Construction of Acylhydrazone-Linked Single-layer Covalent Organic Frameworks on the Surface

Single-layer covalent organic frameworks (SCOFs), featuring atomically thin and ordered networks with diverse functionality, are widely studied due to their unique structure–property relationship. Here, we constructed acylhydrazone-linked SCOFs via on-surface synthesis, and ordered framework structures were obtained using p-toluenesulfonic acid as a catalyst. Scanning tunneling microscopy (STM) revealed the formation of hcb and hxl topologies through the reversible dehydration reaction of linear acylhydrazine with different aldehyde organic building blocks. By the modulation of precursor molar ratios, the structural evolution of monomer assemblies, acylhydrazone-linked oligomers, and SCOFs has been systematically investigated. The incorporation of acylhydrazone linkages enhances the stability of these frameworks. The construction of acylhydrazone-linked SCOFs further diversifies the classes of surface covalent nanostructures.