Convenient synthesis and anion recognition property of acylhydrazone-based molecular tweezer receptors

Three acylhydrazone-based compounds were designed as novel neutral sensors for anions, and synthesized by simple steps in good yields. Their anion recognition properties were studied by UV-vis and (1) H-NMR spectroscopy. The results showed that the receptors 1, 2, and 3 all had a better selectivity for F- and CH3COO-, but no evident binding with Cl-, Br-, I-, NO3-, H2PO4-, or HSO4-. The results indicated that anion recognition was achieved via convergent hydrogen bond interactions from acylhydrazone functionality on the side arms. The UV-vis data indicated that a 1: 1 stoichiometry complex was formed between compounds 1, 2, or 3 and anions. The binding and selectivity were also tuned by the change of the place of the nitro group attached to the phenyl. Moreover, receptor 3 can act as the colorimetric sensor for such anions as F- and CH3COO-, and the recognition mechanism and binding mode were discussed.