Chemisorption Induced Formation of Biphenylene Dimer on Surfaces

TL;DR

This study demonstrates how different brominated biphenyl molecules react on Ag(111) surfaces, leading to distinct surface-supported reactions and the formation of specific polycyclic aromatic hydrocarbons, elucidated through combined experimental and theoretical methods.

Contribution

It reveals the surface-supported reaction pathways of brominated biphenyls and their dependence on molecular structure, advancing understanding of surface-induced molecular transformations.

Findings

Different brominated biphenyls lead to distinct reaction pathways.

Surface stabilization of radicals influences reaction outcomes.

Atomic-scale characterization of biphenylene dimers was achieved.

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-dibromo-biphenyl (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 bi-radical 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 the bond length alternation of biphenylene dimer product with atomic precision, which contains four-, six-, and eight-membered rings. The four-membered ring units turn out to be radialene structures.