Highly luminescent and multi-sensing aggregates co-assembled from Eu-containing polyoxometalate and an enzyme-responsive surfactant in water

Abstract

Hybrid co-assembly of polyoxometalates (POMs) with cationic organic matrices offers a preferable way to greatly enhance POM functionality as well as processability. Thus, multi-stimulus responsive supramolecular materials based on lanthanide-containing POMs with improved luminescence may be fabricated from appropriate components through this convenient strategy. Herein, we reported that the co-assembly of Na₉(EuW₁₀O₃₆)·32H₂O (EuW₁₀) and a commercially available cationic surfactant, myristoylcholine chloride (Myr), in water could produce enhanced red-emitting luminescent aggregates, with their photophysical properties highly dependent on the molar ratio (R) between Myr and EuW₁₀. The R of 36 was finally selected owing to the displayed superior luminescence intensity and good aggregate stability. The Myr/EuW₁₀ hybrids induced by electrostatic and hydrophobic forces presented practically as multilamellar spheres with diameters varying from 80 to 300 nm. Compared to an aqueous solution of EuW₁₀ nanoclusters, a 12-fold increase in absolute luminescence quantum yield (∼23.3%) was observed for the hybrid spheres, which was ascribed to the efficient shielding of water molecules. An unusual aggregation arrangement mechanism and the excellent photophysical properties of these aggregates were thoroughly investigated. Both the enzyme substrate character of Myr and the sensitive coordination structure of EuW₁₀ to the surrounding environment made Myr/EuW₁₀ aggregates exhibit multi-stimulus responsiveness to enzymes, pH, and transition metal ions, thus providing potential applications in fluorescence sensing, targeted-release, and optoelectronics.