Progress in Benzimidazole/Benzimidazolium-Derived Supramolecular Gelators in Ion Recognition

The benzimidazole moiety, being a versatile heterocyclic unit, finds potential utility in multiple applications ranging from material science to medicinal chemistry. Benzimidazole derivatives are widely chosen as a multifunctional unit for the synthesis of bioactive organic compounds because of their structural similarities to the natural nucleotides. They are also used as heteroaromatic scaffolds in molecular probes for sensing and bio-imaging. Amphoteric nature of the benzimidazole ring forms the basis of designing new fluorescent architectures for various metal ions, anions, nitroaromatics as well as neutral organic molecules. Alongside, recent years have also witnessed the emerging development of benzimidazole-based supramolecular gels, useful in sensing and water purification. Supramolecular gels are a special class of self-assembled structures formed by weak noncovalent interactions between the molecules and are easily tuned by external stimuli. Such stimuliresponsive gels serve as smart materials because of their abilities to undergo gel-to-gel, or gel-to-sol transition upon subtle change of the gel environment. Of various stimuli, ion coordination draws attention for their visual detection and to adapt material properties. The ion-sensitive gels act as fascinating biomaterials with potential applications in drug delivery, optoelectronics and catalysis. Thus, designing of such ion-responsive gels is challenging. The rising popularity of benzimidazole based-gels is related to its advanced properties such as π-bridging, hydrogen bonding, fluorescence and ion coordinating abilities. This review focuses on recently developed various ion-responsive benzimidazole motif-based supramolecular gelators by summarising the crucial role of the structural parameters of benzimidazole gelators. Beside ion sensing, we also desire to summarize other possible applications of gelators in material chemistry. Finally, the necessity and possibility of further exploration of benzimidazole/ benzimidazolium derived gelators are briefly described.