All-in-One Step from a Radical Monomer: Vacuum Synthesis of Electroswitchable Radical Polymer Thin Films by Solvent-Free Surface Polymerization

Polyradicals-radical polymers with open-shell structures-are unique one-dimensional quantum materials that can be envisaged as spin chains with one radical (i.e., one unpaired electron) per repeating unit. Due to their unique electronic structure, polyradicals with electroswitchable charge states find uses in lightweight batteries and resistive memory devices for flexible electronics. Ultrathin (<10 nm) memristors with polyradical active layers satisfy the high-density data storage and energy efficiency requirements of next-generation computing and battery technologies. However, wet chemistry has so far offered the only route available for the synthesis of ambipolar 6-oxoverdazylpolyradicals, which requires the postsynthesis fabrication of polyradical devices by spin coating, printing, or drop casting, by using solvents with harmful effects on the environment and health, and reproducibility issues over large areas. Here, the synthesis of 6-oxoverdazyl polyradicals in a thin-film form by ultrahigh-vacuum surface polymerization is shown in what is, to the best of our knowledge, the first-ever demonstration of surface-induced ring-opening metathesis polymerization to produce polyradicals. The polyradical thin films thus obtained exhibit nonvolatile, reproducible, and electroswitchable memory effects, thus enabling their use in large-scale transparent and flexible electronics.