Fluoride ion detection in aqueous medium: Colorimetric and turn-off fluorescent Schiff base chemosensor

The work described is focused on a newly developed colorimetric Schiff base fluorescent sensor that exhibits a "turn-off" response when detecting fluoride ions (F^-) in an aqueous environment. The confirmation of the recognition event is accomplished through fluorescence titration, absorbance titration, and Density Functional Theory (DFT) calculation study. From the results, it is determined that the detection limit of F^- is 2.35 × 10^-8 M which is much lower than the World Health Organization (WHO) permissible limit for drinking water while the binding constant was obtained to be 0.1 × 10⁶ M^-1 indicating a moderate affinity for the fluoride ions. Furthermore, the binding stoichiometry between the Probe L and F^- was found to be 1:1 which is evidenced by the Job's plot and DFT calculation study. Overall, the novel sensor's impressive sensitivity and selectivity make it a promising candidate for the detection of fluoride ions in aqueous media, particularly for monitoring drinking water quality to ensure compliance with WHO guidelines.