Dual-emissive 2-(2'-hydroxyphenyl)oxazoles for high performance organic electroluminescent devices: discovery of a new equilibrium of excited state intramolecular proton transfer with a reverse intersystem crossing process.
Dual-emissive 2-(2'-hydroxyphenyl)oxazoles for high performance organic electroluminescent devices: discovery of a new equilibrium of excited state intramolecular proton transfer with a reverse intersystem crossing process.
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用于高性能有机电致发光器件的双发射2-(2'-羟基苯基)恶唑：发现激发态分子内质子转移与反向系间窜越过程的新平衡
DOI：
10.1039/c7sc04464j
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发表时间：
2018-02-07
期刊：
影响因子：
8.4
通讯作者：
You J
中科院分区：
文献类型：
--
作者：
Li B;Zhou L;Cheng H;Huang Q;Lan J;Zhou L;You J
研究了2-（2′-羟基苯基）恶唑的烯醇式和酮式双发光及其在有机电致发光器件中的应用。系统研究了两种高效激发态分子内质子转移（ESIPT）分子--含一个三苯胺（TPA）的2-（2′-羟基苯基）恶唑（1）和含两个TPA的2-（2′-羟基苯基）恶唑（2）的光致发光（PL）和电致发光（EL）性质. 1和2的烯醇式均具有高度杂化的局域电荷转移（HLCT）激发态特征，而它们的酮式激发态不具有明显的HLCT特征。基于1的器件表现出绿-白色电致发光，具有国际照明委员会（CIE）坐标（0.25，0.41）和高达5.3%的高外量子效率（EQE），这是单分子白色发光材料记录的最高EQE值。基于2的器件显示出天蓝色发射，CIE坐标为（0.18，0.16），EQE为8.0%，这是所报道的HLCT材料中最高的EQE。1和2的烯醇式结构在EL光谱中的荧光强度相对于它们的PL光谱显著增强。实验数据和理论计算揭示了一个新的ESIPT平衡与反向系间穿越（RISC）过程所产生的HLCT字符。在EL中，烯醇形式激子从三重态到单重态的RISC触发烯醇形式单重态激子的数量增加，这进一步导致ESIPT平衡向增强的烯醇形式发射的偏移。因此，在PL和EL中的ESIPT平衡之间的差异可以归因于烯醇式激发态的HLCT特征。
Dual-emission of the enol-forms and keto-forms of 2-(2′-hydroxyphenyl)oxazoles and their application in OLEDs are investigated. The photoluminescence (PL) and electroluminescence (EL) properties of two highly efficient excited state intramolecular proton transfer (ESIPT) molecules, 2-(2′-hydroxyphenyl)oxazoles containing one triphenylamine (TPA) (1) and two TPAs (2) respectively, are studied systematically. The enol-forms of both 1 and 2 possess highly hybridized local and charge transfer (HLCT) excited state character, while their excited-state keto-forms are not of obvious HLCT character. A 1-based device exhibits green-white electroluminescence with Commission Internationale d’Eclairage (CIE) coordinates of (0.25, 0.41) and a high external quantum efficiency (EQE) up to 5.3%, which is the highest EQE value recorded for single molecular white light-emitting materials. A 2-based device shows sky-blue emission with CIE coordinates of (0.18, 0.16) and an EQE of 8.0%, which is the highest EQE in the reported HLCT materials. The fluorescence intensities of the enol-forms of 1 and 2 in EL spectra are increased remarkably relative to their PL spectra. Experimental data and theoretical calculations reveal a new ESIPT equilibrium with a reverse intersystem crossing (RISC) process arising from the HLCT character. In EL, the RISC of the enol-form excitons from the triplet state to the singlet state triggers an increase in the number of enol-form singlet excitons, which further leads to a shift of the ESIPT equilibrium towards an enhanced enol-form emission. Thus, the difference between the ESIPT equilibria in PL and EL may be ascribed to the HLCT character of the enol-form excited state.
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