Pinning-down molecules in their self-assemblies with multiple weak hydrogen bonds of C-H•••F and C-H•••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 C-H center dot center dot center dot F and C-H center dot center dot center dot 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 C-H center dot center dot center dot F and C-H center dot center dot center dot N can be efficiently applied to tune the molecular orientations and the self-assembly structures accordingly. (C) 2016 Chinese Chemical Society and Institute of Materia Medica, Chinese Academy of Medical Sciences. Published by Elsevier B.V. All rights reserved.