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.
Para-, or 4-nitrophenol, and related nitroaromatics are broadly used compounds in industrial processes and as a result are among the most common anthropogenic pollutants in aqueous industrial effluent; this requires development of practical remediation strategies. Their catalytic reduction to the less toxic and synthetically desirable aminophenols is one strategy. However, to date, the majority of work focuses on catalysts based on precisely tailored, and often noble metal-based nanoparticles. The cost of such systems hampers practical, larger scale application. We report a facile route to bulk cobalt oxide-based materials, via a combined mechanochemical and calcination approach. Vibratory ball milling of CoCl2(H2O)6 with KOH, and subsequent calcination afforded three cobalt oxide-based materials with different combinations of CoO(OH), Co(OH)2, and Co3O4 with different crystallite domains/sizes and surface areas; Co@100, Co@350 and Co@600 (Co@###; # = calcination temp). All three prove active for the catalytic reduction of 4-nitrophenol and related aminonitrophenols. In the case of 4-nitrophenol, Co@350 proved to be the most active catalyst, therein its retention of activity over prolonged exposure to air, moisture, and reducing environments, and applicability in flow processes is demonstrated.
J-dimer emission is an emergent property that occurs when pairs of ground-state fluorophores associate within multivariate MOFs producing tunable red shifted emission.
Realization of organic-based substitutional solid solutions will facilitate the preparation of solid-state materials with properties that arise from phenomena only displayed by molecules in solution. We demonstrate that multivariate metal-organic frameworks, MOFs, exhibit organic-based substitutional solid solution behavior by tuning their fluorescence, dictated exclusively by predetermined ratios of multivariate organic links. By combining non-fluorescent links with dilute mixtures of red, green, and blue fluorescent links we prepared zirconia-type MOFs that exhibit features of solution-like fluorescence. Our study found that MOFs with fluorophore link concentration of around 1 %mol exhibit fluorescence with decreased inner filtering demonstrated by changes in spectra profiles, 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. These materials emit multicolor and white light with high quantum yields, long shelf life, and superb hydrolytic stability at ambient conditions.
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