Liquid-crystalline medium, method for the stabilization thereof, and liquid-crystal display

A liquid-crystalline medium comprising

• a) one or more compounds of formula I
• in which
• n denotes 1, 2, 3 or 4,
• m denotes (4-n),
• denotes an organic radical having 4 bonding sites,
• 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, also independently of one another, one or both of the pairs (Y11 and Y12) and (Y13 and Y14) together denote a divalent group having 3 to 6 C atoms,
• R11 denotes O—R13, O. or OH, preferably O—R13 or O.,
• 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 denote
• a straight-chain or branched alkyl having 1 to 10 C atoms, cycloalkyl, cycloalkylalkyl or alkylcycloalkyl,
• and
• in the case where n=2 and R11=O—R13,
• R13 does not denote n-C1-9-alkyl, and
• Compounds of the formula
• are excluded from formula 1,
• b) one or more compounds of the formula III-O
• in which
• R31 denotes an unsubstituted alkyl radical having 1 to 7 C atoms,
• R32 denotes an unsubstituted alkyl radical having 1 to 7 C atoms or an unsubstituted alkoxy radical having 1 to 6 C atoms, and
• i denotes 0 or 1.