Liquid-crystalline ordering as a concept in materials science: from semiconductors to stimuli-responsive devices

Synthesis of Side-Chain Liquid Crystalline Polyacrylates with Bridged Stilbene Mesogens

In recent years, π-conjugated liquid crystalline molecules with optoelectronic functionalities have garnered considerable attention, and integrating these molecules into side-chain liquid crystalline polymers (SCLCPs) holds potential for developing devices that are operational near room temperature. However, it is difficult to design SCLCPs with excellent processability because liquid crystalline mesogens are rigid rods, have low solubility in organic solvents, and have a high isotropization temperature. Recently, we developed near-room-temperature π-conjugated nematic liquid crystals based on "bridged stilbene". In this work, we synthesized a polyacrylate SCLCP incorporating a bridged stilbene that exhibited a nematic phase near room temperature and could maintain liquid crystallinity for more than three months. We conducted a thorough phase structure analysis and evaluated the optical properties. The birefringence values of the resulting polymers were higher than those of the corresponding monomers because of the enhanced order parameters due to the polymer effect. In addition, the synthesized polymers inherited mesogen-derived AIE properties, with high quantum yields (Φfl = 0.14-0.35) in the solid state. It is noteworthy that the maximum fluorescence wavelength exhibited a redshift of greater than 27 nm as a consequence of film formation. Thus, several unique characteristics of the SCLCPs are unattainable with small molecular systems.

Nanoscale View of Alignment and Domain Growth in a Hexagonal Columnar Liquid Crystal

Highly ordered liquid crystalline (LC) phases have important potential for organic electronics. We studied the molecular alignment and domain structure in a columnar LC thin film with nanometer resolution during in situ heating using four-dimensional scanning transmission electron microscopy (4D STEM). The initial disordered vapor-deposited LC glass thin film rapidly ordered at its glass transition temperature into a hexagonal columnar phase with small (<10 nm), well-aligned, planar domains (columns oriented parallel to the surface). Upon further heating, the domains coarsen via bulk diffusion, then the film crystallizes, then finally transforms back to an LC phase at an even higher temperature. The LC phase at high temperature shows straight columns of molecules, which we attribute to structure inherited from the intermediate crystalline phase. Nanoscale 4D STEM offers direct insight into the mechanisms of domain reorganization, and intermediate crystallization is a potential approach to manipulate orientational order and texture at the nano- to mesoscale in LC thin films.

Enhancing Optoelectronic Anisotropy in Highly Oriented Thin Films by Fluorine Substitution in Novel Semiconducting Polymers

The recent past has witnessed remarkable progress in organic electronics, driven by the quest for flexible, lightweight, and cost-effective electronic devices. Semiconducting polymers (SCPs) have emerged as key materials in this field, offering unique electronic and optoelectronic properties along with mechanical flexibility. This study focuses on designing, synthesizing, and utilizing novel donor-acceptor (D-A) copolymer-based SCPs introducing a difluorothiophene moiety in the polymeric backbone. The importance of fluorine substitution for backbone planarity was verified by density functional theory calculations, comparing it with a nonfluorine substituted counterpart. Through the Unidirectional Floating Film Transfer Method (UFTM), we fabricated highly oriented thin films, resulting in increased optical anisotropy with dichroic ratios reaching 19.3 in PC20-FT thin films, one of the highest optical anisotropy observed for solution processable SCP thin films. X-ray diffraction and atomic force microscopy results validated the increase in the crystallinity and domain size with the increasing alkyl chain length. Finally, we elucidate these findings in the context of electrical applications by fabricating organic field-effect transistors revealing anisotropic charge transport achieving a promising mobility of 1.24 cm2V-1s-1 and mobility anisotropy of 39.5. This study offers insights into the design principles and performance optimization of SCP-based devices, paving the way for advancements in plastic electronics.

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.

Electrochemical Detection of Selective Anion Transport through Subnanopores in Liquid-Crystalline Water Treatment Membranes

The anion-selective transport through subnanoporous liquid-crystalline (LC) water treatment membranes was quantitatively detected by the deposition and electrochemical analysis of the LC membrane on the GaN electrode. The time course of the capacitance and Warburg resistance of the LC membrane suggest that the interaction of the LC membrane with monovalent Cl- ions is distinctly different from that with SO42- ions. A continuous decay in capacitance suggests the condensation of Cl- ions in subnanopores, whereas the interaction between SO42- ions and the inner wall of subnanopores is much weaker. The chronoamperometry data further suggest that SO42- ions are transported through subnanoporous channels 10 times faster than Cl- ions. These results, together with the previous X-ray emission spectroscopy, suggest that SO42- ions, which possess similar hydrogen-bonded structures to the hydrogen-bonded networks inside the subnanopores, can exchange the associated water molecules and hop along the network of water molecules, but Cl- ions bind and accumulate inside subnanopores. The well-controlled supramolecular self-assembly of LC building blocks opens a large potential toward the fine adjustment of hydrogen-bonding networks in nanospace providing materials new functions, which cannot be realized by bulk water.

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.

Calamitic Liquid Crystals for Reversible Light-Modulated Phase Regulation Based on Arylazopyrazole Photoswitches

The design of responsive liquid crystals enables a diversity of technological applications. Especially photochromic liquid crystals gained a lot of interest in recent years due to the excellent spatiotemporal control of their phase transitions. In this work we present calamitic light responsive mesogens based on a library of arylazopyrazole photoswitches. These compounds show liquid-crystalline behavior as shown by differential scanning calorimetry, grazing incidence X-ray diffraction and polarized optical microscopy. UV-vis spectroscopy and NMR analysis confirmed the excellent photophysical properties in solution and thin film. Additionally, polarized optical microscopy studies of the pristine compounds show reversible phase transition upon irradiation with light. Moreover, as a dopant in the commercially available liquid crystal 4-cyano-4'-pentylbiphenyl (5CB), the temperature range was reduced to ambient temperatures while preserving the photophysical properties. Remarkably, this co-assembled system shows reversible liquid-crystalline to isotropic phase transition upon irradiation with light of different wavelengths. The spatiotemporal control of the phase transition of the liquid crystals offers opportunities in the development of optical devices.

Synthesis and mesomorphic properties of "side-on" hybrid liquid crystalline silsesquioxanes

Novel hybrid silsesquioxane-based liquid crystalline derivatives with varied lengths of spacers and tails have been synthesized by hydrosilylation reactions of octakis(dimethylsiloxy)silsesquioxane and side-on mesogens via a platinum catalyst. The thermal behavior of three types of silsesquioxane-based liquid crystals (LCs), differentiated by the molecular structure of mesogens, was investigated by differential scanning calorimetry (DSC) and polarising optical microscopy (POM). Temperature-dependent small and wide-angle X-ray scattering was used to verify liquid crystalline phases, revealing that the silsesquioxane-based derivatives formed hexagonal columnar and nematic mesophases, and the effect of the molecular structure of the mesogens and the spacer length on the formation of LC phases is discussed. This investigation demonstrated that the choice of the "side-on" attachments plays a crucial role in enhancing the emergence of the nematic phase.

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.

Lyotropic liquid crystal elastomers for drug delivery

Silicone elastomers like polydimethylsiloxane (PDMS) possess a combination of attractive material and biological properties motivating their widespread use in biomedical applications. Development of elastomers with capacity to deliver active therapeutic substances in the form of drugs is of particular interest to produce medical devices with added functionality. In this work, silicone-based lyotropic liquid crystal elastomers with drug-eluting functionality were developed using PDMS and triblock copolymer (diacrylated Pluronic F127, DA-F127). Various ternary PDMS-DA-F127-H₂O compositions were explored and evaluated. Three compositions were found to have specific properties of interest and were further investigated for their nanostructure, mechanical properties, water retention capacity, and morphology. The ability of the elastomers to encapsulate and release polar and nonpolar substances was demonstrated using vancomycin and ibuprofen as model drugs. It was shown that the materials could deliver both types of drugs with a sustained release profile for up to 6 and 5 days for vancomycin and ibuprofen, respectively. This works demonstrates a lyotropic liquid crystal, silicone-based elastomer with tailorable mechanical properties, water retention capacity and ability to host and release polar and nonpolar active substances.

Synthesis and characterization of new imine liquid crystals based on terminal perfluoroalkyl group

New organic derivatives named, (E)-3(or4) -(alkyloxy)-N-{(trifluoromethyl)benzylidene}aniline, 1a-f, were synthesized and examined their liquid crystalline behaviors. FT-IR, ¹H NMR, ¹³C NMR, ¹⁹F NMR, elemental analyses and GCMS were used to validate the prepared compounds' chemical structures. We used differential scanning calorimetry (DSC) and polarized optical microscopy (POM) to investigate the mesomorphic characteristics of the formed Schiff bases. All tested compounds of series 1a-c have mesomorphic behaviour of nematogenic temperature ranges while the group 1d-f show non-mesomorphic properties. Moreover, it was found that the enantiotropic N phases included all of the homologue 1a-c. Computational studies using DFT (density functional theory) validated the experimental mesomorphic behavior results. All the analyzed compounds had their dipole moments, polarizability, and reactivity characteristics explained. Theoretical simulations showed that as the length of the terminal chain is increased, the polarizability of the stuided compounds increases. Consequently, compounds 1a and 1d have the least polarizability.

Design of Liquid Crystal Materials Based on Palmitate, Oleate, and Linoleate Derivatives for Optoelectronic Applications

Herein, liquid crystalline derivatives based on palmitate, oleate, and linoleate moieties with azomethine cores were synthesized, and their physical, chemical, optical, and photophysical properties were investigated in detail. The mesomorphic activity of these materials was examined through polarized optical microscopy (POM) and differential scanning calorimetry (DSC). The observed results revealed that the stability of the thermal mesophase depends on the terminal polar as well as on the fatty long-chain substituents. Purely smectogenic phases were detected in all three terminal side chains. A eutectic composition with a low melting temperature and a broad smectic A range was found by constructing a binary phase diagram and addressing it in terms of the mesomorphic temperature range. The energy bandgap of the palmitate-based derivative (Ia) was determined as 3.95 eV and slightly increased to 4.01 eV and 4.05 eV for the oleate (Ib) and linoleate (Ic) derivatives, respectively. The optical constants (n, κ, ε_r, and ε_i) were extracted from the fitting of measured spectroscopic ellipsometer data. The steady-state spectra of these samples exhibited a broad emission in the range 400-580 nm, which was found to be blue shifted to 462 nm for both Ib and Ic derivatives. The average fluorescence decay lifetime of the Ia derivative was found to be 598 ps, which became faster for the Ib and Ic derivatives and slower for the sample with a chloride end polar group.

Conjugation Extension and Halochromic Behaviors of S-Fused Polycyclic Aromatic Hydrocarbons Bearing Cyclopenta[b]thiopyran Moieties

Three S-fused polycyclic aromatic hydrocarbons (PAHs) bearing cyclopenta[b]thiopyran moieties have been designed and successfully synthesized. With the conjugation extension, the absorption onset of the longest PAH reaches 1110 nm. All the three S-fused PAHs exhibit significant halochromic properties in both solution and solid states. Upon protonation, the proton is incorporated on the cyclopentadiene ring while the positive charge is localized on the thiopyrylium ring. Moreover, no significant difference can be found for the two shorter PAHs upon the protonation by different organic acids, such as trifluoroacetic acid (TFA) and trifluoromethanesulfonic acid (TfOH), while the longest PAH can be only mono-protonated by TFA but di-protonated by stronger TfOH. Furthermore, after protonation, the non-emissive S-fused PAHs exhibit strong fluorescence and can be regenerated by simply neutralization with triethylamine. The enhanced emission of mono-protonated products stem from S₂ →S₀ transitions, which disobey the Kasha's rule.

Optical nonlinearity of a dual-frequency nematic liquid crystal via temperature-mediated mapping of dielectric anisotropy

Liquid crystals are of great interest in the field of nonlinear optics due to their efficient response to low intensity light fields. Here we present a new, to the best of our knowledge, mechanism of a nonlinear optical response which is observed for a dye-doped dual-frequency nematic liquid crystal. The local increase in temperature caused by the absorption of light beam in the liquid crystal medium leads to spatial variation and inversion of the sign of the dielectric anisotropy. When an alternating current electric field with a frequency close to the cross-over frequency is applied to the liquid crystal cell, the planar orientation sustains at the beam periphery, but elastic deformation occurs in the irradiation region. In the case of a dye dopant with negative absorption dichroism, a first-order orientational transition with large bistability region is obtained.

Nematic-to-Isotropic Phase Transition in Poly(L-Lactide) with Addition of Cyclodextrin during Abiotic Degradation Study

Poly(L-lactide) is capable of self-assembly into a nematic mesophase under the influence of temperature and mechanical stresses. Therefore, subsequent poly(L-lactide) films were obtained and characterized, showing nematic liquid crystal properties both before and after degradation. Herein, we present that, by introducing β-cyclodextrin into the polymer matrix, it is possible to obtain a chiral nematic mesophase during pressing, regardless of temperature and time. The obtained poly(L-lactide) films exhibiting liquid crystal properties were subjected to degradation tests and the influence of degradation on these properties was determined. Thermotropic phase behavior was investigated using polarized optical microscopy, X-ray diffraction, and differential scanning calorimetry. The degradation process demonstrated an influence on the liquid crystal properties of pressed polymer films. The colored planar texture of the chiral nematic mesophase, which was not observed prior to degradation in films without the addition of β-cyclodextrin, appeared after incubation in water as a result of the entrapment of degradation products in the polymer matrix. These unusual tailor-made properties, obtained in liquid crystals in (bio)degradable polymers using a simple method, demonstrate the potential for advanced photonic applications.

Nanographenes and Graphene Nanoribbons as Multitalents of Present and Future Materials Science

As cut-outs from a graphene sheet, nanographenes (NGs) and graphene nanoribbons (GNRs) are ideal cases with which to connect the world of molecules with that of bulk carbon materials. While various top-down approaches have been developed to produce such nanostructures in high yields, in the present perspective, precision structural control is emphasized for the length, width, and edge structures of NGs and GNRs achieved by modern solution and on-surface syntheses. Their structural possibilities have been further extended from "flatland" to the three-dimensional world, where chirality and handedness are the jewels in the crown. In addition to properties exhibited at the molecular level, self-assembly and thin-film structures cannot be neglected, which emphasizes the importance of processing techniques. With the rich toolkit of chemistry in hand, NGs and GNRs can be endowed with versatile properties and functions ranging from stimulated emission to spintronics and from bioimaging to energy storage, thus demonstrating their multitalents in present and future materials science.

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.

Poly(l-Lactide) Liquid Crystals with Tailor-Made Properties Toward a Specific Nematic Mesophase Texture

This paper presents the liquid crystal (LC) properties of poly(l-lactide) (PLLA). Mesophase behavior is investigated using polarized optical microscopy, X-ray diffraction, and differential scanning calorimetry. The performed analyses confirm that pressed PLLA films exhibit the unique capability of self-assembling into a nematic mesophase under the influence of mechanical pressure, temperature, and time. It was originally demonstrated that the chiral nematic mesophase can be obtained by introducing fine powders into the polymer. Based on the research conducted, it was proved that the pressed PLLA films have a chiral nematic mesophase with a nematic-to-isotropic phase transition and a large mesophase stability range overlapping the temperature of the human body, which can persist for years at ambient temperature. The obtained films show tailor-made properties toward a nematic mesophase with a specific texture, including colored planar texture of the chiral nematic mesophase and blue-phase (BP) LC texture. The BP, described for the first time in plain PLLA, occurred over a wider than usual temperature range of stability between isotropic and chiral nematic thermotropic phases (ΔT ≈ 9 °C), which is an advantage of the obtained polymer material, in addition to ease of preparation. This opens up new prospects for advanced photonic green applications.

Liquid crystalline 2D borophene oxide for inorganic optical devices

Borophene has been recently proposed as a next-generation two-dimensional material with promising electronic and optical properties. However, its instability has thus far limited its large-scale applications. Here, we investigate a liquid-state borophene analogue with an ordered layer structure derived from two-dimensional borophene oxide. The material structure, phase transition features and basic properties are revealed by using X-ray analysis, optical and electron microscopy, and thermal characterization. The obtained liquid crystal exhibits high thermal stability at temperatures up to 350 °C and an optical switching behaviour driven by a low voltage of 1 V.

Transition from lamellar to nanostructure mesophases in azobenzene-based hockey-stick polycatenars

Tuning from 1D to 3D mesophases by alkyl chain engineering. Multichain π-conjugated hockey-stick molecules form lamellar SmA and meso-structure Ia3̄d with continuous networks. The effect of the position of the central bent-core unit on helical self-assembly is discussed.

Liquid Crystals: Versatile Self-Organized Smart Soft Materials

Smart soft materials are envisioned to be the building blocks of the next generation of advanced devices and digitally augmented technologies. In this context, liquid crystals (LCs) owing to their responsive and adaptive attributes could serve as promising smart soft materials. LCs played a critical role in revolutionizing the information display industry in the 20th century. However, in the turn of the 21st century, numerous beyond-display applications of LCs have been demonstrated, which elegantly exploit their controllable stimuli-responsive and adaptive characteristics. For these applications, new LC materials have been rationally designed and developed. In this Review, we present the recent developments in light driven chiral LCs, i.e., cholesteric and blue phases, LC based smart windows that control the entrance of heat and light from outdoor to the interior of buildings and built environments depending on the weather conditions, LC elastomers for bioinspired, biological, and actuator applications, LC based biosensors for detection of proteins, nucleic acids, and viruses, LC based porous membranes for the separation of ions, molecules, and microbes, living LCs, and LCs under macro- and nanoscopic confinement. The Review concludes with a summary and perspectives on the challenges and opportunities for LCs as smart soft materials. This Review is anticipated to stimulate eclectic ideas toward the implementation of the nature's delicate phase of matter in future generations of smart and augmented devices and beyond.

Versatile Pendant Polymer for Selective Charge Carrier Transport via Controlling the Supramolecular Self-Assembly

Polyvinyl carbazole (P0)-based pendant polymers were synthesized by modifying carbazole motifs with pyrene derivatives (P1 and P4) to manipulate the bandgap and frontier orbital energy levels. To establish the electronic properties of pendant polymers according to structural differences, the polymers were utilized as additional hole transport layers in planar-type perovskite solar cells and organic photovoltaic cells. When P4 with thiophene-pyrene pendant was used as hole transport layer, all device parameters, except open-circuit voltage, were significantly improved in comparison with P0 and P1 (conjugated with t-butyl pyrene derivatives). Since P4 had more electrically conductive thiophene units than benzene units with fewer alkyl groups, the supramolecular assembly of P4 was found to be more favorable in electronic devices. Furthermore, devices with P4 demonstrated lower dark current than others, which could potentially be useful for charge carrier transport and sensitive photo detecting devices.

Transition kinetics of defect patterns in confined two-dimensional smectic liquid crystals

Topological defects in liquid crystals under confined geometries have attracted extensive research interests. Here, we perform molecular dynamics simulations to investigate the formation and transition of defect patterns in two-dimensional smectic Gay-Berne liquid crystals with a simple rectangular confinement boundary. Two typical types of defect patterns, bridge and diagonal defect patterns, are observed, which can be transformable continuously between each other over time. The transition usually starts from the line or point defect regions, and the competition between neighboring and opposite boundary effects induces the continuous realignments of the smectic layers to connect the neighboring or opposite walls. The relative stability of these two defect patterns can be controlled by changing the confinement conditions. These results deepen our understanding of transition kinetics of defect patterns in confined liquid crystals.

Advanced Functional Luminescent Metallomesogens: The Key Role of the Metal Center

The use of liquid crystals for the fabrication of displays incorporated in technological devices (TVs, calculators, screens of eBook's, tablets, watches) demonstrates the relevance that these materials have had in our way of living. However, society evolves, and improved devices are looked for as we create a more efficient and safe technology. In this context, metallomesogens can behave as multifunctional materials because they can combine the fluidic state of the mesophases with properties such as photo and electroluminescence, which offers new exciting possibilities in the field of optoelectronics, energy, environment, and even biomedicine. Herein, it has been established the role of the molecular geometry induced by the metal center in metallomesogens to achieve the self-assembly required in the liquid-crystalline mesophase. Likewise, the effect of the coordination environment in metallomesogens has been further analyzed because of its importance to induce mesomorphism. The structural analysis has been combined with an in-depth discussion of the properties of these materials, including their current and potential future applications. This review will provide a solid background to stimulate the development of novel and attractive metallomesogens that allow designing improved optoelectronic and microelectronic components. Additionally, nanoscience and nanotechnology could be used as a tool to approach the design of nanosystems based on luminescent metallomesogens for use in bioimaging or drug delivery.

Self-healing and shape memory functions exhibited by supramolecular liquid-crystalline networks formed by combination of hydrogen bonding interactions and coordination bonding

We here report a new approach to develop self-healing shape memory supramolecular liquid-crystalline (LC) networks through self-assembly of molecular building blocks via combination of hydrogen bonding and coordination bonding. We have designed and synthesized supramolecular LC polymers and networks based on the complexation of a forklike mesogenic ligand with Ag+ ions and carboxylic acids. Unidirectionally aligned fibers and free-standing films forming layered LC nanostructures have been obtained for the supramolecular LC networks. We have found that hybrid supramolecular LC networks formed through metal-ligand interactions and hydrogen bonding exhibit both self-healing properties and shape memory functions, while hydrogen-bonded LC networks only show self-healing properties. The combination of hydrogen bonds and metal-ligand interactions allows the tuning of intermolecular interactions and self-assembled structures, leading to the formation of the dynamic supramolecular LC materials. The new material design presented here has potential for the development of smart LC materials and functional LC membranes with tunable responsiveness.

Smart Supramolecular Self-Assembled Nanosystem: Stimulus-Responsive Hydrogen-Bonded Liquid Crystals

In a liquid crystal (LC) state, specific orientations and alignments of LC molecules produce outstanding anisotropy in structure and properties, followed by diverse optoelectronic functions. Besides organic LC molecules, other nonclassical components, including inorganic nanomaterials, are capable of self-assembling into oriented supramolecular LC mesophases by non-covalent interactions. Particularly, huge differences in size, shape, structure and properties within these components gives LC supramolecules higher anisotropy and feasibility. Therefore, hydrogen bonds have been viewed as the best and the most common option for supramolecular LCs, owing to their high selectivity and directionality. In this review, we summarize the newest advances in self-assembled structure, stimulus-responsive capability and application of supramolecular hydrogen-bonded LC nanosystems, to provide novel and immense potential for advancing LC technology.

A phase-dependent photoluminescent discotic liquid crystal bearing a graphdiyne substructure

In recent years, graphdiyne and its derivatives with fascinating electro-optic properties have attracted tremendous scientific attention. Here we design and synthesize a graphdiyne-derived discotic liquid crystal material by decorating six wedge-shaped 3,4,5-tris(dodecyloxy)benzoate groups on the fundamental structural unit of graphdiyne, the dehydrotribenzo[18]annulene core. This graphdiyne-derived liquid crystal material exhibits a cubic phase and a hexagonal columnar phase at varied temperatures. Most interestingly, this molecule displays a tunable phase-dependent photoluminescence behavior. Under the irradiation of 365 nm wavelength ultraviolet light, the luminescent material emits pale blue, green and azure light in the cubic, hexagonal columnar and isotropic phases respectively. This graphdiyne-derived discotic liquid crystal with excellent optical characteristics might have application potentials in organic optoelectronic functional materials and devices.

Emergence of uniform tilt and π-stacking in triangular liquid crystalline honeycombs

The synclinic tilted organization of specifically designed polyphilic oligo(p-phenylene ethynylene) rods in cylindrical shells around triangular prismatic cells on the <5 nm scale leads to a new kind of liquid crystalline honeycomb composed of helical shells with alternating helix sense. Core fluorination at the outer ring modifies the core-core interactions, thus resulting in triangular arrays with face-to-face π-stacking along the honeycomb.

Green Synthesis of Zr-Based Metal-Organic Framework Hydrogel Composites and Their Enhanced Adsorptive Properties

Metal-organic frameworks (MOFs) have emerged as promising candidates for a wide range of applications due to their high surface area and customizable structures, however, the minimal external hydrophilicity of MOFs has limited their biomedical implementations. Structuring of MOFs within polymer frameworks is an approach used to create hybrid materials that retain many of the MOF characteristics (e.g. high adsorption capacity) but expand the range of mechanical and surface properties as well as form factors accessible. Using this approach, hybridizing MOFs with hydrophilic hydrogels can give rise to materials with improved hydrophilicity and biocompatibility. Here, we describe the synthesis of the first Zr-based MOF-hydrogel hybrid material (composite 3) using a green chemistry approach, in which only water was used as the solvent and relatively low temperature (50 °C) was applied. Using methylene blue (MB) as a probe molecule, composite 3 exhibited greater adsorption capacity than the MOF or the hydrogel alone in aqueous solution at most tested pH values (all except pH 13). At an initial MB concentration of 0.0096 mg/mL (30.014uM) and neutral pH conditions, this new hybrid presented the highest loading of MB among similar materials (MB adsorbed = 4.361 ± 0.092 mg MB/g Zr, partition coefficient = 0.172 ± 0.004 mg/g/uM) and largely retained its adsorption capacity under varied conditions (pH 1-13 and 0.2-1.0M NaCl), rendering possible applications in drug delivery and the removal of tumor contrast agent/dye with minimal leakage due to its broad chemical stability.

Magnetic hybrid materials in liquid crystals

The integration of nanoparticles with magnetic, ferroelectric or semiconducting properties into liquid crystals (LCs) has attracted great interest both for fundamental investigations and for technological applications. Here, an overview of hybrid materials based on magnetic nanoparticles (MNPs) and thermotropic LCs is given. After a general introduction to thermotropic LCs and LC-MNP hybrid materials, various preparation methods established by us are presented. The synthesis of shape-(an)isotropic MNPs, their functionalization by tailored (pro)mesogenic ligands with linear or dendritic structures and their integration into LC hosts are discussed. The characterization of the MNPs, (pro)mesogenic ligands and resulting MNP-LC hybrid materials is described to show the influence of MNP functionalization on the MNP-LC interactions including aspects such as colloidal stability and structuring in the LC host. Overall, we show that the physical properties of the hybrid material are significantly influenced not only by the MNPs (i.e., their size, shape and composition) but also by their surface properties (i.e., the structure of the (pro)mesogenic ligands).

Optocapillarity-driven assembly and reconfiguration of liquid crystal polymer actuators

Realizing programmable assembly and reconfiguration of small objects holds promise for technologically-significant applications in such fields as micromechanical systems, biomedical devices, and metamaterials. Although capillary forces have been successfully explored to assemble objects with specific shapes into ordered structures on the liquid surface, reconfiguring these assembled structures on demand remains a challenge. Here we report a strategy, bioinspired by Anurida maritima, to actively reconfigure assembled structures with well-defined selectivity, directionality, robustness, and restorability. This approach, taking advantage of optocapillarity induced by photodeformation of floating liquid crystal polymer actuators, not only achieves programmable and reconfigurable two-dimensional assembly, but also uniquely enables the formation of three-dimensional structures with tunable architectures and topologies across multiple fluid interfaces. This work demonstrates a versatile approach to tailor capillary interaction by optics, as well as a straightforward bottom-up fabrication platform for a wide range of applications.