Controlling the Reaction Steps of Bifunctional Molecules 1,5-Dibromo-2,6-dimethylnaphthalene on Different Substrates

Using scanning tunneling microscopy, we reveal that the methyl groups of 1,5-dibromo-2,6-dimethylnaphthalene suppress Ullmann-type intermolecular coupling on Au(111), Ag(111), and Cu(111) and steer the reactions toward different final products on the three substrates. On Au(111), the molecules form ordered structures stabilized by intermolecular halogen bonds and desorb from the surface at above 420 K. On Ag(111), the molecules form halogen-bonded structures but are converted into organometallic structures at 360 K and desorb from the surface at above 600 K. On Cu(111), the molecules form organometallic structures at 300 K and undergo an intermolecular cyclodehydrogenation reaction at above 480 K. The reaction yields C-C bonds between debrominated carbons and methyl groups, resulting in dibenz[a,h]anthracene derivates and ultranarrow chiral-edge graphene nanoribbon motifs. This comparative study demonstrates a novel concept of using side groups to control the reaction steps that lead to specific final products on different substrates.