Organising molecules at the solid-liquid interface

Gold nanoparticles (Au NPs) have attracted substantial attention in recent years owing to their small size and quantum properties leading to a wide range of potential applications as molecular devices and catalysts compared to their macromolecular counterparts. Since the physical and chemical properties of Au NPs are known to be dramatically affected by their size, shape and spatial arrangement, the potential of the concept to produce new Au NPs tailored to possess desired properties was investigated through careful selection of the passivating ligands.
The aim of this thesis with respect to gold nanoparticles is two fold. First, multidentate thioether based ligands were designed based on structural considerations, and synthesized. Then, the interactions of these novel well-defined ligands with Au55 nanoparticles were investigated. Ligand exchange attemps to replace phosphine ligands with more stable benzothioether ligands could not be achieved. In fact, coagulation of Au55 nanoparticles into bigger particles or even into bulk gold was observed. Alternatively, the potential of multidentate macrocyclic ligands as stabilizing and size steering additives during the direct synthesis of new gold clusters with the Brust-Schiffrin method was investigated. Significantly, a very narrow size distribution with mainly 1.1 nm gold nanoparticles was obtained as demonstrated by TEM analysis. Calculations utilizing the characterization data showed that two of our bulky ligands stabilized one gold nanoparticle composed of 34 gold atoms. It was also observed that the newly formed gold nanoparticles are additionally stabilized with the help of the ionic phase transfer reagent and showed very high stability in solution or solid phase.
In the second part of this study, the potential of tert-butoxycarbonyl (BOC) protected arylamine structures as supramolecularly organized building blocks which might be subsequently interlinked via reactive intermediates accessed by deprotection chemistry was investigated. Besides common usage as a protection group, Boc groups can also play an important role in the self assembly of molecules by forming intermolecular hydrogen bonds due to the H-bond donor and acceptor capability. Being thermally cleavable, Boc protected molecules are not only ideal candidates to arrange ordered structures but also to release active species at well defined positions as building blocks of a network consisting of interlinked deprotected molecules. Several Boc protected aromatic structures were synthesized and their ability to form ordered structures on surfaces using the concepts of supramolecular chemistry and the formation of new N-N and N-C covalent bonds were investigated.