Solvent Effect on Host–Guest Two-Dimensional Self-Assembly Mediated by Halogen Bonding

Host–guest self-assemblies of methyl 5-bromo-2-(hexadecyloxy)­benzoate (host) and 1-bromohexadecane (guest) molecules were investigated at the liquid/solid interface by scanning tunneling microscopy. Polar solvent (1-octanoic acid) and nonpolar solvents (1-phenyloctane, n-pentadecane, n-tetradecane, and n-decane) were selected to study the solvent effect on the self-assembly of the host–guest system. It is observed that the host–guest system self-assembles into different morphologies at low concentrations due to the solvent adsorption. Only a linear structure can be obtained at high concentration in different kinds of solvents. In particular, the different self-assembled patterns obtained at low concentration will eventually transform to the same linear structure. Owing to the participation of guest molecules, a strong Br···OC halogen bond is formed between host and guest molecules, further leading to the occurrence of physisorbed monolayers and structural transition. The density functional theory calculations are performed to reveal the underlying mechanisms of halogen bond formation.