Anions play a fundamental role in a wide range of chemical and biological processes. For example, the carboxylate anions exhibit specific biochemical behaviors in the enzymes and antibodies and are also critical components of numerous metabolic processes [1]. In particular, Cl− which has relatively high extracellular concentrations is essential to human health and is transported across cell membranes by various Cl− proteins, often in conjunction with cation transportation [2].The design and synthesis of receptors for biologically important and environmentally harmful anion pollutants has attracted considerable attention in supramolecular chemistry [3,4]. More and more attentions have been paid to the design and synthesis of the receptors that selectively recognize specific anions such as fluoride [5], In particular, the selective sensing of fluoride has gained attention due to its significant role in clinical treatments e.g. dental care [6], osteoporosis [7] and for the detection of fluoride in bones as a result of over-accumulation [8]. we designed and synthesized new benzimidazole motifs –based molecular receptor 1 for the selective sensing of anions by investigating the effect of the addition of tetrabutylammonium salts ([Bu4N]+X−, X = F−, Cl−, Br−, I−, ClO4 − and HSO4 −. Receptor 1 was particularly important as a chemosensor for fluoride owing to its noticeable UV-vis and fluorescence responses in the presence of F− ions.

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