The Influence of Electric Fields on Electron Transfer in Inorganic Mixed Valency and Catalysis

University Of California-San Diego, La Jolla CA

Investigators

Abstract

In this project, funded by the Chemical Mechanism, Function, and Properties Program of the Chemistry Division, Professor Clifford P. Kubiak and his research group of the Department of Chemistry at UCSD is developing an understanding of the effects of electric fields on electron transfer (ET) at interfaces. The goal of this research is to control and utilize these effects to create switchable and tunable ET and catalytic systems. Electron transfer is the engine that powers living systems and is the basis of every electronic device. A deeper understanding of interfacial ET will lead to advances in semiconductor chip design and fabrication, and ultimately computation. When applied to catalytic processes, electric field effects of surface bound catalysts can provide a tunable dial of control for product activity and selectivity that can be deployed by changing a voltage, rather than the synthesis of numerous new catalysts in attempts to optimize them. Such a clean electric field-controlled approach to catalysis molecule can lead to reduction of industrial and pharmaceutical chemical waste. This interdisciplinary project incorporates elements of inorganic, materials, and physical chemistry and therefore provides a broad educational intersection for all scientists and trainees involved. Electro-inductive effects on electrode-bound molecules show promise for control over interfacial electron transfer and control of rates and selectivity of catalytic processes. Through specialized in-house spectroelectrochemical techniques (i.e. infrared and UV-Vis-NIR), electron transfer in mixed-valent complexes and interfacial electric field effects on electrode-bound complexes are being studied as electrical bias is applied. The proposed project includes the immobilization of well-understood mixed-valent ruthenium clusters and transition metal catalysts on planar Au electrodes and Au nanomaterials using N-heterocyclic carbene (NHC) based linkers, which extend the potential window of stability over traditional thiol- and isocyanide- based Self Assembled Monolayer (SAM) attachment strategies. Specific goals for the implementation of a specialized surface-sensitive Phase Modulated – Infrared Reflection Absorption (PM-IRRAS) spectroelectrochemical cell involves the study of NHC-bound systems on gold including: 1) electronically bi-stable mixed-valent ruthenium clusters, and 2) electric field influences on transition metal catalysts on Au surfaces in situ. They will also expand their library of NHC attachment motifs for these purposes. The proposed goals embark on answering the following questions: a) Can electric fields tune the charge distribution of mixed-valent NHC-bound ruthenium dimers as they step the potential through the mixed-valent state? Will this induce switchable intramolecular electronic behavior? b) How are the ET dynamics of ruthenium clusters affected by colloidal Au nanomaterials acting as bridging motifs? c) How does an interfacial electric field affect closely confined transition metal catalysts? Can these effects be used to target products and control catalytic reaction rates? Such understanding and control over charge distributions and catalytic activity could lead to broad advances in the life sciences, industrial chemical processes, and technology. 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.