Liquid crystal displays and liquid crystalline media with homeotropic alignment

A compound of formula I

• R1-A1-(Z2-A2)m1-R2 (I)
• in which:
• R2 denotes a group of the formula (A2)
• in which
• Sp denotes a spacer group or a single bond,
• X1 denotes a group —NH2, —NHR11, —NR112, —OH, —(CO)OH or a group of the formula
• R0 denotes H or alkyl having 1 to 12 C atoms,
• X2 in each case independently denotes —NH—, —NR11—, —O— or a single bond,
• R12 denotes H, F, Cl, CN, —OH, —NH2, or a halogenated or unsubstituted alkyl radical having 1 to 15 C atoms, where, in addition, one or more CH2 groups in this radical may each be replaced, independently of one another, by —C≡C—, —CH═CH—, —(CO)O—, —O(CO)—, —(CO)—, —O—, —NH— or —NR1— in such a way that O and N atoms are not linked directly to one another,
• n denotes 1, 2 or 3,
• R11 in each case independently denotes a halogenated or unsubstituted alkyl radical having 1 to 15 C atoms, where, in addition, one or more CH2 groups in this radical may each be replaced, independently of one another, by —C≡C—, —CH═CH—, —(CO)O—, —O(CO)—, —(CO)— or —O— in such a way that O atoms are not linked directly to one another, and where two radicals R11 may be linked to one another to form a ring,
• A1 and A2 each, independently of one another, denote an aromatic, heteroaromatic, alicyclic or heterocyclic group, which may also contain fused rings, and which may also be mono- or polysubstituted by a group L,
• L in each case, independently of one another, denotes —OH, —(CH2)n1—OH, F, Cl, Br, I, —CN, —NO2, —NCO, —NCS, —OCN, —SCN, —C(═O)N(R0)2, —C(═O)R0, —N(R0)2, —(CH2)n1—N(R0)2, in which n1 is 1-4, optionally substituted silyl, optionally substituted aryl or alicyclyl having 6 to 20 C atoms, or straight-chain or branched alkyl, alkoxy, alkylcarbonyl, alkoxycarbonyl, alkylcarbonyloxy or alkoxycarbonyloxy having 1 to 25 C atoms, in which, in addition, one or more H atoms may be replaced by F or Cl,
• Z2 in each case, independently of one another, denotes a single bond, —O—, —S—, —CO—, —CO—O—, —OCO—, —O—CO—O—, —OCH2—, —CH2O—, —SCH2—, —CH2S—, —CF2O—, —OCF2—, —CF2S—, —SCF2—, —(CH2)n1—, in which n1 is 1, 3 or 4, —CF2CH2—, —CH2CF2—, —(CF2)n1—, in which n1 is 1-4, —CH═CH—, —CF═CF—, —C≡C—, —CH═CH—COO—, —OCO—CH═CH— or CR0R00,
• R0 and R00 each, independently of one another, denote H or alkyl having 1 to 12 C atoms,
• R1 denotes H, halogen, straight-chain, branched or cyclic alkyl having 1 to 25 C atoms, in which, in addition, one or more non-adjacent CH2 groups may be replaced by —NR2, —NR—, —0—, —S—, —CO—, —CO—O—, —O—CO—, —O—CO—O— in such a way that O and/or S atoms are not linked directly to one another, and in which, in addition, one or more H atoms may be replaced by F or Cl, and
• m1 denotes 2, 3 or 4.