Stable Crystalline Nanohoop Radical and Its Self‐Association Promoted by van der Waals Interactions

Abstract A stable nanohoop radical (OR3) combining the structures of cycloparaphenylene and an olympicenyl radical is synthesized and isolated in the crystalline state. X‐ray crystallographic analysis reveals that OR3 forms a unique head‐to‐tail dimer that further aggregates into a one‐dimensional chain in the solid state. Variable‐temperature NMR and concentration‐dependent absorption measurements indicate that the π‐dimer is not formed in solution. An energy decomposition analysis indicates that van der Waals interactions are the driving force for the self‐association process, in contrast with other olympicenyl derivatives that favor π‐dimerization. The physical properties in solution phase have been studied, and the stable cationic species obtained by one‐electron chemical oxidation. This study offers a new molecular design to modulate the self‐association of organic radicals for overcoming the spin‐Peierls transition, and to prepare novel nanohoop compounds with spin‐related properties.