Chirality, once considered unrelated to magnetism, has recently been recognized to couple with magnetic fields through magneto‐chiral anisotropies (MChAs), such as magneto‐chiral dichroism (MChD). However, only a limited number of chiral molecular systems exhibiting clear MChD responses have been reported, and the mechanism remains insufficiently understood. In this study, copper phthalocyanines substituted with eight ( R )/( S )‐2‐methylbutoxy groups (( R )‐CuPc/( S )‐CuPc) were synthesized, and their chiroptical and magneto‐optical properties, namely circular dichroism (CD), magnetic circular dichroism (MCD), and magneto‐chiral dichroism (MChD), were investigated. In these thin films, face‐to‐face type H‐aggregates were preferentially formed. Upon annealing, intense and reproducible CD signals were observed, indicating that the ( R )‐ and ( S )‐2‐methylbutoxy groups induced right‐ and left‐handed helicities in the stacked phthalocyanine planes, respectively. Moreover, intense MChD signals were observed for these chiral thin films. These findings provide valuable insights for designing novel molecule‐based chiroptical and magneto‐optical materials.
Ishii et al. (2026) studied this question.