Assemblies Of Assemblies: Supramolecular Ordering Of Nanoscopic Ruthenium Polypyridyl Building Blocks
Wouters, Kelly Lyle
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Biological systems have long since perfected the development of nanoengineering. Cellular structure and machinery is based, to a significant extent, on the formation of nanometer to micron-sized assemblies of proteins. These architectures start with unique primary, secondary, tertiary, and quaternary structural complexity and can be constructed from a relatively simple set of building blocks. Using this strategy as inspiration, assemblies based on [Ru(phenanthroline)3]2+ building blocks have been synthesized forming polyruthenium species bridged by the tpphz (tetrapyrido[3,2-a:2’,3’-c:3’’,2’’-h:2’’’,3’’’-j]phenazine) and tatpp (9,11,20,22- tetraaza tetrapyrido[3,2-a:2’,3’-c:3’’,2’’-l:2’’’’,3’’’’-n]-pentacene) ligands. Importantly, these assemblies exhibit unique hierarchical structural components which arise directly from the chirality inherent in the octahedral tris chelate [Ru(phen)3]2+ building blocks. The use of optically pure starting materials allows for the formation of distinct diastereomers, and ultimately, the local stereochemistry can be used to direct the global structure of these complexes. These rigid and robust molecules have been shown to develop primary, secondary, tertiary, and quaternary structural elements, yet, like proteins, are synthesized from a simple set of nanoscopic building blocks. The quaternary structure arises from the tendency of these complexes to form aggregates. Light scattering experiments have revealed the presence of polydisperse colloids in solution. Further studies using electric birefringence have demonstrated that the nature of these colloids changes with respect to the shape, or tertiary structure of the complexes. This dissertation describes the behavior of these aggregate structures, these “assemblies of assemblies”, and the effect aggregation has on some of the properties of the complexes. Scanning tunneling microscopy experiments were conducted in order to observe the native packing structure of these complexes in the solid state. Based on this data as well as crystallographic data of several related compounds, we believe that these complexes assume a stacked columnar arrangement aligned along their central bridging ligands. Additionally, the conductivity of thin films of these compounds was measured which revealed differences with respect to such factors as counterions, temperature, and global structure. One particular complex, the tatpp-bridged dimer [Ru2(phen)4(tatpp)]4+ (P), has been shown to undergo a multielectron photoreduction in the presence of a sacrificial electron donor. It is hoped that it may be possible to affect the efficiency of the photochemical processes via control of the supramolecular ordering of the molecules. One particular complex, the tatpp-bridged dimer [Ru2(phen)4(tatpp)]4+ (P), has been shown to undergo a multielectron photoreduction in the presence of a sacrificial electron donor. It is hoped that it may be possible to affect the efficiency of the photochemical processes via control of the supramolecular ordering of the molecules.