Effect of conjugation in 4-amino phenazone based Schiff bases on their chemosensing of F- and OH- ions - Experimental and DFT study

Abstract

Abstract Selectivity and sensitivity of A (1-phenyl-2,3-dimethyl-4-(N-2-hydroxybenzylidene)-3-pyrazolin-5-one) and B (1-phenyl-2,3-dimethyl-4-(N-2-hydroxynaphthylidene)-3-pyrazolin-5-one) toward different anions i.e. Cl-, I-, H2PO4-, Br-, SCN-, HSO4-, F- and OH- in acetonitrile was determined using naked eye sensing and UV-Visible spectrophotometry. Studies showed a prominent color change from colorless to yellow and a concomitant UV-Vis red shift on addition of F- and OH- to A and B both. In order to understand the mechanism of interaction between anions (F- and OH-) and Schiff base receptors (A and B), DFT calculations have also been performed which revealed a a proton transfer mechanism from Schiff base to F- and OH-. However, the interaction between B and OH- proved to be unstable. Moreover, a gradual increase in fluoride and hydroxide ions concentration resulted in gradual color intensification. The detection limits of fluoride were determined to be 4.09x10-5M with A, 1.32 x10-5 M with B and hydroxyl ion 2.12x10-5M with A using calibration curves. Findings of the Job’s plot investigation indicated a 1:1 binding of F-with both A and B and OH- with A. The binding constant (Ka) values of OH- and F- with A are 1.51x108 M-1 and 4.98 × 106 M-1 respectively, whereas, B has a Ka value of 2.45x103M-1 with F-.