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

Abstract

Alkylamide (-CONHC nH2 n+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 ( Pr) 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.