Electron-Induced Switching Processes of Phthalocyanine Molecules on ( 3 × 3 ) Bi/Ag(111)R30°: Tautomerization Accompanied by Rotation

We investigated single deprotonated phthalocyanine molecules (HPc) on ( 3 × 3 ) Bi/Ag­(111)R30° by means of scanning tunneling microscopy (STM). Atomic-resolution topographic data reveal that the HPc adsorbs flat on top of a Bi atom. At sufficient bias voltage, STM-induced rotation and tautomerization of the HPc molecule are observed. Current- and bias voltage-dependent studies show that both processes are triggered via the molecule’s N–H stretching mode by a single electron. A constant ratio between the tautomerization and the rotation rate is observed, corroborating that both processes originate from the same stimulus. Furthermore, molecular nanoprobe (MONA) experiments provide insight into the ballistic charge transport properties of the ( 3 × 3 ) Bi/Ag­(111)R30° substrate. A distance-dependent study shows that the excitation rate decays with ∼d –1, indicating that ballistic transport mainly proceeds via the substrate’s surface state. Direction-dependent MONA measurements reveal that the HPc molecule exhibits two different faces with distinct excitation probabilities.