Busse Carsten, Weigelt Sigrid, Petersen Lars, Laegsgaard Erik, Besenbacher Flemming, Linderoth Trolle R, Thomsen Anne H, Nielsen Morten, Gothelf Kurt V
Interdisciplinary Nanoscience Center, iNANO, University of Aarhus, Aarhus C, Denmark.
J Phys Chem B. 2007 May 31;111(21):5850-60. doi: 10.1021/jp0707891. Epub 2007 May 9.
Adsorption structures formed from a class of planar organic molecules on the Au(111) surface under ultrahigh vacuum conditions have been characterized using scanning tunneling microscopy (STM). The molecules have different geometries, linear, bent, or three-spoke, but all consist of a conjugated aromatic backbone formed from three or four benzene rings connected by ethynylene spokes and functionalized at all ends with an aldehyde, a hydroxyl, and a bulky tert-butyl group. Upon adsorption, the molecules adopt different surface conformations some of which are chiral. For the majority of the observed adsorption structures, chirality is expressed also in the molecular tiling pattern, and the two levels of chirality display a high degree of correlation. The formation and chiral ordering of the self-assembled structures are shown to result from dynamic interchanges between a diffusing lattice gas and the nucleated islands, as well as from a chiral switching process in which molecules alter their conformation by an intramolecular rotation around a molecular spoke, enabling them to accommodate to the tiling pattern of the surrounding molecular structures. The kinetics of the conformational switching is investigated from time-resolved, variable temperature STM, showing the process to involve an activation energy of approximately 0.3 eV depending on the local molecular environment. The molecule-molecule interactions appear primarily to be of van der Waals character, despite the investigated compounds having functional moieties capable of forming intermolecular hydrogen bonds.
利用扫描隧道显微镜（STM）对一类平面有机分子在超高真空条件下于Au(111)表面形成的吸附结构进行了表征。这些分子具有不同的几何形状，线性、弯曲或三辐状，但均由由三个或四个通过乙炔辐条连接的苯环形成的共轭芳族主链组成，并在所有末端用醛基、羟基和庞大的叔丁基官能化。吸附后，分子采取不同的表面构象，其中一些是手性的。对于大多数观察到的吸附结构，手性也在分子平铺图案中表现出来，并且这两个手性水平显示出高度的相关性。自组装结构的形成和手性有序性表明是由扩散晶格气体与成核岛之间的动态交换以及手性转换过程导致的，在手性转换过程中分子通过围绕分子辐条的分子内旋转改变其构象，使其能够适应周围分子结构的平铺图案。从时间分辨、可变温度STM研究了构象转换的动力学，结果表明该过程涉及约0.3 eV的活化能，这取决于局部分子环境。尽管所研究的化合物具有能够形成分子间氢键的官能团，但分子间相互作用主要表现为范德华性质。
