Reaction-based sensing of fluoride ions using desilylation method for triggering excited-state intramolecular proton transfer

Naphthalene based benzothiazole (NBT) has been investigated as new colorimetric and ratiometric fluorescent chemosensor for fluoride. The selectivity of NBT has been explored based on combination of desilylation reaction and modulation of the excited-state intramolecular proton transfer (ESIPT) from the desilylation product to F−. The method exhibited a high selectivity and a great sensitivity toward fluoride anions through 'turn-on' chromogenic activity and sensitivity. The structure of HNBT has been established by single-crystal XRD. Density functional theory and TDDFT calculations were performed in order to demonstrate the electronic properties of HNBT, NBT and their anion. Upon treatment with fluoride in aqueous CH3CN solution, the TBS protective group of probe NBT was removed readily and ESIPT of the probe was switched on, which resulted in a decrease of the emission band at 415 nm and an increase in a new fluorescence peak around 586 nm. An easy-to-prepare test paper, obtained by dipping the paper into the solution of NBT, was able to detect fluoride ions in practical samples. The detection limit of the probe in the determination of fluoride ions was 10.18 μM.