STM Study of Trans-stilbene Self-organized on the Ag/Ge (111)-(√3×√3) R30°Surface
C.-S. Tsai, C. Su, J.-K. Wang and J.-C. Lin
The advent of scanning tunneling microscopy (STM) has permitted a detailed atomic view of organic molecules adsorbed on solid surfaces. In this work, we make use of the STM to provide an unprecedented direct single-molecule perspective on the cis−trans photoisomerization of stilbene molecules within ordered monolayers physisorbed on the Ag/Ge(111)−(√3×√3)R30° surface. The STM view of the molecular structure transformation upon irradiation provides direct evidence for the generally accepted one-bond-flip mechanism proposed for the photoisomerization process. We also find that the surface environment produces a profound effect on the reaction mechanism. The reaction is observed to proceed mainly through pairs of co-isomerizing molecules situated at domain boundaries. To explain these observations, we propose a mechanism whereby excitation migrates to the domain boundary and the reaction occurs through a biexciton reaction pathway.