Controlling the Rates, Distance, and Direction of Electron Transfer in Ultrafast Inorganic Ground States

University Of California-San Diego, La Jolla CA

Investigators

Abstract

In this project, funded by the Chemical Structure, Dynamics, and Mechanisms B Program of the Chemistry Division, Professor Clifford Kubiak of the Department of Chemistry and Biochemistry at the University of California San Diego is developing new assemblies of metal complexes that undergo fast electron electron transfer (ET) reactions. These reactions are monitored by infrared spectroscopy which has picosecond (1 trillionth of a second) time resolution to follow such ultrafast reaction. The goal of these studies is to develop a fundamental understanding of the chemical factors that determine the rate, distance, and direction of ET reactions. This work may ultimately pave the way towards the design of molecular electronic devices such as switches and memory that function far faster than the current generation of computers and sensors. This project lies at the intersection between synthetic chemistry and physical characterization, providing a rich opportunity for the training of graduate and undergraduate students in cutting-edge research. Controlling the rates, distance, and direction of electron transfer broadly impacts the life sciences, technology, and energy sectors. This project represents basic research but, if successful, could ultimately benefit society in important areas including treatments for genetic disorders caused by damage to DNA; a new generation of faster, smaller, and less expensive integrated circuits; advances in artificial and natural photosynthesis and improvements in agricultural food production. Professor Kubiak involves undergraduate students in research and engages K-14 students. The group has established a new undergraduate exchange program with Cal State University Monterey Bay (CSUMB) for students to pursue research projects that can be performed partly at CSUMB and partly at UCSD during summers and school breaks. The research team also develops visualizations of complex scientific ideas and their videos are also being shared broadly with both researchers, educators and the general public. Mixed-valence dimers of triruthenium acetate clusters display rich spectroscopic evidence of ultrafast ET over long distances. They have proven to be fruitful systems in illustrating how different bridging moieties, electronic structures, and chemical environments and dynamics can impact the kinetic barriers of ET. Professor Clifford Kubiak and his group plan to develop a more complete physical chemical description of how electron transfer occurs across hydrogen bonds. They will expand the synthesis of new complexes to better understand the interplay between electron delocalization and hydrogen bonding. Additionally, they will conduct the first two-dimensional infrared spectroscopy (2D-IR) studies of intramolecular ET on the picosecond timescale. They will use synthetic studies to probe bridging ligand dynamics and its relation to ET. This research will attempt to demonstrate vibrational control of the ET coordinate to change its rate and direction. Finally, the team will design and synthesize new supramolecular assemblies that exhibit mixed valency between pendant tri-ruthenium redox centers through semiconducting metal oxide nanoparticles. 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.