Novel distyrylcarbazole derivatives as hole-transporting blue emitters for electroluminescent devices
作者:Fang-Iy Wu、Ping-I Shih、Mao-Chuan Yuan、Ajay Kumar Dixit、Ching-Fong Shu、Zhu-Ming Chung、Eric Wei-Guang Diau
DOI:10.1039/b510035f
日期:——
We have synthesized three novel distyrylcarbazole derivatives for use as simultaneously hole-transporting and light-emitting layers in blue light-emitting diodes. Each compound, which contains a rigid carbazole core and two 2,2-diphenylvinyl end groups substituted through either the 3,6- or the 2,7- position, forms films satisfactorily and exhibits a blue emission with its PL maximum in the range 459–470 nm. Photophysical measurements indicate that twisting of the adjacent C–C bonds in the 3,6-position of the carbazole core in dilute solutions causes an efficient nonradiative relaxation to occur, yielding a much smaller quantum yield for fluorescence in 3,6-linked carbazoles. As intense emissions of 2,7-linked carbazoles are observed, such deactivation from an excited-state is inefficient therein. Electrochemical studies revealed that incorporation of the carbazole core increased the HOMO energy effectively; this feature facilitates hole injection. These distyrylcarbazole derivatives are promising bifunctional, blue-emitting, hole-transporting molecules for use in simple double-layer devices of a general structure ITO/emitting layer/TPBI/Mg : Ag, in which TPBI—1,3,5-tris(N-phenylbenzimidazol-2-yl)benzene—serves as a hole-blocking and electron-transporting material. The devices prepared using 2,7-distyrylcarbazole as the emitter produced bright blue emissions having activating voltages below 3.0 V. A DPVTCz-based device attained a luminance efficiency of 3.11 cd A−1 at 5 V, a brightness of 3062 cd m−2, and CIE color coordinates of (0.14, 0.22).
我们合成了三种新型二苯乙烯基咔唑衍生物,可同时用作蓝色发光二极管中的空穴传输层和发光层。每种化合物均含有刚性咔唑核和两个通过 3,6- 或 2,7- 位取代的 2,2-二苯基乙烯基端基,可令人满意地形成薄膜,并呈现蓝色发射,其 PL 最大值在 459 范围内–470 纳米。光物理测量表明,稀溶液中咔唑核 3,6 位上相邻 C-C 键的扭曲会导致有效的非辐射弛豫发生,从而在 3,6-连接咔唑中产生更小的荧光量子产率。由于观察到2,7-连接咔唑的强烈发射,因此从激发态的这种失活在其中是低效的。电化学研究表明,咔唑核的掺入有效提高了HOMO能量;该特征有利于空穴注入。这些二苯乙烯基咔唑衍生物是有前途的双功能、蓝光发射、空穴传输分子,可用于通用结构 ITO/发射层/TPBI/Mg : Ag 的简单双层器件,其中 TPBI-1,3,5-tris( N-苯基苯并咪唑-2-基)苯—用作空穴阻挡和电子传输材料。使用2,7-二苯乙烯基咔唑作为发射体制备的器件产生亮蓝色发射,激活电压低于3.0 V。基于DPVTCz的器件在5 V时获得了3.11 cd A−1的发光效率,亮度为3062 cd m−2 ,CIE 颜色坐标为 (0.14, 0.22)。