Bipolar cyano-substituted pyridine derivatives for applications in organic light-emitting devices
作者:Juanjuan You、Shiu-Lun Lai、Weimin Liu、Tsz-Wai Ng、Pengfei Wang、Chun-Sing Lee
DOI:10.1039/c2jm00078d
日期:——
A novel series of cyano-substituted pyridine derivatives have been synthesized and characterized. Besides the expected electron-transporting (ET) properties stemming from the pyridine structure, the cyanopyridines also show light-emitting (EM) as well as bipolar transporting properties upon incorporation of larger π-conjugated groups, such as N,N-dimethylbenzenamine and triphenylamine groups. With these multifunctional cyanopyridines, device structures can be simplified to use only two layers or even a single layer. Low turn-on and driving voltages, relatively high power efficiency ηp and mild efficiency roll-off were demonstrated by the devices based on the compounds with better bipolar properties. The compound 2,6-bis(4-(diphenylamino)phenyl)-4-phenylpyridine-3,5-dicarbonitrile (PPPD) containing triphenylamine groups has relatively better hole-transporting (HT) ability. A device with a configuration of ITO/NPB (10nm)/PPPD (60nm)/BPhen (30nm)/LiF (0.5nm)/Mg: Ag (100nm) (where NPB is α-napthylphenylbiphenyl diamine, and BPhen is 7-diphenyl-1,10-phenanthroline), using PPPD as HT and EM layer, yields high efficiencies of 8.5 cd A−1 and 6.9 lm W−1 due to the balanced charge transporting. It is also found that substituting larger π-conjugated groups at the 4-position of the pyridine ring has a weak effect on the molecular properties because of the steric hindrance of the two cyano groups, suggesting a good linkage type for joining the cyano-substituted pyridine moiety with other HT moieties for further bipolar molecular design strategies.
我们合成并鉴定了一系列新型氰基取代吡啶衍生物。除了吡啶结构带来的预期电子传输(ET)特性外,氰基吡啶在加入较大的π共轭基团(如 N,N-二甲基苯胺和三苯胺基团)后,还显示出发光(EM)和双极传输特性。有了这些多功能氰基吡啶,器件结构可以简化到只使用两层甚至单层。基于具有更好双极特性的化合物的器件具有较低的开启电压和驱动电压、相对较高的功率效率ηp和温和的效率滚降。含有三苯胺基团的 2,6-双(4-(二苯基氨基)苯基)-4-苯基吡啶-3,5-二甲腈(PPPD)化合物具有相对较好的空穴传输(HT)能力。ITO/NPB(10nm)/PPPD(60nm)/BPhen(30nm)/LiF(0.5nm)/Mg:Ag(100nm)(其中 NPB 为 α-萘基联苯二胺,BPhen 为 7-二苯基-1,10-菲罗啉),使用 PPPD 作为 HT 和 EM 层,由于电荷传输平衡,产生了 8.5 cd A-1 和 6.9 lm W-1 的高效率。研究还发现,由于两个氰基的立体阻碍作用,在吡啶环的 4 位取代较大的 π-共轭基团对分子性质的影响较弱,这为氰基取代的吡啶分子与其他 HT 分子的连接提供了一种良好的连接类型,可用于进一步的双极分子设计策略。