A compound of the formula or silicic acid (hetero)polycondensate comprising hydrolytically condensable structures of the formula, wherein R 2 is a hydroxy group or a free carboxylic acid residue or a carboxylic acid ester or a salt derived therefrom, R 3 denotes a radical having a hydrocarbon-containing, branched or unbranched backbone which is bonded to the silicon via carbon and may be interrupted at will by heteroatoms or coupling groups or other groups containing heteroatoms, the zigzag line designating the hydrocarbon-containing backbone purely schematically, the three unspecified bonds of the Si atom representing further radicals bonded to the silicon atom, selected from radicals which can be hydrolysed from silicon, hydroxy groups and radicals bonded to the silicon via a carbon atom, which may have the same meaning as R 3 or a different meaning, or which represent oxygen bridges to other silicon atoms and/or other metal atoms, if the structure is part of a silicic acid (hetero)polycondensate, the radical Y is either divalent and then has the meaning -S-, -NR 4 - or -P (R 4) c (Z') d -with Z' = OR 4, c = 0 or 1, d = 0 or 1 and (c+d) = 1, or is trivalent and denotes -N= or - P =, R 4 represents a hydrocarbon-containing radical and can also represent hydrogen in the radical -NR 4-, W is a substituted or unsubstituted hydrocarbon radical which is bonded to Y and whose chain may be interrupted by -S-, -0-, -NH-, -NR 4 -, -C O-, -NHC -, -C NH-, -NHC O-, -C NHC -, -NHC NH-, -S -, -C O-, -C NH-, -NHC -, - NHC O-, Ar is a radical carrying at least one aromatic group which is unsubstituted or which is substituted by one or more radicals, the aromatic groups being free from substituents chosen from the boronic acid group, the carboxylic acid group, the phosphinic acid group, the phosphonic acid group and the sulphonic acid group and from hydroxy groups, where Ar must be bound to W if a # 0, the index a is 0 or 1 or 2, the index b = 1, 2, 3 or an integer greater than 3 if a ≠ 0, and b = 1 or 2 if a = 1, the index m is 1, 2 or an integer greater than 2, the index n is 0, 1, 2 or greater than 2 and the index o is 1 or 2 or greater than 2. R 2 is a hydroxy group or a free carboxylic acid residue or a carboxylic acid ester or a salt derived therefrom, R 3 denotes a radical having a hydrocarbon-containing, branched or unbranched backbone which is bonded to the silicon via carbon and may be interrupted at will by heteroatoms or coupling groups or other groups containing heteroatoms, the zigzag line designating the hydrocarbon-containing backbone purely schematically, the three unspecified bonds of the Si atom representing further radicals bonded to the silicon atom, selected from radicals which can be hydrolysed from silicon, hydroxy groups and radicals bonded to the silicon via a carbon atom, which may have the same meaning as R 3 or a different meaning, or which represent oxygen bridges to other silicon atoms and/or other metal atoms, if the structure is part of a silicic acid (hetero)polycondensate, the radical Y is either divalent and then has the meaning -S-, -NR 4 - or -P (R 4) c (Z') d -with Z' = OR 4, c = 0 or 1, d = 0 or 1 and (c+d) = 1, or is trivalent and denotes -N= or - P =, R 4 represents a hydrocarbon-containing radical and can also represent hydrogen in the radical -NR 4-, W is a substituted or unsubstituted hydrocarbon radical which is bonded to Y and whose chain may be interrupted by -S-, -0-, -NH-, -NR 4 -, -C O-, -NHC -, -C NH-, -NHC O-, -C NHC -, -NHC NH-, -S -, -C O-, -C NH-, -NHC -, - NHC O-, Ar is a radical carrying at least one aromatic group which is unsubstituted or which is substituted by one or more radicals, the aromatic groups being free from substituents chosen from the boronic acid group, the carboxylic acid group, the phosphinic acid group, the phosphonic acid group and the sulphonic acid group and from hydroxy groups, where Ar must be bound to W if a # 0, the index a is 0 or 1 or 2, the index b = 1, 2, 3 or an integer greater than 3 if a ≠ 0, and b = 1 or 2 if a = 1, the index m is 1, 2 or an integer greater than 2, the index n is 0, 1, 2 or greater than 2 and the index o is 1 or 2 or greater than 2.