Zhang Qing, Liu Tao, Shi Zhouyang, Zheng Zhong, Lv Chunyan, Wang Xin, Zhang Yujian
Department of Materials Chemistry, Huzhou University, East 2nd Ring Rd. No. 759, Huzhou, 313000, People's Republic of China.
Zhejiang Jiuhe Geological and Ecological Environment Planning and Design Co., LTD, Huzhou, 313002, People's Republic of China.
Phys Chem Chem Phys. 2024 Feb 7;26(6):5147-5155. doi: 10.1039/d3cp05439j.
Narrowband emitters with thermally activated delayed fluorescence (TADF) features, known as multi-resonant TADF (MR-TADF) emitters, are drawing increasing research interest owing to their properties of high efficiency and excellent color purity. However, MR-TADF-based devices often face serious efficiency roll-off at high luminance intensity, which could be attributed to undesired triplet-triplet annihilation (TTA) caused by the structural planarity and relatively small reverse intersystem crossing rate constants () of MR-TADF emitters. Herein, combining a sp-C inserted strategy to suppress harmful bimolecular interactions and chalcogens to improve the , a series of asymmetric narrowband emitters, namely, DMAC-O, DMAC-S, and DMAC-Se, have been theoretically designed to break the slow rate-limiting step of of experimental BN-DMAC. For comparison, both O and Se atoms were doped into the MR skeleton to substitute two sp-inserted units, yielding BN-O-Se. The combination of TD-DFT and the wavefunction-based STEOM-DLPNO-CCSD approach exhibits that those asymmetric molecules are promising for simultaneously exhibiting narrow emission spectral full-width at half-maximums (FWHMs) and high luminous efficiencies. The contributions of chalcogens to hole distributions result in red-shifted fluorescent peaks, and the asymmetric strategy also helps with twisted molecular configuration, which is beneficial for suppressing unfavorable TTA. Furthermore, the incorporation of chalcogens is sufficient to promote the intersystem crossing and reverse intersystem crossing channels of asymmetric emitters. More importantly, the doped heavy Se atom results in a significantly increased of 2.32 × 10 s for DMAC-Se, which is more than 200 times larger than 1.09 × 10 s of pristine BN-DMAC. These results suggest that the combination of the heavy Se atom and an sp-inserted unit is a feasible strategy for achieving poor planarity and significantly enhancing , which will help in harvesting triplet excitons, thereby inhibiting efficiency roll-off in corresponding narrowband devices.
具有热激活延迟荧光（TADF）特性的窄带发射体，即多共振TADF（MR-TADF）发射体，因其高效率和出色的色纯度特性而吸引了越来越多的研究兴趣。然而，基于MR-TADF的器件在高亮度强度下常常面临严重的效率滚降，这可能归因于MR-TADF发射体的结构平面性和相对较小的反向系间窜越速率常数（）导致的不期望的三重态-三重态湮灭（TTA）。在此，结合sp-C插入策略以抑制有害的双分子相互作用和硫族元素以改善，理论上设计了一系列不对称窄带发射体，即DMAC-O、DMAC-S和DMAC-Se，以打破实验性BN-DMAC的缓慢限速步骤。为了进行比较，将O和Se原子都掺杂到MR骨架中以替代两个sp插入单元，得到BN-O-Se。TD-DFT和基于波函数的STEOM-DLPNO-CCSD方法的结合表明，那些不对称分子有望同时展现出窄的发射光谱半高宽（FWHM）和高的发光效率。硫族元素对空穴分布的贡献导致荧光峰红移，并且不对称策略也有助于扭曲分子构型，这有利于抑制不利的TTA。此外，硫族元素 的引入足以促进不对称发射体的系间窜越和反向系间窜越通道。更重要的是，掺杂的重Se原子使DMAC-Se的显著增加至2.32×10 s，这比原始BN-DMAC的1.09×10 s大200多倍。这些结果表明，重Se原子和sp插入单元的结合是实现不良平面性并显著提高的可行策略，这将有助于捕获三重态激子，从而抑制相应窄带器件中的效率滚降。
