Design,Synthesis And Photoelectronic Property Of Red-Emitting Iridium(Ⅲ) Complexes With Phenylquinoline-Carbazole Derivatives As Main Ligands

Solution-processed phosphorescent organic light-emitting diodes（OLEDs） are attracting a lot of attention in the past decades owing to their potential application in the field of large-area and cost-effective manufacturing of full-color flat panel displays and solid-state lighting sources. Over the past decade, numerous Ir（III）-based phosphorescent materials have been developed. The performance of OLEDs can be greatly improved by using Ir（III）-based phosphorescent emitters because both the singlet and triplet excitons can be harvested for radiative decay and the internal quantum efficiency can reach close to 100%. Phenylquinoline-carbazole（PQCz） is a donor-acceptor structure, which can improve carrier transportion. We optimized the PQCz and synthesized a series of red-emitting Ir（III） complexes based on PQCz derivatives as main ligands. Furthermore, the photoelectric propertiy of these complexes were investigated systematically. Details are as follows:（1） A novel red-emitting Ir（III） complex Ir-CHO with formyl-functionalized phenylpyridine ligands was synthesized and characterized to investigate the impact of the electron-withdrawing formyl group on the optoelectronic properties. The resulting Ir（III） complexes showed excellent thermal stability and can be fabricated via solution processing. Remarkably, the introduction of the electron-withdrawing ppy-CHO aids to enhance the phosphorescence properties. Ir-CHO-doped red OLED exhibited the highest performance, achieving a maximum luminous efficiency（LE） of 14.3 cd/A and external quantum efficiency（EQE） of 8.4%, which was superior to those of Ir-OH and Ir-PQCz based red OLEDs. Furthermore, WOLEDs with Ir-CHO as the red emitters achieved an excellent high LE of 26.1 cd/A and EQE of 10.9%. Keeping the results in mind, we believe that this study suggests a simple and useful strategy to design novel Ir（III） complexes for highly efficient phosphorescent OLEDs by exploring the potential of electron-withdrawing formyl functional groups.（2） We have presented the synthesis and properties of a red-emitting homopolymer Ir-P that contains a norbornenyl derived backbone and Ir（III） complexes “side chains”. The polymer is more thermally stable than the parent complex Ir-ppy and possesses good film-forming properties. According to the photophysical measurements in the solution and the neat film, efficient PL was still obtained despite the close proximity of the Ir（III） complexes along the polymer backbone. More importantly, Ir-P solution can be directly inkjet-printed on photo paper and PET to form a special pattern emitting red light under UV lamp. Remarkably, even upon bending, the pattern can evenly emit. Finally, we show that the red OLED based on Ir-P exhibited a lower turn-on voltage and a better Commission Internationale de L?Eclairage（CIE） coordinates relative to Ir-ppy.（3） A series of star-shaped red-emitting Ir（III） complexes Ir-x F with fluorine-based branches was synthesized and the thermal, photophysical, electrochemical and electroluminescent properties of these Ir（III） complexes were measured. The resulting Ir（III） complexes showed excellent thermal stability. The photoluminescent quantum yield(Ф_PL) Ir-xF were higher than Ir-0, which because the fluorine-based branches can control the intermolecular interactions effectively. The turn-on voltages of OLEDs based on the resulting Ir（III） complexes were very low（2.8-4.6 V）. Moreover, all the OLEDs had the similar and good performance（LE were around 20 cd/A） at the low dopant content of Ir（III） complexes. When the dopant content over 10 wt%, the OLEDs based on Ir-x F exhibited better performance than Ir-0. More importantly, the non-doped OLED based on Ir-2F achieved a maximum LE of 5.2 cd/A and EQE of 3.1%.（4） A novel star-shaped red-emitting Ir（III） complexes Ir-D1 with triphenylamine（TPA）-based branches was synthesized. To investigate the influence of the incorporation of TPA, another complex（Ir-D0） were also prepared. The thermal, photophysical, electrochemical and electroluminescent properties of these Ir（III） complexes were measured. The photoluminescent quantum yield(Ф_PL) Ir-D were higher than Ir-0, which because the TPA-based branches can control the intermolecular interactions effectively. The turn-on voltages of OLEDs based on the resulting Ir（III） complexes were very low（2.5-2.8 V）. Moreover, the maximum LE for all the OLEDs were recorded between 17.5 and 20.6 cd/A.