This research program is based around the preparation and study of molecules derived from arylacetylene scaffolding, namely dehydrobenzoannulenes (DBAs), tetrakis(arylethynyl)benzenes (TAEBs), and azaacenes, to answer fundamental scientific questions as well as to explore their materials properties. With the support of this award from the Chemical Synthesis Program of the Division of Chemistry at the National Science Foundation, Professor Michael Haley of the Department of Chemistry at the University of Oregon will explore the development of facile synthetic methods for the assembly of functional molecules comprised of benzene and acetylene building blocks. The study of such molecules answers fundamental questions regarding the electronic structure of organic (carbon-based) materials, and also presents opportunities for practical applications, particularly in the area of nanotechnology.
This project serves as an excellent training ground for graduate and undergraduate researchers in fundamental and applied chemical synthesis. The studies will provide the researchers with broad experience in organic synthesis, computational chemistry, x-ray crystallography, and fundamental aspects of aromaticity, electron delocalization, and molecular architecture. The broader impacts of this program include industrial internships of graduate students at local and regional companies and national labs, the exchange of graduate students with those of foreign collaborators in Germany, Denmark, and Japan, the hosting of extended stays of visiting scientists including professors from PUIs, and continued substantial involvement of undergraduates in state-of-the-art chemical research via programs which promote the participation of underrepresented groups.
The last twenty years has seen a tremendous resurgence in the chemistry of the carbon-carbon triple bond. New synthetic methods tailored towards the construction of the alkyne moiety, combined with use of transition metal complexes for carbon-carbon bond formation, have revolutionized the assembly of acetylene-containing systems. In particular, advances in Pd-mediated cross-coupling reactions have allowed for the production of arylacetylene derivatives from an alkyne sp-carbon atom and the sp2 center of an arene, while construction of butadiynes and longer oligoynes has become routine practice in the laboratory via homo- or heterocoupling of terminal acetylene units. Alternatively, cyclization reactions of alkyne-containing molecules mediated by ‘alkynophilic’ late transition metals salts have recently become a powerful method for the assembly of complex and/or highly substituted aromatic systems. Consequently, these synthetic discoveries have now made the assembly (and thus study) of novel acetylene-containing molecules, which was previously a laborious process, something that can be accomplished with relatively ease. One field that has benefited significantly from the synthetic advances is a family of molecules comprised extensively of benzene rings and carbon-carbon triple bonds. A new generation of chemists recognized in the 1990s that, in addition to the traditional question of induced ring currents, these π-electron-rich phenylacetylene systems possess significant potential for use in technologically important materials applications. The ability to create new scaffolds utilizing the aforementioned synthetic advances has allowed chemists to functionalize easily the hydrocarbon backbone and thus tailor the chemical reactivity and physical properties of the molecules. Indeed, arylacetylene scaffolds exhibit a myriad of interesting properties, including nonlinear optical and liquid crystalline behavior, two-photon absorption, supramolecular complexation, polymerization to give stair-step or tubular polymers, and explosive decomposition to give ordered carbon nanostructures. The research funded by this NSF grant generated new discoveries in three areas of phenylacetylenic chemistry: (1) cyclization reactions of conjugated ‘azo-arene-alkyne’ structures for synthesis of heterocycles utilizing a combined computational/experimental approach. This work, which started in 2000 and concluded during this funding cycle, led to a deeper understanding of an unusual class of reactions called "coarctate" cyclizations. Culmination of this work was the ability to prepare both electron-poor and electron-rich heterocycles from a shared synthetic intermediate. (2) donor/acceptor-functionalized arylacetylene scaffolds for advanced materials applications. Studies during this project showed that this class of molecules could function as useful systems for two-photon absorption, which could eventually lead to better molecules for photodynamic therapy. Systems functionalized with boron-dipyrromethene units as part of the scaffold are highly fluorescent dye molecules. (3) preparation and study of molecules based on or inspired by the indenofluorene skeleton. A exciting spin-off of the basic phenyl-acetylene motif, the Haley groups has worked to answer fundamental scientific questions of this strongly electron-accepting molecular core as well as to explore its materials properties. We have examine the optical and electronic properties with an emphasis towards organic field effect transistor (OFET) and organic photovoltaic (OPV) applications and use in devices. Importantly, we demonstrated that single crystals of one derivative could serve as an active layer in OFETs that exhibit ambipolar behavior. The molecules developed in these studies present opportunities for practical applications, particularly in the area of nanotechnology and low-cost electronics. Moreover, this project serves as an excellent training ground for graduate and undergraduate researchers in fundamental and applied chemical synthesis. The studies provide the researchers with broad experience in organic synthesis, computational chemistry, x-ray crystallography, and the interplay between electronic structure and molecular architecture. The broader impacts of this program include industrial internships of graduate students at local and regional companies and national labs, the exchange of graduate students with those of foreign collaborators in Germany, Denmark, and Japan, the hosting of extended stays of visiting scientists including professors from PUIs, and continued substantial involvement of undergraduates in state-of-the-art chemical research via programs which promote the participation of underrepresented groups.
