Monolayer Properties of Asymmetrically Substituted Sexithiophene

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• 作者：Jingbo Wang ; Wim H. de Jeu ; Ulrich Ziener ; Marina S. Polinskaya ; Sergei A. Ponomarenko ; Ulrich Ruecker ; Matthias A. Ruderer ; Eva M. Herzig ; Peter M眉ller-Buschbaum ; Martin Moeller ; Ahmed Mourran
• 刊名：Langmuir
• 出版年：2014
• 出版时间：March 18, 2014
• 年：2014
• 卷：30
• 期：10
• 页码：2752-2760
• 全文大小：541K
• 年卷期：v.30,no.10(March 18, 2014)
• ISSN：1520-5827

文摘

We present a structural comparison of monolayers on a SiO₂ substrate of two asymmetrically substituted sexithiophenes (6T). Molecule 1 consists of 6T with a branched alkyl chain at one end only and shows a crystalline structure. In molecule 2, the bifunctional 6T has in addition at the other end a linear alkyl chain. It displays thermotropic liquid crystalline (LC) behavior. Both compounds form readily single molecular layers from solution. Remarkably, full monolayer coverage can be achieved before multilayer growth starts. LC properties promote preordering near the interface as well as exchange of molecules between the growing domains, thus regulating the domain sizes. As a result, the LC compound 2 forms single-molecule islands with larger domain sizes compared to compound 1. Surface X-ray investigations indicate that the 6T cores are tilted relative to the layer normal. The tilt angle is as large as 54掳 for compound 2 compared to 28掳 for compound 1. For molecule 2, interfacial constraints and packing requirements because of the asymmetric substitution cause a rather loosely organized core structure.