A smart ratiometric red fluorescent chemodosimeter for fluoride based on anthraquinone nosylate

Abstract

The present work reports a smart design of a chemodosimeter, namely 4-(6,11-dihydro-6,11-dioxo-1H-anthra[1,2-d]imidazol-2-yl)phenyl-4-nitrobenzenesulfonate (AH), which recognises F⁻ specifically through a naked eye colour change from light yellow to light orange and remarkable ratiometric fluorescence from green to red from the matrix of a large number of similar anions in acetonitrile solution. The sensing mechanism was worked out as fluoride-triggered deprotonation of imidazole accompanied by deprotection of nosylate group (p-nitrobenzenesulfonate group). AH was fully characterized through single crystal X-ray diffraction studies along with FT-IR, ¹H and ¹³C NMR and ESI-MS. The detection limit calculated through fluorescent titration was found to be 3.45 × 10⁻¹⁰ M. Theoretical calculations at density functional level were in agreement with experimental observations. AH also showed its practical applicability in the form of test paper strips.