Zhang Zhipeng, Zhao Xiaoyang, Miao Xinrui, Deng Wenli
College of Materials Science and Engineering, South China University of Technology, Guangzhou 510640, People's Republic of China.
Langmuir. 2024 Aug 20;40(33):17826-17834. doi: 10.1021/acs.langmuir.4c02528. Epub 2024 Aug 8.
Scanning tunneling microscopy (STM) is a powerful way to realize the recognition of self-assembled nanostructures on the atomic scale. In this article, dihexadecyl 6,9-bis((4-(hexadecyloxy)phenyl)ethynyl) phenanthro[9,10-]thiophene-1,3-dicarboxylate (D-PT) and dihexadecyl 6-bromo-9-((4-(hexadecyloxy) phenyl)ethynyl)phenanthrol[9,10-]thiophene-1,3-dicarboxylate (S-BrPT) with different substituents were chosen as the target system. D-PT with four side chains as the target molecule and S-BrPT with three side chains and a bromine substituent as the byproduct were mixed in a molar concentration ratio of 20:1. The effect of solution concentration on the molecular self-assembly of the mixture was investigated by STM at the hexadecane/HOPG interface. At high concentrations, only D-PT molecules formed a dimer pattern resulting from the intermolecular van der Waals force and self-adaption. Further diluting the solution, D-PT formed the coexisting dimer and linear structures, in which the linear pattern was formed via solvent coadsorption. At low concentrations, S-BrPT molecules forming N-shaped dimers appeared and filled the linear structure fabricated by D-PT molecules. With further decrease in the concentration, S-BrPT molecules formed N-shaped dimers covering almost half of the surface area, resulting from the C-Br···π and Br···H-C bonds. At very low concentrations, S-BrPT molecules formed N-shaped dimers to arrange the matrix architecture due to the coadsorption of more hexadecane molecules. Density functional theory (DFT) calculations demonstrated that the stronger intermolecular C-Br···π and Br···H-C bonds were significant factors in determining the formation of N-shaped dimers and the stability of this nanostructure. This work enriches the diversity of self-assembled motifs and provides a strategy to characterize different symmetric molecules with trace amounts in a mixed system by STM.
扫描隧道显微镜（STM）是一种在原子尺度上实现对自组装纳米结构进行识别的强大方法。在本文中，选择了具有不同取代基的二十六烷基 6,9 - 双（（4 - （十六烷氧基）苯基）乙炔基）菲并[9,10 - ]噻吩 - 1,3 - 二羧酸酯（D - PT）和二十六烷基 6 - 溴 - 9 - （（4 - （十六烷氧基）苯基）乙炔基）菲并[9,10 - ]噻吩 - 1,3 - 二羧酸酯（S - BrPT）作为目标体系。将具有四条侧链的 D - PT 作为目标分子，与具有三条侧链和一个溴取代基的 S - BrPT 副产物以 20:1 的摩尔浓度比混合。通过 STM 在十六烷/HOPG 界面研究了溶液浓度对混合物分子自组装的影响。在高浓度下，仅 D - PT 分子由于分子间范德华力和自适应性形成二聚体图案。进一步稀释溶液，D - PT 形成共存的二聚体和线性结构，其中线性图案是通过溶剂共吸附形成的。在低浓度下，形成 N 形二聚体的 S - BrPT 分子出现并填充由 D - PT 分子构建的线性结构。随着浓度进一步降低，S - BrPT 分子形成覆盖几乎一半表面积的 N 形二聚体，这是由 C - Br···π 和 Br···H - C 键导致的。在极低浓度下，由于更多十六烷分子的共吸附，S - BrPT 分子形成 N 形二聚体来排列基质结构。密度泛函理论（DFT）计算表明，较强的分子间 C - Br···π 和 Br···H - C 键是决定 N 形二聚体形成和这种纳米结构稳定性的重要因素。这项工作丰富了自组装基序的多样性，并提供了一种通过 STM 表征混合体系中痕量不同对称分子的策略。
