Division of Frontier Materials Science, Graduate School of Engineering Science, Osaka University , Toyonaka, Osaka 560-8531, Japan.
Department of Chemistry and Beckman Institute for Advanced Science and Technology, University of Illinois at Urbana-Champaign , Urbana, Illinois 61801, United States.
Langmuir. 2017 Oct 31;33(43):12453-12462. doi: 10.1021/acs.langmuir.7b03007. Epub 2017 Oct 16.
We present here hexagonal tiling using hexagonal phenylene-ethynylene and phenylene-butadiynylene macrocycles attached by alkyl ester groups, PEM-C6 and PBM-C8, respectively, or triethylene glycol ester groups, PEM-TEG and PBM-TEG, respectively, at each vertex of the macrocyclic periphery at the liquid/solid interface. In this study, we focused on the effects of macrocyclic core size and the chemical properties of side chains attached to macrocyclic cores as well as solute concentrations on the hexagonal geometry of self-assembled monolayers. STM observations at the 1,2,4-trichrolobenzene/graphite interface revealed that PEM-C6 formed a honeycomb structure by van der Waals interactions between the interdigitated alkyl chains. However, upon increasing solute concentration, it changed to more dense hexagonal structure (tentatively called loose hexagonal structure I). In contrast, PBM-C8 formed loose hexagonal structure II of a slightly different packing mode at low concentration, while at high concentration it formed a high-density hexagonal structure in which alkyl chains are not adsorbed on the surface (dense hexagonal structure). In the dense hexagonal structure, macrocyclic cores are linked by hydrogen bonds between the ester carbonyl oxygen and the aromatic hydrogen atoms of the neighboring macrocycles. The packing geometries of loose hexagonal structures of PEM-C6 and PBM-C8 are different due to the different distance between the attachment of the alkyl ester groups which are located in confined space. On the other hand, PEM-TEG and PBM-TEG formed dense hexagonal structures, similar to PBM-C8 at high concentration, with their TEG units not adsorbed on the surface.
我们在此展示了使用通过烷基酯基团（分别为 PEM-C6 和 PBM-C8）或三乙二醇酯基团（分别为 PEM-TEG 和 PBM-TEG）连接在大环边缘每个顶点的六方苯并二乙炔和苯并丁二炔大环上的六方平铺。在这项研究中，我们主要关注大环核尺寸、连接到大环核上的侧链的化学性质以及溶质浓度对自组装单分子层的六方结构的影响。在 1,2,4-三氯苯/石墨界面上的 STM 观察表明，PEM-C6 通过互穿插的烷基链之间的范德华相互作用形成了蜂窝状结构。然而，随着溶质浓度的增加，它转变为更密集的六方结构（暂称为疏松六方结构 I）。相比之下，PBM-C8 在低浓度时形成了略微不同堆积模式的疏松六方结构 II，而在高浓度时，它形成了一种高密度的六方结构，其中烷基链不吸附在表面上（密集六方结构）。在密集六方结构中，大环核通过酯羰基氧和相邻大环的芳环氢原子之间的氢键连接。PEM-C6 和 PBM-C8 的疏松六方结构的堆积几何形状不同，这是由于连接在受限空间中的烷基酯基团的位置不同所致。另一方面，PEM-TEG 和 PBM-TEG 在高浓度时形成类似于 PBM-C8 的密集六方结构，其 TEG 单元不吸附在表面上。
