Odd–Even Effect in the Surface Structure of Alkyloxy-Substituted Anthraquinone on HOPG Observed by Scanning Tunneling Microscope
作者:Yoshinori Tamaki、Kosuke Muto、Kazuo Miyamura
DOI:10.1246/bcsj.20120283
日期:2013.3.15
Self-assembled adlayers of a series of anthraquinone derivatives, 2-alkoxyanthraquinone (n-ant, n = 14, 15, 16, 17, 18, 20, and 22) where n stands for the alkyl (CnH2n+1) chain length, on highly oriented pyrolytic graphite (HOPG) surface are investigated by scanning tunneling microscope (STM). Anthraquinone derivatives are found to form C–H···O hydrogen-bonded dimers. However, the self-assembled 2D pattern of monolayer depends on the parity (odd/even) of carbon atoms and the length of the alkyl chains. When n is even in number, the aggregating structure in the monolayer is interdigitated lamellar structure. The specific feature of these lamellae is the propagation of dislocations. The frequency of dislocation increased as the alkyl chain elongated. However, when n is odd in number, molecules adopt different conformation (type B) and the aggregating structure changes drastically. This indicates that the orientation of the terminal methyl of the alkyl group induces the surface structural change, i.e., the odd–even effect.
自组装的层合物由一系列蒽醌衍生物构成,包括2-烷氧基蒽醌(n-ant,n = 14, 15, 16, 17, 18, 20和22),其中n代表烷基(CnH2n+1)链的长度,这些层合物在高度定向的热解石墨(HOPG)表面上通过扫描隧道显微镜(STM)进行研究。研究发现,蒽醌衍生物形成了C–H···O氢键二聚体。然而,自组装的单层二维模式则取决于碳原子的奇偶性(奇数/偶数)和烷基链的长度。当n为偶数时,单层中的聚集结构为交错的层状结构。这些层状结构的一个特征是位错的传播。随着烷基链的延长,位错的频率增加。然而,当n为奇数时,分子采用不同的构象(B型),聚集结构发生显著变化。这表明,烷基末端甲基的取向引发了表面结构的变化,即奇偶效应。