Highly Efficient Green‐Emitting Phosphorescent Iridium Dendrimers Based on Carbazole Dendrons

Abstract

Green‐emitting iridium dendrimers with rigid hole‐transporting carbazole dendrons are designed, synthesized, and investigated. With second‐generation dendrons, the photoluminescence quantum yield of the dendrimers is up to 87 % in solution and 45 % in a film. High‐quality films of the dendrimers are fabricated by spin‐coating, producing highly efficient, non‐doped electrophosphorescent organic light‐emitting diodes (OLEDs). With a device structure of indium tin oxide/poly(3,4‐ethylenedioxythiophene):poly(styrene sulfonic acid)/neat dendrimer/1,3,5‐tris(2‐N‐phenylbenzimidazolyl)benzene/LiF/Al, a maximum external quantum efficiency (EQE) of 10.3 % and a maximum luminous efficiency of 34.7 cd A–1 are realized. By doping the dendrimers into a carbazole‐based host, the maximum EQE can be further increased to 16.6 %. The integration of rigid hole‐transporting dendrons and phosphorescent complexes provides a new route to design highly efficient solution‐processable dendrimers for OLED applications.

Solution processable phosphorescent rhenium(i) dendrimers

“…Infrared analysis of the complexes in the carbonyl region (1880-2025 cm 21 , Table 1) revealed that there were three stretches, which was consistent with the complexes only having the facial configuration. 26 In the facial configuration there are only two carbonyl environments and two of the stretches correspond to the symmetric and asymmetric stretches of the two carbonyls in the same plane, with the third stretch due to the third carbonyl which is opposite the chlorine atom.…”

“…[7][8][9][10][11][12][13][14][15] While much of the work on phosphorescent emitters has been focusing on small molecules [1][2][3][4][5][6] there has been an increasing focus on developing phosphorescent light-emitting dendrimers to control the processing and intermolecular interactions that govern device performance. [16][17][18][19][20][21] We have shown that by controlling the generation and/or number of dendrons, 17,18 and dendron type, 22 it is possible to control charge transport 22,23 and light-emission 24 in iridium(III) complex cored dendrimers and form simple highly efficient dendrimer light-emitting diodes (DLEDs). 16 OLEDs with solution processed layers comprised of polymers with rhenium(I) units in the backbones or with rhenium(I) complexes blended with a polymer host have generally given very poor performance.…”

Blue Light Emitting Polyphenylene Dendrimers with Bipolar Charge Transport Moieties

“…Dendrimer-based OLEDs have been investigated in the last two decades, due to their numerous advantages over small molecules and polymers, i.e., cost-effective solution processability, high performance reproducibility thanks to their well-defined structures, in contrast to polymers, and precise functionalization of dendrimers at multiple positions [9][10][11][12][13]. Dendrimers for OLEDs generally include two types: one designed for better charge transport (conjugated scaffold) [14][15][16][17][18][19] and one for surface-to-core energy transfers (non-conjugated scaffold) [20][21][22][23][24].…”

Design and Synthesis of Phosphorescent Iridium Containing Dendrimers for Potential Applications in Organic Light‐Emitting Diodes

“…[20][21][22][23] Given that carbazole-based materials are widely used as hosts for triplet emitters in OLEDs, it is not surprising that a variety of carbazole oligomers have been attached to iridium complexes. [10,12,24] In this study, we designed and synthesized two branched carbazole oligomers and then attached them to a core iridium complex by Suzuki coupling. The linkage between each carbazole unit was specifically designed to maintain high triplet energy level of the ligand.…”

“…[10] In these materials, the core chromophores are various phosphorescent organometallic complexes and jointed by multiple hyperbranched oligomers or dendrons to prevent undesired triplet-triplet annihilation. [11][12][13] By rational design on the core chromophores and the hyperbranched ligands, phosphorescence from these complexes can be tuned from sky blue to deep red, [14] and a remarkable external quantum efficiency of 16% has been achieved for green phosphorescent dendrimer based devices. [11] In this study, we prepared a new series of phosphorescent dendrimers (IrC1, IrC3, and IrF2) with an identical iridium complex core consisting of one ancillary and two cyclometalating ligands.…”