Rigidized trimethine cyanine dyes

Disclosed are analogues of trimethine cyanine dyes which are useful for imparting fluorescent properties to target materials by covalent and non-covalent association. The compounds have the following general formula: 1 optionally substituted by groups R 2 -R 9 wherein groups R 6 , R 7 , R 8 and R 9 are attached to the rings containing X and Y or, optionally are attached to atoms of the Z a and Z b ring structures and groups R 1 -R 9 are chosen to provide desired solubility, reactivity and spectral properties to the fluorescent compounds; A is selected from O, S and NR 11 where R 11 is the substituted amino radical: 2 where R′ is selected from hydrogen, a C 1-4 alkyl and aryl and R″ is selected from C 1-18 alkyl, aryl, heteroaryl, an acyl radical having from 2 - 7 carbon atoms, and a thiocarbamoyl radical; Z a and Z b each represent a bond or the atoms necessary to complete one, two fused or three fused aromatic rings each ring having five or six atoms, selected from carbon atoms and, optionally, no more than two oxygen, nitrogen and sulphur atoms.