Synthesis of a chiral ionic liquid based on L-tryptophan ester and evaluation of enantiomeric recognition properties using fluorescence spectroscopy

This paper describes the synthesis, characterization, and investigation of enantiomeric recognition properties for a fluorescent chiral ionic liquid (FCIL)​, L- tryptophan ethyl ester bis(trifluoromethane) sulfonimide [TrpC2] [NTf2], used as a solvent and chiral selector. This FCIL, [TrpC2] [NTf2], was synthesized using an anion exchange reaction between commercially available L- tryptophan ethyl ester chloride [TrpC2] [Cl] and lithium bis(trifluoromethane) sulfonimide (LiNTf2). The product FCIL, [TrpC2] [NTf2], was obtained as a liquid at room temperature and is stable to thermal decomposition up to 260 ℃. This tryptophan based FCIL has a higher quantum yield of 0.19 compared to 0.14 for tryptophan amino acid. Using fluorescence spectroscopy, [TrpC2] [NTf2] FCIL demonstrated enantiomeric recognition of various fluorescent and nonfluorescent chiral analytes of pharmaceutical and environmental importance.