Department of Chemistry, National University of Singapore, 3 Science Drive 3, Singapore 117543.
Nat Nanotechnol. 2013 Feb;8(2):113-8. doi: 10.1038/nnano.2012.238. Epub 2013 Jan 6.
One of the main goals of organic and molecular electronics is to relate the performance and electronic function of devices to the chemical structure and intermolecular interactions of the organic component inside them, which can take the form of an organic thin film, a self-assembled monolayer or a single molecule. This goal is difficult to achieve because organic and molecular electronic devices are complex physical-organic systems that consist of at least two electrodes, an organic component and two (different) organic/inorganic interfaces. Singling out the contribution of each of these components remains challenging. So far, strong π-π interactions have mainly been considered for the rational design and optimization of the performances of organic electronic devices, and weaker intermolecular interactions have largely been ignored. Here, we show experimentally that subtle changes in the intermolecular van der Waals interactions in the active component of a molecular diode dramatically impact the performance of the device. In particular, we observe an odd-even effect as the number of alkyl units is varied in a ferrocene-alkanethiolate self-assembled monolayer. As a result of a more favourable van der Waals interaction, junctions made from an odd number of alkyl units have a lower packing energy (by ∼0.4-0.6 kcal mol(-1)), rectify currents 10 times more efficiently, give a 10% higher yield in working devices, and can be made two to three times more reproducibly than junctions made from an even number of alkyl units.
有机和分子电子学的主要目标之一是将器件的性能和电子功能与其内部有机成分的化学结构和分子间相互作用联系起来，有机成分可以是有机薄膜、自组装单层或单个分子。这一目标很难实现，因为有机和分子电子器件是复杂的物理有机系统，至少由两个电极、一个有机成分和两个（不同的）有机/无机界面组成。要单独确定这些组成部分中的每一个的贡献仍然具有挑战性。到目前为止，主要考虑强π-π相互作用来合理设计和优化有机电子器件的性能，而忽略了较弱的分子间相互作用。在这里，我们通过实验表明，分子二极管的有源组件中分子范德华相互作用的细微变化会显著影响器件的性能。具体来说，我们观察到在二茂铁-烷硫醇自组装单层中烷基单元数量变化时出现奇偶效应。由于范德华相互作用更有利，由奇数个烷基单元组成的结具有更低的堆积能（约 0.4-0.6 kcal/mol），整流电流的效率提高了 10 倍，在工作器件中具有 10%的更高产率，并且比由偶数个烷基单元组成的结更可重复地制成两倍至三倍。
