Abstract
Six novel Ir(C^N)2(L^X)-type heteroleptic iridium complexes with deep-red and near-infrared region (NIR)-emitting coverage were constructed through the cross matching of various cyclometalating (C^N) and ancillary (LX) ligands. Here, three novel C^N ligands were designed by introducing the electron-withdrawing group CF3 on the ortho (o-), meta (m-), and para (p-) positions of the phenyl ring in the 1-phenylisoquinoline (piq) group, which were combined with two electron-rich LX ligands (dipba and dipg), respectively, leading to subsequent iridium complexes with gradually changing emission colors from deep red (≈660 nm) to NIR (≈700 nm). Moreover, a series of phosphorescent organic light-emitting diodes (PhOLEDs) were fabricated by employing these phosphors as dopant emitters with two doping concentrations, 5% and 10%, respectively. They exhibited efficient electroluminescence (EL) with significantly high EQE values: >15.0% for deep red light0 (λmax = 664 nm) and >4.0% for NIR cases (λmax = 704 nm) at a high luminance level of 100 cd m−2. This work not only provides a promising approach for finely tuning the emission color of red phosphors via the easily accessible molecular design strategy, but also enables the establishment of an effective method for enriching phosphorescent-emitting molecules for practical applications, especially in the deep-red and near-infrared region (NIR).
Highlights
Publisher’s Note: MDPI stays neutralOrganic near-infrared (NIR) materials and their light-emitting devices were developed rapidly since they are widely used in information-secured displays and nightvision/photodynamic therapy/signal processing devices [1,2,3]
Thermally activated delayed fluorescence (TADF) organics [2] and phosphorescent transition-metal complexes based on the platinum (II) and osmium (II) family [3] seem to be ideal candidates for efficient NIR organic light-emitting diodes (OLEDs) due to both 25% singlet and 75%
All phosphorescence lifetimes are generally shorter than 0.70 μs, suggesting that efficient spin–orbit coupling of these phosphors is beneficial for reducing efficiency roll-off in the corresponding phosphorescent organic light-emitting diodes (PhOLEDs)
Summary
Organic near-infrared (NIR) materials and their light-emitting devices were developed rapidly since they are widely used in information-secured displays and nightvision/photodynamic therapy/signal processing devices [1,2,3]. The preparing processes of Ir(CN) (LX)-typed complexes are usually cheaper and easier than those of the homoleptic cases, and in the former cases, CN and LX provide two relatively independent channels to adjust the opto-electronic characteristics of Ir (III) complexes, their emission color, frontier orbitals, and excited states can be precisely and finely tuned by coordinately altering and matching different CN/LX combinations This strategy avoids the complex optimization route through contraction or extension of the π-conjugation system, and their steric and/or electronic constraints may increase the difficulty of preparing chloride-bridged [Ir(CN) (μ-Cl)]2 complexes, which are necessary precursors in the common synthesis of iridium-based phosphorescent molecules [12]. Molecules 2022, 27, 286 possessing desirable optoelectronic characteristics in the deep-red and NIR region are, expected
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