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

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(2n+1)Br, n = 15-18). The experiments by cocrystallization of OPV3-CHO/C(n)H(2n+1)X (X = 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.