We report unambiguous experimental evidence for an achiral orthogonal biaxial smectic-A phase which exhibits antiferroelectric switching behavior. The evidence is based on x-ray-diffraction measurements, texture observation, and the results of dielectric and electro-optical measurements.

Considerable progress has been achieved in understanding the fascinating structure and physical properties of the ferroelectric liquid crystalline phases formed by bent-core liquid crystals (BLC). In this review, we discuss a manifold of polar structures and phases found in BLCs such as orthogonal and tilted ferro-/antiferroelectric phases, smectic phases, switchable columnar phases, modulated structures and phases stabilised by a periodic lattice of defects such as dark conglomerate and nanofilament phases. We review the theoretical aspects of ferroelectricity in BLCs including existing microscopic theories and computer simulations, polarity and chirality phenomena. The last part of the paper is devoted to the peculiarities of the behavior of BLCs in a restricted geometry (freely suspended films and filament) and the perspective technological applications.

A new achiral banana-shaped mesogen is presented which exhibits a nematic phase and an isotropic mesomorphic phase with spontaneous chiral ordering.

A new series of achiral five-ring banana-shaped compounds is presented which exhibit a cyano substituent in the 4-position of the central core. It follows from X-ray investigations and from NMR, microscopical and electro-optical measurements that all members of the series do not only form the chiral B₂ phase characteristic of a bent molecular shape, but also SmA and SmC (in one case also nematic) phases. The electro-optical studies on the B₂ phase prove an antiferroelectric ground state which can be switched into ferroelectric states. On the base of the experimental data plausible structure models have been proposed.

The recent discovery of the ferroelectric nematic phase has opened the door to experimental investigation of one of the most searched liquid crystal phases in decades, with high expectations for future applications. However, at this moment, there are more questions than answers. In this work, we examine the formation and structure of large polar nematic domains of the ferroelectric nematic material RM734 in planar liquid crystals cells with different aligning agents and specifications. We observe that confining surfaces have a strong influence over the formation of different types of domains, resulting in various twisted structures of the nematic director. For those cells predominantly showing mm-scale domains, we investigate the optical and second harmonic generation switching behaviour under applications of electric fields with a special focus on in-plane fields perpendicular to the confinement media rubbing direction. In order to characterise the underlying structure, the polar optical switching behaviour is reproduced using a simplified model together with Berreman calculations. Graphical abstract

Two homologous achiral five-ring mesogens with lateral fluorine substituents on the core and on the outer rings are presented. Both compounds exhibit two B₅ phases and the B₂ phase. The high-temperature B₅ phases possess an antiferroelectric ground state. The low-temperature B₅ phase was found to be ferroelectric, which is indicated by the bistable switching. The assignment and characterization of the mesophases is based on XRD measurements, ¹H-, ¹⁹F-, ¹³C-NMR and electro-optical measurements.