Intramolecular proton transfer through the adjoining π-conjugated system in Shiff base: Application for colorimetric sensing of fluoride anion

• The phenol derivative L2 could selectively sense F− among test anions.
• Intramolecular proton transfer happened when L2 was bonded with F−.
• It is the first antipyrine-based anion receptor.

In this paper, a new kind of phenol-based chemsensor L2 comprised of a Schiff base and azo groups was rationally designed and synthesized. It could selectively recognize fluoride anion among tested anions such as F−, AcO−, H2PO4−, Cl−, Br−, and I− with obvious color changes from yellow to fuchsia. The intramolecular PT (proton transfer) in L1 and L2 was responsible for the sensing ability, which was certified by the 1H NMR and Uv–vis experiments.

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