Mixed-valent macrocyclic ruthenium complexes as conductive, molecular loops

本项目有两个主要目标：1)合成和综合研究具有强电子耦合的混价氧化态的大环三、四铀配合物。为此，我们将使用具有半疏水、杂环螯合配体的自互补单铀络合物构建块，这些配体在乙炔基团和各自的螯合、配位官能团之间提供不间断的圆周率共轭。2)直接评估这些分子导电回路的导电性。对于这些实验，我们将使用自制的、基于STM的装置来进行单分子测量，该装置是根据我们尊敬的同事Latha Venkataraman的建造计划制造的。该仪器于2019年成功投入使用，所取得的成果与该领域专家小组取得的成果不相上下。为此，我们将使用项目1中的锚基修饰的大环配合物，以及文献中已知的具有已证实的高电荷离域混合价状态的新的锚基修饰的大环衍生物。锚基是确保测试分子结合到STM装置的纳米级金电极上所必需的。这将使我们能够成功地解决以下基本问题：通过空间或通过化学键的电子耦合相对于分子水平上的电荷传输效率是如何比较的，以及两条传导路径的可用性是否使金属环结构优于它们的线性类似物。在一个强大的合成集团中，STM断路器设置的可用性和成功实施使我们处于一个理想的位置来解决这些基本的和大部分未回答的问题。如果成功，这个项目将使我们处于分子电导界的前沿。

This project has two main goals: 1) The synthesis and comprehensive investigation of macrocyclic tri- and tetraruthenium complexes with strong electronic coupling in their mixed-valent oxidation states. For this purpose, we will employ self-complementary monoruthenium complex building blocks with hemilabile, heterocyclic chelate ligands, which offer uninterrupted pi-conjugation between the ethynyl group and the respective chelating, coordinating functionality. 2) The direct assessment of the electrical conductivity of these molecular, conductive loops. For these experiments, we will employ a home-built, STM-based setup for single molecule measurements that we fabricated according to the construction plan of our esteemed colleague Latha Venkataraman. This instrumentation was successfully put into operation in 2019 and has provided results that equal those obtained by expert groups in this field. To these ends, we will use anchor group-modified, macrocyclic complexes from project 1) as well as new anchor-group-modified derivatives of literature-known macrocycles with proven, high charge delocalization in mixed-valent states. The anchor groups are required to ensure that the test molecules bind to the nanoscale gold electrodes of the STM setup. This will put us into a position to successfully address the fundamental questions of how electronic coupling through space or through chemical bonds compare with regard to the efficiency of charge transport at the molecular level and whether the availability of two conduction paths makes metallacyclic structures superior to their linear analogs. The availability and successful implementation of a STM break junction setup in a strong synthetic group puts us in an ideal position to tackle such fundamental and largely unanswered questions. If successful, this project will put us at the forefront within the molecular conductance community.