Synthesis, Structures, and Chiroptical Properties of NBN-Doped Helicenes with Boron Atoms in the Inner Rims

The precise synthesis of helicenes with topologically defined length and specific heteroatomic perturbation in the screw-like conjugated skeletons plays an emerging role in the manipulation of chiral materials. Facile, selective, and programmable routes to helicenes or heterohelicenes are highly desirable yet challenging for structure–chiroptical property relationship studies. Herein, we report the synthesis and characterization of NBN-doped helicenes with boron atoms in the inner rims, enabled by the highly regioselective one-pot borylation of rationally designed precursors with, namely, fold-in or pan-out manner. The incorporation of nonbonded boron and nitrogen atoms resulted in narrow-band emission and improved optical properties for the single-stranded carbon helix. In addition, numbers and arrangement modes of fused six-membered rings have distinct effects on configurational stability and chiroptical properties, revealing that BN-[6]­H with strong circular dichroism is a promising candidate for chiral sensors. The combination of experimental and theoretical studies on these helical structures might provide insights into the design of helically chiral small-molecule-based sensors or emitters.