Compounds having the general structure where n = 0 or 1 and salts thereof, wherein Z is either Z = 4-pyridyl to form structure I, or Z = 3-pyridyl to form structure II, or Z = 2-pyridyl to form structure III, and R2 and/or R7 are each a reactive group A bound via a linker L for covalently bonding compounds of the structures I, II or III to a molecule K to be marked, wherein A is an amine (-NH 2), hydroxy (-OH) or phosphoramidite function (-O-P-[O-CH 2 -CH 2 -CN]-N[(CH(CH 3) 2] 2), a carboxylic acid (-COOH), an alkyl or active ester derived therefrom (NHS ester, sulfo-NHS ester, tetrafluorophenyl ester, p-sulfotetrafluorophenyl ester); a carboxylic acid hydrazide (-CONHNH 2); or a carboxylic acid amide (-CONHR12) where R12 is -(CH 2) t -Y, wherein Y is -OH, -NH 2, -NH 3 +, maleimide (-N[CO-CH] 2), -NCS, -NCO, -NH-CO-CH 2 -I, -NH-CO-CH 2 -Br, azide (-N3), alkyne (-CCH) or phosphoramidite (-O-P-[O-CH 2 -CH 2 -CN]-N-[CH-(CH 3) 2] 2), and K is a covalently bound component selected from the group haptens, proteins (antibodies), low molecular weight drug compounds, peptides, nucleotides, nucleosides, DNA oligomers, polymers, and t represents the numbers of 1-10, L is a linker selected from a group featuring -(CH 2) s -, -[(CH 2) m -O] p -(CH 2) m -, -NR10-(CH 2) s -, -O-(CH 2) s -, -NR10-C -(CH 2) s -, -NR10-C -O-(CH 2) s -, or -NR10-C -NR11-(CH 2) s -, wherein R10 and R11 are each independently hydrogen, alkyl and alkoxy-alkyl (-[(CH 2) m -O] p -CH 3), ω-sulfoalkyl (-(CH 2) r -SO 3), m represents the numbers of 2-5, p, r and s each independently represent the numbers of 1-10, R1 and R3 - R6 are each independently hydrogen, chlorine, bromine or a sulfonic acid moiety, in case R2 is LA, L is -NR10-(CH 2) s -, -O-(CH 2) s -, -NR10-C -(CH 2) s -, -NR10-C -O-(CH 2) s - or -NR10-C -NR11-(CH 2) s -, in case R2 is not LA, R2 is equal to ω-sulfoalkoxy (-O-(CH 2) r - SO 3), alkoxy, polyalkoxy (-O-[(CH 2) m -O]p-CH 3), an amine function (-NR8R9), wherein R8 and R9 are each independently hydrogen, alkyl, ω-sulfoalkyl (-(CH 2) r -SO 3), -CO-alkyl, -CO-NR10-alkyl or -CO-O-alkyl, in case R7 is LA, L is equal to -(CH 2) s - or -[(CH 2) m -O]p-(CH 2) m -, in case R7 is not LA, R7 is equal to ω-sulfoalkyl (-(CH 2) r -SO 3), in case that in the structures I and III R3-R4 are bridged -(CR13=CR14) 2 -, wherein R13 and R14 are each independently hydrogen and/or a sulfonic acid moiety, R1, R2, R5 and R6 are each hydrogen or a sulfonic acid moiety, wherein at least one of R1, R2, R13, R14 is a sulfonic acid moiety, and R7 is equal to -LA where L is - (CH 2) s - or -[(CH 2) m -O]p-(CH 2) m -, in case that in the structures I and III R5-R6 are bridged -(CR13=CR14) 2 -, wherein R13 and R14 are each independently hydrogen and/or a sulfonic acid moiety, R1, R3 and R4 are each hydrogen, chlorine, bromine and a sulfonic acid moiety, and R2 is sulfoalkoxy (-O-(CH 2) r -SO 3), C1-C18-alkoxy or polyalkoxy (-O-[(CH 2) m -O] p -CH 3), and R7 is equal to -LA where L is -(CH 2) s - or -[(CH 2) m -O] p -(CH 2) m -, in case that in the structures I and III R3-R4 and R5-R6 are bridged -(CR13=CR14) 2 -, wherein R13 and R14 are each independently hydrogen and/or a sulfonic acid moiety, R1 and R2 are each hydrogen or a sulfonic acid moiety, wherein at least one of R1, R2, R13, R14 is a sulfonic acid moiety, and R7 is equal to -LA where L is -(CH 2) s - or -[(CH 2) m -O] p -(CH 2)-.