Oxonium-Embedded Benzo[ B ]perylene: A Redox-Switchable Closed-Shell Π-Cation, and Its Paramagnetic Charge-Transfer Salt with TCNE•–

Abstract Organic cations and radicals are promising building components for organic optoelectronics, spintronics and quantum information processing. Realizing their full potential requires strategies to enhance their stability and precisely control their solid-state organization. Herein, we describe a modular synthetic strategy via photoelectrocyclization in the presence of tetracyanoethylene (TCNE) to access a series of closed-shell phenalenyl-derived cations featuring an oxonium-embedded benzo[b]perylene (OBP+) π-skeleton. The resulting OBP+ cations can be reversibly reduced to generate neutral open-shell phenalenyl-derived radicals. Noteworthily, we discovered a single crystal of OBP3·TCNE• that readily formed from the reaction mixture, displaying one-dimensional (1D) π-stacked arrays of alternating closed-shell OBP3+ cation and open-shell TCNE•– radical anion. This solid-state arrangement stabilizes otherwise reactive TCNE•– species, preserving its open-shell character even after one month of ambient exposure. OBP3·TCNE• is a rare example of purely organic paramagnetic salt and has been systematically investigated using integrated spectroscopic, magnetic, and computational analyses, together with preliminary photoconductivity measurements (ϕΣμ = 1.4 × 10–5 cm2 V–1 s–1). Overall, this work heralds a versatile photochemical route to redox-switchable cationic π-scaffolds and persistent open-shell crystalline organic materials.