Aggregation by metallophilic interaction (AMI)

In the past the self-assembly of organic nanostructures on surfaces has triggered a lot of interesting experiments, e. g., porous networks can be used to assemble other molecules in a periodic array. Besides aesthetic aspects, these structures are important to study the fundamental interaction between the adsorbed molecules and between the adsorbates and the substrate surface. Most commonly these structures, which can be also simple one dimensional stacks of molecules on the surface, are based on covalent bonding, hydrogen bonding or weak van der Waals forces. Until now, metallophilic interactions were not recognized by the scientific community in this context. These interactions reach their maximum gold compounds. It is often called aurophilic interaction. The project focuses on the investigation of volatile Au(I) compounds featuring aurophilic interactions in the solid state. For this purpose, new Au(I)-compounds will be synthesized and characterized. In the solid state, the selected classes of complexes polymerise to 1D-chains or 2D-sheets via aurophilic interactions. Hence, it is expected that these aurophilic interactions will also govern the aggregation of the complexes on the surface leading to 1D- and 2D-aggregates. Because they represent very different properties, we will use gold, silver and TiO2 substrates to elucidate the influence of the substrates. To gain a fundamental understanding of the aggregation process on the surface, we will apply different techniques with real-time capabilities: Photoelectron emission microscopy (PEEM) and optical differential reflectance spectroscopy (DRS) can both monitor simultaneously the surface properties during a deposition experiment. Especially PEEM can be used to acquire topographic and electron spectroscopic information down to the scale of sub-m-sized crystallites. The combination of different surface sensitive techniques will allow us to observe, to understand, and finally to control the aggregation from the first nucleus to small crystallites in ultrathin films. Above all, we will use an iterative approach to modify the ligands of the Au(I) complexes to growth self-assembled structures with different dimensionality and/or different distances between the Au atoms.

The self-assembly of organic nanostructures on surfaces has triggered in the past a lot of interesting experiments, e. g., porous networks can be used to assemble other molecules in a periodic array. Besides aesthetic aspects, these structures are important to study the fundamental interaction between the adsorbed molecules and between the adsorbates and the substrate surface. Most commonly these structures, which can be also simple one-dimensional stacks of molecules on the surface, are based on covalent bonding, hydrogen bonding or weak van der Waals forces. Until now, metallophilic interactions were not recognized by the scientific community in this context. Heavy metal atoms, which are incorporated in coordination compounds, play a special role for this special van der Waals interaction between the individual molecules. Relativistic effects lead to significant shorter distances between the metal atoms than expected based on the van der Waals radii. The strongest interaction among metals is found for complexes with a central gold atom in the oxidation state +1. Therefore, it is often called aurophilic interaction. In this project, not only new gold(I) compounds were synthesized and characterized. In a second step, the aggregation of selected compounds on different surfaces was examined. Aggregation is the process in which molecules assemble into a larger association (aggregate). On surfaces this can be, e.g, islands that are exactly the height of a molecule and in which the molecules themselves form well-ordered structures. To gain a fundamental understanding of the aggregation process on the surface, we will apply different techniques with real-time capabilities: For this purpose, the molecules were deposited in an ultra-high vacuum chamber, while the surfaces to be coated were observed with the photoelectron emission microscope (PEEM) and (polarization dependent) differential reflectance spectroscopy (DRS). In particular, the PEEM can record not only the topographical, but also electron spectroscopic information down to the sub-m scale of the (two-dimensional) islands and (three-dimensional) crystallites that are forming.