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UBC Theses and Dissertations

On-surface self-assembly and characterization of a macromolecular charge transfer complex by scanning tunneling microscopy and spectroscopy Capsoni, Martina Carla


Organic-based technologies have recently attracted significant interest. Characterization of their structure and properties at native length scales are essential for their implementation in devices. On-surface self-assembly of metal-organic frameworks is a simple way to fabricate molecular systems with specific functionalities. In this thesis work, the morphology and electronic structure of self-assembled linear nanochains, featuring a triiron linkage between two bisterpyridine-based ligands on an Ag(111) surface, have been investigated with scanning tunneling microscopy and spectroscopy. An in situ, clean and reliable on-surface preparation technique was developed for thermally-activated self-assembly of complexes based on the metal-organic motif of dyes used in photovoltaic and catalysis applications. Tunneling spectroscopy on the metal-organic nanostructures obtained suggests the formation of a coordination bond with charge transfer between metal and ligand. Furthermore, the electronic structure indicates the presence of the desired metal-to-ligand charge transfer optical transitions, characteristic of the related complexes. The unprecedented triiron coordination link has potential for being an efficient reaction center for catalysis applications, as well as for having interesting magneto, spin, and electronic properties. Each step and aspect of the chains formation process has been characterized via scanning tunneling microscopy measurements and growth studies, and the results are supported by density functional theory calculations. Additionally, the relevance and influence of the silver metal substrate on both bare ligands and chains has been investigated. Bare molecules show a strong interaction with the substrate, as demonstrated by their specific adsorption configurations and an electronic structure which is distinct from when they are electronically decoupled from the surface by an NaCl bilayer. When the molecules are in chains the silver plays a key role in the structure of the coordination link. This work shows the potential of using on-surface self-assembly and scanning tunneling microscopy and spectroscopy, not only to prepare with high-fidelity clean and controlled structures but also as a flexible platform to investigate and tailor functional properties of different systems for a large variety of applications where a solid support is essential.

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