Reusable colorimetric and fluorescent chemosensors based on 1,8-naphthalimide derivatives for fluoride ion detection

Abstract

Two 1, 8-naphthalimide derivatives, 2-(2-ethylhexyl)-6-(2-(4-(5-phenyl-1,3,4-oxadiazol-2-yl)benzylidene)hydrazinyl)-1H-benzo[de]isoquinoline-1,3(2H)-dione (named as NAOZ) and 2-(2-ethylhexyl)-6-(2-(4-(5-phenyl-1,3,4-thiadiazol-2-yl)benzylidene)hydrazinyl)-1H-benzo[de]isoquinoline-1,3(2H)-dione (named as NATZ), containing hydrazone and thiadiazole/oxadiazole, were successfully synthesized. Compounds NAOZ and NATZ were further served as efficient reversible colorimetric and fluorescent chemosensors for fluoride ion over a wide range of other anions (Cl−, Br−, I−, NO3−, ClO4−, HSO4−, BF4−, and PF6− as their (C4H9)4N+ salts) because fluoride ion can deprotonate the hydrazone moiety, leading to the observed long-wavelength color change. Interestingly, CO2 can recover the charge transfer (CT) absorption and photoluminescence intensities of compound NAOZ/NATZ + F−, because CO2 can react with a small amount of water to form acids, which can provide protons.