Thermal, structural and photophysical properties of the organic semiconductor Alq3

This review describes the thermal, structural and photophysical properties of different polycrystalline phases of the organic semiconductor Alq(3). In particular the new blue luminescent delta-phase is shown to contain the facial isomer. The results obtained by using differential scanning calorimetry, X-ray diffraction, infrared spectroscopy, transient and delayed photoluminescence measurements clearly demonstrate the existence of this isomer. From the results presented it is now possible to obtain the pure facial isomer of Alq(3) in large quantities, providing the basis for further investigations to determine its effects on the performance of organic light-emitting diodes. Furthermore, recent results on the properties of the triplet states in Alq are presented. This includes the population of the electronic excited triplet state due to inter-system crossing and the spectrum of the phosphorescence. (C) 2004 WILEY-VCH Veriag GmbH & Co. KGaA, Weinheim.