Acylhydrazones as sensitive fluorescent sensors for discriminative detection of thorium (IV) from uranyl and lanthanide ions

Thorium, as a radioactive element, is always associated with rare earth in nature. So it is an exacting challenge to recognize thorium ion (Th 4+ ) in the presence of lanthanide ions because of their overlapping ionic radii. Here three simple acylhydrazones ( AF , AH and ABr , with the functional group fluorine, hydrogen and bromine, respectively) are explored for Th 4+ detection. They all exhibit excellent “turn-on” fluorescence selectivity toward Th 4+ among f-block ions in aqueous medium with outstanding anti-interference abilities, where the coexistence of lanthanide and uranyl ions in addition with other ordinary metal ions have negligible effects during Th 4+ detection. Interestingly, pH variation from 2 to 11 has no significant influence on the detection. Among the three sensors, AF displays the highest sensitivity to Th 4+ and ABr the lowest with the emission wavelengths in the order of λ AF -Th  < λ AH -Th  < λ ABr -Th . The detection limit of AF to Th 4+ can reach 29 nM (pH = 2) with a binding constant of 6.64 × 10 9 M −2 . Response mechanism for AF toward Th 4+ is proposed based on the results of HR-MS, 1 H NMR and FT-IR spectroscopies together with DFT calculations. This work provides important implications on the development of related series of ligands in nuclide ions detection and future separation from lanthanide ions.