Nematic materials with negative dielectric anisotropy for display applications

The recent move towards liquid crystal displays based on the electrically controlled birefringence (ECB) effect of the vertically aligned nematic (VAN) material has brought improvements in terms of contrast, viewing angle and switching times. However, different types of nematic liquid crystalline materials are required with a negative dielectric anisotropy, in addition to the usual requirements such as low viscosity, optimised mesomorphic behaviour, and tailored elastic constants and birefringence. There are particular difficulties in generating the ideal combination of mesomorphic and physical properties in such materials. This paper outlines the various liquid crystal display device configurations in terms of the material requirements, and discusses in more detail the design, synthesis, mesomorphic and physical properties of suitable nematic materials of negative dielectric anisotropy.