Dynamic exchange of heterocyclic subunits during halogen substitution in chloroheptamethinecyanine dyes by benzoazolium salts

The chlorine atom present in the rigidifying cyclohexane ring incorporated in the polymethine chain of heptamethinecyanine dyes was replaced by a 2-methylbenzoazolium salt conveniently substituted through an ether linkage furnished by residual water present in the reactional mixture. The expected substituted cyanines were obtained along with other related triheterocyclic cyanine dyes, resulting from the replacement of the terminal heterocyclic moieties of the starting chloro dye or of an already substituted dye, by an exogenous benzoazolium residue.