Orthogonal Oriented Bisanthrancene-Bridged Bis(Triarylamine) Diradical Dications: Isolation, Characterizations and Crystal Structures.

Two bis(triarylamine) diradical dication salts 12+ 2[Al(ORF )4 ]- and 22+ 2[Al(ORF )4 ]- bridged with an orthogonal oriented bisanthrancene motif were synthesized. Their solid state and electronic structures were investigated by various experimental approaches in conjunction with theoretical calculations. Superconducting quantum interference device measurements and density functional theory calculations reveal that both of 12+ and 22+ feature open-shell singlet ground states with rather small singlet-triplet energy gaps; thus, they can be regarded as nearly pure diradicals (biradicals). Their diradical characters are enhanced by the orthogonal configuration of the bisanthrancene moiety which demonstrates the importance of the geometry of bridging units in turning the electronic structures of bis(triarylamine) dications.