Rational Design of ferroelectric liquid crystals

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Chirality is a unique property that many natural and man-made substances and almost all living things possess. Chiral objects exist in right- and left-handed forms (enantiomers), e.g., gloves, shoes and golf clubs, and are non-superposable on their mirror images. Chirality is also manifest at the molecular scale., e.g., amino acids, carbohydrates, and many other natural products. These chiral building blocks assemble via covalent and non-covalent interactions to form larger chiral structures such as proteins and nucleic acids, which themselves assemble into crystalline structures with chiral topographies. Such manifestation of molecular chirality at the macroscopic level, which was first shown by Pasteur in 1848 with sodium ammonium tartrate, is also observed in the chiral smectic C* (SmC*) liquid crystal phase in the form of a ferroelectric polarization (Ps). The polarization of a ferroelectric liquid crystal (FLC) can be coupled to an electric field to produce a fast switching light shutter that can be used in high-resolution display applications. In order to produce FLC films suitable for displays, SmC* liquid crystal mixtures with a minimum amount of chiral material are required. To address this important requirement, our research program focuses on the induction of chirality in smectic phases, and how an axially chiral dopant can propagate its handedness most effectively in a non-chiral SmC host to produce increasingly large polarization powers. This can be achieved by matching the molecular structures of chiral dopants and SmC hosts to maximize chirality transfer via intermolecular interactions. A second aspect of this program focuses on the rational design of SmC liquid crystals that undergo a transition from the non-tilted smectic A (SmA) phase to the tilted SmC phase with minimal layer contraction. Our molecular design strategy is based on achieving a 'frustration' between two structural elements that promote the formation of SmA and SmC phases. These so-called 'de Vries-like' materials will provide a solution to one of the main roadblocks to the use of FLC technology in LCD projectors and large flat panel displays: the formation of zigzag defects caused by layer contraction upon cooling a FLC mixture from the chiral SmA* to the SmC* phase.