Spectroscopic Studies on the Interaction of Dye and Surface Active Ionic Liquid

The interaction of both cationic dye Safranine T (ST) and anionic dye Congo red (CR) with anionic and cationic surface active ionic liquid 1-butyl-3-methyl imidazolium octyl sulfate ([BMIM][OS]) and 1-decyl-3-methyl imidazolium chloride ([DMIM][Cl]) was investigated by absorbance and emission spectroscopy, time-resolved fluorescence study, and anisotropy methods at premicellar and postmicellar regions. The interaction of dye with both of the ionic liquids occurred electrostatically as well as hydrophobically. In the case of ST, initially absorbance decreases up to a certain concentration without any shift of lambda(max), and then it increases with red shift of lambda(max). Absorption spectra of CR gave red-shifted wavelength with addition of [BMIM][OS], but at a higher concentration of surface active ionic liquid (SAIL), no shifting was observed. Again, blue-shifted lambda(max) was found in lower range of [DMIM][Cl]; but at higher concentration, it was further red-shifted. Emission intensity increases in both dye-SAIL systems; for ST in both SAIL media, blue-shifted spectra were observed, but there was no shift of emission maxima in case of CR in those media. Dye-IL binding ratio, binding sites, and binding constants were also calculated from fluorescence measurements. Anisotropy measurement showed that movement of dye in pre- and postmicellar regions was different in different SAIL systems. Time-resolved fluorescence lifetime confirmed microenvironment of dye-SAIL systems.