Theoretical perspective for luminescent mechanism of thermally activated delayed fluorescence emitter with excited-state intramolecular proton transfer
Theoretical perspective for luminescent mechanism of thermally activated delayed fluorescence emitter with excited-state intramolecular proton transfer
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DOI：
10.1039/c9tc05299b
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发表时间：
2020-01-07
影响因子：
6.4
通讯作者：
Lin, Lili
中科院分区：
文献类型：
--
作者：
Jiang, Guanyu;Li, Feiyan;Lin, Lili
激发态分子内质子转移（ESIPT）和热激活延迟荧光（TADF）是发光材料有趣的光化学和光物理性质。最近，ESIPT [ACS Cent. 2017] 在 TQB 分子中实现了一种新颖的 TADF 分子设计策略。科学, 2017, 3(7), 769-777];然而，该分子的 TADF 和 ESIPT 机制尚不清楚。本工作基于势能曲线、能级和激发态衰减率的计算，研究了溶液和固相中TQB的TADF和ESIPT机制。结果发现，在 DMF 和固相中，TQB 的 S-1 中的质子转移都很容易。相比之下，DMF中T-1和T-2的质子转移稍微困难，而固相TQB的T-1中的势垒与室温能量相当。 T(2)TQB-TA -> S(1)TQB-TB 上转换路径对溶剂中 TQB 的 TADF 起着至关重要的作用，而 T(2)TQB-TB -> S(1)TQB-TB 对固相中 TADF 的贡献占主导地位。基于对TQB的研究，我们设计了两个分子，具有单个氢键的TQB*和具有两个氢键的TQB**。我们的计算结果表明，TQB**分子可以通过ESIPT实现双发射，是一种潜在的白光发光材料。 TQB* 中无法实现 ESIPT，而较高激发态和最低激发态之间存在较大的能隙。我们的研究为ESIPT和TADF机制提供了新的视角，有助于理解TQB的发光特性，并为新型功能性发光分子的设计提供一些见解。
Excited-state intramolecular proton transfer (ESIPT) and thermally activated delayed fluorescence (TADF) are interesting photochemical and photophysical properties for light-emitting materials. Recently, a novel design strategy for TADF molecules was realized in the TQB molecule by ESIPT [ACS Cent. Sci., 2017, 3(7), 769-777]; however, the TADF and ESIPT mechanisms for this molecule are not very clear. In this work, the TADF and ESIPT mechanisms for TQB in both solution and the solid phase were studied based on the calculation of potential energy curves, energy levels and decay rates of the excited states. It was found that proton transfer in S-1 for TQB is quite easy in both DMF and the solid phase. In contrast, the proton transfer in T-1 and T-2 in DMF is slightly difficult, while the barrier in T-1 for TQB in the solid phase is comparable with room temperature energy. The T(2)TQB-TA -> S(1)TQB-TB upconversion path plays a crucial role in the TADF of TQB in solvent, while T(2)TQB-TB -> S(1)TQB-TB has a dominant contribution to the TADF in the solid phase. Based on the investigation of TQB, we designed two molecules, TQB* with a single hydrogen bond and TQB** with two hydrogen bonds. Our calculation results indicate that the TQB** molecules can realize dual emission by ESIPT and are a potential light-emitting material for white light. No ESIPT can be realized in TQB*, while large energy gaps are found between the higher excited states and lowest excited states. Our investigation provides new perspectives for the ESIPT and TADF mechanisms, which can help in understanding the light-emitting properties of TQB and provide some insights on the design of new functional luminescent molecules.