A benzimidazole‐based chromogenic anion receptor

A benzimidazole‐based anion receptor 1 has been designed and synthesized. The structure of 1 is confirmed through single crystal X‐ray diffraction analysis. Anion‐binding studies carried out using 1 H NMR and UV–visible revealed that this compound exhibits selective recognition toward F − over other halide anions. The highest selectivity for F − among the halides is attributed mainly to the strongest hydrogen‐bond interaction of the receptor with F − ; in addition, the higher match in geometry between the receptor and F − also plays a role in the selective recognition of the receptor for F − . Receptor 1 (1 × 10 −5  M) shows dramatic color change from light‐yellow to red in the presence of tetrabutylammonium fluoride (TBAF) (1 × 10 −5  M). Moreover, F − ‐induced color changes remain the same even in the presence of a large excess of Cl − , Br − , I − . Copyright © 2006 John Wiley & Sons, Ltd.