Fractal Nanoarchitectures

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TECHNICAL SUMMARY: The properties of macromolecular materials constructed by directed- and self-assembly techniques will be studied. The ability to precisely craft non-dendritic, metal-based (charged) fractal polymers (via terpyridine-metal-terpyridine connectivity) will lay the foundation to create many new materials based on ionic interactions (with species such as dendrimers, classical polymers, and other fractal-based constructs). It has been demonstrated that these fractals self-assemble to give ordered fibers and rods; the introduction of appropriately charged species as counter ions, (such as dendrimers, porphyrins, and oxidized carbon nanotubes) is expected to (1) lead to novel materials possessing new and interesting electronic phenomena and (2) provide energy storage and release devices. Incorporation of rigid shape-persistence within the building blocks of the polymeric fractals will stabilize a 3-dimensional framework for forming "macromolecular-sized" void regions capable of acting as sites for (1) catalysis, (2) molecular inclusion or (3) connectors for single-walled carbon nanotubes. Work in the area of terpyridineCuII coordination with carboxylate ions has already led to the crafting of reversible carbon nanotube networks. Combining this coordination phenomenon with carboxylate-terminated dendrimers will allow the creation of "spheres-within-spheres" with unrestricted rotation predicated on the ability to form a polymerized network around the copper-bound dendrimer (followed by quantitative removal of the Cu-coordinating species). Employing terpyridine moieties possessing masked, carboxylate termini will facilitate the creation of multiple spheres-within-spheres that can be likened to "bucky onions." Multiple layers with differing metals will be crafted and their tunable electronic characteristics will be investigated.NON-TECHNICAL SUMMARY:New materials will be constructed based on the physical interactions of charged species and their potential to fit, or pack, in a precisely ordered manner. This will lead to new types of electronic devices, such as molecular batteries. New spherical materials possessing freely rotating internal spherical elements will be studied for use as shields for toxic materials and a molecular-scale compass. These areas of research are important with respect to the "miniaturization" of components for micro-electro-mechanical systems, sensors, and new photovoltaic devices. Educational opportunities arise from the training and development of scientists at all levels. Educational outreach is promulgated through the principal investigator's website (www.dendrimers.com), which currently averages 6,000-7,000 visits per month, as well as presentations at area schools, universities and conferences. Industrial and international collaborations will continue supporting the necessity of interdisciplinary integration.