Light-powered electrical switch based on cargo-lifting azobenzene monolayers
Light-powered electrical switch based on cargo-lifting azobenzene monolayers
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DOI：
10.1002/anie.200705339
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发表时间：
2008-01-01
影响因子：
16.6
通讯作者：
Rampi, Maria Anita
中科院分区：
文献类型：
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作者：
Ferri, Violetta;Elbing, Mark;Rampi, Maria Anita
受自然界中发现的复杂分子机器的启发，化学家们开发了更简单的分子发动机。[1-3]其中，已经提出了几种引入偶氮苯的系统，其利用由光[4]或电场[5]触发的可逆的反-顺异构化，用于诸如光学数据存储设备，[6]可切换的超分子腔和传感器等应用。[7]最近的研究表明，含偶氮苯的聚合物链的光致异构化过程可以表示机械功。[8]根据这些发现，人们可以预见芳香族偶氮苯的自组装单分子膜（SAM）[9，10]作为能够通过利用集体亚纳米结构变化来表达前所未有的力量的分子系统。我们最近设计了一种刚性和完全共轭的偶氮苯，暴露出硫醇锚定基团，[11]这能够在Au（111）上形成紧密堆积的SAM（SAMAZO）。扫描隧道显微镜（STM）的研究表明，在光照射的化学吸附的自组装膜，集体异构化的整个分子结晶域发生了突出的高方向性。[11]基于这些结果，相邻的AZO分子的异构化的合作性质已被提出。此外，SAM中分子的联合作用提供了一个理想的系统作为潜在的“货物”升降机。在此，我们表明，在辐照下，掺入Au（111）表面和汞滴之间的结中的偶氮苯自组装膜能够1）提升“重”汞滴，以及2）可逆地光开关流过结的电流（图1）.电流-电压（I-V）图2a中显示了超过30个结合反式和顺式构象的AZO SAM的结的平均特性。在由反式构象最初形成的SAMAZO的UV光照射下，以极高的产率（98%）获得顺式构象的SAMAZO。[11]所测量的电流的差异，其总计约1.4个数量级，与方程（1）所描述的穿键隧穿机制一致。[13个国家]
Inspired by the complex molecular machines found in nature, chemists have developed much simpler molecular motors.[1–3] Among them, several systems incorporating azobenzene have been proposed, which exploit the reversible trans–cis isomerization triggered by light [4] or an electric field [5] for applications such as optical data-storage devices,[6] switchable supramolecular cavities, and sensors.[7] Recently, it has been demonstrated that the photoisomerization process of individual polymer chains incorporating azobenzenes can express mechanical work.[8] In light of these findings, one can foresee self-assembled monolayers (SAMs)[9, 10] of aromatic azobenzenes as molecular systems able to express forces of unprecedented magnitude by exploiting a collective subnanometer structural change. We recently designed a rigid and fully conjugated azobenzene exposing a thiol anchoring group,[11] which was able to form a tightly packed SAM on Au (111)(SAMAZO). Scanning tunneling microscopy (STM) studies revealed that upon light irradiation of the chemisorbed SAMs, a collective isomerization of entire molecular-crystalline domains occurred with an outstandingly high directionality.[11] Based on these results, a cooperative nature of the isomerization of adjacent AZO molecules has been proposed. Furthermore, the joint action of the molecules in the SAM provides an ideal system as a potential “cargo” lifter. Herein, we show that, upon irradiation, azobenzene SAMs incorporated in a junction between an Au (111) surface and a mercury drop are able to 1) lift the “heavy” Hg drop, and 2) reversibly photoswitch the current flowing through the junction (Figure 1).Current–voltage (I–V) characteristics averaged over more than 30 junctions incorporating AZO SAMs in the trans and the cis conformations are shown in Figure 2 a. The SAMAZO in the cis conformation was obtained with extremely high yield (98%) upon irradiation by UV light of the SAMAZO initially formed by the trans conformer.[11] The difference in the measured currents, which amounts to about 1.4 orders of magnitude, is in agreement with a through-bond tunneling mechanism described by Equation (1).[13]