Building Low-Dimensional Conjugated Materials Based On The Structures Of Self-Assembled Monolayers

On surface self-assembly of physisorbed molecules is a spontaneous process in the formation of well-ordered structures by non-covalent interactions of adsorbed molecules. For decades, molecular self-assembly has been investigated by means of scanning tunneling microscope(STM), exhibiting various structures, such as close-packed structures, chiral, and two dimensional host-guest strutures. Since the driving forces to direct on surface self-assemly are non-covalent interactions, self-assembled monolayers have a relatively low thermal stability, which limits its’ applications in many surface-contained chemical processes. On the other hand, surface supported reactions provide an effective way for the synthesis of stable 1D and 2D covalently connected materials on surfaces. However, due to the characteristic of on surface reactions, e.g. random and uncontrollable fashion, structural control of produced 1D and 2D materials still represents a challenge. Therefore, this thesis will focus on the development of a stragegy to combine techniques in self-assembly and on-surface reactions for structural control of 1D and 2D covalently connected materials.1. Chirality transfer via on surface reactionsChiral structures of self-assembled prochiral 1,4-dibromo-2,5-didodecylbenzene(12DB) on Au(111) surface have been investigated by STM in ultra-high vacuum conditions. 12 DB molecules adsorb flatly on Au(111), leading to a symmetry breaking of 12 DB and chiral self-assembly on surfaces. STM investigations reveal that aryl-aryl coupling reaction occurs by connection of the nearest neighboring precursors without affecting the self-assembled(SA) lamellar structure. The SA structures of 12 DB precursors can determine the final structures of produced oligo-p-phenylenes(OPP) on the surface. Pure homochiral domains give rise to homochiral domains of OPP.2. On surface synthesis in a controllable way by tuning stoichiometric ratio of componentsSurface-supported coupling reaction between 1,3,5-tris(4-formylphenyl)-benzene(TFPB) and aromatic amines has been investigated on Au(111) by STM under ultrahigh vacuum. Various products, including the discrete supramolecules and the surface covalent organic frameworks(SCOF) are obtained through a thermal annealing of self-assembled monolayers on metal surfaces. Systemic experiments reveal that the stoichiometric composition of the reactants is vital to the chemical structures of final products. A covalently bonded honeycomb networks has been successfully prepared by tuning the ratio of two molecular precursors.