Dynamics and Mechanisms of Electron Delocalization over Supramolecular Mixed Valence Systems

University Of California-San Diego, La Jolla CA

Investigators

Abstract

In this project, supported by the Chemical Structure, Dynamics & Mechanism B Program of the Chemistry Division, Professor Clifford Kubiak of the Department of Chemistry at the University of California, San Diego (UCSD) is developing new classes of inorganic materials for use in next generation computers. The goal of this research is to develop and study new complexes that undergo picosecond (a trillionth of a second) electron transfer or structural rearrangements that occur in electronic grounds states. Such ultrafast molecular changes may be used to make novel molecular devices including those for information storage. This project has the potential to impact the broader scientific and engineering communities involved in electronic device technologies where a critical goal is to extend information processing by the current Complementary Metal-Oxide-Semiconductor (CMOS) platforms. The Kubiak group is well-positioned to provide a highly technical level of education and training for students. Outreach activities involving K-12 students, especially those from the Preuss School at UCSD and Torrey Pines High School. The focus of the project is the investigation of ultrafast (picosecond) electron transfer in mixed valence systems. Mixed-valent complexes typically consist of two identical redox active centers that are separated by a bridge. In their mixed-valent state, the redox centers differ only in their oxidation states and are stabilized relative to disproportionation by electron self-exchange. The group has showed that when the bridging interaction is composed of a hydrogen bond, electron transfer (ET) in the mixed-valent state stabilizes hydrogen-bonding interactions by about 5 kcal per mole relative to the neutral, isovalent, hydrogen-bonded dimers. A core question of this project is whether the hydrogen bond precedes, follows, or occurs in concert with ET. The specific goals are: to develop a complete physical description of how ET occurs across hydrogen bonds; to continue the synthesis of new complexes to better understand the interplay between electron delocalization and hydrogen bonding; and to investigate the switched-on self-assembly of supramolecular structures that can form stronger hydrogen bonds when reduced. A collaboration with a 2-dimensional infrared spectroscopy lab (2D IR) provides new spectroscopic insights into the dynamics and mechanisms of ET and molecular rearrangements that occur in ultrafast ground state molecules. 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.