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−, NO3-, CH3COO−, HSO4-, H2PO4- and ClO4- anions. Fluoride ion mediated 'ON-OFF-ON' switching behaviour of 4 provides opportunities for ratiometric estimation of fluoride ions.

Competitive intra- and intermolecular proton transfer in receptor 4 in the presence of fluoride ions leads to 'ON-OFF-ON' switching in its emission behaviour and provides an opportunity for highly selective ratiometric estimation of fluoride ions.