Novel acridine-based thiosemicarbazones as ‘turn-on' chemosensors for selective recognition of fluoride anion: a spectroscopic and theoretical study

Abstract

New thiosemicarbazide-linked acridines <b>3a-c</b> were prepared and investigated as chemosensors for the detection of biologically and environmentally important anions. The compounds <b>3a-c</b> were found selective for fluoride (F^-) with no affinity for other anions, i.e. ^-OAc, Br^-, I^-, HSO₄^-, SO₄^2-, PO₄^3-, 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 <b>3a-c</b> 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 <b>3a-c</b> 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.