Dumbbells, trikes and quads: organic-inorganic hybrid nanoarchitectures based on "clicked" gold nanoparticles.

The controlled assembly of gold nanoparticles in terms of the spatial arrangement and number of particles is essential for many future applications like electronic devices, sensors and labeling. Here an approach is presented to build up oligomers of mono functionalized gold nanoparticles by the use of 1,3-bipolar azide alkyne cycloaddition click chemistry. The gold nanoparticles of 1.3 nm diameter are stabilized by one dendritic thioether ligand comprising an alkyne function. Together with di-, tri- and tetra-azide linker molecules the gold nanoparticle can be covalently coupled by a wet chemical protocol. The reaction is tracked with IR and UV-vis spectroscopy and the yielded organic-inorganic hybrid structures are analyzed by transmission electron microscopy. To evaluate the success of this click chemistry reaction statistical analysis of the formed oligomers is performed. The geometric and spatial arrangements of the found oligomers match perfectly the calculated values for the used linker molecules. Dimers, trimers and tetramers could be identified after the reaction with the corresponding linker molecule. The results of this model reaction suggest that the used click chemistry protocol is working well with mono functionalized gold nanoparticles.

Add a third hook: S-acetyl protected oligophenylene pyridine dithiols as advanced precursors for self-assembled monolayers.

Self-assembled monolayers (SAMs) of thiols on gold substrates are potentially important systems for future technologies such as molecular electronics and sensing. Especially in molecular electronics a strong interaction and coupling between the "device" molecules and substrate is crucial. In this context, we present here two series of novel SAM precursors, viz. bidentate oligophenylenes with either 1,3-phenylenedimethanethiol or pyridine-2,6-diyldimethanethiol anchoring group. Both series are shown to form densely packed monolayers with a low level of contamination and a high orientational order that are additionally promoted by the interaction between the terminal pyridine moiety and the substrate in the second series. At the same time, most of the SAM constituents do not exhibit a strictly bidentate bonding to the substrate - whereas one anchor group has a thiolate-type bonding, the other is weakly coordinated, unbound, or participating in a disulfide bridge with the adjacent molecules. We believe that such a bonding heterogeneity stems from the fundamental problems of molecular self-assembly in the given case.

Monofunctionalized gold nanoparticles stabilized by a single dendrimer form dumbbell structures upon homocoupling.

The assembly of dumbbell structures as organic-inorganic hybrid materials is presented. Gold nanoparticles (NPs) with a mean diameter of 1.3 nm were synthesized in very good yields using a stabilizing dendrimer based on benzylic thioether subunits. The extended dendritic ligand covers the NP surface and contains a peripheral protected acetylene, providing coated and monofunctionalized NPs. These NPs themselves can be considered as large molecules, and thus, applying a wet-chemical deprotection/oxidative acetylene coupling protocol exclusively provides dimers of NPs interlinked by a diethynyl bridge. The concept not only enables access to novel organic/inorganic hybrid architectures but also promises new approaches in labeling technology.

Gold nanoparticles stabilized by thioether dendrimers.

Ligand-stabilized gold nanoparticles (Au NPs) are promising materials for nanotechnology with applications in electronics, catalysis, and sensors. These applications depend on the ability to synthesize stable and monodisperse NPs. Herein, the design and synthesis of two series of dendritic thioether ligands and their ability to stabilize Au NPs is presented. The dendrimers have 1,3,5-trisubstituted benzene branching units bridged by either meta-xylene or ethylene moieties. A comparison between the two ligands shows how both size control and the stability of the NPs are influenced by the nature of the ligand-NP wrapping interaction. The meta-xylene-bridged ligands provided NPs with a narrow size distribution centered around a diameter of 1.2 nm, whereas the NPs formed with ethylene-bridged dendrimers lack long-term stability with NP aggregation detected by UV/Vis spectroscopy and transmission electron microscopy. The bulkier tert-butyl-functionalized meta-xylene bridges form larger ligand shells that inhibit further growth of the NPs and thus provide a simple route to stable and monodisperse Au NPs that may find use as functional components in nanoelectronic devices.

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. Herein we review our efforts to develop oligomeric thioether ligands able to direct the synthesis of Au NPs and their surface functionalization. A screening of different oligomeric thioethers indicates that the NPs become more stable and monodisperse with increasing length of the thioether oligomer. The heptameric benzylic thioether 4 stabilizes monodisperse NPs with a diameter of 1 nm and excellent long-term stability in solution. It is further monofunctionalized with a central protected acetylene. After NP formation in the presence of the ligands we utilize the peripheral functionality to interlink the NPs. A mild oxidative diacetylene coupling protocol is used to covalently bind these 'artificial molecules'. This wet-chemical procedure leads to the formation of hybrid organic-inorganic superstructures.