基于菲并咪唑衍生物的激发态调控及其在蓝光/白光OLED中的应用

Excited State Regulation Based on Phenanthrimidazole Derivatives and Its Application in Blue/White Light OLED

摘要:

有机发光二极管的应用已经步入我们的生活领域，但是高效率的蓝色发光材料仍然是限制其效率进一步提高的瓶颈。基于“交叉长短轴”结构模型，以菲并咪唑作为蓝光的构筑基元，设计合成了两个纯蓝光/天蓝光分子NPD和NCNPD。实验和理论计算结果表明：NCNPD分子由于N1位点引入了较强吸电子能力的氰基而表现出了更强的CT态特征，在溶液和薄膜中表现出了比NPD更红的发射和更低的荧光量子产率（PLQY），在此基础上NPD及NCNPD在非掺杂/掺杂器件的最大外量子效率（EQE）分别为1.84%/6.90%和0.76%/6.38%，充分说明在菲并咪唑长轴骨架上引入强CT态组分，以及再配合短轴修饰氰基来增强分子CT态特征，会对分子的光电性能造成不利的影响，凸显出合理调控蓝光材料激发态中的LE/CT态组分的分布和强度的必要性；基于NPD分子开发了一系列高性能的荧磷混合白光OLED，通过调控蓝光层/黄光层的厚度，暖白光及正白光器件的最大EQE达到了23.45%和15.24%；通过调控间隔层的厚度，制备了低滚降、光色稳定的正白光OLED，最高EQE为11.54%，显色指数（CRI）达到了了50。

Abstract:

The application of organic light-emitting diodes （OLEDs） has been widely used in our life，but the high efficiency blue light-emitting materials are still the bottleneck restricting their further improvement. Based on the “crossed long-short axis” structure model，we designed and synthesized two pure-blue/sky-blue luminescent molecules，NPD and NCNPD，using phenanthroimidazole （PI） as the building block. Based on the experimental results and theoretical calculation，it is found that the NCNPD exhibits a stronger CT property due to the introduction of an electron-withdrawing cyano group at the N1 position of PI. As a result，NCNPD shows red shifted emission peaks and lower photoluminescence quantum yields （PLQYs） than NPD in solution and neat film. What’s more，the maximum external quantum efficiencies （EQEs） of NPD and NCNPD in nondoped/doped OLEDs are 1.84%/6.90% and 0.76%/6.38%，respectively，indicating that introducing strong CT components to the long-axis backbone of PI，combined with the modification of the short-axis skeleton to increase the CT intensity，will negatively affect the optoelectronic performances of molecules，and it is critical to modulate the distribution of the LE/CT component in the excited states of blue-emitting molecules in a reasonable manner. Finally，a series of high-performance hybrid white OLEDs were developed using NPD as a blue emitter. By regulating the thickness of blue- and yellow-emitting layers，the maximum EQEs of the warm-white and pure-white OLEDs reached 23.45% and 15.24%，respectively. On this basis，by adjusting the thickness of the interlayer，a pure-white OLED with low-efficiency roll-off and stable spectra was fabricated，achieving a maximum EQE of 11.54% with a color rendering index （CRI） exceeding 50.