Pyridinic Nitrogen Modification for Selective Acetylenic Homocoupling on Au(111)

Abstract

On-surface acetylenic homocoupling has been proposed to construct carbon nanostructures featuring sp hybridization. However, the efficiency of linear acetylenic coupling is far from satisfactory, often resulting in undesired enyne products or cyclotrimerization products due to the lack of strategies to enhance chemical selectivity. Herein, we inspect the acetylenic homocoupling reaction of polarized terminal alkynes (TAs) on Au(111) with bond-resolved scanning probe microscopy. The replacement of benzene with pyridine moieties significantly prohibits the cyclotrimerization pathway and facilitates the linear coupling to produce well-aligned N-doped graphdiyne nanowires. Combined with density functional theory calculations, we reveal that the pyridinic nitrogen modification substantially differentiates the coupling motifs at the initial C−C coupling stage (head-to-head vs head-to-tail), which is decisive for the preference of linear coupling over cyclotrimerization.

Accurate Simulations of Scanning Tunneling Microscope: Both Tip and Substrate States Matter

“…With the guidance of the final product, we explored the coupling mechanism by a model system of 3-ethynylpyridine (EPy) (Figure b). The calculated results reveal that the coupling barrier of the head-to-head route that generates the linear acetylene is 0.27 eV lower than that of the head-to-tail route that produces cyclopolymerization, due to the replacement of benzene with pyridine moieties . Thus, we can conclude that the selective acetylenic homocoupling of 5,5′-DEBPy on the Au(111) surface is a kinetic control reaction.…”

“…(e) Calculated minimum-energy path between the adsorption configurations in panel d. The values in parentheses represent the relative energies in eV with respect to the trans configuration. Panels a and b were reproduced with permission from ref , copyright 2023 American Chemical Society. Experimental images in panel c were reproduced with permission from ref , copyright 2006 American Physical Society.…”

“…Our experimental collaborators deposited 5,5′diethynyl-2,2′-bipyridine (5,5′-DEBPy) molecules onto Au(111) held at room temperature and then thermally annealed up to 390 K, which resulted in well-aligned nanowire arrays (Figure 3a, left panel). 49 The simulated STM image (Figure 3a, right panel) shows that the nanowire is a polymerization product of 5,5′-DEBPy with an all-trans configuration. 49 With the guidance of the final product, we explored the coupling mechanism by a model system of 3-ethynylpyridine (EPy) (Figure 3b).…”

“…49 The simulated STM image (Figure 3a, right panel) shows that the nanowire is a polymerization product of 5,5′-DEBPy with an all-trans configuration. 49 With the guidance of the final product, we explored the coupling mechanism by a model system of 3-ethynylpyridine (EPy) (Figure 3b). The calculated results reveal that the coupling barrier of the head-to-head route that generates the linear acetylene is 0.27 eV lower than that of the head-to-tail route that produces cyclopolymerization, due to the replacement of benzene with pyridine moieties.…”

“…One example is selective acetylenic homocoupling on Au(111). Our experimental collaborators deposited 5,5′-diethynyl-2,2′-bipyridine (5,5′-DEBPy) molecules onto Au(111) held at room temperature and then thermally annealed up to 390 K, which resulted in well-aligned nanowire arrays (Figure a, left panel) . The simulated STM image (Figure a, right panel) shows that the nanowire is a polymerization product of 5,5′-DEBPy with an all-trans configuration .…”