Zwitterionic Surfactant Micelle-Directed Self-Assembly of Eu-Containing Polyoxometalate into Organized Nanobelts with...

Recently, hybrid coassembly between polyoxometalates (POMs) and cationic building blocks provides an efficient strategy to greatly optimize POMs' functionality as well as their aggregate structural diversity. Adaptive hybrid supramolecular materials with enhanced luminescence have then been obtained from lanthanide-containing POMs. In this work, a commercially available and pH-switchable zwitterionic surfactant, tetradecyldimethylamine oxide (C₁₄DMAO), was chosen to coassemble with a lanthanide-containing anionic POM [Na₉(EuW₁₀O₃₆)·32H₂O, abbreviated as EuW₁₀] in water. The much improved red-emitting luminescent nanobelts at a C₁₄DMAO/EuW₁₀ molar ratio ( R) of 20 were obtained, which exhibited longer luminescence lifetime and higher quantum yield compared with EuW₁₀ aqueous solution. After careful characterization of morphology and structure of nanobelts, an unusual axial lamellar aggregation arrangement mechanism was proposed. It was the partial protonation of C₁₄DMAO at the solution pH of about 6.5 that led to positively charged micelles, being bridged by anionic EuW₁₀ clusters to aggregate into such novel nanobelts under the synergetic effects of appropriate electrostatic, hydrogen-bonding, and hydrophobic interactions. The resulted pH-responsive luminescent nanobelts and their aggregation model should offer attractive references for preparing smart optical supramolecular materials.