Chiral tether-guided selective synthesis of Dn-symmetric chiral conjugated nanorings

Abstract

Chiral conjugated nanorings with D_n symmetry exhibit extraordinary circularly polarized luminescence (CPL) properties due to their unique cylindrical helical conjugated system. However, their synthesis faces challenges such as numerous atropisomers and tedious separation and chiral resolution processes, which severely hinder their development. In this work, we report a chiral tether-guided synthesis strategy. By introducing a strained planar chiral alkyl chain tether into the fused-ring building unit of the nanoring, the energy differences between the various atropisomers of the nanoring are significantly increased. This guides the formation of the thermodynamically most stable D_n-symmetric isomer during synthesis, thus greatly enhancing the selectivity. Four chiral nanorings, D₃-(P)-NR1, D₄-(P)-NR1, D₃-(M)-NR2, and D₄-(M)-NR2, as well as their enantiomers, were facilely obtained through this method. All molecules have shown remarkable and stable CPL capability, with a luminescence dissymmetry factor up to 0.076.