Multinuclear Iridium Complex Encapsulated by Oligocarbazole Dendrons for Enhanced Nondoped Device Efficiency.

Abstract

A dendritic multinuclear Ir complex, namely Cz–3IrB–IrG, has been designed and synthesized by introducing the second-generation oligocarbazole dendrons into its periphery. Because of the characteristic encapsulation, the intermolecular interactions could be effectively alleviated to prevent the unwanted triplet–triplet annihilation stemmed from the outer blue Ir complexes. Compared with 3IrB–IrG in the absence of dendrons, the film photoluminescence quantum yield of Cz–3IrB–IrG is greatly increased from 0.46 to 0.82 together with a small blue-shifted emission from 524 to 520 nm. On the basis of Cz–3IrB–IrG as the emitting layer alone, the nondoped device realizes a promising luminous efficiency of 40.9 cd/A (12.0%), much higher than that of 3IrB–IrG (32.6 cd/A, 9.7%). The obtained improvement clearly indicates that further dendronization toward multinuclear Ir complex will provide an alternative strategy to construct highly efficient phosphors used for nondoped phosphorescent organic light-emitting diodes.