Highly Sensitive Fluorescence Turn-On Indicator for Fluoride Anion with Remarkable Selectivity in Organic and Aqueous Media

A simple, convenient, and inexpensive method has been developed to quantitatively determine fluoride anion concentration in acetonitrile as well as in water. The method exhibited a high selectivity and a great sensitivity toward fluoride anions through turn-on chromogenic and fluorogenic dual modes. The fluoride driven silyl deprotection and the subsequent spectral changes of hydroxyl coumarin were the operating foundations for the observed selectivity and sensitivity. H-1 NMR spectral titration with F- revealed that complete deprotection of a triisopropylsilyl (TIPS) group needed exactly 1 equiv of TBAF. UV-vis and fluorescence titration studies exhibited the appearance of a new intense absorption band centered at 434 nm and green emission peak at 500 nm, accompanied by bright yellow color development to the naked eye. An easy-to-prepare test paper, obtained by dipping the paper into the solution of TIPS-protected coumarin derivative, was able to detect F- in aqueous media. The method has also shown highly promising results in detecting all kinds of fluoride salts, regardless of being organic or inorganic, and thus could be potentially useful in real applications.