Persistent Chiral Diradicals via SUMO-LUMO Inversion: Modular Synthesis, Electronic Structures, and Redox-Switching...

Integrating chirality into organic open-shell architectures holds immense promise for molecular spintronics and advanced optoelectronics. However, achieving simultaneous chemical persistence, configurational stability, and practical synthetic accessibility remains a formidable challenge. Here, we report a modular strategy for persistent singlet chiral diradicals based on a C₂-symmetric bibenzo[g]quinoline scaffold. Enantiopure π-extended precursors were efficiently synthesized via a one-pot multicomponent Povarov cyclization from commercially available BINAM, bypassing chiral HPLC resolution. Upon reduction, the monoradical intermediates exhibit a rare singly unoccupied molecular orbital SUMO-LUMO inversion (SLI) electronic configuration. Strategic N-protonation and steric shielding at high spin-density sites dramatically enhance stability while preserving the SLI character, enabling unambiguous assignment of a singlet ground state of the reduced chiral diradicals. The resulting diradicals can serve as robust chiral redox switches, enabling highly reversible, fatigue-free electrochemical cycles between the closed-shell dication and neutral diradical states with full retention of the embedded chiroptical information. This work demonstrates successful implementation of the SLI pathway for persistent chiral diradicals and provides a practical platform for the rational design of configurationally stable, redox-tunable open-shell materials with tailored electronic and chiroptical properties.