Ionic liquid-induced aggregation behavior of kryptocyanine dye

In this paper, we report the unusual aggregation behavior of an important cyanine dye 1,1′-diethyl-4,4′-carbocynine iodide (DECI), also known as kryptocyanine, which interestingly depends on the type of the ionic liquid (IL) present in the aqueous solutions of the dye. Notably, the presence of a small amount of ILs containing [BF₄]⁻, [PF₆]⁻ and [OTf]⁻ anions induced the process of J-aggregation instantly, and the added ILs acted as promoters for J-aggregation, followed by time-dependent precipitation. In contrast to the above-mentioned ILs, the presence of a small amount of ILs containing Tf₂N⁻ anions induced the process of J- and H-aggregation simultaneously, followed by time-dependent conversion of H-aggregates to J-aggregates. Furthermore, the aggregation behavior of the dye was also found to be dependent on the concentration of the dye, temperature conditions, and nature of solubilizing media (polarity of the solvent and pH).