Thorium, as a radioactive element, is always associated with rare earth in nature. So it is an exacting challenge to recognize thorium ion (Th4+) 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 Th4+ detection. They all exhibit excellent "turn-on" fluorescence selectivity toward Th4+ 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 Th4+ 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 Th4+ and ABr the lowest with the emission wavelengths in the order of λAF-Th < λAH-Th < λABr-Th. The detection limit of AF to Th4+ can reach 29 nM (pH = 2) with a binding constant of 6.64 × 109 M-2. Response mechanism for AF toward Th4+ is proposed based on the results of HR-MS, 1H 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.
Keywords: Acylhydrazone; Chemosensor; Lanthanide; Nuclide; Thorium recognition.
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