Low Molar Mass Carbazole-Based Host Materials for Phosphorescent Organic Light-Emitting Diodes: A Review

The second-generation phosphorescent organic light-emitting diodes are formed using phosphorescent emitters, which can theoretically achieve 100% internal quantum efficiency. However, these emitting materials usually suffer from triplet-triplet annihilation (TTA) and/or concentration-quenching effects. To address the disadvantages, host-guest systems are used in the emitting layer, where the guest is dispersed into a host matrix. Carbazole is one of the most commonly used electron-donating fragments, which is widely applied as a building block for the synthesis of the mentioned host materials. In this review article, we describe the synthesis, thermal, electrochemical, and optoelectronic properties of the hosts with carbazolyl units as well as application of the matrixes in the phosphorescent devices. This review is written from the perspective of structural chemistry and the host materials are divided in several groups as 9-arylcarbazoles, twin derivatives containing two carbazolyl fragments, 3(2)-aryl(arylamino)-substituted, and 3,6(2,7)-diaryl(diarylamino)-substituted carbazoles.