High Reorganization Energy Electron Transfer Systems

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With this award, the Organic and Macromolecular Chemistry Program supports Stephen Nelsen of the University of Wisconsin whose research will study charge localized symmetrical intervalence (IV) compound electron transfer (ET) cations that transfer an electron across a bridge between two ends of the molecule (Hy(+)-B-Hy(0) - Hy(0)-B-Hy(+)) without an intermediate. The hydrazine charge-bearing units (Hy) are being "tuned" to provide the right combination of reorganization energy and electronic coupling to put their ET rate constants in the correct range for measurement by ESR for several bridge sizes, allowing significant tests of ET theory. 'Electron hopping' that involves bridge-centered intermediates (Hy(0) -B(+)-Hy(0) an energy minimum ) is clearly involved in biological ET reactions that move charge over large distances, but no simple IV model compounds are yet available. Systems with Hy groups having NN bond rotation unrestricted to maximize their reorganization energy should generate electron-hopping systems, even for a small, p-phenylene bridge. Other systems are being studied that have a Marcus-Hush-type two-state diagram in their excited states instead of their ground states. Examples include neutral compounds, diradical diions and charge delocalized IV radical ions. Application of the rather new Zhu-Nakamura (ZN) theory to interpreting ET kinetic measurements appears promising for better understanding of both intramolecular and intermolecular ET experiments.This award from the Organic and Macromolecular Chemistry Program supports Professor Stephen Nelsen of the University of Wisconsin whose research recognizes that understanding electron transfer reactions is of fundamental importance to both chemistry and biology, and understanding how to manipulate electronic interactions is fundamental to the developing field of molecular electronics. Students trained doing this work will receive exceptionally broad training in organic synthetic methods in making their compounds, as well as in doing computational chemistry and making physical measurements involving electrochemistry, NMR and ESR, and optical spectroscopy.