Fluorinated heterocycles and their use in liquid-crystal mixtures

A compound of formula (I),

• wherein
• R1 and R2 are, each independently,
• a) H
• b) a straight-chain or branched alkyl radical having 1 to 16 carbon atoms, or a straight-chain or branched alkenyl radical having 2 to 16 carbon atoms, in which
• b1) one or more nonadjacent and nonterminal CH2 groups may be replaced by —O—, —C(═O)O—, —O—C(═O)—, —O—C(═O)—O—, —C(═O)— or —Si(CH3)2— and/or
• b2) one CH2 group may be replaced by —C≡C—, cyclopropane-1,2-diyl, cyclobutane-1,3-diyl, cyclohexane-1,4-diyl or phenylene-1,4-diyl and/or
• b3) one or more hydrogen atoms may be replaced by F and/or Cl,
• c) —M1—A1—R5,
• p, q are, each independently, 0 or 1, and in case p or q is zero, —H is present instead of —F,
• M1 is —CO—O—, —O—CO—, —CH2—O—, —O—CH2—, —CF2—O—, —O—CF2—, —CH═CH—, —CF═CF—, —C≡C—, —CH2—CH2—CO—O—, —O—CO—CH2—CH2—, —CH2—CH2—, —CF2—CF2—, —(CH2)4—, —OC(═O)CF═CF— or a single bond,
• A1 is 1,4-phenylene in which one or two hydrogen atoms may be replaced by F, Cl, CN and/or OCF3, or three hydrogen atoms may be replaced by fluorine, 1,4-cyclohexylene in which one or two hydrogen atoms may be replaced by CH3 and/or F, 1-cyclohexene-1,4-diyl in which one hydrogen atom may be replaced by CH3 or F, pyrimidine-2,5-diyl, pyridine-2,5-diyl or 1,3-dioxane-2,5-diyl
• R5 has the same definition as specified for R1 and R2, with the exception of —M1—A1—R5, but independently of the definition of R1 and R2,
• X is H, F, OCF3, CF3, or OCF2H, with the following provisos:
• a) at least one of p, q has to be 1,
• b) R1 and R2 must not at the same time be H,
• c) R2 and X must not at the same time be H.