Structural, thermal, and spectral characterization of the different crystalline forms of Alq3, tris(quinolin-8-olato)aluminum(III), an electroluminescent material in OLED technology

The interest in organic materials for use in organic light-emitting diodes (OLEDs) began with the pioneering report of efficient green electroluminescence from Alq3, tris(quinolin-8-olato)aluminum(III), by Tang and Van Slyke [C.W. Tang, S.A. Van Slyke, Appl. Phys. Lett. 51 (1987) 913]. After more than 20 years of intense research and development in OLEDs, Alq3 continues to be a widely used electroluminescent material in OLED technology. Alq3 is used in the electron-transport and/or electron-injecting layer in multilayer device structures and also as an effective host material for various dyes. Much is known about the properties of this metal chelate complex, yet much remains unknown despite numerous studies. In recent years, five crystalline phases (α, β, γ, δ, and ε) of Alq3 have been identified. In the present report, a combined structural, thermal, and spectroscopic (Raman, fluorescence, and nuclear magnetic resonance) analysis of different crystalline phases of Alq3 is presented.