Heteroleptic Tris-cyclometalated Iridium Complex Research Articles

Red, green, and blue radio-luminescent polymer dots doped with heteroleptic tris-cyclometalated iridium complexes.

In this study, we synthesized radioexcitable luminescent polymer dots (P-dots) doped with heteroleptic tris-cyclometalated iridium complexes that emit red, green, and blue light. We investigated the luminescence properties of these P-dots under X-ray and electron beam irradiation, revealing their potential as new organic scintillators.

New Red Phosphorescent Heteroleptic Tris-Cyclometalated Iridium Complex with 1-phenylisoquinoline and 2,4-diphenylquinoline

The synthesis and photophysical study of efficient phosphorescent iridium(III) complexes having two different (C^N) ligands are reported. In order to improve luminescence efficiency by avoiding triplet–triplet (T-T) annihilation, a heteroleptic iridium complex, Ir(dpq)2(piq), is designed and prepared, where dpq and piq represent 2,4-diphenylquinoline and 1-phenylquinoline, respectively. Dpq and piq ligands can act as a source of energy. When Ir(dpq)2(piq) is placed in the lowest excited state, the excitation energy is neither quenched nor deactivated but quickly transferred intermolecularly from two dpq ligands to one luminescent piq ligand. Such transfer can occur because the triplet energy level of dpq is higher than that of piq and light is emitted mainly from the piq ligand in the end. Thus, Ir(dpq)2(piq) shows strong photoluminescence from piq ligands. To analyze this luminescent mechanism, we calculated these complexes theoretically using a computational method.

Red Organic Light-Emitting Diode Using the Heteroleptic Tris-Cyclometalated Iridium Complex

A novel red phosphorescent heteroleptic tris-cyclometalated iridium complex, Ir(ppy)2(dpq) based on 2-phenylpyridine (ppy) and 2,4-diphenylquinoline (dpq) ligand was synthesized and characterized for application in organic light-emitting diodes (OLEDs). The heteroleptic tris-cyclometalated iridium complex leads to a significant improvement in luminescence efficiency by cascade exciton transfer and the avoidance of triplet-triplet (T-T) annihilation. A ppy ligand with triplet state energies intermediate between that of the host and the emitting ligand can be successfully employed as “sensitizing ligand” allowing for efficient energy transfer from the host to the emitting ligand. A maximum luminance efficiency of ηc = 14.06 cd/A was achieved at a current density of J = 20.94 mA/cm2. At a higher current density of J = 100 mA/cm2, an efficiency of ηc = 10.77 cd/A was obtained.

Optimization of White Organic Electroluminescent Devices with Sensitized Heteroleptic Ir Complex

In this study, the heteroleptic tris-cyclometalated iridium complex, bis(2-phenylquinoline)(2-phenylpyridine)iridium(III) [Ir(pq)2(ppy)], used as red emitting dopant for white organic light-emitting diodes (WOLEDs) had higher maximum luminescence efficiency (13.80 cd/A) than that of the homoleptic tris-cyclometalated iridium complex, tris(2-phenylquinoline)iridium(III) [Ir(pq)3], due to the presence of a sensitizing ppy ligand. Thus, WOLEDs combining the Ir(pq)2(ppy) as a red emissive phosphorescent material and 4,4′-bis(9-ethyl-3-carbazovinylene)-1,1′-biphenyl (BCzVBi) as a blue emissive fluorescent material have been studied. The WOLEDs were optimized by adjusting the device structure, the optimized WOLED (device 10) had a maximum luminescence efficiency of 16.90 cd/A and CIE coordinates of (0.407, 0.337) at the applied voltage of 12 V.

Efficient red electrophosphorescent organic light-emitting diodes based on the new sensitized heteroleptic tris-cyclometalated Ir(III) complexes

Organic light-emitting device (OLED) was fabricated using the novel red phosphorescent heteroleptic tris-cyclometalated iridium complex, bis(2-phenylpyridine)iridium(III)[2(5′-methylphenyl)-4-diphenylquinoline] [Ir(ppy) 2(dpq–5CH 3)], based on 2-phenylpyridine (ppy) and 2(5′-methylphenyl)-4-diphenylquinoline (dpq–5CH 3) ligand. Generally, the ppy ligand in heteroleptic iridium complexes plays an important role as “sensitizer” in the efficient energy transfer from the host (CBP; 4,4, N, N′-dicarbazolebiphenyl) to the luminescent ligand (dpq–5CH 3). We demonstrated that high efficiency through the “sensitizer” can be obtained, when the T 1 of the emitting ligand is close to T 1 of the sensitizing ligand. The device containing Ir(ppy) 2(dpq–5CH 3) produced red light emission of 614 nm with maximum luminescence efficiency and power efficiency of 8.29 cd/A (at 0.09 mA/cm 2) and 5.79 lm/W (at 0.09 mA/cm 2), respectively.

Red Electrophosphorescent Devices Based on Heteroleptic Tris-cyclometalated Iridium Complexes with Fluorinated 2,4-diphenylquinoline Ligands

New heteroleptic tris-cyclometalated iridium complex having two different (C∧N) ligands, [Ir(dpq)2(dpq-3F)] (dpq = 2,4-diphenylquinoline, dpq-3F = 2-(3′-fluorophenyl)-4-phenylquinoline), have been synthesized and characterized for an efficient red organic light-emitting diodes (OLEDs). The iridium phosphors emit bright red light with its maximum at 608 nm. The heteroleptic tris-cyclometalated iridium complex [Ir(dpq)2(dpq-3F)] is shown to be a more efficient electrophosphor than the homoleptic tris-cyclometalated iridium complex [Ir(dpq-3F)3] to avoid the T-T annihilation by decreasing the number of the luminescent ligand. A maximum luminous efficiency was 10.9 cd/A at a current density of J = 0.6 mA/cm2. At a higher current density of J = 100 mA/cm2, the luminous efficiency maintained 54% of its maximum value as 5.9 cd/A.

Inter-Ligand Energy Transfer of Heteroleptic Tris-Cyclometalated Iridium Complexes and Their Applications to OLEDs

Novel red phosphorescent heteroleptic tris-cyclometalated iridium complex, Ir(ppy)2(dpq-3F) based on 2-phenylpyridine (ppy) and 2-(3-fluorophenyl)-4-phenylquinoline (dpq-3F) ligands have been synthesized and characterized for the application in organic light-emitting diodes (OLEDs). The heteroleptic tris-cyclometalated iridium complex leads to a significant improvement in a luminous efficiency at high currents to avoid the T–T annihilation by the exciton transfer from two ppy ligands to one luminescent dpq-3F ligand decreasing the number of the luminescent ligand. This inter-ligand energy transfer (ILET) can occur because the dpq-3F-centered 3MLCT state is lower than that of the ppy-centered 3MLCT state and because the ILET time from the ppy-centered 3MLCT state to the dpq-3F-centered 3MLCT state is shorter than the radiative lifetime of Ir(ppy)3. A maximum luminous efficiency of ηc = 13.70 cd/A and power efficiency of ηp = 10.80 lm/W are achieved at a current density of J = 0.07 mA/cm2. At a higher current density of J = 100 mA/cm2, ηc = 9.17 cd/A and ηp = 2.42 lm/W are obtained.

New heteroleptic Tris-cyclometalated iridium complex for red electrophosphorescent light-emitting diodes

New heteroleptic Tris-cyclometalated iridium complex having two different (C∧N) ligands, [Ir(dpq)2(dpq-3F)] (dpq=2,4-diphenylquinoline, dpq-3F=2-(3′-fluorophenyl)-4-phenyl quinoline), have been synthesized and characterized for an efficient red organic light-emitting diodes (OLEDs). The iridium phosphors emit bright red light with its maximum at 615nm. The heteroleptic Tris-cyclometalated iridium complex [Ir(dpq)2(dpq-3F)] is shown to be a more efficient electrophosphor than the homoleptic Tris-cyclometalated iridium complex [Ir(dpq-3F)3] to avoid the triplet–triplet (T–T) annihilation by decreasing the number of the luminescent ligand. The highest occupied molecular orbital (HOMO) energy level of Ir(dpq-3F)3 is lower than that of Ir(dpq)3. Thus, the luminescence of the heteroleptic Ir(dpq)2(dpq-3F) occurs mainly at the dpq-3F ligand because the Ir(dpq-3F)3 has more MLCT characteristic. To analyze luminescent mechanism, we calculated these complexes theoretically by using computational method.

Heteroleptic tris-cyclometalated iridium(III) complexes with phenylpridine and diphenylquinoline derivative ligands

The synthesis and photophysical study of efficient phosphorescent heteroleptic tris-cyclometalated iridium(III) complexes having two different (C^N) ligands are reported. In order to improve the luminescence efficiency by avoiding triplet–triplet (T–T) annihilation, new heteroleptic tris-cyclometalated iridium complexes, Ir(ppy) 2(dpq), Ir(ppy) 2(dpq-3-F) and Ir(ppy) 2(dpq-CF 3), are designed and prepared where ppy, dpq, dpq-3-F and dpq-CF 3 represent 2-phenylpyridine, 2,4-diphenylquinoline, 2-(3-fluorophenyl)-4-phenylquinoline, and 4-phenyl-2-(4-(trifluoromethyl)phenyl)quinoline, respectively. Ppy ligands and dpq derivatives can act as a source of energy supply. When new heteroleptic tris-cyclometalated iridium complex, Ir(ppy) 2(dpq-3-F) is placed in the lowest excited state, the excitation energy is neither quenched nor deactivated but quickly intermolecularly transferred from two ppy ligands to one luminescent dpq-3-F ligand. Such transfer can occur because the triplet energy level of Ir(ppy) 3 is higher than that of Ir(dpq-3-F) 3 and because Ir(dpq-3-F) 3 was known to have a shorter lifetime than that of Ir(ppy) 3. As a result, Ir(ppy) 2(dpq-3-F) shows strong emission band at 620 nm from dpq-3-F ligand in the end. Thus it allows more reddish luminescent color and improves the luminescence by the decrease of quenching or energy deactivation by decreasing the number of the luminescent ligand. To analyze luminescent mechanism, we calculated these complexes theoretically by using computational method.

Highly Efficient, Selective, and General Method for the Preparation of Meridional Homo- and Heteroleptic Tris-cyclometalated Iridium Complexes

A highly efficient and general method based on transmetalation with an organozinc reagent is developed for selective preparation of homo- and heteroleptic meridional tris-cyclometalated iridium complexes. The molecular structure of mer-Ir(1-piq)2(ppy) (2) has been determined by a single-crystal X-ray diffraction analysis. The emission properties of a series of meridional complexes are reported.