We have used single-molecule-resolved scanning tunneling microscopy to measure the
photomechanical switching rates of azobenzene-derived molecules at a gold surface during
exposure to UV and visible light. This enables the direct determination of both the forward
and reverse photoswitching cross sections for surface-mounted molecules at different
wavelengths. In a dramatic departure from molecular behavior in solution-based
environments, visible light does not efficiently reverse the reaction for azobenzene-derived …