The synthesis of chloroheptamethinecyanine dyes in the absence of water

The chlorine atom present in the exocyclic conjugated bridge of the polymethine chain in heptamethinecyanine dyes undergoes in situ substitution with a third, oxygenated heteroaromatic group. The reaction is promoted by residual water and its success critically depends on the solubility of the chloro dye in the reaction solvent. To prevent this undesirable substitution, a modified synthesis has been developed that excludes water and which affords the desired chloroheptamethinecyanine dyes bearing different N-alkyl chains in good yield. The spectroscopic characterization of five new chloroheptamethinethia- and chloroheptamethineselenacyanine dyes is described.