Described are compounds that are capable of forming adlayers, the compounds comprising at least one headgroup A, an optional linker B, a polymer C, a terminal group D and an optional crosslinking group R, wherein the headgroup A is a compound of the following formula wherein X is independently selected from an acidic group, Y is a group derived from a convenient coupling group, Z1, Z3, and Z4 are C or N+ Z2, Z5 and Z6 are C-L1 or N+-L, wherein L1 is H or an electron withdrawing group, L is C1-C6 alkyl, in particular C1-C4 alkyl L2 and L3 are independently selected from H or C1-C6 alkyl, or L2 may form together with L1 or L of Z6 a heterocycle, in particular a positively charged heterocycle, n is 0, or 1, or 2, or 3, m is 0 or 1.
