Abstract
Halogen bonding (XB) with definite directivity and moderate strength like hydrogen bonding has been widely utilized in medical science, organic optoelectronics, and crystal engineering. Whereas, the mechanisms of hetero-halogen bonding (Br···S) induced 2D supramolecular self-assembly are still poorly understood. In this paper, an asymmetrical Br-substituted thiophene-based benzothiadiazole derivative (BTZ-Br) was selected as a building block to explore the self-assembly behaviors driven by XBs using scanning tunneling microscopy (STM). Besides, the short-chain solvents (heptanoic acid and nonanoic acid) and long-chain solvents (n-tridecane and n-tetradecane) were used to study the solvent effect on the BTZ-Br’s assemblies. The BTZ-Br molecules could form frame-like patterns on graphite in all solvents at relatively high concentrations. Whereas, at lower concentration, bamboo-like and linear arrangements were observed in short-chain solvents and long-chain solvents, respectively. Such structural difference is partially caused by the co-absorption of long-chain solvents, which changes the intermolecular bonding mode and stabilizes the molecular arrays via van der Waals forces between BTZ-Br and n-alkanes. Density functional theory (DFT) calculation further confirms the important role of XBs during assembling. This work is helpful for the in-depth understanding of XBs and may provide feasible guidance for the fabrication of novel 2D textures via XBs.
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