White Light Emitting Silsesquioxane Based Materials: the Importance of a Ligand with Rigid and Directional Arms

The synthesis of a novel polyhedral oligomeric silsesquioxane functionalized with eight rigid and directional terpyridine-based arms (Ter-POSS) was successfully achieved via Sonogashira reaction. The POSS based ligand was extensively characterized via different techniques including 1H, 13C and 29Si NMR as well as UV-Vis and fluorescence spectroscopies. The assembly of this 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 via absorption and emission spectroscopy. The final materials display an evident emission in different region of the visible as function of the cation employed. Additional insights on the structural organization of the Ter-POSS in the presence of metal cations were obtained via molecular mechanics and molecular dynamics simulations. The polymeric material resulting from a complex with europium displays a white light emission ascribed to the presence of combined contributions in the blue, green and red. The final self-assembled organizations display elevate 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.