Fluorescent Ionic Liquids: Synthesis, Properties, and Applications

Fluorescent ionic liquids (FILs) are an emerging class of tunable luminescent materials that combines the versatile physicochemical properties of ILs with highly fluorescent organic dyes. While the inherent fluorescent properties of ILs containing imidazolium and pyridinium cations have been previously explored, their optical properties are not strong enough to serve relevant applications as FILs. This review explores the synthesis, physical and optical properties, and applications of FILs, with emphasis room-temperature FILs (RTFILs), which fluorescence in the neat state, and find applications in chemical sensing. RTFILs are a relatively new class of materials that exhibit highly intense fluorescence properties in the neat state, which is a unique phenomenon as opposed to the aggregation induced quenching of fluorescence that usually occur in either the liquid state or in the solid state. Applications in chemical sensing, including the detection of metal ions, organic compounds, gases, pH, and chiral analytes are also discussed alongside a wide breadth of applications. Challenges of FILs will be delved, including the lack of universality in reporting fluorescence quantum yields in the neat state. This review aims to identify opportunities for expanding design strategies of FILs to accelerate their development for chemical sensing, photonics, and advanced functional materials.