Solvent Effect on Halogen-Bonded Self-Assembled Nanostructures of a 2,9-Dibromo-Phenanthridine Derivative at the Liquid–Solid Interface

Abstract

Probing the halogen-bonded nanostructures of two-dimensional (2D) supramolecular self-assembly is essential to understand and engineer the nature of halogen bonding. However, exploring the formation mechanism of the halogen bond still remains a challenge because it is a new weak noncovalent interaction. Herein, we introduce nitrogen atoms and Br groups in the conjugated core to synthesize 2,9-dibromo-6-(hexadecyloxy)phenanthridine (2,9-DHP) in order to fabricate multiple action sites of halogen bonds. We investigate the solvent effect on the 2D molecular self-assembly at the liquid–solid interface by using scanning tunneling microscopy. 1-Octanoic acid, n-tridecane, n-tetradecane, and n-hexadecane are chosen as the solvents. The coadsorption of 1-octanoic acid molecules at low concentrations by the molecule–solvent Br···O halogen bonds could change the molecular arrangement. n-Tridecane, n-tetradecane, and n-hexadecane also coadsorb in the adlayers; however, the molecular packing and intermolecular interactions of 2,9-DHP remain the same at different solution concentrations. The results demonstrate that the molecule–molecule N···Br···H halogen bonds are strong enough to overcome the transformation of intermolecular interactions.