From Mononuclear to Dinuclear Iridium(III) Complex: Effective Tuning of the Optoelectronic Characteristics for Organic Light-Emitting Diodes

Phosphorescent dinuclear iridium­(III) complexes that can show high luminescent efficiencies and good electroluminescent abilities are very rare. In this paper, highly phosphorescent 2-phenylpyrimidine-based dinuclear iridium­(III) complexes have been synthesized and fully characterized. Significant differences of the photophysical and electrochemical properties between the mono- and dinuclear complexes are observed. The theoretical calculation results show that the dinuclear complexes adopt a unique molecular orbital spatial distribution pattern, which plays the key role of determining their photophysical and electrochemical properties. More importantly, the solution-processed organic light-emitting diode (OLED) based on the new dinuclear iridium­(III) complex achieves a peak external quantum efficiency (η_ext) of 14.4%, which is the highest η_ext for OLEDs using dinuclear iridium­(III) complexes as emitters. Besides, the efficiencies of the OLED based on the dinuclear iridium­(III) complex are much higher that those of the OLED based on the corresponding mononuclear iridium­(III) complex

Asymmetric <i>tris</i>-Heteroleptic Iridium^III Complexes Containing a 9‑Phenyl-9-phosphafluorene Oxide Moiety with Enhanced Charge Carrier Injection/Transporting Properties for Highly Efficient Solution-Processed Organic Light-Emitting Diodes

A cyclometalating ligand containing a 9-phenyl-9-phosphafluorene oxide (PhFlPO) moiety has been synthesized and used to construct asymmetric <i>tris</i>-heteroleptic cyclometalating Ir^III complexes in combination with other ppy-type (Hppy = 2-phenylpyridine) ligands containing a functional group with a different charge carrier injection/transporting character. Their photophysical properties, electrochemical behaviors, and electroluminescent (EL) performances have been characterized in detail. Time-dependent density functional theory (TD-DFT) and natural transition orbital (NTO) calculation were carried out to gain insight into the photophysical properties of these complexes. The NTO results show that the characters of the lowest triplet excited states (T₁) can be delicately manipulated through the combination of different cyclometalating ligands. In addition, the strong electron injection/transporting (EI/ET) ability associated with the PhFlPO moiety can confer EI/ET properties to the asymmetric <i>tris</i>-heteroleptic cyclometalating Ir^III complexes. Consequently, the solution-processed organic light-emitting diodes/devices (OLEDs) based on these asymmetric <i>tris</i>-heteroleptic Ir^III phosphorescent complexes can exhibit outstanding electroluminescent (EL) performances with the maximum external quantum efficiency (η_ext) of 19.3%, current efficiency (η_L) of 82.5 cd A^–1, and power efficiency (η_P) of 57.3 lm W^–1 for the yellow-emitting device. These results show the great potential of a PhFlPO moiety in developing phosphorescent emitters and functional materials with excellent EI/ET properties

Phosphorescent Platinum(II) Complexes Bearing 2‑Vinylpyridine-type Ligands: Synthesis, Electrochemical and Photophysical Properties, and Tuning of Electrophosphorescent Behavior by Main-Group Moieties

A series of 2-vinylpyridine-type platinum­(II) complexes bearing different main-group blocks (B­(Mes)₂, SiPh₃, GePh₃, NPh₂, POPh₂, OPh, SPh, and SO₂Ph, where Mes = 2-morpholinoethanesulfonic acid) were successfully prepared. As indicated by the X-ray single-crystal diffraction, the concerned phosphorescent platinum­(II) complexes exhibit distinct molecular packing patterns in the solid state to bring forth different interactions between individual molecules. The photophysical characterizations showed that the emission maxima together with phosphorescent quantum yield of these complexes can also be affected by introducing distinct main-group moieties with electron-donating or electron-withdrawing characters. Furthermore, these 2-vinylpyridine-type platinum­(II) complexes exhibit markedly different photophysical and electrochemical properties compared with their 2-phenylpyridine-type analogues, such as higher-lying highest occupied molecular orbital levels and lower-energy phosphorescent emissions. Importantly, these complexes can show good potential as deep red phosphorescent emitters to bring attractive electroluminescent performances with Commission Internationale de L’Eclairage (CIE) coordinates very close to the standard red CIE coordinates of (0.67, 0.33) recommended by the National Television Standards Committee. Hence, these results successfully established structure–property relationship concerning photophysics, electrochemistry, and electroluminescence, which will not only provide important information about the optoelectronic features of these novel complexes but also give valuable clues for developing novel platinum­(II) phosphorescent complexes

Phosphorescent Platinum(II) Complexes Bearing 2‑Vinylpyridine-type Ligands: Synthesis, Electrochemical and Photophysical Properties, and Tuning of Electrophosphorescent Behavior by Main-Group Moieties

A series of 2-vinylpyridine-type platinum­(II) complexes bearing different main-group blocks (B­(Mes)₂, SiPh₃, GePh₃, NPh₂, POPh₂, OPh, SPh, and SO₂Ph, where Mes = 2-morpholinoethanesulfonic acid) were successfully prepared. As indicated by the X-ray single-crystal diffraction, the concerned phosphorescent platinum­(II) complexes exhibit distinct molecular packing patterns in the solid state to bring forth different interactions between individual molecules. The photophysical characterizations showed that the emission maxima together with phosphorescent quantum yield of these complexes can also be affected by introducing distinct main-group moieties with electron-donating or electron-withdrawing characters. Furthermore, these 2-vinylpyridine-type platinum­(II) complexes exhibit markedly different photophysical and electrochemical properties compared with their 2-phenylpyridine-type analogues, such as higher-lying highest occupied molecular orbital levels and lower-energy phosphorescent emissions. Importantly, these complexes can show good potential as deep red phosphorescent emitters to bring attractive electroluminescent performances with Commission Internationale de L’Eclairage (CIE) coordinates very close to the standard red CIE coordinates of (0.67, 0.33) recommended by the National Television Standards Committee. Hence, these results successfully established structure–property relationship concerning photophysics, electrochemistry, and electroluminescence, which will not only provide important information about the optoelectronic features of these novel complexes but also give valuable clues for developing novel platinum­(II) phosphorescent complexes

Phosphorescent Iridium(III) Complexes Bearing Fluorinated Aromatic Sulfonyl Group with Nearly Unity Phosphorescent Quantum Yields and Outstanding Electroluminescent Properties

A series of heteroleptic functional Ir^III complexes bearing different fluorinated aromatic sulfonyl groups has been synthesized. Their photophysical features, electrochemical behaviors, and electroluminescent (EL) properties have been characterized in detail. These complexes emit intense yellow phosphorescence with exceptionally high quantum yields (Φ_P > 0.9) at room temperature, and the emission maxima of these complexes can be finely tuned depending upon the number of the fluorine substituents on the pendant phenyl ring of the sulfonyl group. Furthermore, the electrochemical properties and electron injection/transporting (EI/ET) abilities of these Ir^III phosphors can also be effectively tuned by the fluorinated aromatic sulfonyl group to furnish some desired characters for enhancing the EL performance. Hence, the maximum luminance efficiency (η_L) of 81.2 cd A^–1, corresponding to power efficiency (η_P) of 64.5 lm W^–1 and external quantum efficiency (η_ext) of 19.3%, has been achieved, indicating the great potential of these novel phosphors in the field of organic light-emitting diodes (OLEDs). Furthermore, a clear picture has been drawn for the relationship between their optoelectronic properties and chemical structures. These results should provide important information for developing highly efficient phosphors

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