Ionic Liquid Induced Aggregation and Precipitation Behavior of Pinacyanol

In this paper, we demonstrate the unique role of ionic liquids (ILs) as dye aggregation and precipitation promoter. Specifically, we have observed that the presence of small amount of IL such as 1-butyl-3-methylimidazolium hexaflurophosphate ([bmim][PF6]), 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([bmim][Tf2N]), 1-butyl-3-methylimidazolium trifluoromethanesulfonate ([bmim][OTf]), 1-butyl-3-methylimidazolium tetrafluoroborate ([bmim][BF4]) and 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide ([bmpyrr][Tf2N]) in aqueous milieu can help in the conversion of a cyanine dye 1,1'-Diethyl-2,2'-carbocyanine iodide (Pinacyanol iodide) into J- and H-aggregates followed by time dependent precipitation of the dye. The anion of the added IL strongly affects the aggregation process in aqueous solution. Addition of small amount of BF4- anion based IL [bmim][BF4] to aqueous solution of the dye initially induces J- and H-aggregation followed by quick precipitation of the dye in time dependent manner. Presence of small amount of other anion containing ILs such as ([bmim][PF6]), ([bmim][OTf]), ([bmim][Tf2N]) and ([bmpyrr][Tf2N]) strongly supports H-aggregation of the dye in aqueous solution whereas higher wt % of added ILs also caused precipitation of the dye in a time dependent manner. The nature of the IL anion, wt % of added IL and temperature conditions decides efficiencies of aggregation and precipitation processes. The dual yet unique behavior of ILs as an additive influence the aggregation of cyanine dyes and precipitation has been demonstrated. The observed results can contribute towards various application for dye aggregates and in the removal of dyes from water. The developed process can find potential applications in the field of material science, wastewater treatment, future light harvesting systems, and opto-electronics related fields. The presence of small amount of ionic liquids in aqueous milieu can help in the conversion of cyanine dye 1,1'-Diethyl-2,2'-carbocyanine iodide (Pinacyanol iodide) into J- and H-aggregates followed by time dependent precipitation of the dye. image