Red-Emitting AIEE-Active Rhodamine-Based Ionic Liquid for the Ultrasensitive and Selective Detection of Mercury Ions

A highly fluorescent, red-emitting rhodamine-based imidazolium ionic liquid (RhB-IL) was synthesized, and its structure was extensively verified using various spectroscopic techniques. The novel molecule showed exceptional selectivity toward Hg²⁺ ions over other competitive metal ions. Additionally, inspired by the solution results, a paper-based device was fabricated by embedding RhB-IL on paper strips and tested for the on-site detection of Hg²⁺ ions using a portable UV light source. Significantly, the device displayed excellent PL sensing behavior toward Hg²⁺ with a detection limit of 0.21 nM. In addition, RhB-IL showed the phenomena of aggregation-induced enhanced emission. In fact, when compared to the pure THF solution of RhB-IL, a remarkable 7.7-fold increase in PL intensity was seen for the 90% water fraction. Evidently, this is the first report of a paper-based Hg²⁺ detection system that uses a red fluorescent ionic liquid.