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Oxygen-Bridged Boron NHC-Based Red-Emitting Iridium Complexes Exhibiting Tri-Charge (0, -1, -2) Ligands
Wenqing Yu1, Fuzheng Zhang1, Zhenghao Zhang2
1School of Environmental and Chemical Engineering, Jiangsu University of Science and Technology, Zhenjiang212003, P. R. China.
Inorganic Chemistry
|July 18, 2026
Summary
Researchers developed novel red-emitting phosphorescent iridium complexes using oxygen-bridged boron N-heterocyclic carbene ligands. These complexes show promise for efficient organic light-emitting diode applications.
Area of Science:
- Materials Science
- Organic Chemistry
- Photochemistry
Background:
- Phosphorescent iridium complexes are crucial for organic light-emitting diodes (OLEDs).
- Violet and blue emitters are well-developed, but efficient red emitters remain a challenge.
- N-heterocyclic carbene (NHC) ligands offer tunable electronic properties for iridium complexes.
Purpose of the Study:
- To synthesize and characterize novel red-emitting phosphorescent iridium complexes.
- To investigate the impact of rigid oxygen-bridged boron NHC ligands on luminescence properties.
- To evaluate the performance of these complexes as dopants in OLED devices.
Main Methods:
- Synthesis of four neutral iridium complexes incorporating oxygen-bridged boron NHC ligands (Bpmi, Bpmb), a biphenyl ligand, and bipyridine or phenanthroline ligands.
- Single-crystal X-ray diffraction analysis to determine molecular structures and intermolecular interactions.
- Photoluminescence spectroscopy to characterize emission wavelengths and efficiencies.
- Fabrication and testing of OLED devices using the synthesized complexes as dopants.
Main Results:
- All four synthesized iridium complexes exhibited efficient red luminescence in the range of 637-650 nm.
- The phenanthroline and Bpmb ligands contributed to enhanced luminescence efficiency due to increased rigidity.
- OLED devices doped with Ir(Bpmi)phen, Ir(Bpmb)bpy, and Ir(Bpmb)phen achieved maximum external quantum efficiencies (EQEs) of 9.8%, 4.3%, and 10.3%, respectively, with emission peaks below 632 nm.
- Structural analysis revealed specific trans-C-C and trans-C-N arrangements and significant intermolecular interactions (π-π, C-H···π, C-H···O).
Conclusions:
- The study successfully developed novel red-emitting phosphorescent iridium complexes using oxygen-bridged boron fused-ring NHC ligands.
- Rigidity introduced by the phenanthroline and Bpmb ligands is key to enhancing luminescence efficiency.
- These findings offer valuable insights for designing advanced red phosphorescent iridium complexes for optoelectronic applications, particularly in OLEDs.
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