Vibrational Damping Reveals Vibronic Coupling in Thermally Activated Delayed Fluorescence Materials.
Vibrational Damping Reveals Vibronic Coupling in Thermally Activated Delayed Fluorescence Materials.
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DOI：
10.1021/acs.chemmater.0c03783
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发表时间：
2021-05-11
期刊：
影响因子：
--
通讯作者：
Bryce MR
中科院分区：
文献类型：
--
作者：
Hempe M;Kukhta NA;Danos A;Fox MA;Batsanov AS;Monkman AP;Bryce MR
我们研究了一系列以螺环为供体，2-亚苯基嘧啶为受体的D-A分子。在其中两种材料中，螺环中心有效地将D单元从光学上无害但在结构上有影响的金刚烷基侧基中分离出来。在第三种材料中，直接连接到受体上的金刚烷基对电子性质有很大影响。在溶液、Zeonex聚合物基质和Nat薄膜中的稳态和时间分辨光物理研究表明，取代基影响与反向系间交叉(RISC)和热激活延迟荧光(TADF)相关的单态和三态之间的振动耦合效率，而不显著改变材料中的单态-三态能隙。金刚烷基用于增加链段的质量和惯性，从而抑制分子内的运动(振动和旋转)。这种替代模式揭示了大幅度(主要是D-A二面角摇摆)运动对系统间反向交叉(RISC)的作用，以及固体中低幅度或衰减振动的较小贡献。我们证明了当Zeonex中的高振幅运动被抑制时，RISC仍然发生，并讨论了各种振动耦合场景，这些场景指出在刚性固体中持续存在的节间运动的作用被低估了。我们的结果强调了振动耦合在RISC调节中的复杂性，并提供了一种合成工具，使未来能够通过选择性机械阻尼来研究振动耦合，而不会对电子系统产生影响。
We investigate a series of D–A molecules consisting of spiro[acridan-9,9′-fluorene] as the donor and 2-phenylenepyrimidine as the acceptor. In two of the materials, a spiro center effectively electronically isolates the D unit from (consequently) optically innocent yet structurally influential adamantyl side groups. In a third material, adamantyl groups attached directly to the acceptor strongly influence the electronic properties. Steady-state and time-resolved photophysical studies in solution, Zeonex polymer matrix, and neat films reveal that the substituents impact the efficiency of vibronic coupling between singlet and triplet states relevant to reverse intersystem crossing (rISC) and thermally activated delayed fluorescence (TADF), without significantly changing the singlet–triplet gap in the materials. The adamantyl groups serve to raise the segmental mass and inertia, thereby damping intramolecular motions (both vibrational and rotational). This substitution pattern reveals the role of large-amplitude (primarily D–A dihedral angle rocking) motions on reverse intersystem crossing (rISC), as well as smaller contributions from low-amplitude or dampened vibrations in solid state. We demonstrate that rISC still occurs when the high-amplitude motions are suppressed in Zeonex and discuss various vibronic coupling scenarios that point to an underappreciated role of intersegmental motions that persist in rigid solids. Our results underline the complexity of vibronic couplings in the mediation of rISC and provide a synthetic tool to enable future investigations of vibronic coupling through selective mechanical dampening with no impact on electronic systems.
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