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Metal-Organic Frameworks

Chemistry In Pictures

Chemistry in Pictures: Turning red (and pink)

by Brianna Barbu
May 3, 2022

fluorescent red crystals.
Credit: Muhammad Abbas
a vial containing bright pink glowing solids.
Credit: Muhammad Abbas
The MOFs after being cooled with liquid nitrogen.

These neat, rectangular metal-organic framework (MOF) crystals fluoresce bright red under ultraviolet light thanks to the rare earth metals embedded in the crystal structure. And that’s not all they can do—when the crystals are cooled with liquid nitrogen to 77 K, the fluorescence color turns from red to hot pink. Muhammad Abbas, a PhD student in Kenneth Balkus’s lab at the University of Texas at Dallas, is exploring the relationship between the elemental makeup of rare earth MOFs and their color-changing fluorescence. MOFs made with europium give off red light when they fluoresce. If the MOF contains a bit of another rare earth element such as terbium, the metal ions can undergo an energy transfer that changes the fluorescence wavelength. The energy transfer—and therefore the color change—is sensitive to temperature, which could make the MOFs useful as thermal sensors.

Submitted by Muhammad Abbas. Follow him on Twitter @MAbbas003

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