Polar nematic phases with enantiotropic ferro- and antiferroelectric behaviour

The recent discovery of a new ferroelectric nematic (NF) liquid crystalline phase has become of utmost interest for the liquid crystal (LC) and the whole soft and condensed matter fields. Contrary to the previously known ferroelectric LC materials, whose ferroelectric characteristics were much weaker, new polar nematics exhibit properties comparable to solid ferroelectrics. This discovery brought about tremendous efforts to further explore compounds showing these phases, and fascinating physical properties have been reported. Herein, we present the first synthesized compounds with the enantiotropic ferro- (NF) and antiferroelectric (NX) nematic phases. The enantiotropic nature and an unprecedentedly broad temperature range of NF and NX phases are confirmed by various experimental techniques: polarized-light optical microscopy (POM) observations, different scanning calorimetry (DSC), dielectric spectroscopy, second harmonic generation (SHG), and molecular modeling. The presented achievements in designing achiral compounds that exhibit enantiotropic polar nematic phases with ferro- and antiferroelectric properties significantly contribute to the development of multicomponent mixtures with a broad temperature range of NF and NX phases down to room temperature. Furthermore, this accomplishment considerably enhances the general understanding of the structural correlations that promote polar nematic liquid crystal phases with high thermodynamic stability. Finally, this work may benefit various applications in photonic devices.