Green synthesis of fluorescent N,O-chelating hydrazone Schiff base for multi-analyte sensing in Cu²⁺, F⁻ and CN⁻ ions

Abstract

© 2018 Elsevier B.V. A colorimetric and fluorometric hydrazone Schiff's base derived from dehydroacetic acid by three-steps and high-yield syntheses under green approach employing ethanol as a solvent has been prepared. Multi-analyte sensing for both metal cation (Cu2+) and anions (F− and CN−), with high sensitivity and competitive selectivity, was encountered. The sensing mechanism of anion detection found to be deprotonation of N–H and O–H moieties in the presence of ions. However, metal cation like copper(II) ions chelation with sensor, leads to diminish intra-molecular charge transfer (ICT) with chelation induced quenching of fluorescence (CHQF). Contrary, anionic interaction ensued in heightened ICT as well as photo-induced electron transfer (PET) processes. The Job's plots interpretation rendered stoichiometry of 2:1 with Cu2+/F− and 1:1 with CN−. Moreover, the detection limits of 0.962 ppm (Cu2+), 0.023 ppm (F−) and 0.073 ppm (CN−) were much lower than WHO guidelines. Further, either water or methanol was employed to differentiate F−/CN− ions with sensor in THF, with prominent visible naked eye and fluorometric responses.