New electron-transporting materials for light emitting diodes: 1,3,4-oxadiazole–pyridine and 1,3,4-oxadiazole–pyrimidine hybrids
作者:Changsheng Wang、Gun-Young Jung、Andrei S. Batsanov、Martin R. Bryce、Michael C. Petty
DOI:10.1039/b106907c
日期:2002.1.24
We describe the synthesis of three new isomeric 1,3,4-oxadiazoleâpyridine hybrids, namely: 2,6-, 3,5- and 2,4-bis[2-(4-tert-butylphenyl)-1,3,4-oxadiazol-5-yl]pyridine, (PDPy-2,6, PDPy-3,5 and PDPy-2,4, respectively) and a 1,3,4-oxadiazoleâpyrimidine hybrid, namely: 2,5-bis[2-(4-tert-butylphenyl)-1,3,4-oxadiazol-5-yl]pyrimidine (PDPmDP). The X-ray crystal structures are reported for PDPy-2,4 and the known phenylene analogue 1,3-bis[2-(4-tert-butylphenyl)-1,3,4-oxadiazol-5-yl]benzene (OXD-7) as a 1â¶1 toluene solvate. The packing motif for molecules of both PDPy-2,4 and OXD-7 is that of discrete layers with the mean planes of all the molecules in the crystals parallel to within 6°. We have fabricated light-emitting diodes (LEDs) using poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV) doped
with rubrene as the emissive material, with and without a thermally evaporated electron conducting/hole-blocking (ECHB) layer of PDPy-2,6, PDPy-3,5 and PDPy-2,4, PDPmDP and OXD-7, in the device configuration ITO/MEH-PPV(Ru)/ECHB layer/Al. Electroluminescence spectra indicate that light is emitted only from the MEH-PPV layer. The bilayer LEDs are considerably more efficient than single layer devices, e.g. the external quantum efficiences of devices incorporating PDPy-2,6, PDPy-3,5 and OXD-7 are 0.14, 0.04 and 0.06% at 40Â mAâmâ2, respectively, cf. 0.007% for the reference single-layer MEH-PPV(Ru) device. There is no clear correlation between experimental EQE values and the PM3 calculated LUMO levels of the materials.
我们描述了三种新的同分异构体1,3,4-恶二嗪-吡啶杂化物的合成,分别为:2,6-、3,5-和2,4-双[2-(4-叔丁基苯基)-1,3,4-恶二嗪-5-基]吡啶(PDPy-2,6、PDPy-3,5和PDPy-2,4)以及一种1,3,4-恶二嗪-嘧啶杂化物,即:2,5-双[2-(4-叔丁基苯基)-1,3,4-恶二嗪-5-基]嘧啶(PDPmDP)。我们报告了PDPy-2,4的X射线晶体结构,以及已知的苯基类似物1,3-双[2-(4-叔丁基苯基)-1,3,4-恶二嗪-5-基]苯(OXD-7),作为1:1的甲苯溶剂合物。PDPy-2,4和OXD-7的分子堆积模式为离散层,所有分子的平均平面在晶体内的平行度在6°以内。我们采用掺锂的聚[2-甲氧基-5-(2-乙基己基氧基)-1,4-苯乙烯](MEH-PPV)作为发光材料制造了发光二极管(LED),并在器件配置ITO/MEH-PPV(Ru)/ECHB层/Al中加入或不加入热蒸发的电子导电/孔阻挡(ECHB)层,材料包括PDPy-2,6、PDPy-3,5、PDPy-2,4、PDPmDP和OXD-7。电致发光光谱表明,光仅从MEH-PPV层发射。双层LED的效率明显高于单层器件,例如,包含PDPy-2,6、PDPy-3,5和OXD-7的器件在40 mA m⁻²下的外量子效率分别为0.14%、0.04%和0.06%,而参考的单层MEH-PPV(Ru)器件的效率为0.007%。实验得到的外量子效率(EQE)值与材料的PM3计算的LUMO能级之间没有明显的相关性。