Aromatic electron donor-acceptor interactions in novel supramolecular assemblies
Molecular self-assembly using non-covalent interactions mediate the structure and function of many critical biological and synthetic molecules. Aromatic donor-acceptor interactions are a type of non-covalent interaction that have been utilized by the Iverson group in the development of aedamers, a class of foldamers that adopt specific secondary structures in aqueous solution. These molecules and their derivatives exploit the complexation of electron-rich 1,5-dialkoxy-naphthalene (Dan) with electron-deficient 1,4,5,8-naphthalene tetracarboxylic diimide (Ndi) within linear charged oligomers to achieve both inter and intra-molecular assemblies not found in nature. This dissertation describes the use of the Dan:Ndi interaction in new systems and environments, expanding the potential and scope for applications of this chemistry. This work specifically focuses on inter-molecular assemblies, with novel molecular designs for solution interactions as well as the group’s first exploration of designed solid state and bulk properties. Chapter 2 describes incorporation of either Dan or Ndi units into independent polymer strands. When mixed together, the Dan and Ndi polymers are shown to associate in solution and upon processing form macrostructures in films and fibers. Chapter 3 reports experiments in which a series of Dan and Ndi monomers are synthesized, melted together, and then allowed to cool to afford columnar mesophases. The results demonstrate the ability to predictably control the structure and phase transition temperatures of mesophases by mixing and matching Dan and Ndi components. Chapter 4 presents the solution phase synthesis of neutral Dan oligomers and describes their potential to increase the association constants of Dan and Ndi oligomers in aqueous solution. Chapter 5 describes work developing alternative designs in the structure and connectivity of Dan and Ndi units for intermolecular assembly. Overall the work described herein implements aromatic electron donor-acceptor interactions in novel supramolecular chemistry, with a focus on the use of Dan and Ndi complexation in the formation of materials. These studies have taken the first difficult steps towards making uniquely controllable and functional materials based on noncovalent aromatic interactions a practical reality.