Homoleptic Iridium Complexes Research Articles

Homoleptic iridium complexes with dibenzothiophene sulfone and triphenylamine groups for orange polymer light-emitting diodes

We have designed and synthesized two new orange light-emitting homoleptic iridium complexes ((p-FSOPyTPA)3Ir and (m-FSOPyTPA)3Ir) containing dibenzothiophene sulfone and triphenylamine frameworks. Solution-processed polymer light-emitting devices (PLEDs) are also prepared using these as-synthesized iridium complexes with a single-emission-layer (SEL) structure of ITO/PEDOT:PSS/poly-TPD/EML/TPBI/Ba/Al. Both the iridium complexes exhibited good thermal stability with a Td > 430 °C. Compared to (p-FSOPyTPA)3Ir, (m-FSOPyTPA)3Ir displayed much better thermal, photophyscial and electroluminescent properties owing to the different coordinate positions of dibenzothiophene sulfone. More importantly, the orange-emitting PLEDs based on (m-FSOPyTPA)3Ir exhibited a maximum luminous efficiency (LE) of 4.65 cd/A, a maximum external quantum efficiency (EQE) of 2.03%, and the Commission Internationale de L'Eclairage (CIE) coordinates of (0.54, 0.42), when the iridium complex doped into a matrix of PVK/OXD-7 with a concentration of 4 wt %. Our preliminary work could provide a promising orange emitters candidate for the development of solution-processable highly efficient white PLEDs.

Homoleptic iridium complexes based on furo[3,2-c]pyridine ligand for efficient phosphorescent OLEDs

Abstract Two novel homoleptic Ir complexes Ir(pfupy)3 and Ir(thfupy)3 have been designed and synthesized, which bear 4-phenylfuro[3,2-c]pyridine and 4-(thiophen-2-yl)furo[3,2-c]pyridine as the CˆN ligand, respectively. Because of the lower π-π* energy of thiophene than phenyl, Ir(thfupy)3 shows an obvious red-shifted emission peaked at 577 nm relative to Ir(pfupy)3 (533 nm). Moreover, the photoluminescent quantum yield (PLQY) and lifetime of Ir(pfupy)3 are determined to be 0.83 and 0.92 μs, whereas they are 0.35 and 2.09 μs for Ir(thfupy)3 due to the energy gap law and weak spin-orbital coupling. Benefiting from the good thermal stability, both Ir(pfupy)3 and Ir(thfupy)3 can be vacuum deposited without decomposition to fabricate the corresponding phosphorescent OLEDs (PhOLEDs). Maximum external quantum efficiencies as high as 26.7% (97.9 cd/A) and 15.3% (46.6 cd/A) together with Commission Internationale de l’Eclairage coordinates of (0.42, 0.57) and (0.56, 0.42) are realized for Ir(pfupy)3 and Ir(thfupy)3, respectively. The obtained promising device performance clearly indicates the great potential of homoleptic furo[3,2-c]pyridine based Ir complexes for efficient PhOLEDs.

High efficiency green OLEDs based on homoleptic iridium complexes with steric phenylpyridazine ligands.

A series of steric phenylpyridazine based homoleptic iridium(iii) complexes (1-3) have been synthesized with novel one-pot methods. Single X-ray structural analyses are conducted on complexes 1 and 2 to reveal their coordination arrangement. These complexes exhibit a very strong green phosphorescence emission with high quantum yields of over 64%. The relationship between photophysical properties and the substituent nature of the complexes is discussed by density functional theory (DFT) and time-dependent DFT. Self-quenching is significantly reduced for these complexes in solid even at very high concentrations because the sterically hindered bicyclo [2.2.2] oct-2-ene and m-substituted CF3 spacers in the phosphor molecules lead to minimum bimolecular interactions. Accordingly, the electroluminescence device based on complex 3 exhibits a maximum luminous efficiency of 64.1 cd A-1 with a high EQE of 25.2% at a high doping concentration of 15 wt%. Meanwhile, when neat 3 was adopted as the emitting layer, the non-doped green device gives a state-of-the-art EQE as high as 15.2% (40.1 cd A-1) along with CIE coordinates of (0.346, 0.599).

Theoretical investigation of photophysical properties for a series of iridium(iii) complexes with different substituted 2,5-diphenyl-1,3,4-oxadiazole

A quantum chemical investigation from structural and electronic properties and some charge-transport parameter viewpoints was performed on several homoleptic iridium complexes [(C∧N)2Ir(pic)] with the 2,5-diaryl-1,3,4-oxadia-zoles moiety in C∧N ligands, where pic represents the picolinate ancillary ligand.

New homoleptic iridium complexes with C∧NN type ligand for high efficiency orange and single emissive-layer white OLEDs

Two new iridium complexes were prepared. With one of the complexes, both high efficiency orange EL and single-EML WOLED were constructed.

Influences of fluorination on homoleptic iridium complexes with C∧N=N type ligand to material properties, ligand orientation and OLED performances

Two new iridium complexes with C∧N=N type ligand (i.e., Ir(BFPPya)3{tris[3,6-bis(4-fluorophenyl)pyridazine]iridium(III)} and Ir(BDFPPya)3{tris[3,6-bis (2,4-di-fluorophenyl)pyridazine]iridium(III)}) attaching with fluorine atoms, were synthesized and the effects of fluorination on the material properties and device performance were investigated. Compared with our previously reported fluorine-free analogue material, that is Ir(BPPya)3{tris[3,6-bis(phenyl)pyridazine]iridium(III)}, blue shifts in the emission spectra as well as in the long wavelength region of the absorptions were observed. The photoluminescence quantum yield (PLQY) (0.44 and 0.84 vs 0.29), phosphoresces lifetime (0.88 and 1.31 vs 0.66 ms), and oxidation potential (1.10 and 1.37 vs 0.95 V) increased obviously after fluorinating the ligand. In contrast, the thermal stability of the iridium complexes decreased slightly (Td: 435 and 402 vs 440 °C). In the density functional theory (DFT) calculations, by comparing the steric shape of the three ligands within one optimized molecule, orientational differences among the complexes were observed. In OLED device studies, bluish green electroluminescence with peak emission of 500 nm, using the electron-transporting host of TPBI [2,2′,2″-(1,3,5-benzenetriyl)tris(1-phenyl- 1H-benzimidazole)] and the most fluorinated dopant of Ir(BDFPPya)3, was achieved with maximum efficiency of 20.3 cd/A. On one hand this efficiency is not satisfactory considering a high PLQY of 0.84. On the other hand with the similar device structure, that the (HOMO-LUMO)s of all the dopants are wrapped within that of the host TPBI, and all the triplet energies of the dopants are smaller than that of the host TPBI, it is abnormal that the ordering of device efficiencies is contradictory to that of PLQY. Assisting with the phosphorescent spectrum of TPBI and the absorption spectra of the dopant, the contradiction was interpreted reasonably.

Highly efficient phosphorescent organic light-emitting diodes using a homoleptic iridium(III) complex as a sky-blue dopant

Homoleptic triscyclometalated iridium(III) complex Ir(dbi)3 was used as a dopant for sky blue phosphorescent organic light-emitting diodes (PHOLEDs). Its photophysical, thermal, electrochemical properties as well as the device performances were investigated. Ir(dbi)3 exhibited high quantum yield of 0.52 in solution at room temperature. A maximum current efficiency and external quantum efficiency (EQE) of 61.5cdA−1 and 23.1% were obtained, which are the highest ever reported for blue homoleptic iridium complexes. High efficiencies of 53.5cdA−1 and 20.1% EQE were achieved even at the luminance of 1000cdm−2.

Homoleptic vs. Heteroleptic Orange Light-Emitting Iridium Complexes Chelated with Benzothiazole Derivatives

The homoleptic and heteroleptic iridium(III) complexes exhibiting orange phosphorescence were investigated to compare their emission colors, luminance efficiency, and stability. The homoleptic iridium complexes, Ir(pbt-R)3, were prepared from the reaction of the iridium(III) precursor and phenylbenzothiazole derivatives. The heteroleptic ones containing the anions of 4-methyl-2,3-diphenylquinoline (4-Me-dpq) and 2-phenylbenzothiazole (pbt) as ligands, Ir(pbt-OMe)2(4-Me-2,3-dpq) and Ir(4-Me-2,3-dpq)2(pbt-OMe), were synthesized via the chloro-bridged iridium dimer. We investigated photoabsorption and photoluminescence (PL) properties of the iridium complexes and studied their bandgaps with cyclic voltammetry (CV). Orange phosphorescence with the PL maxima of 530–620 nm was observed with these complexes, and the bandgaps between their highest occupied molecular orbitals (HOMOs) and the lowest unoccupied molecular orbitals (LUMOs) were correlated with CV data. The electro-luminescence (EL) study of these complexes was not possible due to lack of sublimability. The light-emitting mechanisms regarding the phosphorescence colors were discussed.

First-Principles Studies on the Efficient Photoluminescent Iridium(III) Complexes with C∧N═N Ligands

The electronic structures and photophysical properties of several homoleptic iridium complexes IrL(3) with C^N═N ligands, including 1 (L = 3,6-diphenylpyridazine), 2 (L = 1,4-diphenylphthalazine), 3 (L = 3-phenyl-5H-indeno[1,2-c]pyridazine), and 4 (L = 3-phenylbenzo[h]cinnoline), are investigated using the density functional method. The comparison between the calculated results of the four complexes shows that the assumed complex 4 may possess higher photoluminescent quantum efficiency than complexes 1-3 and is the potential candidate to be an efficient green-emitting material. The photophysical properties of the assumed complex 3 can be comparable to that of experimentally found complex 1. For 1 and 3, the emission energies are nearly the same, consistent with their similar HOMO-LUMO energy gaps. Their emission characters are also similar and mainly dominated by one ligand. For 4 and the experimentally found complex 2, although they have similar HOMO-LUMO energy gaps, and their luminescent nature is nearly the same and dominated by the three ligands, the emission spectrum of 4 is blue-shifted as compared to that of 2.

Strong Luminescent Iridium Complexes with CˆN=N Structure in Ligands and Their Potential in Efficient and Thermally Stable Phosphorescent OLEDs

Homoleptic iridium complexes with CˆN=N type ligands, i.e., 1,4-bis (phenyl) phthalazine (BPPa) and 3,6-bis(phenyl)pyridazine (BPPya), are strong phosphorescents, easy to synthesize, and thermally stable, thus having great potential in optical electronic applications, as demonstrated in Ir(BPPa)3-based OLED devices. A quantum chemistry study shows that CˆN=;N type ligands can bond to Ir more strongly.