Supramolecular Assembly Mediated by Metal Ions in Aqueous Solution and Its Application in Their Analysis

A water‐soluble fluorescent sensor based on the interaction of twisted cucurbit[14]uril (tQ[14]) and thiazole orange (TO) in aqueous solution was developed. Formation of the tQ[14]/TO complex gives rise to stronger fluorescence in both neutral and acidic aqueous solutions compared with that of free TO. Further experiments on the interaction of the tQ[14]/TO complex with metal ions revealed that, from a series of nineteen selected common metal ions, 1) only Hg2+ can lead to fluorescence enhancement and then quenching of the tQ[14]/TO (2:1) complex in neutral aqueous solution; 2) only Ba2+ can induce fluorescence quenching of the tQ[14]/TO (2:1) complex in aqueous HCl solution (pH 2); furthermore, the tQ[14]/TO/Ba2+ systems exhibit reversible changes in fluorescent intensity on successively adding SO42− and Ba2+; and 3) only Ba2+ or Pb2+ can induce fluorescence quenching of the tQ[14]/TO (15:1) complex in aqueous HCl solution (pH 2). Thus, the tQ[14]/TO complex can act as a supramolecular fluorescence‐based sensor for the determination of Hg2+, Ba2+, and Pb2+ ions. Uniquely responsive: The interaction of thiazole orange (TO) with twisted cucurbit[14]uril (tQ[14]) was investigated, and formation of a stable fluorescent tQ[14]/TO complex was observed. The tQ[14]/TO complex exhibited unique fluorescence responses to Hg2+, Ba2+, and Pb2+ cations in different aqueous media (see figure). Thus, a fluorescent sensor for three heavy‐metal ions was developed.