Liquid crystalline compound, medium and display

#The invention relates to a liquid crystalline compound, especially suitable as a component of a liquid crystalline medium with positive dielectric anisotropy and high optical anisotropy. Furthermore, the invention also relates to such a liquid crystalline medium and its use in electrooptical displays and projection systems, in particular reflective displays, LCoS™ displays and displays based on a birefringence effect, such as OCB displays.

#Displays of the OCB (optically compensated bend) are based on a birefringence effect and comprise a liquid crystal layer with a bend structure. The bend cell, also known as pi-cell, was first proposed by P. Bos et al., SID 83 Digest, 30 (1983) for an electrically controllable half-wave plate, whereas the OCB mode for displays was described by Y. Yamaguchi, T. Miyashita and T. Uchida, SID 93 Digest, 277 (1993), followed by papers of T. Miyashita et al. in, inter alia, Proc. Eurodisplay, 149 (1993), J. Appl. Phys. 34, L177 (1995), SID 95 Digest, 797 (1995), and C. -L. Kuo et al., SID 94 Digest, 927 (1994). An OCB cell comprises a liquid crystal cell with bend alignment and a liquid crystal medium with positive Δε. Furthermore, OCB displays as reported in the above papers comprise one or more birefringent optical retardation films to eliminate light leakage by the bend cell in the black state. OCB displays bear several advantages like for example a wider viewing angle and shorter switching times than conventional displays based on twisted nematic (TN) cells.

#The above mentioned papers have shown that liquid-crystalline phases must have high values for the optical anisotropy Δn and a relatively high positive value for the dielectric anisotropy Δε, and preferably should have rather low values for the ratio between the elastic constants K33/K11 and for the viscosity, in order to be usable for high-information display elements based on the OCB effect. The industrial application of the OCB effect in electro-optical display elements requires LC phases which must satisfy a multiplicity of requirements. Particularly important here are chemical resistance to moisture, air and physical effects such as heat, radiation in the infra-red, visible and ultra-violet regions and direct and alternating electrical fields. Furthermore, LC phases which can be used industrially need a liquid-crystalline mesophase in a suitable temperature range, a relatively high birefringence, a positive dielectric anisotropy and a low viscosity.

#1.1 Synthesis of the Boronic Acid (3) 134

#1.375 mol Mg in 100 ml THF are reacted with 1.25 mol 1-brom-3-fluorobenzene (1) in 350 ml THF under the conditions of a Grignard reaction at boiling heat. After the addition of the fluorobenzene, the reaction mixture is refluxed for 30 min. Afterwards 1.375 mol trimethylborate (2) in 300 ml THF are added to the reaction mixture dropwise. After one hour 500 ml MTB are added and then 200 ml concentrated HCl are added dropwise at a maximum of 20° C., while cooling. The following work up is conventional.

#1.2 Synthesis of 3-fluoro-4′-(trans-4-propyl-cyclohexyl)-biphenyl (5) 135