Fluorescent Acridine-Based Receptors for H2PO4–

Two new pseudopeptidic molecules (one macrocyclic and one open chain) containing an acridine unit have been prepared. The fluorescence response of these receptors to a series of acids was measured in CHCl3. Receptors are selective to H2PO4– versus HSO4–, and an even higher selectivity is found over other anions such as Cl–, Br–, CH3COO–, and CF3COO–. We show that the macrocyclic receptor is more selective for H2PO4– than the related open chain receptor. The supramolecular interactions of triprotonated receptors with different anions have been modeled in silico and have been studied by different experimental techniques. Optimized geometries obtained by computational calculations agree well with experimental data, in particular fluorescence experiments, suggesting that the selective supramolecular interaction takes places through coordination of the anions to the triprotonated form of the receptor.