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.