Hosts for High-Performance Phosphorescent Organic Light-Emitting Diodes Based on Carbazole Derivatives

Organic electroluminescent (EL) materials have many advantages when compared with their inorganic counterparts and, therefore, they have a wide range of potential applications in communication, information display, illumination, and so on. Phosphorescent organic light-emitting diodes (PHOLEDs) that contain late transition-metal complexes as emitters are particularly attractive due to their ability to harvest singlet and triplet excitons, which makes it possible to achieve an internal quantum efficiency of 100%. To suppress concentration quenching, a phosphorescent emitter is usually dispersed in a suitable host to obtain a high photoluminescent quantum yield. Developing a host with a suitable triplet energy level, charge-transporting ability, and thermal and film stability is thus the key to improving the performance of PHOLEDs. Carbazole-based chromophores are widely used in the synthesis of highly efficient hosts for PHOLEDs. However, these compounds are not universal or unique segments for constructing high performance hosts. Herein, up-to-date methods for chemical modifications to obtain hosts for high-performance PHOLEDs based on carbazole derivatives are presented in detail. These methods include heterocycle replacement and extension of the conjugated structure of the carbazole skeleton. Finally, some issues to be addressed and hotspots to be further investigated are also discussed. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.