White light emitting silsesquioxane based materials: the importance of a ligand with rigid and directional arms

Abstract

The synthesis of a novel polyhedral oligomeric silsesquioxane functionalized with eight rigid and directional terpyridine-based arms (Ter-POSS) was successfully achieved via a Sonogashira reaction. The POSS based ligand was extensively characterized using different techniques including ¹H, ¹³C and ²⁹Si NMR as well as UV-Vis and fluorescence spectroscopies. The assembly of these nano-caged units in the presence of different transition metal ions (Fe²⁺, Zn²⁺ and Cu²⁺) as well as of a cation from the lanthanides (Eu³⁺) was investigated using absorption and emission spectroscopies. The final materials display an evident emission in different regions of the visible spectrum as a function of the cation employed. Additional insights into the structural organization of Ter-POSS in the presence of metal cations were obtained via molecular mechanics and molecular dynamics simulations. The polymeric material resulting from the complexation with europium displays a white light emission ascribed to the presence of combined contributions from the blue, green and red regions. The final self-assembled organizations display an increased quantum yield with the highest value (29.6%) obtained in the presence of Zn²⁺. Moreover, the white-light emitting europium-based nanostructure exhibits one of the highest quantum yields reported in the literature for similar solids.