Characterization of isomers in aluminum tris(quinoline-8-olate) by one-dimensional²⁷ Al nuclear magnetic resonance under magic-angle spinning

Utz, Marcel, Nandagopal, Magesh, Mathai, Mathew and Papadimitrakopoulos, Fotios (2003) Characterization of isomers in aluminum tris(quinoline-8-olate) by one-dimensional²⁷ Al nuclear magnetic resonance under magic-angle spinning. Applied Physics Letters, 83 (19), 4023. (doi:10.1063/1.1623945).

Abstract

Solid-state ²⁷ Al NMR spectra under magic-angle spinning of different forms of aluminum tris(quinoline-8-olate) (Alq₃) are presented. Alq₃ is an organometallic complex of great importance in the context of organic light-emitting diodes. Our results demonstrate a strong difference in the asymmetry of the electric field gradient (EFG) tensor at the aluminum site between the α and the recently discovered δ polymorph of Alq₃. While the EFG is nearly planar (η=1) in the α phase, it is nearly axially symmetric (η=0) for the δ phase. This result provides strong support to the hypothesis that the δ phase contains the facial isomer of Alq₃. While the spectra of both the α and the δ polymorphs exhibit sharp features, highly disordered forms of Alq₃ obtained from rapid vapor deposition onto a cold substrate, yield broadened spectra, indicating substantial structural disorder in the local geometry of different Alq₃ molecules.

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Contributors

Author: Marcel Utz

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