Chiral BN-Heteroacenes Embedded with B←N Coordination: Acid-Triggered Reversible Bond Switching and Optical Limiting Behavior.

Boron-nitrogen coordination (B←N) bonds have emerged as a versatile motif for engineering π-conjugated systems with tunable optoelectronic properties. Herein, we report the synthesis, structures, and properties of chiral heteroacenes (-) featuring B←N coordination within highly twisted π-frameworks. - were synthesized via a four-step approach, where the final cyclization simultaneously forged six- and five-membered rings bearing both B-N covalent and B←N dative bonds. Crystal structure analysis revealed the distorted backbone and intrinsically chiral character of -, which were successfully resolved into enantiomers by chiral-phase HPLC. The enantiomers of - were characterized by circular dichroism spectroscopy, and the enantiomers and exhibit circularly polarized luminescence with the luminescence dissymmetry factors () reaching 10 in both solid state and solution phase. Furthermore, the B←N coordination unit induces strong intramolecular charge-transfer (ICT) transitions, resulting in low-energy absorption band at 420-600 nm. The ICT band can be reversibly modulated by acid-base treatment through dynamic cleavage and restoration of B←N bond. Moreover, - show strong third-order nonlinear optical responses, making them promising candidates for optical limiting materials. This study highlights the potential of B←N-embedded chiral heteroacenes as multifunctional materials.