Department of Chemistry, University of Copenhagen , Universitetsparken 5, DK-2100 Copenhagen Ø, Denmark.
Kavli Institute of Nanoscience, Delft University of Technology , Lorentzweg 1, 2628 CJ Delft, The Netherlands.
J Org Chem. 2016 Sep 16;81(18):8406-14. doi: 10.1021/acs.joc.6b01579. Epub 2016 Sep 1.
Development of molecules that can switch between redox states with paired and unpaired electrons is important for molecular electronics and spintronics. In this work, a selection of redox-active indenofluorene-extended tetrathiafulvalenes (IF-TTFs) with thioacetate end groups was prepared from a readily obtainable dibromo-functionalized IF-TTF building block using palladium-catalyzed cross-coupling reactions, such as the Suzuki reaction. The end groups served as electrode anchoring groups for single-molecule conductance studies, and the molecules were subjected to mechanically controlled break-junction measurements with gold contacts and to low-bias charge transport measurements in gated three-terminal electromigration junctions. The neutral molecules showed clear conductance signatures, and somewhat surprisingly, we found that a meta-meta anchoring configuration gave a higher conductance than a para-meta configuration. We explain this behavior by "through-space" coupling between the gold electrode and the phenyl on which the anchoring group is attached. Upon charging the molecule in a gated junction, we found reproducibly a Kondo effect (zero-bias conductance) attributed to a net spin. Ready generation of radical cations was supported by cyclic voltammetry measurements, revealing stepwise formation of radical cation and dication species in solution. The first oxidation event was accompanied by association reactions as the appearance of the first oxidation peak was strongly concentration dependent.
开发能够在具有配对和非配对电子的氧化还原态之间切换的分子对于分子电子学和自旋电子学很重要。在这项工作中，从一种容易获得的二溴官能化 IF-TTF 构建块中，使用钯催化的交叉偶联反应（如 Suzuki 反应）制备了一系列具有硫乙酸端基的氧化还原活性的茚并氟烯扩展四硫富瓦烯（IF-TTF）。端基作为单分子电导研究的电极锚定基团，并用金接触进行机械控制的断键测量，并在门控三端电迁移结中进行低偏压电荷传输测量。中性分子表现出明显的电导特征，令人惊讶的是，我们发现元-元锚定构型比对位-元构型具有更高的电导。我们通过附着在锚定基团上的苯基和金电极之间的“隔空”耦合来解释这种行为。在门控结中对分子进行充电时，我们重复发现了归因于净自旋的科顿效应（零偏压电导）。循环伏安测量支持自由基阳离子的快速生成，这表明在溶液中逐步形成自由基阳离子和二价阳离子物种。第一个氧化事件伴随着缔合反应，因为第一个氧化峰的出现强烈依赖于浓度。
