Wang Xiaorui, Zou Haipei, Liu Huanling, Mu Qingfang, Zhang Kai, Xu Yuanyuan, Fan Jianzhong
Shandong Province Key Laboratory of Medical Physics and Image Processing Technology, Institute of Materials and Clean Energy, School of Physics and Electronics, Shandong Normal University, Jinan 250014, China.
School of Science, Qilu University of Technology (Shandong Academy of Sciences), Jinan 250353, China.
Phys Chem Chem Phys. 2023 Apr 12;25(15):10977-10990. doi: 10.1039/d2cp05848k.
In recent studies, thermally activated delayed fluorescence (TADF) molecules with a through space charge transfer (TSCT) feature have attracted wide attention. Nevertheless, studies on the substitution effects on the photophysical properties of TSCT-based TADF molecules are insufficient, and the corresponding theoretical investigations and effective molecular design strategies are highly desired. Herein, in order to reveal the inner mechanisms between the substitution effects from the donor unit and the luminescent properties for TSCT-based TADF molecules, the photophysical properties of nine TSCT-based TADF molecules (including one molecule with dual configurations) are theoretically studied. Based on density functional theory (DFT) and time-dependent density functional theory (TD-DFT) coupled with the thermal vibration correlation function (TVCF) method, basic physical parameters such as geometric changes, electron-donating abilities, adiabatic singlet-triplet energy gaps, TSCT ratios, hole and electron distributions and excited state decay rates are calculated and analyzed. The relationships between molecular structures and luminescent properties are determined. Our results show that molecules with carbazole as the donor possess large oscillator strengths and transition dipole moments, and a prominent radiative decay process is determined. Moreover, molecules with phenazine as the donor present small geometric changes, strong electron-donating capability and tiny adiabatic singlet-triplet energy gap, and all these factors contribute to the effective reverse intersystem crossing process (RISC), and this feature makes these molecules promising TSCT-based TADF molecules. Furthermore, dual configurations for 2CTF molecules are determined (2CTF2.1 and 2CTF2.2), and 2CTF2.1 with a large TSCT ratio possessing a fast fluorescence decay process and high luminescence efficiency can be achieved. As for 2CTF2.2 with a small TSCT ratio, a remarkable RISC process is determined and high exciton utilization can be realized. Thus, 2CTF can be regarded as a self-doping TADF molecule and a remarkable TADF feature is detected. Our investigations provide a perspective for experimental measurements and propose an effective design strategy for efficient TSCT-based TADF molecules.
在最近的研究中，具有空间电荷转移（TSCT）特征的热激活延迟荧光（TADF）分子引起了广泛关注。然而，关于基于TSCT的TADF分子的取代基对其光物理性质影响的研究并不充分，因此迫切需要相应的理论研究和有效的分子设计策略。在此，为了揭示供体单元的取代效应与基于TSCT的TADF分子发光性质之间的内在机制，对九个基于TSCT的TADF分子（包括一个具有双重构型的分子）的光物理性质进行了理论研究。基于密度泛函理论（DFT）、含时密度泛函理论（TD-DFT）以及热振动相关函数（TVCF）方法，计算并分析了诸如几何变化、给电子能力、绝热单重态-三重态能隙、TSCT比率、空穴和电子分布以及激发态衰减率等基本物理参数。确定了分子结构与发光性质之间的关系。我们的结果表明，以咔唑为供体的分子具有较大的振子强度和跃迁偶极矩，并确定了显著的辐射衰减过程。此外，以吩嗪为供体的分子几何变化小、给电子能力强且绝热单重态-三重态能隙小，所有这些因素都有助于有效的反向系间窜越过程（RISC），这一特性使这些分子成为有前景的基于TSCT的TADF分子。此外，确定了2CTF分子的双重构型（2CTF2.1和2CTF2.2），具有大TSCT比率的2CTF2.1能够实现快速的荧光衰减过程和高发光效率。对于具有小TSCT比率的2CTF2.2，确定了显著的RISC过程并可实现高激子利用率。因此，2CTF可被视为一种自掺杂TADF分子，并检测到了显著的TADF特征。我们的研究为实验测量提供了一个视角，并为高效的基于TSCT的TADF分子提出了一种有效的设计策略。
