One of the most important issues of the organic light-emitting diode (OLED) is the highly efficient blue-emissive material, which demands both excellent photoluminescent quantum yield (PLQY) and balanced carrier mobilities. Herein, a series of blue-emissive donor-π-acceptor (D-π-A) materials with fluorene π-bridge and their D-A analogues are synthesized and discovered with a theoretical combined experimental method. Based on the excellent electron mobility of the oxadiazole (OXZ) acceptor, it is further proven that the insertion of the fluorene π-bridge can not only contribute to the formation of hybrid local and charge-transfer excited state with high PLQY, but also give rise to the hole mobilities by enhanced intermolecular face-to-face stacking. As a result, the non-doped OLED of TPACFOXZ exhibits a high maximum external quantum efficiency approaching 10% with boosted and balanced hole and electron mobilities of 5.60 × 10 −5 and 6.60 × 10 −5 cm 2 V −1 s −1 , respectively, which are among the best results of the non-doped blue fluorescent OLEDs.

Novel host materials and their molecular design methods for phosphorescent materials are crucial for the application of phosphorescent organic light emitting diodes (PhOLEDs), which require balanced carrier injection and sufficient triplet energy levels (ET). Herein, two host materials, namely PPI22PPPBO and PPI33PPPBO, are designed by varying the linkage of benzoxazole (PBO) and phenanthroimidazole (PPI) groups with appropriate ET for green, yellow, and red phosphors. The meta‐link PPI33PPPBO is not only of smaller π‐conjugation, but also of more ordered face‐to‐face stacking for enhanced and more balanced carrier mobility. As a result, the green, yellow, and red PhOLEDs utilizing PPI33PPPBO as host materials show low turn‐on voltages of 2.8 V. The maximum external quantum efficiency (EQEmax) of the corresponding devices reaches 22.8%, 26.7%, and 17.6%, which is superior to that of the traditional host materials CBP and mCP, showing great application potential. More importantly, when the luminance is 1000 cd m−2, their EQE can still be as high as 21.9%, 25.5%, and 16.4%, corresponding to negligible efficiency roll‐offs of only 3.9%, 4.5%, and 6.8%. To the best of authors knowledge, it is the first time that PBO is applied to PhOLED host materials using a twisted connection method.

High efficiency and luminance are critical for commercialized blue organic light‐emitting diodes (OLEDs). Herein, a novel donor–acceptor (D–A) blue‐emissive molecule with a weak donor and acceptor is synthesized. The moderate hybrid local and charge transfer (HLCT) state character endows PPIBPO with blue fluorescence and high quantum efficiency. More importantly, the rigid, rod‐like molecular structure gives rise to the regularity of the stacking pattern of PPIBPO, which enables its extraordinary carrier mobilities in non‐doped OLED, the hole mobility and electron mobility are as high as 5.09 × 10−5 cm2 V−1 s−1 and 3.22 × 10−4 cm2 V−1 s−1, respectively. The non‐doped blue OLED of PPIBPO achieves a maximum external quantum efficiency (EQE) of 12.0% and a maximum luminance of 55023 cd m−2, which is one of the best values among the non‐doped blue OLEDs based on HLCT molecules. Furthermore, high‐efficiency two‐color hybrid warm white OLED with a maximum EQE up to 22.5% and maximum power efficiency of 87.0 lm W−1 is also achieved using PPIBPO as blue‐fluorophor.

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