Porosity-Induced Selective Sensing of Iodide in Aqueous Solution by a Fluorescent Imidazolium-Based Ionic Porous Framework

Developing a chemosensor for rapid, sensitive, and visual detection of iodide (I^–) by a simple synthetic strategy is still challenging. Herein, we report a highly efficient iodide sensor by simply introducing ionic imidazolium groups into the porous network. This sensor, that is, a fluorescent ionic porous framework (IPF), was prepared by the quaternization reaction of octa­((benzylchloride)­ethenyl)­silsesquioxane and 1,4-bis­(1H-imidazole-1-yl)­benzene and exhibited moderate porosity with a Brunauer–Emmett–Teller surface area of 379 m² g^–1 and blue fluorescence when excited by UV light. The IPF suspension in water can detect I^– with high sensitivity and selectivity among various anions and quick response by fluorescence quenching. In contrast to no response toward I^– by the linear model compound and the enhanced sensing performance with an increment of porosity, this finding indicates that the porosity of IPF is important for the detection of I^– and an inducement of the sensing process. A fluorescent paper sensor was further developed, which shows high efficiency for the visual detection of I^– similar to the abovementioned sensor, suggesting its potential in convenient and on-site sensing of I^–. In addition, the paper sensor is recyclable with a remarkable fluorescence resuming ratio of 83% after 10 times cycle detection. Moreover, the developed sensor is used for the analysis of real samples. This work represents the first example of the detection of I^– by an ionic porous polymer. Compared with conventional iodide sensors, the present sensor does not require unique structures to form the pseudocavity during sensing I^– and can easily achieve high efficiency by incorporating ionic hydrogen bond donors into the porous network, indicating the importance of porosity and the feasibility of replacing the pseudocavity with a real cavity (or pore). More iodide sensors with high efficiency can be designed and fabricated by this novel and simple strategy.