Conformation and Aromaticity Switching in a Curved Non‐Alternant sp(2) Carbon Scaffold

A curved sp(2) 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 1 (2+). 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. 1 (2+) 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)(SbF(6))(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.