Active matrix displays having high contrast values

A liquid crystal mixture comprising a chiral smectic liquid crystal mixture where the liquid crystal mixture is characterized by the phase sequence I—N*—SmC*, a spontaneous polarization in the operating temperature range of <40 nC/cm2 and a pitch of >10 μm at at least one temperature in the nematic or cholesteric phase and comprises at least one compound each from at least two of the substance classes (A), (B) and (C) and from 0.1 to 50% by weight, based on the liquid crystal mixture, of one or more compounds from substance class (D) R20—M18—(—A14—M14)a(—A15—M15)b—(—M16—A16)c—(—M17—A17)d——M19—R21 (D)

• where:
• R1, R2, R3, R4, R5, R6 are each, independently of one another,
• hydrogen or a straight-chain or branched alkyl or alkenyl radical (with or without asymmetric carbon atoms) having 2 to 18 carbon atoms, where one or two nonterminal, nonadjacent —CH2— groups may be replaced by —O— and/or one —CH2— group may be replaced by —C≡C— or —Si(CH3)2— and one or more H atoms may be replaced by F with the provisos that heteroatoms cannot be adjacent and that in each case only one of R1, R2 or R3, R4 or R5, R6, respectively, can be hydrogen;
• Y1, Y2, Y3, Y4, Y5, Y6 are each, independently of one another, —O—, —OC(═O)—, —C(═O)O—, —OC(═O)O— or a single bond;
• Z1 is —OC(═O)— or —C(═O)O—,
• is phenylene-1,4-diyl, unsubstituted, monosubstituted, disubstituted or trisubstituted by F, pyrimidine-2,5-diyl, unsubstituted or monosubstituted by F, pyridine-2,5-diyl, unsubstituted or monosubstituted by F, pyridazine-2,5-diyl, unsubstituted or monosubstituted by F,
• is phenylene-1,4-diyl, unsubstituted, monosubstituted, disubstituted or trisubstituted by F, pyrimidine-2,5-diyl, unsubstituted or monosubstituted by F, pyridine-2,5-diyl, unsubstituted or monosubstituted by F, pyridazine-2,5-diyl, unsubstituted or monosubstituted by F
• with the proviso that one of the rings A, B is one of the nitrogen heterocycles mentioned,
• are each phenylene-1,4-diyl, independently of one another unsubstituted, monosubstituted, disubstituted or trisubstituted by F
• with the proviso that at least one of the rings C, D, E is fluorophenylene-1,4-diyl or ortho-difluorophenylene-1,4-diyl,
• are each, independently of one another, phenylene-1,4-diyl, unsubstituted, monosubstituted, disubstituted or trisubstituted by F, pyrimidine-2,5-diyl, unsubstituted or monosubstituted by F, pyridine-2,5-diyl, unsubstituted or monosubstituted by F, pyridazine-5-diyl, unsubstituted or monosubstituted by F
• with the proviso that at least one of the rings F, G, K is one of the nitrogen heterocycles mentioned,
• R20, R21 are each, independently of one another,
• c) hydrogen or an alkyl, alkenyl, alkyloxy or alkenyloxy radical having 2 to 12 carbon atoms, where one or two nonadjacent —CH2— groups may be replaced by —OC(═O)—, —(O═)C—O—, —Si(CH3)2— or cyclopropane-1,2-diyl and one or more H atoms may be replaced by F or
• d) a moiety having at least one asymmetric carbon atom which is either part of an alkyl group having 3 to 16 carbon atoms, where 1 to 4 nonadjacent —CH2— groups may be replaced by —O—, —OC(═O)— or —(O═)C—O— and one of the substituents of the asymmetric carbon atom is —CH3, —CF3, —OCH3, —CH3, Cl, F, CN or —OCF3, or part of a 3- to 7-membered heterocycle, where one or two nonadjacent —CH2— groups may be replaced by —O— or one —CH2— group may be replaced by —OC(═O)— or —(O═)C—O—, with the proviso that the moiety as defined in b) having at least one asymmetric carbon atom is present in at least one of R20, R21 and M18 or M19 is a single bond if the moiety having the asymmetric carbon atom is part of an alkyl chain,
• A14, A15, A16, A17 are each, independently of one another, 1,4-phenylene, unsubstituted, monosubstituted or disubstituted by F or Cl, 1,3-phenylene, unsubstituted, monosubstituted or disubstituted by F or Cl, cyclohexane-1,4-diyl, unsubstituted or monosubstituted by F or CN, cyclohex-1-ene-1,4-diyl, 1-fluorocyclohex-1-ene-1,4-diyl, cyclohex-2-ene-1,4-diyl, 2-oxocyclohexane-1,4-diyl, 2-cyclohexen-1-one-3,6-diyl, 1-alkyl-1-sila-cyclohexane-1,4-diyl, bicyclo[2.2.2]octane-1,4-diyl, spiro[4.5]decane-2,8-diyl, spiro[5.5]undecane-3,9-diyl, indane-2,5-diyl, naphthalene-2,6-diyl, unsubstituted, monosubstituted or disubstituted by F or CN, pyrimidine-2,5-diyl, unsubstituted or monosubstituted by F, pyridine-2,5-diyl, unsubstituted or monosubstituted by F, pyrazine-2,5-diyl, unsubstituted or monosubstituted by F, pyridazine-3,6-diyl, quinoline-2,6-diyl, quinoline-3,7-diyl, isoquinoline-3,7-diyl, quinazoline-2,6-diyl, quinoxaline-2,6-diyl, 1,3-dioxane-2,5-diyl, thiophene-2,4-diyl, thiophene-2,5-diyl, 1,3-thiazole-2,4-diyl, 1,3-thiazole-2,5-diyl, isoxazole-3,5-diyl, benzthiazole-2,6-diyl, unsubstituted, monosubstituted or polysubstituted by F, benz-thiazole-2,5-diyl, unsubstituted, monosubstituted or polysubstituted by F, 1,3,4-thiadiazole-2,5-diyl, piperidine-1,4-diyl or piperazine-1,4-diyl,
• M14, M15, M16, M17 are each, independently of one another, a single bond, —OC(═O)—, —(O═)C—O—, —OCH2—, —CH2—O—, —CH2CH2—, —(CH2)4— or —C≡C—,
• M18, M19 are each, independently of one another, —OC(═O)—, —(O═)C—O—, —OCH2—, —CH2—O— or a single bond, and
• a, b, c, d are each, independently of one another, zero or 1 with the proviso 1≦{a+b+c+d}≦3.