From ligand-stabilized gold nanoparticles to hybrid organic-inorganic superstructures

Gold nanoparticles (Au NPs) have many potential applications including nanoelectronics, catalysts and sensors. These future devices depend on stable and monodisperse NPs and their directed assembly. Different macromolecular multidentate thioether ligands were synthesized and used for the stabilization of Au NPs with diameters of around 1.2 nm and narrow size distributions. The NPs were prepared from soluble gold (III) precursors in a two-phase process in presence of the respective ligand. The properties of the thioether ligands concerning the sizes as well as the stability and dispersity of Au NPs were thereby investigated and it was found that the size and surface functionalization of NPs can be controlled by varying the size and shape of the thioether ligands. Bifunctional NPs were formed in the presence of linear octadentate ligands and their functionality, an oligo phenylene ethynylene (OPE) rod with a protected terminal acetylene, was used to form NP superstructures upon homocoupling. Switching from benzene to pyridine as anchor of the functionality induced a perpendicular arrangement of the rod on the NP surface. Theoretical calculations suggested that this controlled orientation was directed by coordination of the nitrogen’s lonepair to the gold surface. Thioether dendrimers were used to enlarge the ligand structure and thus its denticity. Their stabilizing ability strongly depended on the size of the protective ligand shell showing the importance of the tert-butyl functionalized benzene units. By using icosadentate dendrimers (20 thioether moieties) we were able to form monofunctionalized NPs. These artificial molecules were used to form dumbbell structures with satisfying yields and controlled interparticle distances