Dye compositions and dye syntheses

A composition which comprises an unsymmetrical cyanine dye of Formula A, together with symmetrical cyanine dyes of Formula B and Formula C:

• wherein:c
• the molar ratio of A:B and also A:C in said composition is at least 46:1;
• R1 and R2 are independently H, —SO3M1 or Ra, where M1 is H or Bc, and Bc is a biocompatible cation;
• R3 is H or an Rd group;
• R4 and R5 are independently an Rd group;
• R6 to R9 are independently C1-3 alkyl or an Rc group, and are chosen such that in Formula A, at least one of R6 to R9 is Rc;
• Ra is C1-4 sulfoalkyl;
• Rb is C1-6 carboxyalkyl;
• Rc is an Ra or Rb group;
• Rd is C1-5 alkyl or an Rc group;
• with the provisos that in Formula A:
• (i) at least one of the pairs of substituents R1/R2, R4/R5, R6/R8, and R7/R9 is different;
• (ii) the cyanine dye comprises at least one Rb group and a total of 3 to 6 sulfonic acid substituents from the R1, R2, Ra and Rc groups.