Ultra bright dimeric or polymeric dyes

A compound having the following structure (I):

• or a salt or tautomer thereof, wherein:
• M is, at each occurrence, independently a monovalent moiety comprising two or more carbon-carbon double bonds and at least one degree of conjugation;
• M′ is, at each occurrence, independently a divalent moiety having one of the following structures:
• L is, at each occurrence, independently an alkylene or alkenylene linker, wherein the alkylene or alkenylene linker is unsubstituted;
• L2 and L3 are, at each occurrence, independently an optional alkylene, alkenylene, alkynylene, heteroalkylene, heteroalkenylene, heteroalkynylene or heteroatomic linker;
• L1 is at each occurrence, independently either:
• i) an optional 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;
• L4 is, at each occurrence, independently an alkylene, alkenylene, alkynylene, heteroalkylene, heteroalkenylene, carbocyclic or heterocyclic linker;
• R1 is, at each occurrence, independently H, alkyl or alkoxy;
• R2 and R3 are each independently H, OH, SH, alkyl, alkoxy, alkylether, heteroalkyl, —OP(═Ra)(Rb)Rc, Q or L′;
• R4 is, at each occurrence, independently OH, SH, O−, S−, ORd or SRd;
• R5 is, at each occurrence, independently oxo, thioxo or absent;
• Ra is O or S;
• Rb is OH, SH, O−, S−, ORd or SRd;
• Rc is OH, SH, O−, S−, ORd, OL′, SRd, alkyl, alkoxy, heteroalkyl, heteroalkoxy, alkylether, alkoxyalkylether, phosphate, thiophosphate, phosphoalkyl, thiophosphoalkyl, phosphoalkylether or thiophosphoalkylether;
• Rd is a counter ion;
• Q is, at each occurrence, independently a moiety comprising a reactive group, or protected analogue thereof, capable of forming a covalent bond with an analyte molecule, a targeting moiety, a solid support or a complementary reactive group Q′;
• 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 (I);
• m1 and m2 are, at each occurrence, independently an integer of zero or greater;
• n, x and y are each independently an integer of zero or greater for each integral value of z;
• and
• z is an integer of 1 or greater,
• provided that x is 1 or greater for at least one integral value of z, and at least one of n or y is 1 or greater for at least one integral value of z.