Dendritic europium complex as a single dopant for white-light electroluminescent devices
作者:Shangfeng Li、Gaoyu Zhong、Weihong Zhu、Fuyou Li、Jianfeng Pan、Wei Huang、He Tian
DOI:10.1039/b504738b
日期:——
Three novel dendritic europium complexes containing grafted carbazole units as their functional peripheries were prepared and characterized. The Förster energy transfer from the peripheries of carbazole units to β-diketonates as well as from the ligands to the central Eu(III) ions in these complexes has been demonstrated. Under the indirect excitation of carbazole units, a characteristic red emission peak at 615 nm due to the Eu(III) ion transition of 5D0
→
7F2 was observed for the complexes in solution or solid films. As a result of the light-harvesting and site isolation of carbazole dendrons, compared with the reference compound Eu(BPPD)3(Phen), PL efficiencies of Eu(MCPD)3(Phen), Eu(BCPD)3(Phen) and Eu(TCPD)3(Phen) in the film state are 3.3, 7.9 and 4.5 fold increased, respectively. Notably, white light emission with the CIE coordinates of (0.333, 0.348) has been achieved with a single dopant of Eu(TCPD)3(Phen) in an EL device of configuration ITO/NPB/CBP : Eu(TCPD)3(Phen)/BCP/Mg : Ag. Its maximum external quantum efficiency is more than 1.1% and maximum brightness reached 229 cd m−2. The origin of the blue and green emission is attributed to the dendron-grafted carbazole units forming an exciplex and an electroplex with CBP (4,4′-N,N′-dicarbazole biphenyl) and ligand β-diketonate, respectively. The results suggest that modifying ligands can not only tune the carrier-transporting properties of complexes, but also provide a useful clue to the use of electroplexes or exciplexes to realize broad or even white electroluminescence.
制备并表征了三类含有嫁接咔唑功能单元的树枝状铕配合物,验证了从咔唑单元到β-二酮、从配体到中心Eu(III)离子的福斯特能量转移过程。间接激发树枝状咔唑单元时,配合物在溶液或固体薄膜中均能够观察到波长为615 nm的Eu(III)离子的特征红光发射峰,对应着5D0到7F2的跃迁。由于咔唑树枝状单元的光诱捕器和位点隔离作用,与参考化合物Eu(BPPD)3(Phen)比较,Eu(MCPD)3(Phen)、Eu(BCPD)3(Phen)和Eu(TCPD)3(Phen)薄膜状态下的PL效率分别提高3.3、7.9和4.5倍。引人注意的是,在ITO/NPB/CBP:Eu(TCPD)3(Phen)/BCP/Mg:Ag结构配置的EL器件中,通过单一Eu(TCPD)3(Phen)掺杂实现了白光发射,CIE坐标为(0.333,0.348),最大外部量子效率大于1.1%,最大亮度达到229 cd m-2。将蓝、绿发射归因于树枝状单元嫁接的咔唑分别与CBP(4,4′-N,N′-二咔唑基联苯)和β-二酮配体形成激发离子对和电荷转移离子对。研究结果表明,改性配体不仅能调控配合物的载流子传输性质,而且为利用电荷转移离子对或激发离子对实现广谱或白光发射提供了一种可行的参考方法。