Shandong Province Key Laboratory of Medical Physics and Image Processing Technology, School of Physics and Electronics, Shandong Normal University, Jinan 250358, China.
Shandong Province Key Laboratory of Medical Physics and Image Processing Technology, School of Physics and Electronics, Shandong Normal University, Jinan 250358, China.
Spectrochim Acta A Mol Biomol Spectrosc. 2020 Mar 15;229:117964. doi: 10.1016/j.saa.2019.117964. Epub 2019 Dec 19.
Pure organic molecules with blue emission have attracted much attention due to its important application in organic light emitting diodes (OLEDs), especially for which with aggregation induced emission (AIE) and thermally activated delayed fluorescence (TADF) properties. Theoretical study to reveal the inner luminescent mechanisms can promote its development. In this work, four kinds of molecules with perfluorobiphenyl (PFBP) unit as acceptor, non-substituted and tert-butyl substituted 9,9-dimethyl-9,10-dihydro-acridine (DMAC) unit as donors, are selected and their photophysical properties are studied in detail. The surrounding environment effects in toluene and solid phase are taken into consideration by the polarized continuum model (PCM) and the combined quantum mechanics and molecular mechanics (QM/MM) method respectively. Results show that geometric changes between the first singlet excited state (S) and ground state (S) are restricted in solid phase with decreased root-mean squared displacement (RMSD). Moreover, the Huang-Rhys factors and reorganization energies we calculated are all decreased in solid phase, which indicates that the non-radiative energy consumption process of S is hindered by enhanced intermolecular interactions in rigid environment, and it brings aggregation induced emission phenomenon. Furthermore, the substitution effect of tert-butyl in donor unit can efficiently decrease the energy gap and increase the spin-orbit coupling (SOC) constant, further promotes the intersystem crossing (ISC) and reverse intersystem crossing (RISC) rates. Meanwhile, molecules with donor-acceptor-donor (D-A-D) configuration have more efficient luminous performance than D-A type molecules due to the enhanced ISC and RISC processes. Thus, tert-butyl substituted D-A-D type molecules have outstanding TADF features. Our investigations provide a theoretical perspective for AIE and TADF mechanisms and propose a design strategy for efficient TADF molecules, which could promote the development of OLEDs.
具有蓝色发射的纯有机分子因其在有机发光二极管（OLED）中的重要应用而受到广泛关注，特别是对于具有聚集诱导发射（AIE）和热激活延迟荧光（TADF）性质的有机分子。理论研究揭示其内在发光机制可以促进其发展。在这项工作中，选择了四种以全氟联苯（PFBP）单元为受体、非取代和叔丁基取代的 9,9-二甲基-9,10-二氢吖啶（DMAC）单元为给体的分子，并详细研究了它们的光物理性质。通过极化连续体模型（PCM）和量子力学与分子力学相结合（QM/MM）方法分别考虑了周围环境在甲苯和固态中的影响。结果表明，固态中 S 态和基态（S）之间的几何变化受到限制，均方根位移（RMSD）减小。此外，我们计算的 Huang-Rhys 因子和重组能在固态中均减小，这表明在刚性环境中增强的分子间相互作用阻碍了 S 态的非辐射能量消耗过程，从而产生聚集诱导发射现象。此外，给体单元中叔丁基的取代效应可以有效地减小能隙并增加自旋轨道耦合（SOC）常数，进一步促进了体系间交叉（ISC）和反向体系间交叉（RISC）速率。同时，由于增强的 ISC 和 RISC 过程，具有给体-受体-给体（D-A-D）构型的分子比 D-A 型分子具有更高的发光性能。我们的研究为 AIE 和 TADF 机制提供了理论视角，并提出了高效 TADF 分子的设计策略，这将促进 OLED 的发展。
