Liao Szu-Hung, Shiu Jin-Ruei, Liu Shun-Wei, Yeh Shi-Jay, Chen Yu-Hung, Chen Chin-Ti, Chow Tahsin J, Wu Chih-I
Institute of Chemistry, Academia Sinica, Taipei, Taiwan 11529, ROC.
J Am Chem Soc. 2009 Jan 21;131(2):763-77. doi: 10.1021/ja807284e.
A series of group III metal chelates have been synthesized and characterized for the versatile application of organic light-emitting diodes (OLEDs). These metal chelates are based on 4-hydroxy-1,5-naphthyridine derivates as chelating ligands, and they are the blue version analogues of well-known green fluorophore Alq(3) (tris(8-hydroxyquinolinato)aluminum). These chelating ligands and their metal chelates were easily prepared with an improved synthetic method, and they were facially purified by a sublimation process, which enables the materials to be readily available in bulk quantity and facilitates their usage in OLEDs. Unlike most currently known blue analogues of Alq(3) or other deep blue materials, metal chelates of 4-hydroxy-1,5-naphthyridine exhibit very deep blue fluorescence, wide band gap energy, high charge carrier mobility, and superior thermal stability. Using a vacuum-thermal-deposition process in the fabrication of OLEDs, we have successfully demonstrated that the application of these unusual hydroxynaphthyridine metal chelates can be very versatile and effective. First, we have solved or alleviated the problem of exciplex formation that took place between the hole-transporting layer and hydroxynaphthyridine metal chelates, of which OLED application has been prohibited to date. Second, these deep blue materials can play various roles in OLED application. They can be a highly efficient nondopant deep blue emitter: maximum external quantum efficiency eta(ext) of 4.2%; Commision Internationale de L'Eclairage x, y coordinates, CIE(x,y) = 0.15, 0.07. Compared with Alq(3), Bebq(2) (beryllium bis(benzoquinolin-10-olate)), or TPBI (2,2',2''-(1,3,5-phenylene)tris(1-phenyl-1H-benzimidazole), they are a good electron-transporting material: low HOMO energy level of 6.4-6.5 eV and not so high LUMO energy level of 3.0-3.3 eV. They can be ambipolar and possess a high electron mobility of 10(-4) cm(2)/V s at an electric field of 6.4 x 10(5) V/cm. They are a qualified wide band gap host material for efficient blue perylene (CIE(x,y) = 0.14, 0.17 and maximum eta(ext) 3.8%) or deep blue 9,10-diphenylanthracene (CIE(x,y) = 0.15, 0.06 and maximum eta(ext) 2.8%). For solid state lighting application, they are desirable as a host material for yellow dopant (rubrene) in achieving high efficiency (eta(ext) 4.3% and eta(P) 8.7 lm/W at an electroluminance of 100 cd/m(2) or eta(ext) 3.9% and eta(P) 5.1 lm/W at an electroluminance of 1000 cd/m(2)) white electroluminescence (CIE(x,y) = 0.30, 0.35).
已合成并表征了一系列第III族金属螯合物，用于有机发光二极管（OLED）的多种应用。这些金属螯合物基于4-羟基-1,5-萘啶衍生物作为螯合配体，它们是著名的绿色荧光团Alq(3)（三（8-羟基喹啉）铝）的蓝色类似物。这些螯合配体及其金属螯合物通过改进的合成方法易于制备，并通过升华过程进行表面纯化，这使得材料能够大量获得，并便于其在OLED中的使用。与目前大多数已知的Alq(3)蓝色类似物或其他深蓝色材料不同，4-羟基-1,5-萘啶的金属螯合物表现出非常深的蓝色荧光、宽带隙能量、高电荷载流子迁移率和优异的热稳定性。在OLED制造中使用真空热沉积工艺，我们成功证明了这些不寻常的羟基萘啶金属螯合物的应用非常通用且有效。首先，我们解决或缓解了空穴传输层与羟基萘啶金属螯合物之间发生的激基复合物形成问题，迄今为止，其OLED应用一直被禁止。其次，这些深蓝色材料在OLED应用中可以发挥多种作用。它们可以是高效的非掺杂深蓝色发射体：最大外量子效率η(ext)为4.2%；国际照明委员会（CIE）x、y坐标，CIE(x,y)=0.15,0.07。与Alq(3)、Bebq(2)（双（苯并喹啉-10-醇）铍）或TPBI（2,2',2''-（1,3,5-亚苯基）三（1-苯基-1H-苯并咪唑）相比，它们是良好的电子传输材料：低HOMO能级为6.4-6.5 eV，LUMO能级不那么高，为3.0-3.3 eV。它们可以是双极性的，在6.4×10(5)V/cm的电场下具有10(-4)cm(2)/V s的高电子迁移率。它们是用于高效蓝色苝（CIE(x,y)=0.14,0.17，最大η(ext)3.8%）或深蓝色9,10-二苯基蒽（CIE(x,y)=0.15,0.06，最大η(ext)2.8%）的合格宽带隙主体材料。对于固态照明应用，它们作为黄色掺杂剂（红荧烯）的主体材料是理想的，可实现高效率（在100 cd/m(2)的电致发光下，η(ext)为4.3%，η(P)为8.7 lm/W；或在1000 cd/m(2)的电致发光下，η(ext)为3.9%，η(P)为5.1 lm/W）的白色电致发光（CIE(x,y)=0.30,0.35）。
