|Smectic liquid crystal phases are normally formed by rod-like molecules with a rigid aromatic core and two aliphatic side chains. The fluid SmA and SmC phases are characterized by a diffuse layer structure described by a density wave with a period d corresponding to the smectic layer spacing. In the uniaxial SmA phase, the director n is parallel to the layer normal z; in the biaxial SmC phase, n is tilted relative to z by a tilt angle θ that varies with temperature. According to a classic rigid-rod model, the SmA-C transition is accompanied by a layer contraction that scales with the cosine of θ, which is typically on the order of 7-8%. In ferroelectric liquid crystal (FLC) display applications based on chiral SmC materials, this layer contraction on cooling from the isotropic liquid phase results in a buckling of the smectic layers and the formation of zigzag defects that severely degrade the optical quality of FLC films. One solution to this problem is to develop materials with minimal layer contraction at the SmA-C phase transition, which are known as de Vries-like materials . This reference stems from the diffuse cone model proposed by de Vries that describes the SmA phase as a lamellar structure in which molecules have a tilted molecular orientation and random azimuthal distribution . We have shown that one can promote de Vries-like character in a mesogen by imposing a molecular frustration between SmA- and SmC-promoting elements . For example, in compounds 1 and 2, which exhibit de Vries-like properties, the trisiloxane-terminated side-chain is a strong SmC-promoter, whereas the chloro-terminated side-chain in 1 and the 5-phenylpyrimidine core in 2 are strong SmA-promoters. This seminar will provide an overview of our work in this area, and of recent efforts to develop useful materials for commercial FLC formulations.|
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