Strong NIR-II Magneto-Optical Activity of a Chiral Sm15Cu54 Cage

The magneto-optical response of chiral materials holds significant potential for applications in physics, chemistry, and biology. However, exploration of the near-infrared (NIR) magneto-optical response remains limited. Herein, we report the synthesis and strong NIR-II magneto-optical activity of three pairs of chiral 3d–4f clusters of R/S -Ln 15 Cu 54 (Ln = Sm, Gd, and Dy). Structural analysis reveals that R/S -Ln 15 Cu 54 features a triangular prism cage with C 3 symmetry. Interestingly, magnetic circular dichroism (MCD) spectra exhibit remarkable magneto-optical response in the NIR-II region, driven by the f–f transition. The maximum g-factor of R/S -Sm 15 Cu 54 reaches 5.5 × 10–3 T–1 around 1300–1450 nm, surpassing values associated with DyIII and CuII ions. This remarkable NIR-II magneto-optical activity may be attributed to strong magnetic-dipole-allowed f–f transitions and helix chirality of the structure. This work not only presents the largest Ln-Cu clusters to date but also demonstrate the key role of magnetic-dipole-allowed transitions on magneto-optical activity.