CAREER: Tabletop Extreme Ultraviolet Spectroscopy of Femtosecond Spin Crossover Dynamics

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With this award, the Chemical Structure, Dynamics and Mechanisms (CSDM-A) Program of the Division of Chemistry is funding Professor Joshua Vura-Weis at the University of Illinois at Urbana-Champaign (UIUC) to investigate the mechanism of light-induced processes where the electronic spin state changes. After certain iron and iron-cobalt complexes absorb visible light, they undergo a rapid rearrangement (spin flip) and become trapped in a long-lived state that may be useful for practical applications. The experimental technique used in this project is tabletop extreme ultraviolet (XUV) spectroscopy. Two workshops designed to foster deep and sustained undergraduate engagement in spectroscopy research are established in association with the International Symposium on Molecular Spectroscopy (ISMS) at UIUC. A weeklong "Spectroscopy in the Snow" intensive winter course gives sophomores the foundational knowledge required for physical chemistry research and allows them to begin high-level work in their home institutions one year ahead of schedule. A two-day ISMS pre-conference for undergraduates, analogous to the Gordon Research Seminar series for graduate students, builds a community of young researchers and raises the level of undergraduate presentations at the main conference. The new spectroscopic methods demonstrated in this proposal are applicable for a wide range of problems in physical and inorganic chemistry, from photocatalysis to solar cell design.Extreme ultraviolet (XUV) transient absorption spectroscopy at femtosecond resolution is used to resolve the details of the spin relaxation process in a series of transition metal complexes. The Vura-Weis group further extends its capabilities to measure vibrational dynamics during the spin crossover. The interplay between electron transfer and spin dynamics is a key factor in the photophysics and reactivity of complexes containing open-shell transition metals. The Vura-Weis group uses the spin-state specificity and femtosecond time resolution of XUV transient absorption to measure the relaxation cascade of iron polypyridyl complexes, specifically focusing on the potential role of a short-lived metal-centered triplet state. The interplay between electron transfer and spin crossover in Prussian Blues is being measured in a series of discrete cyano-bridged iron-cobalt systems. In this case, the element specificity of XUV absorption allows the dynamics of each metal to be independently probed. The particular molecular motions that gate the electron dynamics are identified by element-specific XUV impulsive coherent vibrational spectroscopy. To make research in physical chemistry more accessible to undergraduates, a winter school on spectroscopy takes place at the University of Illinois, Urbana-Champaign, in connection with the International Symposium on Molecular Spectroscopy (ISMS). In addition, a two-day undergraduate meeting preceding this conference develops a supportive community of young researchers.