Search

Mechanical stretching is commonly used for mesogen alignment which is essential for the muscle-like actuations of liquid crystal elastomers (LCEs). Despite the simplicity of the method, the mesogens are typically aligned in the stretching direction, limiting exclusively the LCE to an actuation mode of cooling-induced elongation. Here, we design an interpenetrating double network consisting of an LCE network and an elastomer network, with one polymerized network stretched before the polymerization of the other network. Depending on the polymerization sequence of the two networks, the double network shows two opposite actuation modes, namely, the conventional cooling-induced elongation or an unusual cooling-induced contraction. Strategic integration of the two opposite behaviors into the same LCE leads to sophisticated actuation difficult to achieve with a conventional LCE design. Coupled with 3D printing, geometrically complexed LCEs with diverse multimodal four-dimensional actuation behaviors are illustrated. Our work expands the design scope of LCE actuators and their potential device applications. [ABSTRACT FROM AUTHOR]

Liquid crystals, which have both liquid and solid properties, inevitably exhibit fluctuations. Some frustrated liquid-crystalline phases with a hierarchical structure, such as cybotactic nematic, modulated smectic, and bicontinuous cubic phases, are fascinating fluctuation-induced phases. In addition to these equilibrium phases, a pattern formation that is a nonequilibrium order through fluctuation is one of the most attractive research areas in soft matter. In this review, the studies on producing these fluctuation-induced orders in liquid crystals are described. Liquid-crystalline supermolecules in which several mesogens are connected via a flexible spacer have been designed. They have not only a characteristic shape but also an intra-molecular dynamic order. The supermolecules induce the fluctuations in layer structures at a molecular level, producing from the frustrated hierarchical to dynamic dissipative structures. In addition to reviewing molecular design for the hierarchical structures, the pattern propagation in a smectic phase is discussed based on the rotation of smectic blocks through Rayleigh–Bénard convection. [ABSTRACT FROM AUTHOR]

Mesogens, which are typically stiff rodlike or disklike molecules, are able to self-organize into liquid crystal (LC) phases in a certain temperature range. Such mesogens, or LC groups, can be attached to polymer chains in various configurations including within the backbone (main-chain LC polymers) or at the ends of side-chains attached to the backbone in an end-on or side-on configuration (side-chain LC polymers or SCLCPs), which can display synergistic properties arising from both their LC and polymeric character. At lower temperatures, chain conformations may be significantly altered due to the mesoscale LC ordering; thus, when heated from the LC ordered state through the LC to isotropic phase transition, the chains return from a more stretched to a more random coil conformation. This can cause macroscopic shape changes, which depend significantly on the type of LC attachment and other architectural properties of the polymer. Here, to study the structure–property relationships for SCLCPs with a range of different architectures, we develop a coarse-grained model that includes torsional potentials along with LC interactions of a Gay–Berne form. We create systems of different side-chain lengths, chain stiffnesses, and LC attachment types and track their structural properties as a function of temperature. Our modeled systems indeed form a variety of well-organized mesophase structures at low temperatures, and we predict higher LC-to-isotropic transition temperatures for the end-on side-chain systems than for analogous side-on side-chain systems. Understanding these phase transitions and their dependence on polymer architecture can be useful in designing materials with reversible and controllable deformations. [ABSTRACT FROM AUTHOR]

The liquid crystal state (LC) in polymer chemistry is a topic discussed in varied materials research. The anisotropic properties typical of these compounds are mostly the result of the presence of mesogens in the structure of liquid crystals. This article traces the development of liquid crystal science, focusing on liquid crystal epoxy resins (LCERs) and emphasizing the crucial role of mesogens and their diverse effect on the materials. It also highlights the importance of understanding the morphology of LC polymers, explaining their profound impact on material properties and performance. It explores the cross-linking process of liquid crystal resins and composites, describing how changes in structural factors affect material structure. The article also provides information about hardeners and their influence on the cross-linked structure. Various nanofillers were also discussed, elucidating their impact on the resulting composites. [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]

A novel homologous series of cinnamoyl ester comprising of elven (C1 to C16) homologues liquid crystal (LC) samples have been synthesized and characterized using instrumental methods (spectral and thermal) of analysis and DFT approach. As results, middle ordered melting type of series with exhibition of nematic mesophase were observed. The observed mesogenic properties and transition temperature are affected by the size of alkyl chains that shows mesomorphism is susceptible to molecular structure. The prepared LCs of cinnamoyl ester derivatives were further examined for their biological activities and the obtained results indicates a good biological potential for the studied LC materials. [ABSTRACT FROM AUTHOR]

Liquid crystalline nanoparticles (LC NPs) are a kind of polymer NPs with LC mesogens, which can form special anisotropic morphologies due to the influence of LC ordering. Owing to the stimuli‐responsiveness of the LC blocks, LC NPs show abundant morphology evolution behaviors in response to external regulation. LC NPs have great application potential in nano‐devices, drug delivery, special fibers and other fields. Polymerization‐induced self‐assembly (PISA) method can synthesize LC NPs at high solid content, reducing the harsh demand for reaction solvent of the LC polymers, being a better choice for large‐scale production. In this review, we introduced recent research progress of PISA‐LC NPs by dividing them into several parts according to the LC mesogen, and discussed the improvement of experimental conditions and the potential application of these polymers. [ABSTRACT FROM AUTHOR]

The recent identification of ferroelectricity within the nematic phase of liquid crystals has triggered significant interest. However, prior to this discovery; the potential existence of ferroelectricity in the nematic phase had already been investigated in the context of cybotactic nematic phases of liquid crystals. Ferroelectricity has previously been reported in chiral and achiral smectic phases. While the presence of nano-sized smectic clusters in the nematic phase of rod-shaped molecules, termed as cybotactic nematic, was recognised, it did not earn substantial attention. However, the cybotactic nematic phase in bent-core mesogens has gained significant attention due to its unconventional ferroelectric-like behaviour. To link the recent advancements in understanding ferroelectricity in the nematic phase, a comprehensive review has been conducted on the cybotactic nematic phase. This review encompasses a foundational explanation of the cybotactic model, followed by an overview of cybotactic phases in rod-shaped mesogens. The central focus lies in evaluating cybotactic phases within bent-core nematic systems, covering early debates, fundamental experimental evidences, and a compilation of mesogens that exhibit the cybotactic nematic phase. Furthermore, the review describes into the physical attributes of mesogens featuring cybotactic nematic phases, including discussions on repolarisation, dielectric properties, and optical characteristics. [ABSTRACT FROM AUTHOR]

To develop smart ionic skins capable of multi‐responsiveness and switchable ionic conductivity, a stimuli‐responsive and ionic conductive azobenzene‐based monomer is newly synthesized, uniaxially oriented, and polymerized for anisotropic liquid crystal elastomers (LCEs). Since the uniaxially oriented monodomain LCE with ionic asymmetric azobenzene monomers (i‐AAM) is prepared by thermal oligomerization, uniaxial stretching, and subsequent photopolymerization, the stimuli‐responsive i‐AAM LCE is thermally contracted by increasing the temperature above TNI as well as is bent along the aligned direction by irradiating it with UV light. In addition to the change of shape, the ionic conductivity of the LCE is reversible in response to heat and light stimuli. Polydomain i‐AAM LCE polymerized without the stretching process exhibits higher ionic conductivity than stretched monodomain LCE due to the initially formed stable ionic pathways. Ionic conductivity can also be switched simultaneously by polarity changes in response to the photoisomerization of i‐AAM, increased mobility from heat, and an elastic mechanoresponse from external stresses. These i‐AAM LCE‐based soft grippers exhibit stimuli‐responsive grasping and releasing actuation and detect ionic conductivity switches finely, suggesting potential as smart skins for advanced soft robots. [ABSTRACT FROM AUTHOR]

Three homologous series of 3‑hydroxy-4-(((-4-benzoxazol-2-yl)phenyl)imino)methyl)phenyl-4-alkoxybenzoate (with ester linkage) and 5-(alkoxy)-2-(((4-(5-benzoxazol-2-yl)phenyl)imino)methylphenol (without ester linkage) Schiff based derivatives, bearing different substituents at 5 position i.e., 5-methylbenzoxazole, benzoxazole and 5-chlorobenzoxazole units at the end of the molecule and their Copper complexes were synthesised. The molecular structure of all the compounds were elucidated by different spectroscopic techniques such as FT-IR, 1H & 13C NMR and mass spectrometry together with elemental analysis. Their phase transition behaviour was investigated by differential scanning calorimetry, polarizing optical microscopy and X-ray diffraction. The structure-property relationships, compounds bearing a variety of polar substituents and changing the spacer from ester linked to without ester-linked has been studied. Substituents with stronger electron-withdrawing properties gave a wider mesomorphic temperature domain, in the order Cl > CH3 >H.

This work presents the synthesis and self-organization of the calamitic fluorinated mesogen, 1,1,2,2–tetrafluoro–2–(1,1,2,2–tetrafluoro–4–iodobutoxy)ethanesulfonic acid, a potential model for perfluorosulfonic acid membranes (PFSA). The compound is derived in three steps from 1,1,2,2–tetrafluoro–2–(1,1,2,2–tetrafluoro–2–iodoethoxy)ethanesulfonyl fluoride, achieving a 78% overall yield. The resulting compound exhibits intricate thermal behavior. At 150 °C, a crystal-to-crystal transition is observed due to the partial disordering of calamitic molecules, which is followed by isotropization at 218 °C. Upon cooling, sample ordering occurs through the formation of large smectic liquid crystalline phase domains. This thermotropic state transforms into a layered crystal phase at lower temperatures, characterized by alternating hydrophilic and hydrophobic layers. Using X-ray diffraction, crystalline unit cell models at both room temperature and 170 °C were proposed. Computer simulations of the molecule across varying temperatures support the idea that thermal transitions correlate with a loss of molecular orientation. Importantly, the study underscores the pivotal role of precursor self-organization in aligning channels during membrane fabrication, ensuring controlled and oriented positioning. [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 (LCs), whose refractive index can be changed by light irradiation, can be used as photoresponsive optical materials. In this study, an LC viologen was proposed as a novel photoresponsive compound that induced a change in the alignment of LC molecules (mesogens). An extended viologen with an asymmetric core, that exhibits a low-order LC phase at room temperature, was mixed with the well-known nematic LC compound (5CB) to prepare homogeneously aligned films. The change in the alignment of the mesogens was successfully induced by triggering a one-electron reduction reaction of the viologen moieties by light irradiation. [ABSTRACT FROM AUTHOR]

While the halogen bond has been recognised and studied for over a hundred years, it is only in more recent times that chemists have begun to apply it and see its possibilities as another supramolecular interaction that can be deployed in the preparation of materials. This review takes one of those areas, liquid crystals, and considers examples of motifs that have been deployed successfully to generate new mesogens. In particular, rather than attempting to be comprehensive, the article reviews critically data from well‐characterised systems and seeks to first make some comparisons with analogous hydrogen‐bonded materials, before considering how the lability and flexibility of the halogen bond expresses itself in liquid crystal behaviour. [ABSTRACT FROM AUTHOR]

The effect of core fluorination on the mesomorphic properties of rod-like Schiff base-derived liquid crystalline materials was reported. For this purpose, two new series of laterally fluorinated Schiff base liquid crystals are synthesised and investigated in detail. The two series differ from each other's in the length of the terminal alkoxy chain attached to one end of the aromatic core, where in the first series an octyloxy chain is used and in the second series it is replaced by a longer dodecyloxy chain. At the other end in both series of compounds, in addition to the nonsubstituted end (X = H) four different substituents were used (X = CH3O, C6H13O, CH3 and F). The molecular structures of all synthesised compounds were confirmed using different spectroscopic techniques. The molecular self-assembly was investigated using differential scanning calorimetry (DSC) and polarised optical microscope (POM). Depending on the length of terminal alkoxy chain at one end and nature of the substituent X at the other end, different types of mesophases were observed, including nematic and two different types of smectic phases. [ABSTRACT FROM AUTHOR]

Four series of di-flouro, namely; 4-substituted phenylazo-3-flouro phenyl-4'-n-alkoxy 3-flouro phenylazo benzoates (Ina-d) based on aromatic rings with the azo/ester/azo linkages core, were prepared and investigated for their mesomorphic properties. An alkoxy group with chain length varied from n = 6 to 16 is attached to the terminal phenylazobenzoate moiety and the other terminal is a compact group (X = --CH3O, --CH3, H and Br) attached to phenylazo moiety. The mesophases were investigated by DSC and POM and compared with previously investigated dilaterally methyl substituted analogues. Terminally unsubstituted and Br substituted analogues displayed dimorphic N and SmA phases, except the lower homologue (n = 6), while terminally -- CH3O analogues exhibited monomorphic N phase. For terminally -- CH3 substituted, compounds with n = 6-12 exhibited only N phase, while compounds with n = 14 and 16 displayed N and SmA phases. Meanwhile, the dilateral F substituents result in an enhancement in clearing thermal transitions compared with dilateral methyl substituents with a wide mesophase range. TGA analysis revealed that the prepared compounds are thermally stable within mesophase temperature range, except -- CH3O, --CH3 and Br derivatives with n = 6. Binary mixtures of I6a-d/I16a-d derivatives were investigated. The photo-physical property was also studied. [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]

The synthesis and thermotropic behaviour of some di-alkyloxy-phenyl-1,2,4-triazolium trifluoromethane-sulfonate salts bearing a seven-carbon atom perfluoroalkyl chain on the cation is herein described. The fluorinated salts presenting a 1,2,4-triazole as a core and differing in the length of two alkyloxy chains on the phenyl ring demonstrated a typical liquid crystalline behaviour. The mesomorphic properties of this set of salts were studied by differential scanning calorimetry and polarized optical microscopy. The thermotropic properties are discussed on the grounds of the tuneable structures of the salts. The results showed the existence of a monotropic, columnar, liquid crystalline phase for the salts tested. An increase in the temperature mesophase range and the presence of two enantiotropic mesophases for the sixteen-atom alkyloxy chain salt can be observed by increasing the length of the alkyloxy chain on the phenyl ring. [ABSTRACT FROM AUTHOR]

The correlation between the size of nanoparticles, the structure and shape of mesogenic ligands and the ensuing assembly behaviour is not really understood. Closer inspection shows very surprising features. Here, 2‐ and 4‐nm gold nanoparticles (NPs) were synthesized, and grafted with a forked ligand containing two rod‐like mesogens in its branches: one cholesterol, the other with azobenzene. The 4‐nm NPs also contained n‐hexylthiol as co‐ligand. They were found to form a FCC cubic superlattice, whereas the 2‐nm NPs form hexagonal HCP with weak birefringence, hence with partially oriented ligands. The structures were compared with those of related systems containing a range of different azobenzene‐to‐cholesterol ratios, all giving body‐centred tetragonal superlattices with various degrees of anisotropy. Geometric analysis is presented in terms of the asphericity of the NPs' surroundings, requirement for space‐filling and structural anisotropy. Some general rules are derived to help design the soft corona around the NPs in order to obtain superlattices with the desired structure and anisotropy. [ABSTRACT FROM AUTHOR]

Magnetorheological fluids (MRFs) are promising smart materials that can respond to an external field. In order to obtain stable suspension and investigate the settlement law of these synthesised MRFs, polymerised ionic liquid crystalline (PILC) ferroferric oxide nanocomposites (Fe3O4@PILCs), the dispersed phase in MRFs, were obtained by self-assembly of magnetic Fe3O4 nanoparticles with PILCs. The structural properties, thermotropic liquid crystal characteristics, morphology and microscopic magnetic response characteristics were investigated in this study. Fe3O4@PILCs showed nematic liquid crystal behaviour, and the mesogenic phase range was affected by the content of cholesteryl-based LC mesogen containing carboxylic acid groups. Series of MRFs were prepared by the Fe3O4@PILCs with 5% particles mass fractions in different volume fractions. The settlement stability as well as the settlement laws was investigated comprehensively and systematically for these MRFs. The Fe3O4@PILC-based MRFs exhibited better sedimentation stability than the bare Fe3O4-based MRFs, indicating that the Fe3O4 particles self-assembled with PILCs could reduce the density of the dispersed phase and showed the good compatibility with silicone oil carrier fluid. The sedimentation velocity curves of the Fe3O4@PILC-based with different particle volume fractions were investigated by use of some relevant theoretical models, indicating that they were the most consistent with the Dick's model. [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]

Multiple shape manipulation of soft materials, including reversible deformation, shape memory effect, and shape remolding, are highly desirable in morphing structures and soft actuators. Although liquid crystal network (LCN) is a promising candidate for realizing anisotropic reversible deformation, developing LCN with multiple shape manipulation remains a multitude of challenges, which is limited to the regulation of mesogens alignment and network topological rearrangement. Here, multiple shape manipulation is demonstrated by a newly designed LCN containing azobenzene moieties and a dynamic Diels‐Alder (DA) network. Photodeformation of the LCN is attributed to the ordered lamellar structure of mesogens formed by annealing‐induced self‐assembly. Light‐induced shape memory effect leads to reprogrammable shape changes due to the light‐switchable glass transition temperature of the azobenzene‐containing LCN. Moreover, the dynamic equilibrium of the DA network endows the LCN with liquid state remoldability and solid state plasticity, which further contributes to diverse 3D geometric shapes in shape remolding. Such LCN exhibiting flexible deformation and remolding properties provides a new photoresponsive block for the fabrication of soft actuators. [ABSTRACT FROM AUTHOR]

In their thermotropic liquid-crystalline state, molecular semiconductors can show charge transport with high carrier mobility. Polymerization of the corresponding mesogens into a cross-linked network often deteriorates the charge transport. Here, we report that mesogens consisting of a terthiophene core and discrete oligodimethylsiloxane side-chains terminated by acrylate units can be photopolymerized in the columnar phase with retention of nanoscale order and charge transport capabilities. We argue that the strong tendency for microphase segregation protects the semiconducting block from reacting with free radicals during polymerization. This work provides new insights into the design of electroactive materials with charge transport properties. [ABSTRACT FROM AUTHOR]

Miniature liquid crystal elastomer (LCE) based soft robots with multidirectional locomotion ability and multifunctionality have captured the extensive interest of researchers for a wide range of potential applications. Generally, the subsistent actuation modes for most LCE soft robots present several simple shape‐changing under external stimuli. Although elaborately designed for complicated structures, they still achieve limited mobility, restricting the practical applications severely. Herein, a photo‐controllable helical soft robot (PHSR) prepared with near‐infrared (NIR) light active LCE is reported. The 3D helical architecture of PHSR is constructed by manually twisting the LCE strip. The irradiation of NIR light transforms the basic reversible shape deformations (shrinking/elongating, winding/unwinding, and bending) of PHSR to macroscopic photomobility. As the torsional orientation of mesogens generated by manually twisting process, the rolling direction can be controlled by the scanning direction of the NIR spot. The flexible steering motion is in favor of performing various tasks such as traversing gap, climbing, and outputting mechanical work, suggesting that PHSR with directional photomobility and multifunction can be extended to a variety of applications. [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

• Two series of amphiphilic mesogens based on thiophene and cyanostyrene were synthesized. • The decrease in the number of thiophene induces the disappearance of cubic mesophase with P m 3 ‾ n lattice. • The change in the number of thiophene induces alternative aggregation-induced emission/aggregation-induced emission enhancement behavior and solid-state emission. Two novel series of amphiphilic mesogens containing one rod-like π-conjugated unit which consisted of thiophene and cyanostyrene, one terminal hydrophilic glycerol group at one terminal and three terminal lipophilic alkyl chains at the other terminal were prepared by Williamson etherification, oxidation, palladium-catalyzed Suzuki coupling and Knoevenagel condensation reactions. The impact of the number of thiophene on the mesogenic self-assembly and photophysical characteristics were explored. The dithiophene-containing amphiphiles exhibited much broader mesomorphic range compared with the monothiophene-containing amphiphiles, attributing to the larger π-conjugated skeleton which could increase intermolecular π-π stacking. The monothiophene-containing amphiphiles exhibited a mesomorphic transformation from hexagonal columnar mesophase to cubic mesophase with P m 3 ‾ n lattice with increasing temperature. Whereas, only hexagonal columnar mesophase could be formed by the dithiophene-containing amphiphiles. The dramatic differences in mesomorphic transition induced by the number of thiophene were generated owing to the decrease in interface curvature induced by the incorporation of more thiophene in the π-conjugated aromatic core. Both series of mesogens exhibited aggregation-induced emission/aggregation-induced emission enhancement and solid-state emission behaviors attributed to the cyanostyrene and hydrogen bond which induced specific molecular stacking in aggregated states. Therefore, the change of thiophene in the π-conjugated aromatic unit can induce complex self-assemblies and different photophysical behaviors, which have benefits on the application of mesogenic materials. [Display omitted] [ABSTRACT FROM AUTHOR]

[Display omitted] • We synthesized novel liquid crystal gelators with cholesterol and thiacrown-annelated tetrathiafulvalenes moieties. • Compounds 1b and 1d formed stable gels and exhibited nematic liquid crystalline phases with different nanostructures. • The gels 1d obtained from n-hexane readily adsorbed the toxic dye rhodamine B from water. We synthesized a series of novel liquid crystal (LC) gelators by attaching two cholesterol groups through two ω-thioalkanoyloxy spacers of varying length to thia-crown-annulated tetrathiafulvalene (TTF) moieties (1a – e). Among these compounds, 1b and 1d underwent gelation to form stable supramolecular gels in various organic solvents, and their self-assembled morphology and structure indicated that Van der Waals interactions were the driving force of gel formation. In addition, more than half of the gels (1a – d) transformed into nematic LCs in a certain temperature range, while gelators that did not crystallize during cooling from the isotropic melt formed glassy mesogens. Notably, gelators obtained from n -hexane readily adsorbed rhodamine B in solution, which was considered useful for removing toxic dye molecules in wastewater. LC molecules described herein were capable of gelation and have useful oxidation and stimulus-responsive properties. They may therefore be useful for developing sensors and optoelectronic materials. [ABSTRACT FROM AUTHOR]

[Display omitted] • Two series of dibenzofuran- and dibenzothiophene-based liquid crystals were designed and synthesised respectively. • All of the obtained mesogens possessed large negative dielectric anisotropy values. • The calculated orientation of the dipole moment in these compounds was almost perpendicular to their long molecular axis. • A new negative LC mixture with excellent low-temperature stability was formulated. Two series of dibenzofuran- and dibenzothiophene-based liquid crystals were designed and synthesised respectively. The structures of the intermediates and the target mesogens were confirmed by nuclear magnetic resonance and mass spectrometry. The melting points of dibenzofuran-based liquid crystals were lower than dibenzothiophene-based ones if the 3-position was long-chain alkoxy while a reversed result was obtained when cyclohexyl and tetrahydropyran were introduced. All of the designed dibenzofuran- and dibenzothiophene-based liquid crystals possessed large negative dielectric anisotropy (Δ ε) values when compared with the reference compounds, which proved the effectiveness of these two heterocycle core units in the improvement of the negative Δ ε. The DFT calculations found that the elevation of the negative Δ ε values might be owed to the orientation of the dipole moment in these new compounds was almost perpendicular to their long molecular axis. A new liquid crystal mixture LTNLCM-1 was finally formulated, which could be stored at −20 °C (−40 °C when filled in liquid crystal cell) for two weeks without any obvious precipitation, illustrating the vital function of the dibenzothiophene-based compounds in improvement of the low-temperature stability of liquid crystal mixtures. [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]

We demonstrate here a novel method for the design of liquid crystals (LCs) via the cyclization of mesogens by flexible chains. For two azobenzene-4,4′-dicarboxylate derivatives, the cyclic dimer, cyclic bis(tetraethylene glycol azobenzene-4,4′-dicarboxylate) (CBTAD), shows LC properties with smectic A phase, while its linear counterpart, bis(2-(2′-hydroxyethyloxy)ethyl azobenzene-4,4′-dicarboxylate (BHAD), has no LC phase. The difference is ascribed to the shackling effect from the cyclic topology, which leads to the much smaller entropy change during phase transitions and increases the isotropic temperature greatly for cyclics. In addition, the trans-to-cis isomerization of azobenzene groups under UV-light is also limited in CBTAD. With the reversible isomerization of azobenzene groups, CBTAD showed interesting isothermal phase transition behaviors, where the LC phase disappeared upon photoirradiation of 365 nm UV-light, and recovered when the UV-light was off. Combined with the smectic LC nature, a novel UV-light tuned visible light regulator was designed, by simply placing CBTAD in two glass plates. The scattered phase of smectic LC was utilized as the "OFF" state for light passage, while the UV-light induced isotropic phase was utilized as the "ON" state. The shackling effect outlined here should be applicable for the design of cyclic LC oligomers/polymers with special properties. [ABSTRACT FROM AUTHOR]

Cholesteryl chloroformate which is known liquid crystal material was modified to give the new molecules a long-lasting LC phases with the stability of the carbamate and aromatic functions. Two new mesogens cholesteryl 1H-imidazole-1-carboxylate (Cho-Imi) and Cholesteryl (4-((E)-phenyldiazenyl) phenyl) carbamate (Cho-Diazo) were synthesized starting from Cholesteryl chloroformate and (E)-4-(phenyldiazenyl) aniline in the presence of triethylamine (TEA) as an acid scavenger at room temperature. Structural characterization of the obtained LC compounds was performed by FTIR and H-NMR. These new compounds, which show more than one LC phase different from the LC phases of the starting material, showed that they are promising as a result of the analyses. The mesomorphic properties were examined by polarized optical microscope (POM) and thermal properties of the LC compounds were determined by DSC and TGA. The dielectric properties of synthesized liquid crystal samples were investigated using dielectric spectroscopy technique. It was seen that both new syntheses mesogen cholesteryl carbamates-based liquid crystal samples exhibit non-Debye type relaxation properties. The cole–cole analysis by dielectric spectroscopy was used to determine the equivalent devices of this new Cholesteryl carbamate-based mesogens. The samples have different dielectric properties in different frequency regions will provide significant flexibility as a working frequency region in engineering, biological and genetic application areas. [ABSTRACT FROM AUTHOR]

Pillar[5]arene (P5A) mesogens were synthesized by decorating the central P5A core with ten benzylether dendron via click reaction. Each benzylether dendron was terminated with multialkoxy chains. Such P5A mesogens can self-assemble into liquid crystal (LC) phases with layer structure (Smectic A phase) and tubular structure (Colhex/p6mm phase). Molecular packing models for these mesophases were initially established. Additionally, such P5A mesogens can act as chemo-sensor to recognize Fe3+ and Cu2+. The influence of the number of terminal alkoxy chain on the self-assembly and chemo-sensor properties of these P5A derivatives were investigated. [ABSTRACT FROM AUTHOR]

Comprehensive Summary: Molecular motions of the luminescent liquid crystals (LLCs) show a significant effect on fluorescent emission and heat generation. In this article, a series of cyanostilbene‐based LLCs (CSs: CS1‐6, CS1‐12, CS2‐6 and CS2‐12) are synthesized to investigate how the photoluminescence and photothermal effect balanced. Among these materials, the mesogens peripheried by single alkyl chains formed enantiotropic nematic (CS1‐6) or smectic C (CS1‐12) phase with different alkyl tail lengths. When the single aliphatic chain is replaced by mini‐dendrons, room temperature (RT) monotropic hexagonal columnar phase (CS2‐12) or molecular liquid (CS2‐6) is formed. The results revealed that all these materials exhibited high efficiency emission with the highest quantum yield reaching 59.0%. The photoluminescence and photothermal effect can be effectively tuned by dispersing CSs into a commercially available RT liquid crystal matrix 8CB, which output significantly improved photothermal conversion efficiency of 63.2%. Furthermore, the photothermal can rapidly trigger the Smectic A‐Nematic‐Isotropic sequence transitions of 8CB doped with CSs. This work paves a way of adjusting the balance of photoluminescence and photothermal properties of the LLC materials. [ABSTRACT FROM AUTHOR]

We demonstrate a fast-switching optically compensated bend (OCB) mode with polymerized liquid crystal photoalignment (PAL). The polymerized liquid crystal PAL is achieved by spin coating a mixture of reactive mesogens and a photoinitiator and polymerizing it with ultraviolet (UV) light on top of the PAL material, which is illuminated with linear-polarized ultraviolet light to introduce anisotropy and a pretilt angle for liquid crystal alignment. The experimental results show the dependency of the electro-optical properties of OCB cells on the morphology-modulated surface anchoring of polymerized liquid crystal PAL. Furthermore, the polymerized liquid crystal PAL exhibits superior stability against UV exposure and thermal stress, which makes PAL applicable in spatial light modulator application. [ABSTRACT FROM AUTHOR]

• A new class of bisphenol-A linked azo mesogens has been designed and characterized. • All four dimeric azo mesogens showed columnar hexagonal phase. • The structure-property relationship has been discussed for parent azo mesogens. • These azo-ester based dimers adopted good photophysical properties. A series of bent-shaped liquid crystals containing an azo group and a bisphenol A core were synthesized, and characterized using various techniques. The presence of mesogenic properties in these azo-based dimers was confirmed through POM, DSC, and high-temperature XRD analysis. The structure-property relationship is further studied to confirmed the effect of the variable alkyl side chain on the terminal position, which also affects the liquid crystalline properties of the compounds in terms of mesophase temperature range and thermal stability. All the compounds exhibited enantiotropy columnar hexagonal phase with wide temperature range and thermal stability. Their photophysical properties were investigated using UV–visible spectroscopy and spectrofluorometry. It was observed that all four columnar mesogens underwent cis and trans azo isomerization upon exposure to photoisomerization. [Display omitted] [ABSTRACT FROM AUTHOR]

[Display omitted] • D-A-D mesogens CBC /n and CTBTC/16 were synthesized. • They can self-assemble into SmA and Col hex / p 6 mm structures in LCs and gels. • Their solid fluorescence quantum yields differ greatly. • CBC/12 showed different Φ Fs in its three different solid aggregation states. • Application of CBC/12 as white LED was realized. Three carbazole(C)-benzothiadiazole(B) based D-A-D mesogens CBC/ n ( n = 12, 16) and CTBTC/16 containing terminal N -trialkoxylbenzyl carbazoles at both side of central benzothiadiazole core have been designed and synthesized. By inserting thiophene (T) unit between B and C units, the rigid core was elongated and the molecular conformation changed from twist to planar one, thereby the liquid crystal (LC) phase changed from SmA to Col/ hex phase. Such molecular packings caused by inserting T unit remained in their organogels formed in organic solvents. The long-core compound CTBTC/16 containing T unit with a more planar and tighter π-π packing structure showed a significant optical red shift and a stronger intramolecular charge transfer (ICT) effect than the short-core compounds CBC/ n without thiophene unit. These compounds are all strong fluorescent in solution with fluorescence quantum yields (Φ F) ranging from 38 % to 86 %. But their solid fluorescence quantum yields (Φ Fs) differ greatly with values of 43 %, 11 % and 0.6 % for CBC/12, CBC/16 and CTBTC/16 respectively. Further, short core compound CBC/12 with the highest Φ Fs showed different Φ Fs in its three different solid aggregation states. The application of the short twist core compound CBC/12 as white light-emitting diodes (LEDs) has been realized. The influence of the thiophene unit as well as the terminal alkyl chain length on self-assembly and Φ Fs of these compounds is discussed. [ABSTRACT FROM AUTHOR]

The synthesis and thermotropic behaviour of some di-alkyloxy-phenyl-1,2,4-triazolium trifluoromethane-sulfonate salts bearing a seven-carbon atom perfluoroalkyl chain on the cation is herein described. The fluorinated salts presenting a 1,2,4-triazole as a core and differing in the length of two alkyloxy chains on the phenyl ring demonstrated a typical liquid crystalline behaviour. The mesomorphic properties of this set of salts were studied by differential scanning calorimetry and polarized optical microscopy. The thermotropic properties are discussed on the grounds of the tuneable structures of the salts. The results showed the existence of a monotropic, columnar, liquid crystalline phase for the salts tested. An increase in the temperature mesophase range and the presence of two enantiotropic mesophases for the sixteen-atom alkyloxy chain salt can be observed by increasing the length of the alkyloxy chain on the phenyl ring.

Design and synthesis a series of azo multi-arm liquid crystal monomers (M1-M3) with cholic acid as the chiral core, followed by side chain graft copolymerisation with polymethylhydrosiloxane (PMHS) to synthesise the liquid crystal polymer PM series. All liquid crystal monomers and polymers were conformed to the molecular design in structure by FT-IR and NMR. The liquid crystal performance was tested by DSC and POM, and the results revealed that M1 and M2 were thermotropic enantiotropic cholesteric phase liquid crystals. Liquid crystal monomer M3 has no liquid crystal behaviour in both the up and down temperature processes. Polymers of the PM series exhibited different liquid crystal phases depending on the monomer content, with Grand-Jean texture at lower percentage and oil filament texture at higher percentage. The glass transition temperature and melting temperature decrease progressively with the increase in the liquid crystal monomer content, as opposed to the isotropic temperature. [ABSTRACT FROM AUTHOR]

Crosslinked liquid crystal polymers (CLCPs) have recently attracted much attention because they exhibit unique properties in stimuli responsiveness. We have recently focused on the photoinduced deformation behavior of CLCP containing N-benzylideneaniline (NBA) as a photoresponsive moiety. We prepared two types uniaxially aligned NBA-containing crosslinked liquid crystalline polymer film, homogeneous and homeotropic, and evaluated its photomechanical properties. The initial alignment of photoactive mesogens significantly affects the bending behavior of the CLCP films: the homogeneous films bent toward the irradiation direction of the actinic UV light, while the homeotropic films bent away from the light source. [ABSTRACT FROM AUTHOR]

Abstract Within the past two decades, chromophores, which show aggregation‐induced emission (AIE), have gained considerable attention with respect to the development of luminescent liquid crystals. In contrast to common luminogens, AIE emitters do not suffer from aggregation‐caused quenching of the emission in the solid state. In this review, we summarize the recent development in the field of AIE‐active liquid crystals and show first model devices, which already prove the application potential of these materials. Currently, three different approaches are followed, to get access to luminescent liquid crystals––namely the synthetic approach yielding luminescent mesogens, the doping approach, and the supramolecular approach, which will be described and discussed in detail in this review.

Beyond a traditional stimuli‐responsive soft actuator that shows a single motion by a stimulus, multidirectional actuation reversal with a single stimulus is highly required in applications such as shape morphing sensors and soft robotics. Liquid crystal elastomers (LCEs) are one of the most attractive candidates for the soft actuator due to their capability of stimuli‐responsive shape changing in 3D, which is programmable with local orientation of LC mesogens. Here, a simple but effective method to fabricate monolithic LCE actuators that are capable of reversible curvature reversal in bending and twisting deformation by a single stimulus—heat—is reported. The curvature reversal of the LCE film can be programmed by means of asymmetric crosslinking density along the thickness and the orientation of the LC mesogens. The curvature reversal of the monolithic LCE film exhibits highly reversible (more than 100 times) and fast actuation (≈3–5 s) by heating and cooling, allowing new concept of a practical application using LCE material: a self‐regulated smart valve that is capable of qualitatively sorting liquids by temperature. It is believed that this system is potentially applied to a self‐regulated sorting platform for various endothermic and exothermic chemical or biological reactions [ABSTRACT FROM AUTHOR]

Featured Application: Fluorinated ionic liquid crystals, due to their easy synthetic modulation, inertness, and potential as quasi solid-state electrolytes, can find perspective application in DSSCs solar cells, but also in many other electronic and optoelectronic devices, such as supercapacitors, smart windows, and lithium batteries. The synthesis and characterization of a new class of 1,2,4-oxadiazolylpyridinium as a cationic scaffold for fluorinated ionic liquid crystals is herein described. A series of 12 fluorinated heterocyclic salts based on a 1,2,4-oxadiazole moiety, connected through its C(5) or C(3) to an N-alkylpyridinium unit and a perfluoroheptyl chain, differing in the length of the alkyl chain and counterions, has been synthesized. As counterions iodide, bromide and bis(trifluoromethane)sulfonimide have been considered. The synthesis, structure, and liquid crystalline properties of these compounds are discussed on the basis of the tuned structural variables. The thermotropic properties of this series of salts have been investigated by differential scanning calorimetry and polarized optical microscopy. The results showed the existence of an enantiotropic mesomorphic smectic liquid crystalline phase for six bis(trifluoromethane)sulfonimide salts. [ABSTRACT FROM AUTHOR]

Poly(thiophene-co-phenylene) type π-conjugated polymers having two mesogens in monomer repeat unit were synthesized using the Migita–Kosugi–Stille coupling reaction. Thermotropic liquid crystal behavior of the series of polymers was examined with polarizing optical microscopy observations and differential scanning calorimetry. The produced polymers showed unique optical textures of smectic liquid crystal. [ABSTRACT FROM AUTHOR]

2-(4-Alkoxyphenyl)-5-(p-tolyl)-1,3,4-thiadiazoles (alkoxy: O(CH2)nH, n = 1–8) (6a–h) (as a series of 1,3,4-thiadiazole derivatives) and their silver(I) complexes: bis(2-(4-alkoxyphenyl)-5-(p-tolyl)-1,3,4-thiadiazole)-silver(I) complexes (alkoxy: O(CH2)nH, n = 1–8) (7a–h) were prepared and characterized with different techniques: microelemental analysis, FTIR, UV–Vis, 1H NMR, 13C NMR and mass (for the organic compounds) spectra, in addition to the molar conductivity measurements (for Ag(I) complexes). Liquid crystal behavior of the two series of compounds was evaluated using polarized light optical microscopy (POM). The study revealed that both series are enantiotropic liquid crystalline materials (exhibiting wide mesomorpic temperature ranges) with different behavior and properties. 6a–f displayed only nematic mesophase upon heating and cooling, while 6g and 6h exhibited both of SmC and nematic mesophases upon heating and cooling. Upon complexation of 1,3,4-thiadiazoles (6a–h) to silver(I), the liquid crystal behavior and properties are significantly changed (different mesophases, and lower mesophase and clearing temperatures). However, 7b–h exhibited SmA mesophase upon heating and cooling, while 7a shows no mesomorphic properties (simply melted to isotropic liquid). [ABSTRACT FROM AUTHOR]

Two new families of dimeric borondifluoride complexes derived from β-enaminoketones containing terminal phenyl and naphthalenyl groups were prepared, and their mesomorphic and optical properties investigated. One single crystallographic structure of mesogenic complex 1a-BF2 (n = 12) was determined by X-ray analysis; it crystallises in a monoclinic space group P21/c and the geometry on boron atoms was all tetrahedral. The crystal was considered as linear-shaped with a length of ~51.95 Å. A relatively large dihedral angle of ~38.85° between the central phenyl spacer and tetrahedral BF2 moiety was observed. Mesomorphic properties were crucially impacted by the structure of the central spacer and terminal group; all bis(borondifluoride) complexes formed SmC or SmA phase except complexes 1b-BF2 (m = 2, 3) and 1c-BF2. H–bond interactions supported by FT-IR spectra were attributed to the induction of SmA phase in compound 2 c-BF2. The optical property of the boron complexes was related with their molecular structures, and they emitted blue-to-green emissions at λmax = 420–538 nm in CH2Cl2. This is the first twin liquid crystal of bis(BF2) complexes derived from Schiff baseβ-enaminoketones. [ABSTRACT FROM AUTHOR]

In this study, novel chiral pyridine-based rod-like mesogens, consisting of a chloro or bromo group substituted pyridine head core which is connected to one or two aromatic rings through ester linkers and a flexible (S)-2-methylbutoxy or (S)-3,7-dimethyloctyloxy chiral end chain have been synthesised. The liquid crystal properties of new compounds were investigated by various experimental techniques such as DSC, POM and SAXS. Depending of the nature of the halogen end group, the derivatives with two aromatic rings are non-mesogenic compounds whereas a smectic A phase (SmA) enantiotropically occurs for the members with three aromatic rings of the series. Additionally, chloro group substituted compound composed of three aromatic rings carrying a (S)-2-methylbutoxy end chain exhibits an enantiotropic chiral nematic phase (N*). [ABSTRACT FROM AUTHOR]

[Display omitted] • Periodically grafted amphiphilic polymers (PGAPs) leads to microphase separated lamellar morphologies with sub-10 nm domain sizes. • Installation of functional elements, such as mesogens, within the backbone or pendant segment leads to layering of the mesogens. • Zigzag folding of PGAPs can be induced by the addition of segment-selective solvent and could be utilized to generate single-chain crosslinked nanoparticles. Controlling chain conformation is a challenge that has drawn the attention of researchers for several decades; achieving control in solution is inspired by the remarkably elegant strategies seen in biological macromolecules, like proteins, RNA, DNA etc. On the other hand, controlling the chain conformation of polymers in the solid state is a more difficult task, but it is one that could have important ramifications, especially to elicit interesting properties that require distances between different function-imparting units to be precisely controlled. Most of the strategies examined for conformational control utilize intra-chain noncovalent interactions , such as H-bonding, π-stacking, charge-transfer, metal-ion coordination, etc. During the past decade, we have explored an alternate approach, wherein suitably designed periodically grafted amphiphilic polymers (PGAP) carrying long alkylene backbone segments and pendant PEG segments, were shown to adopt a folded zigzag conformation so as to collocate the alkylene segments at the center with PEG segments on either side; the crystallization of the central alkylene segments stabilize the folded conformation and leads to lamellar morphologies with fine tunable layer dimensions. This strategy was more recently exploited to precisely locate functional units, such as mesogens, within layered morphologies at well-defined distances in bulk samples. In this short perspective article, we shall discuss the genesis and design of periodically grafted amphiphilic polymers, and illustrate its utility to generate functional polymeric materials, wherein specific units are located at well-orchestrated distances in the bulk polymer; thus, revealing the power of design at the molecular level to impact properties in the bulk. [ABSTRACT FROM AUTHOR]

Two novel rod-like mesogens containing one cyanostyrene, one pyridine and one pyrene as π-conjugate rigid core were designed and synthesized by Suzuki coupling and Knoevenagel reactions. The effect of the position of nitrogen-atom on the thermodynamic behavior, liquid crystalline self-assembly, optical behavior, mechanochromism behavior and acidochromism behavior was investigated. The rod-like mesogen in which the nitrogen atom is adjacent to the pyrene displays a phase transition from smectic A to smectic C by increasing temperature, whereas the other rod-like mesogen can only self-assemble into smectic C phase. This difference in mesophase transition behavior might be attributed to the position of nitrogen-atom which induces the change in molecular configuration. Both mesogens exhibit positive solvatochromism and high fluorescence in both solution state and aggregated state which might be attributed to the intramolecular charge transfer and twisted molecular configurations, respectively. Reversible mechanochromism behavior due to changes in molecular stacking and acidochromism behavior due to protonation and deprotonation were also achieved. These multi-stimuli responsive behaviors of the designed rod-like mesogens demonstrate potential applications in the field of multifunctional materials. [Display omitted] • Two novel rod-like mesogens containing multiple functional building blocks are synthesized. • The position of nitrogen atom induces distinct mesophase transition behavior. • High-contrast mechanochromic and acidochromic behaviors are achieved. [ABSTRACT FROM AUTHOR]