UCLA

Carbon-based nanostructures are viewed as the next-generation components for advanced nanoelectronics. Offering exceptional properties such as low-current requirements and design-based optimization, these π-conjugated molecular structures show promise in outpacing the use of current transistor technologies. To fabricate and accurately study these molecules, it is necessary to utilize synthetic strategies that produce precise and defect-free structures. Thankfully, on-surface synthesis allows for the fabrication of defect-free conjugated polymers allowing in-situ visualization via scanning probe microscopies. This method typically uses a combination of polymerization and cyclization reactions to afford graphene-based nanostructures on a metal surface. Through on-surface synthesis, a number of organic molecular precursors can be sublimed into gas phase and vapor-deposited onto a metal surface, usually gold(111), which is held at a constant temperature. Due to the catalytic activity and mobility of the selected metal, this annealing process often affords organized networks of organic building blocks. Further heating leads to the cleavage of C-X bonds in the aryl-halogen precursors, giving radicals that recombine to form covalent bonds that are typically uncontrolled in solution or gas-phase reactions. Chapter 1 of this work is meant to outline the background of organic materials in electronic applications and introduce a timeline of graphene nanoribbons synthesized on metal surfaces. Chapter 2 describes the synthesis of tetraphenyl-hex-3-en-1,5-diyne, a molecular model for the Hopf cyclization reaction leading to polycyclic aromatic compounds, here chrysene derivatives. We wanted to study the potential of this π-system as reaction pathway to chrysene and larger polycyclic aromatic compounds on Au(111), and ultimately, graphene nanoribbons. It was found that this molecule undergoes two sequential Hopf cyclizations at temperatures that are much lower than calculated or experimental Hopf cyclization reactions. Chapter 3 expands on this work by discussing the synthesis of a diiodo derivative of tetraphenyl-hex-3-en-1,5-diyne. This molecular precursor is capable of pre-polymerizing on gold(111), providing an entry into the fabrication of graphene nanoribbons. Chapter 4 of this works explores the possibilities of using combinatorial Ullman coupling and Hopf cyclization to generate graphene nanoribbons from annulated tetraphenyl-hex-3-en-1,5-diyne. Overall, this works aims to divulge new and exciting synthetic pathways for developing carbon-based materials for electronic applications. Chapters 2 through 4 were conducted in collaboration with EMPA − Swiss Federal Laboratories for Materials Science and Technology, Dübendorf, Switzerland, and the University of Bern, Switzerland. Chapter 5 of this work looks at the synthesis of a 1,4-butadiyne molecular precursors for the fabrication of graphene nanoribbons on Au(111) Chapter 6 was motivated by the dramatic switch to remote-learning during the COVID-19 pandemic at UCLA. During this time, student interactions in online discussion sections were monitored to determine the best course characteristics for break-out room engagement. This work hopes to highlight important features that could be useful for in-person or remote courses in the future.