Ferroelectric Nematic and Smectic Liquid Crystals with Sub-Molecular Spatial Correlations

TL;DR

This study reports the synthesis of polar thiophene-based liquid crystals that exhibit strong spatial correlations, high polarization, and a novel smectic phase with antipolar molecular packing, advancing understanding of ferroelectric and smectic liquid crystal behaviors.

Contribution

It introduces new thiophene compounds with enhanced ferroelectric polarization and reveals a previously unobserved smectic phase with antipolar molecular arrangement.

Findings

Thiophene compounds show ferroelectric nematic phases with L/3 spatial correlations.

Polarizations are about 20% larger than typical NF materials.

A novel smectic phase with ~1/3 molecular length periodicity was observed.

Abstract

A number of highly polar three ring rod-shaped compounds with a terminal thiophene ring have been synthesized and the physical properties of a subset are reported in detail. On cooling from the isotropic fluid, they directly transition to a ferroelectric nematic liquid crystal (NF) phase that shows the strongest spatial correlations corresponding to 1/3 of the molecular length (L/3). The set of thiophene compounds reported here have ferroelectric polarizations about 20% larger than that of usual ferroelectric nematic liquid crystal materials. Such large polarization values are due to the ~20% larger mass densities of these thiophene compounds compared to most of the NF materials with short terminal chains. These unusual properties are consequences of tighter molecular packing due to the lack of flexible terminal chains. Below the NF phase, compounds with a single nitro or two cyano polar groups on the terminal benzene ring exhibit a so far never observed smectic phase with periodicity ~1/3 the molecular length. Based on our experimental results, we propose a model of this phase featuring antipolar packing of the molecules within the layers.