Chirality and the Ferroelectric Nematic Phase

Liquid crystals (LCs) combine fluidity with molecular ordering, endowing them a unique duality of properties. Nematic (N) LC-based technology is now vital to modern life, found in almost all LC displays. In the conventional N phase the rod-like molecules all more-or-less line-up in the same direction but their positions are random. The molecules are not distinguished in terms of pointing up or down and so the phase is apolar. A new NLC phase was discovered in 2017, the ferroelectric nematic phase (NF) in which the molecules are also distinguished by their direction and the phase is spontaneously polar. The NF phase exhibits remarkable electro-optical properties, has huge potential to revolutionise LC-based technologies, and is predicted to dominate LC science and technology for years to come. At the fundamental level, the recent surge in global research into the NF phase has led to the discovery of several new polar LC phases. Technologically, exploiting the potential of the NF and associated phases necessitates the design of new materials with appropriate chemical and thermal stability, fluidity, and optical performance for real-world applications. NF materials reported to date are not suitable in these aspects. To develop the next generation of materials, research is now urgently required to enhance our understanding of how molecular structure affects NF phase formation. This project addresses a critical issue in the development of new NF materials, what is the effect of molecular chirality on the NF phase? Molecular chirality drives the formation of the helical ferroelectric nematic phase (NF*). The combination of a helical structure and local electric polarity endows the NF* phase with unique and exciting properties such as tuneable light reflection with minimal energy input, having application potential in new optical devices including adjustable lenses for virtual/augmented-reality headsets and versatile multi-wavelength lasers. Research on NF* systems has focussed on mixing chiral additives with non-polar NF materials. The outcomes are difficult to interpret at the molecular level due to the mixtures’ complexity. To date only two single-component chiral materials (synthesised by the New Investigator) have shown the NF* phase. This study will be the first dedicated to understanding the structure-property relationships associated with the NF* phase, with the goal of discovering new compounds with working temperatures and physical attributes ideal for use in new state-of-the-art proof-of-principle devices. The proposed research will unite a multidisciplinary team of researchers in organic and physical chemistry, physics and device engineering from internationally-leading institutions to meet its objectives: (1) Synthesis of novel chiral ferroelectric materials to explore how molecular structure affects NF* phase formation, and the aim of discovering new chiral and ferroelectric LC phases. (2) Extensive characterisation of these materials to establish a profile of thermal, electronic and optical behaviour, and ultimately an understanding of the relationships between structure, incidence of LC behaviour and specific physical properties. (3) Test new materials' potential in devices like fast-switching displays and adjustable lasers, either neat or as part of multi-component mixtures with other LC materials. Understanding how chirality and ferroelectricity interact at the molecular level in these new LCs could lead to major new innovations in display and optical technologies. By creating a clearer fundamental understanding of how molecular structure influences thermal and optical behaviour, and device performance, our findings could guide the design of next-generation LCs with tailored properties for wide-ranging applications.