Ultrastable Imidazole-linked Porous Organic Cages for Ammonia Capture and Detection

Here, we report the facile synthesis of imidazole-linked porous organic cages (IPOCs) via an in situ cyclization reaction protocol. Specifically, three IPOCs with [2+4] lantern-like structures and one with a [3+6] triangular prism structure were successfully prepared through condensation reactions between tetraformyl-functionalized calix[4]arene and bis(o-phenylenediamine) monomers in a single pot. Notably, these IPOCs exhibit high porosity, with Brunauer-Emmett-Teller (BET) specific surface areas reaching up to 1162 m² g^-1. Moreover, they demonstrate excellent chemical stability in both strong acidic and alkaline solutions. Furthermore, IPOC-2 and IPOC-4 display a remarkable NH₃ capturing capability, with uptakes of up to 11.5 mmol g^-1 at 1 bar and 298 K, surpassing most reported porous organic materials. Additionally, IPOC-1 exhibits highly efficient fluorescent quenching sensing of aqueous NH₃, with a detection limit as low as 3.35×10^-6 M. These findings strongly suggest the potential for widespread use of imidazole linkages in the development of robust functional porous organic cage materials for diverse applications.