Compounds selected from the following formulae: in which R a denotes an anchor group of the formula p denotes 1 or 2, o denotes 0 or 1, where o = 0 for the formulae IC-3 to IC-4, X 1, independently of one another, denotes H, alkyl, fluoroalkyl, -OH, -SH, -NH 2, -NHR 11, -NR 11 2, NHC -R 11, -OR 11, -C OH or -CHO, where at least one group X 1 denotes a radical selected from -OH, -SH, -NH 2, -NHR 11, -C OH and -CHO, R 11 denotes alkyl having 1 to 12 C atoms, Sp a, Sp c in each case, independently of one another, denote a spacer group or a single bond, Sp b denotes a tri- or tetravalent group, R 1, independently of one another, denotes H, halogen, straightchain, branched or cyclic alkyl having 1 to 25 C atoms, in which, in addition, one or more non-adjacent CH 2 groups may be 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, in addition, one or more H atoms may be replaced by F or Cl, or a group -Sp-P, P denotes a polymerisable group, Sp denotes a spacer group or a single bond, R 2 in each case, independently of one another, denotes straightchain 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, -NO 2, -NCO, -NCS, -OCN, -SCN, -C(=O)N(R 0) 2, -C(=O)R 0, optionally substituted aryl or cycloalkyl having 3 to 20 C atoms, R 0 in each case, independently of one another, denotes alkyl having 1 to 12 C atoms, R 00 in each case, independently of one another, denotes H or alkyl having 1 to 12 C atoms. R a denotes an anchor group of the formula p denotes 1 or 2, o denotes 0 or 1, where o = 0 for the formulae IC-3 to IC-4, X 1, independently of one another, denotes H, alkyl, fluoroalkyl, -OH, -SH, -NH 2, -NHR 11, -NR 11 2, NHC -R 11, -OR 11, -C OH or -CHO, where at least one group X 1 denotes a radical selected from -OH, -SH, -NH 2, -NHR 11, -C OH and -CHO, R 11 denotes alkyl having 1 to 12 C atoms, Sp a, Sp c in each case, independently of one another, denote a spacer group or a single bond, Sp b denotes a tri- or tetravalent group, R 1, independently of one another, denotes H, halogen, straightchain, branched or cyclic alkyl having 1 to 25 C atoms, in which, in addition, one or more non-adjacent CH 2 groups may be 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, in addition, one or more H atoms may be replaced by F or Cl, or a group -Sp-P, P denotes a polymerisable group, Sp denotes a spacer group or a single bond, R 2 in each case, independently of one another, denotes straightchain 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, -NO 2, -NCO, -NCS, -OCN, -SCN, -C(=O)N(R 0) 2, -C(=O)R 0, optionally substituted aryl or cycloalkyl having 3 to 20 C atoms, R 0 in each case, independently of one another, denotes alkyl having 1 to 12 C atoms, R 00 in each case, independently of one another, denotes H or alkyl having 1 to 12 C atoms.