Mixed-valent macrocyclic ruthenium complexes as conductive, molecular loops

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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.