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Abstract
Controlling the flow of electrical current at the nanoscale typically requires complex top-down approaches. Here, a bottom-up approach is employed to demonstrate resistive switching within molecular wires that consist of double-helical metallopolymers and are constructed by self-assembly. When the material is exposed to an electric field, it is determined that ≈25% of the copper atoms oxidize from CuI to CuII , without rupture of the polymer chain. The ability to sustain such a 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 CuII . This mixed-valence structure exhibits a 104 -fold increase in conductivity, which is projected to last on the order of years. The increase in conductivity is explained as being promoted by the creation, upon oxidation, of partly filled 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.
Highlights
Organic-based molecular materials offer to demonstrate resistive switching within molecular wires that consist of double-helical metallopolymers and are constructed by self-assembly
Upon exposure to an electric field, we find the polymer to adopt a novel mixed-valence structure, wherein ≈25% of the copper atoms in the chain oxidize from CuI to CuII, without rupture of the polymer chain
The inset depicts a schematic representation of 1 dispersed between the gold electrodes. d) AFM height image of a thin film deposited under the same coating conditions as for the devices, highlighting that the film consists of slightly elongated domains of metallopolymer 1 with an average size for the long side of 420 nm (Figure S4, Supporting Information). e) Absolute value of current density versus voltage for a 50mer of metallopolymer 1, showing the higher currents obtained as the device was scanned to progressively higher maximum voltages (Vmax)
Summary
Organic-based molecular materials offer to demonstrate resistive switching within molecular wires that consist of double-helical metallopolymers and are constructed by self-assembly. The ability to sustain such a high level of oxidation is unprecedented the structural complexity necessary to build functionality at the nanoscale and from the bottom up.[1,2,3] In hybrid metal– organic materials, the oxidation state of metal ions provides a further handle to engineer new properties.[4,5,6,7,8,9,10,11] Manipulain a copper-based molecule: it is made possible here by the double helix compressing in order to satisfy the new coordination geometry required by CuII This mixed-valence structure exhibits a 104-fold increase in conductivity, which is projected to last on the order of years.
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