Modified carbocyanine dyes and their conjugates

A compound having a structure of the formula:

• A-BRIDGE-B
• wherein A has a structure of Formula I and B has a structure of Formula VII;
• BRIDGE has a structure of the Formula VIII;
• wherein Y represents the atoms necessary to form one to two fused aromatic rings having 6 atoms in each ring, wherein the atoms are selected from —CH, —C, —CR1, and —N(R2)β;
• wherein each β is 0 or 1, each R1 is Cl-C6 alkyl, C1-C6 alkoxy, C1-C6 alkylamino, or C2-C12 dialkylamino;
• X is O, S, or —CR3R4;
• R3 is -L-Rx;
• L is a linkage containing 1-20 nonhydrogen atoms selected from the group consisting of C, N, O, P and S;
• Rx is an activated ester of a carboxylic acid or a phosphoramidite;
• R2 and R4 are independently C1-C22 alkyl or C7-C22 arylalkyl;
• α is 0 or 1;
• W represents the atoms necessary to form one to two fused aromatic rings having 6 atoms in each ring, wherein the atoms are selected from —CH, —C, —CR1′, and —N(R12)β′;
• wherein each β′ is 0 or 1, each R1′ is C1-C6 alkyl, C1-C6 alkoxy, C1-C6 alkylamino, or C2-C12 dialkylamino;
• Z is O, S, or —CR13R14;
• each of R13 and R14 is C1-C6 alkyl;
• R12 is C1-C22 alkyl or C7-C22 arylalkyl;
• and
• δ is 0 or 1;
• a is 0 or 1;
• b is 0 or 1;
• and
• each of R21, R22, R23, R24, R25, R26, and R27, when present, is H.