Molecular packing in self-assembled p-n and n-p-n heterostructure co-oligomers

The molecular packing structure in the self-assembled p-n and n-p-n heterostructure oligomers (OT₂O and T₂O₂) was investigated. The macroscopic properties of the two oligomers were systemically investigated by differential scanning calorimetry (DSC), polarized optical microscopy (POM) and X-ray diffraction (XRD), which revealed that the 3D (three-dimensional) assemblies of the two oligomers exhibited obvious differences. The two-dimensional assemblies (2D) of them were identified by scanning tunneling microscopy (STM) on a highly oriented poyrolytic graphite (HOPG) surface. Well-ordered monolayer assembly structures were fabricated by symmetric molecules (OT₂Os), while the ordered dormain of asymmetric molecule (T₂O₂s) could not be clearly resolved. This system, as an excellent example, may provide guidance for the design of the novel p-n heterostructure oligomer and polymer.