CAREER: Structural and solvent control of nonadiabatic bond formation probed with ultrafast time-resolved spectroscopies

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With this CAREER award, the Chemical Structure, Dynamics and Mechanisms (CSDM-A) Program of the Division of Chemistry is funding Professor Arthur Bragg of Johns Hopkins University to conduct experimental investigations on how the course of light-driven nonadiabatic bond formation is controlled by reactant structure and chemical environment. Nonadiabatic processes are fundamental relaxation pathways of energetically excited molecules and give rise to fast and efficient photochemical processes. Aims include improved understanding of energy conversion mechanisms, for example, in photochemistry and photobiology, and determination of conditions under which light-driven chemical processes can be controlled. Multiple state-of-the-art research methods are employed, providing high level training opportunities for student researchers. These students are also involved in development of webcam-based spectrometers and associated secondary-level chemistry curricula, enabling exploration of basic concepts in chemistry, spectroscopy, and instrument design. Educational objectives are met through development of curricular units and professional development workshops for training educators, with administrative program assistance provided by the Center for Educational Outreach (CEO) at JHU. Curriculum development targets integration of basic quantitative spectroscopic experimentation into classroom projects that meet new targets outlined in the Next Generation Science Standards. The spectrometers and curricular materials will be provided to teachers and students in the Baltimore City Schools. The goal of this research is to determine how the nature of nuclear dynamics associated with nonadiabatic electrocyclic bond formation and its overall efficacy are affected fundamentally by reactant structure and chemical environment. The work focuses specifically on the photochemical dynamics of ortho-arenes and related systems, as these are tractable systems for detailed experimental interrogation. Time-resolved absorption and Raman spectroscopies are used to probe dynamics of excited molecules on timescales down to tens of femtoseconds, as these are the timescales on which bonds form and break. These measurements and supportive quantum chemical computations target characterization of molecular dynamics that occur on the approach to and crossing through intersections between electronic states upon excitation, giving rise to bond formation or other energy deactivation pathways. The photoinduced dynamics of these systems is also studied to probe solvent-solute interactions that impact the course of solution-phase chemistry. Findings are expected to provide experimental benchmarks on the structure and solvent dependence of these processes, supporting prediction of relaxation and energy transfer pathways of large molecules both empirically and computationally.