Homocentric Chirality and Magnetism Enable Strong NIR Magneto-Optical Activity in a Chiral DyFe ₃ Cluster

A single metal center that supports both the chirality and magnetism is a crucial design factor expected to achieve strong magneto-optical response, as it maximizes the coupling between magnetic and optical degrees of freedom. However, achieving such integration in molecular systems remains highly challenging. Here, we report a pair of chiral clusters, R / S -DyFe 3, in which the magnetic Dy III ion simultaneously acts as the chiral and magnetic center within a propeller-like framework. Magneto-optical measurements reveal pronounced and fully reversible magnetic modulation circular dichroism (CD) signal of the NIR f–f transitions, with strong enhancement and clear signal inversion under ±1.6 T. Particularly, the field-dependent CD intensity corresponding to the 6 H 15/2 → 6 F 11/2 hypersensitive transition increases by approximately 40 times under an applied magnetic field compared to zero field. The exceptional responsiveness arises from Zeeman splitting and magnetic-field-induced mixing of 4f sublevels, which markedly amplify the magnetic circular dichroism (MCD) contribution within the overall CD signal. These findings provide the first chiral molecular demonstration of magnetic-field-controlled CD signal in a chiral cluster with structural centers that support both chirality and magnetism, offering crucial insights into designing chiroptical materials with magnetic field modulation.