Multidentate thioether-based ligands controlling the stability and size of gold nanoparticles

The aim of this project was to find a way how to precisely control and enlarge the size of small gold nanoparticles by using multidentate thioether-based ligands. Our strategy and design was based on previously reported benzylic thioether-based macrostructures (see 1. Introduction). The scope of this field is geared, as a consequence, towards the synthesis of more complex systems with different bulkiness and exhibiting larger backbone-moieties (i.e. larger sulfur-sulfur distance); and the exploration of their feasibility in terms of size control and stability of the resulting AuNPs. We were interested in both: 1) AuNPs enwrapped by a low number of capping macromolecules, with a potential for mono-functionalization at their periphery for further wet chemical applications, and 2) size control of AuNPs, which will enable tuning of the physical and optical properties for future applications. As desired wet chemical processability requires long-term thermal stability of AuNPs and enhanced redispersibility features in common organic solvents, we focused mainly on the design and investigation of novel sterically bulky ligand structures.
This thesis is divided into three major parts, each describing the challenges of the ligands' synthesis and discussing the results of the as-synthesized AuNPs. The first part (Chapter 3) discusses linear oligomers with various backbone motifs of different bulky robustness and different length (sulfur- sulfur distance), and the influence of these parameters on the stability and size of the resulting AuNPs. The second part (Chapter 4) is based on tripodal dendritic molecular systems attached with various in length varying backbone-moieties, or cage-like structures with distinct cavity sizes and their ability to confine AuNPs. The last part (Chapter 5) describes a systematic study of two independent parameters and their effect on the size of the AuNPs enwrapped by various linear heptamers.