Single-Atom Protecting Group for on-Surface Synthesis of Graphdiyne Nanowires
Huan Shan; Ya-hui Mao; Ai-di Zhao<sup>*</sup>
On-surface synthesis enables the polymerization of isolated long molecular nanowires by overcoming the critical solubility of oligomers in traditional solution methods. However, the on-surface synthesis of semiconducting graphdiyne nanowires usually suffer severe side reactions owing to the high reactivity of the butadiynylene units confined on the 2D metallic surfaces, limiting the production of isolated nanowires. In this work, we report the high-yield synthesis of branchless graphdiyne nanowires [-C≡C-Ph2-C≡C-]n via on-surface Ullmann coupling of 1,4-bis(4-bromophenyl)-1,3-butadiyne molecules with chemical vapor deposition method. Non-contact atomic force microscopy with single-bond resolution reveals that single gold adatoms act as effective protecting groups for butadiynylene units by forming Au-π ligand bonds, preventing unwanted branched coupling reactions and enabling the synthesis of ultralong isolated graphdiyne nanowires. This study will stimulate further investigation on the role of various surface adatoms in protecting on-surface reactions and will provide new insights for high-efficiency on-surface polymerization reactions.