A highly selective fluorescent sensor for fluoride in aqueous solution based on the inhibition of excited-state intramolecular proton transfer

A 3-hydroxyflavone derivative (L) was synthesized and its red-emitting ternary complex, composed of Zr–EDTA and L, was developed as a highly selective and sensitive fluorescent sensor for ratiometric detection of F− in aqueous solution with a physiological pH region. Fluorescent intensity at 610 nm of Zr–EDTA–L increased with addition of F−, concomitantly the emission at 470 nm decreased together with an obvious color change by naked eyes. However, other competitive anions such as Cl−, Br−, I−, NO3−, HSO4−, AcO− and H2PO4− did not induce any distinct changes in fluorescence spectra. The results can be reasonably interpreted by the inhibition of excited-state intramolecular proton transfer (ESIPT), which arises from the ligand exchange of L coordinated to Zr–EDTA and fluoride anions.