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We report on measurements of dielectric permittivity epsilon, electrical conductivity sigma, elastic moduli k(ii), and rotational viscosity gamma for a bent-core nematic liquid crystal. The static permittivity anisotropy epsilon(a) = epsilon(parallel)-epsilon(perpendicular) is negative; at a given temperature in the interval 107-123 degrees C, epsilon(parallel) shows two relaxations falling in the frequency bands 20-200 kHz and 0.9-2 MHz; epsilon(perpendicular) also shows a relaxation between 0.9 and 5 MHz. The conductivity anisotropy sigma(a) = sigma(parallel)-sigma(perpendicular) is negative at low frequencies; it changes sign twice at frequencies f(1) and f(2) that increase with temperature, in the ranges 6.5-10 and 95-600 kHz, respectively. Surprisingly, the splay modulus k(11) is considerably greater than the bend modulus k(33) in the entire nematic range. Viscous relaxation is more complex than in calamitic systems involving at least a two-step process. The gamma values are an order of magnitude greater compared to calamitics.

Controllable manipulation of self-organized dynamic superstructures of functional molecular materials by external stimuli is an enabling enterprise. Herein, we have developed a thermally driven, self-organized helical superstructure, i.e., thermoresponsive cholesteric liquid crystal (CLC), by integrating a judiciously chosen thermoresponsive chiral molecular switch into an achiral liquid crystalline medium. The CLC in lying state, in both planar and twisted nematic cells, exhibits reversible in-plane orthogonal switching of its helical axis in response to the combined effect of temperature and electric field. Consequently, the direction of the cholesteric grating has been observed to undergo 90° switching in a single cell, enabling non-mechanical beam steering along two orthogonal directions. The ability to reversibly switch the cholesteric gartings along perpendicular directions by appropriately adjusting temperature and electric field strength could facilitate their applications in 2D beam steering, spectrum scanning, optoelectronics and beyond.

We report on the converse flexoelectric effect in two bent-core nematic liquid crystals with opposite dielectric anisotropies. The results are based on electro-optic investigations of inplane field-driven distortions in homeotropic samples (the Helfrich method). They are interpreted by an extension of the Helfrich theory that takes into account the higher order distortions. The bend flexocoefficient for both the compounds is of the usual order of magnitude as in calamitics, unlike in a previously investigated bent-core nematic for which giant values of the bend flexocoefficient are reported. In order to resolve this discrepancy, we propose a molecular model with nonpolar clusters showing quadrupolar flexoelectricity. The study also includes measurements on surface polarization instabilities in the dielectrically positive material; the splay flexocoefficient thereby deduced is also of the conventional order.

Two series of new, photoluminescent star-shaped discotic liquid crystals, recently termed as "hekates", derived from tris(N-salicylideneaniline)s (TSANs), were synthesized by the facile threefold condensation of 3,4-bis(alkoxy)phenyl 4-aminobenzoates/3,4,5-tris(alkoxy) phenyl 4-aminobenzoates with 1,3,5-triformylphloroglucinol and characterized. These two series of discotics with six and nine peripheral n-alkoxy tails were especially designed and accomplished to understand the relation between mesomorphic/photophysical properties and molecular structure. Proton NMR spectral analysis revealed their existence as an inseparable mixture of two keto-enamine tautomeric forms featuring C(3h) and C(s) rotational symmetries. A systematic study into the thermotropic liquid crystal behavior using polarizing optical microscopy, differential scanning calorimetry, and X-ray scattering confirmed the presence of columnar (Col) phase in vast majority of the TSANs prepared. The two-dimensional (2D) lattices of these fluid columnar phases were found to be characteristic of hexagonal Col (Col(h)), rectangular Col (Col(r)), or oblique Col (Col(ob)) phases depending on the number/length of the peripheral flexible chains. The stabilization of the Col(ob) phase, a less commonly found fluid columnar structure, and the first of its kind in TSAN systems, implies very intensive intermolecular (face-to-face) interactions among the TSAN cores within the column. The photophysical properties were investigated both in solution and the columnar states by UV-vis absorption and photoluminescence; markedly, the solution state emits light in the blue region. The light-emitting ability of the Col phase is particularly significant given the possibility that, in such cores, the protons and electrons interact with each other through the H-bonding environment.

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We report the results of investigations on the anisotropic electrohydrodynamic states arising in a highly conducting, planarly aligned, bent-core nematic liquid crystal driven by ac fields of frequency f in the range from 10 Hz to 1 MHz. Pattern morphologywise, two f regimes are distinguished. The low-f regime, wherein the primary bifurcation is to a state of periodic longitudinal stripes (LS), extends to an unprecedentedly large f, in the range 150-550 kHz, depending on the temperature T. This is followed by the high-f regime wherein periodic normal stripes (NS) constitute the primary instability. Both instabilities involve predominant director modulations and streamlines in the layer plane. The transitional frequency between the two regimes is linear in temperature. The curve V(c)(f) shows a nonlinear increase for the LS state and decrease for the NS state. V(c)(T) is an ever increasing curve close to the nematic-isotropic point for both states. The wavenumber of LS varies directly as V, and that of NS shows nearly the same behavior. The pattern period versus f is increasing for LS but decreasing for NS. Both instability states exhibit complex, light-polarization-dependent lens action. Well above the threshold, disclination loops of regular geometry appear along the stripes. They drift in a coordinated manner along the flow lines. At very high voltages, the instability turns strongly time dependent. The current models of anisotropic convection based on static electrical parameters fail to account for the observed instabilities.