Concentration-Dependent Supramolecular Engineering of Hydrogen-Bonded Nanostructures at Surfaces: Predicting Self-Assembly in 2D

We report a joint computational and experimental study on the concentration-dependent self-assembly of a flat C-3-symmetric molecule at surfaces. As a model system we have chosen a rigid molecular module, 1,3,5-tris(pyridine-4-ylethynyl)benzene, which can undergo self-association via hydrogen bonding (H-bonding) to form ordered 2D nanostructures. In particular, the lattice Monte Carlo method, combined with density functional calculations, was employed to explore the spontaneous supramolecular organization of this tripod-shaped molecule under surface confinement. We analyzed the stability of different weak H-bonded patterns and the influence of the concentration of the starting molecule on the 2D supramolecular packing. We found that ordered, densely packed monolayers and 2D porous networks are obtained at high and low concentrations, respectively. A concentration-dependent scanning tunneling microscopy investigation of the molecular self-assembly at a graphite-solution interface revealed supramolecular motifs, which are in perfect agreement with those obtained by simulations. Therefore, our computational approach represents a step forward toward the deterministic prediction of molecular self-assembly at surfaces and interfaces.