Department of Chemistry, Columbia University, New York, New York 10027, United States.
J Am Chem Soc. 2011 Feb 23;133(7):2136-9. doi: 10.1021/ja111320n. Epub 2011 Jan 25.
Understanding electron transport across π-π-stacked systems will help to answer fundamental questions about biochemical redox processes and benefit the design of new materials and molecular devices. Herein we employed the STM break-junction technique to measure the single-molecule conductance of multiple π-π-stacked aromatic rings. We studied electron transport through up to four stacked benzene rings held together in an eclipsed fashion via a paracyclophane scaffold. We found that the strained hydrocarbons studied herein couple directly to gold electrodes during the measurements; hence, we did not require any heteroatom binding groups as electrical contacts. Density functional theory-based calculations suggest that the gold atoms of the electrodes bind to two neighboring carbon atoms of the outermost cyclophane benzene rings in η(2) fashion. Our measurements show an exponential decay of the conductance with an increasing number of stacked benzene rings, indicating a nonresonant tunneling mechanism. Furthermore, STM tip-substrate displacement data provide additional evidence that the electrodes bind to the outermost benzene rings of the π-π-stacked molecular wires.
了解电子在π-π堆积体系中的输运将有助于回答关于生化氧化还原过程的基本问题，并有益于设计新材料和分子器件。在此，我们采用 STM 断键技术测量了多个π-π堆积芳环的单分子电导。我们研究了通过对苯并环己烷支架以重叠方式结合在一起的多达四个堆叠的苯环的电子输运。我们发现，本文研究的受应变的碳氢化合物在测量过程中直接与金电极相连；因此，我们不需要任何杂原子结合基团作为电接触。基于密度泛函理论的计算表明，电极的金原子以η(2)方式结合到最外层环己烷苯环的两个相邻碳原子上。我们的测量结果表明，随着堆叠苯环数量的增加，电导呈指数衰减，表明存在非共振隧穿机制。此外，STM 针尖-基底位移数据提供了额外的证据，表明电极与π-π堆积分子线的最外层苯环结合。
