Fig. 1

Mirror symmetry breaking of helical supramolecular nanoribbons for asymmetric catalysis. a, b Molecular structure of the achiral BTA^BA monomer and schematic representation of the preparation of helical PBTA^BA nanoribbons with either (P)- or (M)-dominant helical handedness by applying rotary stirring during the cooling process of a DMF/water solution of BTA^BA. (P)- and (M)-dominant PBTA^BA display negative ((−)-PBTA^BA) and positive ((+)-PBTA^BA) CD signs at 316 nm, respectively. c Diels–Alder cycloaddition reaction between aza-chalcone and cyclopentadiene catalyzed by Cu²⁺ in combination with (−)-PBTA^BA or (+)-PBTA^BA. The reaction affords the endo isomer preferentially (~90%). The (S)-endo and (R)-endo enantiomers were obtained preferentially when (−)-PBTA^BA and (+)-PBTA^BA were used, respectively