Understanding the Properties of Tailor-Made Self-Assembled Monolayers with Embedded Dipole Moments for Interface Engineering
Understanding the Properties of Tailor-Made Self-Assembled Monolayers with Embedded Dipole Moments for Interface Engineering
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DOI：
10.1021/acs.jpcc.8b09440
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发表时间：
2018-12-20
影响因子：
3.7
通讯作者：
Zharnikov, Michael
中科院分区：
文献类型：
--
作者：
Gaertner, Michael;Sauter, Eric;Zharnikov, Michael
自组装单分子膜（SAMs）是有机电子学和光电子学中常用的界面偶极工程。这主要通过将偶极尾基连接到SAM前体的分子主链上来完成。嵌入偶极子的替代概念涉及将极性基团并入主链中。这允许将SAM的静电性质的调谐与SAM-环境界面的化学特性解耦。在这里，我们提出了设计和合成特别有前途的SAM前体利用这一概念。这些前体具有硫醇对接基团和短的杂芳族主链，由非极性苯环和极性嘧啶基团组成，以两个相反的方向嵌入。堆积密度，分子取向，结构和润湿性能的自组装膜上的Au基板被发现是几乎独立于它们的化学结构，所示的各种互补的实验技术。所研究的自组装膜的另一个重要性质是其良好的导电性，使其能够用作有机电子器件中低接触电阻的电极改性剂。特别感兴趣的是自组装膜的电子性质，这是监测开尔文探针和高分辨率X射线光电子能谱测量。为了在原子水平上对这些性质有一个基本的了解，这些实验与最先进的能带结构计算相结合。这些不仅证实了薄膜的结构特性，而且还解释了C是如何通过其化学环境结合单层内的静电势的局部分布来控制各种原子的核心能级结合能的。
Self-assembled monolayers (SAMs) are frequently used for interfacial dipole engineering in organic electronics and photovoltaics. This is mostly done by the attachment of dipolar tail groups onto the molecular backbone of the SAM precursors. The alternative concept of embedded dipoles involves the incorporation of polar group(s) into the backbone. This allows one to decouple the tuning of the electrostatic properties of the SAM from the chemical identity of the SAM-ambient interface. Here we present design and synthesis of particularly promising SAM precursors utilizing this concept. These precursors feature the thiol-docking group and a short heteroaromatic backbone, consisting of a nonpolar phenyl ring and a polar pyrimidine group, embedded in two opposite orientations. Packing density, molecular orientation, structure, and wetting properties of the SAMs on Au substrates are found to be nearly independent of their chemical structure, as shown by a variety of complementary experimental techniques. A further important property of the studied SAMs is their good electrical conductivity, enabling their application as electrode modifiers for low-contact resistances in organic electronic devices. Of particular interest are also the electronic properties of the SAMs, which were monitored by Kelvin probe and high-resolution X-ray photoelectron spectroscopy measurements. To obtain a fundamental understanding of these properties at an atomistic level, the experiments were combined with state-of-the-art band structure calculations. These not only confirm the structural properties of the films but also explain how the C is core-level binding energies of the various atoms are controlled by their chemical environments in conjunction with the local distribution of the electrostatic potential within the monolayer.