Suppression of Structural Change upon S1-T1 Conversion Assists the Thermally Activated Delayed Fluorescence Process in Carbazole-Benzonitrile Derivatives
Suppression of Structural Change upon S1-T1 Conversion Assists the Thermally Activated Delayed Fluorescence Process in Carbazole-Benzonitrile Derivatives
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S1-T1 转化时结构变化的抑制有助于咔唑-苯甲腈衍生物的热激活延迟荧光过程
DOI：
10.1021/acs.jpclett.9b00810
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发表时间：
2019
期刊：
影响因子：
--
通讯作者：
Onda Ken
中科院分区：
文献类型：
--
作者：
Saigo Masaki;Miyata Kiyoshi;Tanaka Sei’ichi;Nakanotani Hajime;Adachi Chihaya;Onda Ken
热激活延迟荧光（TADF）分子因其在不含贵金属的情况下提高有机发光二极管效率的潜力而受到关注。最小化S1态和T1态之间的能量差（ΔEST）是加速反向系间穿越（RISC）的基本策略。然而，缺乏对该过程的微观理解阻碍了有效TADF材料的适当设计策略。在这里，我们集中在四个咔唑苯甲腈（Cz-BN）衍生物，具有相同的Δ EST，但不同的TADF活动。我们系统地比较了它们的几何动力学的光激发使用时间分辨红外（TR-IR）振动光谱结合量子化学计算。我们发现最具TADF活性的分子4CzBN在光激发后几乎没有结构变化，而无TADF活性的分子在S1-T1转换后显示出相对较大的变形。这意味着在Cz-BN衍生物的情况下，抑制结构变形对于使RISC的活化能势垒最小化是关键的。
Thermally activated delayed fluorescence (TADF) molecules are gathering attention for their potential to boost the efficiency of organic light-emitting diodes without precious metals. Minimizing the energy difference between the S1and T1states (ΔEST) is a fundamental strategy to accelerate reverse intersystem crossing (RISC). However, the lack of microscopic understanding of the process prevents adequate design strategies for efficient TADF materials. Here, we focused on four carbazole-benzonitrile (Cz-BN) derivatives that possess identical ΔESTbut distinct TADF activities. We systematically compared their geometrical dynamics upon photoexcitation using time-resolved infrared (TR-IR) vibrational spectroscopy in conjunction with quantum chemical calculations. We found that the most TADF-active molecule, 4CzBN, shows little structural change after photoexcitation, while the TADF-inactive molecules show relatively large deformation upon S1–T1conversion. This implies that the suppression of structural deformation is critical for minimizing the activation energy barrier for RISC in cases of the Cz-BN derivatives.