Induction and modulation of chirality in smectic 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 ON-OFF light shutter that is used in high-resolution display applications.  In order to obtain defect-free FLC films, SmC* liquid crystal mixtures with a minimum amount of chiral material are required.  To address this important requirement, the proposed research focuses on the INDUCTION of chirality in smectic phases, and how a chiral dopant can propagate its handedness most effectively in a non-chiral SmC host to produce increasingly large Ps values.  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 the proposed research focuses on the design of chiral molecules that can self-assemble via hydrogen bonding to give a polar network in the SmC* phase with enhanced non-linear optical properties.  A third aspect of the proposed research is the design of chiral dopants that undergo a reversible structural change upon irradiation with light without thermal back reaction or degradation.  In a SmC host, the light-induced structural change is intended to MODULATE the magnitude of induced Ps in such a way as to trigger the ON-OFF switching of a FLC light shutter, which would enable the writing of images, diffraction gratings and waveguides in FLC films.