Aggregation behaviour of two thiacarbocyanine dyes in aqueous solution

The J-aggregation behaviour of two cyanine dyes (3,3′-disulfopropyl-4,5,4′,5′-dibenzo-9-methyl-thiacarbocyanine triethylammonium salt (MTC) and 3,3′-disulfopropyl-4,5,4′,5′-dibenzo-9-phenyl-thiacarbocyanine triethylammonium salt (PTC)) has been investigated in the presence of dication chloride using absorption spectroscopy, 1H and multinuclear NMR methods. The promotion efficiency on J-aggregation of the dye molecule and the magnitude of the effective coherence length of the J-aggregate were found to be dependent on the dyes' structure and their ability to coordinate with the metal ions. The interaction between the metal ions and the J-aggregates could be explained by the association between metal ions and J-aggregates, and the apparent association constants were obtained from the chemical shifts in NMR spectra of the metal ions.