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This document, titled "Intermolecular Charge Transfer for High-Performance Organic Light-Emitting Diodes," discusses the use of thermally activated delayed fluorescence (TADF) materials in organic light-emitting diodes (OLEDs) to achieve high-performance devices. Specifically, the authors designed and synthesized two new molecules, CzPh-1 and CzPh-2, which were found to form deep-blue exciple emission with a triazine-containing molecule, CzTrz, through effective intermolecular charge transfer. The photoluminescence spectra and time-resolved photoluminescence studies demonstrated the TADF characteristics of these materials. The authors acknowledge the support from the National Natural Science Foundation of China and the China Postdoctoral Science Foundation. [Extracted from the article]

Abstract: Highly efficient deep blue phosphorescent light emitting diodes were developed using a newly synthesized series of blue emitting tridentate platinum emitters. Devices employing a cohost of hole and electron transport materials yielded high external quantum efficiencies with low turn on voltage and low efficiency roll off. A maximum EQE of 15.7% and CIE coordinates of (0.16,0.13) was achieved in a device based on platinum(II) bis(N-methyl-imidazolyl)benzene chloride (Pt-16). [Copyright &y& Elsevier]

The turn-on voltage of devices are 3.9V, it is worth noting that the efficiency of devices is very low when it is turned on. Wavelength (nm) (b) EQE (%) Luminance (cd/m 2) device 1 device 2 Fig. Energy level of devices 2 4 6 8 10 12 14 16 18 20 0 10 20 30 40 50 60 70 80 90 device 1 device 2 Voltage (V) Current Density (mA/cm 2) 10 0 10 1 10 2 10 3 10 4 (a) Luminance(cd/m 2) 10 0 10 1 10 2 10 3 10 4 10 -2 10 -1 10 0 10 1 10 2 400 500 600 700 0.0 0.2 0.4 0.6 0.8 1.0 Normalized Intensity (a.u.). [Extracted from the article]

Two novel indole-based, bipolar, host materials were designed and synthesized by introducing the triazine unit to the 5-position of indole moiety with a meta -linking strategy. The two host materials exhibited excellence bipolar transport abilities and the meta-linking analog presented a high T g value (>120 °C). Furthermore, their electrochemical and photo-physical properties were also fully characterized and all the results exhibited that the meta -linking strategy made a significant effect on the physical properties of the two hosts. Moreover, the PHOLED devices using 9-(4-(5-(3-(4,6-diphenyl-1,3,5-triazin-2-yl)phenyl)- 1H -indol-1-yl) phenyl)- 9H -carbazole and 9-(4-(5-(4-(4,6-diphenyl-1,3,5-triazin-2-yl)phenyl)- 1H -indol-1-yl)phenyl)- 9H -carbazole as hosts were also fabricated to evaluate the practical utilities of host materials. The devices achieved the maximum external quantum efficiencies of 17.53% for para -linking compound and 14.53% for meta -linking analog, respectively. In particular, para -linking compound based device revealed the maximum external quantum efficiency was twice that of the device using 4,4′-bis( N -carbazolyl)-1,10-biphenyl as the host. [ABSTRACT FROM AUTHOR]

Thermally activated delayed fluorescence (TADF) materials have been regarded as promising host materials for fluorescent and phosphorescent guest materials to achieve high performance organic light-emitting diodes (OLEDs). In this work, three molecules, PhCQ , m -PyCQ and p -PyCQ, using carbazole derivatives as donor and quinazoline units as acceptor were designed and synthesized. Both theoretical and experimental results showed that PhCQ , m -PyCQ and p -PyCQ possess TADF properties with higher triplet excited states than red phosphorescent guest, RD-1. When used as host materials for RD-1, it was found that the emission spectrum of PhCQ has the largest overlap with the absorption spectrum of RD-1, which is conducive to Förster resonance energy transfer (FRET) between the host to the guest. As a result, red phosphorescent OLED device based on PhCQ host exhibited the best performances with the maximum external quantum efficiency (EQE) of 37.2 %. When the brightness is 1000 cd/m2, the EQE is still as high as 33.0 %. [Display omitted] • Three TADF host materials, PhCQ , m -PyCQ and p -PyCQ, for red PhOLEDs were designed and synthesized. • Carbazole and quinazoline derivatives were employed to balance the carrier transport. • The maximum external quantum efficiency of the top-emitting device based on PhCQ was 37.16 %. [ABSTRACT FROM AUTHOR]

[Display omitted] • TADF hosts based on nonbenzenoid aromatic aza-azulene were synthesized. • The k RISC of 9.0 × 106 s−1 was obtained induced by aromaticity and geometry vibration. • Enhanced intra/inter-molecular interaction promotes electron coupling. • Red PhOLED with EQE > 50 % and LT 95 = 52,350 h was accessed. The fast triplet-singlet up-conversion based on thermally activated delayed fluorescence (TADF) molecules is a unique effort to improve the utilization of triplet excitons. We construct two TADF molecules using nonbenzenoid aromatic aza-azulene as donor and triazine as acceptor. The distortion structural resonance of aza-azulene enhances the reverse intersystem crossing (RISC) process, resulting in efficient inter/intramolecular charge transfer (CT) emission. The rate constant of RISC (k RISC) is 9.0 × 106 and 8.4 × 106 s−1 in solid states. Efficient Förster Energy Transfer (FRET) and/or Dexter Energy Transfer (DET) between these molecules and dopants make them suitable host materials to improve the performances of red phosphorescent organic light-emitting diodes (OLEDs). Especially, the top-emitting device achieves an external quantum efficiency (EQE) of 51.3% and a current efficiency of 68.2 cd/A at 1000 cd m−2 with a long device lifetime of LT 95 = 52,350 and LT 50 = 536,200 h. [ABSTRACT FROM AUTHOR]

[Display omitted] • Four bipolar molecules were designed and synthesized for accessing exciplex and electroplex host systems. • Highly efficient green PhOLED with EQE max of 29.9% was achieved. • Extremely small efficiency roll-offs (1.3% at 1,000 cd m−2; 5.4% at 5,000 cd m−2) were obtained. Host materials are of great significance to achieve high-performance host–guest organic light-emitting diodes (OLEDs) through restraining the exciton annihilation in the emissive layer. Herein, four bipolar molecules bearing benzothienocarbazole (BTCz)/benzothienocarboline (BTCb) and benzimidazole (Bi) moieties were designed and synthesized. Using them as hosts, green phosphorescent OLEDs (PhOLEDs) with maximum current efficiency (CE max) of 90.8 cd A−1, power efficiency (PE max) of 76.5 lm W−1, and external quantum efficiency (EQE max) of 27.9% were obtained. More importantly, it was found that these four molecules could be used as electron-donating materials to interact with electron-accepting triazine derivatives to form electroplexes. Employing these electroplexes as hosts, highly efficient green PhOLEDs with CE max of 104.4 cd A−1, PE max of 85.1 lm W−1, EQE max of 29.9%, and extremely small efficiency roll-offs (EQE = 29.5%, 1.3% roll-off at 1,000 cd m−2; EQE = 28.3%, 5.4% roll-off at 5,000 cd m−2) were achieved. The excellent device performances fully exhibit the promising potential of electroplexes as hosts for high-performing OLEDs. [ABSTRACT FROM AUTHOR]

We have developed a high color rendering index (CRI) top-emitting white organic light-emitting diode (TWOLEDs) using single emitter by enhancing the yellow-green part between the monomer and excimer emission of platinum [1,3-difluoro-4,6-di(2-pyridyl)benzene] chloride via microcavity effect. Resonant wavelengths can well-tuned by adjusting the thickness of the hole transport layer to modify the optical cavity length. The TWOLEDs exhibits four-peak spectra at 480, 512, 556, and 600 nm with maximum color rendering index of 83 and full half-maximum width of 200 nm. Meanwhile, the chromaticity of TWOLEDs is quite stable, showing slight Commission Internationale deL'Eclairage coordinate shifts of (±0.005, ±0.004) over the driving voltage range of 4–10 V. [Display omitted] • High color rendering index and chromaticity stable top-emitting white OLEDs with single emitter. • Four peak emission are achieved by combining monomer, excimer emission and resonant cavity. • Weak microcavity white OLEDs were investigated and modelled. • The device emission shows a Lambertian-like characteristic. [ABSTRACT FROM AUTHOR]

As the promising candidates for red phosphorescent organic light-emitting diodes (PhOLEDs), aryl quinoline Ir(III) complexes have attracted enormous and continual attention. The molecular design strategy of introducing methyl group to aryl quinoline unit to tune their optoelectronic properties is reported here. The synthesis, structures, electrochemical and photophysical properties of a series of methyl-substituted aryl quinoline Ir(III) complexes were systematically studied. Red and deep-rep phosphorescent emission with the maximum wavelength from 610 nm to 646 nm were accessed by combing the electron-donating effect of the 3-methyl group to centered Ir atom and increased twist angle between phenyl unit and quinoline group induced by the 2-methyl group. Deep-red PhOLEDs with the emission peak at 620 nm, CIE coordinates of (0.68, 0.32), luminescence of 23720 cd/m2, and an EQE of 40.5% were realized. The position optimization of methyl groups to obtain red and deep-red emitters for phosphorescent organic light-emitting diodes (PhOLEDs). [Display omitted] • The impact of methyl groups on aryl quinoline Ir(III) complexes is explored. • Red and deep-rep phosphorescent emissions from 610 nm to 646 nm are accessed. • Deep-red PhOLED with the CIE of (0.68, 0.32) and EQE of 40.5% is realized. [ABSTRACT FROM AUTHOR]

The strategy to co-deposit copper halide and organic materials to directly generate emissive copper complexes is taken into account as a straightforward and promising way to fabricate organic light-emitting diodes (OLEDs) compared with using presynthesized complexes. In this work, four aza-9,9-Spirobifluorenes (aza-SBFs) with the nitrogen atom at different positions of azafluorene moiety were co-deposited with copper(I) iodide (CuI) to form emissive complexes. Intriguingly, we found that the emission properties of these co-deposited copper complexes contain phosphorescent and thermally activated delayed fluorescent (TADF) characteristics. Through changing the position of nitrogen atom, the TADF process can be effectively enhanced, resulting in PLQY up to 92.2 %. Consequently, green OLED with a high current efficiency of 41.9 cd/A, power efficiency of 32.9 lm/W, and external quantum efficiency (EQE) of 16.8 % were achieved by employing the co-deposited copper complex as the emitter. [Display omitted] • aza-9,9-Spirobifluorenes were co-deposited with CuI to form emissive complexes. • The generated materials possessed phosphorescence and TADF emission processes. • High PLQY up to 92.2 % was realized benefiting from the increased TADF proportions. • Green OLED with the EQE of 16.8 % and current efficiency of 41.9 cd/A was achieved. [ABSTRACT FROM AUTHOR]

We successfully fabricated white organic light-emitting diodes(WOLEDs) based on double light-emitting layers(EMLs) with ultra-high color rendering index (CRI)and stable chromaticity by multiple mechanism four peaks tuning. The phosphorescent blue monomer and red excimer emission from Platinum [1,3-difluoro-4,6-di (2-pyridinyl) benzene]chloride(Pt-4) together with the deep blue fluorescence and yellow phosphorescence emission from a co-emission light-emitting layer realized excellent four-peak tuning WOLEDs. Ultra-high CRI of 94 and extremely stable Commission Internationale deL'Eclairage (CIE) coordinates of (0.420 ± 0.003,0.360 ± 0.002) over a wide voltage range were presented. The high CRI is ascribed to broad and continuous four peaks emission covering the fully visible spectrum. The mixed bipolar interlayer effectively control the distribution of excitons in the two regions of emission, which makes the chromaticity of WOLEDs extremely stable. Also the stable emission mechanism of two EMLs contribute to chromatic stability. Significantly, the devices showed high efficiency under the premise of high CRI and stable chroma by effective strategic of structural design. Image 1 • The double emitting layers (EML 1 and EML 2) separated by bipolar interlayer can achieve high efficiency four-peak emission. • Broad and continuous four-peak spectrum covering the fully visible region can improve CRI(94). • Bipolar interlayer can stabilize the chromaticity by adjusting the distribution ratio of excitons in EML 1 and EML 2. • The stable emission and exciton confinement of EML 1 and EML 2 play a crucial role in chromatic stability. [ABSTRACT FROM AUTHOR]