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) 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 detection. They all exhibit excellent "turn-on" fluorescence selectivity toward Th 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 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 and ABr the lowest with the emission wavelengths in the order of λ < λ < λ. The detection limit of AF to Th can reach 29 nM (pH = 2) with a binding constant of 6.64 × 10 M. Response mechanism for AF toward Th is proposed based on the results of HR-MS, 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.