Date of Award
Doctor of Philosophy (PhD)
David M. Walba
The helical nanofilament (HNF) phase of bent-core liquid crystals (BLCs) is an exotic mesophase characterized by the spontaneous formation of twisted crystalline nanoscale filaments, approximately 30 nm in width, that can extend for microns in length. The unique characteristics of HNFs including: crystallinity, porosity, ability to be aligned, and extremely large aspect ratio, lend this phase to application in next generation organic electronics, including photovoltaic (PV) systems. Effectively functioning as nanoscale wires, the morphology of this phase provides an excellent interface for charge separation, and potentially provides a path to obtain high charge carrier mobility. To be used successfully as the active layer in a PV device, the filaments need to absorb a significant portion of the solar spectrum – a characteristic that has not yet been realized for any known HNF forming materials. The work in this thesis describes three projects developed to address this issue by attempting to expand the structure space of the HNF phase, and to improve our fundamental understanding of the nature of this phase. The first project involves the incorporation of the azulene chromophore into the structural backbone of known HNF forming compounds to probe the structure space of the phase while incorporating the desired absorbances needed for PV device application. The second project involves exploring the possibility of direct chemical modification of the HNF surface without destroying the filament structure. Finally, the third project describes an investigation into the effect nanoconfinement has on a closely related phase, the low temperature dark conglomerate (DC) phase. From these three projects a new azulene derived “bend unit” for BLCs was developed, a gel phase reaction to attach functional molecules to the HNF surface was created, and the first example of the DC phase adopting the HNF morphology using nanoconfinement is reported.
Foley, Lee Michel, "Understanding and Controlling the Helical Nanofilament Phase of Bent-Core Mesogens" (2019). Chemistry Graduate Theses & Dissertations. 2.