Nanophotonic Strategies for Making Molecular Movies of Catalysis

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In this study, supported by the Chemical Structure Dynamics and Mechanism (CSDM-A), Chemical Catalysis (CAT) and Chemical Measurement and Imaging (CMI) Program of the Chemistry Division, Professor Randall Goldsmith and his research team at the University of Wisconsin Madison seek to better understand how chemical catalysts perform their important functions. Catalysts allow difficult chemical reactions to be proceed, but how they do this may involve many individual steps that are difficult to follow. Professor Goldsmith is using a new approach that combines optical microscopy, the light-emitting behaviors of certain molecules (in this case, a property called "fluorescence"), and nanotechnology to to allow observation of single catalyst molecules. The Goldsmith team is essentially developing "molecular movies" of an individual operational catalysts. This research project is not only providing new insights into catalytic chemical reactions, but also developing a laboratory technique that may be useful in many other chemistry, biology and materials science investigations. The students involved in this research are gaining a wide range of skills, from chemical synthesis, optical microscopy, and nano-fabrication. In particular, the project focuses on palladium cross-coupling reactions, which are widely employed in the pharmaceutical industry. A critical element is the use of nanophotonic devices that sculpt light to make it substantially smaller than the diffraction-limit, allowing observation of single-molecule dynamics at chemically relevant concentrations. Individual catalyst molecules are immobilized in these devices and studied via single-molecule fluorescence microscopy. A major readout is the time-varying rate constant of a single catalyst molecule and the timescale of transient intermediates. The broader impacts of this work include the societal benefits of a mechanistic tool that can inform the design of the next generation of catalyst molecules, the training of students in interdisciplinary chemical sciences, and the development of single-molecule visualization demos that can be deployed in schools to broaden participation of STEM minorities.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.