Godlewski Szymon, Engelund Mads, Peña Diego, Zuzak Rafał, Kawai Hiroyo, Kolmer Marek, Caeiro Jorge, Guitián Enrique, Vollhardt K Peter C, Sánchez-Portal Daniel, Szymonski Marek, Pérez Dolores
Centre for Nanometer-Scale Science and Advanced Materials, NANOSAM, Faculty of Physics, Astronomy and Applied Computer Science, Jagiellonian University, Lojasiewicza 11, PL 30-348 Krakow, Poland.
Phys Chem Chem Phys. 2018 Apr 25;20(16):11037-11046. doi: 10.1039/c8cp01094c.
Understanding the mechanisms involved in the covalent attachment of organic molecules to surfaces is a major challenge for nanotechnology and surface science. On the basis of classical organic chemistry mechanistic considerations, key issues such as selectivity and reactivity of the organic adsorbates could be rationalized and exploited for the design of molecular-scale circuits and devices. Here we use tris(benzocyclobutadieno)triphenylene, a singular Y-shaped hydrocarbon containing antiaromatic cyclobutadienoid rings, as a molecular probe to study the reaction of polycyclic conjugated molecules with atomic scale moieties, dangling-bond (DB) dimers on a hydrogen-passivated Ge(001):H surface. By combining molecular design, synthesis, scanning tunneling microscopy and spectroscopy (STM/STS) and computational modeling, we show that the attachment involves a concerted [4+2] cycloaddition reaction that is completely site-selective and fully reversible. This selectivity, governed by the bond alternation induced by the presence of the cyclobutadienoid rings, allows for the control of the orientation of the molecules with respect to the surface DB-patterning. We also demonstrate that by judicious modification of the electronic levels of the polycyclic benzenoid through substituents, the reaction barrier height can be modified. Finally, we show that after deliberate tip-induced covalent bond cleavage, adsorbed molecules can be used to fine tune the electronic states of the DB dimer. This power to engineer deliberately the bonding configuration and electronic properties opens new perspectives for creating prototypical nanoscale circuitry.
理解有机分子与表面共价连接所涉及的机制是纳米技术和表面科学面临的一项重大挑战。基于经典有机化学的机理考量，诸如有机吸附质的选择性和反应性等关键问题可以得到合理阐释，并用于分子尺度电路和器件的设计。在此，我们使用三（苯并环丁二烯）三亚苯基，一种含有反芳香性环丁二烯类环的独特 Y 形烃，作为分子探针来研究多环共轭分子与原子尺度部分，即氢钝化 Ge(001):H 表面上的悬空键（DB）二聚体之间的反应。通过结合分子设计、合成、扫描隧道显微镜和光谱学（STM/STS）以及计算建模，我们表明该连接涉及协同的 [4+2] 环加成反应，该反应具有完全的位点选择性且完全可逆。这种选择性由环丁二烯类环的存在所诱导的键交替所控制，使得能够控制分子相对于表面 DB 图案的取向。我们还证明，通过用取代基对多环苯类的电子能级进行明智的修饰，可以改变反应势垒高度。最后，我们表明在经过有意的针尖诱导共价键断裂后，吸附的分子可用于微调 DB 二聚体的电子态。这种有意设计键合构型和电子性质的能力为创建原型纳米级电路开辟了新的前景。
