Spectroscopy and a theoretical study of colorimetric sensing of fluoride ions by salicylidene based Schiff base derivatives

Abstract

Three colorimetric anion sensors based on salicylidene Schiff bases (salicylaldehyde-o-aminophenol [SA1], 3,5-dimethyl-salicylaldehyde-o-aminophenol [SA2], and 3,5-dichloro-salicylaldehyde-o-aminophenol [SA3] were comprehensively studied based on experimental methods combined with theoretical calculations. All derivatives showed high sensitivity for colorimetric detection of fluoride ions (F−) with a binding stoichiometry of 1:1 in acetonitrile solutions. The color of the sensor solutions visibly changed from light yellow to orange red in the presence of F−. From the experimental results, SA1 and SA2 showed higher potential as F− sensors than SA3 due to their higher selectivity with a limit of detection (LOD) as low as 8 × 10−5, 21 × 10−5 and 7 × 10−5 M, respectively. The optimized structure and electronic transitions were confirmed by DFT and TDDFT studies. In this study, F− detection mechanism is proposed based on experimental and the density functional theory (DFT) calculation.