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

ABSTRACT 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.