Surface-confined Self-assembly And Reaction Investigated With Scanning Tunneling Microscopy

Self-assembly is a process in which molecules and molecules are linked to well-ordered structure via non-covalent bonds.Self-assembly has played an important role in many aspects,such as nanomaterials,membrane materials and bioscience.However,the relative unstability limits the application of the self-assembly in many fields.On the other hand,the surface chemical reactions show potential applications in surface catalysis,synthesising of new materials and researching of the reaction mechanism.However,it is very difficult to control the structure of reaction products due to the irreversibility of the covalent bonds.Therefore,it is of particular importantance to combine the self-assembly and surface reaction to construct a new functional covalently connected system.My researches including the following parts:1.Self-assembly of diselenide molecules at liquid-solid interface and surface-assisted chemical reactions.Diselenide bonds can be broken in very mild conditions for diselenide metathesis,and it can be used to guide the synthesis of asymmetric diselenide compounds.Its reaction rate and yield in solutions is low,thus it is feasible to use the surface catalysis to promote the reaction process.In this work,we studied the self-assembly and reaction behavior of series of diselenide on surface,and obtained the assembly and reaction product of different selenium molecules with different functional groups.We initially confirmed that the surface can promote the reaction process effectively.2.Chiral control of self-assembly on surface.Achiral molecules 1,4-dibromo-2,5-dodecylbenzenpe 2DB)and 1,4-dibromo-2,5-tridecylbenzene(13DB)show chiral assembly struct e on achiral surfaces.The regularity is different because of chains’ odd-even effectts In addition,the structures of assembly of DB series molecules are different on differe surfaces such as HOPG and Au(111).It is a feasible approach to fabricate homoc ral structure on surface by coadsorption with guest molecules.3.Self-assembly and surface chemical reactions of 1,3-butadiene derivatives on surface.The 18,19-dimethylene-octatriacontane self-assemby behavior were studied at liquid-solid interface.We found that the assembly str ture has a reversible phase transition depended on temperature.In addition,the as embly and surface chemical reaction on Au(111)and Au(110)were studied in hig vacuum environment.The scanning tunneling microscopy investigations reveal that alkyl chains adsorbed on(1×3)-Au(110)are more reactive than molecules adsorbed n(1×2)-Au(110).4.Potential-induced phase transition of molecular seif-assembled structures.We investigated the phase transition of N-isobutyryl-L-cysteine(L-NIBC)SAMs on Au(111)surface by in situ electrochemical scanning tunneling microscopy(EC-STM).As-prepared a phase and β phase of NIBC S AMs show various structural changes under the control of electrochemial potentials of the Au(111)in H2SO4 solution.Combined with the density functional theory(DFT)calculations,the phase transition from the β phase to the α phase is explained by the reason of potential induced break of bonding interactions between-COO-and negatively charged gold surfaces.