Structure and structural transition of chiral domains in oligo(p-phenylenevinylene) assembly investigated by scanning tunneling microscopy

Abstract

OPV3-CHO molecules are employed to prepare assembly on highly oriented pyrolytic graphite, and the so-prepared assembly is investigated by scanning tunneling microscopy. In the assembly chiral domains are observed with various structures such as linear and windmill. The chiral structural formation, stability, transition, and possible unification are intensively studied. After thermal annealing, linear structure was the only structure. To achieve a unified assembly with a single structure, an efficient method is proposed by coadsorption of OPV3-CHO with selected molecules. For example, an assembly with side-by-side helix structure is formed by a simple coadsorption of OPV3-CHO with alkyl bromide (C n H 2nþ1 Br, n ¼ 15-18). The experiments by cocrystallization of OPV3-CHO∕ C n H 2nþ1 X (X ¼ Cl, Br, and I) show the important role of halogen bonding in formation of the uniform structure. The results are significant in understanding the intermolecular noncovalent interactions that dominate the surface structure and chirality.coadsorption | halogen bonding | surface chirality U nderstanding the formation and structural transition of molecular nanostructure is an important issue in chemistry, molecular science, and nanodevice fabrication. Among various molecular nanostructures, two-dimensional surface chirality is a property of asymmetry and of great interest in fundamental research and industrial application such as life genesis, nonlinear optics, enantioselective heterogeneous catalysis, and surface modification (1-3). With atomic resolution, scanning tunneling microscopy (STM) is powerful in surface chirality study (4-7). From absolute chirality determination to chiral structure fabrication with chiral molecules or achiral molecules on a solid surface, a few results have been reported (8-13). Xu et al. directly observed the chirality of (R)-and (S)-2-phenylpropionamide molecules on Cu(111) in solution by using electrochemical STM (14). De Feyter et al. studied solvent-induced homochirality in selfassembled monolayers of achiral molecules. The chirality of the solvent directs the macroscopic chirality of the monolayer (15). After these results, we focus on the current challenge in surface chirality, which includes understanding the underlying driving force for the chiral formation, amplification, transition, and controlling the chiral structure.Recently, oligo(p-phenylenevinylene) (OPV) and its derivatives have attracted a lot of attention because of their advanced optical and electronic properties and possible application in organic electronic devices (16)(17)(18). In the present report, an aldehyde-substituted OPV molecule (OPV3-CHO, Scheme 1) is used as a model compound to study its structure on a solid surface. It is found that achiral OPV3-CHO can form chiral domains on highly oriented pyrolytic graphite (HOPG). The OPV3-CHO adlayer is investigated by STM including structural formation, stability, transition, and possible unification of the chiral domains. The OPV3-CHO chiral domains appear in linear and windmil...

Simultaneous construction of two linkages for the on-surface synthesis of imine–boroxine hybrid covalent organic frameworks

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Organic enantiomeric high- T c ferroelectrics

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