Synthesis of N-(2,4-Dinitrophenyl)-N '-(substituted-phenyl)hydrazones and Their Anion Sensing

Four N-(2,4-dinitrophenyl)-N'-(substituted-phenyl)hydrazones (substituent R=H, o-OCH3, o-Cl and o-OH) were synthesized as absorption spectral chemosensors for receptors. The binding properties of these receptors with anions such as Fand AcOin CH3CN were investigated by UV-visible absorption spectroscopy. Results showed that a distinct color change occurred from yellow to light yellow upon addition of Fand AcO-. Substituent was found to exert influence on the spectral response sensitivity and selectivity, with receptor 2 bearing an o-OCH3 substituent showing the highest selectivity and good sensitivity for F-. Job plots indicated a 1∶1 anion binding stoichiometry of the receptors, for which a hydrogen bonding interaction was identified from the H NMR titrations and the effect of competitive solvent MeOH on anion binding. As a distinct solution color change occurs it is possible to detect anions such as fluoride by naked eyes.