Light Triggered Co-Assembly of Photocleavable Copolymers and Polyoxometalates with Enhanced Photoluminescence

A novel co-assembly based on the block copolymer bearing photocleavable groups and macroanionic polyoxometalates Na-9[Ln(W5O18)(2)] (LnW(10), Ln = Eu, Dy) triggered by UV light is realized in aqueous solution. The copolymer synthesized by atom transfer radical polymerization (ATRP) undergoes irreversible cleavage upon UV irradiation to generate primary amine (pKa approximate to 8-9) residues which are completely protonated under a neutral pH in aqueous solution. Electrostatic attractions between the resulting positively charged copolymers and anionic LnW(10) drive the formation of assemblies. In situ small angle X-ray scattering and transmission electron microscopy are used to characterize the morphology of the assemblies. The microenvironments around polyoxometalates in the core of hybrid assemblies become highly hydrophobic, resulting in dramatically enhanced photoluminescence with the obvious intensity enhancement. The solution parameters pH and salt additives show great effects on the formation of assemblies.