High fluorescence enhancement in the case of F− and AcO− might be due to the high selectivity attributed to the strong intramolecular OH⋯N hydrogen bonding is evident from the crystal data previously reported [30,31] for the receptor molecule, from which the hydrogen atoms are fastened, and only the anions exhibiting themost electronegative property have the potential to form additional hydrogen bonding and have the capability to break the existing intramolecular hydrogen bond and construct new intermolecular hydrogen bond. Also the fact that, the R1 shows higher binding to and also the more efficient fluorescence enhancement with F−than any other anions is actually not surprising because of its high charge density and small size, which enables it to be a strong hydrogen bonding interaction with the phenolic OH and NH group.