Stitching Atom-Precise Ag6 NCs in Cyclodextrin Metal-Organic Framework: Chirality Induction and Second Harmonic Generation.

Cyclodextrin-based metal-organic frameworks (CD-MOFs) has attracted considerable attention owing to their high crystallinity, water solubility, and biocompatibility. However, integrating atomically precise metal nanoclusters (MNCs) into CD-MOFs remains largely unexplored. Only a few reports describe encapsulating MNCs within CD-MOFs, but none have crystallographically elucidated the structural aspects of MNCs-embedded CD-MOFs. Moreover, the site-specific positioning of MNCs in MOF-highly desirable for developing active catalysts and modulating properties-remains an unsolved challenge. Herein, we report the atomically precise hybrid assembly of Ag6 nanoclusters (NCs) within γ-cyclodextrin (γ-CD) MOFs. Ultrasmall Ag6 NCs are immobilized within the porous alkali metal ion-coordinated (K+, Rb+, Cs+) γ-CD framework, affording a well-defined metal nanocluster-γ-CD-MOF architecture at the nanoscale. Single-crystal X-ray diffraction unambiguously resolves a series of Ag6 NC-incorporated γ-CD MOFs, denoted as Ag6/M+/γ-CD (M = K, Rb, Cs). Incorporation of the Ag6 NCs profoundly modulates their intrinsic photophysical properties, induces supramolecular chirality, and enables second-harmonic generation (SHG). Furthermore, the Ag6/M+/γ-CD systems exhibit thermally activated delayed fluorescence, as corroborated by detailed theoretical calculations. Notably, these hybrid frameworks display pronounced circularly polarized luminescence, arising from chirality transfer from the γ-CD host and the spatially organized ligand shell surrounding the luminescent Ag6 NC assemblies.