Nitrogen Centered Radicals

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In this project funded by the Chemical Structure, Dynamics & Mechanisms B Program of the Chemistry Division, Drs. Andrzej and S Rajca of the Department of Chemistry at the University of Nebraska-Lincoln investigate organic radicals, molecular structures with a single unpaired electron. These new radical compounds are relevant to the development of novel magnetic, electronic, and optical technologies. Radical-containing compounds usually are unstable species, easily reacting with other molecules. The goal of this research is the design, synthesis, and characterization of stable radical-containing molecules which have unconventional magnetic properties. The new results and insights may provide fundamental understanding of structure and property relationships for organic molecules while advancing the development of new materials. Such materials may serve as contrast agents for magnetic resonance imaging (MRI) and relaxation enhancement agents for nuclear magnetic resonance (NMR) spectroscopy. The materials may also serve as organic spin filters for spintronics, and other applications. The research activities comprise multi-step organic synthesis, diverse physical/materials characterization of organic molecules, and high level computations. This research provides students with opportunities to gain a broad education as well as to develop a wide range of skills. Specific objectives of this project are the synthesis and study of robust high-spin nitrogen-centered radicals. These include: di- and tri-radicals based on tetrazolinyl radical derivatives and diradical dications and triradical trications of double helical pi-systems. The tetrazolinyl radicals possess properties for thin film fabrication by evaporation under ultra-high vacuum. The double helical nitrogen-centered high-spin diradical dications and triradical trications are predicted to be strongly paramagnetic but stable at room temperature. These may provide future building blocks for high-spin polyradical cations. The strength of chiroptical properties of nitrogen-centered high-spin diradical dications of double helical pi-system is comparable to those of [n]helicenes. The combination of strong paramagnetism with double helical pi-systems may render unique properties due to the combination of chirality and delocalized electronic spin. This provides an avenue for development of novel paramagnetic materials with strong chiral properties that could facilitate discovery of new organic magneto-optic materials and devices, including efficient organic spin filters for spintronics. The radicals are prepared by modern organic synthetic methodologies, including newly developed radical-radical cross-couplings, and characterized by electron paramagnetic resonance (EPR) spectroscopy, superconducting quantum interference device (SQUID) magnetometry, as well as computations. This research provides opportunities for students to develop a wide range of professional skills.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.