Maranda-Niedbała Agnieszka, Jaroch Tomasz, Walker Rebecca, Pięta Piotr, Górecka Ewa, Imrie Corrie T, Storey John Md, Proń Adam, Nowakowski Robert
Institute of Physical Chemistry, Polish Academy of Sciences, Kasprzaka 44/52, Warszawa 01-224, Poland.
Faculty of Chemistry, Warsaw University of Technology, Noakowskiego 3, Warszawa 00-664, Poland.
Langmuir. 2025 Apr 15;41(14):9508-9519. doi: 10.1021/acs.langmuir.5c00551. Epub 2025 Apr 2.
Two-dimensional (2D) supramolecular organization of asymmetric liquid crystal dimers containing two chemically different mesogenic groups, namely, cyanobiphenyl and pyreneiminomethyl phenoxy groups, linked with an oligomethylene linker of different length (six or eight -CH- units), was studied using scanning tunneling microscopy. For this purpose, monolayers of these dimers were deposited on an HOPG substrate from their solutions in hexane by drop-casting and imaged at nanometer resolution after drying. A detailed discussion of two possible different supramolecular organizations is presented. In the case of the first one, termed the "lamellar structure", the molecules in each layer are arranged in parallel molecular rows. Comparative analysis of the monolayer structure with already reported XRD data on 3D organization of the same molecules in a single crystal revealed significant differences resulting from (i) different ordering preferences in 2D and 3D systems and (ii) effects of the interactions of the deposited molecules with the graphite substrate. A small extension of the linker by two methylene groups does not change the type of ordering in the monolayer but causes an extension of the unit cell in one direction, indicating that the lamellar structure is stabilized by rows of densely packed large aromatic pyrene units. Studies of the derivative with a longer linker (containing eight -CH- units) also showed the possibility of the occurrence of an alternative type of its monolayer organization, termed here "aggregate structure". In this case, the monolayer consists of ordered aggregates of two molecules. According to the authors' knowledge, this type of structural organization has not yet been reported for this family of compounds. It is, however, qualitatively consistent with the already described supramolecular ordering in CBO5O.Py (CCDC 2019485), a compound closely resembling the dimers studied in this research.
利用扫描隧道显微镜研究了含有两个化学性质不同的介晶基团（即氰基联苯和芘亚胺甲基苯氧基）的不对称液晶二聚体的二维（2D）超分子结构，这两个介晶基团通过不同长度（六个或八个 -CH- 单元）的低聚亚甲基连接基团相连。为此，通过滴铸法将这些二聚体的单层从其在己烷中的溶液沉积在高定向热解石墨（HOPG）衬底上，并在干燥后以纳米分辨率成像。文中给出了两种可能的不同超分子结构的详细讨论。在第一种情况中，称为“层状结构”，每层中的分子排列成平行的分子行。将该单层结构与已报道的同一分子在单晶中的三维组织的X射线衍射（XRD）数据进行比较分析，发现存在显著差异，这是由于（i）二维和三维系统中不同的有序偏好，以及（ii）沉积分子与石墨衬底相互作用的影响。连接基团延长两个亚甲基并不会改变单层中的有序类型，但会导致晶胞在一个方向上的延伸，这表明层状结构是由紧密堆积的大芳香芘单元行稳定的。对具有更长连接基团（含有八个 -CH- 单元）的衍生物的研究还表明，其单层结构可能会出现另一种类型，在此称为“聚集体结构”。在这种情况下，单层由两个分子的有序聚集体组成。据作者所知，该化合物家族尚未报道过这种结构组织类型。然而，这在定性上与已经描述的CBO5O.Py（CCDC 2019485）中的超分子有序性一致，CBO5O.Py是一种与本研究中所研究的二聚体非常相似的化合物。
