Synthesis and optical properties of 1-alkyl-3-methylimidazolium lauryl sulfate ionic liquids

We report the synthesis of a new series of imidazolium-based halogen-free ionic liquids 1-alkyl-3-methylimidazolium lauryl sulfates. By reacting 1-methylimidazole (MIM) with butyl, hexyl, octyl, and decyl bromides and exchanging bromide ion with lauryl sulfate anion, a series of ionic liquids [RMIM][C(12)H(25)OSO(3)] were produced. The high purity of these ionic liquids was verified with (1)H-NMR, (13)C-NMR, FT-IR and mass spectrometry (MS), demonstrating the effectiveness of this synthetic approach. Solubility test of these ionic liquids showed that they are soluble in most organic solvents except nonpolar solvents such as hexane and cyclohexane. The optical properties of [BMIM]Br and [BMIM][C(12)H(25)OSO(3)], where B refers to butyl, were examined. Both ionic liquids absorbed light in the UV region, yet essentially no absorption was recorded beyond 450 nm. Furthermore, both ionic liquids showed excitation wavelength-dependent fluorescence behavior. As an example, with an excitation wavelength of 360 nm, [BMIM][C(12)H(25)OSO(3)] showed an emission band maximum at 447 nm. Increasing the excitation wavelength to 440 nm, the emission band maximum was shifted to approximately 500 nm.