Supramolecular Construction of a [16]-Imidazolium Cage via a Quadruple [2+2] Photocycloaddition and Its Selective Fluorescent Recognition of Pyranine (HPTS).

Polyimidazolium-based cages are considered promising materials based on their fascinating properties and potential applications. These three-dimensional functional structures are highly desirable for the recognition of particular guest molecules, however, their synthesis remains challenging. In this work, we have designed and synthesizes a pure [n]-imidazolium (n=16) cage, the hexadecakisimidazolium salt H16 -2(PF6 )16 , from tetragonal octakisimidazolium salt H8 -1(PF6 )8 . The synthetic method involves formation of metal-carbene templates, a quadruple photochemical [2+2] cycloaddition reaction and subsequent removal of metal ions. Specifically, the synthesized cage, featuring sixteen imidazolium moieties, demonstrated high efficiency for the selective fluorescent recognition of 8-hydroxy-1,3,6-pyrene trisulfonate (HPTS). The present work not only further develops the metal-carbene template strategy by exploiting a new type of polyimidazolium cage, but also provides encouraging prospects for the design of versatile imidazolium-based functional acceptors.