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σ–π and p–π conjugation induced NIR-emitting iridium(iii) complexes anchored by flexible side chains in a rigid dibenzo[a,c]phenazine moiety and their application in highly efficient solution-processable NIR-emitting devices

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Abstract

To systematically investigate the σ–π and p–π conjugation effects on photoluminescence (PL) and electroluminescence (EL) properties, and to obtain high-efficiency near-infrared (NIR)-emitting iridium(III) complexes, in this work, two rigid C^N ligands of dibenzo[a,c]phenazine (DBPz) derivatives, respectively, anchored by flexible side chains of n-octyl and n-octyloxy and their corresponding iridium(III) complexes of Ir-R and Ir-OR were designed and synthesized. Their photophysical and EL properties were systematically investigated. It is found that the σ–π and p–π conjugation effects can make both iridium(III) complexes exhibit a significantly red-shifted NIR emission with high photoluminescence quantum efficiency (PLQY) in comparison with their archetypal iridium complex without any side chains. More intense NIR emissions are achieved for Ir-R at 732 nm (PLQY: 24%) and Ir-OR at 775 nm (PLQY: 8%) in dichloromethane solution. Utilizing Ir-R as the phosphorescent dopant, the solution-processed organic light-emitting diodes (OLEDs) using CBP as the host and polymer light-emitting diodes (PLEDs) using PVK:OXD-7 as the cohost show outstanding EL performances. The highest external quantum efficiency (EQE) of 6.91% and a radiance of 26 100 mW sr−1 m−2 were obtained in the Ir-R based OLEDs with an emission peak at 730 nm, which are 4.7 and 2.2 times higher than those of the complex Ir-OR-based devices. This indicates that introducing σ–π conjugation effects induced by the anchored flexible n-octyl side chains in the rigid dibenzo[a,c]phenazine moiety is a better strategy for obtaining NIR-emitting iridium complexes for application in high-efficiency solution-processed devices.

Graphical abstract: σ–π and p–π conjugation induced NIR-emitting iridium(iii) complexes anchored by flexible side chains in a rigid dibenzo[a,c]phenazine moiety and their application in highly efficient solution-processable NIR-emitting devices

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Supplementary files

Article information


Submitted
28 Jan 2020
Accepted
14 Apr 2020
First published
14 Apr 2020

J. Mater. Chem. C, 2020, Advance Article
Article type
Paper

σ–π and p–π conjugation induced NIR-emitting iridium(III) complexes anchored by flexible side chains in a rigid dibenzo[a,c]phenazine moiety and their application in highly efficient solution-processable NIR-emitting devices

C. You, D. Liu, M. Zhu, J. Yu, B. Zhang, Y. Liu, Y. Wang and W. Zhu, J. Mater. Chem. C, 2020, Advance Article , DOI: 10.1039/D0TC00479K

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