Date of Award
Spring 1-27-2023
Degree Type
Dissertation
Degree Name
Doctor of Philosophy (PhD)
School
Polymer Science and Engineering
Committee Chair
Jason Azoulay
Committee Chair School
Polymer Science and Engineering
Committee Member 2
Derek Patton
Committee Member 2 School
Polymer Science and Engineering
Committee Member 3
Jeffery Wiggins
Committee Member 3 School
Polymer Science and Engineering
Committee Member 4
Xiaodan Gu
Committee Member 4 School
Polymer Science and Engineering
Committee Member 5
Zhe Qiang
Committee Member 5 School
Polymer Science and Engineering
Abstract
Most materials are closed shell in which every electron participates in a bond, resulting in unremarkable magnetometry signatures and functionalities. While rare, modern technologies rely on magnetic materials in which unpaired electrons are localized to inorganic atomic centers. In recent decades, a collection of organic open-shell π-conjugated molecules have shown magnetic ordering, albeit at exceedingly low temperatures; a result of weak noncovalent intermolecular interactions limiting long range electronic exchange. Thus, practically applicable sp orbital magnetism that persists at or above room temperature remains a grand challenge for chemistry and physics. Despite the wide variety of chemical structures afforded by organic synthesis, most organic paramagnetic centers result in chemically unstable or isotropic spins. High-spin conjugated polymers are synthetically accessible, with tunable ground state electronic configurations comprised of delocalized spin densities, affording paramagnetic spins with robust ambient stability. This work discusses new open-shell donor acceptor conjugated polymers, where the integration of configurational admixing, electronic and macromolecular structure, and processing techniques outline new design rules for controlling magnetic interactions within this new class of materials. Electronic paramagnetic resonance and magnetic susceptibility measurements elucidate the diverse magnetic phases that emerge in these semicrystalline polymers, while also pointing towards new technologies that will emerge from this class of organic magnetic materials.
Chapter 1 will be a general introduction into the electronic structure of conjugated polymers (CPs), open-shell CPs, and organic magnetism.
Chapter 2 explores how utilizing a strong configuration interaction in a donor–acceptor copolymerization stabilizes an intermolecular ferromagnetic exchange interaction in a conjugated polymer thin-film. Owing to the unique electronic structure of the resulting CP, the exchange interaction is stable at room temperature, an exceedingly rare phenomena in magnetic organic materials.
Chapter 3 uses a newly synthesized acceptor to widen the open-shell substrate scope to more electronically stable donors, while also characterizing how a weaker configuration interaction increases the degeneracy of the frontier molecular orbitals to ultimately tune the intramolecular exchange interaction.
Copyright
Michael E. Steelman III
Recommended Citation
Steelman, Michael, "Magnetic Interactions in Open-Shell Conjugated Polymers" (2023). Dissertations. 2117.
https://aquila.usm.edu/dissertations/2117
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