Showing papers by "Wenli Deng published in 2013"

Dipole-Controlled Self-Assembly of 2,7-Bis(n-alkoxy)-9-fluorenone: Odd–Even and Chain-Length Effects

Abstract: Fluorenone derivatives (F–OCn) with various lengths of peripheral alkyl chains (with carbon numbers of n = 12–18) were synthesized, and their self-assembled adlayers were investigated in solvents w...

Hydrogen-Bonding-Induced Polymorphous Phase Transitions in 2D Organic Nanostructures

Abstract: The 2D self-assembly of various 2-hydroxy-7-alkoxy-9-fluorenone (HAF) molecules has been investigated by scanning tunneling microscopy (STM) at the liquid/solid interface. A systematic study revealed that HAF molecules with different numbers of carbon atoms in their alkoxy chains could form two or three different kinds of nanostructures, that is, less-ordered, flower-like, and zig-zag patterns, owing to the formation of different types of intermolecular hydrogen bonds. The observed structural transition was found to be driven by molecular thermodynamics, surface diffusion, and the voltage pulse that was applied to the STM tip. The zig-zag pattern was the most stable of these configurations. An odd-even effect on the flower-like structure, as induced by the odd and even number of carbon atoms in the side chain, was observed by STM. The influence of the odd-even effect on the melting point has a close relationship with the molecular self-assembled pattern. Our results are significant for understanding the influence of hydrogen-bonding interactions on the dominant adsorption behavior on the surface and provide a new visual approach for observing the influence of the odd-even effect on the phase transition.

Solvent-dependent self-assembly of 4,7-dibromo-5,6-bis(octyloxy)benzo[c][1,2,5] thiadiazole on graphite surface by scanning tunneling microscopy

Abstract: Solvent effect on self-assembly of 4,7-dibromo-5,6-bis(octyloxy)benzo[c][1,2,5] thiadiazole (DBT) on a highly oriented graphite (HOPG) surface was investigated by scanning tunneling microscopy (STM) by using 1-phenyloctane, 1-octanoic acid, and 1-octanol as the solvents. Two different patternswere obtained in 1-phenyloctane and 1-octanoic acid, suggesting that the self-assembly of DBT was solvent dependent. At the 1-phenyloctane/HOPG interface, a linear structure was revealed due to the intermolecular halogen bonding. When 1-octanoic acid and 1-octanol are used as the solvents, the coadsorption of solvent molecules resulting from the hydrogen bonding between DBT and solvent made an important contribution to the formation of a lamellar structure. The results demonstrate that solvents could affect the molecular self-assembly according to the variational intermolecular interactions.

Two-dimensional self-assembly of dendritic amphiphilic molecule with ferroncenyl subsitutuents at the liquid/solid interface.

Abstract: Two-dimensional self-assembly of dendritic amphiphilic molecule with ferroncenyl subsitutuents (2,3,4-tri-(11-ferroncenyl)undecyloxybenzoic acid, Fc3COOH) on highly oriented pyrolytic graphite surface was investigated by scanning tunneling microscopy at the liquid/solid interface. Fc3COOH molecule formed an ordered molecular nanostructure--an alternating big/small bright dots pattern on the graphite surface extended to several hundred nanometers. On the basis of the simulation and combined with our STM results, it is concluded that the molecular adsorption conformation has an appreciable effect on the interactions of molecule-molecule and molecule-substrate. The pi-pi interactions between ferrocene groups together with the van der Waals interactions between alkyl chains direct the stacking behavior of Fc3COOH molecules. Due to the steric constraints, no hydrogen bonding between the carboxyl groups was formed during the self-assembly.