A microcrystalline carboxyl-functionalized imidazolium chloride, namely 1-carboxymethyl-3-ethylimidazolium chloride, C7H11N2O2+center dot 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 center dot center dot center dot Cl and C-H center dot center dot center dot O hydrogen bonds to create a helix along the [010] direction. Adjacent helical chains are further interconnected through O-H center dot center dot center dot Cl and C-H center dot center dot center dot O hydrogen bonds to form a (10(1) over bar) layer. Finally, neighboring layers are joined together via C-H center dot center dot center dot 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 ((1)pi <- (1)pi*) and spin-forbidden ((1)pi <- (3)pi*) transitions, respectively. The average luminescence lifetime was determined to be 1.40 ns for the short-lived ((1)pi <- (1)pi*) transition and 105 ms for the long-lived ((1)pi <- (3)pi*) transition.