The Correlation between Structure and Physical Properties of Soluble Host for Blue Phosphorescent OLED

Blue phosphorescent organic light-emitting diodes (OLED) were prepared with the host materials designed for solution process. 3,5-di(9H-carbazol-9-yl)-1,1′:2′,1″-terphenyl and 3,5-di(9H-carbazol-9-yl)-1, 1′:2′,1″:2″-quarterphenyl were synthesized to investigate the relationship among the molecular structure, solubility, and optoelectronic properties. These materials used 1,3-bis(carbazole-9-yl)benzene as the core structure and ortho-biphenyl or ortho-terphenyl was introduced into the benzene ring between the two carbazole moieties of 1,3-bis(carbazole-9-yl)benzene for the purpose of reducing symmetry and planarity of the molecules. Design concept in this study is unique in terms of the improvement of solubility without the inclusion of an alkyl group, which is generally disadvantageous for OLED stability. The prepared materials, especially with ortho-terphenyl, showed sufficiently better solubility, thermal stability, and high triplet energy even though the extended state of benzene rings. Therefore, it can be employed as a suitable host design concept capable of forming a solution-processed emitting layer having an improved stability for a fabrication of blue phosphorescent OLEDs.