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.

Emerging Cubic Chirality in γCD‐MOF for Fabricating Circularly Polarized Luminescent Crystalline Materials and the Size Effect

“…Briefly, under ambient condition, the methanol vapor slowly diffused into the aqueous solution of the mixtures of γCD, KOH, and luminophores, transparent crystals were acquired after several days. The powder X‐ray diffraction (XRD) of the crystals has the same pattern as reported, indicating the formation of the cubic framework (Supporting Information, Figure S1) . The emerging of the larger cubic void of γCD‐MOF was expected to greatly expand the encapsulation capability of γCD.…”

“…However, the in situ encapsulation strategy could afford deep‐orange (Ru‐BPy) and light‐yellow (Ru‐BPhen) colored crystals, respectively, which suggested that the two Ru complexes were encapsulated into the crystal grains of γCD‐MOF. The XRD characterization of the lum@γCD‐MOF crystals revealed the preservation of the cubic frameworks after the luminophores encapsulation (Supporting Information, Figure S1) . Furthermore, when such crystals were dipped into methanol overnight, no leak of Ru complexes was observed.…”

“…The preparation of the lum@γCD‐MOF was through an in situ encapsulation strategy reported previously . Briefly, under ambient condition, the methanol vapor slowly diffused into the aqueous solution of the mixtures of γCD, KOH, and luminophores, transparent crystals were acquired after several days.…”

Rare Earth‐Free Luminescent Materials for WLEDs: Recent Progress and Perspectives

“…For example, MOF materials with core–shell structure and white light emission were prepared by using cyclodextrin as the organic ligand, connected with potassium ions, and loaded with 7‐hydroxycoumarin, fluorescein, and rhodamine B dyes. [ 148 ] Another effective strategy to prevent dye leakage is to add the dye during the MOF crystal formation process so that it is stably encapsulated inside the MOF. Recently, Liu et al reported multiple fluorescent dyes encapsulated inside the frame during the formation of zeolite imidazolate frame 8 (ZIF‐8), where the energy transfer process between the dye molecules was controlled by the multilayer encapsulation structure.…”

Emission Color Manipulation in Transparent Nanocrystals‐in‐Glass Composites Fabricated by Solution‐Combustion Process

“…Although various materials including semiconductors, quantum dots, optical or nonlinear optical crystals, and organic dyes have been applied to generate RGB emission simultaneously, the available multicolor sources based on a single material with monolithic structure are still limited. It is constrained by the strict requirement for material growth and sophisticated design for simultaneous RGB oscillation . The demand for efficient white light is stimulating the development for new gain mediums with high efficiency, continuous tunability, low‐cost fabrication, and high compatibility for high‐performance photonic applications.…”