N-octylpyridine hydrogen sulphate ionic liquid for multifunctional fluorescent response in different solvents

Ionic liquids (ILs) have attracted considerable interest in the last two decades owing to their unique fluorescent properties. Herein, N-octylpyridine hydrogen sulphate ([OP]HSO₄) was synthesised and characterised using ¹H NMR and infrared spectroscopies. In addition, the fluorescence spectra of [OP]HSO₄ in water, methanol, ethanol and acetonitrile were studied. In a single solvent, as the concentration of the solvent (methanol, ethanol or acetonitrile) increases, the fluorescence intensity of the IL first increases and then decreases. A similar trend was observed in their mixed solvents with water. Moreover, the fluorescence intensity of [OP]HSO₄ decreases with increasing temperature. A fluorescence intensity reduction of only 4.46% for [OP]HSO₄ after continuous scanning for 40 cycles under the maximum excitation state was analysed. The lack of photobleaching observed in [OP]HSO₄ indicates its good photobleaching resistance.