A spectroscopic study of self-assembled monolayer of porphyrin-functionalized oligo(phenyleneethynylene)s on gold: the influence of the anchor moiety
作者:Somsakul Watcharinyanon、Daniel Nilsson、Ellen Moons、Andrey Shaporenko、Michael Zharnikov、Bo Albinsson、Jerker Mårtensson、Lars S. O. Johansson
DOI:10.1039/b802914h
日期:——
Porphyrin-functionalized oligo(phenyleneethynylene)s (OPE) are promising molecules for molecular electronics applications. Three such molecules (1–3) with the common structure P–OPE–AG (P and AG are a porphyrin and anchor group, respectively) and different anchor groups, viz. an acetyl protected thiol, –S–COCH3 (1), an acetyl protected thiol with methylene linker, –CH2–S–COCH3 (2), and a trimethylsilylethynyl group, –CC–Si(CH3)3 (3) have been synthesized and the corresponding self-assembled monolayers (SAMs) on Au(111) substrates have been prepared. The integrity and structural properties of these films were studied by X-ray photoelectron spectroscopy and near-edge X-ray absorption fine structure spectroscopy. The results suggest that the films formed from 1 have a high orientational order with an almost upright orientation and dense packing of the molecular constituents, i.e. represent a high quality SAM. In contrast, molecule 2 formed disordered molecular layers on Au, even though the molecule–surface bonding (thiolate) is the same as in the case of molecule 1. This suggests that the methylene linker in molecule 2 has a strong impact on the quality of the resulting film, so that a well-ordered SAM cannot be formed. The silane system, 3, is also able to bind to the gold surface but the resulting SAM has a poor quality, being significantly disordered and/or comprised of strongly inclined molecules. The above results suggest that the nature of the anchor group along with a possible linker is an important parameter which, to a high extent, predetermines the entire quality of OPE-based molecular layers.
卟啉功能化低聚亚苯基乙炔基 (OPE) 是分子电子学应用中很有前景的分子。三个这样的分子(1-3)具有共同结构P-OPE-AG(P和AG分别是卟啉和锚定基团)和不同的锚定基团,即。已合成乙酰基保护的硫醇 –S–COCH3 (1)、带亚甲基连接基的乙酰基保护的硫醇 –CH2–S–COCH3 (2) 和三甲基甲硅烷基乙炔基 –CC–Si(CH3)3 (3)并在Au(111)基底上制备了相应的自组装单层(SAM)。通过X射线光电子能谱和近边X射线吸收精细结构光谱研究了这些薄膜的完整性和结构特性。结果表明,由 1 形成的薄膜具有高取向顺序,几乎垂直取向且分子成分紧密堆积,即代表了高质量的 SAM。相比之下,分子 2 在 Au 上形成无序分子层,尽管分子-表面键合(硫醇盐)与分子 1 的情况相同。这表明分子 2 中的亚甲基连接体对金的质量有很大影响。所得薄膜,从而无法形成良好有序的SAM。硅烷系统 3 也能够结合到金表面,但所得 SAM 质量较差,明显无序和/或由强烈倾斜的分子组成。上述结果表明,锚定基团的性质以及可能的连接体是一个重要参数,它在很大程度上预先确定了基于 OPE 的分子层的整体质量。