Helicene‐Fused Propellanes: A Geometrically Rigid Multihelicene Nanocarbon with Amplified Chirality

Abstract Here we report the synthesis of a geometrically distinct three‐dimensional (3D) chiral nanocarbon, which is composed of three π‐extended [6]helicene subunits fused on a [3,3,3]propellane with P,P,M / M,M,P configurations in the helicene subunits. This nanocarbon can isomerize into the thermodynamically more stable isomer with PPP / MMM configurations in the helicene subunits. Both 3D nanocarbons display a very stable configuration, which can be separated by chiral high‐performance liquid chromatography (HPLC). Notably, the nanocarbons display significantly enhanced chiroptical properties compared to the reference π‐extended [6]helicene, due to the improved alignment of magnetic and electric transition dipole moments. The twisted [6]helicene subunits in the nanocarbon provide concave surfaces that are suitable—albeit relatively weak—hosts for C 60 , forming a 1:2 host‐guest complex in the solid‐state.