A water-soluble fluorescent fluoride ion probe based on Alizarin Red S–Al(III) complex

A new water-soluble fluorescent fluoride ion signaling system has been developed based on the ligand exchange mechanism in aqueous medium. This procedure is based on the exchange of two Alizarin Red S (ARS) molecules coordinated to Al(III) by fluoride ion without interference from other common anions. The binary complex of ARS with Al(III) provides a sensitive signaling system for fluoride ion in the concentration range from 5 × 10−6 to 3 × 10−4 M. The ligand exchange reaction of ARS–Al(III) complex with fluoride ion has been investigated by UV–vis and fluorescence spectroscopies combined with the AM1 semi-empirical quantum chemical calculations. The pale orange fluorescence (λmax = 575 nm) exhibited by the complex upon excitation at 435 nm decreases in intensity with fluoride addition with a detection limit of 0.1 mg L−1.