The structural evolution of cobalt phthalocyanine (CoPc) thin films grown on a Bi(1 1 1) surface from the sub-monolayer to the third layer has been investigated with low-temperature scanning tunneling microscopy (STM). Two crucial transitions have been identified during the film epitaxial growth: one is the structural transition from zigzag chains to linear dimerized chains in the monolayer regime; the other is the molecular orientational transition from a flat-lying to a standing-up configuration in the multilayer regime. These results are helpful in understanding the growth mechanism of transition-metal phthalocyanine films on semi-metallic surfaces.
We investigated the chiral self-assembly of rubrene molecules on a semi-metallic Bi(111) surface using low-temperature scanning tunneling microscopy. The absolute configuration of isolated rubrene enantiomers was identified from high-resolution images. Two types of homochiral domains of rubrene monomers and hexamers were observed, respectively. For rubrene monomers, chiral separation was spontaneous with each chiral monomer appearing in their respective domain. For rubrene hexamers, two levels of organization chirality were recorded: one is six heterochiral rubrene molecules arranged alternatively in a rubrene hexamer; and the other is a homochiral arrangement of individual hexamers. After annealing at 350 K, a large area of supramolecular self-assembled L- and R-type triangular heterochiral hexamers was obtained at the narrow terrace of Bi(111). Moreover, a molecular chiral inversion from the L-(R-) type to the R-(L-) type occurs during the formation of the hexamer domain structure and can be attributed to the enhanced intermolecular interactions governed by the intensive intermolecular extrusion at the narrow terrace.
Molecular rotors with an off-center axis and the chiral feature of achiral CuPc molecules on a semi-metallic Bi(111) surface have been investigated by means of a scanning tunneling microscopy (STM) at liquid nitrogen (LN2) temperature. The rotation axis of each CuPc molecular rotor is located at the end of a phthalocyanine group. As molecular coverage increases, the CuPc molecules are self-assembled into various nanoclusters and finally into two-dimensional (2D) domains, in which each CuPc molecule exhibits an apparent chiral feature. Such chiral features of the CuPc molecules can be attributed to the combined effect of asymmetric charge transfer between the CuPc and Bi(111) substrate, and the intermolecular van der Waals interactions.
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