Nanoscale Chemical Imaging of Reversible Photoisomerization of an Azobenzene‐Thiol Self‐Assembled Monolayer by Tip‐Enhanced Raman Spectroscopy |
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Authors: | Li‐Qing Zheng Xing Wang Feng Shao Prof?Dr Martin Hegner Prof?Dr Renato Zenobi |
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Institution: | 1. Department of Chemistry and Applied Biosciences, Swiss Federal Institute of Technology, ETH Zurich, Zurich, Switzerland;2. Center for Research on Adaptive Nanostructures and Nanodevices, School of Physics, Trinity College Dublin, Dublin 2, Ireland |
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Abstract: | An understanding of the photoisomerization mechanism of molecules bound to a metal surface at the molecular scale is required for designing photoswitches at surfaces. It has remained a challenge to correlate the surface structure and isomerization of photoswitches at ambient conditions. Herein, the photoisomerization of a self‐assembled monolayer of azobenzene‐thiol molecules on a Au surface was investigated using scanning tunneling microscopy and tip‐enhanced Raman spectroscopy. The unique signature of the cis isomer at 1525 cm?1 observed in tip‐enhanced Raman spectra was clearly distinct from the trans isomer. Furthermore, tip‐enhanced Raman images of azobenzene thiols after ultraviolet and blue light irradiation are shown with nanoscale spatial resolution, demonstrating a reversible conformational change. Interestingly, the cis isomers of azobenzene‐thiol molecules were preferentially observed at Au grain edges, which is confirmed by density functional theory. |
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Keywords: | azobenzene thiols grain edges photoisomerization substrate-mediated charge transfer tip-enhanced Raman spectroscopy |
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