Positive impact of chromophore flexibility on the efficiency of red thermally activated delayed fluorescence materials.
Positive impact of chromophore flexibility on the efficiency of red thermally activated delayed fluorescence materials.
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DOI：
10.1039/d1mh00028d
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发表时间：
2021-02
影响因子：
13.3
通讯作者：
Yuan-Yuan Wang-Yuan;Kaining Tong;Kai Zhang;Chen‐Han Lu;Xing Chen;Jingtang Liang;Chuan-kui Wang;Chung‐Chih Wu;M. Fung;Jian Fan
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文献类型：
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作者：
Yuan-Yuan Wang-Yuan;Kaining Tong;Kai Zhang;Chen‐Han Lu;Xing Chen;Jingtang Liang;Chuan-kui Wang;Chung‐Chih Wu;M. Fung;Jian Fan
近年来，刚性电子给体(D)和受体(A)被广泛用于构建D-A型热激活延迟荧光(TADF)材料。然而，生色团的稳定性并不总是对TADF材料的高效率做出积极贡献。在这里，通过对两种D-A型红色TADF化合物(PT-TPA和PT-Az)的比较研究，首次证明了生色团的灵活性对TADF材料效率的积极影响。在PT-Az中，末端苯基的转动受到乙烯连接基的抑制，导致其光致发光量子产率(PLQY)较低。相反，苯基自由旋转的PT-TPA对S1→S0跃迁表现出较低的重组能和较大的跃迁偶极矩，从而导致较高的荧光辐射衰减率。结果表明，基于PT-TPA的优化器件在单一基质中掺杂时的最大外量子效率(EQE)为29.7%(632 Nm)，而在激基复合体中的EQE为28.8%(648 Nm)。本研究揭示了生色团的柔性对TADF材料的光物理性质和器件效率的影响，这些结果可能为高效发射体的分子设计提供有价值的指导。
Rigid electron donors (D) and acceptors (A) have been widely used in recent years for the construction of D-A type thermally activated delayed fluorescence (TADF) materials. However, the chromophore robustness does not always make a positive contribution to the high efficiency of TADF materials. Here, the comparison study of two D-A type red TADF compounds (PT-TPA and PT-Az) demonstrated, for the first time, the positive impact of chromophore flexibility on the efficiency of TADF materials. In PT-Az, the rotation of terminal phenyl groups is restrained by an ethylene linker, leading to its inferior photoluminescence quantum yield (PLQY). In contrast, PT-TPA with free rotation of the phenyl groups showed a low reorganization energy and a large transition dipole moment for the S1→ S0 transition, which resulted in a high fluorescence radiative decay rate. As a result, the optimized devices based on PT-TPA gave a maximum external quantum efficiency (EQE) of 29.7% (632 nm) when doped in a single host and an EQE of 28.8% (648 nm) in an exciplex host. This study provided an insight into the impact of chromophore flexibility on the photophysical properties and device efficiency of TADF materials, and these results may provide valuable guidance for the molecular design of efficient emitters.