Benzo[f]benzo[5,6]indolo[3,2-b]indole: a stable unsubstituted 4nπ-electron acene with an antiaromatic 1,4-diazapentalene core.

A stable unsubstituted 4nπ-electron acene with an antiaromatic 1,4-diazapentalene core was prepared via an unprecedented mild oxidation. Further investigation showed that the stability of such acenes was dependent on the fusion patterns of the peripheryl benzene rings to the centre core.