Fluorinated fluorene derivatives

Fluorene derivatives of the formula I

• R1—(—A1—Z1—)k1—(—A2—Z2—)k2—W—(—Z3—A3—)k3—(—Z4—A4—)k4—R2 I
• in which
• W is the
• 19
• group,
• L1 and L2, independently of one another, are H, F, Cl, —CH2F, —CHF2 or —CF3, with the proviso that L1 and L2 are not both H,
• L3 and L4, independently of one another, are H or F,
• R1 and R2, independently of one another, are H, halogen, —CN, —NCS, —SF5 or alkyl having from 1 to 18 carbon atoms, in which, in addition, one or two non-adjacent —CH2— groups may be replaced by —O—, —S—, —CO—, —O—CO—, —CO—O—, —E— and/or —C≡C— and/or in which, in addition, one or more H atoms may be replaced by halogen and/or —CN,
• E is CR4═CR5 or CHR4—CHR5,
• R4 and R5 are each, independently of one another, H, alkyl having 1-6 carbon atoms, F, Cl, CF3 or CN,
• A1, A2, A3
• and A4 are each, independently of one another, 1,4-phenylene, in which one or more CH groups may be replaced by N, 1,4-cyclohexylene, in which one or two non-adjacent CH2 groups may be replaced by O and/or S, 1,4-cyclohexenylene, 1,4-bicyclo[2.2.2]-octylene, piperidine-1,4-diyl, naphthalene-2,6-diyl, decahydronaphthalene-2,6-diyl or 1,2,3,4-tetrahydronaphthalene-2,6-diyl, where, in the meanings given for A1, A2, A3 and A4, one or more H atoms may be substituted by halogen, —CN and/or alkyl having from 1 to 6 carbon atoms, in which one or more H atoms may be replaced by halogen or —CN, and/or in which one or more non-adjacent —CH2— groups may be replaced, independently of one another, by —CO—, —O—CO—, —CO—O—, —O—, —S—, —CH═CH— or —C≡C—, and
• Z1, Z2, Z3
• and Z4, independently of one another, are —O—CO—, —CO—O—, —CH2—O—, —CF2—O—, —O—CH2—, —O—CF2—, —C2H4—, —CH2—CF2—, —CF2—CH2—, —CF2—CF2—, —CH═CH—, —CF═CH—, —CH═CF—, —CF═CF—, —C≡C— or a single bond,
• k1, k2, k3
• and k4, independently of one another, are 0, 1 or 2.