We demonstrate a method to selectively switch the Ullmann coupling reaction of 2,8-dibromodibenzothiophene on a Au(111) support. The Ullmann coupling reaction is effective already at low temperature, but the complete inhibition of the same reaction can be achieved on Au(111) pre-exposed to H2S. The marked difference in reactivity of pretreated Au(111) is explained by the S-passivation of free Au atoms emerging from reconstruction sites. The inhibited state can be fully lifted by removing the S via hydrogen gas post-exposure.

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Lateral heterostructures consisting of 2D transition metal dichalcogenides (TMDCs) directly interfaced with molecular networks or nanowires can be used to construct new hybrid materials with interesting electronic and spintronic properties. However, chemical methods for selective and controllable bond formation between 2D materials and organic molecular networks need to be developed. As a demonstration of a self‐assembled organic nanowire‐TMDC system, a method to link and interconnect epitaxial single‐layer MoS2 flakes with organic molecules is demonstrated. Whereas pristine epitaxial single‐layer MoS2 has no affinity for molecular attachment, it is found that single‐layer MoS2 will selectively bind the organic molecule 2,8‐dibromodibenzothiophene (DBDBT) in a surface‐assisted Ullmann coupling reaction when the MoS2 has been activated by pre‐exposing it to hydrogen. Atom‐resolved scanning tunneling microscopy (STM) imaging is used to analyze the bonding of the nanowires, and thereby it is revealed that selective bonding takes place on a specific S atom at the corner site between the two types of zig‐zag edges available in a hexagonal single layer MoS2 sheet. The method reported here successfully combining synthesis of epitaxial TMDCs and Ullmann coupling reactions on surfaces may open up new synthesis routes for 2D organic‐TMDC hybrid materials.