Hierarchical On-Surface Synthesis of Two-Dimensional Networks via Multipoint SN and SH Bonding

Although electrostatic bonding between chalcogen (Ch) atoms (O, S, Se, and Te) and nitrogen (N) has emerged as a powerful driving force in the fabrication of supramolecular structures; this noncovalent bond has not yet been used to link polymers to form networks. In this study, we took advantage of additive enthalpy in forming multipoint noncovalent bonds to construct a two-dimensional (2D) network via the hierarchical on -surface synthesis of linear polymer chains, followed by multipoint S center dot center dot center dot N and S center dot center dot center dot H bonding. When 4,7-dibromobenzo[c][1,2,5]thiadia- zole was used, only short oligomers with embedded bromine atoms and cross -linked byproducts were formed on Ag(111) or Au(111) surfaces after multiple annealing procedures, and no 2D network was observed. By changing the precursor to a similar iodinesubstituted molecule, long linear polymers were generated and assembled with iodine atoms on Au(111) after annealing at 523 K. After annealing at 603 K, iodine atoms were desorbed and polymer chains were assembled via multipoint noncovalent bonding. The 2D network remained intact after annealing at 653 K, demonstrating its high thermostability. The multipoint noncovalent bonds were investigated by the combination of scanning tunneling microscopy, noncontact atomic force microscopy, and density functional theory calculations, which revealed that S center dot center dot center dot N and S center dot center dot center dot H bonding were the driving forces to construct thermostable and orderly 2D networks.