Thermal and structural properties of the organic electroluminescent material tris(8-hydroxyquinoline)aluminum (Alq_3)

摘要

Using differential scanning calorimetry (DSC) measurements in combination with structural and optical characterization we have investigated the formation conditions of different phases of tris(8-hydroxyquinoline) aluminum (Alq_3). Vibrational analysis by IR and Raman spectroscopy show significant differences between α-phase and δ-phase of Alq_3 that can be explained by less intermolecular interaction between the ligands or a higher symmetry of the molecule in δ-Alq_3. Further we report an efficient method to obtain blue luminescent δ-Alq_3 by a simple annealing process. This allows to prepare large amounts of pureδ-Alq_3 choosing appropriate annealing conditions, which is the prerequisite for further characterization of this blue luminescent phase. Using this method we prepared thin films of blue luminescent Alq_3 that might be of interest for blue organic light emitting devices (OLEDs).