Rational Design, Synthesis and Characterization of Fluorinated Cyano-Terminated Diester Liquid Crystals Exhibiting the Ferroelectric Nematic Phase

The discovery of the ferroelectric nematic (NF) phase has attracted significant attention from the soft matter community, both for exploring the scientific basis of its origin and for advancing its potential applications in devices such as optical modulators and high-energy-density storage supercapacitors. Unlike rigid solid-state ferroelectrics, the fluidic nature of NF materials offers additional flexibility in device fabrication. In the NF phase, these materials exhibit remarkably large saturated spontaneous polarization (≳6 μC/cm2), which is comparable to that of the solid-state ferroelectrics, and consequently, these materials will exhibit exceptionally strong nonlinear electro-optic effects. In this paper, we report the synthesis of three new NF phase compounds with an extended temperature range of up to 103 °C. Two of these compounds show a direct Iso-to-NF phase transition, and in two cases, a monotropic NF phase was observed below 30 °C. The design and synthesis of the materials are described. The compounds are characterized by analysis of textures using polarizing optical microscopy. X-ray measurements show that the effective length of the molecule is smaller in the NF phase than in the N/Iso phase seemingly arising from a better orientational ordering of the polar molecules. Dielectric measurements confirm the presence of a ferroelectric mode of large dielectric strength in the NF phase. Temperature-dependent birefringence data show a large increase in the order parameter at the Iso–NF or N–NF transition temperature. The fundamental properties determined for these materials will support their future applications.