Compounds for the homeotropic alignment of liquid-crystalline media

A compound of the formula I

• R1-[A2-Z2]m-A1-Ra (I)
• in which
• m denotes 4,
• A1 denotes an aromatic, heteroaromatic, alicyclic or heterocyclic group, which may also contain anellated rings and which may also be mono- or polysubstituted by a group L or -Sp-P,
• A2 in each case, independently of one another, identically or differetly, denotes an aromatic, heteroaromatic, alicyclic or heterocyclic group, which may also contain anellated rings and which may also be mono- or polysubstituted by a group L or -Sp-P,
• L in each case, independently of one another, denotes unbranched or branched alkyl, alkenyl, 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, or denotes F, Cl, Br, I, —CN, —NO2, —NCO, —NCS, —OCN, —SCN, —C(═O)N(R0)R00 or cycloalkyl having 3 to 6 C atoms,
• P denotes a polymerisable group,
• Sp denotes a spacer group or a single bond,
• 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—, —CF2CH2—, —CH2CF2—, —(CF2)n1—, —CH═CH—, —CF═CF—, —C≡C—, —CH═CH—COO—, —OCO—CH═CH—, —(CR0R00)n1—, —CH(-Sp-P)—, —CH2CH(-Sp-P)—, —CH(-Sp-P)CH(-Sp-P)—,
• n1 denotes 1, 2, 3 or 4,
• R0 in each case, independently of one another, denotes alkyl having 1 to 12 C atoms,
• R00 in each case, independently of one another, denotes H or alkyl having 1 to 12 C atoms,
• R1 denotes an alkyl radical having 1 to 25 C atoms, where, in addition, one or more CH2 groups in this radical may each be replaced, independently of one another, by —CH═CH—, —C≡C—, —CF2O—, —OCF2—,
• —O—, —S—, —CO—, —CO—O— or —O—CO— in such a way that O/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, or denotes H, or a group -Sp-P,
• Ra denotes an anchor group of the formula
• p denotes 1 or 2,
• q denotes 2 or 3,
• B denotes a substituted or unsubstituted ring system or condensed ring system,
• o denotes 0 or 1,
• X1, independently of one another, denotes OH, SH, NH2, NHR11, NR112, C(O)OH or —CHO,
• R11 denotes alkyl having 1 to 12 C atoms, which may be linear or branched, and in which H may be substituted by fluorine or alkoxy having 1 to 8 C atoms,
• Spa, Spc, Spd in each case, independently of one another, denote a spacer group or a single bond, and
• Spb denotes a tri-or tetravalent group.