Turn Off-On Fluorescent CO₂ Gas Detection Based on Amine-Functionalized Imidazole-Based Poly(ionic liquid)

Poly(ionic liquids) (PILs) have been widely used for CO₂ capture because their characteristics resemble those of an ionic liquid, yet they have properties typically associated with polymers. We studied the application of the amine-functionalized poly(vinylimidazole)-based PIL (PVIm-NH₂) as a chemosensor. The PVIm-NH₂ was successfully prepared by a facile and low-cost method and was characterized by several analytical techniques: proton nuclear magnetic resonance (¹H NMR), Fourier transform infrared (FT-IR) spectroscopy, gel permeation chromatography (GPC), and spectrofluorometry. The ability of PVIm-NH₂ to detect CO₂ gas was evaluated in the presence of triethylamine (TEA). Under optimized conditions, the detection limit was calculated to be 2.86 × 10^-3 M with R ² = 0.9906. Moreover, theoretical and experimental studies suggested a plausible mechanism whereby PVIm-NH₂ generates N-heterocyclic carbenes (NHCs) in the presence of TEA, which further reacts with CO₂ gas in aqueous media to form a carboxylic acid. Analysis of PVIm-NH₂ before and after the addition of TEA using the ¹H NMR technique showed the disappearance of the proton peak, thus suggesting a successful generation of NHC. Further analysis via ¹³C NMR revealed the reaction of CO₂ and NHC to form a carboxylic acid group. Finally, we demonstrated that PIL is a promising candidate as a chemosensor through diverse structural modifications.