Isatinphenylsemicarbazones as efficient colorimetric sensors for fluoride and acetate anions - Anions induce tautomerism

Article abstract of DOI:10.1016/j.saa.2013.12.073

The anion induced tautomerism of isatin-3-4-phenyl(semicarbazone) derivatives is studied herein. The interaction of F^-, AcO ^-, H₂PO4-, Br^- or HSO4- anions with E and Z isomers of isatin-3-4-phenyl(semicarbazone) and N-methylisatin-3-4- phenyl(semicarbazone) as sensors influences the tautomeric equilibrium of these sensors in the liquid phase. This tautomeric equilibrium is affected by (1) the inter- and intra-molecular interactions' modulation of isatinphenylsemicarbazone molecules due to the anion induced change in the solvation shell of receptor molecules and (2) the sensor-anion interaction with the urea hydrogens. The acid-base properties of anions and the difference in sensor structure influence the equilibrium ratio of the individual tautomeric forms. Here, the tautomeric equilibrium changes were indicated by naked-eye experiment, UV-VIS spectral and ¹H NMR titration, resulting in confirmation that appropriate selection of experimental conditions leads to a high degree of sensor selectivity for some investigated anions. Sensors' E and Z isomers differ in sensitivity, selectivity and sensing mechanism. Detection of F^- or CH₃COO^- anions at high weakly basic anions' excess is possible.