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NHC-Based Deep-Red Phosphorescent Iridium Complexes Featuring Three-Charge (0, -1, -2) Ligands
Jing Zhang1, Zhenghao Zhang2, Meng Zhao1
1School of Environmental and Chemical Engineering, Jiangsu University of Science and Technology, Zhenjiang 212003, P. R. China.
Inorganic Chemistry
|January 22, 2025
Summary
Researchers developed new deep-red phosphorescent iridium complexes using N-heterocyclic carbene ligands. These complexes show high efficiency and stability, enabling applications in advanced optical light-emitting diode (OLED) devices.
Area of Science:
- Materials Science
- Organic Chemistry
- Photochemistry
Background:
- N-heterocyclic carbene (NHC)-based phosphorescent iridium complexes are known for optical properties and stability.
- Achieving deep-red emission from these complexes is challenging, with most studies focusing on blue, green, or UV light.
Purpose of the Study:
- To synthesize and characterize a new family of NHC-based deep-red iridium complexes.
- To investigate the structure-property relationships influencing their photophysical behavior.
- To evaluate their performance in organic light-emitting diode (OLED) devices.
Main Methods:
- Synthesis of four novel iridium complexes (Ir1-Ir4) with three-charge ligands.
- Single-crystal X-ray diffraction for structural analysis.
- Photophysical measurements (emission spectra, efficiency, lifetime).
- Density functional theory (DFT) calculations.
- Fabrication and testing of OLED devices using the complexes as dopant emitters.
Main Results:
- All synthesized complexes exhibited effective deep-red emission (650-664 nm).
- Complexes with benzimidazol-2-ylidene (pmb) ligands showed superior emission efficiency and longer lifetimes compared to those with imidazol-2-ylidene (pmi) ligands.
- DFT calculations indicated greater involvement of the pmb ligand in the excited state due to its stronger electron-donating ability.
- OLED devices incorporating Ir2 and Ir4 achieved high external quantum efficiencies (8.5-10.1%) in the deep-red region (624-628 nm) with low turn-on voltage (2.4 V).
Conclusions:
- The study successfully designed and synthesized novel NHC-based deep-red iridium complexes.
- The findings highlight the importance of ligand design, specifically the electron-donating ability of the pmb ligand, for optimizing deep-red emission.
- These complexes demonstrate significant potential for efficient deep-red emission in OLED applications.
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