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.
@article{arxiv.2309.05341,
title = {Chemisorption Induced Formation of Biphenylene Dimer on Surfaces},
author = {Zhiwen Zeng and Dezhou Guo and Tao Wang and Qifan Chen and Adam Matěj and Jianmin Huang and Dong Han and Qian Xu and Aidi Zhao and Pavel Jelínek and Dimas G. de Oteyza and Jean-Sabin McEwen and Junfa Zhu},
journal= {arXiv preprint arXiv:2309.05341},
year = {2023}
}