Direct Synthesis of Vinylene-Linked Conjugated Polymers by Selective Methyl/Methylene C─H Activation on Gold Surfaces

Vinylene (C═C) linkage facilitates the distribution of highly conjugated electrons along the polymer chain, thereby playing a crucial role in the development of conductive polymers for promising applications in organic electronics. Directly connecting two methyl groups to construct a vinylene linkage would streamline the synthesis process considerably, reducing the number of reaction steps required. However, reactions through alkyl groups normally form C─C single bonds as linkages. Achieving vinylene bonds via further dehydrogenation remains a significant challenge. Here, we demonstrate the successful synthesis of vinylene linkages by selectively activating methyl/methylene C─H bonds using the predesigned monomers bearing methylthiophenes on Au(111) and Au(110) surfaces. Noncontact atomic force microscopy confirms the formation of vinylene linkage by bond-resolved imaging on both surfaces, achieving a vinylene linkage yield of 97%. Density functional theory calculations and control experiments reveal that the strong adsorption of the thiophene ring on the gold substrate effectively reduces the energy barriers for methyl and methylene C─H dissociation, enabling the two-step dehydrogenation for the formation of vinylene-linked polymers with up to 27 units. Our findings present a novel strategy for polymerization or oligomerization via vinylene linkages on surfaces.