Overcrowded 14,14′‐Bidibenzo[a,j]anthracenes: Challenges in Syntheses and Atypical Property of Lacking Symmetry‐Breaking Charge Transfer (SBCT)

Abstract

14,14'‐Bidibenzo[a,j]anthracenes (BDBAs) were prepared by iridium‐catalyzed annulation of 5,5'‐biterphenylene with alkynes. Overcrowded BDBAs with highly distorted molecular halves and a small interplanar angle between two anthryl moieties (down to approximately 31º, currently the lowest reported value) were verified by X‐ray crystallography. The strong intramolecular interactions and electronic couplingsbetween two molecular halves resulted in upfield 1H NMR signals, redshifted absorption and emission bands, and a reduced HOMO–LUMO gap. Photodynamic investigations on BDBAs indicated that the formation of the conventional symmetry‐breaking charge transfer (SBCT) state was suspended by restricted rocking around the central C–C bond. Such a mechanism associated with this highly constrained conformation was examined for the first time.