Tris(8-hydroxyquinolinato)aluminum (Alq3 for short) is a coordination complex of aluminum(III) and the anion of 8-hydroxyquinoline (8-HQ). The nitrogen and oxygen atoms of 8-HQ are coordinated to the aluminum atom so that the complex takes an octahedral configuration. Alq3 has two isomers, meridional (mer, the 3-D structure on the left) and facial (fac, right). Each isomer forms multiple crystalline phases.
Alq3’s principal application is in organic light-emitting diodes (OLEDs). It is relatively inexpensive to make and has been used since the 1980s in devices that require fluorescent green light. It was later discovered that mer-Alq3 gives the green fluorescence; fac-Alq3 alone fluoresces blue. In 2006, R. Katakura and Y. Koide at Kanagawa University (Yokohama) reported synthetic methods for making both isomers in good yield and purity.
The ball that is dropped in Times Square in New York City on New Year’s Eve contains LEDs. As you watch it drop, think of Alq3!
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