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

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.