Conformation and Aromaticity Switching in a Curved Non‐Alternant sp 2 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 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(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.
A curved non‐alternant polycyclic aromatic hydrocarbon (PAH) containing fused heptagon and pentagon units is presented, as well as its conformational changes upon stepwise oxidation. Single‐crystal X‐ray analyses for neutral, cationic, dicationic, and a mixed valence species 1⋅(1 .+)3 enabled the observed functional properties to be related to the molecular and supramolecular structures.