On-surface synthesis of disilabenzene-bridged covalent organic frameworks

Substituting carbon with silicon in organic molecules and materials has long been an attractive way to modify their electronic structure and properties. Silicon-doped graphene-based materials are known to exhibit exotic properties, yet conjugated organic materials with atomically precise Si substitution have remained difficult to prepare. Here we present the on-surface synthesis of one- and two-dimensional covalent organic frameworks whose backbones contain 1,4-disilabenzene (C(4)Si(2)) linkers. Silicon atoms were first deposited on a Au(111) surface, forming a AuSi(x) film on annealing. The subsequent deposition and annealing of a bromo-substituted polyaromatic hydrocarbon precursor (triphenylene or pyrene) on this surface led to the formation of the C(4)Si(2)-bridged networks, which were characterized by a combination of high-resolution scanning tunnelling microscopy and photoelectron spectroscopy supported by density functional theory calculations. Each Si in a hexagonal C(4)Si(2) ring was found to be covalently linked to one terminal Br atom. For the linear structure obtained with the pyrene-based precursor, the C(4)Si(2) rings were converted into C(4)Si pentagonal siloles by further annealing. [Image: see text]