Self-assembly Nanostructure Of OPE And PBM Molecules On Graphite Studied By STM

In this thesis,on the basis of the new research ideas,the assembly structure is controlled by the concentration of the guest molecule,we have systematically investigated the adsorption behavior of organic molecules on graphite surface,with the help of scanning tunneling microscopy(STM)and density functional theory(DFT)simulations.We have chosen several typical systems,and studied the adsorption behavior of these molecules on graihite surface,which can help us well understand the characteristics and laws of surface-confined moleculsular self-assembly.The main results of this thesis are as follows:(1)A series of conjugated oligo(p-phenylene-ethynylene)(OPE)molecules with different backbone lengths and side chains were synthesized.The self-assembled structures of these OPE molecules were studied on a HOPG surface by STM in combination with DFT calculations.The results showed that these oligomers can form different self-assembled monolayers depending on their chemical structure,with the intermolecular interactions via the side chains being the main contributing factor.These assembled structures are stabilized by van der Waals forces between the interdigitated side chains as well as between the molecules and the HOPG substrate.These observations will provide animportant guidance in the design of functional conjugated molecules for specific applications.(2)The self-assembly of two conjugated aromatic macrocyclic molecules(PBM)on the graphite surface was studied by STM.Size,shape and concentration controlled experiments have been performed to investigate the PBMs/COR host-guest system with the structural polymorphism phenomenon.The STM images showed that the PBM1(The main part is a triangle)molecules presented a regular linear network structure while the PBM2(The main part is a quadrilateral)molecules formed a well-ordered nanoporous network structure.When the COR molecules were introduced,the selfassembled structures of PBM1 remained unchanged while for PBM2,co-assembly structures were formed.Furthermore,the PBM2/COR networks underwent a structural transformation with the increase of the concentration of COR guest molecules.With the DFT calculations,revealed that size matching and concentration dependent effects play a significant role in the structural transformation of the PBM2 host-network after the introduction of COR guest molecules.The results will help us gain insight into dynamic procedures of self-assembly and control molecular pattern formation on the surface.