Probing Molecular Dynamics Near Plasmonic Surfaces by Optical two-dimensional Coherent Spectroscopy

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With this award, the Chemical Measurement and Imaging Program in the Chemistry Division, with co-funding from the Atomic, Molecular and Optical Physics - Experiment Program in the Physics Division, is funding Drs. Hebin Li and Jin He at Florida International University (FIU) to develop a novel integrated ultrafast spectroscopy and imaging technique for studying molecular dynamics. The ability to probe ultrafast chemical behavior of molecules and electrons at the nanometer scale is essential for studying and understanding materials, such as deoxyribonucleic acid (DNA) molecules, proteins linked to photosynthesis, novel solar cell layers, and exotic quantum materials. Advanced laser spectroscopy, such as optical two-dimensional coherent spectroscopy (2DCS), excels in studying chemical behavior in complex systems, while the spatial resolution is usually limited to the millionth of meter scale. On the other hand, the scanning tunneling microscope (STM) provides nanometer resolution for single-molecule studies, while the measurements in STM are limited to the millisecond timescale. Drs. Hebin Li and Jin He and their research team integrate optical 2DCS and STM-based single-molecule techniques to acquire chemical information about surfaces with nanometer resolution spatial mapping and femtosecond time resolution. The novel imaging technique enables understanding and improving numerous chemical and materials systems. By engaging students in active research and connecting to local science teachers, the project also makes an important contribution to the goal of FIU, a minority-serving institution, to strengthen the education of underrepresented groups in science, technology, engineering, and mathematics (STEM) fields, and to promote public interest in science in South Florida.The primary goal of this project is to develop surface-enhanced optical two-dimensional coherent spectroscopy (2DCS) to probe molecular dynamics on plasmonic surfaces by implementing optical 2DCS on a metal nanoelectrode (NE) to achieve a high spatial resolution. The developed technique has integrated advantages of both STM and optical 2DCS, including high spatial resolution, high detection sensitivity, femtosecond temporal resolution, and multidimensional capability. Using this technique to study molecules on the metal NE surface and molecular junctions in the nanogap between two metal nanostructures, the research enables new capabilities to probe charge transfer dynamics at molecule-metal and molecule-molecule interfaces, intermolecular interactions in small molecule pairs, and the dynamics of hydrogen-bonding patterns and networks in proteins at metal-molecule-metal junctions. The unique capabilities of this approach can potentially lead to novel applications in studying other systems such as two-dimensional and perovskite materials, photosynthetic proteins, and biological molecules.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.