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

Three colorimetric anion sensors based on salicylidene Schiffbases (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 calcu- lations. 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.