Conformation and Aromaticity Switching in a Curved Non-Alternant sp² Carbon Scaffold

A curved sp² carbon scaffold containing fused pentagon and heptagon units (1) was synthesized by Pd-catalyzed [5+2] annulation from a 3,9-diboraperylene precursor and shows two reversible oxidation processes at low redox potential, accompanied by a butterfly-like motion. Stepwise oxidation produced radical cation 1^.+ and dication 1²⁺ . In the crystal structure, 1 exhibits a chiral cisoid conformation and partial π-overlap between the enantiomers. For the radical cation 1^.+ , a less curved cisoid conformation is observed with a π-dimer-type arrangement. 1²⁺ adopts a more planar structure with transoid conformation and slip-stacked π-overlap with closest neighbors. We also observed an intermolecular mixed-valence complex of 1⋅(1^.+ )₃ that has a huge trigonal unit cell [(1)₇₂ (SbF₆ )₅₄ ⋅(hexane)₁₀₁ ] and hexagonal columnar stacks. In addition to the conformational change, the aromaticity of 1 changes from localized to delocalized, as demonstrated by AICD and NICS(1)_zz calculations.