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We present a Monte Carlo simulation study of helical Yukawa rods as a model for chiral liquid crystal mesogens. To simulate the cholesteric phase, we introduce a newsimulation method that uses softwalls and self-determined boundary conditions. We observe that the isotropic-nematic phase transition is shifted to lower volume fractions with decreasing salt concentration as well as with increasing internal pitch of the rods. For particular sets of interaction parameters, the sense of the cholesteric pitch inverts, i.e., depending on concentration, mesogens of a given handedness can produce cholesteric phases of both chiral senses. [ABSTRACT FROM AUTHOR]

We prepared and studied new series of mesogens with a molecular core based on two biphenyls connected via ester linkage, with the biphenyl in central part laterally substituted by a chlorine atom. The studied compounds have two lactate groups and methylbutyl in the chiral chain and they exhibit the SmA phase in a very broad temperature range. We pursued the mesomorphic property and confirmed the phase identification by X-ray measurements. Additionally, we compared the studied compounds with previously prepared analogous materials. In comparison with homologues with different positions of the lateral substitution, we attempted to explain modified mesomorphic properties and absence of tilted mesophases for the studied series. We performed ab-initio calculations and found that the dipole moment is oriented along the long molecular axis, so its small transversal component probably causes the stability of the SmA phase and lack of ferroelectricity or antiferroelectricity. [ABSTRACT FROM AUTHOR]

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]

Liquid crystalline (LC) polymers find still a lot of interest, whereby the focus is—at present—on LC‐elastomers with different phases and their application for mechanical actuation. While the LC‐phases in LC‐polymers can—generally—be well described in analogy to their low molar mass counterparts, some special properties became evident for some systems with smectic phases. They are related to the modulation of the nanophase segregation within the smectic layers and include often the formation of sublayers consisting of poorly compatible parts of the polymer like bulky (=non mesogenic) units, ionic groups, or poorly miscible parts of the main chain (e.g., polysiloxanes). Such a behavior can be found for semiflexible LC‐main chain polymers and for LC‐side chain polymers. Here the authors i) describe polymers for which such a modification of the smectic structure is observed, ii) discuss the origin of the deviation, and iii) describe possible application for the design of functional materials. The formation of the substructures can allow, for example, a mixing of the LC‐polymers with other polymers, which have a good affinity to the second sublayer. It also allows it to separate, to some extent, the network structure from the packing of the mesogens in LC‐polysiloxanes. [ABSTRACT FROM AUTHOR]

The self‐assembly of umbrella‐shaped mesogens is explored with subphthalocyanine cores and oligo(thienyl) arms with different lengths in the light of their application as light‐harvesting and photoconducting materials. While the shortest arm derivatives self‐assemble in a conventional columnar phase with a single mesogen as a repeating unit, the more extended derivatives generate dimers that pile up into liquid crystalline columns. In contrast to the antiparallel arrangement known from single crystals, the present mesogens align as parallel dimers in polar columnar phases as confirmed by X‐ray scattering, experimental densities, dielectric spectroscopy, second harmonic generation, alignment, and conductivity studies. UV–vis and fluorescence spectroscopies reveal a broad absorption in the visible range and only weak emission of the Q‐band. Thus, these light‐collecting molecules forming strongly polar columnar mesophases are attractive for application in the area of photoconductive materials. [ABSTRACT FROM AUTHOR]

We investigate the temperature dependence of the helical pitch of a cholesteric liquid crystal by means of Monte Carlo simulations. We carry out both lattice and off-lattice simulations to assess the impact of geometric and modelling constraints on the properties of the cholesteric phase. For the off-lattice simulations we develop boundary conditions commensurate with the cholesteric phase and derive an analytic expression for the helical wavenumber q that works well qualitatively. We find that the common simplification of constraining the orientation of the mesogens to planes normal to the helical axis makes q temperature-independent, as predicted by a mean-field theory of van der Meer et al. [J. Chem. Phys. 65 , 3935 (1976)]. However, if mesogens are allowed to rotate in three dimensions, q will increase with temperature, as the isotropic-cholesteric transition is approached from below, in agreement with experiments for a number of substances. Our simulations indicate that the temperature-independent q is merely a consequence of the overly restricted orientational degrees of freedom to points on the unit circle in the model on which the mean-field theory is based. [ABSTRACT FROM AUTHOR]

Four rod-like mesogens in which biphenyl and bithiophene units are located at one terminus are synthesised and the occurrence of enantiotropic nematic phase is established by hot-stage optical polarising microscopy and differential scanning calorimetry. For biphenyl based mesogens (BP-1 and BP-2), the mesophase is observed irrespective of number of phenyl rings in the amine moiety. For bithiophene (BT-1), on the other hand, the mesophase is only noted when the amine component has two rings. The mesophase range for BP-1 is found to be 163.7◦C and for BT-1 and BP-2, the values are 84.7◦C and 11.1◦C, respectively. BP-1 and BT-1 are subjected to 13C NMR investigation in nematic phase to determine the local order and accordingly, oriented 1D 13C and 2D SAMPI-4 NMR experiments are accomplished. The remarkable feature of the SAMPI-4 spectrum of BP-1 measured at 145◦C in nematic phase is observation of the 13C-1H dipolar coupling value of 16.67 kHz for terminal carbon (C18). For BT-1, however, the dipolar coupling value for C18 is found to be 8.60 kHz in nematic phase (138◦C). Such large values of 13C-1H dipolar couplings for the terminal ring carbons of the nematogens offer orientation of the rings of the core unit directly. [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]

• Schiff base derivatives of 6-amino coumarin were designed and synthesized. • Lower alkoxy chain showed enantiotropic nematic mesophase. • Higher alkoxy chain showed stable enantiotropic SmA mesophase. • Compounds of both the series were studied by the DFT calculations. In first series, 6-amino coumarin Schiff base derivatives 10a-g were synthesized with alkoxy chain n = 6–18 and studied for their mesomorphic properties. In this series, compounds 10b with n = 8 showed monotropic nematic mesophase, while enantiotropic smectic A mesophase for higher analogues compounds 10c-g (with n = 10–18) was observed. In another series of Schiff base derivatives 12a-h additional ester linkage was introduced at the aldehyde end and were studied for their mesomorphic behavior. In second series, compounds 12a-c (with n = 4–8) showed enantiotropic nematic mesophase with very good thermal stability. Higher analogues of the second series with n = 12–18 showed stable enantiotropic smectic A mesophase. Compounds of both series were studied by DFT calculations. Different electronic parameters such as dipole moment, polarizability, molecular electrostatic potentials, frontier molecular orbitals, and thermodynamic variables were calculated and compared with the observed mesomorphic trends in both the studied series. Further, electronic parameters of compounds 10b and 12c and that of reference compound 4 were calculated and discussed to understand the effect of the removal of a hydroxyl group on the ortho position of the aldehyde part. [Display omitted] [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]

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]

The mesomorphic properties of linear shaped homologous series based on two linkage group have been designed and synthesized with different side chain substituents (-OR) on the one end of terminal side with presence of lateral nitro group and second terminal iodo substituted group. Novel series consists thirteen members (C1 to C8, C10, C12, C14, C16, C18). Compounds (C1 to C6) showed nonliquid crystalline properties while compound (C7 to C18) displayed smectic and nematogenic mesophase properties. The textures of smectic C and nematic phase are fan, schlieren and droplets type. All these compounds were characterized by spectroscopic techniques such as [FTIR] and 1H Nuclear magnetic resonance [NMR] spectroscopy. The mesomorphic properties of these compounds were observed by POM and further confirmed by DSC and XRD. Chalconyl ester based compounds (C3 to C12) shows good antibacterial as well as antifungal activity compared with corresponding standard drugs. [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 1976, Meyer predicted that bend distortions of the nematic director field are complemented by deformations of either twist or splay, yielding twist-bend and splay-bend nematic phases, respectively. Four decades later, the existence of the splay-bend nematic phase remains dubious, and the origin of these spontaneous distortions uncertain. Here, we conjecture that bend deformations of the nematic director can be complemented by simultaneous distortions of both twist and splay, yielding a twist-splay-bend nematic phase. Using theory and simulations, we show that the coupling between polar order and bend deformations drives the formation of modulated phases in systems of curved rods. We find that twist-bend phases transition to splay-bend phases via intermediate twist-splay-bend phases, and that splay distortions are always accompanied by periodic density modulations due to the coupling of the particle curvature with the non-uniform curvature of the splayed director field, implying that the twist-splay-bend and splay-bend phases of banana-shaped particles are actually smectic phases. The so-called twist-bend and splay-bend nematic liquid crystal phases are important concepts for studying bent-core mesogens. Chiappini et al. use a theory/simulation approach to suggest that the transition proceed via a twist-splay-bend phase which may be obscured by density modulations. [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]

Fischer indole reaction of Weiss diketone with 4‐bromophenylhydrazine provided the 2,8‐dibromo‐hexahydropentaleno[2,1‐b:5,4‐b']diindole key intermediate, which was converted to the target compounds by N‐protection/Suzuki cross‐coupling. Variation of protecting groups, mesogenic units, and their alkoxy substitution gave calamitic diindole mesogens. Both N‐protection and alkoxy chain influenced the mesomorphic properties of phenyl diindoles. Among the differently N‐protected derivatives only ethylcarbamate‐protected ones formed enantiotropic mesophases. Mesophase range and type were controlled by the chain lengths: chains≤C12 gave nematic (N) phases, diindoles with side chains≥C14 formed additional lower temperature smectic (SmA) phases. Irrespective of the chain lengths 4′‐alkyloxybiphenyl diindoles formed N and SmA phases upon first heating but tended to decomposition below their clearing points. X‐ray crystal structure analysis of bis(4′‐decyloxy)biphenyl diindole reveals that in the solid‐state the folding angle of the hydropentalene core caused an almost perpendicular orientation of the two indole/biphenyl parts with respect to each other. [ABSTRACT FROM AUTHOR]

Fabricating functional materials via molecular self-assembly is a promising approach, and precisely controlling the molecular building blocks of nanostructures in the self-assembly process is an essential and challenging task. Blue phase liquid crystals are fascinating self-assembled three-dimensional nanomaterials because of their potential information displays and tuneable photonic applications. However, one of the main obstacles to their applications is their narrow temperature range of a few degrees centigrade, although many prior studies have broadened it to tens via molecular design. In this work, a series of tailored uniaxial rodlike mesogens disfavouring the formation of blue phases are introduced into a blue phase system comprising biaxial dimeric mesogens, a blue phase is observed continuously over a temperature range of 280 °C, and the range remains over 132.0 °C after excluding the frozen glassy state. The findings show that the molecular synergistic self-assembly behavior of biaxial and uniaxial mesogens may play a crucial role in achieving the ultrastable three-dimensional nanostructure of blue phases. Blue phases are spatially ordered yet fragile liquid crystalline structures, bearing applications in optoelectronics and photonics. Hu et al. show that self-assembly within a mixture of different mesogens may significantly broaden the temperature range over which they are stable. [ABSTRACT FROM AUTHOR]

In this review, methods to obtain the orientational order of topologically variant molecular mesogens using by one‐ and two‐dimensional (2D) solid‐state 13C nuclear magnetic resonance (NMR) spectroscopy are described. Besides 13C chemical shifts, the 13C─1H dipolar couplings measured from 2D‐separated local field (SLF) technique are used for computing the order parameters of a variety of mesogens. The investigated molecules are composed of a variable number of rings in the core, that is, core ranging from simply one ring to five rings. Among the mesogens investigated, a special focus has been placed on mesogens with thiophene rings, which are gaining popularity as liquid crystalline organic semiconductors. The replacement of a phenyl ring by thiophene in the core has a dramatic influence on molecular topology, as observed from the measured order parameters. The review highlights the advantages of the 2D SLF method for understanding the local dynamics and for mapping the topology of mesogens through the measured order parameters. SLF NMR studies of as many as 24 molecular mesogens that vary in terms of the molecular structure as well as topology are covered in the review. Order parameters of the rings have been estimated from the 13C─1H dipolar couplings in the nematic, smectic A, smectic C, and tilted hexatic phases as well as in B1 and B2 mesophases of various mesogens. It is anticipated that, in the years to come, the 2D SLF method would provide advanced molecular information on structurally complex mesogens that are emerging in liquid crystal science through the incessant efforts of synthetic chemists. The mini review covers the orientational order of topologically variant molecular mesogens determined by 1D and 2D solid‐state 13C NMR spectroscopy. Accordingly, rod‐like, bent‐core, and thiophene mesogens were subjected to 2D SLF measurements to get the order parameters from which the topology was established. The replacement of phenyl ring by thiophene and its influence on order parameters as well as on molecular topology is also discussed. [ABSTRACT FROM AUTHOR]

We demonstrate the reversible photomanipulation of the bulk mechanical properties in the azobenzene‐containing bent‐core liquid crystal. The azobenzene groups in the mesogens exhibit reversible cis‐trans photoisomerization abilities. An unprecedentedly large reduction by the factor of more than 5 of the splay elastic constant in a cybotactic‐type nematic phase was found under exposure to the UV. This opens up the possibility to manipulate the mechanical properties of liquid crystals using light. The liquid crystal material is also distinguished by the sign inversion of low‐frequency temperature‐dependent dielectric anisotropy. Such behavior can be related to the presence of smectic‐like nanoclusters both in the isotropic phase near the clearing point and in the cybotactic nematic phase. [ABSTRACT FROM AUTHOR]

One of the most exciting classes of organic materials that is able to self-assemble at nanoscopic scale are those exhibiting the liquid crystalline (LC) behaviour which can be distantly tuned by an external stimulus. Under UV/Vis light irradiation, the reversible photoisomerisation process can take place if the compounds possess the photosensitive group, e.g. N=N or cinnamoyl group incorporated in their molecular structure. This can drastically affect the LC behaviour. However, the compounds possessing the cinnamoyl fragment with C=C double bond are capable of both photoisomerisation and photocycloaddition processes. Several cinnamoyl-based reactive mesogens with polymerisable vinyl group have been designed; their mesomorphic and structural behaviour have been studied. Depending on the molecular structure, the reactive mesogens exhibit nematic, orthogonal smectic A and tilted smectic C phases; the kinetics of the phase transition temperatures has been checked. The structure of the mesophases is confirmed by small-angle X-ray scattering. The main objective of the present work is to contribute to better understanding of molecular structure – mesomorphic property relationship for new functional cinnamoyl-based photosensitive reactive mesogens which can be further used for design of smart self-assembling macromolecular materials. [ABSTRACT FROM AUTHOR]

Shape‐persistent conjugated mesogens with oligothiophene arms of different lengths have been synthesized. Such mesogens possess free intrinsic space between their conjugated arms. They form columnar liquid‐crystalline phases, in which the void is filled by dense helical packing in the neat phase similar to an oligo(phenylene vinylene) derivative of equal size. The void can also be compensated by the inclusion of the small acceptor molecule 2,4,7‐trinitrofluorenone. In solution, the acceptor interacts with the core as the largest π‐surface, while in the solid material, it is incorporated between the arms and sandwiched by the star‐shaped neighbours along the columnar assemblies. The TNF acceptors are not nanosegregated from the star‐shaped donors, thus the liquid crystal structure converts to a nano‐reservoir for TNF (endo‐receptor). These host–guest arrangements are confirmed by comprehensive X‐ray scattering experiments and solid‐state NMR spectroscopy. This results in ordered columnar hexagonal phases at high temperatures, which change to helical columnar mesophases or to columnar soft crystals at room temperature. [ABSTRACT FROM AUTHOR]

The azo homologous series of (E)-2-chloro-3-((4-n-alkoxynaphthalene-1-yl) diazenyl) pyridine consisting of 11 homologs was synthesized. All homologs of synthesized homologous series are mesogenic in behavior. All homologs of the homologous series are enantiotropic nematic. The textures of the nematic phase are of the threaded or schlieren type. Transition curves showing phase behavior in a phase diagram behave in normal manner. An odd–even effect is observed for the nematic–isotropic transition curve. Thermal phase transitions were observed through an optical polarizing microscope equipped with a heating stage. Analytical and spectral data support the molecular structures of the homolog molecules. Smectogenic character is totally absent from all the novel homologs. [ABSTRACT FROM AUTHOR]

Stimulated by the paper that precedes this, our aim is to correct an error made concerning the twist-bend nematic phase and to place its development, both theoretical and experimental, in their proper context. The prediction starts with R.B.Meyer in 1973 but then jumps to 2001 and a different direction with I. Dozov and to 2002 with R. Memmer. There was then a gap until 2011 when a team of thirteen European scientists, while studying a liquid crystal dimer formed from achiral bent molecules, identified a nematic phase as the missing twist-bend nematic. This was based on a detailed study of its defining characteristics such as the chirality of the phase and its helicoidal structure with its degenerate handedness. This discovery proved to be of considerable interest and has prompted numerous investigations resulting in the discovery of many other mesogens forming the twist-bend nematic phase. However, as we shall see this view has not been universally shared; indeed, amongst others, Samulski, Vanakaras and Photinos claim that cyanobiphenyl mesogens instead of producing the NTB nematic, form the polar twisted phase, NPT so that the twist-bend nematic has yet to be discovered. It is this error that we shall correct.The Doubly Degenerate Heliconical Structure [ABSTRACT FROM AUTHOR]

We review the physics underlying Meyer's conjecture of how macroscopic-scale twist and bend conspire within the Frank-Oseen elasticity theory of nematics to create a heliconical arrangement of the uniaxial, apolar nematic director, the so-called 'twist bend nematic' NTB. We show that since 2011 a second, lower-temperature nematic phase observed in odd methylene-linked cyanobiphenyl dimers discovered by Toriumi and called NX, has been incorrectly identified as NTB. Moreover, as more quantitative data on the NX emerged, Meyer's simple prediction has been distorted to accommodate those findings. In fact, the molecular organisation in the NX conforms to the NPT phase, a polar, twisted arrangement of nonlinear mesogens advanced in 2016. The attributes of the NPT are summarised and differentiated from those of the NTB in an effort to contribute to a better understanding of the NX phase and, equally important, to encourage researchers to continue to search for a liquid crystal that exhibits Meyer's pioneering theoretical suggestion, namely that form-chirality can exist in simple nematics composed of achiral molecules. [ABSTRACT FROM AUTHOR]

The evolution of the liquid crystalline order during the cure of a reactive thermotropic liquid crystal (LC) is studied using two phenylethynyl-terminated biphenol and naphthalenediol model compounds. The nematic order in the melt of both model compounds at elevated temperature is monitored with X-ray Diffraction (XRD) and C-13 Nuclear Magnetic Resonance (13C NMR). XRD shows a cybotactic nematic phase; the global nematic order decreases with curing and eventually the resulting cross-linked liquid crystal thermoset (LCT) exhibits an isotropic morphology. The NMR method tracks the phenylethynyl end-group and yields data about the cure kinetics of this class of reactive LC mesogens. The observations may be used to make inferences about the cure behaviour and morphology of phenylethynyl-terminated random copolyester macromonomers. [ABSTRACT FROM AUTHOR]

In previous research, we have found that the incorporation of three lateral substituents on bent-core oxadiazole-based liquid crystals has allowed for the presence of a nematic phase that supercooled to room temperature. X-ray diffraction (XRD) studies of these derivatives have confirmed that the nematic phase consists of cybotactic clusters. Moreover, the wide-angle XRD pattern showed a splitting indicative of local biaxial ordering within this phase. In this paper, we report the phase behaviour of two series of compounds that contain up to four lateral methyl groups. In one series, the arrangement of the lateral groups is symmetrical, and in the other case, the groups are not symmetrically distributed. All of the non-symmetric derivatives supercool to room temperature in the nematic phase, while symmetric derivatives tend to crystallise well above room temperature. XRD analysis of all of these compounds indicates the presence of cybotactic order. However, a splitting of the wide-angle XRD pattern is observed only in derivatives with lateral groups on the outer benzene rings, regardless of their supercooling behaviour, indicating the crucial influence of these substituents on the molecular packing. [ABSTRACT FROM AUTHOR]

New bent-core mesogens with thiophene central ring were designed to obtain fluorescent and conductive liquid crystlline phases. Depending on the number of terminal chains and the length of lateral substituent at central unit either calamitic or columnar phases were formed. All the synthesised compounds showed high quantum efficiency of fluorescence in solution, ~0.9, that was however reduced to ~0.15 in condensed state. The light emitted from nematic or columnar phase was linearly polarised. Quenching of fluorescence in condensed state, together with observed red shift of emission maximum wavelength, evidenced formation of J-aggregates or weak excimers. Aggregation was also monitored by dynamic light scattering in water/tetrahydrofuran (THF) solutions. [ABSTRACT FROM AUTHOR]

Liquid crystalline elastomers (LCEs) have been actively investigated as stimuli‐controlled actuators and soft robots. The basis of these applications is the ability of LCEs to undergo a reversible shape change upon a liquid crystalline (LC)‐isotropic phase transition. Herein, we report the synthesis of a novel LCE based on a side‐chain liquid crystalline polymer (SCLCP). In contrast to known LCEs, this LCE exhibits a striking anomalous shape change. Subjecting a mechanically stretched monodomain strip to LC‐disorder phase transition, both the length and width of the strip contract in isotropic phase, and both elongate in LC phase. This thermally induced behaviour is the result of a subtle interplay between the relaxation of polymer main chain oriented along the stretching direction and the disordering of side‐group mesogens oriented perpendicularly to the stretching direction. This finding points out potential design of LCEs of this peculiar type and possible applications to exploit. [ABSTRACT FROM AUTHOR]

Transparency and stability to UV light are important and desirable properties for modern tunable optical elements and active soft robots. A library of novel reactive mesogens for liquid crystal polymer networks resilient and transparent to UV light has been synthetised and characterised. Phase behaviours of the reactive mesogens have been determined by polarised optical microscopy and differential scanning calorimetry. Liquid crystal polymer networks based on the combination of these novel reactive mesogens have been evaluated and compared to those based on common commercially available compounds. The results showed a twofold increase in transparency in a broad UV spectral region (200–400 nm) and importantly showed no degradation upon prolonged UV exposure contrary to the networks composed from commercial counterparts. [ABSTRACT FROM AUTHOR]

Photoresponsive linear liquid crystal polymers (LLCPs) are attractive because of the excellent stimuli-responsibility and the good processability. In this study, a new photoresponsive LLCP containing azoester (PC11AE6) with good mesophase stability was synthesized by ring-opening metathesis polymerization. By introducing photoresponsive azoester mesogenic unit, which has high rigidity and a large length-diameter ratio, the resultant polymer possesses a broad mesophase temperature interval (isotropic temperature = 180 °C). A study on mesophase by 2D-wide angle X-ray diffraction indicated that the mesogens were orientated spontaneously into smectic A phase after annealing. The orientated films and fibres exhibited macroscopic, rapid and reversible deformations under light irradiation as a result of the photoisomerization of azoester as confirmed by UV-Vis absorption spectrophotometry. We anticipate that this work provides a strategy for preparing LLCP with a broad mesophase temperature range, which is positive for potential applications. [ABSTRACT FROM AUTHOR]

Mechanical responses to electric stimulation in a liquid crystalline elastomer composed of cholesterol-derived mesogens were investigated. An electric-field-induced polar deformation resembling the motion of the flukes of a dolphin was observed in the temperature region of the pseudo-isotropic state of the elastomer prepared by cross-linking reaction under splay distortion. The emergence of polarisation was also confirmed above the SmA* to the pseudo-isotropic phase transition temperature, whereas no polarisation emerged in the SmA* phase. We tentatively conclude that the flexoelectric effect within splay distortion fixed by cross-linking caused the emergence of polarisation and the polar deformation. [ABSTRACT FROM AUTHOR]

A new Click procedure have been recently presented, in which a mixture of a female piece (star mesogen with shape-persistent conjugated arms and intrinsic free space) and a male building block (the same star mesogen sterically overcrowded with fullerenes attached via spacers to the arms) self-assemble in highly ordered filled liquid crystal structures. This self-assembly is based on the space-filling of the intrinsic free space and the nanosegregation of the fullerenes in helices. Here we highlight the synthesis of larger phthalocyanine star mesogens and fullerenes attached via long spacers and their mixtures as well as mixtures of the components with the stars of intermediate size and spacer length. While the system with long spacers do not show any alignment and π-stacking, the click procedure reappears successfully for the combination of a large female star and the intermediate male star. [ABSTRACT FROM AUTHOR]

Four new mesomorphic triphenylene-fused nitrogen-containing heterocyclic systems, including three benzimidazole and one perimidine derivatives with extended triphenylene core of different sizes are synthesised from the condensation reaction between aromatic diamines and our developed triphenylene dicarboxylic anhydrides. These discotic mesogens self-assemble into supramolecular columnar hexagonal mesophases with high clearing transition temperatures, demonstrating a strong tendency for π-stacking aggregation in the LC state owing to their good planar molecular structures. Four triphenylene-fused mesogens exhibit strong absorption bands in the range of 262 nm to 450 nm and corresponding emission bands between 468 nm and 615 nm, respectively. Both the experimental results and computational calculations show that the mesomorphic and electronic properties of four mesogens are strongly affected by the expansion of triphenylene core and the electronic nature of the nitrogenated benzimidazole or perimidine ring. Besides, these mesogens also possess higher HOMO energies and narrower HOMO-LUMO gaps than parent anhydride. Furthermore, the solution of TDPI or TDP in THF at a concentration as low as 0.45 wt % exhibited organogel phases due to strong intermolecular π-π interactions between the large aromatic cores. All these properties qualify this new type of discotic liquid crystals as potential applications as organic semiconductor materials and sensors. [ABSTRACT FROM AUTHOR]

Two partially fluorinated ferroelectric liquid crystals (2F3R, 3F3R) with biphenylyl benzoate core have been investigated by frequency domain dielectric spectroscopy and electro-optic method. Both the compounds exhibit SmC* phase over a wide range of temperature along with tilted hexatic phase SmF* and soft crystal phases SmJ* (in 2F3R) and SmG* (in 3F3R) and one coexistence phase of (SmF*+SmC*). Both BOO phason and tilt phason relaxations are observed in SmF* phase and cooperative relaxation behaviour is also observed in crystal-like smectic phases. Goldstone mode relaxation is observed in SmC* phase and Maxwell Wagner mode is observed in all the phases. In 2F3R soft mode is detected in both SmC* and SmA* phases but not in 3F3R which melts directly to isotropic phase from SmC* phase. Compounds possess moderate values of spontaneous polarisation and exhibit quite sharp electrical response especially in 2F3R. Rotational viscosities, pitch and elastic constant are also measured. Effect of chain length and fluorination on various physical parameters has been discussed. [ABSTRACT FROM AUTHOR]

Herein, we report selectively designed, synthesized and characterized bent-core molecules bearing methyl and chloro substituents at the lateral positions on the phenyl rings of the azobenzene wings. Preliminary structural characterizations were carried out using 1H NMR, IR and mass spectroscopy. The mesomorphic and photoswitching properties were studied by using polarizing optical microscopy (POM), differential scanning calorimetry (DSC) and UV-Vis spectroscopy. All of the bent-core mesogens exhibit liquid crystalline phases and excellent photo-switching behavior. When they were irradiated with a light of 365 nm wavelength, photo-saturation occurred in around 30 s and the system took a longer time to reach its original state during thermal back-relaxation. The photoisomerization of bent-core azo compounds is very crucial for creating optical storage devices with longer thermal back-relaxation times. The devices fabricated from these materials are excellent candidates for optical image storage applications. This study provides strong evidence for the structure–property relationship, where one can tune the structures according to their behavior. [ABSTRACT FROM AUTHOR]

A series of bent‐shaped 4‐cyanoresorcinol bisterephthalates is reported. Some of these achiral compounds spontaneously form a short‐pitch heliconical lamellar liquid‐crystalline phase with incommensurate 3‐layer pitch and the helix axis parallel to the layer normal. It is observed at the paraelectric‐(anti)ferroelectric transition, if it coincides with the transition from random to uniform tilt and with the transition from anticlinic to synclinic tilt correlation of the molecules in the layers of the developing tilted smectic phase. For compounds with long chains the heliconical phase is only field‐induced, but once formed it is stable in a distinct temperature range, even after switching off the field. The presence of the helix changes the phase properties and the switching mechanism from the naturally preferred rotation around the molecular long axis, which reverses the chirality, to a precession on a cone, which retains the chirality. These observations are explained by diastereomeric relations between two coexisting modes of superstructural chirality. One is the layer chirality, resulting from the combination of tilt and polar order, and the other one is the helical twist evolving between the layers. At lower temperature the helical structure is replaced by a non‐tilted and ferreoelectric switching lamellar phase, providing an alternative non‐chiral way for the transition from anticlinic to synclinic tilt. [ABSTRACT FROM AUTHOR]

Liquid crystal lenses have promise in optical systems owing to their tunability combined with low electrical power, cost, and weight. A good example of such a system is switchable contact lenses for the correction of age‐related presbyopia. Sufficiently large phase modulation can be done using nematic liquid crystals in a meniscus lens configuration. However, the birefringent materials are inherently polarisation dependent, usually requiring orthogonal polarisations to be focussed separately. A novel method is presented for producing polarisation independent lenses based on reactive mesogens. Results are presented for a 2‐level and 3‐level diffractive Fresnel lenses, and the promise of the technique for use in refractive lenses such as contact lenses is discussed. [ABSTRACT FROM AUTHOR]

Three new homologous series of coumarin heterocycles-derived mesogens have been synthesised and characterised. The symmetric dimers of coumarin contain two Schiff base moieties as connecting groups with phenyl or biphenyl central cores. Chemical structures were evaluated using IR, NMR and CHN analysis techniques. Thermal, mesophase behaviours and textural types were studied by DSC and POM instrumentations. The nematic mesophase was enhanced prominently for most of the compounds, and which is appeared in relatively medium to long alkyl chain at both terminals of the molecules. [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]

In the article "Ionic Conductivity Switchable and Shape Changeable Smart Skins with Azobenzene-Based Ionic Reactive Mesogens," researchers Kwang-Un Jeong and colleagues discuss the development of a new type of smart skin using a synthesized azobenzene-based ionic monomer. This liquid crystal elastomer (LCE) is capable of shape-changing and has switchable ionic conductivity. The researchers suggest that this new material could be used as a multi-responsive and reversible smart actuator and ionic skin for soft robotic applications. [Extracted from the article]

• Three series of AIE-active cyanostilbene-based amphiphilic mesogens with different degree of fluorination were synthesized. • The mesomorphic transition from Col hex / p 6 mm to Cub I / I m 3 ¯ m was achieved. • The increase in the degree of fluorination led to the disappearance of Cub I / I m 3 ¯ m. Three series of amphiphilic mesogens containing a cyanostilbene core with zero, one or two lateral fluorine atoms, which attach one polar glycerol group at one end and three lipophilic alkyl chains at the other end were synthesized by Suzuki coupling and Knoevenagel reactions. The thermodynamics, liquid crystalline and photophysical properties of these amphiphilic mesogens were evaluated by polarized optical microscopy, differential scanning calorimetry, small-angle X-ray diffraction, density functional theory calculation, absorption and emission spectra. The non-fluoro and mono-fluoro amphiphilic mesogens display a mesophase transition from hexagonal columnar phase to three-dimensional micellar cubic phase with I m 3 ¯ m lattice by the increase of temperature or the elongation of terminal lipophilic alkyl chains. The bi-fluoro amphiphilic mesogens can only self-organize into hexagonal columnar mesophase. Similar spectral properties and weak solvatochromism in these amphiphilic mesogens are observed attributed to the weak intramolecular charge transfer and weak influence of fluorine atom on the electronic properties in both ground and excited states. In addition, aggregation-induced emission behavior could be achieved in these amphiphilic mesogens due to the twisted molecular configuration. Therefore, complex self-assembly structures and interesting photophysical properties may be altered by varying the degree of fluorination of amphiphilic mesogens, which could promote the application of liquid crystalline materials. [Display omitted] [ABSTRACT FROM AUTHOR]

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.

Aiming at developing a new type of materials for functional applications, three series of new compounds were prepared, 3-(biphenylyl)-1,2,4-oxadiazoles, Series I; laterally mono-fluorinated 3-(biphenylyl)-1,2,4-oxadiazoles, Series II; and 5-(biphenylyl)-1,2,4-oxadiazoles, Series III. Liquid crystalline properties of these compounds were studied using differential scanning calorimetry and polarizing optical microscopy. Ten of the thirteen compounds in Series I are mesogenic forming either N or SmA phases depending on the length-to-width molecular ratio. Mesogens of the positional isomers, Series III are both N and SmA. Monofluorination of the biphenylyl group at either the central or the terminal phenylene rings, Series III, resulted in the formation of nematic mesogens with low phase transition temperatures and broad nematic phase range. [ABSTRACT FROM AUTHOR]

Wedge‐shaped molecules, such as dendrons, are among the most important building blocks for directed supramolecular self‐assembly. Here we present a new approach aimed at widening the range and complexity of potential mesophases by introducing double‐tapered mesogens. Two series of compounds are presented, both alkali metal salts (Li, Na, Cs) of 3,4,5‐tris‐alkoxybenzoic acid with a second tapered tris‐alkoxyaryl group attached at the end of an alkoxy chain. The double‐tapered compounds all display an unusual hexagonal columnar phase consisting of one ionic and three non‐ionic columns per unit cell. The cation size has an unexpectedly drastic effect on unit cell size. Unlike most columnar phases, the current phases show unusually high dimensional stability on heating, and high stiffness in spite of being 80–85 % aliphatic, attributed to their molecular topology. The described approach may lead to co‐assemblies of multifunctional materials, for example, parallel p‐ and n‐semiconducting nanowires or parallel ionic and electronic conductors. [ABSTRACT FROM AUTHOR]