Search

Responsive and adaptive soft-matter systems represent an advanced category of materials with potential applications in drug delivery. Among these, liquid crystals (LCs) emerge as multifunctional anisotropic scaffolds capable of reacting to temperature, light, electric or magnetic fields. Specifically, the ordering and physical characteristics of thermotropic LCs are primarily contingent on temperature as an external stimulus. This comprehensive review aims to bridge a notable gap in the biomedical application of thermotropic mesogens by exclusively focusing on drug delivery. Anticipated to inspire diverse ideas, the review intends to facilitate the elegant exploitation of controllable and temperature-induced characteristics of LCs to enhance drug permeation. Here, we delineate recent advancements in thermally-driven LCs with a substantial emphasis on LC monomer mixtures, elastomers, polymers, microcapsules and membranes. Moreover, special emphasis is placed on the biocompatibility and toxicity of LCs as the foremost prerequisite for their application in healthcare. Given the promising prospect of thermotropic LC formulations in a clinical context, a special section is devoted to skin drug delivery. The review covers content from multiple disciplines, primarily targeting researchers interested in innovative strategies in drug delivery. It also appeals to those enthusiastic about firsthand exploration of the feasible biomedical applications of thermotropic LCs. To the best of our knowledge, this marks the first review addressing thermotropic LCs as tunable soft-matter systems for drug delivery., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 The Author(s). Published by Elsevier B.V. All rights reserved.)

Liquid crystal (LC)-based nanoformulations may efficiently deliver drugs and therapeutics to targeted biological sites. Lyotropic liquid crystalline phases (LLCPs) have received much interest in recent years due to their unique structural characteristics of both isotropic liquids and crystalline solids. These LLCPs can be utilized as promising drug delivery systems to deliver drugs, proteins, peptides and vaccines because of their improved drug loading, stabilization, and controlled drug release. The effects of molecule shape, microsegregation, and chirality are very important in the formation of liquid crystalline phases (LCPs). Homogenization of self-assembled amphiphilic lipids, water and stabilizers produces LLCPs with different types of mesophases, bicontinuous cubic (cubosomes) and inverse hexagonal (hexosomes). Moreover, many studies have also shown higher bioadhesivity and biocompatibility of LCs due to their structural resemblance to biological membranes, thus making them more efficient for targeted drug delivery. In this review, an outline of the engineering aspects of LLCPs and polymer-based LLCPs is summarized. Moreover, it covers parenteral, oral, transdermal delivery and medical imaging of LC in targeting various tissues and is discussed with a scope to design more efficient next-generation novel nanosystems. In addition, a detailed overview of advanced liquid crystal-based drug delivery for vaccines and biomedical applications is reviewed., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier B.V. All rights reserved.)

Thermotropic mesogens typically exist as liquid crystals (LCs) in a narrow region of high temperatures, making lowering their melting point with the temperature expansion of the mesophase state an urgent task. Para -substituted benzoic acids can form LCs through noncovalent dimerization into homodimers via hydrogen bonds, whose strength and, consequently, the temperature region of the mesophase state can be potentially altered by creating asymmetric heterodimers from different acids. This work investigates equimolar blends of p - n -alkylbenzoic ( k BA, where k is the number of carbon atoms in the alkyl radical) and p - n -alkyloxybenzoic ( k OBA) acids by calorimetry and viscometry to establish their phase transitions and regions of mesophase existence. Non-symmetric dimerization of acids leads to the extension of the nematic state region towards low temperatures and the appearance of new monotropic and enantiotropic phase transitions in several cases. Moreover, the crystal-nematic and nematic-isotropic phase changes have a two-step character for some acid blends, suggesting the formation of symmetric and asymmetric associates from heterodimers. The mixing of 6BA and 8OBA most strongly extends the region of the nematic state towards low temperatures (from 95-114 °C and 108-147 °C for initial homodimers, respectively, to 57-133 °C for the resulting heterodimer), whereas the combination of 4OBA and 5OBA gives the most extended high-temperature nematic phase (up to 156 °C) and that of 6BA and 9OBA (or 12OBA) provides the existence of a smectic phase at the lowest temperatures (down to 51 °C).

Lipid-based lyotropic liquid crystals, also referred to as reversed liquid crystalline mesophases, such as bicontinuous cubic, hexagonal or micellar cubic phases, have attracted deep interest in the last few decades due to the possibility of observing these systems at thermodynamic equilibrium in excess water conditions. This becomes of immediate significance for applications in the colloidal environment, such as in the food, cosmetic and pharmaceutical arenas. One possible application regarded as very promising is that of controlled delivery of functional ingredients. Different crystallographic structures of the lipid mesophase give access to different diffusion coefficients and distinct diffusion modes. It becomes thus crucial to engineer the space group of the mesophase in a controlled way, and ideally, in a stimuli-responsive manner. In this article we review the state of the art on diffusion and molecular transport in lipid-based mesophases and we discuss recent contributions to the controlled delivery of molecules and colloids through these systems. In particular we focus on the different available strategies relying on either endogenous or exogenous stimuli to induce changes in the symmetry and transport properties of lipid-based mesophases and we discuss the impact and implications this may have on controlled drug delivery., (Copyright © 2014 Elsevier B.V. All rights reserved.)

Hybrid Organic‐Inorganic Halide Perovskites (HOIHPs) represent an emerging class of semiconducting materials, widely employed in a variety of optoelectronic applications. Despite their skyrocket growth in the last decade, a detailed understanding on their structure–property relationships is still missing. In this communication, we report two unprecedented perovskite‐like materials based on polyfluorinated imidazolium cations. The two materials show thermotropic liquid crystalline behavior resulting in the emergence of stable mesophases. The manifold intermolecular F ⋅ ⋅ ⋅ F interactions are shown to be meaningful for the stabilization of both the solid‐ and liquid‐crystalline orders of these perovskite‐like materials. Moreover, the structure of the incorporated imidazolium cation was found to tune the properties of the liquid crystalline phase. Collectively, these results may pave the way for the design of a new class of halide perovskite‐based soft materials. [ABSTRACT FROM AUTHOR]

A visible‐light responsive ionic liquid crystalline (LC) system based on gallic ester and tetra‐ortho‐substituted azobenzene is designed and synthesized. All the prepared derivatives exhibit columnar hexagonal mesophases at room temperature either in their pristine form or on cooling from isotropic states. The strategic design of these molecules allows for rapid photoisomerization, which is further aided by the dynamic LC phase. These systems attains photostationary states (PSSs) within 5 min of charging and discharging. The maximum Z conversion on charging in the solid‐state at room‐temperature is ≈80% with a highest temperature rise of 9.1 °C on discharging. This new molecular design enables the efficient working of solar thermal fuels (STFs) even in low sunlight intensity conditions, potentially promoting widespread adoption for mitigating global energy demands. [ABSTRACT FROM AUTHOR]

We report the synthesis and experimental studies on the liquid crystalline phase of a homologous series of compounds comprised of strongly asymmetric bent-core banana shaped molecules. Our x-ray diffraction studies clearly indicate that the compounds exhibit a frustrated tilted smectic phase with layer undulated structure. The low value of the dielectric constant as well as switching current measurements indicate the absence of polarization in this layer undulated phase. In spite of the absence of polarization, a planar aligned sample can be transformed irreversibly to a higher birefringent texture on the application of a high electric field. The zero field texture can only be retrieved by heating the sample to the isotropic phase and cooling it subsequently to the mesophase. We propose a double tilted smectic structure having layer undulation to account for the experimental observations with the layer undulation arising due to the leaning of the molecules in the layer. [ABSTRACT FROM AUTHOR]

Recently, a large family of at least 14 discotic liquid crystals was discovered that are exceptions to the conventional paradigm that discotic mesogens tend to feature long, flexible tails on their periphery. To understand why these materials are liquid crystals, as well as the structural determinants of discotic phase behavior, we studied a group of closely related small tail-free disk-like molecules, including both mesogenic and non-mesogenic compounds differing only in the position of a single fluorine substituent. The rigidity and structural simplicity of these molecules make them well suited to for study by large, fully all-atom simulations. Using a combination of static and dynamic metrics, we were able to identify several key features of the columnar mesophase and, thereby, conclusively identify a columnar liquid crystalline mesophase present in a subset of our systems. Our simulations feature molecules hopping between columns in the columnar mesophase and distinctive molecular rotations in 60° steps about the columnar axis. The ability to create and characterize columnar mesophases in silico provides a potent tool for untangling the structural determinants of liquid crystalline behavior in these and other tail-free discotic liquid crystals. [ABSTRACT FROM AUTHOR]

Self-assemblies of anisotropic colloidal particles into colloidal liquid crystals and well-defined superlattices are of great interest for hierarchical nanofabrications that are applicable for various functional materials. Inorganic nanosheets obtained by exfoliation of layered crystals have been highlighted as the intriguing colloidal units; however, the size polydispersity of the nanosheets has been preventing precise design of the assembled structures and their functions. Here, we demonstrate that the anionic titanate nanosheets with monodisperse size reversibly form very unusual superstructured mesophases through finely tunable weak attractive interactions between the nanosheets. Transmission electron microscopy, polarizing optical microscopy, small-angle x-ray scattering, and confocal laser scanning microscopy clarified the reversible formation of the mesophases (columnar nanofibers, columnar nematic liquid crystals, and columnar nanofiber bundles) as controlled by counter cations, nanosheet concentration, solvent, and temperature. [ABSTRACT FROM AUTHOR]

The discovery of a new polar nematic phase; the ferroelectric nematic, has generated a great deal of excitement in the field of liquid crystals. To date there have been around 150 materials reported exhibiting the ferroelectric nematic phase, in general, following three key archetypal structures with these compounds known as RM734, DIO and UUQU‐4N. In this review, the relationship between the molecular structure and the stability of the ferroelectric nematic, NF, phase will be described from a chemist's perspective. This will look to highlight the wide variety of functionalities which have been incorporated into these archetypal structures and how these changes influence the transition temperatures of the mesophases present. The NF phase appears to be stabilised particularly by reducing the length of terminal alkyl chains present and adding fluorines laterally along the length of the molecular backbone. This review will look to introduce the background of the ferroelectric nematic phase before then showing the molecular structures of a range of materials which exhibit the phase, describing their structure–property relationships and therefore giving an up–to–date account of the literature for this fascinating new mesophase. [ABSTRACT FROM AUTHOR]

Optical spatial solitons are self-guided wave packets that maintain their transverse profile due to the self-focusing effect of light. In nematic liquid crystals (NLC), such light beams, called nematicons, can be induced by two principal mechanisms: light-induced reorientation of the elongated molecules and thermal changes in the refractive index caused by partial light absorption. This paper presents a detailed investigation of the propagation dynamics of light beams in nematic liquid crystals (NLCs) doped with Sudan Blue dye. Building on the foundational understanding of reorientational and thermal solitons in NLCs and the effective breaking of the action–reaction principle in spatial solitons, this study examines the interaction of infrared (IR) and visible beams in a [-4-(trans-4′-exylcyclohexyl)isothiocyanatobenzene] (6CHBT) NLC. Our experimental results highlight the intricate interplay of beam polarizations, power levels, and the nonlinear properties of NLCs, offering new insights into photonics and nonlinear optics in liquid crystals. [ABSTRACT FROM AUTHOR]

Bent-core liquid crystals, a class of mesogenic compounds with non-linear molecular structures, are well known for their unconventional mesophases, characterized by complex molecular (and supramolecular) ordering and often featuring biaxial and polar properties. In the nematic phase, their unique behavior is manifested in the formation of nano-sized biaxial clusters of layered molecules (cybotactic groups). While this prompted their consideration in the quest for nematic biaxiality, experimental evidence indicates that the cybotactic order is only short-ranged and that the nematic phase is macroscopically uniaxial. By combining atomic force microscopy, neutron reflectivity and wide-angle grazing-incidence X-ray scattering, here, we demonstrate that multilayer films of a bent-core nematic, deposited on silicon by a combined Langmuir–Blodgett and Langmuir–Schaefer approach, exhibit macroscopic in-plane ordering, with the long molecular axis tilted with respect to the sample surface and the short molecular axis (i.e., the apex bisector) aligned along the film compression direction. We thus propose the use of Langmuir films as an effective way to study and control the complex anchoring properties of bent-core liquid crystals. [ABSTRACT FROM AUTHOR]

New Janus-type compounds were synthesised with two different hemispheres structures and properties. The structures contain cyanobiphenyl units linked with 3,4,5-tribenzyloxybenzene or 3,4,5-tridecyloxybenzene units. Also, the influence of the 1,3,4-thiadiazole heterocycle was studied. The mesomorphic properties were studied by differential scanning calorimetry, polarised light optical microscopy and thermal gravimetric analysis. The mesophases obtained depend on the structure of the hemispheres, even obtaining mesophases different from the initial ones. The new materials synthesised presented photoluminescent properties, which were studied in solution. [ABSTRACT FROM AUTHOR]

The mini‐review is devoted to the influence of the structure and properties of chiral macroheterocyclic dopants on the induction of helical liquid‐crystalline phases. Using the example of solutions of synthetic porphyrins, camphor substituted hemiporphyrazines and tetrapyrazinoporphyrazines, as well as chemically modified natural macrocycles based on chlorin e6 derivatives and their metal complexes in nematic liquid crystals, the features of the mesomorphic, dielectric and rheological properties of induced spiral mesophases are discussed. [ABSTRACT FROM AUTHOR]

It is found that the disordered growth of bottom perovskite film deteriorates the buried interface of perovskite solar cells (PSCs), so developing a new material to modify the buried interface for regulating the crystal growth and defect passivation is an effective approach for improving the photovoltaic performance of PSCs. Here, we developed a new ionic liquid crystal (ILC, 1‐Dodecyl‐3‐methylimidazolium tetrafluoroborate) as both crystal regulator and defect passivator to modify the buried interface of PSCs. The high lattice matching between this ILC and perovskite promotes preferential growth of perovskite film along [001] direction, while the oriented ILC with mesomorphic phase has a strong chemical interaction with perovskite to passivate the interface defect, as a result, the modified buried interface exhibits suppressed defects, improved band alignment, reduced nonradiative recombination losses, and enhanced charge extraction. The ILC‐modified PSC delivers a power conversion efficiency of 24.92 % and maintains 94 % of the original value after storage in ambient for 3000 h. [ABSTRACT FROM AUTHOR]

Liquid crystalline polymer networks (LCN) with azobenzene monomers bend reversibly under UV‐light irradiation, combining photomechanical and photothermal effects. However, the harmful nature of UV‐light limits their use in biology and soft robotics. Although visible light‐absorbing tetra‐ortho‐fluoro‐substituted azobenzenes exist, liquid crystalline monomers have never been prepared. Previously, such azobenzenes were added as photoactive additives (up to 10%) to otherwise passive liquid crystalline polymer networks. In this work, a molecular design of a liquid crystalline, polymerizable azobenzene switchable by visible light is presented. The monomer assembles in a highly fluid nematic phase, but polymerizes in a layered smectic C phase. The films are produced solely from the monomer without additional liquid crystalline components and are actuated with visible light. Bending experiments in air and under water differentiate photomechanical and photothermal effects. Remarkably, a 60 µm splay aligned film maintains its deformation for hours, slowly reverting over days. Monomer liquid crystallinity is characterized using differential scanning calorimetry (DSC), wide‐angle X‐ray scattering (WAXS), and polarized optical microscopy (POM); polymer films are analyzed using WAXS and DSC on a homogeneously aligned film. The synthetic procedure is high yielding and polymer film fabrication is scalable, which enables the use of safe and efficient photomechanical LCNs in soft robotics, engineering and biology. [ABSTRACT FROM AUTHOR]

We study the nature of the nematic to smectic-A phase transition under confinement conditions in the context of Landau-de Gennes theory. The effect of quenched disorder on the nematic to smectic-A transition temperature, order parameter, enthalpy, and thermal hysteresis are discussed followed by phase diagrams. The tricritical behavior of the nematic to smectic-A phase under confinement conditions is predicted. [ABSTRACT FROM AUTHOR]

A series of 2,3-difluorophenylene-based negative liquid crystals which own different terminal groups has been synthesised in high yields through many classical named reactions such as Suzuki coupling and Williamson etherification. Thermal properties of these mesogens were tested by differential scanning calorimetry and the effects of the terminal groups on the melting points of molecules were evaluated. Dielectric anisotropies of the synthesised molecules were then measured and found that relatively long alkyl substituents would decrease the Δε value when compared with the ethyl. For the compound with a polar substitute on the long molecular axis, the introduction of 2,2-difluoroethyl would increase the negative Δε when it was put into the opposite direction of the original polar group, making this strategy a new access for the improvement of negative Δε. DFT calculations were carried out to analyse the orientation of the dipole moment in molecules and found that the introduction of 2,2-difluoroethyl had changed the orientation of the dipole moment into nearly perpendicular to the long molecular axis, which benefited the growth of the negative Δε value, revealing the mechanism of this strategy from the view of molecular level to some extent. [ABSTRACT FROM AUTHOR]

Liquid crystals have already been widely used in reconfigurable microwave devices through external electrically controlled dielectric properties. The traditional method is to sandwich liquid crystals between two metal layers etched on hard substrates. However, this method of adding external electric fields tends to cause short-circuiting between the upper and lower electrodes of liquid crystals in the bending state for the case of electrodes on flexible substrates. In this paper, a novel method is proposed to realise a frequency tunable resonator using liquid crystal fabricated on flexible substrates. The resonator is composed of coplanar waveguide structures. Since the metal layers of the coplanar waveguide placed on the same horizontal plane do not touch each other when bending, it allows the controlled electric field direction to be parallel to the electrode layers. Liquid crystals are placed under the coplanar metals for the electric field control. In order to maximise tunability, the structural parameters of the proposed structure were analysed in detail. The test results agree with the theory and simulation to verify the reliability of this frequency tunable resonator. Furthermore, the test results also illustrate that the applied electric field method can achieve the frequency continuous electrically tunable function when the flexible resonator is bending. [ABSTRACT FROM AUTHOR]

We present a theoretical study of the simultaneous effects of ferroelectric nanoparticles and ion impurities on the order parameter of liquid crystals. We have focused on the effect of ion impurities on the ordering behavior and electrical response of a ferroelectric nano-doped liquid crystal near the nematic-isotropic phase transition. In this study, a statistical theory based on the orientational distribution of the nanoparticle dopants is used. We have performed the calculations using the Poisson–Boltzmann equation and a modified Landau-De Gennes model. The total density of free energy of the system is obtained within the framework of this theory, and the changes in the concentration of mobile ions due to the presence of ferroelectric nanoparticles are investigated. It is shown that the screening effect of the ion impurities plays a dominant role in the ordering behavior and electrical response of a ferroelectric nano-doped liquid crystal. The ion generation and the consequent changes are also described in some physical properties of a nano-doped system under an applied electric field. [ABSTRACT FROM AUTHOR]

Previous theoretical studies of calamitic (i.e., rod-like) ionic liquid crystals (ILCs) based on an effective one-species model led to indications of a novel smectic-A phase with a layer spacing being much larger than the length of the mesogenic (i.e., liquid–crystal forming) ions. In order to rule out the possibility that this wide smectic-A phase is merely an artifact caused by the one-species approximation, we investigate an extension that accounts explicitly for cations and anions in ILCs. Our present findings, obtained by grand canonical Monte Carlo simulations, show that the phase transitions between the isotropic and the smectic-A phases of the cation–anion system are in qualitative agreement with the effective one-species model used in the preceding studies. In particular, for ILCs with mesogens (i.e., liquid–crystal forming species) carrying charged sites at their tips, the wide smectic-A phase forms, at low temperatures and within an intermediate density range, in between the isotropic and hexagonal crystal phases. We find that in the ordinary smectic-A phase, the spatial distribution of the counterions of the mesogens is approximately uniform, whereas in the wide smectic-A phase, the small counterions accumulate in between the smectic layers. Due to this phenomenology, the wide smectic-A phase could be interesting for applications, which hinge on the presence of conductivity channels for mobile ions. [ABSTRACT FROM AUTHOR]

Liquid crystals are assemblies of rod-like molecules which self-organize to form mesophases, in between ordinary liquids and anisotropic crystals. At each point, the molecules collectively orient themselves along a privileged direction, which locally defines an orientational order. Sometimes, this order is broken, and singularities appear in the form of topological defects. This tutorial article is dedicated to the geometry, topology, and physics of these defects. We introduce the main models used to describe the nematic phase and discuss the isotropic–nematic phase transition. Then, we present the different families of defects in nematics and examine some of their physical outcomes. Finally, we show that topological defects are universal patterns of nature, appearing not only in soft matter, but also in biology, cosmology, geology, and even particle physics. [ABSTRACT FROM AUTHOR]

Columnar liquid crystals with very small molecular masses that form anisotropic glasses well above room temperature are obtained by mixed dissymmetric substitution of sym‐triazine with ester‐bearing phenyl and phenanthryl or tetrahelicenyl moieties. The combination of low molecular symmetry with configurational flexibility and short polar ester moieties stabilizes the mesophase over large temperature ranges and induces pronounced calorimetric glass transitions within the anisotropic fluid despite the smallness of the molecules. In contrast to more symmetrical homologs, no ester tails longer than ethyl are necessary to induce the liquid crystalline state, allowing for the near‐absence of any insulating and weight‐increasing alkyl periphery. Films drop‐cast from solution show in all cases emission spectra that do not show significant change of fluorescence emission upon annealing, indicating that the columnar hexagonal mesoscopic order is obtained directly upon deposition from solution and is resistant to crystallization upon annealing. [ABSTRACT FROM AUTHOR]

The synthesis and characterisation of the 4-({[4'-nitro-(1,1'-biphenyl)−4-yl]oxy}carbonyl)phenyl 2-alkoxy-4-methoxybenzoates are reported: the 1O(m-On)PEPEBNO2 series. These materials include an additional phenyl ring compared to the extensively studied ferroelectric nematogen RM734, added to increase the liquid crystal transition temperatures. All members of the series exhibited both conventional nematic (N) phase and ferroelectric nematic (NF) phases; TNI and TNFN both decrease on increasing n, the length of the lateral alkoxy chain. The properties of this four-ring series are compared with analogous three-ring laterally substituted variants of RM734; the addition of the extra phenyl ring has a significantly more pronounced effect on the value of TNI than on TNFN. The increase in TNI may be attributed to the enhanced structural anisotropy and more favourable intermolecular interactions arising from the insertion of the phenyl ring, whereas the much weaker effect on TNFN may reflect a change in the shape of the molecule. We also report two materials with three-ring structures, the 4'-nitro-(1,1'-biphenyl)-4-yl 2-alkoxy-4-methoxybenzoates: 1O(m-On)PEBNO2 (n = 1 and 2). The removal of the ester linkage between RM734 and 1O(m-O1)PEPNO2 extinguishes the NF phase and this appears to be consistent with a model in which the molecules are described in terms of a longitudinal surface charge density wave. [ABSTRACT FROM AUTHOR]

We present nonlinear dynamic equations for nematic and smectic A liquid crystals in the presence of an alternating electric field and explain their derivation in detail. The local electric field acting in any liquid-crystalline system is expressed as a sum of external electric field, the fields originating from feedback of liquid crystal order parameter, and a field, created by charged impurities. The system tends to decrease the total electric field, because it lowers the energy density. This basically nonlinear problem is not a pure academic interest. In the realm of liquid crystals and their applications, utilized nowadays modern experimental techniques have progressed to the point where even small deviations from the linear behavior can be observed and measured with a high accuracy. We follow hydrodynamic approach which is the macroscopic description of condensed matter systems in the low frequency and long wavelength limit. Nonlinear hydrodynamic equations are well established to describe simple fluids. Similar approaches (with degrees of freedom related to the broken orientational or translational symmetry included) have been used also for liquid crystals. However to study behavior of strongly perturbed (well above the thresholds of various electro-hydrodynamic instabilities) liquid crystals, the nonlinear equations should include soft electromagnetic degrees of freedom as well. There are many examples of such instabilities, e.g., classical Carr-Helfrich instability triggered by the competitive electric and viscous torques, flexoelectric instability, and so one. Therefore the self-consistent derivation of the complete set of the nonlinear electro-hydrodynamic equations for liquid crystals became an actual task. The aim of our work is to present these equations, which is a mandatory step to handle any nonlinear phenomenon in liquid crystals. [ABSTRACT FROM AUTHOR]

Most organic thermochromic fluorescent materials exhibit thermo‐induced hypsochromic emission due to the formation of excimers in ordered molecular solids; however, it is still a challenge to endow them with bathochromic emission despite its significance in making up the field of thermochromism. Here, a thermo‐induced bathochromic emission in columnar discotic liquid crystals is reported realized by intramolecular planarization of the mesogenic fluorophores. A three‐armed discotic molecule of dialkylamino‐tricyanotristyrylbenzene was synthesized, which preferred to twist out of the core plane to accommodate ordered molecular stacking in hexagonal columnar mesophases, giving rise to bright green monomer emission. However, intramolecular planarization of the mesogenic fluorophores occurred in isotropic liquid increasing the conjugation length, and as a result led to thermo‐induced bathochromic emission from green to yellow light. This work reports a new concept in the thermochromic field and provides a novel strategy to achieve fluorescence tuning from intramolecular actions. [ABSTRACT FROM AUTHOR]

Investigation of mesomorphic properties of new 1,3,4-thiadiazolines (which are synthesised via many steps in Scheme 1) was carried out in this study. These compounds are designed to have a heterocyclic unit, a carboxylate linkage group and a polar ether chain at the end of the molecule adjacent to the benzene ring, which enhance the dipolar interactions forces (varied from one to eight carbons) to investigate the association properties of their phases. The structure of the target compounds and the intermediates were confirmed by 1H NMR, 13C NMR, mass and FTIR spectral techniques. Polarised microscopic studies revealed that all the compounds in the series exhibited enantiotropic liquid crystalline properties. This was further confirmed using differential scanning calorimetric experiments. The synthesised compounds type [V]n in this study displayed different liquid crystalline mesophases and the homologous [V] having an alkoxy terminal group (n = 1–3) exhibited nematic phase, whilst the last derivatives of the series (4–8), displayed smectic A phase. [ABSTRACT FROM AUTHOR]

Triply phenanthryl‐ and tetrahelicenyl‐substituted triazine‐hexaalkyl esters with short alkyl chains show glass transitions conveniently above room temperature within the hexagonal columnar liquid crystalline state, resulting in a solid columnar order at room temperature. As the hexagonal columnar mesophase is easily aligned with the director perpendicular to a solid substrate, such glassy columnar liquid matrices are aimed at for the orientation of guest emitters, to obtain anisotropic emission. A condition for face‐on alignment on substrates are attainable melting and clearing temperatures, which is achieved with the moderately nonplanar tetrahelicenyl derivatives in spite of their short alkyl periphery. An unusual phase transition between two columnar mesophases of same hexagonal symmetry, but very different long‐distance regularity of the column lattice, is found in one phenanthryl homolog. [ABSTRACT FROM AUTHOR]

Determining the phase transition temperature of different types of liquid crystals based on their structural parameters is a complex problem. The experimental work might be eliminated or reduced if prediction strategies could effectively anticipate the behavior of liquid crystalline systems. Neuro-evolutive modeling based on artificial neural networks (ANN) and a differential evolution (DE) algorithm was applied to predict the phase transition temperatures of bent-core molecules based on their resorcinol core. By these means, structural parameters such as the nature of the linking groups, the position, size and number of lateral substituents on the central core or calamitic wings and the length of the terminal chains were taken into account as factors that influence the liquid crystalline properties. A number of 172 bent-core compounds with symmetrical calamitic wings were selected from the literature. All corresponding structures were fully optimized using the DFT, and the molecular descriptors were calculated afterward. In the first step, the ANN-DE approach predicted the mesophase presence for the analyzed compounds. Next, ANN models were determined to predict the transition temperatures and whether or not the bent-core compounds were mesogenic. Simple structural, thermophysical and electronic structure descriptors were considered as inputs in the dataset. As a result, the models determined for each individual temperature have an R2 that varied from 0.89 to 0.98, indicating their capability to estimate the transition temperatures for the selected compounds. Moreover, the impact analysis of the inputs on the predicted temperatures showed that, in most cases, the presence or not of liquid crystalline properties represents the most influential feature. [ABSTRACT FROM AUTHOR]

A new, 19 π‐delocalized electrons planar Blatter radical building block was developed and used to obtain paramagnetic bent‐core liquid crystals. The mesogens were investigated by optical, thermal, powder XRD and DFT methods in the pure form and as binary mixtures. Comparison of their properties with those of the classical Blatter radical analogues revealed that planarization of the central angular element results in a significantly higher stability of the mesophases and increased molecular organization suitable for the formation of ordered banana and columnar mesophases with tighter π–π interactions. These results indicate access to a new, potentially rich class of functional paramagnetic soft materials. [ABSTRACT FROM AUTHOR]

We analyse an energy minimisation problem recently proposed for modelling smectic-A liquid crystals. The optimality conditions give a coupled nonlinear system of partial differential equations, with a second-order equation for the tensor-valued nematic order parameter Q and a fourth-order equation for the scalar-valued smectic density variation u. Our two main results are a proof of the existence of solutions to the minimisation problem, and the derivation of a priori error estimates for its discretisation of the decoupled case (i.e., q = 0) using the C0 C 0 $ {\mathcal{C}}^0$ interior penalty method. More specifically, optimal rates in the H1 and L2 norms are obtained for Q, while optimal rates in a mesh-dependent norm and L2 norm are obtained for u. Numerical experiments confirm the rates of convergence. [ABSTRACT FROM AUTHOR]

A series of benzimidazole-based liquid crystal compounds containing laterally difluoro-substituted and ethynyl linking groups, namely, 2-(4-(2-(2,3-difluoro-4-(alkoxy) phenyl)ethynyl)phenyl)-1-methyl-1 H-benzimidazolem derivatives (nPF(2,3)EPMx), are synthesised and investigated for their mesomorphic properties. These compounds mainly display enantiotropic nematic mesophases in the ranges of 32.0–44.5°C (heating process) and 50.0–64.0°C (cooling process). 10PF(2,3)EPMx exhibits lower clearing points and broader nematic phase ranges than nonfluorinated reference compound 10PEPMx, because of their slightly increased dipole moment. nPF(2,3)EPMx displays much larger theoretical birefringence (0.43–0.55) and experimental birefringence (0.42–0.53) than the common tolane-based liquid crystals, which is ascribed to its large π-conjugated molecule composed of benzene core, ethynyl linking group and benzimidazole terminated unit. The theory results of three-dimensional molecular conformations with dipole moment (µ), ratio of length to width (L/W), polarisability anisotropy (Δα) and average polarisability (Δα) calculated with density functional theory are also helpful in explaining the experimental results. [ABSTRACT FROM AUTHOR]

We present a theoretical study of the electric behaviour of a ferroelectric liquid crystal (FLC) doped with ferroelectric nanoparticles (FNPs). According to the recent reports on industrial developments based on liquid crystal materials, FLCs are increasingly used not only in displays but also in preparing new materials with unconventional properties. In this work, we focus on the anomalies caused by the nanoparticles on ordering behaviour, dielectric permittivity, and polarization of the system, as well as the pre-transitional effects near the Isotropic-Smectic A (I-SmA) phase transition. We obtain the polarization of a nano-doped system under an applied electric field and discuss the influence of the concentration of nanoparticles on the phase transition for both isotropic and mesomorphic phases. The calculations are based on the phenomenological Landau theory. Our results show weak induced orientational order in the isotropic phase of the I-SmA phase transition. Considering the Kerr effect in the nano-doped system under the influence of macroscopic polarization, we find that the FNPs significantly affect such induced orientational behaviour. Our results confirm a pre-transitional anomaly of dielectric permittivity for the I-SmA phase transition. The strong influence of nanoparticles on the pre-transitional behaviour in both isotropic and mesomorphic phases is also revealed. [ABSTRACT FROM AUTHOR]

The molten phase of transition metal and lithium salts self‐assemble with non‐ionic surfactants to form lyotropic liquid crystalline (LLC) mesophases, which are important in the development of gel‐electrolytes and mesoporous materials. Here, we show that LiH2PO4 forms a semi‐stable LLC mesophase with 10‐lauryl ether (C12H25(OCH2CH2)10OH, C12E10), decoded as Li−EO−X (X is LiH2PO4/C12E10 mole ratio and between 2 and 200). The stability of the Li−EO−X phase is improved by increasing salt concentration (X>20) in the media. The semi‐stable Li−EO−X mesophase is further stabilized by adding either water by controlling the humidity or H3PO4 (PA) to the media. The phase behaviour of the above samples was investigated using POM, XRD, conductivity, and ATR‐FTIR measurements. The addition of PA not only brings stability and higher conductivity (increase from 0.1 to 8.9 mS/cm) to the mesophase but also produce an LLC gel‐electrolyte with a high buffer capacity that may be useful and important in various applications. [ABSTRACT FROM AUTHOR]

The synthesis of bent-shaped mesogens and mesogenic dimers has renewed the field of liquid crystals in many ways during the previous decades, for example, through the discovery of 'exotic' mesophases such as the twist-bend nematic phase and the biaxial SmA phase (SmAb). Recently, we reported on the observation of a SmAb with a bent-shaped dimer, and on its fast electro-optic effect that we interpreted as a biaxial Fréedericksz transition (BFrTr) of the secondary m-director under applied electric field (C. Meyer et al., Phys. Rev. X, 11, 031012 (2021)). In this study, we used dielectric and birefringence techniques to directly measure the splay, K 11 m , and bend, K 33 m , elastic constants that characterise the elastic distortion modes of the m-director. We observed that during the BFrTr, domains of opposite tilt appear and are often enclosed in elliptical defect loops, just like those observed during the usual Fréedericksz transition of common nematics, which allowed us to obtain the third (twist) elastic constant K 22 m , from the defect loop ellipticity. Although K 11 m and K 33 m are of the same order of magnitude as K 11 and K 33 in the nematic phase of bent-shaped dimers, K 22 m is an order of magnitude smaller than K 11 m and K 33 m and also than K 22 of 5CB. We argue that these features could be generic for the intercalated SmAb phase of bent-shaped dimers. [ABSTRACT FROM AUTHOR]

• A series of novel bis-tolane luminescence liquid crystals (LLCs) with SO 2 CF 3 as terminal were firstly achieved. • Adjustable tri-response thermochromic fluorescent materials (TFMs) were obtained. • TFMs of (CH 3) 2 N-2F-SO 2 CF 3 exhibit excellent character which promise candidate for information encryption. A series of novel bis-tolane luminescence liquid crystals (LLCs) with SO 2 CF 3 as terminal were first time achieved. These SO 2 CF 3 -based LLCs act as thermally responsive emission sources combined with a series of thermosensitive long-chain carboxylic acids with self-crystallization properties to obtain adjustable tri-response thermochromic fluorescent materials (TFMs). Notably, TFMs of (CH 3) 2 N-2F-SO 2 CF 3 exhibit excellent temperature sensitivity and tri-response thermochromic fluorescent character, which display outstanding thermochromic properties from 45 °C to 165 °C. These TFMs displayed an intuitively evident orange under ultraviolet (UV) irradiation then changed to orange-yellow color after adding long-chain carboxylic acids. Notably, it changed to yellow-green when heated to the long-chain carboxylic acids melting point of these phase change materials, further emitting a blue color at the mesophases transition when increasing temperature at 165 °C of (CH 3) 2 N-2F-SO 2 CF 3. Interestingly, the various thermochromic abilities and stimuli-responsive fluorescence of these TFMs could be regulated by substituents of LLCs and long-chain carboxylic acids. Therefore, such tri-response and high-contrasted thermochromic fluorescent character of TFMs are different from previous reports which promise candidates for information encryption. [ABSTRACT FROM AUTHOR]

[Display omitted] • Misinformation of the experimental data in a recent publication is discussed. • Parasitic effects (artefacts) influencing the dielectric results are also deliberated. • Representation of Cole-Cole diagram with the dielectric data is scrutinised. A research article titled as "Hydrogen-bonded liquid crystal complexes: A comprehensive study of structure, behaviour and potential applications" has been recently published by Meddeb et al., J. Mol. Liq. 395 (2024) 123838. Authors have reported and analysed thermodynamic and dielectric studies on highly ordered SmB and SmG mesophases in 14OBAF/DABCO complexes. But explanations of the dielectric data reported on the material are flawed based on various facts. Unintended wrong interpretations by the authors in reporting and explaining the thermodynamic and dielectric results are discussed here. Influence of various artefacts on acquired dielectric data has also been discussed in order to avoid such problems in further reports. [ABSTRACT FROM AUTHOR]

The paper presents basic types of liquid-crystalline phases obtained in different ways and supermolecular arrangement in those phases. Characteristic features of molecular structure of mesogens are discussed, moreover their influence on liquid-crystalline properties are described too. Examples of the effect of intermolecular interactions on the phase situation of a liquid crystal are given. Keywords: liquid crystals, mesophases, polymorphism, mesogens, molecular structure

Thermofluorochromic materials exhibit tunable fluorescence emission on heating or cooling. They are highly desirable for applications ranging from temperature sensing to high-security anti-counterfeiting. Luminescent matrices based on liquid crystals are very promising, particularly those based on liquid crystals with intrinsic fluorescence. However, only a few examples have been reported, suggesting ample margins for development in the field, due to the wide range of fluorophores and supramolecular organizations to be explored. Moreover, thermofluorochromic liquid crystals can be tailored with further functionalities to afford multi-stimuli responsive materials. For the first time, herein we report the thermofluorochromism of thienoviologen liquid crystals, already known to show bulk electrochromism and electrofluorochromism. In particular, we studied their photophysics in the 25 °C–220 °C range and as a function of the length of the N-linear alkyl chains, m (9 ≤ m ≤ 12 C atoms), and the type of anion, X (X = OTs-, OTf-, BF4-, NTf2-). Interestingly, by changing the parameters m, X and T, their fluorescence can be finely tuned in the whole visible spectral range up to the NIR, by switching among different mesophases. Importantly, by fixing the structural parameters m and X, an interesting thermofluorochromism can be achieved for each thienoviologen in a homologous series, leading to a switch of the emitted light from red to green and from white to blue as a consequence of the temperature-induced variation in the supramolecular interactions in the self-assembled phases. [ABSTRACT FROM AUTHOR]

Copyright of Chinese Journal of Liquid Crystal & Displays is the property of Chinese Journal of Liquid Crystal & Displays and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

An optical filter is one of the indispensable devices in massive and high-speed communication, optical signal processing, and display. Twist-structure liquid crystals, cholesteric liquid crystals, blue-phase liquid crystals, and sphere-phase liquid crystals show potential application in optical filters originating from the periodic nanostructures. Wavelength and bandwidth tuning can be controlled via temperature, electric fields, light, angle, spatial control, and templating technology. In this review, we discuss the recent developments of twist-structure liquid crystal filters. [ABSTRACT FROM AUTHOR]

Targeted, on‐demand delivery has been of interest using materials responsive to environmental stimuli. A delivery technique based on precise release of aqueous microdroplets from a liquid crystal (LC) medium with contactless stimulation is presented. A nematic LC is doped with a photothermal dye that produces heat under near IR light exposure. The heat is used to overcome the elastic strains in the LC phase, promoting the release of initially entrapped water droplets to the neighboring aqueous solution. Designing the geometry of LC‐based emulsions and tuning the light intensity and position allows for manipulation of the release in two distinct modes defined as pulsated and continuous. In the pulsated mode, water droplets are released transiently from the casted water‐in‐LC emulsion layer based on sweeping by the moving isotropic‐nematic phase boundary controlled by light. In the continuous mode, water droplets are ejected continuously from a droplet‐shaped water‐in‐LC emulsion, due to a heating‐induced internal flow controlled by light. The droplet release by contactless stimulation is used for the on‐demand dosing of dopamine and its oxidizing reagent from isolated reservoirs to obtain an in situ reaction signal for a hydrogen peroxide assay. A new dual‐mode release system developed with photothermal LCs holds potential in drug release, controlled mixing, and photothermal therapy. [ABSTRACT FROM AUTHOR]

Nematic mesophase formation in disc‐like systems remains relatively rare compared to higher‐order columnar organisation, but it is observed in some rigid dimeric systems. Mesophase formation in rigid discotic dimers has been sequentially probed and is shown to be predictably controlled through structural choice of the bridge. Moderately bent bridges shorten the discogen separation and reduce conformational freedom. Severely bent dimers (1,2‐phenylene bridge) show no mesophases but, as the angle is widened, columnar and nematic organisation becomes possible and progressively more favoured. The linear arrangement gives the most stable columnar mesophase and a narrow‐range nematic mesophase. [ABSTRACT FROM AUTHOR]

Photoresponsive nanostructured materials are of great importance for photonic applications. Herein we report the design, synthesis, and liquid crystal (LC) self-assembly of two new series of photoresponsive hockey-stick LCs (HSLCs). The new HSLCs are azobenzene-based polycatenars derived from the 4-cyanoresorcinol bent-core unit. The long arm is a fork-like triple alkoxylated wing, while the short arm is terminated with a single variable alkoxy chain. The molecular self-assembly of these HSLCs is characterized using polarizing optical microscopy (POM), differential scanning calorimetry (DSC), X-ray diffraction (XRD) and electro optical measurements. In both series of LC materials differing in the chain volume at the crowded end, wide temperature ranges of lamellar Smectic A phases (up to 170 K) are observed beside achiral isotropic liquid phases (Iso1) for the shorter derivatives. On chain elongation helical self-assembly of the π-conjugated rods in networks occurs resulting in the formation of nanostructured bicontinuous cubic network phases with Ia3¯d space group (Cubbi/Ia3¯d), in most cases stable even around room temperatures on cooling. At the transition from SmA to Cubbi phases, an additional unknown three-dimensional (3D) phase is formed. A possible explanation for the disappearance of the triple network Cubbi phases with I23 symmetry (Cubbi[*]/I23) in these HSLCs is represented based on the phase behaviour of a new material having the central 4-cyanoresorcinol unit shifted to a terminal position of the rod-like core. Finally, the reversible trans–cis photoisomerization for some selected examples was investigated in chloroform solution. [ABSTRACT FROM AUTHOR]

A series of azobenzene liquid crystals containing one amino acid residue were synthesized. They exhibit smectic mesophases. The compounds derived from alanine can self-assemble into twisted nanoribbons. The molecules organized in a monolayer structure within the nanoribbon. Circular dichroism characterization indicated that the neighboring liquid crystal cores packed in a chiral structure. FT-IR spectra indicated that the nanoribbons were caused by H-bonding and association of hydrocarbon chains. [ABSTRACT FROM AUTHOR]

Liquid-crystal columns were prepared and observed under microgravity aboard suborbital TEXUS rocket flights. The microgravity phase of each flight lasted for approximately six minutes. We tested structures in different liquid-crystalline mesophases. In the isotropic and nematic phases, the Rayleigh-Plateau instability led to the collapse of the columns. However, in the smectic A and C mesophases, it was found that the columns survived the extension to slenderness ratios (length/diameter) of over 4.5 (and in one case, more than 6). The liquid-crystalline material in the millimeter-sized columns was macroscopically disordered. Thus, regular shell-like internal layer structures that stabilized the columns can be excluded. Instead, the reason for their persistence was the yield stress of the material, which is quite different for the different mesophases. In the columnar mesophase, the cylindrical bridge even survived the strong deceleration when the rocket re-entered the atmosphere. During the breakup of the filaments, the neck thinning dynamics were determined. [ABSTRACT FROM AUTHOR]

Two series of ten ester derivatives with four aromatic rings linked together by three different linkages (azo/ester/imine), 4‐((4‐substituted)diazenyl)phenyl 4‐((4‐alkoxybenzylidene)amino)benzoate (IVn X=OCH3 and Vn X=Br) were synthesized. These derivatives have an alkoxy chain in the para position of the phenyl ring with different lengths (n=3, 4, 6, 7, and 12) on one terminal side while the other side was substituted by methoxy and bromo groups linked to the p‐position of phenyl. The structures of all synthesized derivatives were proven by nuclear magnetic resonance (1H‐NMR, 13C‐NMR), elemental analysis (C,H,N), and Fourier‐transform infrared spectroscopy (FT‐IR). The Mesophase textures of the final esters were observed by polarized optical microscopy (POM) and differential scanning calorimetry (DSC). Only the nematic texture was observed in the methoxy derivatives while nematic and smectic A textures were shown in the bromo mesogens. All the homologous showed mesogenic behavior with wide thermal stability. From the results, it was found that the liquid crystalline behaviors of these derivatives are dependent on the substituted group (‐X) and the length of the alkoxy chain. The mesogenic behavior of these compounds was compared with other mesogens that have similar structures. [ABSTRACT FROM AUTHOR]

Bent-core liquid crystals (BLCs) are a class of thermotropic LCs that exhibit chiral and polar superstructures in achiral molecules. Progress in design and synthesis of novel bent-core architectures in search of unconventional properties enriched the field of BLCs. Here, we present a comprehensive review of the recent bent-shaped LCs, discuss relevant simulation and theoretical models, which draws a comparison to experimental results, survey the advances in the molecular design and structure-property correlation, and predict the future directions from chemical and physical perspectives. This review article is dedicated in commemoration of Prof. B K Sadashiva, a pioneer chemist who made a notable contribution to the field of bent-core liquid crystals. [ABSTRACT FROM AUTHOR]

In ancient Roman religion and myth, Janus is the god of beginnings, gates, transitions, time, duality, doorways, passages, frames, and endings. He is usually depicted as having two faces looking in opposite directions, one towards the past and the other towards the future. This article is dedicated to Professor BK Sadashiva for his contributions to the science of liquid crystals, and new beginnings in the design and creation of mesomorphic materials. In the studies of metallomesogens based on copper(II) complexes of β-diketones, Ohta and his colleagues reported the first-established discotic-lamellar phase, in which the board-like complexes are able to form lamellar packing arrangements, and at the same time stacking into columns. Casagrande et al. later prepared synthetically modified beads with one hemisphere being hydrophobic and the other hydrophilic. These particles were considered to be amphiphilic solids, and called Janus Beads. Synthetic Janus Mesogens with supermolecular architectures having one chiral nematic hemisphere and the other with smectic tendencies were made in 2003. These complexes, particles, and supermolecules, were termed Janus to describe the structure of the material. In this article we use Janus liquid crystals to describe a material that combines two different packing motifs in a single uniform phase structure. [ABSTRACT FROM AUTHOR]