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

Abstract

Existing\ncore–shell structured metal–organic frameworks\n(MOFs) are typically constructed by epitaxial growth with metal or/and\norganic ligands (the two basic components for MOFs) changing from\ncore to shell, whereas in this contribution, we propose a new concept\nfor constructing core–shell structured MOF featuring hierarchic\nencapsulation of various guest molecules into the framework. The cyclodextrin\nmetal–organic frameworks (CD-MOFs) were chosen as the host\nto encapsulate organic dyes for light-emitting applications, and the\ncavity structure of γ-cyclodextrin and cage structure of MOF\nexhibited remarkable synergistic effects on fluorescence enhancement.\nFurthermore, core–shell structured CD-MOFs with hierarchical\nencapsulation of different dyes were developed to realize polychromatic\nlight emitting via spectrum superposition. On the basis of this new\nmethod, we further fabricated a white-light emitting core–shell\ncrystal, CD-MOF⊃7-HCm@FL@RhB (shell@core). With three sequentially\nformed and adjustable layers of different dyes, the core–shell\ncrystal emitted bright white light with a CIE coordinate of (0.35,\n0.32). Our approach provides a new method for the rational design\nof multicolor emission crystals. Meanwhile, our findings may stimulate\nfuture investigations on multifunctional host–guest systems\nin crystalline state.