Benzo-Extended Heli(aminoborane)s: Inner Rim BN-Doped Helical Molecular Carbons with Remarkable Chiroptical Properties

Atomically precise synthesis of three-dimensional boron-nitrogen (BN)-based helical structures constitutes an undeveloped field with challenges in synthetic chemistry. Herein, we synthesized and comprehensively characterized a new class of helical molecular carbons, named benzo-extended [n]heli(aminoborane)s (<b>[n]HAB</b>s), in which the helical structures consisted of <i>n</i> = 8 and <i>n</i> = 10 <i>ortho</i>-condensed conjugated rings with alternating BN atoms at the inner rims. X-ray crystallographic analysis, photophysical studies, and density functional theory calculations revealed the unique characteristics of this novel <b>[n]HAB</b> system. Owing to the high enantiomerization energy barriers, the optical resolution of <b>[8]HAB</b> and <b>[10]HAB</b> was achieved with chiral high-performance liquid chromatography. The isolated enantiomers of <b>[10]HAB</b> exhibited record absorption and luminescence dissymmetry factors (|<i>g</i>_abs|=0.061; |<i>g</i>_lum|=0.048), and boosted CPL brightness up to 292 M^-1 cm^-1, surpassing most helicene derivatives, demonstrating that the introduction of BN atoms into the inner positions of helicenes can increase both the |<i>g</i>_abs| and |<i>g</i>_lum| values.