可升华离子型铱配合物具有光电性质易调、合成提纯简单等优势，可作为一大类新型磷光材料应用于有机发光二极管（organic light-emitting diode, OLED），展现出广阔的应用前景，取得了一定的进展。然而目前，基于可升华离子型铱配合物的红光OLED报道很少，效率较低，难以满足平板显示和白光照明的需要。因此，本论文设计合成了一系列新型红光可升华离子型铱配合物，深入研究其光物理、电化学性质，并设计合适的热活化延迟荧光（thermally activated delayed fluorescence, TADF）主体材料进行敏化，研究电致发光性能。主要研究成果如下：1. 通过扩大配体共轭体系和减小辅助配体电子云密度，调节前线轨道能级并抑制非辐射跃迁，设计合成了2-苯基喹啉主配体和咪唑类辅助配体，开发了一系列橙红光发射的可升华离子型铱配合物。实验结果表明，在溶液中，配合物的光致发光波长位于560-580 nm之间，量子产率高达83%；由此制备的OLED的色坐标（0.49, 0.49），最大外量子效率14.7%，实现了基于离子型铱配合物的橙红光OLED的最优性能。2. 通过主配体上引入氮原子，调节前线轨道能级并增强辐射跃迁，设计合成了2,3-二苯基喹喔啉主配体，开发了两种红光发射的可升华离子型铱配合物。实验结果表明，在溶液中，配合物在650 nm处呈现无肩峰的发射，量子产率高达82%，这是因为配合物具有较强的金属到配体的电荷转移跃迁特征。由此制备的OLED实现了标准红光发射，电致发光波长632 nm，色坐标（0.67, 0.33），最大外量子效率10.3%，实现了基于离子型铱配合物的红光OLED的最优性能。3. 通过引入具有强给受体性质、大共轭体系和强刚性的芴基蒽醌类受体基团和咔唑类给体基团，调节前线轨道能级、抑制非辐射跃迁并增强辐射跃迁，设计合成了一系列TADF主体材料，与以上可升华离子型铱配合物的能级相匹配，发光效率高。使用这种TADF主体敏化红光可升华离子型铱配合物制备OLED，电致发光波长640 nm，色坐标（0.69，0.31），最大外量子效率15.1%，实现了基于可升华离子型铱配合物的OLED的最红光色、最佳性能。
Sublimable cationic iridium(III) complexes show great promise in phosphorescent organic light-emitting diode (OLED), due to their advantages in material design, synthesis, purification and photophysical properties. However, it remains challenging to realize high-efficiency red OLEDs based on sublimable cationic iridium(III) complexes – that restricted their applications in flat-panel displays and white lightings. Here we develop a series of red-emitting sublimable cationic iridium(III) complexes, and explore their photophysical and electrochemical behaviors. We then report thermally activated delayed fluorescence (TADF) host materials to sensitize these cationic iridium(III) complexes, fabricated OLEDs, and achieved superior electroluminescence performance.We highlight the main results as follows:1. We develop a series of orange-red-emitting sublimable cationic iridium(III) complexes based on ligands with extended π-conjugation and reduced electron cloud density. The use of 2-phenylquinoline as the main ligands and imidazole derivatives as the ancillary ligand enables orange-red emission with narrow energy gap and high efficiency due to suppression of the non-radiative transitions. In solutions, these complexes show orange emissions at 560-580 nm with a high photoluminescence quantum yield (PLQY) of 83%. We then fabricate OLEDs based on these complexes by vacuum evaporation deposition, achieving orange-red emission with color coordinates of (0.49, 0.49) and a maximum external quantum efficiency (EQE) of 14.7%, which is the highest performance of orange-red-emitting OLEDs based on sublimable cationic iridium(III) complexes to date.2. We develop two red-emitting sublimable cationic iridium(III) complexes based on the ligand with extra nitrogen heteroatoms. The use of 2,3-phenylquinoxaline as the main ligand enables high-efficiency red emission. In solutions, these complexes exhibit featureless emission peaked at 650 nm with PLQY of 82%, owing to their strong metal-to-ligand charge transfer (MLCT) character. The OLEDs show standard red emission peaked at 632 nm with color coordinates of (0.67, 0.33), and the maximum EQE reaches 10.3%, which breaks through the highest performance of red-emitting OLEDs based on sublimable cationic iridium(III) complexes.3. We develop three TADF host materials to sensitize these sublimable cationic iridium(III) complexes to further improve the device performance. The fluorenyl anthraquinone derivative is selected as the acceptor and carbazole derivatives act as donors, due to their strong donor/acceptor properties, extended π-conjugated system, and strong rigidity. These TADF host materials show closed frontier orbital energy levels to those of red-emitting complexes and fast reverse intersystem crossing, that enables OLEDs with a peak wavelength of 640 nm, color coordinates of (0.69, 0.31), and a maximum EQE of 15.1%, exceeding the previous record.
