Events Calendar

The Department of Chemistry presents Prof. Stephen E. Bradforth, colloquium speaker. 

Title: "Electron and Electronic Dynamics in Liquid Solutions"

“Electron and Electronic Dynamics in Liquid Solutions”

Stephen E. Bradforth
Department of Chemistry, University of Southern California

Website:  Bradforth Group

In the liquid phase, intermolecular interactions often control electronic structure, and therefore chemical reactivity and excited state photochemistry, but are complex to quantify.

Photoelectron spectroscopy applied to liquid microjets has emerged as powerful way to access both solvent and solute electronic structure directly. Using liquid phase XPS, we have investigated the peculiar property liquid ammonia possesses at being able to stably support excess electrons, transitioning from an electrolyte to a metal. At low concentrations, electrons exist as localized solvated electrons and, with modest concentration increase, spin pair to form diamagnetic solutions, the basis for Birch’s reagent in organic synthesis. Further concentration increase yields a shiny golden liquid metal. Our experiments map out how the electronic band structure changes on approach to the metallic threshold. Complementary experiments have been conducted to explore metallic water solutions. 

Cycloadditions and ring closings leading to highly strained cyclobutane structural motifs are often targets of interest in synthesis planning. Our efforts are to characterize such pathways from the perspective of high-throughput excited state reaction discovery.  The overall goal is to design a closed loop between theory and photochemical experiment at the level of individual observables - screening tens of substrate substituents and reaction conditions in a single excited state dynamics experiment. Hexafluorobenzene (HFB) and pyrimidines will be described as initial targets for the high throughput approach.

Background references:

1. Buttersack, T. et al. Photoelectron spectra of alkali metal–ammonia microjets: From blue electrolyte to bronze metal. Science 368, 1086–1091 (2020).

2 .Mason, P. E. et al. Spectroscopic evidence for a gold-coloured metallic water solution. Nature 595, 673–676 (2021).

3. Cox, J. M.; Bain, M.; Kellogg, M.; Bradforth, S. E. & Lopez, S. A. Role of the Perfluoro Effect in the Selective Photochemical Isomerization of Hexafluorobenzene. J Am Chem Soc 143, 7002–7012 (2021).

Bio: Stephen Bradforth started his independent career at USC in 1996 at the Department of Chemistry. He has led the physical and theoretical chemistry section, and then served as vice chair (2013-14) and then department chair (2014-16).  He currently directs one of five nationwide department demonstration project son Effective Teaching Evaluation as part of the AAU STEM initiative. As divisional dean, first for the Natural Sciences and Mathematics (2017-2020) and then for the Physical Sciences and Mathematics (2020-21), Bradforth coordinated strategic planning, faculty appointments and research advancement within the USC Dornsife Division of Natural Sciences and Mathematics. He is currently Senior Advisor to the Dean in the Dornsife College responsible for Research Startegy and Development. 

As a physical chemist, his lab designs experiments to gain a deeper understanding of how the inter-connected motions of molecules impact chemical reactions in complex but frequently encountered environments such as the aqueous milieu of cells or in functional molecular materials. His research applies ultrafast laser techniques to address contemporary scientific challenges such as UV damage to DNA, photochemistry, mechanisms for solar energy harvesting and condensed phase ionization and is funded by NSF, DOE and ONR. His honors include a Packard Fellowship in Science and Engineering and a Cottrell Scholarship and STAR award from the Research Corporation for Scientific Advancement. He is Fellow of the American Physical Society, the Royal Society of Chemistry and the American Association for the Advancement of Science.