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.