A Reusable Fluorescent Molecular Self-Assembly Cage for Simultaneous Detection and Recycling of Silver(I) Ion

Although molecular self-assembled porous materials capable of ratiometric fluorescence probing and recycling of metal ions are both economically and environmentally attractive, very few current efforts have been devoted. Herein, we demonstrated a three-dimensional pure organic cage, namely 4-cage, which can serve as a fluorescent probe for simultaneous ratiometric detection and recycling of Ag⁺ ion. Taking advantage of the promising emission behavior of its rigidified tetraphenylethylene scaffolds and the chelating ability of its dynamically reversible imine moieties, on one hand, upon the addition of Ag⁺ , 4-cage undergoes coordination to form a stable but poorly soluble fluorescent complex, Ag⁺ @4-cage, accompanied by a fluorescence color change from bluish-green to yellowish-green. This allows us to differentiate Ag⁺ from other cations with high selectivity. On the other hand, upon the addition of Cl^- anion, Ag⁺ @4-cage can be effectively converted into free 4-cage due to the competitive coordination of Cl^- with Ag⁺ . Through this process, secondary usage of 4-cage and the recycling of Ag⁺ ion can be achieved.