Alkaline earth cation-mediated photoluminescent complexes of thioflavin T with twisted cucurbit[14]uril

Abstract

We report alkaline earth metal ion-mediated solid photoluminescent complexes of thioflavin T (ThT) with twisted cucurbit[14]uril (tQ[14]) for the first time. The interaction with tQ[14] enhanced the fluorescence of ThT in aqueous solution. Indeed, the fluorescence intensity of ThT increased rapidly with increasing amount of tQ[14] up to a tQ[14] : ThT ratio of 15. Interestingly, at lower tQ[14] : ThT ratios (1 : 1), the introduction of alkaline earth metal cations (AE²⁺) into the tQ[14]–ThT interaction system led to fluorescence quenching of ThT, except in the case of Mg²⁺ cation, which led to an initial fluorescence enhancement, followed by gradual fluorescence quenching of ThT. At higher tQ[14] : ThT ratios (1 : 15), the introduction of alkaline earth metal cations into the tQ[14]–ThT interaction system led to the precipitation of solid tQ[14]/ThT/AE²⁺ interaction products, which emitted strong blue fluorescence, except in the case of Sr²⁺ cation, which exhibited fluorescence quenching of ThT without any solid precipitation. Thus, the tQ[14]–ThT interaction system shows potential applications not only for preparing stimuli-responsive supramolecular photoluminescent materials, but also for identifying Mg²⁺ at lower tQ[14] : ThT ratios and Sr²⁺ at higher tQ[14] : ThT ratios.