The exotic properties associated with graphene and other 2D layered inorganic materials have attracted great interests from a variety of research fields. Single-layered covalent organic frameworks (sCOFs), featuring covalent bond linked functional groups in a well ordered manner in two-dimension, are structurally similar to graphene but have designable properties, readily integrated functionalization sites, and show great application prospects in many emerging fields. Taking advantage of the template effect of surface, on surface bottom up synthesis has been regarded as one of most prominent strategy to synthesize high quality sCOFs. Nevertheless, sCOF structures were generally suffered from poor orderliness and limited domain size, which limits the understanding of their intrinsic properties.
The well-studied suparmolecular assembly of organic molecules into highly ordered nanoarchitectures provides inspiring examples for on surface sCOF synthesis. In this presentation, we will discuss the bottom up fabrication of highly ordered 2D networks on single crystalline solid supports. We demonstrate the construction of well-ordered 2D covalent networks via the dehydration of di-borate aromatic molecules via the chemical equilibrium regulation. By introducing small amount of water into a closed reaction system, the chemical equilibrium of boroxine ring formation reaction can be regulated to favor the occurrence of reverse reaction and therefore improves the abilities of the self-adjustment or self-healing of the sCOFs. We also present that the growth kinetic control is another key element to achieve highly ordered sCOFs with binary monomers. The detailed investigation of reaction intermediate reveals the important roles of surface diffusion of precursors and oligmers for the growth of highly ordered sCOFs. Further extension of this strategy to other kinds of chemical reactions to fabricate 2D nanostructures will be also discussed. References: [1] X.-H. Liu, C.-Z. Guan, S.-Y.Ding, W. Wang, H.-J.Yan, D.Wang, L.-J.Wan, On-Surface Synthesis of Single-Layered Two-Dimensional Covalent Organic Frameworks via Solid–Vapor Interface Reactions, J. Am. Chem. Soc., 2013, 135, 10470–10474. [2] C. Z. Guan, D. Wang, L.-J. Wan, Construction and repair of highly ordered 2D covalent networks by chemical equilibrium regulation. Chem. Commun. 2012, 2943-2945