Supramolecular Self-assembly Using Flexible Molecules As Building Blocks On Metal Surfaces

Supramolecular self-assembly represents a promising strategy for the fabrication of the nanoscale materials and devices,because it creates nanostructures with well-controlled,tailor-made properties and functionality at the single-molecule level.As surfaces provide additional control over the design of structures and properties of the two-dimensional selfassembly materials,supramolecular self-assembly confined on metal surfaces manifests distinct characteristics that are inaccessible in three-dimensional space.Supramolecular selfassembly at solid surfaces is governed by the subtle interplay between molecule–molecule and molecule–substrate interactions,which can be tuned by the rational selects of organic molecular building blocks,by tuning surface chemistry and structures,and by varying thermodynamic and kinetic conditions.Precisely controlling self-assembled structures is the key to the application in nano devices.In this paper,we have studied the surface supramolecular self-assembly of the organic molecules with flexible chains in the presence of various non-covalent interactions,by using ultrahigh vacuum scanning tunneling microscopy(UHV-STM).The main research contents include the following three aspects:(1)In chapter 3,we described a metal-organic coordination self-assembly on Au(111)by using molecule 1 with a flexible side-chain.STM study shows that the flexible side chain in molecule 1 vibrates at room temperature,and thus regulates the self-assembly by adding the entropy over the self-assembly system.By tuning the vibration of the side chain,we have obtained a large scale ordered two-dimensional nanoporous network at the single-molecule level.(2)In chapter 4,we demonstrated that the molecular flexible side chains can be used to tune the distance between the assembled nano chains.The organic molecule 1 is composed of a carbazole skeleton with two pyridyl group and a tetradecyl side chain.On an Au(111)surface with predeposited Cu atoms,the molecules 2 coordinate with Cu via the pyridyl terminals into chains,while.STM study shows that the tetradecyl side chain of the molecule L vibrates on the surface due to its thermal energy.Analysis based on high-resolution images reveals that the steric hindrance caused by the side chain vibration regulates the arrangement of the assembled metal-organic coordination chains.(3)In chapter 5,the supramolecular self-assembly of flexible molecule 3 at Au(111)surface at low temperature(90 K)and room temperature(300 K)was studied.The supramolecular self-assembly of flexible molecules 2,3,4 with the cooperation of molecule 5 at room temperature on Au(111)were studied respectively.The STM experimental results show that the molecules with flexible alkyl chains can change their conformational structures in order to adapt to the surrounding self-assembly structure.The chiral separation in the selfassembled structures is also discussed.