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.
L.-W. Chou, Y.-R. Lee, C.-M. Wei, J.-C. Jiang, J.-C. Lin and J.-K. Wang
J. Phys. Chem. C.
The adsorption and self-organization of trans-azobenzene (TAB) on Ag/Ge(111)-(√3×√3)R30°(Ag/Ge(111)-√3) were studied by low temperature scanning tunneling microscopy (LT-STM) in ultrahigh vacuum (UHV). High-resolution STM images allow the observation of individual TAB molecules and the commensurate TAB chain domains formed via the hydrogen bond enhanced intermolecular interaction and molecule–substrate interaction on Ag/Ge(111)-√3. From in situ observation of the substrate lattice, the TAB monolayers were found to form a (2x1) structure. Some coexisting cis-azobenzene (CAB) molecules were observed on the domain boundary of TAB overlayer. The structural model and the molecule registry corresponding to STM images for the monolayer of TAB on Ag/Ge(111)-√3 are proposed and discussed
L-W. Chou, Y-R. Lee , J.-C. Jiang, J.-C. Lin and J.-K. Wang
J. Phys. Chem. C
Temperature-programmed reaction/desorption, Auger electron spectroscopy, X-ray photoelectron spectroscopy, and near-edge X-ray absorption fine structure in combination of calculations based on density functional theory have been employed to investigate adsorption and reaction of 1,3-C6H4I2 on Cu(100). At 100 K, the surface species after 1,3-C6H4I2 adsorption are found to be 1,3-C6H4I2, C6H4I, and 1,3-C6H4. The formation of these adsorbates is dependent on the adsorption sites of 1,3-C6H4I2. 1,3-C6H4I2 adsorbed with the ring at a hollow site and parallel to the surface is predicted to be unstable and preferentially leads to CI bond dissociation. 1,3-C6H4, the intermediate from 1,3-C6H4I2 decomposition, has a tilted adsorption geometry with a distorted ring.H2 is the only reaction product observed after 550Kin the 1,3-C6H4I2 decomposition onCu(100), with all of the carbon atoms left on the surface. Dimerization of 1,3-C6H4 molecules on Cu(100) has been described computationally,showing an activated and exothermic process.With the theoretically obtained activation energy of 28.2 kcal/mol and estimated surface coverages, coupling of 1,3-C6H4 can occur by second-order kinetics beforeH2 evolution. Dimerization of 1,3-C6H4 onCu(100) shows a different intermolecular interaction behavior from those of 1,2-C6H4 and 1,4-C6H4 on copper single crystal surfaces.