title: Contrasting behavior of classical salts versus ionic liquids toward aqueous phase J-aggregate dissociation of a cyanine dye.
abstract: The effect of addition of ionic liquids (ILs) on the aggregation behavior of a cyanine dye, 5,5',6,6'-tetrachloro-1,1'-diethyl-3,3'-di(4-sulfobutyl)-benzimidazolocarbocyanine (TDBC), was investigated. In basic aqueous buffer solutions (pH ≥ 10), TDBC preferably exists in its J-aggregated form. Addition of hydrophilic ILs > 5 wt % is observed to disrupt the TDBC J-aggregates, converting them to monomer form most likely because of the interaction between bulky IL cation and the J-aggregates in a time-dependent fashion. This is evidenced by the observed increase in monomer band absorbance at the expense of the absorbance band due to J-aggregates over time. Inorganic salts at similar molar concentrations do not cause this phenomenon but instead induce TDBC precipitation. At low concentrations (<5 wt %), the added IL acts similarly to the inorganic salts, reducing the overall absorbance of TDBC in the solution most likely due to cation exchange causing TDBC precipitation. Addition of a molecular solvent, ethanol, at 15 wt % results in an initial increase in monomer absorbance, albeit to a much lesser extent than for the corresponding molar fraction of IL, which then decreases over time with recovery of J-aggregate absorbance--quite opposite the time-dependent behavior seen for TDBC in PB at pH 12.0 with >5 wt % IL. The unique and dual behavior of ILs as an additive toward affecting cyanine dye aggregation is demonstrated.
authors.affiliation: Department of Chemistry, Indian Institute of Technology Delhi, Hauz Khas, New Delhi-110016, India.
authors.forename: Vinod
authors.initials: V
authors.lastname: Kumar
authors.forename: Gary A
authors.initials: GA
authors.lastname: Baker
authors.forename: Shubha
authors.initials: S
authors.lastname: Pandey
authors.forename: Sheila N
authors.initials: SN
authors.lastname: Baker
authors.forename: Siddharth
authors.initials: S
authors.lastname: Pandey