Liquid Crystal Displays (LCDs) are widely used to display information. Electro-optical modes employed are, e.g., the twisted nematic (TN)-, the super twisted nematic (STN)-, the optically compensated bend(OCB)- and the electrically controlled birefringence (ECB)-mode with their various modifications, as well as others. Besides these modes, which all use an electrical field which is substantially perpendicular to the substrates, respectively to the liquid crystal layer, there are also electro-optical modes employing an electrical field substantially parallel to the substrates, respectively the liquid crystal layer, like, e.g., the In-Plane Switching(IPS) mode, as disclosed, e.g., in DE 40 00 451 and EP 0 588 568. Especially this electro-optical mode is used for LCDs for modern desk top monitors. In IPS displays, like in Ferroelectric Liquid Crystal Displays (FLCDs), the liquid crystals are switching their axis of preferred orientation in the plane of the display. Thus there is almost no birefringence change during switching and consequently the optical effect is color neutral.
Displays using the flexoelectric effect in cholesteric liquid crystals in the Uniformly Lying Helix texture have been proposed (Phys. Rev. Lett. 58 (15), p. 1538–1540 (1987)). Throughout this application the terms chiral nematic and cholesteric are used synonymously, unless explicitly stated otherwise. The flexoelectric effect itself is known from Meyer (Phys. Rev. Lett. 22, p. 918 ff (1969)) and has more recently been reviewed by Rudquist et al. (Liq. Cryst. 22 (4), 445–449 (1997).
Liquid crystal compositions with short cholesteric pitch for flexoelectric devices are known from EP 0 971 016, GB 2 356 629 and Coles et al., J. Mater. Chem., 11, p. 2709–2716 (2001). EP 0 971 016 teaches mesogenic estradiols, which, as such, have a high flexoelectric coefficient. GB 2 356 629 teaches bimesogenic compounds and their use in flexoelectric devices.