Pinning-down molecules in their self-assemblies with multiple weak hydrogen bonds of CH⋯F and CH⋯N

Two-dimensional self-assemblies of four partially fluorinated molecules, 1,4-bis(2,6-difluoropyridin-4-yl)benzene, 4,4′-bis(2,6-difluoropyridin-4-yl)-1,1′-biphenyl, 4,4′-bis(2,6-difluoropyridin-4-yl)-1,1′:4′,1″-terphenyl and 4,4′-bis(2,6-difluoropyridin-3-yl)-1,1′-biphenyl, involving weak intermolecular CH⋯F and CH⋯N hydrogen bonds were systematically investigated on Au(111) with low-temperature scanning tunneling microscopy. The inter-molecular connecting modes and binding sites were closely related to the backbones of the building blocks, i.e., the molecule length determines its binding sites with neighboring molecules in the assemblies while the attaching positions of the N and F atoms dictate its approaching and docking angles. The experimental results demonstrate that multiple weak hydrogen bonds such as CH⋯F and CH⋯N can be efficiently applied to tune the molecular orientations and the self-assembly structures accordingly.