School of Chemistry, The University of New South Wales , Sydney, New South Wales 2052, Australia.
Acc Chem Res. 2014 Feb 18;47(2):385-95. doi: 10.1021/ar400127g. Epub 2013 Oct 28.
Electron transfer (ET) reactions through molecules attached to surfaces, whether they are through single molecules or ensembles, are the subject of much research in molecular electronics, bioelectronics, and electrochemistry. Therefore, understanding the factors that govern ET is of high importance. The availability of rigid hydrocarbon molecular scaffolds possessing well-defined configurations and lengths that can be systematically varied is crucial to the development of such devices. In this Account, we demonstrate how suitably functionalized norbornylogous (NB) systems can provide important insights into interfacial ET processes and electrical conduction through single molecules. To this end, we created NB bridges with vic-trans-bismethylenethiol groups at one end so they can assemble on gold electrodes and redox species at the distal ends. With these in hand, we then formed mixed self-assembled monolayers (SAMs) containing a small proportion of the NB bridges diluted with alkanethiols. As such, the NB bridges served as molecular rulers for probing the environment above the surface defined by the diluent species. Using this construct, we were able to measure the interfacial potential distribution above the diluent surface, and track how variation in the ionic distribution in the electrical double layer impacts ET kinetics. Using the same construct, but with a redox molecule that remains neutral in both oxidized and reduced states, we could explore the impact of the chemical environment near a surface on ET processes. These results are important, because with conventional surface constructs, ET occurs across this interfacial region. Such knowledge is therefore relevant to the design of molecular systems at surfaces involving ET. With a second family of molecules, we investigated aspects of single-molecule electrical conduction using NB bridges bearing vic-trans-bismethylenethiol groups at both ends of the bridge. This gave us insights into distance-dependent electron transport through single molecules and introduced a method of boosting the conductance of saturated molecules by incorporating aromatic moieties in their backbone. These partially conjugated NB molecules represent a new class of molecular wires with far greater stability than conventional completely conjugated molecular wires. Of particular note was our demonstration of a single molecule switch, using a NB bridge containing an embedded anthraquinone redox group, the switching mechanism being via electrochemically controlled quantum interference.
电子转移（ET）反应通过附着在表面上的分子进行，无论是通过单个分子还是分子集合，都是分子电子学、生物电子学和电化学研究的主题。因此，了解控制 ET 的因素非常重要。具有明确配置和长度的刚性碳氢分子支架的可用性可以系统地进行变化，对于此类设备的发展至关重要。在本报告中，我们展示了如何通过适当官能化的降冰片烷（NB）系统为界面 ET 过程和通过单个分子的电传导提供重要见解。为此，我们在一端创建了具有顺式双亚甲基硫醇基团的 NB 桥，以便它们可以在金电极上组装，并在远端处形成氧化还原物质。有了这些，我们然后形成了包含少量 NB 桥的混合自组装单层（SAM），用烷硫醇稀释。因此，NB 桥充当了用于探测由稀释剂物种定义的表面上方环境的分子标尺。使用该结构，我们能够测量稀释剂表面上方的界面势分布，并跟踪双电层中离子分布的变化如何影响 ET 动力学。使用相同的结构，但使用在氧化和还原状态下均保持中性的氧化还原分子，我们可以探索表面附近化学环境对 ET 过程的影响。这些结果很重要，因为在传统的表面结构中，ET 发生在这个界面区域。因此，这种知识与涉及 ET 的表面上的分子系统设计有关。使用 NB 桥在桥的两端都带有顺式双亚甲基硫醇基团的第二组分子，我们研究了 NB 桥的单分子电传导的各个方面。这使我们深入了解了通过单个分子的距离依赖性电子传输，并引入了一种通过在其主链中包含芳族部分来提高饱和分子电导的方法。这些部分共轭的 NB 分子代表了一类具有比传统完全共轭分子线更高稳定性的新型分子线。值得注意的是，我们使用含有嵌入的蒽醌氧化还原基团的 NB 桥演示了单个分子开关，其开关机制是通过电化学控制的量子干涉。
