New Synthetic Routes to Well-Defined Nanocarbon Materials

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With the support of the Macromolecular, Supramolecular, and Nanochemistry Program in the Division of Chemistry at the National Science Foundation, Professor T. Don Tilley of the University of California, Berkeley is exploring synthetic routes to prepare large-sized polycyclic aromatic hydrocarbons (PAHs), which represent a family of molecular nanocarbon materials. Graphene, an extended two-dimensional nanocarbon material, is well known for interesting electronic properties; however, its structure is irregular, which complicates its utility in nanoelectronic devices. In contrast, the PAHs under investigation exhibit well-defined molecular structures with graphene-like electronic properties. The project is geared toward providing fundamental knowledge regarding the effect of specific molecular structural features on desired electronic properties. The project is expected to impact the field of nanoscience, and especially the availability of carbon-based semiconducting organic materials as components for emergent applications in areas such as quantum information science, communications, and sensing. During the course of conducting this research, the students involved will be trained in advanced organic synthesis and material characterization techniques. The associated outreach activities include participation in the ACS Summer Experiences for the Economically Disadvantaged (SEED) Project and the Bay area scientists in school at Berkeley (BASIS) Program targeting elementary school students.The project develops synthetic methodologies for the efficient introduction of multiple fused aromatic rings in the controlled construction of large, tailored polycyclic aromatic hydrocarbons (PAHs). This is accomplished with high yielding [2+2+n] cycloadditions that produce multiple fused aromatic rings in a single synthetic step. The scalable reactions are used to access a wide range of new carbon nanostructures, including helicenes, nanobelts, cycloarenes, and nanoribbons. A specific target is a family of expanded, helical PAHs that are to be studied in the context of host-guest chemistry and interactions with polarized light. Other targets include macrocyclic PAHs and their assembly by way of supramolecular interactions, and elongated, nanoribbon structures expected to exhibit properties as 1-dimensional semiconductors. Nanobelt structures that represent molecular cut-outs of carbon nanotubes are being synthesized and studied. An additional interest is development of strategies for linking the PAHs together to form well-defined, extended structures that help bridge the gap between bottom-up organic synthesis and top-down synthesis of carbon allotropes. The research aims to first understand the behavior of new nanocarbon materials from a fundamental perspective, and then (as a longer-term goal) take advantage of the modularity of the syntheses to rationally tune structures for desired applications in organic electronics and quantum information science (QIS).This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.