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[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]

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 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]

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]