  The recent discovery of a new ferroelectric nematic (NF) liquid crystalline
phase became 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.
