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We report the challenging synthesis of two very long bis(anthraoxa)quinodimethanes with nine ( ABA ) and ten ( ANA ) consecutively fused six-membered rings. The former is stable with negligible diradical character, while the latter with a moderate diradical character ( y 0 = 25.0%) is reactive and an unexpected trifluoroacetic substituted product ( ANA-TFA ) was isolated. X-ray crystallographic analysis revealed a planar backbone with a typical quinoidal character for both. Their dications can be regarded as the isoelectronic structures of the respective nonacene and decacene. The dication ABA 2+ and dianion ABA 2– are open-shell singlet diradicaloids, while the longer dication ANA-TFA 2+ and dianion ANA 2– have closed-shell ground state, which can be explained by the different intramolecular Coulomb interactions. Both dianions have a bent backbone and can be considered as an isoelectronic structure of the tetraanion of nonacene and decacene, respectively.
Dong et al. (Wed,) studied this question.