Towards Hierarchical Structural Self-Assembly of Conjugated Polyelectrolyte Light Harvesting Complexes

The dramatic decrease in the world’s finite reserve of fossil fuels has led to an increasedemand for alternative energy resources. Inspired by natural photosystems that werefine-tuned by nature through billion year of evolution. The focus of this research aimsto mimic and improve upon nature's approach of capturing solar energy by constructingan artificial photosystem. The method of approach was done by creating 'softsupramolecular complexes' based on conjugated polyelectrolyte (CPE) complexes asanalogs to nature's light harvesting machinery. Conjugated polyelectrolytes (CPEs) area class of quasi-1D structures whose delocalization of pi-electrons through theirbackbone enables the motion and transport of electrical charge and excitation energy;In addition, they bear ionic sides chains per repeating monomer unit that enable thesenon-polar macromolecules to be water soluble and facilitate their microstructural selfassembly.In order to construct efficient 'light harvesting complexes' it is important tounderstand the physics that drive the self-assembly and microstructure of the CPEcomplexes and how this relates to their electronic energy transfer (EET) dynamicsbetween the donor and acceptor units of the CPE complexes. The initial phase of thiswork focused on constructing 'light harvesting complexes' centered on pairingoppositely charged and electronically coupled CPEs PFPI-donor and PTAK-acceptor.Results from this initial investigation showed evidence of EET between the donorxiacceptor complexes as well as the ability to tune the EET dynamics of the system byvarying the molar charge composition of the CPEs. The design of projects forward ledto a natural trajectory focused on building on the complexity by first incorporation ofionic surfactants, mixed micelle systems with varying charge densities and finally thetemplating of donor-acceptor CPEs as a layer-by-layer assembly onto a chargedliposome scaffold. The local micro and macrostructural morphology of the CPEcomplexes was characterized using a combination of Dynamic light scattering (DLS),small x-ray scattering (SAXS) and Confocal Laser Scanning microscopy (CLSM)techniques. The use of scattering techniques and light microscopy are complementaryto one another since they access different length scales from nanometer details to thevisualization of CPE-liposome micron sized structures. These structural techniquescombined with optical techniques provided insight to the relation of morphology andphoto-physical properties of these CPEC-Surfactant/Lipid interactions. The results ofthis dissertation demonstrate the capability to ironically assemble a stablemulticomponent modular light harvesting system. The influence of surface charge,charge density of amphiphilic systems had on both the electronic structure andmicrostructure of CPE was deeply explored. It was found that through careful choice,ternary molecules and self-assembled structures such as surfactants and liposomes canbe used to manipulate the electronic structure and thus the energy transfer dynamics ofhigher order CPE systems. This research forms a basis for the creation of a soft, lightweightartificial photosystem with the potential of converting sunlight into chemicalfuels