H-bond stabilization of a tautomeric coumarin-pyrazole-pyridine triad generates a PET driven, reversible and reusable fluorescent chemosensor for anion detection

•A novel fluorescent coumarin-pyrazole-pyridine triad (1) was synthesized and characterized for detection anions.•1 has remarkable sensitivity for fluoride detection in DMSO at the stoichiometric ratio of 1:1.•1 exhibits naked-eye visible ON-OFF-ON states.•1 exhibits acidochromic property and significant “light-up” effect is observed after interaction 1 with TFA in CH2Cl2.

A coumarin based anion sensor utilizing pyrazole both as an electron donor and hydroxyl H-bond donor and pyridine as a tautomer stabilizer is reported. The chemosensor exhibits ON-OFF-ON states and is more sensitive to F− at the stoichiometric ratio of 1:1. The OFF state is due to PET and the role of pyrazole is two fold, both stabilization of the enol tautomer via H-bonding and hosting domain of electrons enabling PET. Moreover, the absorption and emission properties of chemosensor change drastically upon acidification.

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