Fluorescence quenching of p-tert-buthylthiacalix[4]arene by 1-ethyl-3-methylimidazolium bromide

The interaction between the ionic liquid 1-ethyl-3-methylimidazolium bromide (EMIMBr) and the macrocyclic compound p-tert-buthylthiacalix[4]arene (TC4) in solution ethanol/water 3/1 V/V was investigated by spectrophotometry and spectrofluorimetry. The UV-Vis spectra of the system (EMIMBr + TC4) were completely additive. The addition of EMIMBr decreases the fluorescence of the TC4 significantly, excited at 325.0 nm. The Stern-Volmer quenching constants were determined at different temperatures (15.0, 25.0, and 35.0 °C), and the obtained values were the same, with an average value of K_Q^av = (3.8 ± 0.9) 10³ M^-1 for the quenching constant. No changes in the emission spectra of TC4 were obtained by the addition of inorganic salts, such as NaCl, KBr, NH₄Cl, and NH₄PF₆ or the organic compound N-methylimidazole (NMI). More evidence of EMIMBr-TC4 interaction was found with the determination of the fluorescence lifetime and the anisotropy of the mixture. Also, the slope of the quenching plot was the analytical sensitivity of calibration for EMIMBr using TC4 as an indirect sensor, and a LOD = (26 ± 2) μM was obtained.