A Self-Organized Ensemble of Fluorescent 3-Hydroxyflavone-Al (III) Complex as Sensor for Fluoride and Acetate Ions

Aluminum chloride addition results in a self-organized TURN-ON fluorescence of 3-hydroxyflavone (3HF) by a complexation reaction in MeOH and subsequent ligand exchange reaction with fluoride or acetate ions causes a fluorescence TURN-OFF of this complex, delivering a quantitative estimation route for fluoride and acetate ions. The ternary complex of 3HF with Al (III), a hard acid provides for a sensitive signalling system for fluoride ion, a hard base in the concentration range from 6 μM to 50 mM by a concerted co-ordination of fluoride ion involving an intermediate mechanistic pathway, while the complex is sensitive to acetate addition between 0–68 μM. The ligand exchange reaction of Al (3HF)₂ complex by fluoride or acetate ion, without interference from other common anions, has been investigated by UV-visible and fluorescence spetroscopies. The structure of the in-situ intermediate isolated at higher Al (3HF)₂ complex and acetate concentrations was inferred from the FT-IR spectrum and ESI-MS of the sample.