A microcrystalline carboxyl-functionalized imidazolium chloride, namely 1-carboxymethyl-3-ethylimidazolium chloride, C7H11N2O2+·Cl-, has been synthesized and characterized by elemental analysis, attenuated total reflectance Fourier transform IR spectroscopy (ATR-FT-IR), single-crystal X-ray diffraction, thermal analysis (TGA/DSC), and photoluminescence spectroscopy. In the crystal structure, cations and anions are linked by C-H...Cl and C-H...O hydrogen bonds to create a helix along the [010] direction. Adjacent helical chains are further interconnected through O-H...Cl and C-H...O hydrogen bonds to form a (10-1) layer. Finally, neighboring layers are joined together via C-H...Cl contacts to generate a three-dimensional supramolecular architecture. Thermal analyses reveal that the compound melts at 449.7 K and is stable up to 560.0 K under a dynamic air atmosphere. Photoluminescence measurements show that the compound exhibits a blue fluorescence and a green phosphorescence associated with spin-allowed (1π←1π*) and spin-forbidden (1π←3π*) transitions, respectively. The average luminescence lifetime was determined to be 1.40 ns for the short-lived (1π←1π*) transition and 105 ms for the long-lived (1π←3π*) transition.
Keywords: carboxyl-functionalized imidazolium salt; crystal structure; hydrogen-bonding interaction; ionic liquids; photoluminescence spectroscopy; thermal analysis.