Exclusive fluoride ion recognition and fluorescence turn-on response with a label-free DMN Schiff base

A label-free DMN Schiff base (4) has been explored as a highly selective and sensitive fluoride ion receptor. Fluoride-induced deprotonation results in a charge transfer (CT) transition red shifted with a fluorescence 'turn-on'. Anion selectivity can be tuned by the electron push-pull property of substituents at the phenyl para-position. Selectivity for F- is attributed to the suitable acidity of -NH2.