Substituted Septithiophenes with End Groups of Different Size: Packing and Frustration in Bulk and Thin Films
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- 作者：Wim H. de Jeu ; Khosrow Rahimi ; Ulrich Ziener ; Roman Vill ; Eva M. Herzig ; Peter Müller-Buschbaum ; Martin Möller ; Ahmed Mourran
- 刊名：Langmuir
- 出版年：2016
- 出版时间：February 16, 2016
- 年：2016
- 卷：32
- 期：6
- 页码：1533-1541
- 全文大小：554K
- ISSN：1520-5827
文摘
We report on three different liquid crystalline compounds with a central septithiophene core and alkylated end groups of strongly increasing bulkiness. In principle, the thiophene cores prefer to pack parallel to optimize their π–π interactions, which becomes sterically impossible for the bulkier end groups. Using X-ray diffraction, we find that the way out of this packing dilemma is toward liquid-crystal phases of higher dimensionality in the order smectic → columnar ↔ bicontinuous cubic. For the smectic phase, packing in a monolayer is no problem; for the other ones packing considerations become more stringent in films due to the boundaries. Surface X-ray techniques and atomic force microscopy indicate an appreciable difference between monolayer and three-layer films, in which the monolayers appear to escape from packing frustration by generating superstructures. We propose a basic structure of columns parallel to the substrate that provides a compromise between preserving some π–π interactions and packing the bulky alkyl groups.