Synthesis of a π-Extended Double [9]Helicene

Double helicenes are appealing chiral frameworks. Their p-extension is desirable to achieve (chir)optical response in the visible and near-infrared (NIR) region, but access to higher double [n]helicenes (n=8) has remained challenging. Herein, we report an unprecedented p-extended double [9]helicene (D9H), unambiguously revealing its structure by single-crystal X-ray diffraction. D9H shows remarkable NIR emission from 750 to 1100 nm with a high photoluminescence quantum yield of 18 %. In addition, optically pure D9H exhibits panchromatic circular dichroism with a notable dissymmetry factor (g(CD)) of 0.019 at 590 nm, which is among the highest in the visible region for reported helicenes.

Automated summary

An unprecedented p-extended double [9]helicene has been reported, with its structure unequivocally revealed by single-crystal X-ray diffraction. This helicene exhibits remarkable near-infrared emission from 750 to 1100 nm, along with a high photoluminescence quantum yield of 18%. Optically pure D9H also displays panchromatic circular dichroism with a notable dissymmetry factor (g(CD)) of 0.019 at 590 nm, which is one of the highest reported for helicenes in the visible region.