Chemisorption-Induced Formation of Biphenylene Dimer on Ag(111)

Abstract

We report an example that demonstrates the clear interdependence between surface-supported reactions and molecular-adsorption configurations. Two biphenyl-based molecules with two and four bromine substituents, i.e., 2,2′dibromobiphenyl (DBBP) and 2,2′,6,6′-tetrabromo-1,1′-biphenyl (TBBP), show completely different reaction pathways on a Ag(111) surface, leading to the selective formation of dibenzo[e,l]pyrene and biphenylene dimer, respectively. By combining low-temperature scanning tunneling microscopy, synchrotron radiation photoemission spectroscopy, and density functional theory calculations, we unravel the underlying reaction mechanism. After debromination, a biradical biphenyl can be stabilized by surface Ag adatoms, while a four-radical biphenyl undergoes spontaneous intramolecular annulation due to its extreme instability on Ag(111). Such different chemisorption-induced precursor states between DBBP and TBBP consequently lead to different reaction pathways after further annealing. In addition, using bond-resolving scanning tunneling microscopy and scanning tunneling spectroscopy, we determine with atomic precision the bond-length alternation of the biphenylene dimer product, which contains 4-, 6-, and 8-membered rings. The 4-membered ring units turn out to be radialene structures.

Selective Activation of Aromatic C–H Bonds Catalyzed by Single Gold Atoms at Room Temperature

“…We claim that this significant difference between positions A and B explains the experimentally observed regioselectivity of the C−H dissociation. The 19 kcal/mol barrier represents a significant reduction relative to comparable C−H activation reactions with barriers of 30−40 kcal/mol (1.3−1.8 eV), experimentally occurring in a temperature window of 400−700 K. 60,68,69,72 Furthermore, other onsurface reactions with barriers of ∼20 kcal/mol (∼0.87 eV) have been observed at RT, 71,73 supporting the interpretation of our experimental results as RT C−H activation.…”

Scanning probe microscopy in probing low-dimensional carbon-based nanostructures and nanomaterials

“…Moreover, due to the surface confinement and facilitation, some unique 0D carbon-based nanostructures, such as those embedded with non-benzenoid n-membered rings, have been demonstrated to be accessible by on-surface reactions. Simultaneously, SPM techniques play a significant role in the detection of intermediates and revelation of reaction pathways [55,56], visualization of bond structures and topographies [55,[57][58][59][60][61][62][63][64], characterization of electronic properties [58,59,65], tip-induced structural transformations [59,66], etc. Notably, Zeng et al applied a tetrabromobiphenyl molecular precursor with dibromo groups functionalized at the bay region of both sides and selectively fabricated biphenylene dimers containing four-, six-, and eight-membered rings on Ag (111) (figure 3(e)) [55].…”

“…Simultaneously, SPM techniques play a significant role in the detection of intermediates and revelation of reaction pathways [55,56], visualization of bond structures and topographies [55,[57][58][59][60][61][62][63][64], characterization of electronic properties [58,59,65], tip-induced structural transformations [59,66], etc. Notably, Zeng et al applied a tetrabromobiphenyl molecular precursor with dibromo groups functionalized at the bay region of both sides and selectively fabricated biphenylene dimers containing four-, six-, and eight-membered rings on Ag (111) (figure 3(e)) [55]. Intriguingly, a unique reaction pathway was determined based on STM and synchrotron radiation photoemission spectroscopy.…”

Real-space visualization of sequential debromination of polybrominated benzenes on Ag(111)

“…5,11 To regulate the target nanostructures and reaction pathways of dehalogenation reactions, catalytic substrates, 12 kinetics, 13,14 thermodynamics, 13,15 and molecular precursors 16,17 have been subtly modified and controlled. The influence of substituents at different sites, 18 closely related to the precursor design, has also been extensively investigated in previous reports, where substituents could affect the dehalogenation sequence 19 as well as the reactivity of adjacent sites. 20 Moreover, distinct interaction with the substrate can greatly affect the activation sequence of symmetric sites through manipulation and thermal activation on surfaces.…”