Supramolecular organization of liquid-crystal dimers – bis-cyanobiphenyl alkanes on HOPG by scanning tunneling microscopy†,Nanoscale

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Supramolecular organization of liquid-crystal dimers – bis-cyanobiphenyl alkanes on HOPG by scanning tunneling microscopy†
Nanoscale ( IF 5.8 ) Pub Date : 2018-08-13 00:00:00 , DOI: 10.1039/c8nr02069h
Klaudyna Krzyżewska _{1,

2,

3,

4} , Tomasz Jaroch _{1,

2,

3,

4} , Agnieszka Maranda-Niedbała _{1,

2,

3,

4} , Damian Pociecha _{4,

5,

6,

7} , Ewa Górecka _{4,

5,

6,

7} , Ziauddin Ahmed _{8,

9,

10,

11} , Chris Welch _{8,

9,

10,

11} , Georg H. Mehl _{8,

9,

10,

11} , Adam Proń _{4,

6,

12,

13} , Robert Nowakowski _{1,

2,

3,

4}

Affiliation

2D supramolecular organization of a series of six cyanobiphenyls bimesogens deposited on highly oriented pyrolytic graphite (HOPG) is studied by scanning tunneling microscopy (STM). The adsorbates are 1,ω-bis(4-cyanobiphenyl-4′-yl)alkanes (CBnCB) with different lengths of their flexible alkyl spacer (containing from 7 to 12 methylene groups). Microscopic investigations at the molecular resolution allow for detailed analysis of the effect of the alkyl spacer length on the type and the extent of the resulting 2D organization. It was demonstrated that bimesogens with shorter spacers (7 and 8 methylene units) organize in a similar manner characterized by the formation of two types of differently ordered monolayers: dense packed, wherein the molecules are oriented in one direction and ordered into parallel rows (layer structure), or less densely packed where they are organized into a chiral windmill-like structure. For derivatives with longer spacers (ranging from 9 to 12 methylene units) the additional effect of parity of carbon atoms in the spacer (even versus odd) is observed. In this range of the spacer lengths even membered bimesogens are also organized in a typical layer structure. However, odd-membered dimers exhibit a much more complex 2D supramolecular organization with a larger unit cell and a helical arrangement of the molecules. Careful comparison of this structure with the 3D structural data derived from the X-ray diffraction investigations of single crystals indicates that for these bimesogens a clear correlation exists between the observed complex 2D supramolecular organization in the monolayer and the organization in one of the crystallographic planes of the 3D nematic twist-bent phase.

中文翻译：

液晶二聚体的超分子组织-通过扫描隧道显微镜†在HOPG上的双氰基联苯烷†

通过扫描隧道显微镜（STM）研究了沉积在高度取向的热解石墨（HOPG）上的一系列六个氰基联苯双生源分子的二维超分子组织。吸附物为1，ω-双（4-氰基联苯-4'-基）烷烃（CB nCB）具有不同长度的柔性烷基间隔基（包含7至12个亚甲基）。以分子分辨率进行的微观研究可以详细分析烷基间隔基长度对所得2D组织类型和范围的影响。已证明具有较短间隔基（7和8个亚甲基单元）的双生源素以相似的方式组织，其特征在于形成两种类型的不同有序的单层：密集堆积，其中分子沿一个方向取向并排列成平行行（层）结构），或者将它们组织成类似手性风车的结构，密度较小。对于具有更长间隔基（范围为9至12个亚甲基单元）的衍生物，间隔基中碳原子均等的附加影响（即使相对于奇数）。在间隔物长度的这个范围内，甚至成元的双生源素也以典型的层结构组织。但是，奇数元二聚体表现出更为复杂的2D超分子组织，具有更大的晶胞和分子的螺旋排列。将该结构与从单晶X射线衍射研究得出的3D结构数据进行仔细比较，结果表明，对于这些双生源而言，在单层中观察到的复杂2D超分子组织与在一个晶体平面中的组织之间存在明显的相关性。 3D向列扭曲弯曲阶段。

更新日期：2018-08-13

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