Combined Single-Molecule Raman and Conductance Spectroscopies for Understanding Electric Field-Controlled Chemistry

University Of California-Davis, Davis CA

Investigators

Abstract

With support from the Chemical Measurement and Imaging (CMI) program and partial co-funding from the Chemical Structure, Dynamics, and Mechanisms - B (CSDM-B) program in the Division of Chemistry, Joshua Hihath and his research team at the University of California, Davis aim to understand the effects of applied external electric fields on molecular switching processes. As electric fields are emerging as “smart reagents” that can selectively catalyze reactions, understanding their role in chemical reactions is critical. The Hihath group is working to develop a novel and powerful approach for simultaneously applying an electric field and quantitatively measuring the effect of this field before, during, and after a chemical process. Their approach leverages a recently developed system for performing single-molecule Raman spectroscopy and conductance measurements simultaneously. The ability to track the effects of electrical and optical fields, charge transfer, and heating on individual molecules will impact a broad range of fields where controlling chemical processes is important. The project is providing research opportunities for graduate and undergraduate researchers, including individuals actively recruited from groups underrepresented in STEM (science, technology, engineering and mathematics). The combination of Raman spectroscopy with single-molecule electrical measurements provides detailed information about the configuration, binding energy, mechanical strain, vibrational modes, and local effective temperature in a single molecule bound between two electrodes. This multidimensional information allows resolution of electric field, mechanical, charge transfer, and heating effects on chemical processes occurring within the molecule. This project sets out to probe the mechanisms by which two distinctive single-molecule photoswitches undergo conformational changes in an applied field. The study will provide information about how the electrical field enables bypassing orbital symmetry selection rules, and how these processes differ from photochemical switching processes. Specific objectives include i) in situ identification of electrically controlled isomerization processes in single-molecule systems from the Raman signature of a molecule bound to two electrodes; ii) improved understanding of the effects of electric field orientation and magnitude on bond reorganization and transition states during electrical isomerization processes; iii) determination of the interplay between applied field and mechanical strain on isomerization processes; and iv) disambiguation between current-driven and field-driven isomerization processes. 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.