Macrocyclic bis(amidonaphthol)s for anion sensing: tunable selectivity by ring size in proton transfer process

The investigation on anion sensing properties for a series of macrocyclic bis(amidonaphthol)s 3a–3c reveals the significant effects of macrocyclic ring size. Among them, macrocycle 3c with the largest ring size shows F− ion selectivity by causing clear red shift (24 nm) in fluorescence emission after complexation with F−, which results in significant color change of fluorescence from blue to green. This excellent selectivity toward F− ion might be attributed to the fitness between the acidity of –OH group and the basicity of F− ion. Further exploration indicates that the acidity of –OH group can be tuned by ring size to give it the capability to discriminate the subtle difference in the affinity of F−, CH3COO−, and H2PO4− to –OH proton.