Smectic liquid crystals modified by tail and core fluorination

The systematic substitution of fluorine for hydrogen in mesogenic materials has proved to be of great value for the modification of a wide range of physical properties. This is especially true in the case of ferroelectric liquid crystals in which the fluorine has been strategically introduced into the aromatic core (k), at or near the chiral center (Z) or in the achiral tail (n) in the generic liquid crystal (with X equals O, S and Z equals Me, halogen): H/F(CF2)n(CH2)mOC6H(4 - k)FkCOXPhOCOC*HZR. In this system the fluorine can be introduced in any of these three specific locations, or any combinations thereof, with the intent of enhancing performance such as broadening of the ferroelectric Sc* phase temperature range, enhancement of the magnitude of spontaneous polarization Ps and a variety of more subtle yet important modifications such as viscosity and dielectric and optical anisotropy. The ramifications of the incorporation of fluorine on these physical properties are discussed with a variety of examples.© (1991) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.