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Electrically-Induced Mixed Valence Causes Resistive Switching in Copper Helical Metallopolymers
preprintsubmitted on 21.12.2020, 23:16 and posted on 23.12.2020, 05:42 by Jake L. Greenfield, Daniele Di Nuzzo, Emrys Evans, Satyaprasad P. Senanayak, Sam Schott, Jason T. Deacon, Adele Peugeot, William K. Myers, Henning Sirringhaus, Richard Friend, Jonathan Nitschke
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 dz2
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.