“…X-ray diffraction analysis of single crystals of 6 (solvent: CHCl 3 , antisolvent: MeOH) showed a nearly planar structure of the NBN-dibenzophenalene scaffold (maximum deviation from planarity: 6.0°), with each azaborine ring depicting a slight distortion, likely originated by repulsion between the peri - N -mesityl groups (Figure ). The B–N bond lengths of 1.438 and 1.448 Å denote a partial double bond character, as previously observed with other peripherally doped NBN-containing PAHs. ,,,, X-ray analysis of terarylene 1 Ph (solvent: toluene, antisolvent: MeOH) showed two crystallographically independent molecules, both displaying a planar polyaromatic core (maximum deviation from planarity: 1.7°–2.8°), in the asymmetric unit, and B–N bond lengths for the NBN unit (1.438–1.450 Å) consistent with those measured for derivative 6 . The peripheral azaborine-like B–N bond lengths fall within the 1.413–1.421 Å range, suggesting a distinct double bond character that is peculiar to 9,10-azaboraphenanthrenes − (see SI, section 4, for 5 Me , 5 Ph , and 5 Mes ).…”