Quaternary ammonium salt-based chromogenic and fluorescent chemosensors for fluoride ions

Chemosensors 5–7 possessing a quaternary ammonium cation (for electrostatic interactions) and an N–H group(s) (for H-bonding) as recognition sites and an anthracene-9,10-dione as both a chromogenic and fluorescent moiety exhibit absorption and emission changes with fluoride ions only. No significant response to other anions such as Cl−, Br−, I−, NO 3 - , CH3COO−, HSO 4 - , H 2 PO 4 - and ClO 4 - is observed. The dual emission at λmax 580 nm (free 5/6) and λmax 510 and 540 nm (5/6 + F−) in chemosensors 5 and 6 enables ratiometric analysis of fluoride ions.