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[Display omitted] • Binary mixtures of bent-core liquid crystals show columnar and smectic phases with good miscibility. • All mixtures show mesomorphic behaviour, with reductions in their clearing points and liquid crystalline ranges. • The mixtures show strong dielectric response mainly promoted by the presence of ester groups in the bent-core molecules. • Reversible trans -to- cis photoisomerization of azobenzenes is applied to tune the molecular dipole moment, assessed by DFT. • Irradiation increases the conductivity of the equimolar mixture by two orders of magnitude. We report the mesomorphic behaviour, dielectric and ferroelectric properties, and computational modelling of binary mixtures containing two bent-core liquid crystals: the so-called NG75-COO (3,4́- Bis[4-(4-n-tetradecyloxybenzoyloxy)benzoyloxy]biphenyl), which forms smectic phases, and IP31- AzB (3,4′ - Bis[4-(4-n-tetradecyloxyphenylazo)benzoyloxy]biphenyl), which forms columnar phases. The phase diagram, assessed by polarised optical microscopy, shows that the binary mixtures retain the mesophase behaviour of the major component, whilst the equimolar mixture displays smectic-type phases. Dielectric and ferroelectric analyses were carried out on samples containing 10%, 50%, and 90% of IP31-AzB (molar %), and we also investigated structure–property correlations by differential functional theory. The NG75-COO/IP31-AzB mixtures undergo strong dielectric and ferroelectric response due to the presence of highly polarisable groups in the bent-core components, particularly at the ester groups. All the mixtures under study exhibit light-responsiveness induced by reversible E -to- Z photoisomerization (trans -to- cis) of the azobenzene group in IP31-AzB, together with an increase in the molecular dipole moment. The potential to tune the phase behaviour of the mixtures, as well as their dielectric and ferroelectric responses, are investigated by light irradiation under different conditions of intensity and temperature. [ABSTRACT FROM AUTHOR]

Abstract Nano-doping of bent-core liquid crystals are of recent interest because the blending of bent-core liquid crystals with nanoparticles opens a new avenue both for fundamental research and the development of smart materials with desired properties for different types of applications. A four-ring achiral bent-core liquid crystal possessing only the nematic phase was doped with titanium dioxide (TiO 2) nanoparticles and its dielectric and electro-optical properties are investigated. The experimental result shows both an increase in the moving ion concentration and a drastic increment in the dielectric permittivity of the doped sample. The large increase in the dielectric permittivity at lower frequency is due to the combined effect of space charge polarization and the change in the viscosity of material due to dilution effect. Due to dilution effect, the transition temperature of all the doped samples is decreased by about 10 °C–13 °C. Highlights • Addition of TiO 2 nanoparticles changes the transport properties of bent-core LCs. • Modification of transport properties is due to increase in ions concentration. • The transition temperature of the doped sample decreases by about 10 °C–19 °C. • The decrease in transition temperature is attributed to dilution effect. • Useful for display and non-display based application depending on ions in LCs. [ABSTRACT FROM AUTHOR]

[Display omitted] • Bent-core liquid crystals containing tetra(ethylene-oxide) moieties were doped with lithium triflate salts. • The doped materials display smectic mesophases inside indium tin oxide cells. • Lithium ions are selectively solvated in the ethylene-oxide blocks. • The presence of lithium ions promotes direct current conductivity at low frequencies. • The materials show potential as new nanostructured electrolytes, controllable by light irradiation. We report the dielectric and conductivity response of three materials containing bent-core and tetra(ethylene-oxide) moieties, and their complexes doped with lithium triflate salts, as new potential nanostructured electrolytes. Whilst the pristine bent-core compounds do not show mesomorphism, the doped materials display smectic mesophases inside indium tin oxide cells assisted by the selective solvation of the lithium ions in the ethylene-oxide blocks. The dielectric response of the materials in the high-frequency range is controlled by the chemical composition of the bent-core structure, and the presence of lithium ions promotes direct current conductivity at low frequencies, in the σ dc ∼ 10-5 S cm−1 range, which can be enhanced to σ dc ∼ 10-4 S cm−1 via trans -to- cis photoisomerization of azobenzene groups. The dynamic and dual character of these materials (responding to low and high frequency electrical fields), the formation of ferroelectric crystals capable to store energy, and their interactions with light, will be applied to develop new energy devices. [ABSTRACT FROM AUTHOR]

[Display omitted] • New symmetrical fluorurated bent-core molecules are reported. • Compounds organize into SmC s P A and SmC A P A antiferroelectric structures. • High values of polarisation (900–600 nC/cm2) were obtained. • Bent-core compounds are good candidates for high power capacitors. The synthesis of several symmetrical bent-core compounds with two or four fluorine atoms as substituents on the calamitic units is reported. The influence of fluorine substitution concerning its effect upon the mesophase structure and switching behavior was investigated. The synthesized compounds are built from resorcinol as central core and contain seven phenyl rings linked by ester, imine and azo units with terminal decyloxy/dodecyloxy chains. The mesophases were characterized by polarizing optical microscopy, differential scanning calorimetry, electro-optical investigations and X-ray diffraction (XRD) studies. The photochemical characterisation of bent-core azobenzene compounds confirmed the structure of E isomer. The temperature range of mesophases increases upon the introduction of fluorine substituents, as compared with the corresponding unsubstituted compound. All the compounds exhibit antiferroelectric properties. Depending on the number of the F substituents, racemic SmC S P A mixtures and SmC A P A homochiral structures were identified. High values of spontaneous polarization up to 900 nC/cm2 were recorded. DFT studies were used to calculate the minimum energy molecular structures, the dipole moments and the electrostatic potential surfaces of the compounds. [ABSTRACT FROM AUTHOR]

[Display omitted] • Triazole bent-core mesogens based on bis -1,2,3-triazoles were synthesized. • The triazoles exhibited mesogenic phase transition over a wide temperature range. • The mesophases and textures were studied by employing POM, DSC, and XRD. • SEM investigation revealed highly ordered columnar architectures of the compounds. • The self-assembly was driven by van der Waals and π-π stacking interactions. Triazole bent-core mesogens based on symmetrical bent-shaped of two 1,2,3-triazole ring arms were synthesized and characterized. The the thermail stability of those new synthesised mesogens from the embient temperature to 215 °C giving mesogenic phase transitions over a wide temperature range is investigated. A study of different substituents located on the rigid bentcore was carried out for compact supramolecular innovated architectures which were produced by self-assembly of many triazoles soft crystals with a liquid crystals behaviour. The synthetic procedures, characterizations and polymorphism of four novel bent-core mesogens comprising symmetrical 1,2,3-triazole arms were demonstrated. The preparation process was carried out through"click chemistry" via Cu-catalyzed azide-alkyne cycloaddition of nitro- and alkyl-substituted aromatic azides with aromatic compounds, comprising terminal alkyne groups and long alkyl or alkoxy side-chains. The triazole derivatives were fully characterized by 1H/13C NMR, Fourier-transform infrared spectroscopy (FTIR) and elemental analysis. The mesophases and textures were examined by employing polarizing optical microscope (POM), differential scanning calorimetry (DSC) and X-ray Diffraction (XRD). The analogues with shorter alkoxy terminal substituents displayed higher mesomorphic properties with wide mesomorphic temperature ranges compared to analogues with shorter alkoxy terminals. The morphological characteristics of the self-assembled triazoles were investigated by scanning electron microscopy (SEM) which demonstrated arrangement of highly ordered columnar architectures. These orders were driven by layer to next layer adjacent influences and π-π stacking. The effect of 1,2,3-triazole ring and length of terminal aliphatic chains on the liquid crystalline performance were discussed. Through an appropriate choice of lateral structures employing "click chemistry", both transition temperature and mesophases ranging from isotropic to columnar or B1/B4-like supramolecular liquid crystalline aggregates can be tuned. [ABSTRACT FROM AUTHOR]

• The synthesis of bent-core amphiphiles with a TEG tail and their materials containing [1/1] lithium ions are reported. • TEG-decorated bent-core molecules are versatile amphiphiles to build nanostructured soft materials. • The Li-doped materials stabilize layered bent-core liquid crystal phases such as the SmCP or HNF-like organizations. • The compounds form organogels with nonpolar solvents that provide platelets, helical fibers, and tubular morphologies. • By self-assembly, non-chiral bent core-based materials transfer conformational chirality to nanostructures. The synthesis, supramolecular self-assembly and structural characterization of a new family of tetraethylene oxide (TEG)-based bent-core compounds and their 1/1 lithium-containing complexes are reported. TEG-based bent-core amphiphiles, even joining the TEG/Li+ tandem, are suitable building-blocks to achieve supramolecular nanostructures, in some cases showing chiral features from achiral molecules either in the mesophase or in solvents. The thermal and liquid crystal behavior of these materials studied by polarizing optical microscopy and X-ray diffraction confirmed that Li-based materials stabilized polar smectic C and helical nanofilament-type mesophases, in contrast to the non-liquid crystalline pure TEG-compounds. Alternatively, both the pure amphiphiles and the lithium-doped materials self-assemble into physical gels in non-polar solvents, displaying three-dimensional networks composed of long fibers with lamellar molecular organizations as shown by transmission electron microscopy and X-ray diffraction. Interestingly, biphenyl- and azobenzene-based bent core amphiphiles aggregate in solvent into chiral nanostructured morphologies with supramolecular trends comparable to their molecular arrangement in their liquid crystalline phases. [ABSTRACT FROM AUTHOR]

The right- and left- handed helices of the twist bend nematic phase arising from the chiral symmetry breaking of achiral molecules. [Display omitted] • Largest negative dielectric anisotropy in N and N TB phases observed so far. • Determination of the spontaneous polarization. • Pyroelectric technique and its advantages. • Electro-optics in terms of first and second harmonics. • Dielectric data in terms of dielectric strength and frequency. Experimental and theoretical investigations of the twist-bend nematic (N TB) phase in liquid crystals have recently received significant attention for reasons of unusual and interesting characteristics of the N TB. Though N TB was predicted to exist for rigid bent-core LCs by Ivan Dozov in 2001, nevertheless it has unambiguously been proven to exist only in a few bent-core systems so far. Here the characteristics of both the nematic (N) and N TB phases are investigated for a hockey shaped achiral rigid bent-core LC, called BCI, in planar and homeotropic aligned cells, using polarizing optical microscopy, electro-optics, pyroelectricity and wide band dielectric spectroscopy. Spontaneous polarization measured for a bias field of 2.2 V/μm of a chiral domain using the pyroelectric effect is found to be only ∼5 nC/cm2. A measurement of the spontaneous polarization using pyroelectricity in general is unaffected by the sample's dc conductivity except when its conductance dominates the admittance. As helix of N TB is partially unwound by the field, results lead to the identification of N TB as polar and chiral. The first and the second harmonics of the applied field are observed of higher amplitudes in N TB and N phases, respectively. The hockey-shaped bent-core system exhibits a large negative dielectric anisotropy over a wide range of temperatures than observed for any other compound so far. The large negative dielectric anisotropy is the highly desirable characteristic parameter of the N TB for exploring the field induced phases at relatively lower field strengths. The orientational order parameter characteristically jumps at the N-N TB transition temperature. The complex dielectric permittivity is measured as a function of frequency in the range 1 Hz to 10 MHz, the analysis of results reveales two collective modes in the dielectric spectra. Amplitude of the lower frequency mode is much higher than of higher frequency, former is assigned to the hydrodynamic mode q = q z z ^ with z-dependent rotation of the heloconical director n ^ (r ), this in turn involves compression and dilation of the pseudo-layers. The higher frequency mode corresponds to fluctuations of the tilt director and closer to the transition temperature, it exhibits a typical soft mode characteristic feature. [ABSTRACT FROM AUTHOR]

• First examples of photo-sensitive hockey-stick polycatenar liquid crystals are reported. • The liquid crystal self-assembly was characterized by DSC, PLM and XRD. • Network formation in addition to transition from 1D to 3D liquid crystalline phases are observed. • Fast and reversible photo switching between different types of liquid crystalline phases is achieved. Photo switchable liquid crystalline (LC) materials are of great interest for optical and photonic applications. Herein we report the design, synthesis, and molecular self-assembly of the first examples of photosensitive hockey-stick (HS) polycatenars. Therefore, two new series of HSLCs derived from 4-cyanoresorcinol bent-core unit connected to a short azobenzene-based side arm with one variable alkoxy chain and a long ester-based wing terminated with two alkoxy chains at 3 and 5 positions of the terminal benzene ring are reported. They differ from each other in the length of the terminal chains connected to the long arm. The LC self-assembly of these HSLCs was investigated by polarized optical microscopy (POM), differential scanning calorimetry (DSC), X-ray diffraction (XRD) and electro optical investigations. Depending on length of terminal chains a transition from one dimensional (1D) tilted and non-tilted smectic phases to three dimensional (3D) achiral bicontinuous cubic phases with Ia 3 ¯ d symmetry (Cub bi / Ia 3 ¯ d) upon chain elongation is observed. Moreover, achiral isotropic liquid networks were observed for medium and long chain homologues. Most of mesophases are room temperature LCs phases with wide ranges as observed in the cooling cycles, where once they are formed on heating, no sign of crystallization is detected down to ambient temperature. Finally, UV light irradiation results in fast and reversible photoinduced transformation between different types of LCs phases as well as between LC phase and isotropic liquid. [ABSTRACT FROM AUTHOR]

• Three series of BCLCs were studied for photoswitching. • The effect of linking groups on azodyes was responsible for this effect. • Resorcinol with benzoate ester showed the slowest thermal back relaxation. • Potential materials for optical storage device. • Exhibiting strong structure–property relationship. In this paper, we report on the photoisomerization process of three series of photosensitive bent-core liquid crystals with a lateral chlorine atom in the central resorcinol core and various linkers. The effect of linkers, such as benzoate ester, biphenyl, cinnamate, Schiff base and stilbene on the photoisomerization and thermal back relaxation have been studied using UV–Vis spectroscopy. Resorcinol with benzoate ester showed the longest thermal back relaxation of 7 h, whereas, the bent-cores with the stilbene linker rendered the shortest relaxation time of 4 h. The compiled results suggest the influence of linkers, central resorcinol core and position of the azobenzene moiety on the photoisomerization. Additionally, optical storage device fabricated using cinnamate containing bent-core LC (A3), showed the visibility of bright and dark regions in a crossed polarizers upon illumination at λ = 365 nm, indicating the changes from the ordered to disordered state. The observed properties of constructed device demonstrate the potential application of reported azobenzene derivatives in optical storage devices. [ABSTRACT FROM AUTHOR]

We present two isomeric series of photosensitive bent-core liquid crystals possessing a lateral chlorine atom in the central resorcinol unit and various linking units in the side arms. With the aim to tune properties of the nematic phase, we have varied the type of the linking unit in the lengthening arm with rising rigidity from benzoate ester, biphenyl, cinnamate, Schiff base to stilbene moieties. In addition to that, we have changed the position of the lateral substituent (chlorine) as well. The mesomorphic properties of the materials have been determined from differential scanning calorimetry, polarizing optical microscopy, dielectric spectroscopy and X-ray studies. We show that synergy of the linking unit with the effect of the lateral substituent gives rise to broad temperature range of mesophases — the nematic phase as well as a SmCP phase. Thanks to the presence of the photosensitive group in the molecular structure, we have been able to transform both mesophases to the isotropic phase under UV light. The chemical structure–mesomorphic properties relationships are discussed with the aid of ab initio calculations and the results presented in context with experimental data. • Two series of 4-chlororesorcinol-based photosensitive bent-core nematogens are presented. • Mutual position of chlorine atom on the central core and the azo group is crucial for mesomorphic behaviour. • Broad stable nematic phase below 100 °C and switchable SmC A P A phase are observed. • Photosensitivity of bulk mesophases is documented by X-ray profile and polarizing microscopy measurements. [ABSTRACT FROM AUTHOR]

We discuss three series of substituted resorcinol based bent-core liquid crystals with azobenzene wings, substituents consisting of methyl (-CH 3) and halogens (F, Cl, Br) on the resorcinol core connected to azobenzene wings with variable alkoxy chains. The effect of electron-donating (-CH 3) and electron-withdrawing (halogens) group on the photoisomerization and thermal back relaxation studied using UV–Vis spectroscopy. 4-methyl resorcinol bent-core (BC) exhibits the longest thermal back relaxation of about 16.33 h; whereas, the fluoro substituted BCs show the shortest relaxation time of 4.0 h. In the case of fluoro/bromo lateral substituted BCs at terminal azobenzene phenyl ring in 4-methyl resorcinol exhibits longer thermal back relaxation time of ~16.16 h, which is noteworthy. These results envisage the effect of substituents on the central unit as well as the lateral and/or terminal position of azobenzene wings on the photoisomerization. The reversible trans (E) - cis (Z) isomerization occurs in 60 s and 4–16 h, respectively. The prolonged thermal back relaxation attributed to the diazo linkage and the polar substituents. A prototype of optical storage device tested under crossed polarisers at λ = 365 nm, the change from order to disorder state upon illumination with the bright and dark regions was visible and represents ideal candidates for optical storage devices. Compiled results show powerful tuning of structure-property effects using light as external stimuli. Influences of substitutions on resorcinol based bent-core with diazobenzene wings for the application in optical storage devices. Unlabelled Image • A prototype of optical storage device tested under crossed polarisers at λ = 365 nm. • Liquid crystalline phase change observed from order to disorder upon illumination. • High contrast ratio (1:1670) could be seen, representing ideal candidates for devices. • Two diazo groups in bent-core molecule makes synergetic, long thermal back relaxation in photo isomerization are remarkable. • Compiled results show powerful tuning of structure-property effects using light as external stimuli. [ABSTRACT FROM AUTHOR]