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Bent-core liquid crystals (BCLCs) have high potential for device applications. However, efficient strategies for aligning them on suitable substrates, which is a necessary prerequisite, are limited. We have recently reported investigations on the alignment of BCLCs on indium tin oxide substrates chemically modified with BC compounds containing a dimethylchlorosilane moiety located either at the end of a terminal alkyl chain (BC-t) or a lateral alkyl chain (BC-l). We now report dielectric studies carried out to test the suitability of these substrates for quantitative studies, using the BCLC, C1Pbis-12BB. Comparisons made with Instec cells exhibiting homeotropic and planar alignment show that temperature and frequency-dependent responses exhibit typical trends expected of BCLCs and that BC-t substrates yield better alignment. Further, it is found that the BC molecules used for functionalizing the substrates do not affect the dielectric properties of the sample BCLC, showing that these substrates are stable and well-suited for device applications. [ABSTRACT FROM AUTHOR]

Here, we report the relationship between helical pitch of the helical nanofilament (HNF) phase formed by bent-core molecule NOBOW and the concentration of achiral dopants 5CB and octane, using linearly polarized resonant soft X-ray scattering (RSoXS). Utilizing theory-based simulation, which fits well with the experiments, the molecular helices in the filament were probed and the superstructure of helical 5CB directed by groove of HNFs was observed. Quantitative pitch determination with RSoXS reveals that helical pitch variation is related to 5CB concentration with no temperature dependence. Doping rodlike immiscible 5CB led to a pitch shortening of up to 30%, which was attributed to a change in interfacial tension. By shedding light not only on phase behavior of binary systems but also enabling control over pitch length, our work may benefit various applications of HNF-containing binary systems, including optical rotation devices, circularly polarized light emitters, and chirality transfer agents.

We introduce a mean-field theory to describe uniaxial and biaxial nematic phases in binary mixtures of banana-shaped molecules. We extend our previous theory for pure banana-shaped molecules to the binary mixtures and calculate phase diagrams on the temperature-concentration plane. We predict uniaxial-biaxial nematic phase transitions and Landau points in the binary mixtures. The biaxial nematic phases of banana-shaped molecules are promoted by mixing the two components with different bend angles. [ABSTRACT FROM AUTHOR]

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

Two types of binary mixtures were prepared. One consisted of a calamitic nematogen and bent-core molecule with a helical nanofilament, whereas the other contained a calamitic nematogen and bent-core molecule with a dark conglomerate. The chiroptical features of these two mixtures were investigated using polarized optical microscopy and circular dichroism. In addition, X-ray diffraction analysis was performed on the two binary mixtures. The chiroptical features of the two mixtures were remarkably different. One mixture showed enhanced chiroptical features, whereas the other did not show chiroptical features. This method may help in distinguishing between helical nanofilaments and dark conglomerates which originate from bent-core molecular systems. [ABSTRACT FROM AUTHOR]

In this paper, chiral intermediate phases composed of two achiral molecules are fabricated by utilizing nanophase separation and molecular hierarchical self-organization. An achiral bent-core guest molecule, exhibiting a calamitic nematic and a dark conglomerate phase according to the temperature, is mixed with another achiral bent-core host molecule possessing a helical nanofilament to separate the phases between them. Two nanosegregated phases are identified, and considerable chiroptical changes, such as circular dichroism and circularly polarized luminescence, are detected at the transition temperatures between the different nanophase-separated states. The nanosegregated chiral phase—wherein the helical nanofilament and dark conglomerate phases are phase-separated—exhibits the highest chiroptical intensities. The luminescence dissymmetry factor, |glum|, in this phase is amplified by an order of magnitude compared with that of another nanosegregated phase, wherein the helical nanofilament and nematic phases are phase-separated. [ABSTRACT FROM AUTHOR]

In this paper, a binary mixture system consisting of an achiral bent-core molecule and a bent-core base main-chain polymer is described. The mixture exhibits an intriguing nanosegregated phase generated by the phase separation of the helical nanofilament B4 phase (originating from the bent-core molecule) and the dark conglomerate phase (originating from the bent-core base main-chain polymer). This nanosegregated phase was identified using polarized optical microscopy, differential scanning calorimetry, and X-ray diffraction analysis. In this nanosegregated phase, the enantiomeric domains grew to a few millimeters and a giant circular dichroism was observed. The structural chirality of the helical nanofilament B4 phase affected the conformation of the bent-core base main-chain polymer embedded within the helical nanofilament networks of bent-core molecules. [ABSTRACT FROM AUTHOR]

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

Two types of binary mixtures were prepared. One consisted of a calamitic nematogen and bent-core molecule with a helical nanofilament, whereas the other contained a calamitic nematogen and bent-core molecule with a dark conglomerate. The chiroptical features of these two mixtures were investigated using polarized optical microscopy and circular dichroism. In addition, X-ray diffraction analysis was performed on the two binary mixtures. The chiroptical features of the two mixtures were remarkably different. One mixture showed enhanced chiroptical features, whereas the other did not show chiroptical features. This method may help in distinguishing between helical nanofilaments and dark conglomerates which originate from bent-core molecular systems.

In this paper, chiral intermediate phases composed of two achiral molecules are fabricated by utilizing nanophase separation and molecular hierarchical self-organization. An achiral bent-core guest molecule, exhibiting a calamitic nematic and a dark conglomerate phase according to the temperature, is mixed with another achiral bent-core host molecule possessing a helical nanofilament to separate the phases between them. Two nanosegregated phases are identified, and considerable chiroptical changes, such as circular dichroism and circularly polarized luminescence, are detected at the transition temperatures between the different nanophase-separated states. The nanosegregated chiral phase—wherein the helical nanofilament and dark conglomerate phases are phase-separated—exhibits the highest chiroptical intensities. The luminescence dissymmetry factor, |glum|, in this phase is amplified by an order of magnitude compared with that of another nanosegregated phase, wherein the helical nanofilament and nematic phases are phase-separated.

In this paper, a binary mixture system consisting of an achiral bent-core molecule and a bent-core base main-chain polymer is described. The mixture exhibits an intriguing nanosegregated phase generated by the phase separation of the helical nanofilament B4 phase (originating from the bent-core molecule) and the dark conglomerate phase (originating from the bent-core base main-chain polymer). This nanosegregated phase was identified using polarized optical microscopy, differential scanning calorimetry, and X-ray diffraction analysis. In this nanosegregated phase, the enantiomeric domains grew to a few millimeters and a giant circular dichroism was observed. The structural chirality of the helical nanofilament B4 phase affected the conformation of the bent-core base main-chain polymer embedded within the helical nanofilament networks of bent-core molecules.

The Landau theory of phase transitions with single-order parameter (second rank alignment tensor) has been applied to study the formation of modulated nematic phases in a melt of the symmetric V-shaped molecules. The arms of V-shaped molecule are modelled by rod-like segments composed of monomer units. Molecular architecture is determined by an external angle α between arms. The coefficients of the Landau–de Gennes free energy of melt have been found from microscopic model of V shaped particle. The phase diagram of the system contains regions of stability of the isotropic ( I ), uniform nematic N U , and modulated nematic phases ( N T B and N 0 ). Principal director (the eigenvector of the alignment tensor, which corresponds to the eigenvalue with the largest absolute value) in the N T B phase moves along the helix and forms a fixed acute angle with the helix axis. For the N 0 modulated phase the principal director is orthogonal to the helix axis while one of the two remaining directors is parallel to helix axis. [ABSTRACT FROM AUTHOR]

We investigate the relaxation of an energy functional that originated in the physics literature to study the bistability of polarization modulated orthogonal smectic phases SmAPFmod of bent-core molecule liquid crystals. We show that the interplay between the mixed boundary conditions and the shape of the sample results in boundary defects. We also analyze the bistable switching due to an applied electric field via gradient flow numerical simulations. Our computations reveal a novel dynamic scenario, where switching is achieved by the formation of two internal vortices. [ABSTRACT FROM AUTHOR]

In this paper, a simple and powerful method to control the induced handedness of helical nanofilaments (HNFs) is presented. The nanofilaments are formed by achiral bent-core liquid crystal molecules employing a cholesteric liquid crystal field obtained by doping a rod-like nematogen with a chiral dopant. Homochiral helical nanofilaments are formed in the nanophase-separated helical nanofilament/cholesteric phase from a mixture with a cholesteric phase. This cholesteric phase forms at a temperature higher than the temperature at which the helical nanofilament in a bent-core molecule appears. Under such conditions, the cholesteric liquid crystal field acts as a driving force in the nucleation of HNFs, realizing a perfectly homochiral domain consisting of identical helical nanofilament handedness.

A mean field theory is introduced to describe uniaxial and biaxial nematic phases of banana-shaped liquid crystalline molecules. From a geometric point of view, we derive the tensor order parameter of the banana-shaped molecules as a function of a bend angle and four orientational order parameters. Using the nematic free energy of the Maier-Saupe type, we calculate the phase diagram on the temperature − bend angle ( 0 < θ B < π) plane and find three uniaxial nematic ( N U i ) and three biaxial nematic ( N B i ) phases, where i (= a , b , c) is the primary axis of the orthogonal molecular axis. We also derive the approximate formulas of a nematic-isotropic phase transition ( N I T) and a biaxial-uniaxial phase transition ( B U T) temperature as a function of the bend angle. We also discuss the effects of the external field on the N I T temperature and find the negative dependence of the N I T temperature on the external field. [ABSTRACT FROM AUTHOR]

A mean field theory is introduced to describe cholesteric (Ch) phases of banana-shaped liquid crystalline molecules. From a geometric point of view, we derive the tensor order parameter of the banana-shaped molecules as a function of a bend angle () and four orientational order parameters. Using the tensor order parameter, we derive the free energy of the cholesteric phase for the banana-shaped molecules and obtain the approximate formula of a cholesteric-isotropic phase transition (CIT) temperature as a function of the bend angle. We find a cholesteric C phase for < 70.5 or > 109.5 where the the two arm vectors of the banana-shaped molecule tend to parallel to the director and a cholesteric C phase for 70.5 < < 109.5 where the two arm vectors tend to perpendicular to the director. These Ch phases are also distinguished by using the primary axis of the orthogonal molecular axis. [ABSTRACT FROM AUTHOR]

We construct a tensor model for nematic phases of bent-core molecules from molecular theory. The form of free energy is determined by molecular symmetry, which includes the couplings and derivatives of a vector and two second-order tensors, with the coefficients determined by molecular parameters. We use the model to study the nematic phases resulting from the hardcore potential. Unlike most macroscopic models, we are able to obtain the phase diagram about the molecular parameters, but not merely some phenomenological coefficients. The tensor model is applicable to other molecules with the same symmetry, which we demonstrate by studying the phase diagram of star molecules [ABSTRACT FROM AUTHOR]

In this study, a polymerized twisted nematic (TN) network was used as an extrinsic chiral platform to overcome the heterogeneity during spontaneous symmetry breaking in a mixed system comprising an achiral bent-core molecule and rod-like mesogen. The TN platform was prepared by photopolymerizing a reactive mesogen dispersed in a low molecular weight liquid crystal with TN orientation. The use of TN orientation to correct the degeneracy in bent-core molecular systems has been previously reported; however, to the best of our knowledge, this is the first study that uses an extrinsic chiral platform of a polymerized TN network. The heterogeneity in the nano-segregated phase of the achiral mixture was suppressed using the extrinsic TN platform with a twisted angle θ of ≥ |±30°|. When an achiral mixture doped with a luminescent guest molecule was refilled into the extrinsic chiral platform, preferential deracemization with one-handedness occurred, corresponding to the handedness of the TN platform. Therefore, circularly polarized luminescence with a preferential handedness can be achieved using this extrinsic chiral platform.

Although several methods exist for the synthesis of circularly polarized luminescent (CPL) materials, the methods are extremely complex and tedious. In recent years, the chiral host-achiral luminescent guest method and the achiral host-achiral luminescent guest method have been employed to fabricate CPL materials; however, the main disadvantage of the latter is the small luminescence dissymmetry factor (glum) that limits the practical applications of the method. Therefore, this study reports on the enhancement of glum in a nano-segregated phase system, generated by the phase separation between helical nanofilaments (HNFs; originating from an achiral bent-core molecule) and a liquid-crystalline (LC) smectic A (SmA) phase (originating from an achiral rod-like mesogen). The observed glum value in the nano-segregated phase between the HNFs and LC SmA phase was larger than that in the nano-segregated phase between the HNFs and LC nematic (N) phase. The enhancement of the glum value was attributed to the order parameter (S) of the dye molecules in the SmA phase being larger than that in the N phase. Therefore, we concluded that the S value of the fluorescent dye molecules, doped into the embedded LC phase between the HNFs, strongly influenced the glum value.

The bent-core B1RevTilted phase is a smectic tilted columnar phase in which the macroscopic polarization can be reversed via an electric Field. In the switching, the molecules can rotate either around the tilt cone or around the molecular axis, with one mechanism preferred over the other depending on various properties of the material. In this paper, we compare a local and a nonlocal Landau-de Gennes-type energy functional modeling this phenomenon, and show that for small polarization splay coefficients they give the same qualitative behavior. The explicit form of the limiting functional allows us to also characterize the parameter regime where switching around the molecular axis is preferred. Finally, we describe the setup needed to obtain a standard existence result for the L²-gradient ow in metric spaces of the full local energy. [ABSTRACT FROM AUTHOR]

Dielectric spectroscopy in the frequency range from 10−2 to 107 Hz was applied to investigate the dynamics of the relaxation processes in a banana-shaped liquid crystal compound with fluorinated chain segments. The dielectric spectra indicate the presence of two relaxation processes and a conductivity contribution. The high-frequency process shows Arrhenius-like temperature dependence in the B4 and SmCP phases and can be assigned to the hindered rotation of the bent-shaped molecules around their long molecular axis. The low-frequency process can be related to the dynamics of the periodic superstructures in B4 phase and fluctuations of the modulated ferroelectric domains in the SmCP phase. In the B7 (or SmCG) phase, both processes show the nonlinear dependence of the relaxation frequencies especially close to the isotopic phase transition. The dielectric measurements confirm the existence of the SmCP - B7 (or SmCG) second order or weakly first-order phase transition. [ABSTRACT FROM AUTHOR]

The effects of molecule structure and concentration of achiral bent-core molecules on the blue phase liquid crystal stabilization have been investigated. Blue phase mixtures are formed doping bent-core molecules and BP temperature range is able to widen doping bent-core molecules with different substituents. Bent-core molecules with different substituents are found to cause a decrement in the threshold and turn-on voltages of the bent-core doped blue phase liquid crystal samples, as a result of the difference in their molecular shape and dipole moments. Use of bent core LC as dopants for a blue phase LC mixture led to a reduction of the driving voltage by more than 50%. [ABSTRACT FROM AUTHOR]

We construct the molecular model and the tensor model for the dynamics of the nematic phases of bent-core molecules and star molecules in incompressible fluid. We start from the molecular interaction and the molecule–fluid friction, and write down a general formulation based on the molecular shape and the free energy. Then we incorporate an Onsager-theory-based static tensor model to obtain the dynamic molecular model fully determined by the molecular architecture. The tensor model is obtained by adopting the quasi-equilibrium approximation that maintains energy dissipation. For bent-core molecules and star molecules that have the same molecular symmetry, the form of the model is identical. The molecular architecture is differentiated by the coefficients that are derived as functions of molecular parameters. Numerical simulation is carried out for the shear flow problem using both the molecular and the tensor models, focusing on the effect of altering molecular architecture. When the equilibrium phase is biaxial, novel flow modes are found, and the flow mode sequences show delicate dependence on the molecular architecture. The tensor model proves to exhibit all the flow modes found in the molecular model. [ABSTRACT FROM AUTHOR]

The orientational elasticity of the uniaxial and the biaxial nematic phases is deduced earlier. For bent-core molecules with hardcore interaction, we examine how the molecular shape affects the elastic constants of these phases. The calculation is built on a tensor model based on the Onsager theory. The elastic constants are expressed by the coefficients in the tensor model, and these coefficients are derived from molecular parameters. We calculate the elastic constants of bent- core molecules as functions of the bending angle, concentration and thickness. We also examine the elastic constants of star molecules, where we focus on the effect of the extra arm. [ABSTRACT FROM AUTHOR]

Bent-core materials exhibiting lamellar crystals (B4 phase), when dissolved in organic solvents, formed gels with helical ribbons made of molecular monolayers and bilayers, whereas strongly deformed stacks of 5-6 layers were found in the bulk samples. The width and pitch of the helical filaments were governed by molecular length; they both increased with terminal-chain elongation. It was also found that bulk samples were optically active, in contrast to the corresponding gels, which lacked optical activity. The optical activity of samples originated from the internal structure of the crystal layers rather than from the helicity of the filaments. A theoretical model predicts a strong increase in optical activity as the number of layers in the stack increases and its saturation for few layers, thus explaining the smaller optical activity for gels than for bulk samples. A strong increase and redshift in fluorescence was detected in gels as compared to the sol state. [ABSTRACT FROM AUTHOR]

We consider a model originally introduced to study layer-undulated structures in bent-core molecule liquid crystals. We first prove existence of minimizers, then analyze a simplified version used to study how in columnar phases the width of the column affects the type of switching, which occurs under an applied electric field. We show via Γ-convergence that as the width of the column tends to infinity, rotation around the tilt cone is favored, provided the coefficient of the coupling term, between the polar parameter, the nematic parameter, and the layer normal is large. [ABSTRACT FROM AUTHOR]

The dielectric response of the ferroelectric smectic-A phase made of bent-core molecules in thin planar cells in low bias field is studied theoretically. The dependence of the analytically calculated phase mode frequency on the cell thicknesses and magnitude of the bias field is compared to the dependencies obtained by numerical calculations and recently reported experimental measurements, which show that in thin planar cells the phase mode frequency decreases with increasing bias field. [ABSTRACT FROM AUTHOR]

Bent-core smectic liquid crystal (LC) phases (B phases) have been widely studied since their unusual polar and chiral properties were discovered in the 1990s. Relatively few studies have examined the mechanisms by which the orientation of the B phase may be controlled to produce the type of macroscopic domain that is essential for organic semiconductor, optical device and patterning applications. This review is intended to cover recent progress towards controlling the B phases upon layering, including anisotropic treatment methods and topographical confinement methods. Finally, this review closes with a discussion of B smectic phases that have been fabricated for use in certain applications. [ABSTRACT FROM AUTHOR]

Density functional theory is used to describe the phase behaviors of rigid molecules. The construction of the kernel function is discussed. Excluded-volume potential is calculated for two types of molecules with C symmetry. Molecular symmetries lead to the symmetries of the kernel function and the density function, enabling a reduction of configuration space. By approximating the kernel function with a polynomial, the system can be fully characterized by some moments corresponding to the form of the kernel function. The symmetries of the kernel function determine the form of the polynomial, while the coefficients are determined by the temperature and molecular parameters. The analysis of the impact of coefficients helps us to choose independent variables in the moments as order parameters. Combining the analysis and some simulation results, we propose a minimal set of order parameters for bent-core molecules. [ABSTRACT FROM AUTHOR]

Herein, two asymmetric chiral bent-core molecules, 3-[(4-{[4-(heptyloxy)benzoyl]oxy}benzoyl)oxy]-phenyl-4-[(4-{[(1 R)-1-methylheptyl]oxy}benzoyl)oxy] benzoate (BC7R) and 3-[(4-{[4-(heptyloxy)benzoyl]oxy}benzoyl)oxy]-phenyl-4-[(4-{[(1 S)-1-methylheptyl]oxy}benzoyl)oxy] benzoate (BC7S), were synthesized to demonstrate control of the helicity of their self-assembled hierarchical superstructures. Mirror-imaged CD spectra showed a split-type Cotton effect after the formation of self-assembled aggregates of BC7R and BC7S, thereby suggesting the formation of intermolecular exciton couplets with opposite optical activities. Both twisted and helical ribbons with preferential helicity that corresponded to the twisting character of the intermolecular exciton couplet were found in the aggregates. The formation of helical ribbons was attributed to the merging of twisted ribbons through an increase in width to improve morphological stability. As a result, control of the helicity of hierarchical superstructures from the self-assembly of bent-core molecules could be achieved by taking advantage of the transfer of chiral information from the molecular level onto the hierarchical scale. [ABSTRACT FROM AUTHOR]

The important parameter of the mesogens which governs nearly all fascinating physical properties is its order parameter. In the biaxial liquid crystals (LCs), there are two order parameters: primary (long axis) and secondary (short axis). The secondary orientational order parameter (η) of an achiral bent core (BC) LC material with terminal alkyl chain length 8 was estimated from the temperature dependent field induced biaxiality measurements in SmAPA phase for the first time. The Haller's extrapolation technique is used for the estimation of η as it can directly apply to biaxiality measurements rather than to refractive indices. [ABSTRACT FROM PUBLISHER]

Non-polar biaxial SmAb mesophase was observed in a 4-cyanoresorcinol bisbenzoate with two terephthalate–based wings bent-core (BC) compound (PAL 29) having 16 carbon atoms in the terminal alkyl chain. Electro-optic and dielectric properties of this phase have been studied in detail. The biaxial SmAb phase transforms to ferroelectric state by the application of higher voltage. The field dependent biaxiality is very small and the polarizing microscopic texture observations support the corresponding measurements. Dielectric study exhibits two relaxation processes in the polar phase temperature region and one in the apolar biaxial SmAb phase. [ABSTRACT FROM PUBLISHER]

We present the properties of different achiral orthogonal polar smectic phases observed in a homologous series of bent-core molecular compounds. The macroscopically uniaxial SmAPR phase transforms to biaxial state by the application of higher electric fields and biaxial SmAPA phase undergoes biaxial-uniaxial-biaxial texture transformation with increasing electric fields, i.e., initial antiferroelectric structure transforms into ferroelectric state under higher electric fields and it shows three different optically distinguishable states. The SmAPAR phase shows an entirely different response compared to other polar smectic phases under study. The dielectric measurements in the SmAPAR phase is the evidence of antiferroelectric behavior of uniaxial state. The polarizing microscopy texture observation supports the corresponding biaxiality measurements. [ABSTRACT FROM PUBLISHER]

The mesomorphic properties of a homologous series of achiral bent-core compounds are studied by polarizing optical microscopy, electro-optics and polarization measurements. Induction of a new orthogonal smectic phases with the increase of alkyl side chain length was observed. One of the compounds exhibits a unique phase transition between four non-tilted smectic phases (SmAPA–SmAPAR-SmAPR-SmA). The uniaxial but antiferroelectric nature of SmAPAR phase was confirmed by POM, current response, the 2nd harmonic electro-optic response and polarization measurements. The structure of SmAPAR phase was studied theoretically by Next-Nearest-Neighbor model and was identified as SmAPα. [ABSTRACT FROM PUBLISHER]

We report the observation of biaxial nematic phase in a bent-core molecular system in which the biaxiality exists on a microscopic scale using polarizing microscopy, electro-optics and dielectric spectroscopy. An application of electric field induces a macroscopic biaxiality and therefore electro-optic switching. The observed electro-optic switching is explained in terms of the interaction of the ferroelectric clusters with the electric field. Dielectric spectra of the sample shows existence of low-frequency collective processes related to the microscopic polar clusters. The dielectric constant changes its sign from positive to negative and again to positive values. [ABSTRACT FROM AUTHOR]

We report the structural and relaxation investigations of an achiral bent-core compound in SmAPA phase. The studied material undergoes transition from one biaxial state to the other via a uniaxial state under electric field. These transformations are explained as successive transition from antiferroelectric to ferroelectric states, where, the intermediate uniaxial state has the molecular secondary directors in the neighbouring smectic layers perpendicular to each other. We also found that near SmAPR to SmAPA phase transition the second harmonic electro-optic response, induced polarization, and the dielectric behaviour hint softening behaviour in the material. [ABSTRACT FROM AUTHOR]

Mesostructures in inversed Langmuir-Schaefer films of each of two contrasting bent-core molecules are explored via atomic force microscopy. One of the molecules forms Langmuir films that are optically isotropic and the other those that are optically anisotropic. Both show suboptical mesostructures in the 100 nm range, in spite of appearing optically uniform. The anisotropic films are effective in aligning nematic bent-core samples, but not rod-like liquid crystals such as 5CB. [ABSTRACT FROM AUTHOR]

The dielectric relaxation behavior of a bent-core liquid-crystalline (BC) material showing B2 phase and its 17% mixture with another rod-like material (R-BC) has been investigated. The appearance of a newly induced B1 phase has been detected in the R-BC system. We found comparatively lower value of dielectric permittivity of the R-BC system than that of BC material. Moreover, a lower value of relaxation frequency of the long axis rotation mode in BC material compared to that of the R-BC material has been observed. These results have been discussed on the basis of molecular origin for the formation of B phases in the materials. [ABSTRACT FROM AUTHOR]

In the present work, oxalic amorphous porous anodic alumina membranes with highly ordered porous arrays and average nanometric porous dimensions of 70 nm in diameter and 17 microns in depth (nanotubes) were prepared and successfully used as host matrix for fluorinated bent-core liquid crystals. Atomic force microscopy studies were performed on the organic-inorganic hybrid samples in order to explore surface morphology and optimal insertion of these liquid crystalline (LC)-compounds into this environment. The quadratic nonlinear optical (NLO) and spectroscopic properties of the implemented mesogen with the nanotube-like confinement were systematically studied in order to evaluate its optical performance. Bent core molecules have shown interesting optical properties which have not yet been intensively investigated in solid-state hybrid structures. Hence, the obtained hybrid composites represent a promising field of investigation in the route to functional bent-core based materials, where different bent-core mesomorphic structures can be obtained and are of interest for new and improved applications in nanotechnology. [ABSTRACT FROM AUTHOR]

The article presents an experiment on the influence of bias field on the dielectric spectra of smectic B2 phase of bent-core molecules. The experiment utilizes the bias field to partially align B2 phase to conduct spontaneous polarization measurements in 1,3-Phenylene bis(4-[(4-dodecyloxybenzoyl)sulfanyl]- benzoate) (12OSOR) and 12R9AF mixture. Results show that both materials are antiferroelectric in B2 phases based from the polarization measurements.

Soft matter results from relatively weak interparticle interactions. Liquid crystals exhibit the largest variety of soft matter, and have fascinating physical properties and technological applications. de Gennes showed that the seemingly complex properties are often amenable to phenomenological descriptions, based on the underlying macroscopic symmetry of the medium. The latter ultimately depends on subtle intermolecular interactions, as exemplified by the discoveries of new types of liquid crystals made of banana-shaped (or bent-core (BC)) molecules. In this article, we review some aspects of these liquid crystals, with an emphasis on our own contributions. These include a simplified theoretical description of the most frequently observed B6-B1-B2 sequence of phases in homologous series of compounds with BC molecules, experimental studies on induced phases in mixtures of compounds with BC and rod-like molecules and on some novel properties exhibited in the nematic phase of such mixtures. [ABSTRACT FROM AUTHOR]

We implemented the catalyst-free sonogel method to disperse and encapsulate a chlorine substituted thermotropic bent shaped liquid crystalline compound. By this means, advanced organic-inorganic hybrid materials with high optical and mechanical quality, suitable for different kind of optical applications, were obtained. Bent-core molecules have shown interesting optical properties, which have not yet been investigated in the solid-state. Therefore, we implemented the sonogel route to fabricate highly pure SiO2 porous glassy networks which allowed the inclusion of this kind of mesogens in the colloidal sol-state. In this work, we present the preparation and optical performance of these amorphous “banana”-based hybrids via absorption and fluorescence spectroscopies, electro-optical and cubic third-harmonic generation nonlinear optical measurements. [ABSTRACT FROM AUTHOR]

Recently a theoretical model of the polarization modulated and layer undulated (B7) structure in the systems formed by bent-core (bow-shaped) molecules was presented. In contradiction to the general expectation the model suggests that polarization splay is possible only when the molecules are tilted with respect to the layer normal, i. e. when the chiral symmetry of the system is broken. In this paper we present a detailed stability analysis of the tilted and the nontilted structure with respect to polarization modulation and show, that polarization modulation in the nontilted phase is not possible because the system has no possibility to relieve the stress in the domain walls, neither by bending the layers nor by reducing the smectic order. [ABSTRACT FROM AUTHOR]

To investigate the vacuum-deposited films of the banana-shaped mesogens, we prepared a three-ring bent-core (that is, banana-shaped) compound m-bis(4-poctoxysryrenyl)benzene (m-OSB) and used it as a prototype for studying the related film physics. Herein the synthesis and the structural characterization of m-OSB are reported. 13C and ¹H NMR spectra and IR spectrum confirm that m-OSB has a symmetric and all-trans conformation. The results of differential scanning calorimetry, polarizing optical microscopy and X-ray diffractometry indicate that no liquid crystalline phase but two crystalline phases are present in this material: phase I (T<66°C) and phase II (66°C

In this paper, a simple and powerful method to control the induced handedness of helical nanofilaments (HNFs) is presented. The nanofilaments are formed by achiral bent-core liquid crystal molecules employing a cholesteric liquid crystal field obtained by doping a rod-like nematogen with a chiral dopant. Homochiral helical nanofilaments are formed in the nanophase-separated helical nanofilament/cholesteric phase from a mixture with a cholesteric phase. This cholesteric phase forms at a temperature higher than the temperature at which the helical nanofilament in a bent-core molecule appears. Under such conditions, the cholesteric liquid crystal field acts as a driving force in the nucleation of HNFs, realizing a perfectly homochiral domain consisting of identical helical nanofilament handedness. [ABSTRACT FROM AUTHOR]