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1. Liquid-crystal medium having positive dielectric anisotropy, characterised in that
a) one or more compounds selected from the group of the compounds of the formula I and TINUVIN 770®, in which n denotes an integer from 1 to 4, m denotes (4-n), denotes an organic radical having 4 bonding sites, in which, in addition to the m groups R12 present in the molecule, but independently thereof, a further H atom may be replaced by R12 or a plurality of further H atoms may be replaced by R12, in which one —CH2— group or a plurality of —CH2— groups may be replaced by —O— or —(C═O)— in such a way that two 0 atoms are not bonded directly to one another, or denotes a substituted or unsubstituted aromatic or heteroaromatic hydrocarbon radical having 1 to 4 valences, in which, in addition to the m groups R12 present in the molecule, but independently thereof, a further H atom may be replaced by R12 or a plurality of further H atoms may be replaced by R12,
Z11 and Z12, independently of one another, denote —O—, —(C═O)—, —(N—R14)— or a single bond, but do not both simultaneously denote —O—,r and s, independently of one another, denote 0 or 1,Y11 to Y14 each, independently of one another, denote alkyl having 1 to 4 C atoms and alternatively, independently of one another, one or both of the pairs (Y11 and Y12) and (Y13 and Y14) together also denote a divalent group having 3 to 6 C atoms,R11 denotes O—R13, O. or OH,R12 on each occurrence, independently of one another, denotes H, F, OR14, NR14R15, a straight-chain or branched alkyl chain having 1-20 C atoms, in which one —CH2— group or a plurality of —CH2— groups may be replaced by —O— or —C(═O)—, but two adjacent —CH2— groups cannot be replaced by —O—, or denotes a hydrocarbon radical which contains a cycloalkyl or alkylcycloalkyl unit, and in which one —CH2— group or a plurality of —CH2— groups may be replaced by —O— or —C(═O)—, but two adjacent —CH2— groups cannot be replaced by —O—, and in which one H atom or a plurality of H atoms may be replaced by OR14, N(R14)(R15) or R16, or denotes an aromatic or heteroaromatic hydrocarbon radical, in which one H atom or a plurality of H atoms may be replaced by OR14, N(R14)(R15) or R16,R13 on each occurrence, independently of one another, denotes a straight-chain or branched alkyl chain having 1-20 C atoms, in which one —CH2— group or a plurality of —CH2— groups may be replaced by —O— or —C(═O)—, but two adjacent —CH2— groups cannot be replaced by —O—, or denotes a hydrocarbon radical which contains a cycloalkyl or alkylcycloalkyl unit, and in which one —CH2— group or a plurality of —CH2— groups may be replaced by —O— or —C(═O)—, but two adjacent —CH2— groups cannot be replaced by —O—, and in which one H atom or a plurality of H atoms may be replaced by OR14, N(R14)(R15) or R16, or denotes an aromatic or heteroaromatic hydrocarbon radical, in which one H atom or a plurality of H atoms may be replaced by OR14, N(R14)(R15) or R16,
or can be (1,4-cyclohexylene), in which one or more —CH2— groups may be replaced by —O—, —CO— or —NR14—, or an acetophenyl, isopropyl or 3-heptyl radical,R14 on each occurrence, independently of one another, denotes a straight-chain or branched alkyl or acyl group having 1 to 10 C atoms or an aromatic hydrocarbon or carboxyl radical having 6-12 C atoms,R15 on each occurrence, independently of one another, denotes a straight-chain or branched alkyl or acyl group having 1 to 10 C atoms or an aromatic hydrocarbon or carboxyl radical having 6-12 C atoms,R16 on each occurrence, independently of one another, denotes a straight-chain or branched alkyl group having 1 to 10 C atoms, in which one —CH2— group or a plurality of —CH2— groups may be replaced by —O— or —C(═O)—, but two adjacent —CH2— groups cannot be replaced by —O—,with the provisos that,in the case where n=1, R11═O. and—[Z11—]r—[Z12—]s—═—O—, —(CO)—O—, —O—(CO)—, —O—(CO)—O—, —NR14— or—NR14—(CO)—, does not denotestraight-chain or branched alkyl having 1 to 10 C atoms, also cycloalkyl, cycloalkylalkyl or alkylcycloalkyl, where in all these groups one or more —CH2— groups may be replaced by —O— in such a way that no two O atoms in the molecule are bonded directly to one another,in the case where n=2 and R11═O., does not denote andin the case where n=2 and R11═O—R13,R13 does not denote n-C1-9-alkyl, and b) one or more compounds selected from the group of the compounds of the formulae II and III in which R2 and R3, independently of one another, denote alkyl, alkoxy, fluorinated alkyl or fluorinated alkoxy having 1 to 7 C atoms, alkenyl, alkenyloxy, alkoxyalkyl or fluorinated alkenyl having 2 to 7 C atoms, and R2 and R3 preferably denote alkyl or alkenyl, to on each appearance, independently of one another, denote L21, L22, L31 and L32, independently of one another, denote H or F, X2 and X3, independently of one another, denote halogen, halogenated alkyl or alkoxy having 1 to 3 C atoms or halogenated alkenyl or alkenyloxy having 2 or 3 C atoms, Z3 denotes —CH2CH2—, —CF2CF2—, —COO—, trans-CH═CH—, trans-CF═CF—, —CH2O— or a single bond, and m and n, independently of one another, denote 0, 1, 2 or 3, and/or c) one or more compounds of the formula IV in which R41 and R42, independently of one another, have the meaning indicated for R2 above under formula II, preferably R41 denotes alkyl and R42 denotes alkyl or alkoxy or R41 denotes alkenyl and R42 denotes alkyl, independently of one another and, if occurs twice, also these independently of one another, denote preferably one or more of denote(s) Z41 and Z42, p independently of one another and, if Z41 occurs twice, also these independently of one another, denote —CH2CH2—, —COO—, trans-CH═CH—, trans-CF═CF—, —CH2O—, —CF2O—, —C≡C— or a single bond, preferably one or more of them denote(s) a single bond, and p denotes 0, 1 or 2, preferably 0 or 1. |
