Anthraimidazoledione Based Reversible and Reusable Selective Chemosensors for Fluoride Ion: Naked-Eye, Colorimetric and Fluorescence “ON-OFF”

Novel anthraimidazoledione-based compounds (1–3) are synthesized as selective colorimetric and fluorescent sensors for fluoride ion. The binding properties of the probes (1–3) are studied with different anions in acetonitrile solvent. Spectral red shifts in the absorption spectra and ‘turn-off’ emission are observed when fluoride is added to 1–3. The striking green to orange color change in the ambient light is thought to be due to the deprotonation of the N–H proton of the imidazole moiety of the probes by the basic F − ion. Interestingly, in all three cases the nonfluorescent probe-F − solutions, on treatment with copper perchlorate, show distinct color change from orange to golden yellow with resumption of fluorescence intensity. Furthermore, the reversibility of sensors (1–3) for the detection of F − ion is tested for four cycles indicating that “ON-OFF-ON” mechanism is operative. Test strip based on sensor 2 acts as a reusable cost-effective F − sensor.