A Stable Open-Shell Polycyclic Hydrocarbon With Schlenk-Chichibabin Hybrid Conjugation

Open-shell polycyclic hydrocarbons (PHs) have emerged as a promising class of molecular materials for organic electronics and spintronics due to their unique electronic structures and properties. However, the design and synthesis of open-shell π-systems with intricate internal spin interactions remain a significant challenge in synthetic chemistry. Herein, we report our efforts toward a novel tetraradicaloid system 1 by integrating two distinct conjugation motifs derived from Schlenk and Chichibabin hydrocarbons into a linear PH framework. Its model compounds 2 (Schlenk-type) and 3 (Chichibabin-type) were also prepared and compared. Comprehensive experimental and theoretical analyses reveal that 1 exhibits an open-shell singlet ground state with moderate tetraradical character, effectively bridging the electronic properties of 2 and 3. All three systems display pronounced open-shell diradical character, characterized by small singlet-triplet energy gaps, narrow energy gaps, and amphoteric redox behavior. Notably, the dication and dianion of 1 show significant open-shell diradical character while its tetracation adopts a closed-shell configuration. Furthermore, the dianions of 2 and 3 exhibit electronic structures analogous to their respective isoelectronic counterparts, pentacene, and heptaphane. This work will shed new light on the design and synthesis of novel open-shell PHs with complex internal structural features and adjustable electronic properties.