A Xanthene-Benzimidazole Receptor with Multiple H-Bond Donors for Carboxylic Acids

The combination of two benzimidazole moieties with a spacer formed by a leucine unit and a xanthene skeleton provides an efficient receptor for neutral guests with oxygen atoms such as sulfoxides, ketones, or alcohols. H-1 NMR and UV spectroscopic techniques have been used to evaluate its binding ability. These experiments indicated the largest association constants for carboxylic acids and different binding stoichiometries. The structures of these different complexes were studied both in solution and in the solid state. Fluorescence of anthracenecarboxylic acid is strongly quenched in the presence of receptor 1, and therefore, this system could be used to sense the presence of stronger carboxylic acids and anions like chloride.