Synthesis of new bipolar host materials based on 1,2,4-oxadiazole for blue phosphorescent OLEDs

• Novel 1,2,4-oxadiazole based host materials were facile synthesized and used in organic light-emitting diodes.
• Their thermal stabilities and optical energy levels revealed that they were suitable for good host materials.
• High triplet energies were achieved.
• Good blue phosphorescence were obtained.

Two novel bipolar host materials, namely 3,5-bis(4-(9H-carbazol-9-yl)phenyl)-1,2,4-oxadiazole (pCzmOXD) and 3,5-bis(3-(9H-carbazol-9-yl)phenyl)-1,2,4-oxadiazole (mCzmOXD) were designed and synthesized, by incorporating a new block 1,2,4-oxadiazole as the n-type moiety and changing its linking pattern with carbazole. As expected, high triplet energy (over 2.81 eV) for mCzmOXD was achieved due to the intrinsic meta-linkage of 1,2,4-oxadiazole. When both materials were applied in blue phosphorescent organic light-emitting diodes, good performance of 13.0 cd A−1/16.0 cd A−1 were achieved for pCzmOXD and mCzmOXD in iridium(III) bis[(4,6-difluorophenyl)pyridinato-N,C′2]bis[(4,6-difluorophenyl)pyridinato-N,C2′] picolinate (FIrpic)-based devices, respectively.

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