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⁻, , CH₃COO⁻, , and is observed. The dual emission at λ_max 580 nm (free 5/6) and λ_max 510 and 540 nm (5/6 + F⁻) in chemosensors 5 and 6 enables ratiometric analysis of fluoride ions.