Dendritic Iridium(III)-Encapsulated Complexes for Organic Light Emitting Diodes
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0965-S03-22
Dendritic Iridium(III)-Encapsulated Complexes for Organic Light Emitting Diodes Ho-Jin Son1, Won-Sik Han1, Kyu-Bum Choi1, Dae-Hyun Kim1, Jaejung Ko1, Seung-Uk Noh2, Changhee Lee2, and Sang Ook Kang1 1 Advanced Material Chemistry, Korea University, 208 Seochang, Jochiwon, 339-700, Korea, Republic of 2 Electrical Engineering and Computer Science, Seoul National University, Shillim-dong, Gwanak-gu, Seoul, 151-744, Korea, Republic of
ABSTRACT The synthesis, photo-physics and electroluminescence of new types of Iridium(III)encapsulated dendrimers are described. Thus, four different iridium complexes [Ir(III)(C^N)2(LX), Blue-DCBP, Green-DCBP, Yellow-DCBP, and Red-DCBP] with ancillary ligand tethered to the CBP dendritic unit were synthesized and investigated for their photophysical properties. A large enhancement in electroluminescence performance was observed by using these dendrimers as host/dopant hybrid materials in layered emitting diodes. In particular, host/dopant ratio can be systematically adjusted by varying dendritic generations. These results demonstrate that new Ir(III)-encapsulated dendrimers can be used as potential single-layer materials for organic light emitting diodes. Large difference in the intra-molecular charge transfer phosphorescence quantum yields and electroluminescence effiencies were observed among dendriritic generations.
INTRODUCTION Dendritic macromolecules containing π-conjugated systems have attracted a great deal of attention owing to their potential to act as photosynthetic attennas [1] and molecular wires for electron and energy transfer [2] and also to their potential applications in organic photo- and electroluminescent devices [3]. The majority of electroluminescent dendrimers reported to date have been prepared using dendrons or cores with chromophoric centers [4]. Although chromophore-functionalized dendrimers have received much attention [5], Ir-encapsulated complexes adorned with carbazole derivatives were reported by only a little groups. Recent results reported by Burn have shown that the dendritic approach can be used to develop solutionprocessable phosphorescent materials that give rise to highly efficient green and red DLEDs (Dendritic Lighting Emitting Diodes) [6]. Ir-cored dendrimer functionalized with charge transporting dendrons revealed the smooth amorphous films and good external quantum efficiency (7.6%) in the literature reported by Tokito [7]. With these considerations in mind, we have synthesized four Ir-cored dendrimers from the first to the fourth generation consisting of Ircomplex and phenyl carbazole dendrons and studied the photophysical and EL properties as the dendrimer generation n (n = 1, 2, 3, 4) while varying the number of dendrons. The systematic study showed the intermolecular interaction of phosphorescent molecules at the core part can be controlled at the molecular level by the number of dendrons attached to the core and the
corresponding dendrons encapsulating Ir-core molecule induces the enhancement of PL quantum efficiency in a s
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