Expanded Azahelicenes with Large Dissymmetry Factors

Expanded azahelicenes, as heteroanalogues of helically chiral helicenes, hold significant potential for chiroptical materials. Nevertheless, their investigation and research have remained largely unexplored. Herein, we present the facile synthesis of a series of expanded azahelicenes NHn (n=1-5) consisting of 11, 19, 27, 35, and 43 fused rings, mainly by Suzuki coupling followed by Bi(OTf)₃-mediated cyclization of vinyl ethers. The structures of NH2, NH3 and NH4 were confirmed through X-ray crystallography analysis, and their (P)- and (M)- enantiomers were also isolated with chiral high performance liquid chromatography. The enantiomers exhibit large absorption (abs) and luminescence (lum) dissymmetry factors, with |g_abs|_max=0.044; |g_lum|_max=0.003 for NH2, |g_abs|_max=0.048; |g_lum|=0.014 for NH3, and |g_abs|_max=0.043; |g_lum|_max=0.021 for NH4, which are superior to their respective all-carbon analogues.