Sequential Linking To Control Growth of a Surface Covalent Organic Framework

Abstract

We report on formation of a new surface covalent organic framework (SCOF) based on a sequential polymerization in two stages. The bifunctional precursor used, p-bromo-benzene boronic acid (BBBA), was vapor deposited in ultra-high-vacuum conditions on a Au(111) surface. In a first step the boronic acid moieties reacted to form trimers linked by covalent boroxine rings. In a second step, an Ullmann coupling reaction was thermally activated to form C–C bonds between the trimers, leading to the final polymeric network. By this procedure the growth mechanism was optimized and the polymerization reaction yield could approach 100%. A well-extended network was obtained, differing from the ideal honeycomb-like network by a substantial number of nonhexagonal pores, which are intrinsic defects to the polymer structure. A comparison of the two competing reactions provides new insights into the complex mechanisms governing growth of two-dimensional covalent networks.