Synthesis, characterization and anion recognition studies of new fluorescent alkyl bis(naphthylureylbenzamide)-based receptors

The synthesis of new alkyl (C3 to C8) bis(naphthylureylbenzamide)-based receptors and the study of their interaction with anions by UV–Vis, molecular fluorescence and 1H NMR were performed. The results suggest both ureylbenzamide units participate in the complexion with anions due to their inherent flexibility, which promotes a cooperative binding effect. The position of the urea and amide groups, as well as, the alkyl chain length, have an important influence in the fluorescent response; meta receptors present an ON1/OFF/ON2 response, while ortho receptor have an OFF/ON response. The most significant changes were observed with dihydrogen phosphate and hydrogen pyrophosphate due to high affinity for these anions. The 1H NMR studies show differences in the interaction sites depending the relative position of the urea and amide groups, as wells as, the anion type. Finally, a theoretical analysis of complexes by DFT support the experimental results.