A highly selective hydrogen‐deuterium exchange in indolium heptamethine cyanines

Chemical shift assignments in ¹H nmr spectra of four tricarbocyanines have been made. Studies by ¹H nmr have shown a rapid acid‐catalyzed proton exchange at positions 1′,7′ and a much slower exchange at positions 3′,5′ of the heptamethine chain. Base catalysis results in a slow exchange at positions 1′,7′ only.