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

New thiosemicarbazide-linked acridines were prepared and investigated as chemosensors for the detection of biologically and environmentally important anions. The compounds were found selective for fluoride (F) with no affinity for other anions, i.e. OAc, Br, I, HSO, SO, PO, ClO, ClO, 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 was observed. The anion-sensing process was studied in detail via UV-visible absorption, fluorescence and H-NMR experiments. Moreover, during the synthesis of acridine probes nickel fluoride (NiF), 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.