Solid State Multicolor Emission in Substitutional Solid Solutions of Metal–Organic Frameworks

Abstract

Preparing crystalline materials that produce tunable organic-based multicolor emission is a challenge due to the inherent inability to control the packing of organic molecules in the solid state. Utilizing multivariate, high-symmetry metal–organic frameworks, MOFs, as matrices for organic-based substitutional solid solutions allows for the incorporation of multiple fluorophores with different emission profiles into a single material. By combining nonfluorescent links with dilute mixtures of red, green, and blue fluorescent links, we prepared zirconia-type MOFs and found that the bulk materials exhibit features of solution-like fluorescence. Our study found that MOFs with a fluorophore link concentration of around 1 mol % exhibit fluorescence with decreased inner filtering, demonstrated by changes in spectral profiles, increased quantum yields, and lifetime dynamics expected for excited-state proton-transfer emitters. Our findings enabled us to prepare organic-based substitutional solid solutions with tunable chromaticity regulated only by the initial amounts of fluorophores. These materials emit multicolor and white light with high quantum yields (∼2–14%), high color-rendering indices (>93), long shelf life, and superb hydrolytic stability at ambient conditions.

J-dimer emission in interwoven metal–organic frameworks

“…What is unique about this mixture is that the links are isostructural, 5,6 and contain complex moieties that can be easily incorporated at varying concentrations, resulting in isoreticular materials that behave like substitutional solid-solutions (SSS) of organic molecules. We previously demonstrated this concept, 7,8 by incorporating highly uorescent and redox active groups, allowing us to observe changes in bulk physical properties directly related to the active link and its concentration in the MOF. In contrast, crystalizing the organic components by themselves into purely organic solid solutions (not within a MOF matrix), brings the challenges that are associated with organic crystals, such as a lack of predictability in structure and type of intermolecular interactions present, phase separation, and loss of molecular properties.…”

“…9,10 During our investigation on dilute uorescent links in MTV MOFs made with mixtures of uorophore links, we found that the bulk uorescence was dependent on the concentration and ratio of such uorophores. 7 We observed that energy exchanges, such as Förster resonance energy transfer (FRET) and selfabsorption, occur as a function of concentration and ratio of links, producing materials that uoresce as a combination of the used links. Utilizing p-rich uorophores, particularly those that contain polycyclic aromatic hydrocarbons (PAH) moieties, can take advantage of uorescence changes that result from pp stacking, such as those observed in J-aggregates.…”

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

“…The CIE coordinates of the sample with the molecular formula Zr 6 O 4 (OH) 4 (R 0.4 G 0.2 B 0.4 ) 0.01 NF 0.99 were (0.31, 0.33), close to the center of the white light region, the quantum yield was 4.3%, and the CRI was 93. [ 150 ]…”

“…The CIE coordinates of the sample with the molecular formula Zr 6 O 4 (OH) 4 (R 0.4 G 0.2 B 0.4 ) 0.01 NF 0.99 were (0.31, 0.33), close to the center of the white light region, the quantum yield was 4.3%, and the CRI was 93. [150] Specifically, the quantum yield of the dye molecule is generally reduced after being encapsulated in the MOF structure. In addition, the thermal and light stability of organic dyes is lower compared with commercial rare earth luminescent materials.…”

“…Two-component substitutional solid solutions (SSS) MOFs: (top) Optical images of samples under λ ex = 365 nm indicating their fluorophore composition, (middle) emission profiles with λ ex = 365 nm, and (bottom) CIE chromaticity coordinates of mixtures of red and blue (left) and mixtures of green and blue (right).Reproduced with permission [150]. Copyright 2019, American Chemical Society.…”