A compound having the following structure: or a stereoisomer, salt or tautomer thereof, wherein: A has, at each occurrence, independently one of the following structures: or M, at each occurrence, independently has one of the following structures: L 1 is at each occurrence, independently either: i) absent, an alkylene, alkenylene, alkynylene, heteroalkylene, heteroalkenylene, heteroalkynylene or heteroatomic linker; or ii) a linker comprising a functional group capable of formation by reaction of two complementary reactive groups, wherein for at least one occurrence of L 1, the functional group can be formed by reaction of an aldehyde, oxime, hydrazone, alkyne, amine, azide, acylazide, acylhalide, nitrile, nitrone, sulfhydryl, disulfide, sulfonyl halide, isothiocyanate, imidoester, activated ester, ketone, α,β-unsaturated carbonyl, alkene, maleimide, α-haloimide, epoxide, aziridine, tetrazine, tetrazole, phosphine, biotin or thiirane functional group with a complementary reactive group; L 2, L 3, L 4 and L 5 are, at each occurrence, independently absent or an alkylene, alkenylene, alkynylene, heteroalkylene, heteroalkenylene, heteroalkynylene or heteroatomic linker; R 1 is, at each occurrence, independently H, alkyl or alkoxy; R 2 and R 3 are each independently H, OH, SH, alkyl, alkoxy, alkylether, -OP(=R a)(R b)R c, Q, a linker comprising a covalent bond to Q, a linker comprising a covalent bond to an analyte molecule, a linker comprising a covalent bond to a solid support or a linker comprising a covalent bond to a further compound of structure, wherein: R a is O or S; R b is OH, SH, O -, S -, OR d or SR d; R c is OH, SH, O -, S -, OR 4, SR d, alkyl, alkoxy, alkylether, alkoxyalkylether, phosphate, thiophosphate, phosphoalkyl, thiophosphoalkyl, phosphoalkylether or thiophosphoalkylether; and R d is a counter ion; R 4 is, at each occurrence, independently OH, SH, O -, S -, OR d or SR d; R 5 is, at each occurrence, independently oxo, thioxo or absent; Q at each occurrence, independently comprises a sulfhydryl, disulfide, activated ester, isothiocyanate, azide, alkyne, alkene, diene, dienophile, acid halide, sulfonyl halide, phosphine, α-haloamide, biotin, amino or maleimide functional group; m is, at each occurrence, independently an integer of zero or greater, provided that at least one occurrence of m is an integer of one or greater; and n is an integer of one or greater, wherein the term "linker" refers to a contiguous chain of at least one atom, which connects a portion of a molecule to another portion of the same molecule or to a different molecule, moiety or solid support and wherein the activated ester is an N-succinimide ester, imidoester or polyfluorophenyl ester. A has, at each occurrence, independently one of the following structures: or M, at each occurrence, independently has one of the following structures: L 1 is at each occurrence, independently either: i) absent, an alkylene, alkenylene, alkynylene, heteroalkylene, heteroalkenylene, heteroalkynylene or heteroatomic linker; or ii) a linker comprising a functional group capable of formation by reaction of two complementary reactive groups, wherein for at least one occurrence of L 1, the functional group can be formed by reaction of an aldehyde, oxime, hydrazone, alkyne, amine, azide, acylazide, acylhalide, nitrile, nitrone, sulfhydryl, disulfide, sulfonyl halide, isothiocyanate, imidoester, activated ester, ketone, α,β-unsaturated carbonyl, alkene, maleimide, α-haloimide, epoxide, aziridine, tetrazine, tetrazole, phosphine, biotin or thiirane functional group with a complementary reactive group; L 2, L 3, L 4 and L 5 are, at each occurrence, independently absent or an alkylene, alkenylene, alkynylene, heteroalkylene, heteroalkenylene, heteroalkynylene or heteroatomic linker; R 1 is, at each occurrence, independently H, alkyl or alkoxy; R 2 and R 3 are each independently H, OH, SH, alkyl, alkoxy, alkylether, -OP(=R a)(R b)R c, Q, a linker comprising a covalent bond to Q, a linker comprising a covalent bond to an analyte molecule, a linker comprising a covalent bond to a solid support or a linker comprising a covalent bond to a further compound of structure, wherein: R a is O or S; R b is OH, SH, O -, S -, OR d or SR d; R c is OH, SH, O -, S -, OR 4, SR d, alkyl, alkoxy, alkylether, alkoxyalkylether, phosphate, thiophosphate, phosphoalkyl, thiophosphoalkyl, phosphoalkylether or thiophosphoalkylether; and R d is a counter ion; R 4 is, at each occurrence, independently OH, SH, O -, S -, OR d or SR d; R 5 is, at each occurrence, independently oxo, thioxo or absent; Q at each occurrence, independently comprises a sulfhydryl, disulfide, activated ester, isothiocyanate, azide, alkyne, alkene, diene, dienophile, acid halide, sulfonyl halide, phosphine, α-haloamide, biotin, amino or maleimide functional group; m is, at each occurrence, independently an integer of zero or greater, provided that at least one occurrence of m is an integer of one or greater; and n is an integer of one or greater, wherein the term "linker" refers to a contiguous chain of at least one atom, which connects a portion of a molecule to another portion of the same molecule or to a different molecule, moiety or solid support and wherein the activated ester is an N-succinimide ester, imidoester or polyfluorophenyl ester.