Anthracene-based ortho-phenylenediamine clefts for sensing carboxylates

Two ortho-phenylenediamine-based new receptors 1 and 2 with an anthracene-coupled benzimidazolium motif have been designed and synthesized. The directed hydrogen bonds (both conventional and unconventional) and charge–charge interactions allowed the open clefts of both 1 and 2 to bind carboxylate, fluoride and dihydrogenphosphate anions with moderate binding constant values. The selectivity and sensitivity were ascertained by 1H NMR, UV–vis and fluorescence spectroscopic methods. The binding cleft of 2 is found to be more effective than that of 1.