Sensing the Hydrophobicity of Ionic Liquids by Using Pyrene

ABSTRACT The central idea of the present work was to study the effect of ionic liquids (ILs) on the photophysical behavior of a scientifically and industrially important probe pyrene. We studied the effect of four ionic liquids (ILs), 1‐butyl‐3‐methylimidazolium tetrafluorate ([bmim][BF 4 ]), 1‐butyl‐3‐methylimidazolium bis(trifluoromethanesulfonyl)imide ([bmim][Tf 2 N]), 1‐butyl‐3‐methylimidazolium trifluoromethanesulfonate ([bmim][OTf]), and 1‐butyl‐1‐methylpyrrolidinium bis(trifluoromethanesulfonyl)imide ([bmpyrr][Tf 2 N]) on the photophysical behavior of pyrene dissolved in water by using electronic absorbance spectroscopy and steady state fluorescence emission spectroscopy. The Uv‐vis absorbance maxima and fluorescence emission maxima values for pyrene varied with the nature of the molecular organic solvents. Furthermore, the presence of small amount of ILs resulted into the decrease in the absorbance as well as fluorescence emission intensity. The same fluorescence emission spectra were obtained for pyrene dissolved in different organic solvents and small amount of IL added aqueous solutions irrespective of the excitation wavelength. Interestingly, the structured absorbance spectra were governed by the nature of ILs present into the aqueous solutions of pyrene. More specifically, the hydrophobic interactions between the pyrene molecules and the surrounding media governed the intensity of vibronic absorption bands. The observed results can be used as pyrene absorbance based hydrophobicity sensors and the present study could contribute in improving the applications of the same dye and ILs.