Temperature-Controlled Synthesis of Corannulene-Based Multi-Helicenes: Highly Integrated Curvature/Planarity for...

Corannulene and hexabenzocoronene (HBC), as archetypal bowl-shaped and planar nanographene, have attracted considerable interest. Highly integrating these complementary motifs into a single architecture, however, remains a challenge owing to considerable intramolecular strains. Here, we report a temperature-controlled synthesis that enables selective hybridization between corannulene and multiple HBC-like motifs, yielding the anticipated quintuple [8]helicene (Cor-5H) and an unexpected triple [8]helicene (Cor-4H) incorporating a rare nonagon, likely involving a phenyl shift rearrangement mechanism. DFT calculations provide insights into the preferential formation of Cor-5H at lower temperatures, while Cor-4H predominates at elevated temperatures. Single-crystal X-ray diffraction confirms their hybrid bowl-helix topologies, in which a central corannulene is fused with four (Cor-4H) or five (Cor-5H) HBC-like blades. The significant steric constraint imposed by the curved core results in high strain energies. This synergistic integration of curvature and planarity endows both compounds with intense deep-red to near-infrared (NIR) fluorescence; enhanced chiroptical responses and high circularly polarized luminescence (CPL) brightness; as well as unusual solid-state fluorescence due to suppressed π-π stacking. As the largest π-extended corannulene-based multiple [n]helicenes reported to date, Cor-5H and Cor-4H demonstrate the powerful potential of fusing curved and planar nanographene motifs to design materials with advanced chiroptical functions.