Structurally Flexible C3-Symmetric Receptors for Molecular Recognition and Their Self-Assembly Properties

The bioinspired design and synthesis of building blocks and their assemblies by the supramolecular approach has ever fascinated scientists to utilize such artificial systems for numerous purposes. Flexibility is a basic feature of natural systems. However, in artificial systems this is difficult to control, especially if there is no preorganization of the component(s) of a system. We have designed and synthesized a series of C3‐symmetric N‐bridged flexible receptors and successfully utilized them to selectively entrap the notorious and toxic nitrate anion in aqueous medium. This was the first report of highest binding affinity for the nitrate anion in aqueous medium. An impressive self‐sorting phenomenon of reversibly formed hydrogen‐bonded capsules, which self‐assembled from flexible tripodal receptors having branches of similar size and bearing the same amide functionality, has been disclosed. Encapsulated nitrate anion has been further utilized for the photochemical [2+2] cycloaddition reaction for the synthesis of strained four‐membered ring structures through dynamic self‐assembly. In this Personal Account, we summarize these results showing the utility of naturally inspired flexibility in artificial systems. Nitrate anion trapping by artificial receptors is a challenging task. Flexible tripodal receptors have been found to reversibly encapsulate the nitrate anion through a dynamic self‐assembly process. The hydrogen‐bonded capsules exhibit a narcissistic self‐sorting phenomenon and are able to trigger a nitrate‐promoted photochemical cycloaddition reaction in response to solvent polarity.