New Dinitrophenyl Hydrazones as Colorimetric Probes for Anions

Anion sensing is a dynamic research field due to the biological and environmental importance of some organic or inorganic anions. Hydrazones show promising properties in the design of anion chemosensors due to the presence of proton donor and acceptor sites in their structure. In this work, two novel dinitrophenyl hydrazones, functionalized with a quinoline moiety, were synthesized and characterized by spectroscopic and spectrometric techniques. The interaction between the new compounds 3a–b with different organic and inorganic anions was assessed. The two compounds showed a change in color from light yellow to magenta in the presence of H2PO4−, CH3COO−, BzO−, CN−, and F−. The interactions were analyzed by spectrophotometric titrations and the stoichiometry of the interaction was assessed by the method of continuous variation. Compound 3b showed a remarkable sensitivity to CN−, with a limit of detection of 0.35 µM. The interaction of compound 3b with CN− and F− was also analyzed by 1H NMR titrations, showing that an increasing concentration of anions induce a deprotonation of the NH and OH groups