Assemblies Of Assemblies: Supramolecular Ordering Of Nanoscopic Ruthenium Polypyridyl Building Blocks
Abstract
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.