Determination of photoswitching dynamics through chiral mapping of single molecules using a scanning tunneling microscope.

Single-molecule-resolved scanning tunneling microscopy of tetra-tert-butyl azobenzene (TTB-AB) molecules adsorbed onto Au(111) reveals chirality selection rules in their photoswitching behavior. This observation is enabled by the fact that trans-TTB-AB molecules self-assemble into homochiral domains. Cis-TTB-AB molecules produced via photoisomerization are found in two distinct conformations with final state chirality determined by the initial trans isomer chirality. Based on these observations and ab initio calculations, we propose a new inversion-based dynamical photoswitching mechanism for azobenzene molecules at a surface.