Probing Hopping Conduction in Long, Pi-Conjugated Molecular Wires Assembled by Click Chemistry

在这项由美国国家科学基金会高分子、超分子和纳米化学项目赞助的奖项中，明尼苏达大学的丹·弗里斯比教授和他的学生旨在了解PAI共轭分子是如何导电的。具体地说，他们的目标是连接金属电极之间的圆周率共轭分子，并在“跳跃模式”下探测传导，在这种模式下，电子被注入分子轨道，并在金属接触之间的电势差的驱动下，沿着分子主干从一个位置跳到另一个位置。构建和表征这些结构的导电性将使我们能够更好地理解分子结构如何影响分子的导电性。它还将允许在分子导线中内置有用的电子功能(例如电流整流)，这可能使新的纳米电子应用成为可能。实验方法包括从金属电极构建圆周率共轭的分子线，使用顺序的“点击化学反应”以循序渐进的方式连接单体。这种化学方法允许合成几十纳米长的分子导线，同时控制1纳米长度的导线结构。导线将具有许多不同的化学功能，包括氧化还原活性中心，并具有有助于单向电子传输(即电流整流)的能级级联。合成后，承载定向导线组件的金属电极将被插入原子力显微镜(AFM)，在原子力显微镜(AFM)中，显微镜探头尖端将在受控的纳米牛顿压缩载荷下与导线组件接触。以这种方式，AFM起到了电子探针站的作用。施加在金属原子力显微镜针尖和金属衬底之间的电压驱动通过导线的电流，并测量导线的电流-电压(I-V)特性。I-V特性将被记录为分子长度、化学官能度和温度的函数。对这些信息的分析将被用来建立对导电分子中结构-传导关系的更完整的理解。这项提议的更广泛的影响将在化学和纳米科学的重要新兴领域的研究生和本科生的培训中。特别是培养学生在分子合成、结构表征、原子力显微镜和电学测量方面的技能。他们还将对分子和纳米电子学中涉及的物理原理有更全面的物理理解。此外，这笔赠款将为来自双子城大都市区的三名高中生提供暑期研究机会，让他们在早期阶段接触科学研究，并对他们对化学概念的理解产生积极影响。

In this award sponsored by the Macromolecular, Supramolecular and Nanochemistry Program of the NSF, Prof. Dan Frisbie of the University of Minnesota and his students aim to understand how pai-conjugated molecules conduct electricity. In particular, their goal is to connect pi-conjugated molecules between metal electrodes and to probe conduction in the "hopping regime" in which electrons are injected into the molecular orbitals and hop from site-to-site along the molecular backbone, driven by the potential difference between the metal contacts. Building and characterizing the conduction of these structures will allow a better understanding of how molecular architecture impacts electrical conductivity in molecules. It will also allow useful electronic functions (e.g. current rectification) to be built into the molecular wires, which may enable new nanoelectronic applications. The experimental approach involves building pi-conjugated molecular wires from metal electrodes using sequential "click chemistry" reactions to connect monomers in a step-wise fashion. This chemistry allows the syntheses of molecular wires that are tens of nanometers in length with simultaneous control of the wire architecture on 1 nanometer length scales. Wires will be made with many different chemical functionalities, including redox-active sites, and with cascades of energy levels that can facilitate uni-directional electron transport (i.e., current rectification). After synthesis, the metal electrodes bearing oriented assemblies of wires will be inserted into an atomic force microscope (AFM), where the microscope probe tip will be brought into contact with the wire assembly with a controlled, nano-newton compressive load. In this manner, the AFM functions as an electrical probe station. Voltages applied between the metal AFM tip and the metal substrate drive current through the wires and the current-voltage (I-V) characteristics of the wires will be measured. The I-V characteristics will be recorded as a function of molecular length, chemical functionality and temperature. Analysis of this information will be used to create a more complete understanding of structure-conduction relationships in conducting molecules.The broader impacts of this proposal will be in the training of graduate students and undergraduates in important emerging areas of chemistry and nanoscience. In particular students will develop skills in molecular synthesis, structure characterization, atomic force microscopy, and electrical measurements. They will also develop a more complete physical understanding of the physical principles involved in electrical conduction in molecules and nanoelectronics, more generally. In addition, this grant will offer summer research opportunities for three high school students from the Twin Cities metropolitan area, exposing them to scientific research at an early stage and positively impacting their understanding of chemical concepts.