Dynamics and Mechanisms of Electron Delocalization over Supramolecular Mixed Valence Systems

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In this project funded by the Chemical Structure, Dynamic & Mechanism B Program of the Chemistry Division, Professor Clifford P. Kubiak of the Department of Chemistry & Biochemistry at the University of California, San Diego (UCSD) will develop and study new systems that undergo ultrafast chemical reactions, those that occur in one-trillionth of a second (1 picosecond) over large supramolecular structures. The goal of this research is to develop molecular devices by the self-assembly of large materials with specific functions related to information storage and switching. The supramolecular mixed valence complexes that will be studied in this project and studies of the dynamics of electron transfer across them offer a chemistry-driven approach to assembling complex structures that can gate, store, and transfer charges. The study of these systems will likely influence and guide broader thought about the specific chemical, physical, and engineering issues that will bring molecular electronic based devices into the mainstream, and findings will be widely disseminated. The project will continue to involve undergraduate students through the UCSD undergraduate research mentor program. The project will also be interfaced with existing outreach programs at UCSD for the recruitment of underrepresented students. There will also be a strong international collaboration with a research group at the University of Uppsala, Sweden.The study of electron transfer processes through non-covalent interactions is important to the broader understanding of how long-range electron transfer occurs in natural and artificial supramolecular systems. This project builds on discoveries from the immediately preceding NSF support period. Specifically, it will involve experimental studies of the dynamics and mechanisms of electron delocalization in supramolecular mixed valence complexes. Synthetic studies will be directed toward the preparation of new supramolecular assemblies linked by weak non-covalent interactions including hydrogen bonds and pi-stacked organic structures. These will be used to test theories of the relationship between infrared spectral lineshape and the dynamical mechanism for electron transfer in mixed valent systems. Studies of ultrafast electron transfer in supramolecular complexes will be conducted to determine the timescale and mechanism of delocalization of an electron after its injection into a supramolecular assembly. This project seeks to explore a new concept in the assembly of complex structures - the use of electron delocalization to "harden" weak interactions like hydrogen bonds to produce more stable assemblies, and position them for more permanent forms of chemical attachment.