Probing the Relationship between Structure and Function of Self-Assembling Conjugated Molecules

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This thesis discusses the synthesis, self-assembly, and conductivity properties of novel oligothiophene derivatives with an emphasis on how molecular structure effects the assembly. In order to facilitate self-assembly in conjugated molecules, specific non-covenant forces were included into the molecular design of several derivatives. First, an amphiphilic oligothiophene derivative consisting of a quater- and quinquethiophene moiety attached to a poly(ethylene glycol) tail was synthesized. At high concentrations in polar solvents, a self-supporting gel forms consisting of molecules ordered into interdigitated bilayers. The number of thiophene repeat units and the length of the poly(ethylene glycol) polymer direct effects the molecular ordering in the gel state. The longer PEG tails disrupt the lamellar ordering due to the crystallization of the polymer. The disruption of the ordering by the longer PEG chain causes a decrease in the measured conductivity. Next, a symmetric oligothiophene derivative containing a hydrogen bond forming segment was synthesized. This symmetric derivative was found to form a gel consisting of self-assembled 1D nanostructures at low concentrations in organic solvents. Hydrogen bond formation was found to be essential for the formation of nanostructures. Conductivity values in the semiconducting range were observed for a quinquethiophene derivative when self-assembled while no conductivity was observed for a quaterthiophene derivative. A peptide-based quinquethiophene amphiphile was synthesized for assembly in aqueous conditions. 1D nanostructures were observed to form upon gel formation aqueous conditions. The composition of the peptidic segment was found to dictate the ordering of the thiophene segment of the molecules in the supramolecular structures. Furthermore, only when a flexible spacer between the hydrogen bonding and π-π stacking segments was included, were both forces able to be balanced in the same assembly. Finally, conjugated surfactants were synthesized to direct the formation of ordered organic/inorganic hybrid materials. Hybrid materials of silicon dioxide and zinc oxide with conjugated surfactants were successfully synthesized using either evaporation induced self-assembly or electrodeposition. Direct inclusion of the conjugated molecules in the deposition process allowed for high dye loading in the hybrid structures. By tuning the molecular structure, conjugated molecules are able to assemble into highly ordered materials in a wide variety of conditions.

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  • 10/02/2018
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