Conformational switching within aromatic, electron donor and acceptor supramolecular architectures
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The Iverson group has utilized favorable interactions between aromatic units in the development of highly ordered amphiphilic foldamers, two-component liquid crystal assemblies and pseudo-DNA assemblies. The above materials are made by taking advantage of the complementary electrostatic interactions between derivatives of electron-rich 1,5-dialkoxynaphthalene (DAN) and derivatives of electron-deficient 1,4,5,8-naphthalenetetracarboxylic diimide (NDI). This dissertation describes the theme of dynamic conformational switching within the context of aromatic stacking interactions. Specifically, this work focuses on switching between an aromatic electron-rich and aromatic electron-deficient alternating stacking geometry and an aromatic electron-rich self stacking geometry. While much of this work can be partially explained using classical notions of aromatic stacking (Hunter and Sanders), a new theory explaining aromatic stacking interactions (Wheeler and Houk) is highlighted which better explains the conformational switching behavior. Chapter 2 elucidates the aggregated structure of two amphiphilic foldamers that irreversibly undergo thermally induced conformational changes to form self-supporting hydrogels. The thermodynamics and morphologies of the foldamer aggregates are similar to amyloid aggregates, the misfolded state of proteins associated in numerous neurodegenerative diseases. Chapter 3 discusses the synthesis and time dependent polymorphism of four conjugated aromatic monoalkoxynaphthalene-naphthalimide (MAN-NI) dyads. Interestingly, two dyads displayed a NI-NI stacking geometry upon slower evaporation from solution and a NI-MAN stacking geometry upon faster evaporation from solution. Chapter 4 further investigates the properties of MAN-NI dyads and demonstrates one of dyads displays solvatochromic, thermochromic, vapochromic and mechanochromic stimuli responsive behaviors. Using applied external stimuli the dyad is thought to undergo a conformational change from an NI-NI stacking geometry to a NI-MAN stacking geometry. Chapter 5 details initial investigations into MAN-NI polymers for liquid crystal polymers and organic electronic materials. Four polymers were synthesized and characterized and found to display liquid crystal mesophase textures at room temperature. Additionally, the electronic behavior of the polymers suggests they may be useful candidates for optoelectronic applications. Overall, this work sheds considerable light on the ability of aromatic materials to under conformational changes in solution and in the solid state as a consequence of favorable direct, electrostatic interactions between the aromatic units.