Core–Shell Structured Cyclodextrin Metal–Organic Frameworks with Hierarchical Dye Encapsulation for Tunable Light Emission

Abstract

Existing core–shell structured metal–organic frameworks (MOFs) are typically constructed by epitaxial growth with metal or/and organic ligands (the two basic components for MOFs) changing from core to shell, whereas in this contribution, we propose a new concept for constructing core–shell structured MOF featuring hierarchic encapsulation of various guest molecules into the framework. The cyclodextrin metal–organic frameworks (CD-MOFs) were chosen as the host to encapsulate organic dyes for light-emitting applications, and the cavity structure of γ-cyclodextrin and cage structure of MOF exhibited remarkable synergistic effects on fluorescence enhancement. Furthermore, core–shell structured CD-MOFs with hierarchical encapsulation of different dyes were developed to realize polychromatic light emitting via spectrum superposition. On the basis of this new method, we further fabricated a white-light emitting core–shell crystal, CD-MOF⊃7-HCm@FL@RhB (shell@core). With three sequentially formed and adjustable layers of different dyes, the core–shell crystal emitted bright white light with a CIE coordinate of (0.35, 0.32). Our approach provides a new method for the rational design of multicolor emission crystals. Meanwhile, our findings may stimulate future investigations on multifunctional host–guest systems in crystalline state.