Hao Zhaoran, Zhang Kai, Chen Kuan, Lu Zhiyun, Wang Pu, Zhu Weiguo, Liu Yu
College of Chemistry, Key Lab of Environment-Friendly Chemistry and Application in Ministry of Education, Xiangtan University, Xiangtan, 411105, China.
School of Materials Science and Engineering, Jiangsu Collaboration Innovation, Center of Photovoltaic Science and Engineering, Jiangsu Engineering Laboratory of Light-Electricity-Heat Energy-, Converting Materials and Applications, National Experimental Demonstration Center for Materials Science and Engineering, Changzhou University, Changzhou, 213164, China.
Chem Asian J. 2020 Oct 1;15(19):3003-3012. doi: 10.1002/asia.202000544. Epub 2020 Sep 1.
Bimetallic complexes have become an emerging hot topic in field of luminous applications in recent years. Unlike the traditional modification on a cyclometalated ligand, grafting an additional metal ion provides a novel approach to tune molecular conjugation as well as the spin orbital coupling (SOC). Herein, we demonstrate a new kind of binuclear platinum(II) complex Pt-3 that possesses an asymmetric thiophenpyridine-isoquinoline bridging ligand. Compared to its mononuclear analogues of Pt-1 and Pt-2, an extremely large redshift emission from 576 and 618 nm to 721 nm was observed in solution. Binding of two metal ions helps to enhance molecular planarity, extend conjugation and suppress excited state distortion. However, their quantum yields tend to remarkably decrease with increasing red-shift emission as following the "energy gap law". The relatively larger HOMO/LUMO separation that induced by the second platinum ion also decreases the oscillator strength at the lowest singlet state, and goes against the fast radiative decay process. Solution-processed organic light-emitting diodes (OLEDs) based on Pt-1, Pt-2 and Pt-3 achieved external quantum efficiencies (EQEs) and luminance/radiant emittance of 13.6% and 13640 cd/m , 3.5% and 3754 cd/m , 0.9% and 7981 mW/Sr/m with the corresponding electroluminescent (EL) emission peaked at 580 nm, 625 nm and 708 nm, respectively. This work emphasizes the complement argument of the commonly largely reported symmetric binuclear configurations, and provides a new view to photophysical mechanism and design strategies for bimetallic species.
近年来，双金属配合物已成为发光应用领域中一个新兴的热门话题。与传统的环金属化配体修饰不同，引入额外的金属离子为调节分子共轭以及自旋轨道耦合（SOC）提供了一种新方法。在此，我们展示了一种新型的双核铂（II）配合物Pt-3，它具有不对称的噻吩吡啶-异喹啉桥联配体。与其单核类似物Pt-1和Pt-2相比，在溶液中观察到发射从576和618 nm发生了极大的红移，至721 nm。两个金属离子的结合有助于增强分子平面性、扩展共轭并抑制激发态畸变。然而，遵循“能隙定律”，随着发射红移增加，它们的量子产率往往会显著降低。由第二个铂离子引起的相对较大的HOMO/LUMO分离也降低了最低单重态的振子强度，不利于快速辐射衰变过程。基于Pt-1、Pt-2和Pt-3的溶液处理有机发光二极管（OLED）的外量子效率（EQE）和亮度/辐射发射率分别为13.6%和13640 cd/m²、3.5%和3754 cd/m²、0.9%和7981 mW/Sr/m²，相应的电致发光（EL）发射峰值分别在580 nm、625 nm和708 nm。这项工作强调了对通常大量报道的对称双核构型的补充观点，并为双金属物种的光物理机制和设计策略提供了新的视角。
