Guest Entrapment in Metal‐Organic Nanosheets for Quantifiably Tuneable Luminescence

Abstract

Luminescent metal‐organic frameworks (LMOFs) are promising materials for nanophotonic applications due to their tuneable structure and programmability. Yet, the 3D nature of LMOFs creates challenges for stability, optical transparency, and device integration. Metal‐organic nanosheets (MONs) potentially overcome these limitations by combining the benefits of metal‐organic frameworks (MOFs) with an atomically thin morphology of large planar dimensions. Herein, the bottom‐up synthesis of few‐layer thin ZIF‐7‐III MONs via facile low‐energy salt‐templating is reported. Employing guest@MOF design, the fluorophores Rhodamine B and Fluorescein are intercalated into ZIF‐7 nanosheets (Z7‐NS) to form light emissive systems exhibiting intense and highly photostable fluorescence. Aggregation and Förster resonance energy transfer, enabled by the MON framework, are revealed as the mechanisms behind fluorescence. By varying guest concentration, these mechanisms provide predictable quantified control over emission chromaticity of a dual‐guest Z7‐NS material and the definition of an “emission chromaticity fingerprint” – a unique subset of the visible spectrum that a material can emit by fluorescence.

Central Metal-Triggered Structural Transformation of a 2D Layered MOF: Mechanistic Studies and Applications

“…Fluorescent dyes are considered interesting chromophore guests because of their excellent optical and electronic properties. Dye encapsulation in 2D MOFs has become a promising method for preparing fluorescent materials. ,, …”

Encapsulation engineering of porous crystalline frameworks for delayed luminescence and circularly polarized luminescence

“…The H-aggregation of RhB in Z7-NS led to the appearance of a new shoulder at 650 nm. 138 In addition, the concentration of guest is also important to transfer and amplify the chirality signals. Zhou et al used achiral metal–organic cages to encapsulate BINOL-substituted BODIPYs (chiral guest molecules) to achieve CPL.…”

Synthesis, characterization & catalysis of ITQ 2D metal–organic frameworks and spectroscopic & photodynamic properties of their composites with organic dyes

“…133 For instance, 2D MOFs might present many advantages over their 3D counterparts, such as a higher surface area, unprecedent electronic properties (with higher carrier mobility and electrical conductivity), high thermal conductivity and excellent optical transparency. 134,135 Consequently, 2D MOFs are expected to surpass the performance of their 3D counterparts in a wide variety of technological applications. This is an incipient field that will provide exciting results in the near future.…”

“…Another recently proposed approach is an eco-friendly salt-templated synthesis of luminescent guests incarcerated within 2D MOF nanosheets (MONs) for tunable emissive materials. 135 This is a promising methodology for synthesizing 2D guest@MON materials, but more information is still required about how to control the entrapment of guests and whether it is possible to incarcerate guests of larger sizes within the 2D sheets. Finally, a recently reported strategy for fine-tuning the MOF color that could be applied also to 2D ITQ MOFs combines postsynthetic modification (PSM) of the chromophoric linkers of an amino-functionalized UiO-68 MOF with computationally guided selection of specific linker modifiers to rationally tune the chromophore band gap.…”

“…In this direction, recent developments have demonstrated the feasibility of scattering-type scanning near-field optical microscopy (s-SNOM) and nano-Fourier transform infrared (nanoFTIR) spectroscopy to characterize MOF-guest interactions at the nanoscale. 135,144 This review has demonstrated the possibility to confer luminescence properties to 2D ITQ MOFs by employing the more classical strategy of encapsulating fluorescent dyes within the MOF structures. 111 This approach has been successfully applied in both 3D and other 2D MOF composites giving rise to materials with tunable optoelectronic properties, such as generating long-lived charge separated states or long-lived photoluminescence.…”