Electrically-Induced Mixed Valence Causes Resistive Switching in Copper Helical Metallopolymers

Controlling the flow of electrical current at the nanoscale typically requires complex top-down approaches. Here we use a bottom-up approach to demonstrate resistive

switching within molecular wires that consist of double-helical metallopolymers and are constructed by self-assembly. When we expose the material to an electric field, we determine that approximately 25% of the copper atoms oxidise from Cu(I) to Cu(II) without rupture of the polymer chain. The ability to sustain such high level of oxidation is unprecedented in a copper-based molecule: it is made possible here by the double helix compressing in order to satisfy the new coordination geometry required by Cu(II).

This mixed-valence structure exhibits a 10⁴-fold increase in

conductivity, which is projected to last over 10 years. We explain the increase in conductivity as being promoted by the creation, upon oxidation, of partly filled d_z²

orbitals aligned along the mixed-valence copper array; the long-lasting nature of the change in conductivity is due to the structural rearrangement of the double-helix, which poses an energetic barrier to re-reduction. This work establishes helical metallopolymers as a new platform for controlling currents at the nanoscale.