Supplementary material from "Novel acridine-based thiosemicarbazones as ‘turn-on' chemosensors for selective recognition of fluoride anion: aspectroscopic and theoretical study"

New thiosemicarbazide-linked acridines 3a–c were prepared and investigated as chemosensors for the detection of biologically and environmentally important anions. The compounds 3a–c were found selective for fluoride (F⁻) with no affinity for other anions, i.e. ⁻OAc, Br⁻, I⁻, HSO₄⁻, SO₄²⁻, PO₄³⁻, ClO₃⁻, ClO₄⁻, CN⁻ and SCN⁻. Further, upon the gradual addition of a fluoride anion (F⁻) source tetrabutylammonium fluoride, a well-defined change in colour of the solution of probes 3a–c was observed. The anion-sensing process was studied in detail via UV–visible absorption, fluorescence and ¹H-NMR experiments. Moreover, during the synthesis of acridine probes 3a–c nickel fluoride (NiF₂), a rarely explored transition metal fluoride salt, was used as the catalyst. Theoretical studies via density functional theory were also carried out to further investigate the sensing and anion (F⁻) selectivity pattern of these probes.