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. (C) 2017 Elsevier Ltd. All rights reserved.