Synthesis of nitrogen-substituted cycloparaphenylenes
Hirst, Elizabeth S.
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Bottom-up synthesis is increasingly becoming the method of choice for assembling and studying novel nanomaterials. Whereas more traditional top-down methods may lead to mixtures of products and suffer from reproducibility issues, bottom-up approaches offer atomistic control over the material's structure. Bottom-up synthesis can also produce materials that would otherwise be unobtainable with top-down methodologies. Finite substructures of carbon nanotubes (CNTs) are one such example. The work encompassed in this thesis details the study of two related classes of CNT substructures: the cycloparaphenylenes (CPPs) and [5.7]ncyclacenes. Cycloparaphenylenes are a class of graphitic material with many unique properties that make them intriguing candidates for study in a variety of electronic applications. Chapter 1 describes the current state of CPP research, from preliminary synthesis to fundamental understanding of their properties. To optimize device performance, carbon materials are often doped with heteroatoms. Towards this end, the synthesis of a series of nitrogen-doped CPPs (N-CPPs) are detailed in Chapter 2. Nitrogen is incorporated into the CPP structure by way of the reductive aromatization strategy used for the all carbon CPPs, replacing 1,4-dibromobenzene with 2,5-dibromopyridine. The synthesis utilizes oxidatively masked benzenes to assemble less strained, macrocyclic precursors. Through the divergent nature of the synthesis, macrocycles containing up to three nitrogen atoms at precise locations are prepared. Macrocycles are aromatized via a single electron reduction to reveal the final N-CPP structures. Chapter 3 details the full characterization of the properties of the novel N-CPPs. The differences between the N-CPPs and CPP are rationalized in the context of DFT studies. Finally, the study of 1N-CPP and CPP as novel electrode materials in supercapacitor cells is presented. Preliminary results show that the CPP electrodes are more conductive than the activated carbon control group, but the specific capacitances are found to be low. Finally, Chapter 4 describes the computational study of a novel family of macrocycle: [5.7]ncyclacenes. [5.7]ncyclacenes are isomers of the sought after [n]cyclacenes. Unlike their isomeric cousins, DFT studies show that [5.7]ncyclacenes have stable, closed-shell singlet ground states with relatively low strain energies. NICS values also show the molecules to be non-aromatic. These results suggest that with proper synthetic design, the [5.7]ncyclacenes should be accessible synthetically.