John H. Dillon Medal (2021): Radicalizing Organic Electronics with Polymer Physics

Electronically-active polymers continue to impact emerging technology landscapes in myriad device applications. The oft-utilized design paradigm associated with conducting polymers is one rooted in molecules containing large degrees of conjugation along their backbones and the inclusion of chemical dopants that serve to change the oxidation state of the polymers. However, moving from this archetype and towards one with a single-component, charge-neutral macromolecule has significant fundamental and practical benefits, as this type of macromolecular conductor should result in materials that can be designed in a more straightforward fashion and should have longer stability when implemented in devices. As such, we will describe redox-active macromolecules known as radical polymers (i.e., macromolecules that are composed of non-conjugated backbones and have pendant groups that contain open-shell entities), and we will demonstrate how controlling their physical properties allows for control of their structure at the local (i.e., ~10 nm) scale. This ordering does not extend to longer scales, which results in radical polymer films that are completely amorphous. Despite lacking any type of conjugation or crystalline domains, these macromolecules demonstrate high electrical conductivity values. Specifically, we show that the solid-state electrical conductivity of a designer radical polymer exceeds 20 S/m, and this places these non-conjugated polymer conductors in the same regime as many grades of common commercially-available, chemically-doped conjugated conducting polymers. Additionally, we highlight how controlling the macromolecular physics of the redox-active materials allows for their utilization in advanced organic electrochemical transistors. Thus, this work showcases how polymer physics insights can lead to next-generation organic electronic materials and their utility in myriad device archetypes including in the realm of stretchable bioelectronics.