The Role of Local Triplet Excited States and D-A Relative Orientation in Thermally Activated Delayed Fluorescence: Photophysics and Devices.
The Role of Local Triplet Excited States and D-A Relative Orientation in Thermally Activated Delayed Fluorescence: Photophysics and Devices.
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DOI：
10.1002/advs.201600080
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发表时间：
2016-12
期刊：
影响因子：
15.1
通讯作者：
Monkman, Andrew P.
中科院分区：
文献类型：
--
作者：
Dias, Fernando B.;Santos, Jose;Graves, David R.;Data, Przemyslaw;Nobuyasu, Roberto S.;Fox, Mark A.;Batsanov, Andrei S.;Palmeira, Tiago;Berberan-Santos, Mrio N.;Bryce, Martin R.;Monkman, Andrew P.
在这里，报道了对发射体分子 DPTZ-DBTO2 的全面光物理研究，显示了热激活延迟荧光 (TADF)，具有近正交的电子供体 (D) 和受体 (A) 单元。结果表明，DPTZ-DBTO2 由于其接近刚性的分子几何形状，具有最小的单线态-三线态能量分裂。然而，局域三重态（3LE）和电荷转移态、单重态和三重态（1CT、3CT）之间的电子耦合，以及 D-A 单元关于正交几何结构的动态摇摆效应对于实现高效 TADF 至关重要。在低极性溶剂中，客体发射单线态 1CT 态直接耦合到近简并 3LE，通过自旋轨道耦合电荷转移机制 (SOCT) 有效地收集三线态。然而，在极性较高的溶剂中，DPTZ-DBTO2 中的发射 CT 状态会移至（静态）3LE 以下，导致 TADF 效率降低。 1CT和3LE态之间相对较大的能量差以及1CT到3CT超精细耦合的极低效率是导致TADF效率降低的原因。因此，1CT 和 3LE 之间的电子耦合以及 D-A 单元的（动态）方向都是决定反向系统间交叉过程以及 TADF 高效率的关键因素。
Here, a comprehensive photophysical investigation of a the emitter molecule DPTZ‐DBTO2, showing thermally activated delayed fluorescence (TADF), with near‐orthogonal electron donor (D) and acceptor (A) units is reported. It is shown that DPTZ‐DBTO2 has minimal singlet–triplet energy splitting due to its near‐rigid molecular geometry. However, the electronic coupling between the local triplet (3LE) and the charge transfer states, singlet and triplet, (1CT, 3CT), and the effect of dynamic rocking of the D–A units about the orthogonal geometry are crucial for efficient TADF to be achieved. In solvents with low polarity, the guest emissive singlet 1CT state couples directly to the near‐degenerate 3LE, efficiently harvesting the triplet states by a spin orbit coupling charge transfer mechanism (SOCT). However, in solvents with higher polarity the emissive CT state in DPTZ‐DBTO2 shifts below (the static) 3LE, leading to decreased TADF efficiencies. The relatively large energy difference between the 1CT and 3LE states and the extremely low efficiency of the 1CT to 3CT hyperfine coupling is responsible for the reduction in TADF efficiency. Both the electronic coupling between 1CT and 3LE, and the (dynamic) orientation of the D–A units are thus critical elements that dictate reverse intersystem crossing processes and thus high efficiency in TADF.
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