Ullmann coupling of 2,7-dibromopyrene on Au(1 1 1) assisted by surface adatoms

Abstract

Ullmann coupling on coinage metals has attracted significant attention in surface chemistry due to its atomic precision of constructing extended covalent nanostructures with predictability, while the elementary reaction mechanism behind has not been comprehensively understood yet. In this study, we demonstrate the active contribution of surface atoms in promoting Ullmann coupling of 2,7-dibromopyrene (Br2Py) on Au(1 1 1) accompanied with the structure transformation from self-assembly to covalently bound one-dimension polymer chains via a combination of scanning tunnelling microscopy (STM), X-ray photoelectron spectroscopy (XPS) and density functional theory calculations (DFT). Even the organometallic intermediate on Au substrate has been occasionally reported before, it is interesting herein to observe organometallic intermediates with the gold-carbon bonding, and demonstrate that surface adatoms specially play an important role in the dehalogenation process of Br2Py on Au(1 1 1) as elucidated by DFT simulations. Step-wise annealing facilitates the decoupling of the coordinated Au atoms from organometallic oligomers and the ultimate formation of extended polymers, which has been consistently interpreted by XPS and DFT calculations. Our study might shed new insights on the atomistic understanding of Ullmann coupling chemistry on Au substrates and proposes an effective approach to comprehensively elucidate the effect of organometallic intermediates towards on-surface Ullmann coupling reaction.