Controlling molecules in direct contact with surfaces is central to molecular electronics. Photochromic molecules immobilized and contacted by a surface promise to provide remote control on the molecular level using light. Combining X-ray absorption spectroscopy, differential reflectance spectroscopy, and density functional theory, we demonstrate highly efficient and bidirectional photochromism of a spirooxazine molecular switch in direct contact with a Au(111) surface. The ring-opening reaction by UV light is 2 orders of magnitude more efficient than previously reported for other surface-adsorbed systems, and even more importantly, the red-light-induced ring-closing is accessible even in contact with a metal surface. This opens new prospects for applications by utilizing the gold surface with directly adsorbed functional units consisting of molecular photochromic switches.
