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

Abstract

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 − , HSO 4 − , SO 4 2− , PO 4 3− , ClO 3 − , ClO 4 − , 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 1 H-NMR experiments. Moreover, during the synthesis of acridine probes 3a–c nickel fluoride (NiF 2 ), 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.