Design and enantioselective synthesis of 3D π-extended carbohelicenes for circularly polarized luminescence

Circularly polarized luminescence (CPL) of chiral organic molecules has attracted attention as next-generation optoelectronic technology, including applications in biotechnology. Higher-order 3D π-extended carbohelicenes would be superb CPL emitters, combining high circular polarization, brightness and stability, but their highly distorted structure has hindered their synthesis and enantiocontrol. Here we report the design of 3D π-extended carbo[11] and [13]helicenes for the CPL emitters and their enantioselective synthesis (up to 87:13 enantiomeric ratio), overcoming high distortions. These helicenes are synthesized via the enantioselective triple [2 + 2 + 2] cycloaddition to construct low-distortion expanded carbo[13] and [15]helicene skeletons and the subsequent π-extension/helix diameter reduction by the Scholl reaction. X-ray crystallographic analyses demonstrate that the 3D π-extended carbo[11] and [13]helicenes with rigid molecular backbones are conglomerates, favouring preferential crystallization, and reveal van der Waals interactions throughout the hexa-peri-hexabenzocoronene layers. Furthermore, their CPL brightness reaches a maximum of 513 M⁻¹ cm⁻¹, the highest value among helicene derivatives.