Stable Ferrocenium Molecular Wires

Open-shell molecular wires offer prospects for achieving enhanced transport, additional functionality, efficient thermoelectric conversion, and they attract attention for future applications as spin qubits. The synthesis of such compounds as bench-stable species is however inherently challenging due to their high reactivity, and their integration into electronic/spintronic devices is complicated by charge transfer phenomena that can erase the open-shell state. Ferrocenium cations can be isolated as bench-stable species in combination with a variety of anions, and we demonstrate here that they can also be integrated in single-molecule devices with preservation of their unique electronic structure, by using molecular designs that prevent strong electronic coupling to the electrodes. The open-shell character grants significantly more efficient charge transport than their close-shell counterparts, along with non-linear current-voltage behaviour even at relatively low biases. Quantum transport calculations show that additional resonances appear in the transmission spectra upon oxidation at energies closer to the Fermi level of the electrodes, leading to increased conductance. These findings present further prospects for the applications of these materials in molecular spintronics and quantum thermoelectrics.