Reversal of circular dichroism responses in coupled CdSe magic clusters by electro-chiral control

Group II-VI magic clusters, featuring precise atomic compositions, well-defined geometric structures, and superior stability, hold great potential in atomic-scale manufacturing. While monodispersed magic clusters exhibit unambiguous characteristics, their response to external stimuli has to be understood. Moreover, strong interaction between clusters and an external field is desirable in order for clusters to assemble or tailor their physicochemical properties instantaneously for device applications. Herein, we explore the effects of an electric field on the absorption and circular dichroism spectra of (CdSe)13 and (CdSe)34 magic clusters. Our first-principles calculations show that the coupling between clusters drastically enhances their electro-optical responses, exhibiting a prominent quantum-confined Stark shift and a reversal of the Cotton effect in circular dichroism spectra. This striking behavior originates from the strong renormalization of both electronic structure and transition dipole moments under the electric field. The field-induced switching of chiroptical signatures and amplified Stark shift endows the group II-VI magic clusters with atomic-precision versatility for optical modulators, chiral spintronics, polarized-light detectors, and quantum information processing.