Dual Circularly Polarized Luminescence from Chiral Boron-Embedded Polycyclic Aromatic Hydrocarbons

Reversible coordination bonds between boron and heteroatoms endow boron-based π-conjugated frameworks with dynamic functionality, as interconversion between tri- and tetracoordinate boron centers induces pronounced changes in both molecular geometry and electronic structure. In this study, we synthesized a series of chiral boron-embedded polycyclic aromatic hydrocarbons featuring an asymmetric boron center intramolecularly coordinated by a proximal P═O moiety. The resulting tetracoordinate enantiomers exhibit high configurational stability, enabling optical resolution by chiral HPLC. Notably, among the compounds, anthracene-fused boracyclic derivatives display dual circularly polarized luminescence (CPL) arising from excited-state dissociation of the intramolecular P═O⋯B bond, a process whose extent varies depending on the degree of π-extension. In these systems, bond-cleavage converts point chirality in the tetracoordinate state into C-B axial chirality in the tricoordinate state. Taking advantage of the intrinsically superior photophysical properties of tricoordinate boranes, one derivative exhibited CPL with a high quantum yield, while another displayed red-shifted CPL extending to the deep-red region. Furthermore, the dynamic P═O⋯B coordination is highly sensitive to hydrogen-bonding ability and polarity of solvent, thereby giving rise to solvent-dependent dual CPL behavior. These findings establish a new strategy for exploiting reversible coordination in chiral boron-PAHs to access responsive chiroptical functionalities.