Highly Efficient Deep Blue Phosphorescent OLEDs Based on Tetradentate Pt(II) Complexes Containing Adamantyl Spacer Groups

Abstract

Tetradentate Pt(II) complexes are promising emitters for deep blue organic light‐emitting diodes (OLEDs) due to their emission energy and high photoluminescence efficiency. However, to obtain a pure blue color, spectral red‐shifts, and additional emission peaks at longer wavelengths, originating from strong intermolecular interactions between parallel Pt(II) complexes, must be avoided. Herein, a new class of deep‐blue emitting tetradentate Pt(II) complexes consisting of a non‐planar ligand and a bulky adamantyl group is reported. The six‐membered metallacycle structure renders the Pt(II) complex non‐planar. In addition, the bulky adamantyl groups increase intermolecular distances and decrease red‐shifts in the emission originating from strong dipole–dipole interactions. Therefore, these Pt(II) complexes exhibit little change in emission color with increasing dopant concentration. OLEDs incorporating these new Pt(II) complexes as emitters exhibit deep blue emission with a Commission International de L'Eclairage (CIE) y under 0.13 and a maximum external quantum efficiency of 22.6%, which is one of the highest observed for deep blue (CIE y < 0.15) phosphorescent OLEDs using Pt(II) complexes. These results provide a new approach for designing Pt(II) complexes for high efficiency deep blue OLEDs.

Boron‐Based Multi‐Resonance TADF Emitter with Suppressed Intermolecular Interaction and Isomer Formation for Efficient Pure Blue OLEDs

“…The transient EL signals with no spikes and changes under different negative biases after the pulse indicate that the injected holes and electrons are well recombined and contribute to light emission via a radiative decay process, remaining less trapped charge carriers or accumulated charges inside the device. [19] The results confirm that the TADF-OLED with the MR-emitter has a good charge balance, which provides reduced polaron-exciton annihilation processes under electrical excitation. [20] As a result, the OLED reached a high EQE of 24.3% close to the theoretical value.…”

Low Efficiency Roll‐Off Blue Phosphorescent OLEDs at High Brightness Based on [3+2+1] Coordinated Iridium (III) Complexes

“…[41,42] Furthermore, the emission behavior of these complexes doped in poly(methyl methacrylate) (PMMA) thin films has also been investigated. As shown in Figure 4c, these complexes generally showed a blue shift when compared to their corresponding emission spectra in the DCM solution and exhibited high PLQYs of up to 90% with short excited state lifetime ranging from 2-5 µs in solid-state thin films, indicating a high k r of 3 × 10 5 s −1 (Table 2), highly comparable to the state-of-the-art iridium(III), [7,27,[43][44][45][46] platinum(II), [47][48][49][50][51][52][53][54] and gold(III) [23,[55][56][57][58] phosphorescent emitters.…”

Tetradentate Platinum(II) and Palladium(II) Complexes Containing Fused 6/6/6 or 6/6/5 Metallocycles with Azacarbazolylcarbazole-Based Ligands

“…Rigid tridentate Pt­(II) complexes demonstrate significantly improved quantum efficiencies; however, their chemical stabilities and thermal stabilities are typically not satisfactory because of the existence of the other monodentate ligand. Tetradentate Pt­(II) − and Pd­(II) − complexes are another kind of ideal emitters for the fabrication of efficient OLEDs with long operational lifetimes or high color purities because of the rigid molecular geometries and the lack of monodentate ligands. Rational ligand design is critical for the regulation of the photophysical property and excited-state property of the complexes.…”

“…Carbazolylpyridine (CzPy) skeleton has been widely employed in the design of the tetradentate ligands to chelate with metal ions to form a six-membered ring metallocycle (Figure ). ,,,− ,,− CzPy connects with phenyl heteroaromatics, carbazolyl heteroaromatics, or acridinyl pyrazole by oxygen or nitrogen to develop various complexes containing fused 5/6/6 metallocycles, whose photophysical properties can be efficiently manipulated through modifying the heteroaromatics or the substituents on the pyridine ring with color across the whole visible region, such as PtONx, ,,,,, PtNxN, , PtN′1N, and their corresponding Pd­(II) complexes, , and the monomer/excimer emissions could be also tuned through intramolecular hydrogen bond design . Two CzPy moieties are linked by an oxygen atom to form symmetrical 6/6/6-type metal complexes, ,,− and PtNON can act as an ideal phosphorescent emitter for efficient and stable blue OLEDs. ,, CzPy moieties directly connect with the pyridinyl or phenyl group to develop a series of 6/5/6-type Pt­(II) complexes with extended conjugation systems, which are good candidates for green to red emitters, , such as Y-Pt, Pt­( bp -7), and Pt­( bp -8) …”