A composition comprising a polymeric dye and a cyclodextrin, wherein the polymeric dye is a compound having the following structure: or a stereoisomer, salt or tautomer thereof, wherein: M is, at each occurrence, independently a fluorescent moiety comprising two or more carbon-carbon double bonds and at least one degree of conjugation; L 1 is at each occurrence, independently an optional 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, alkyl, heteroalkyl, -OP(=R a)(R b)R c, Q, or L'; 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; 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 d, OL', SR d, alkyl, alkoxy, heteroalkyl, heteroalkoxy, alkylether, alkoxyalkylether, phosphate, thiophosphate, phosphoalkyl, thiophosphoalkyl, phosphoalkylether or thiophosphoalkylether; R d is a counter ion; Q is, at each occurrence, independently a moiety comprising a disulfide, isothiocyanate, azide, alkyne, alkene, diene, dienophile, acid halide, sulfonyl halide, phosphine, α-haloamide, biotin, amino functional group or Q comprises one of the following structures: wherein: X is halo; and EWG is an electron withdrawing group; L' is, at each occurrence, independently a linker comprising a covalent bond to Q, a linker comprising a covalent bond to a targeting moiety, a linker comprising a covalent bond to an analyte molecule, a linker comprising a covalent bond to a solid support, a linker comprising a covalent bond to a solid support residue, a linker comprising a covalent bond to a nucleoside or a linker comprising a covalent bond to a further compound of structure; 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; n is an integer of one or greater; x 1, x 2, x 3 and x 4 are, at each occurrence, independently an integer from 0 to 6; z is an integer from 2 to 100; and wherein a "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 via a covalent bond. M is, at each occurrence, independently a fluorescent moiety comprising two or more carbon-carbon double bonds and at least one degree of conjugation; L 1 is at each occurrence, independently an optional 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, alkyl, heteroalkyl, -OP(=R a)(R b)R c, Q, or L'; 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; 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 d, OL', SR d, alkyl, alkoxy, heteroalkyl, heteroalkoxy, alkylether, alkoxyalkylether, phosphate, thiophosphate, phosphoalkyl, thiophosphoalkyl, phosphoalkylether or thiophosphoalkylether; R d is a counter ion; Q is, at each occurrence, independently a moiety comprising a disulfide, isothiocyanate, azide, alkyne, alkene, diene, dienophile, acid halide, sulfonyl halide, phosphine, α-haloamide, biotin, amino functional group or Q comprises one of the following structures: wherein: X is halo; and EWG is an electron withdrawing group; L' is, at each occurrence, independently a linker comprising a covalent bond to Q, a linker comprising a covalent bond to a targeting moiety, a linker comprising a covalent bond to an analyte molecule, a linker comprising a covalent bond to a solid support, a linker comprising a covalent bond to a solid support residue, a linker comprising a covalent bond to a nucleoside or a linker comprising a covalent bond to a further compound of structure; 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; n is an integer of one or greater; x 1, x 2, x 3 and x 4 are, at each occurrence, independently an integer from 0 to 6; z is an integer from 2 to 100; and wherein a "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 via a covalent bond. X is halo; and EWG is an electron withdrawing group; L' is, at each occurrence, independently a linker comprising a covalent bond to Q, a linker comprising a covalent bond to a targeting moiety, a linker comprising a covalent bond to an analyte molecule, a linker comprising a covalent bond to a solid support, a linker comprising a covalent bond to a solid support residue, a linker comprising a covalent bond to a nucleoside or a linker comprising a covalent bond to a further compound of structure; 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; n is an integer of one or greater; x 1, x 2, x 3 and x 4 are, at each occurrence, independently an integer from 0 to 6; z is an integer from 2 to 100; and wherein a "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 via a covalent bond.