Tuning the Mesomorphic Properties of Phenoxy-Terminated Smectic Liquid Crystals

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Thompson, Matthew
Electrochemistry , Organic Synthesis , Liquid Crystals , Physical Organic Chemistry
A new type of liquid crystal display using surface stabilized ferroelectric liquid crystals (SSFLCs) has faster switching times than conventional nematic displays. The application of SSFLCs in large LCD devices such as TVs has been hindered due to a layer contraction at the smectic A-smectic C transition. The layer contraction leads to buckling of the smectic layers and results in zigzag defects. These zigzag defects degrade optical quality of ferroelectric liquid crystal (FLC) films. So-called ‘de Vries-like’ liquid crystals with a smectic A-smectic C layer contraction of less than 1% have been sought to address the problem. In the first section of this thesis, we show that one can tune mesomorphic properties in 2-phenylpyrimidine liquid crystals by addition of a nanosegregating phenoxy end group. In this study, it was shown that nanosegregation can be used to exaggerate the difference in mesophase properties in sterically equivalent isomers. The study also showed that the effect of nanosegregration is not always Smectic C promoting and that, although it may decrease orientational order, it is not the only prerequisite to ‘de Vries-like’ properties in calamitic mesogens. Next, we investigated the phenoxy end group through substituent effects. In this study, it was discovered that the SmC phase can be promoted through increased intermolecular interactions that decrease out of layer fluctuations. We also showed that phenoxy-terminated mesogens exhibit extremely low optical tilt angles for the SmC phase, on the order of ~10 degrees, which were not consistent with the observed layer spacing obtained from X-ray diffraction experiments. In attempts to determine their true optical tilt angle, these mesogens were doped with chiral dopants and electro-optical switching experiments showed higher optical tilt angles.
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