Photoluminescent sensing vesicle platform self-assembled by polyoxometalate and ionic-liquid-type imidazolium gemini surfactants for the detection of Cr3+ and MnO4- ions.

In this paper, in order to successfully achieve a fluorescent polyoxometalate (POM) probe with high luminescence, aggregation enhanced emission of POM is achieved by a self-assembly strategy. In detail, Eu-polyoxometalate (Na9[EuW10O36]·32H2O (EuW10)) and ionic-liquid-type imidazolium gemini surfactants ([C14-n-C14im]Br2, n = 2, 4, 6) constructed a vesicle with aggregation enhanced emission phenomenon. With the introduction of [C14-n-C14im]Br2, the luminescence intensity increased sharply and compared the effect of the different space length of [C14-n-C14im]Br2, the introduction of [C14-2-C14im]Br2 had the best luminescence effect and the strongest luminescence of EuW10/[C14-2-C14im]Br2 was 32 times that of pure EuW10. Thus, a sensitive selective off-luminescence chemical sensor EuW10/[C14-2-C14im]Br2 was developed for the label-free detection of Cr3+ and MnO4- in aqueous solution with lower detection limits of 0.926 µM and 1.70 µM, respectively. Collision between the fluorophore and Cr3+ or MnO4- caused dynamic quenching. Luminescence quenching of Cr3+ was attributed to Förster resonance energy transfer (FRET) while luminescence quenching of MnO4- was attributed to UV-vis competitive absorption. Our strategy for combining polyoxometalates with surfactants to construct aggregation enhanced emission systems is expected to provide new ways to develop simple, economical, fast and sensitive sensors in environmental applications such as metal ion detection.