Temperature-Triggered Sequential On-Surface Synthesis of One and Two Covalently Bonded Porous Organic Nanoarchitectures on Au(111)
Résumé
Subtle variations of surface temperature can drastically influence the on-surface synthesis of two-dimensional covalent graphene nanoarchitectures. The structure of the engineered nanoarchitectures not only results from the temperature-activation of the catalytic process, but it is also governed by the temperature-dependent geometry of intermolecular assembly. The sequential engineering of porous organic nanoarchitectures based on the covalent Ullmann coupling of star-shaped 1,3,5-tris(3,5-dibromophenyl)benzene molecules on Au(111) in vacuum is investigated using scanning tunneling microscopy and X-ray photoemission spectroscopy. This molecule can form one-covalent-bond or two-covalent-bonds with neighboring molecules. At room temperature, the molecules self-assemble into a porous halogen-bonded network stabilized by two types of X 3 synthons. One-covalent-bond dimers appear on the surface after annealing at 145 °C. One-covalent-bond chains are created after annealing at 170 °C. Most of the molecules are bonded to two neighbors. One-covalent-bond hexagons as well as two-covalent-bond dimers are appearing on the surface after annealing at 175 °C. Annealing at 275 °C leads to the formation of a porous 2D hexagonal two-covalent-bond nanoarchitecture. STM images show that the number of intermolecular covalent bonds as well as the number of covalently bonded molecular neighbors increases as the temperature rises. Core level spectroscopy shows that the molecules are fully dehalogenated after annealing at 260 °C. These observations show that dibromophenyl-based molecules are promising organic compounds to hierarchically and selectively engineer covalent porous graphene nanoarchitectures having different structures.