Colorimetric and ratiometric fluorescence sensing of fluoride ions based on competitive intra- and intermolecular proton transfer

Receptors 1 and 4 show fluoride ion selective changes in their absorbance and emission behaviours amongst F−, Cl−, Br−, I−, NO 3 - , CH3COO−, HSO 4 - , H 2 PO 4 - and ClO 4 - anions. Fluoride ion mediated ‘ON–OFF–ON’ switching behaviour of 4 provides opportunities for ratiometric estimation of fluoride ions.