Effect of Atom Substitution in Chalcogenodiazole-Containing Thermally Activated Delayed Fluorescence Emitters on Radiationless Transition
Effect of Atom Substitution in Chalcogenodiazole-Containing Thermally Activated Delayed Fluorescence Emitters on Radiationless Transition
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DOI：
10.1021/jp510751n
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发表时间：
2015-02
影响因子：
3.7
通讯作者：
Hiroyuki Tanaka;Katsuyuki Shizu;Jiyoung Lee;C. Adachi
中科院分区：
文献类型：
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作者：
Hiroyuki Tanaka;Katsuyuki Shizu;Jiyoung Lee;C. Adachi
从分子设计的角度研究了热激活延迟荧光（TADF）中最低单重态（S1）和三重态（T1）激发态之间的无辐射跃迁。比较了两种含硫族重氮化合物的TADF发光体的物理、瞬态光致发光和电致发光特性。其中含有1，3，4-恶二唑或1，3，4-噻二唑。用硫取代氧对TADF的影响是由电子对接受共轭效应引起的。这种效应是由噻二唑杂环中二价硫的3d轨道空位引起的。原子取代使分子最高占据轨道与最低未占据轨道能级间的差距变窄，并增强了S1 → T1的系间跃迁。这些效应是由于硫的空位3d轨道增强了受主强度和轨道角动量。原子取代增加了延迟荧光成分对总电致发光效率的贡献。
Radiationless transition between the lowest singlet (S1) and triplet (T1) excited states in the thermally activated delayed fluorescence (TADF) were investigated with respect to molecular design. The photophysical, transient photoluminescence and electroluminescence (EL) characteristics of two chalcogenodiazole-containing TADF emitters were compared. These contained 1,3,4-oxadiazole or 1,3,4-thiadiazole. The effect of substituting oxygen with sulfur on TADF was caused by an electron-pair-accepting conjugative effect. This effect resulted from the vacant 3d-orbitals of divalent sulfur in the thiadiazole heteroring. Atom substitution narrowed the gap between the highest occupied and lowest unoccupied molecular orbital energy levels, and enhanced S1 → T1 intersystem crossing. These effects resulted from the enhanced acceptor strength and orbital angular momentum by the vacant 3d-orbitals of sulfur. Atom substitution increased the contribution of the delayed fluorescence component to the total EL efficiency (...