Ferroelectric Alkylamide-Substituted Helicene Derivative with Two-Dimensional Hydrogen-Bonding Lamellar Phase

Alkylamide (−CONHC_nH_2n+1)-substituted benzene and its pyrene derivatives have shown a discotic hexagonal columnar liquid-crystalline phase through a one-dimensional (1D) intermolecular N–H···O hydrogen-bonding interaction, the direction of which is inverted through the application of an alternate current voltage. The polar hydrogen-bonding chains and dipole inversion reveal a ferroelectric polarization–electric field (P–E) hysteresis curve. Non-π-planar helicene derivatives bearing two −CONHC₁₄H₂₉ chains also indicate a ferroelectric response. The racemic helicene derivative shows a bilayer lamellar liquid-crystal phase within a temperature range of 330–420 K, whereas there is no liquid crystallinity for the optically active derivative because of the different molecular assembly structure. The racemic phase is constructed through a two-dimensional (2D) N–H···O hydrogen-bonding network, which shows ferroelectric P–E hysteresis curves at above 340 K. The collective dipole inversion in the 2D layer contributes to the ferroelectricity in the lamellar phase. The remanent polarization (P_r) of 11.1 μC cm^–2 is about 6 times higher than those of the π-planar benzene- and pyrene-based 1D ferroelectrics. Both the density of the hydrogen-bonding site and the domain orientation in the 2D system are higher than those of the 1D columnar system.