Compounds for the homeotropic alignment of liquid-crystalline media

A compound of formula IB-1, IB-2, IB-3, IB-4, IC-3 or IC-4

• in which
• R2 denotes a straight-chain or branched alkyl, alkenyl, alkoxy, alkylcarbonyl, alkoxycarbonyl, alkylcarbonyloxy or alkoxycarbonyloxy having 1 to 25 C atoms, in which optionally one or more H atoms are replaced by F or Cl, or denotes F, Cl, Br, I, —CN, —NO2, —NCO, —NCS, —OCN, —SCN,) —C(═O)N(R0)2, —C(═O)R0, or optionally substituted aryl or cycloalkyl having 3 to 20 C atoms,
• P denotes a polymerisable group,
• Sp denotes a spacer group or a single bond,
• Ra denotes an anchor group of the following formula
• p denotes 1 or 2,
• o denotes 0 or 1 for formulae IB-1, IB-2, IB-3 and IB-4, and denotes 0 for formulae IC-3 and IC-4,
• X1 each, independently of one another, denotes H, alkyl, fluoroalkyl, —OH, —SH, —NH2, —NHR11, —NR112, NHC(O)—R11, —OR11, —C(O)OH or —CHO,
• where at least one group X1 denotes —OH, —SH, —NH2, —NHR11, —C(O)OH or —CHO,
• R11 denotes alkyl having 1 to 12 C atoms,
• Spa, Spc each, in each case, independently of one another, denotes a spacer group or a single bond,
• Spb denotes a tri- or tetravalent group,
• R1 denotes H, halogen, straight-chain, branched or cyclic alkyl having 1 to 25 C atoms, in which one or more non-adjacent CH2 groups are optionally replaced by —O—, —S—, —CH═CH—, —C≡C—, —CO—, —CO—O—, —O—CO— or —O—CO—O— in such a way that O and/or S atoms are not linked directly to one another and in which one or more H atoms are optionally replaced by F or Cl,
• or denotes a group -Sp-P, and
• R0 each, in each case, independently of one another, denotes alkyl having 1 to 12 C atoms.