Dibenzofuran and dibenzothiophene derivatives

A compound of formula I

• in which
• W denotes O or S
• R denotes H, an alkyl radical having 1 to 15 C atoms, wherein one or more CH2 groups in these radicals may each be replaced, independently of one another, by —C≡C—, —CF2O—, —OCF2—, —CH═CH—,
• —O—, —CO—O— or —O—CO— in such a way that 0 atoms are not linked directly to one another, and in which one or more H atoms may be replaced by halogen,
• A on each occurrence, identically or differently, denotes a radical selected from the following groups:
• a) the group consisting of trans-1,4-cyclohexylene, 1,4-cyclohexenylene, and decaline-2,6-diyl, in which one or more non-adjacent CH2 groups may be replaced by —O— and/or —S— and in which one or more H atoms may be replaced by F,
• b) the group consisting of 1,4-phenylene and 2,6-naphthylene, in which one or two CH groups may be replaced by N and in which, in addition, one or more H atoms may be replaced by L,
• c) the group consisting of 1,3-dioxane-2,5-diyl, tetrahydrofuran-2,5-diyl, cyclobutane-1,3-diyl, thiophene-2,5-diyl, selenophene-2,5-diyl, and 1,2,3,4-tetrahydronanaphthaline-2,6-diyl, each of which may be mono- or polysubstituted by L,
• d) the group consisting of bicyclo[1.1.1]pentane-1,3-diyl, bicyclo[2.2.2]octane-1,4-diyl, and spiro[3.3]heptane-2,6-diyl, in which one or more H atoms may be replaced by F,
• L on each occurrence, identically or differently, denotes halogen, cyano, alkyl, alkoxy, alkylcarbonyl or alkoxycarbonyl group with 1 to 7 C atoms, wherein one or more H atoms may be substituted by F or Cl,
• Z on each occurrence, identically or differently, denotes a single bond, —CF2O—, —OCF2—, —CH2CH2—, —CF2CF2—,
• —C(O)O—, —OC(O)—, —CH2O—, —OCH2—, —CF═CH—, —CH═CF—, —CF═CF—, —CH═CH— or —C≡C—,
• Y1 and Y2 denote F and Y3 denotes H,
• X denotes OCF3 or CF3 and
• n is 0, 1 or 2,
• wherein the compound has positive dielectric anosotropy.