Efficient, Scalable, and Solvent-free Mechanochemical Synthesis of the OLED Material Alq₃ (q = 8‑Hydroxyquinolinate)

Abstract

The aluminum complex Alq₃ (q = 8-hydroxyquinolinate), which has important applications in organic light-emitting diode materials, is shown to be readily synthesized as a pure phase under solvent-free mechanochemical conditions from Al­(OAc)₂OH and 8-hydroxyquinoline by ball milling. The initial product of the mechanochemical synthesis is a novel acetic acid solvate of Alq₃, and the α polymorph of Alq₃ is obtained on subsequent heating/desolvation of this phase. The structure of the mechanochemically prepared acetic acid solvate of Alq₃ has been determined directly from powder X-ray diffraction data and is shown to be a different polymorph from the corresponding acetic acid solvate prepared by solution-state crystallization of Alq₃ from acetic acid. Significantly, the mechanochemical synthesis of Alq₃ is shown to be fully scalable across two orders of magnitude from 0.5 to 50 g scale. The Alq₃ sample obtained from the solvent-free mechanochemical synthesis is analytically pure and exhibits identical photoluminescence behavior to that of a sample prepared by the conventional synthetic route