Showing papers by "Wenli Deng published in 2012"

Two-Dimensional Self-Assembled Molecular Structures Formed by the Competition of van der Waals Forces and Dipole–Dipole Interactions

Abstract: The self-assembly of 2,7-bis(10-ethoxycarbonyl-decyloxy)-9-fluorenone (BEF) has been investigated by scanning tunneling microscopy at the liquid/solid interface. The coexistence and reversible tran...

Self-Assembly Polymorphism: Solvent-Responsive Two-Dimensional Morphologies of 2,7-Ditridecyloxy-9-fluorenone by Scanning Tunneling Microscopy

Abstract: Two-dimensional self-assembly of 2,7-ditridecyloxy-9-fluorenone (F-OC13) is investigated by scanning tunneling microscopy (STM) in solvents with different polarities and functional groups on a high oriented pyrolytic graphite surface. The STM images reveal that the self-assembly of F-OC13 is strongly solvent-dependent. 1-Phenyloctane can coadsorb on the self-assembly of F-OC13, and the structural transformation of the adlayer from the linear structure to alternate lamella can be observed with the decrease of the concentration. At the 1-octanol/HOPG interface, only a well-ordered linear pattern is obtained. The intermolecular hydrogen bonding between the 1-octanoic acid and the F-OC13 molecule is responsive for the formation of butterfly configuration. When n-tridecane or n-tetradecane is used as solvent, a regular alternate pattern is formed under high concentrations, and a coadsorbed lamellar structure is observed under low concentrations. Furthermore, when the sample with use of the methanol, dichlorome...

Effect of bromine and substituted alkyl chain on the interfacial self-assembly of bromobenzene derivatives by scanning tunneling microscopy.

Abstract: The self-assemblies of four compounds, 1-bromo-4-(hexadecyloxy)benzene (BHB-16), 1-bromo-4-(octadecyloxy)benzene (BOB-18), 1-bromo-4-(pentadecyloxy)benzene (BPB-15) and 1,4-dibromo-2,5-(dioctadecyloxy)benzene (DDB-18), have been studied on highly oriented pyrolytic graphite (HOPG) under ambient conditions by scanning tunneling microscopy (STM), with the aim of understanding the influence of the molecular structure and functional groups on the arrangements. It is found that the bromine atoms of the four molecules are in bright contrast and can be identified in STM images. The neighbouring phenyl head groups of the BHB-16, BOB-18 and BPB-15 molecules in one lamella, with an anti-parallel orientation, are interdigitated with different offset distance, while the aromatic cores of DDB-18 molecules in the same row are in a parallel orientation. Moreover, an odd-even effect is observed in the self-assemblies of the former three molecules as expected. The STM images of the four molecules resemble the calculated HOMO electron density contours somewhat with positive surface bias voltage. On the basis of comparative analysis between the STM images, it is suggested that the electrostatic attractions between the neighbouring molecules play an important role in the self-assemblies of BHB-16, BOB-18 and BPB-15, while it is the van der Waals force and the non-covalent halogen-halogen interaction that dominate the structure of DDB-18 adlayer.