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Syntheses of building blocks for organic materials: Spin-labeled nucleosides and thiophene-based oligomers
This dissertation comprises two research projects, directed at syntheses and characterizations of nitroxide modified nucleosides and π-conjugated thiophene-based oligomers. The multi-step syntheses of these compounds involved optimizations of reaction conditions, purifications, and isolations of products. Various spectroscopic techniques, magnetic measurements, and X-ray crystallography were used to characterize these materials. ^ In the first project, nitroxide modified nucleosides 1 and 2 were synthesized and isolated as red solids. The EPR spectra of 1 and 2 showed that a significant fraction of the spin density is delocalized from a nitroxide radical to the DNA base residue. Importantly, in crystalline solid 1, the crystal packing includes multiple hydrogen bonds, leading to one-dimensional chains of molecules with predominant intrachain ferromagnetic coupling and weaker interchain antiferromagnetic coupling. Thus, these nitroxides may have potential use as building block for magnetic materials. Nucleoside 3 was synthesized and isolated as red solid. The EPR and SQUID magnetic characterizations indicated high-spin S = 1 ground state of the first high-spin labeled nucleoside 3.*^ In the second project, tetrathiophene 4 and thiophene-based helicene 5 were synthesized and characterized. The helicene 5 is functionalized with four alkyl chains for both design of organic chiral glasses with strong chiroptical properties and for enhanced solubility. Preliminary studies were carried out to prepare the π-conjugated network based on 4 and 5. In the final step in the synthesis of helicene 5, a circulene-like compound 6 was also isolated. These thiophene-based oligomers are potential candidates in building materials for optoelectronic devices.*^ *Please refer to dissertation for diagrams.^
Das, Kausik, "Syntheses of building blocks for organic materials: Spin-labeled nucleosides and thiophene-based oligomers" (2007). ETD collection for University of Nebraska - Lincoln. AAI3271933.