Symmetry breaking of highly symmetrical nanoclusters for triggering highly optical activity

Abstract

Developing new approaches to fulfill the enantioseparation of nanocluster racemates and construct cluster-based nanomaterials with optical activity remains highly desired in cluster science, because it is an essential prerequisite for fundamental research and extensive applications of these nanomaterials. We herein propose a strategy termed "active-site exposing and partly re-protecting" to trigger the symmetry breaking of highly symmetrical nanoclusters and to render cluster crystals optically active. The vertex PPh₃ of the symmetrical Ag₂₉(SSR)₁₂(PPh₃)₄ (SSR = 1, 3-benzenedithiol) nanocluster was firstly dissociated in the presence of counterions with large steric hindrance, and then the exposed Ag active sites of the obtained Ag₂₉(SSR)₁₂ nanocluster were partly re-protected by Ag⁺, yielding an Ag₂₉(SSR)₁₂-Ag₂ nanocluster with a symmetry-breaking construction. Ag₂₉(SSR)₁₂-Ag₂ followed a chiral crystallization mode, and its crystal displayed strong optical activity, derived from CD and CPL characterizations. Overall, this work presents a new approach (i.e., active-site exposing and partly re-protecting) for the symmetry breaking of highly symmetrical nanoclusters, the enantioseparation of nanocluster racemates, and the achievement of highly optical activity.