Patent ID: 7887717

Claim:
A liquid-crystalline medium having a helically twisted structure comprising: a nematic component and an optically active component; wherein said optically active component comprises one or more chiral compounds whose helical twisting power and concentration are selected in such a way that the helix pitch of the medium is ≦1 μm; and wherein said nematic component comprises one or more compounds selected from the group consisting of compound of formula I and II in which a is 1 or 2, b is 0 or 1, R 1 and R 2 are each, independently of each other, alkyl having from 1 to 12 C-atoms, wherein one or two non-adjacent CH 2 -groups are each optionally replaced by —O—, —CH═CH—, —C≡C—, —CO—, —OCO— or —COO— in such a way that O atoms are not linked directly to one another, Z 1 and Z 2 are each, independently of each other, —CH 2 CH 2 —, —CH═CH—, —CF 2 O—, —OCF 2 —, —CH 2 O—, —OCH 2 —, —COO—, —OCO—, —C 2 F 4 —, —CF═CF—, —CH═CHCH 2 O—, or a single bond, and Z 1 in formula II may also denote —C≡C—, and L 1-4 are each, independently of each other, F, Cl, OCF 3 , CF 3 , CH 3 , CH 2 F, or CHF 2 .