Chromogenic anion receptors based on 4-nitrophenylhydrazone and phenylhydrazone

Abstract

Chromogenic anion receptors based on 4-nitrophenylhydrazone and phenylhydrazone have been designed and synthesized. UV–Vis and 1H NMR titration showed that receptor 1 responded to anions according to their basicity. Although the nature of hydrogen bonds in hydrazone N–H and vinylic C–H is weak, receptor 1 bound weakly basic anions such as chloride, bromide, iodide and hydrogen sulfate utilizing only hydrogen bond in CH3CN. No color change was observed with these anions. However, for more basic anions such as acetate dihydrogen phosphate and fluoride, color change due to deprotonation observed. Furthermore, the solution color of 1 changed to deep blue with fluoride. Fluoride could be distinguished from acetate and dihydrogen phosphate with naked eye. However, phenylhydrazone based receptor 2 showed only hydrogen bonding association with all anions investigated except fluoride. Due to low deprotonation tendency and its structure, color change of solution 2 was not observed.