Asymmetric Chichibabin diradicaloids: synthesis via oxidation of SOMO–HOMO inversion radicals and near-infrared absorption for electrochromism

Since the discovery of Chichibabin hydrocarbon in 1907, its scaffold has been instrumental in designing diverse open-shell materials. However, synthetic efforts have yielded almost exclusively symmetric diradicaloids; asymmetric variants with two distinct radical centers remain elusive due to the challenge of forming two different radicals simultaneously. Herein, starting from SOMO–HOMO inversion radicals (2a and 2b) bearing polychlorinated trityl and triarylamine scaffolds, asymmetric Chichibabin diradicaloids (2a+·[SbF₆]⁻ and 2b+·[SbF₆]⁻) were successfully obtained through one-electron oxidation for the first time. Their structures were unequivocally confirmed by single-crystal X-ray diffraction, along with EPR and DFT calculations. Owing to their asymmetric architectures with both carbon- and nitrogen-centered radicals, they result in mixed-valence systems displaying broad NIR absorption (949–1105 nm). Furthermore, they serve as efficient redox-active materials in NIR electrochromic devices. This work outlines an effective synthetic route to asymmetric diradicaloids from SOMO–HOMO inversion radicals, and further points toward potential strategies for preparing high-spin species and push–pull-type electron-distributed optical open-shell materials.