Structures and properties of liquid crystalline phases formed by bent-core molecules are reviewed. At least eight phases designated as B1-B8 have been found, being unambiguously distinguished from phases formed by usual calamitic molecules due to a number of remarkable peculiarities. In addition to B1-B8 phases, smectic A-like phases and biaxial nematic phases formed by bent-core molecules are also reviewed. The most attractive aspects of this new class of liquid crystals are in polarity and chirality, despite being formed from achiral molecules. The bent-core mesogens are the first ferroelectric and antiferroelectric liquid crystals realized without introducing chirality. Spontaneous chiral deracemization at microscopic and macroscopic levels occurs and is controllable. Moreover, achiral bent-core molecules enhance system chirality. The interplay between polarity and chirality provides chiral nonlinear optic effects. Further interesting phenomena related to polarity and chirality are also reviewed.

Any polar-ordered material with a spatially uniform polarization field is internally frustrated: The symmetry-required local preference for polarization is to be nonuniform, i.e., to be locally bouquet-like or "splayed." However, it is impossible to achieve splay of a preferred sign everywhere in space unless appropriate defects are introduced into the field. Typically, in materials like ferroelectric crystals or liquid crystals, such defects are not thermally stable, so that the local preference is globally frustrated and the polarization field remains uniform. Here, we report a class of fluid polar smectic liquid crystals in which local splay prevails in the form of periodic supermolecular-scale polarization modulation stripes coupled to layer undulation waves. The polar domains are locally chiral, and organized into patterns of alternating handedness and polarity. The fluid-layer undulations enable an extraordinary menagerie of filament and planar structures that identify such phases.

Helical structures were confirmed for both the SmA b and SmBlue phases of banana-shaped molecular systems from observations of the microscopic fringe pattern and the selective reflection of blue color, respectively. X-ray and optical microscopy indicate that the helical axes in the SmA b and SmBlue phases are normal and parallel to the smectic layer, respectively. In these two helical phases, 13C NMR spectra show two C=O peaks, suggesting two different configurations of ester group, whereas only one C=O peak appears in the isotropic and crystal phases. This indicates that the two C=O groups in the mesogenic core are not in the same plane but are twisted. The addition of chiral dopant makes the dichroic ratio of the right- and left-circularly polarized scattered light positive or negative in the SmBlue phase, although the wavelength (∼430 nm) of the scattering peak does not change significantly. The origin of the helix will be discussed in view of the twisted molecular conformation (conformational chirality) and the escape from macroscopic polarization.

Manipulation of light is in strong demand in information technologies. Among the wide range of linear and nonlinear optical devices that have been used, growing attention has been paid to photonic crystals that possess a periodic modulation of dielectric function. Among many photonic bandgap (PBG) structures, liquid crystals with periodic structures are very attractive as self-assembled photonic crystals, leading to optical devices such as dye lasers. Here we report a new hetero-PBG structure consisting of an anisotropic nematic layer sandwiched between two cholesteric liquid-crystal layers with different helical pitches. We optically visualized the dispersion relation of this structure, displaying the optical diode performance: that is, the non-reciprocal transmission of circular polarized light at the photonic-bandgap regions. Transmittance spectra with circularly polarized light also reveal the diode performance, which is well simulated in calculations that include an electro-tunable diode effect. Lasing action was also confirmed to show the diode effect with a particular directionality.

A cholesteric liquid crystal (CLC) is a self-assembled photonic crystal formed by rodlike molecules, including chiral molecules, that arrange themselves in a helical fashion. The CLC has a single photonic bandgap and an associated one-colour reflection band for circularly polarized light with the same handedness as the CLC helix (selective reflection). These optical characteristics, particularly the circular polarization of the reflected light, are attractive for applications in reflective colour displays without using a backlight, for use as polarizers or colour filters and for mirrorless lasing. Recently, we showed by numerical simulation that simultaneous multicolour reflection is possible by introducing fibonaccian phase defects. Here, we design and fabricate a CLC system consisting of thin isotropic films and of polymeric CLC films, and demonstrate experimentally simultaneous red, green and blue reflections (multiple photonic bandgaps) using the single-pitched polymeric CLC films. The experimental reflection spectra are well simulated by calculations. The presented system can extend applications of CLCs to a wide-band region and could give rise to new photonic devices, in which white or multicolour light is manipulated.

By diminishing the energy barrier between SC; and SC*, antiferroelectricity has become thresholdless in a threecomponent mixture. It shows V-shaped switching, realizing attractive display characteristics: extremely wide viewing angle with very large contrast ratio, high speed response and ideal analogue grey scale with no hysteresis. A simplified model of the phase with this property is presented.

The caption of Figure 4 in article adma.201300776 is hereby corrected to: Emission spectra at 30 °C (a) for a CLC shell of DBR mode (R = 107 µm, a = 72 µm) and (b) for a CLC shell of DFB mode (R = 107 µm, a = 92 µm) by pulsed pumping laser light of wavelengths of 450 nm and 510 nm, respectively. Broken lines in (a) and (b) are RB dissolved in water and emission spectra for DCM dissolved in ZLI2293, respectively. The insets in (a) and (b) show the emitted intensity at wavelengths of 619 nm and 566 nm for DBR and DFB mode lasings of CLC shells, respectively.

No abstract