactions and arrangements at the surface may be an easier target to tackle. A better methodology would be to define a two-dimensional structure and then develop it into a three-dimensional structure and function. According to these backgrounds, this review paper is organized as follows. The introduction is followed by a summary of the three issues; (i) 2D to 3D dynamic structure control: liquid crystal commanded by the surface, (ii) 2D to 3D rational construction: a metal-organic framework (MOF) and a covalent organic framework (COF); (iii) 2D to 3D functional amplification: cells regulated by the surface. In addition, this review summarizes the important aspects of the ultimate three-dimensional nanoarchitectonics as a perspective. The goal of this paper is to establish an integrated concept of functional material creation by reconsidering various reported cases from the viewpoint of nanoarchitectonics, where nanoarchitectonics can be regarded as a method for everything in materials science.

Machine learning methods for liquid crystal research: phases, textures, defects and physical properties

Liquid crystal materials, with their unique properties and diverse applications, have long captured the attention of researchers and industries alike. From liquid crystal displays and electro-optical devices to advanced sensors and emerging technologies, the study and application of liquid crystals continue to be of paramount importance in the fields of materials science, chemistry and physics. With the ever-increasing complexity and diversity of liquid crystal materials, researchers face new challenges in understanding their behaviors, properties, and potential applications. On the other hand, machine learning, a rapidly evolving interdisciplinary field at the intersection of computer science and data analysis, has already become a powerful tool for unraveling implicit correlations and predicting new properties of a wide variety of physical and chemical systems and structures. Here we aim to consider how machine learning methods are suitable for solving fundamental problems in the field of liquid crystals and what are the advantages of this artificial intelligence based approach.

Reversible Molecular Conformation Transitions of Smectic Liquid Crystals for Light/Bias-Gated Transistor Memory

In recent years, organic photonic field-effect transistors have made remarkable progress with the rapid development of conjugated polycrystalline materials. Liquid crystals, with their smooth surface, defined layer thickness, and crystalline structures, are commonly used for these advantages. In this work, a series of smectic liquid crystalline molecules, 2,9-didecyl-dinaphtho-thienothiophene (C10-DNTT), 2,7-didecyl-benzothieno-benzothiopene (C10-BTBT), 3,9-didecyl-dinaphtho-thiophene (C10-DNT), and didecyl-sexithiophene (C10-6T), have been used in photonic transistor memory, functioning as both hole-transport channels and electron traps to investigate systematically the reasons and mechanisms behind the memory behavior of smectic liquid crystals. After thermal annealing, C10-BTBT and C10-6T/C10-DNTT are homeotropically aligned from the smectic A and smectic X phases, respectively. The 3D-ordered structure of these smectic-aligned crystals contributed to efficient photowriting and electrical erasing processes. Among them, the device performance of C10-BTBT was particularly significant, with a memory window of 21 V. The memory ratio could reach 1.5 × 106 and maintain a memory ratio of over 3 orders after 10,000 s, contributing to its smectic A structure. Through the research, we confirmed the memory and light/bias-gated behaviors of these smectic liquid crystalline molecules, attributing them to reversible molecular conformation transitions and the inherent structural inhomogeneity inside the polycrystalline channel layer.

Understanding the Role of Trapezoids in Honeycomb Self-Assembly-Pathways between a Columnar Liquid Quasicrystal and its Liquid-Crystalline Approximants

Quasiperiodic patterns and crystals-having long range order without translational symmetry-have fascinated researchers since their discovery. In this study, we report on new p-terphenyl-based T-shaped facial polyphiles with two alkyl end chains and a glycerol-based hydrogen-bonded side group that self-assemble into an aperiodic columnar liquid quasicrystal with 12-fold symmetry and its periodic liquid-crystalline approximants with complex superstructures. All represent honeycombs formed by the self-assembly of the p-terphenyls, dividing space into prismatic cells with polygonal cross-sections. In the perspective of tiling patterns, the presence of unique trapezoidal tiles, consisting of three rigid sides formed by the p-terphenyls and one shorter, incommensurate, and adjustable side by the alkyl end chains, plays a crucial role for these phases. A delicate temperature-dependent balance between conformational, entropic and space-filling effects determines the role of the alkyl chains, either as network nodes or trapezoid walls, thus resulting in the order-disorder transitions associated with emergence of quasiperiodicity. In-depth analysis suggests a change from a quasiperiodic tiling involving trapezoids to a modified one with a contribution of trapezoid pair fusion. This work paves the way for understanding quasiperiodicity emergence and develops fundamental concepts for its generation by chemical design of non-spherical molecules, aggregates, and frameworks based on dynamic reticular chemistry.

Aquatic Functional Liquid Crystals: Design, Functionalization, and Molecular Simulation

Aquatic functional liquid crystals, which are ordered molecular assemblies that work in water environment, are described in this review. Aquatic functional liquid crystals are liquid-crystalline (LC) materials interacting water molecules or aquatic environment. They include aquatic lyotropic liquid crystals and LC based materials that have aquatic interfaces, for example, nanoporous water treatment membranes that are solids preserving LC order. They can remove ions and viruses with nano- and subnano-porous structures. Columnar, smectic, bicontinuous LC structures are used for fabrication of these 1D, 2D, 3D materials. Design and functionalization of aquatic LC sensors based on aqueous/LC interfaces are also described. The ordering transitions of liquid crystals induced by molecular recognition at the aqueous interfaces provide distinct optical responses. Molecular orientation and dynamic behavior of these aquatic functional LC materials are studied by molecular dynamics simulations. The molecular interactions of LC materials and water are key of these investigations. New insights into aquatic functional LC materials contribute to the fields of environment, healthcare, and biotechnology.

Mesomorphism Modulation of Perfluorinated Janus Triphenylenes by Inhomogeneous Chain Substitution Patterns

Two isomeric series of compounds with "inverted" chains' substitution patterns, 7,10-dialkoxy-1,2,3,4-tetrafluoro-6,11-dimethoxytriphenylene and 6,11-dialkoxy-1,2,3,4-tetrafluoro-7,10-dimethoxytriphenylene, labelled respectively p-TPFn and m-TPFn, and two non-fluorinated homologous isomers, 3,6-dibutoxy-2,7-dimethoxytriphenylene and 2,7-dibutoxy-3,6-dimethoxytriphenylene, p-TP4 and m-TP4, respectively, were synthesized in three steps and obtained in good yields by the efficient transition-metal-free, fluoroarene nucleophilic substitution via the reaction of appropriate 2,2'-dilithium biphenylenes with either perfluorobenzene, C6 F6 , to yield p-TPFn and m-TPFn, or o-difluorobenzene, C6 H4 F2 , for p-TP4 and m-TP4, respectively. The single-crystal structures of p-TPF4, m-TPF4 and p-TP4, unequivocally confirmed that the cyclization reactions occurred at the expected positions, and that the fluorinated molecules stack up into columns with short separation, a propitious situation for the emergence of columnar mesophases. The mesomorphous properties were found to be greatly affected by both chains' length and positional isomerism: a Colhex phase is found for p-TPF4 and m-TPF4, but mesomorphism vanishes in p-TPF6, and changes for the isomeric homologs m-TPFn, with the induction for n≥6 of a lamello-columnar phase, LamColrec . As expected, both non-fluorinated compounds are deprived of mesomorphism. These compounds emit blue-violet colour in solution, independently of the chains' substitution pattern, and the absolute fluorescence quantum yields can reach up to 46 %. In thin films, fluorescence is slightly redshifted.

Surface-dominant micro/nanofluidics for efficient green energy conversion

Green energy conversion in aqueous systems has attracted considerable interest owing to the sustainable clean energy demand resulting from population and economic growth and urbanization, as well as the significant potential energy from water resources and other regenerative sources coupled with fluids. In particular, molecular motion based on intrinsic micro/nanofluidic phenomena at the liquid-solid interface (LSI) is crucial for efficient and sustainable green energy conversion. The electrical double layer is the main factor affecting transport, interaction between molecules and surfaces, non-uniform ion distribution, synthesis, stimulated reactions, and motion by external renewable resources in both closed nanoconfinement and open surfaces. In this review, we summarize the state-of-the-art progress in physical and chemical reaction-based green energy conversion in LSI, including nanoscale fabrication, key mechanisms, applications, and limitations for practical implementation. The prospects for resolving critical challenges in this field and inspiring other promising research areas in the infancy stage (studying chemical and biological dynamics at the single-molecule level and nanofluidic neuromorphic computing) are also discussed.

Effortless Extraction of Structural and Orientational Information from 13C-1H Dipolar Couplings for Thiophene Mesogens

Five molecular mesogens containing phenyl rings and thiophene are subjected to a detailed 13C NMR investigation. The first mesogen contains only phenyl rings, while the other four have thiophene with substitution at position 2 or 3. Two of these also have a spacer inserted between the thiophene and the rest of the core unit. The mesophase properties evaluated by complementary techniques reveal an enantiotropic nematic phase for all the cases and smectic C as well as Crystal J for a few mesogens. In addition to solution 13C NMR, the samples were studied using 1D and 2D solid-state 13C NMR experiments in the liquid crystalline phase. The chemical shifts and 13C-1H dipolar couplings obtained in the mesophase provided cutting-edge information about the molecular structure and orientation of the thiophene mesogens. Accordingly, dramatic differences in these parameters are noted for the mesogens, and consequently, the identification of 2- and 3-substituted thiophene mesogens is accomplished by a simple visual examination of the 2D spectra. Furthermore, for mesogens with a spacer between thiophene and the rest of the core, 13C chemical shifts and 13C-1H dipolar couplings showed remarkable variation, which was directly reflected in the order parameters. For instance, the order parameter (Szz) of thiophene in 2- and 3-substituted mesogens in which the spacer is absent is ∼0.63 whereas for those with spacer, it is reduced to ∼0.14-0.18. In comparison, the mesogen in which the core unit is made up of phenyl rings alone that is used to benchmark the characteristics of thiophene ordering showed an order parameter of ∼0.85. The study unambiguously demonstrates the supremacy of 13C NMR in extracting the structural and orientational information on mesogens in which thiophene is a constituent of the core unit.

Achiral Dichroic Dyes-mediated Circularly Polarized Emission Regulated by Orientational Order Parameter through Cholesteric Liquid Crystals

It is noteworthy that cholesteric liquid crystal (CLC) platforms have been witnessed in high-performance circularly polarized luminescence (CPL) behaviors through the highly organized chiral co-assembled arrangement of achiral dyes. However, most CPL-active design strategies are closely relative to the helix co-assembly structure of CLC rather than achiral dyes. Herein, we developed an intriguing regulation strategy for CPL-active CLC materials. They were regulated using the orientational order parameter (SF ) of achiral dichroic dyes as an incisive probe for the order arrangement degree of achiral dyes in CLC media. The I-shaped phenothiazine derivative PHECN dye (SF =0.30) emitted a strong CPL signal (|glum |=0.47). In contrast, the T-shaped derivative (PHEBen) dye (SF =0.09) showed a weak circular polarization level (|glum |=0.07) at similar CLC textures. Most interestingly, this kind of dichroic PHECN dye with a higher SF could greatly improve the contrast ratio of CPL (Δglum =0.47) and emission intensity (ΔFL=46.0 %) at direct-current electric field compared with the T-shaped PHEBen (Δglum =0.07 and ΔFL=1.0 %) in CLC. This work demonstrates that an induced CPL emission can be mediated using achiral dichroic dye, which will open a new avenue for developing excellent CPL-active display materials.

Thermoreversible helical fibers from photoreactive triphenylene-derived liquid crystals in liquid paraffin

Liquid crystalline triphenylene derivatives, TPC1p-n (n = 6, 12, 14, 16) were prepared using p-alkoxycinnamate as the [2+2] photo-cyclization site. TPC1p-n (n = 12, 14, 16) showed Colr phase and gave crescent-shaped or helical fibers after UV-irradiated in liquid paraffin solutions at 90 and 110 °C in the Colr temperature range. The apparent photoreaction products were shown to be thermally reversible, i.e. they dissolved in liquid paraffin at high temperatures and reappeared on cooling, indicating that they were aggregates of oligomerized TPC1p-n. The reaction mechanism was discussed in terms of the structure of the liquid crystalline phase.

Supramolecular Polymer Polymorphism: Spontaneous Helix-Helicoid Transition through Dislocation of Hydrogen-Bonded π-Rosettes

Polymorphism, a phenomenon whereby disparate self-assembled products can be formed from identical molecules, has incited interest in the field of supramolecular polymers. Conventionally, the monomers that constitute supramolecular polymers are engineered to facilitate one-dimensional aggregation and, consequently, their polymorphism surfaces primarily when the states of assembly differ significantly. This engenders polymorphs of divergent dimensionalities such as one- and two-dimensional aggregates. Notwithstanding, realizing supramolecular polymer polymorphism, wherein polymorphs maintain one-dimensional aggregation, persists as a daunting challenge. In this work, we expound upon the manifestation of two supramolecular polymer polymorphs formed from a large discotic supramolecular monomer (rosette), which consists of six hydrogen-bonded molecules with an extended π-conjugated core. These polymorphs are generated in mixtures of chloroform and methylcyclohexane, attributable to distinctly different disc stacking arrangements. The face-to-face (minimal displacement) and offset (large displacement) stacking arrangements can be predicated on their distinctive photophysical properties. The face-to-face stacking results in a twisted helix structure. Conversely, the offset stacking induces inherent curvature in the supramolecular fiber, thereby culminating in a hollow helical coil (helicoid). While both polymorphs exhibit bistability in nonpolar solvent compositions, the face-to-face stacking attains stability purely in a kinetic sense within a polar solvent composition and undergoes conversion into offset stacking through a dislocation of stacked rosettes. This occurs without the dissociation and nucleation of monomers, leading to unprecedented helicoidal folding of supramolecular polymers. Our findings augment our understanding of supramolecular polymer polymorphism, but they also highlight a distinctive method for achieving helicoidal folding in supramolecular polymers.

Liquid Crystal Emulsions: A Versatile Platform for Photonics, Sensing, and Active Matter

The self-assembly of liquid crystals (LCs) is a fascinating method for controlling the organization of discrete molecules into nanostructured functional materials. Although LCs are traditionally processed in thin films, their confinement within micrometre-sized droplets has recently revealed new properties and functions, paving the way for next-generation soft responsive materials. These recent findings have unlocked a wealth of unprecedented applications in photonics (e.g. reflectors, lasing materials), sensing (e.g. biomolecule and pathogen detection), soft robotics (e.g. micropumps, artificial muscles), and beyond. This Minireview focuses on recent developments in LC emulsion designs and highlights a variety of novel potential applications. Perspectives on the opportunities and new directions for implementing LC emulsions in future innovative technologies are also provided.

Liquid Crystal Materials for Biomedical Applications

Liquid crystal is a state of matter being intermediate between solid and liquid. Liquid crystal materials exhibit both orientational order and fluidity. While liquid crystals have long been highly recognized in the display industry, in recent decades, liquid crystals provide new opportunities into the cross-field of material science and biomedicine due to their biocompatibility, multifunctionality, and responsiveness. In this review, the latest achievements of liquid crystal materials applied in biomedical fields are summarized. The start is made by introducing the basic concepts of liquid crystals, and then shifting to the components of liquid crystals as well as functional materials derived therefrom. After that, the ongoing and foreseeable applications of liquid crystal materials in the biomedical field with emphasis put on several cutting-edge aspects, including drug delivery, bioimaging, tissue engineering, implantable devices, biosensing, and wearable devices are discussed. It is hoped that this review will stimulate ingenious ideas for the future generation of liquid crystal-based drug development, artificial implants, disease diagnosis, health status monitoring, and beyond.

Experimental probing of dynamic self-organized columnar assemblies in colloidal liquid crystals

Self-organized supramolecular assemblies are widespread in nature and technology in the form of liquid crystals, colloids, and gels. The reversible nature of non-covalent bonding leads to dynamic functions such as stimuli-responsive switching and self-healing, which are unachievable from an isolated molecule. However, multiple intermolecular interactions generate diverse conformational and configurational molecular motions over various time scales in their self-assembled states, and their specific dynamics remains unclear. In the present study, we have experimentally unveiled the static structures and dynamical behaviors in columnar colloidal liquid crystals by a coherent X-ray scattering technique using refined model samples. We have found that controlling the size distribution of the colloidal nanoplates dramatically changed their static and dynamic properties. Furthermore, the resulting dynamical behaviors obtained by X-ray photon correlation spectroscopy have been successfully decomposed into multiple distinct modes, allowing us to explore the dynamical origin in the colloidal liquid-crystalline state. The present approaches using a columnar liquid crystal may contribute to a better understanding of the dynamic nature of molecular assemblies and dense colloidal systems and bring valuable insights into rational design of functional properties of self-assembled materials such as stimuli-responsive liquid crystals, self-healing gels, and colloidal crystals. For these materials, the motion of constituent particles and molecules in the self-assembled state is a key factor for structural formation and dynamically responsive performance.

Physical and Thermal Characterizations of Newly Synthesized Liquid Crystals Based on Benzotrifluoride Moiety

The mesomorphic stability and optical activity of new group-based benzotrifluoride liquid crystals, (E)-4-(((4-(trifluoromethyl) phenyl) imino) methyl) phenyl 4-(alkyloxy)benzoate, or In, were investigated. The end of the molecules connected to the benzotrifluoride moiety and the end of the phenylazo benzoate moiety have terminal alkoxy groups which can range in chain length from 6 to 12 carbons. The synthesized compounds' molecular structures were verified using FT-IR, ¹H NMR, mass spectroscopy, and elemental analysis. Mesomorphic characteristics were verified using differential scanning calorimetry (DSC) and a polarized optical microscope (POM). All of the homologous series that have been developed display great thermal stability across a broad temperature range. Density functional theory (DFT) determined the examined compounds' geometrical and thermal properties. The findings showed that every compound is entirely planar. Additionally, by using the DFT approach, it was possible to link the experimentally found values of the investigated compounds' investigated compounds' mesophase thermal stability, mesophase temperature ranges, and mesophase type to the predicted quantum chemical parameters.

Self-assembled discotics as molecular semiconductors

With the advent of a new era of smart-technology, the demand for more economic optoelectronic materials that do not compromise with efficiency is gradually on the rise. Organic semiconductors provide greener alternatives to the conventional inorganic ones, but encounter the challenge of balancing charge carrier mobility with processability in devices. Discotic liquid crystals (DLCs), a class of self-assembling soft organic materials, possess the perfect degree of order and dynamics to address this challenge. Providing unidimensional charge carrier pathways through their nanoscale columnar architecture, DLCs can behave as efficient charge transport systems across a wide range of optoelectronic devices. Moreover, DLCs are solution-processable, thus reducing the fabrication cost. In this article, we have discussed the approaches towards developing DLCs as semiconductors, focusing on their molecular design concepts, supramolecular structures and electronic properties in the context of their charge carrier mobilities.

Network Phases with Multiple-Junction Geometries at the Gyroid-Diamond Transition

A novel phase sequence for the transition from the double diamond to the double gyroid cubic phases via two non-cubic intermediate phases, an orthorhombic Fmmm (O⁶⁹) phase and a hexagonal P6₃/m (H¹⁷⁶) phase, is reported for specifically designed bolapolyphiles composed of a linear rod-like bistolane core with sticky glycerol ends and two branched central and two linear peripheral side chains. These liquid crystalline (LC) phases represent members of a new class of unicontinuous network phases, formed by longitudinal rod bundles with polar spheres acting as junctions and the alkyl chains forming the continuum around them. In contrast to previously known bicontinuous cubic networks, they combine different junctions with different angles in a common structure, and one of them even represents a triple network instead of the usually found double networks. This provides new perspectives for the design of soft network phases with enhanced structural complexity, inspiring the search for new supramolecular networks, nano-particle arrays, and photonic band-gap materials.

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.

Engineering Polymeric Nanofluidic Membranes for Efficient Ionic Transport: Biomimetic Design, Material Construction, and Advanced Functionalities

Design elements extracted from biological ion channels guide the engineering of artificial nanofluidic membranes for efficient ionic transport and spawn biomimetic devices with great potential in many cutting-edge areas. In this context, polymeric nanofluidic membranes can be especially attractive because of their inherent flexibility and benign processability, which facilitate massive fabrication and facile device integration for large-scale applications. Herein, the state-of-the-art achievements of polymeric nanofluidic membranes are systematically summarized. Theoretical fundamentals underlying both biological and synthetic ion channels are introduced. The advances of engineering polymeric nanofluidic membranes are then detailed from aspects of structural design, material construction, and chemical functionalization, emphasizing their broad chemical and reticular/topological variety as well as considerable property tunability. After that, this Review expands on examples of evolving these polymeric membranes into macroscopic devices and their potentials in addressing compelling issues in energy conversion and storage systems where efficient ion transport is highly desirable. Finally, a brief outlook on possible future developments in this field is provided.

New luminescent ordered liquid crystalline molecules with a 3-cyano-2-pyridone core unit

The self-organized states of liquid crystals (LCs) have recently received a lot of attention because of their various applications, especially in the fields of electron transport materials and optoelectronic devices. In most of these applications, molecules containing a donor-acceptor skeleton have been widely employed and generally these molecular frameworks have been designed mainly on the basis of the donor-acceptor concept. Inspired from this concept, we synthesized a series of new donor-acceptor based luminescent molecules, i.e. 4,6-bis(4-alkyloxyphenyl)-2-oxo-1,2-dihydropyridine-3-carbonitrile (Pn-series), carrying variable alkoxy chains [i.e. n = 8, 10, 12, 14, 16]. The structures of the synthesized molecules were confirmed by various spectral analyses. Further, their absorption and emission studies indicated that these molecules show blue light emitting properties. Moreover, the experimentally obtained optical band gap was analogous to the theoretical band gap calculated from the DFT study. The first two members of the Pn-series (n = 8 and 10) are non-mesogens. As the alkyl chain length increased to n = 12 and n = 14, the smectic C phase appeared along with an additional low temperature ordered lamellar phase. When n = 16, the smectic C phase disappeared and the compound exhibited only an ordered lamellar phase. This ordered lamellar phase is mainly due to the face to face alignment which makes these molecules potential candidates for electron transport materials and optoelectronic devices.

Self-growing nano-liquid-crystal film from dynamic swollen hydrogel substrates

A hydrogel which spontaneously swells in an aqueous polymer solution was observed to produce a new hydrogel film coated on its swollen surface. Here, inspired by this phenomenon, we theoretically formulate the dynamics of isotropic-to-nematic (I-N) phase transition caused by swelling a hydrogel substrate (HS) in a dilute nanoplatelet suspension, and quantitatively characterize a self-growing nano-liquid-crystal (NLC) film coated on the swollen HS surface. We show that as the HS gets softer, the resulting NLC film can form earlier and achieve greater thickness (up to hundreds of micrometers). Our results and the existing experiments confirm that the growth dynamics of the NLC film or hydrogel film is exclusively regulated by the swelling behaviors of the HS instead of suspension configurations, e.g., I-N phase transition or sol-gel transition, suggesting a universal signature for the solutes ranging from molecules to colloids. However, both the maximum thickness of the NLC film and the corresponding characteristic time rely highly on the inherent elasticity of the HS and nanoplatelet aspect ratio. We demonstrate that the swelling quasiequilibrium state rather than the equilibrium state of the HS is more qualified to formulate a condition which is practically significant in preestimating the moment when the maximum thickness of the NLC film appears. Our theoretical framework serves as a robust paradigm to extensively rationalize (bio)film coatings which self-integrate with diverse nanostructural configurations via swelling-induced phase transition.

Alignment Control of Smectic Layer Structures in Liquid-Crystalline Polymers by Photopolymerization with Scanned Slit Light

Photoalignment control of hierarchical structures is a key process to enhance the properties of optical and mechanical materials. We developed an in situ molecular alignment method, where photopolymerization with the scanned slit light causes molecular flow, leading to two-dimensional precise alignment of molecules over large areas; however, the alignment control has been explored only on a molecular scale. In this study, we demonstrate this photopolymerization-induced molecular flow, enabling mesoscopic alignment of smectic layer structures composed of anisotropic molecules. Side-chain liquid-crystalline polymers were obtained from two different monomers with or without alkyl spacers by photopolymerization with one-dimensionally scanned slit light. The polymer with an alkyl spacer displayed mesogens aligned parallel to the scanning direction, while the polymer with no alkyl spacer resulted in perpendicular alignment of mesogens to the scanning direction, regulated by the alignment of the polymer main chain along the light scanning direction. Moreover, the polymerization with the scanned light aligned not only the mesogens but also mesoscopic smectic layer structures over large areas, depending on the structure and scanning pattern of light. We envision that such a simple polymerization technique could become a powerful and versatile alignment platform of anisotropic materials in a wide range of scales.

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.

Automated Calculation of Liquid Crystal Sensing Images Based on Deep Learning

Liquid crystal (LC)-based sensors have been extensively applied in the detection of chemical and biological events. However, the calculation of the optical images of the LC-based sensors is usually time-consuming and also might bring some errors due to the use of different judgment criteria by different users. In the present study, an automated calculation method for LC sensing images based on deep learning is provided. A convolutional network is trained with the prepared LC sensing images and their corresponding segmentation annotations to predict the positive responses. The ratio is calculated from the area of positive response to the total area selected by our image processing method. The robustness of the proposed algorithm is validated on both the test set and the label-free Cd²⁺ detection. The results show that the method based on deep learning can detect the positive response area in real time and the speed is much faster than the manual processing method. In addition, deep learning method can be directly applied to other label-free molecular detection assays.

Amphiphilic Liquid Crystalline Polymer Micelles That Exhibit a Phase Transition at Body Temperature

Liquid crystalline polymers (LCPs), which exhibit unique structures and properties intermediate between those of liquids and solids, are widely utilized as functional and advanced materials for fabricating optical devices and high-performance fibers. This utility stems from their ability to abruptly change their organized structures and mobilities at their liquid crystalline-isotropic phase transition temperatures, similar to the properties of biological membranes. Despite these numerous potential applications of LCPs, no study on their use in medical applications such as drug delivery has been reported. In the present study, we synthesized amphiphilic side-chain LCPs (LCP-g-OEGs, where OEG is oligo(ethylene glycol)) for medical applications, where the LCP-g-OEGs undergo a nematic-isotropic phase transition at body temperature. The LCP-g-OEGs formed micelles with a diameter of approximately 130 nm in aqueous media. The micelles were stable and did not dissociate in aqueous media even when the temperature exceeded the nematic-isotropic phase transition temperature (T_NI). Although the release of a dye as a model drug from micelles was suppressed at temperatures lower than T_NI, their dye release was drastically enhanced at temperatures higher than T_NI. The LCP-g-OEG micelles regulated dye release reversibly in accordance with stepwise changes in temperature, without undergoing dissociation, differing from the behavior of standard temperature-responsive micelles. The temperature-responsive dye release behavior is induced by dramatic changes in their well-organized and dynamic structures as a result of the nematic-isotropic phase transition. These results demonstrate that the LCP-g-OEG micelles have a lot of medical applications as reversibly stimuli-responsive drug carriers.

Nanoarchitectonics for conductive polymers using solid and vapor phases

Conductive polymers have been extensively studied as functional organic materials due to their broad range of applications. Conductive polymers, such as polypyrrole, polythiophene, and their derivatives, are typically obtained as coatings and precipitates in the solution phase. Nanoarchitectonics for conductive polymers requires new methods including syntheses and morphology control. For example, nanoarchitectonics is achieved by liquid-phase syntheses with the assistance of templates, such as macromolecules and porous materials. This minireview summarizes the other new synthetic methods using the solid and vapor phases for nanoarchitectonics. In general, the monomers and related species are supplied from the solution phase. Our group has studied polymerization of heteroaromatic monomers using the solid and vapor phases. The surface and inside of solid crystals were used for the polymerization with the diffusion of the heteroaromatic monomer vapor. Our nanoarchitectonics affords to form homogeneous coatings, hierarchical structures, composites, and copolymers for energy-related applications. The concepts using solid and vapor phases can be applied to nanoarchitectonics for not only conductive polymers but also other polymers toward a variety of applications.

Nonpolarizable Force Fields through the Self-Consistent Modeling Scheme with MD and DFT Methods: From Ionic Liquids to Self-Assembled Ionic Liquid Crystals

A key to achieve the accuracy of molecular dynamics (MD) simulation is the set of force fields used to express the atomistic interactions. In particular, the electrostatic interaction remains the main issue for the precise simulation of various ionic soft materials from ionic liquids to their supramolecular compounds. In this study, we test the nonpolarizable force fields of ionic liquids (ILs) and self-assembled ionic liquid crystals (ILCs) for which the intermolecular charge transfer and intramolecular polarization are significant. The self-consistent modeling scheme is adopted to refine the atomic charges of ionic species in a condensed state through the use of density functional theory (DFT) under the periodic boundary condition. The atomic charges of the generalized amber force field (GAFF) are effectively updated to express the electrostatic properties of ionic molecules obtained by the DFT calculation in condensed phase, which improves the prediction accuracy of ionic conductivity with the obtained force field (GAFF-DFT). The derived DFT charges then suggest that the substitution of a hydrophobic liquid-crystalline moiety into IL-based cations enhances the charge localization of ionic groups in the amphiphilic molecules, leading to the amplification of the electrostatic interactions among the hydrophilic/ionic groups in the presence of hydrophobic moieties. In addition, we focus on an ion-conductive pathway hidden in the self-assembled nanostructure. The MD results indicate that the ionic groups of cation and anion interact strongly for keeping the bicontinuous nanosegregation of ionic nanochannel. The partial fractions of hydrophilic/ionic and hydrophobic nanodomains are then quantified with the volume difference from referenced IL systems, while the calculated ionic conductivity decreases in the self-assembled ILCs more than the occupied volume of ionic nanodomains. These analyses suggest that the mobility of ions in the self-assembled ILCs remains quite restricted even with small tetrafluoroborate anions because of strong attractive interaction among ionic moieties.

Biomineral-Inspired Colloidal Liquid Crystals: From Assembly of Hybrids Comprising Inorganic Nanocrystals and Organic Polymer Components to Their Functionalization

Bioinspired organic/inorganic synthetic composites have been studied as high-performance and functional materials. In nature, biominerals such as pearls, teeth, and bones are self-organized organic/inorganic composites. The inorganic components are composed of calcium carbonate (CaCO₃) and hydroxyapatite (HAp), while the organic components consist of peptides and polysaccharides. These composites are used as structural materials in hard biological tissues. Biominerals do not show significantly higher performances than synthetic composites such as glass-fiber- or carbon-fiber-reinforced plastics. However, biominerals consist of environmentally friendly and biocompatible components that are prepared under mild conditions. Moreover, they form elaborate nanostructures and self-organized hierarchical structures. Much can be learned about material design from these biomineral-based hierarchical and nanostructured composites to assist in the preparation of functional materials.

Inspired by these biological hard tissues, we developed nanostructured thin films and bulk hybrid crystals through the self-organization of organic polymers and inorganic crystals of CaCO₃ or HAp. In biomineralization, the combination of insoluble components and soluble acidic macromolecules controls the crystallization process. We have shown that poly(acrylic acid) (PAA) or acidic peptides called polymer additives induce the formation of thin film crystals of CaCO₃ or HAp by cooperation with insoluble organic templates such as chitin and synthetic polymers bearing the OH group. Moreover, we recently developed CaCO₃- and HAp-based nanostructured particles with rod and disk shapes. These were obtained in aqueous media using a macromolecular acidic additive, PAA, without using insoluble polymer templates. At appropriate concentrations, the anisotropic particles self-assembled and formed colloidal liquid-crystalline (LC) phases.

LC materials are generally composed of organic molecules. They show ordered and mobile states. The addition of stimuli-responsive properties to organic rod-like LC molecules led to the successful development of informational displays, which are now widely used. On the other hand, colloidal liquid crystals are colloidal self-assembled dispersions of anisotropic organic and inorganic nano- and micro-objects. For example, polysaccharide whiskers, clay nanosheets, gibbsite plate-shaped particles, and silica rod-shaped particles exhibit colloidal LC states.

In this Account, we focused on the material design and hierarchical aspects of biomineral-based colloidal LC polymer/inorganic composites. We describe the design and preparation, nanostructures, and self-assembled behavior of these new bioinspired and biocompatible self-organized materials. The characterization results for these self-assembled nanostructured colloidal liquid crystals found using high-resolution transmission electron microscopy, small-angle X-ray scattering, and neutron scattering and rheological measurements are also reported. The functions of these biomineral-inspired liquid crystals are presented. Because these biomineral-based LC colloidal liquid crystals can be prepared under mild and aqueous conditions and they consist of environmentally friendly and biocompatible components, new functions are expected for these materials.

Luminescent columnar discotics as highly efficient emitters in pure deep-blue OLEDs with an external quantum efficiency of 4.7

Development of materials that serve as efficient blue emitters in solution-processable OLEDs is challenging. In this study, we report three derivatives of C₃-symmetric 1,3,5-tris(thien-2-yl)benzene-based highly luminescent room temperature columnar discotic liquid crystals (DLCs) suitable as solid-state emitters in OLED devices. When employed in solution-processed OLEDs, one of the derivatives having the highest photoluminescence quantum yield exhibited a maximum EQE of 4.7% and CIE chromaticity of (0.16, 0.05) corresponding to the ultra deep-blue emission. The finding is sufficiently significant in the field of DLC-based deep blue emitters.

Advanced Functional Liquid Crystals

Liquid crystals have been intensively studied as functional materials. Recently, integration of various disciplines has led to new directions in the design of functional liquid-crystalline materials in the fields of energy, water, photonics, actuation, sensing, and biotechnology. Here, recent advances in functional liquid crystals based on polymers, supramolecular complexes, gels, colloids, and inorganic-based hybrids are reviewed, from design strategies to functionalization of these materials and interfaces. New insights into liquid crystals provided by significant progress in advanced measurements and computational simulations, which enhance new design and functionalization of liquid-crystalline materials, are also discussed.