A carbazole derivative substituted with two diphenylphosphine oxide groups at asymmetric positions of carbazole is synthesized and the substitution position is correlated with the photophysical ...properties and device performances of blue phosphorescent organic light‐emitting diodes. The carbazole type host with substituents at 2‐ and 5‐ positions of carbazole shows the merits of low driving voltage of 2‐position substitution, and high thermal stability and high quantum efficiency of 5‐ position substitution. Therefore, the carbazole type host exhibits excellent thermal and morphological stability up to 140 °C and record high quantum efficiency of 31.4% and power efficiency of 53.1 lm W‐1 without any outcoupling enhancement and p‐ or n‐doped charge transport layer in blue phosphorescent organic light‐emitting diodes.
Excellent thermal stability and high quantum efficiency above 30% in blue phosphorescent organic light emitting diodes are achieved using a high triplet energy host material with two electron withdrawing substituents at asymmetric positions of carbazole.
Carbazole‐ and triazine‐derived thermally activated delayed fluorescent (TADF) emitters, with three donor units and an even distribution of the highest occupied molecular orbital, achieve high ...external quantum efficiencies of above 25% in blue and green TADF devices.
The highly sensitive optical detection of oxygen including dissolved oxygen (DO) is of great interest in various applications. We devised a novel room‐temperature‐phosphorescence (RTP)‐based oxygen ...detection platform by constructing core–shell nanoparticles with water‐soluble polymethyloxazoline shells and oxygen‐permeable polystyrene cores crosslinked with metal‐free purely organic phosphors. The resulting nanoparticles show a very high sensitivity for DO with a limit of detection (LOD) of 60 nm and can be readily used for oxygen quantification in aqueous environments as well as the gaseous phase.
Gl‐O2‐w!: A dissolved oxygen (DO)‐detection platform based on core–shell nanoparticles with a water‐soluble polymethyloxazoline shell and oxygen‐permeable polystyrene core crosslinked with metal‐free purely organic phosphors is reported. The resulting nanoparticles show a very high sensitivity and can be used for oxygen quantification in a variety of environments.
•High triplet energy host material from carbazole and phenylphosphine oxide.•High triplet energy of 3.01eV as a host material for deep blue phosphorescent organic light emitting diodes.•High quantum ...efficiency of 18.8% in deep blue devices at 3% doping concentration.
A high triplet energy material with carbazole and phosphine oxide, phenylbis(9-phenyl-9H-carbazol-3-yl)phosphine oxide (3DCPO), was synthesized as a bipolar host material for deep blue phosphorescent organic light emitting diodes. The 3DCPO host material showed a high triplet energy of 3.01eV, which was high enough for deep blue phosphorescent organic light-emitting diodes. Deep blue phosphorescent organic light-emitting diodes with the 3DCPO host material exhibited high external quantum efficiency of 18.8% at 3% doping concentration.
High quantum efficiency above 18% and extended lifetime three times longer than that of phosphorescent organic light‐emitting diodes (OLEDs) are demonstrated in blue thermally activated delayed ...fluorescent OLEDs.
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•Improved efficiency in white phosphorescent organic light emitting diodes.•Donor–acceptor type host structure for bipolar charge transport properties.•Yellow phosphorescent organic ...light-emitting diodes with a high quantum efficiency above 25%.
Highly efficient white phosphorescent organic light-emitting diodes (OLEDs) were reported using a donor–acceptor type material as a host material. A donor–acceptor type material, 10-phenyl-10H-spiroacridine-9,9′-fluorene-2′,7′-dicarbonitrile (ACRFLCN), was doped with a yellow emitting iridium(III) bis(4-phenylthieno3,2-cpyridinato-N,C2′) acetylacetonate (PO-01) dopant and high quantum efficiency of 26.9% was realized in the yellow phosphorescent OLEDs using the ACRFLCN host material. Efficient energy transfer and bipolar charge transport properties of ACRFLCN increased the quantum efficiency of the PO-01 doped yellow phosphorescent OLEDs. In addition, white phosphorescent OLEDs with the PO-01 doped ACRFLCN yellow emitting layer exhibited a high quantum efficiency of 22.8% and a high power efficiency above 50.0lm/W.
Molecular design principles of thermally activated delayed fluorescent (TADF) emitters having a high quantum efficiency and a color tuning capability was investigated by synthesizing three TADF ...emitters with donors at different positions of a benzonitrile acceptor. The position rendering a large overlap between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) enhances the quantum efficiency of the TADF emitter. Regarding the orbital overlap, donor attachments at 2‐ and 6‐positions of the benzonitrile were more beneficial than 3‐ and 5‐substitutions. Moreover, an additional attachment of a weak donor at the 4‐position further increased the quantum efficiency without decreasing the emission energy. Therefore, the molecular design strategy of substituting strong donors at the positions allowing a large molecular orbital overlap and an extra weak donor is a good approach to achieve both high quantum efficiency and a slightly increased emission energy.
Overlap to emit: The substitution of strong donors at the positions rendering a large HOMO–LUMO overlap and the addition of a weak donor constitute an effective design approach to realize TADF emitters having high efficiency.
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•A bicarbazole derived host material with a benzonitrile substituent showed bipolar charge transport properties.•A high external quantum efficiency above 20% was obtained in green ...thermally activated delayed fluorescent device.•Para substitution of CN was better than metal substitution for high efficiency.
A bicarbazole based donor–acceptor compound, 4,4′-(3,4′-bicarbazole-9,9′-diyl)dibenzonitrile (4CN34BCz), was synthesized as a host material for thermally activated delayed fluorescent emitter and the device performances of the green devices with the synthesized host and (4s,6s)-2,4,5,6-tetra(9H-carbazol-9-yl)isophthalonitrile (4CzIPN) delayed fluorescent emitter were investigated. 4CN34BCz with CN unit at para-position could effectively assist delayed fluorescent emission of 4CzIPN and achieved a high external quantum efficiency of 20.8% compared to 13.8% of the similar host with CN unit at meta-position because the orientation of the CN functional group at para position of the benzonitrile was favourable for charge balance in the emitting layer.
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► Host material with substituent at 4-position of carbazole. ► Correlation of substitution position with photophysical properties of hosts. ► Relationship between device performances ...and substitution position.
A synthetic method to synthesize 4-substituted carbazole derivative was developed to study the effect of substitution position of carbazole on photophysical properties and device performances of host materials. Two high triplet energy host materials with substituents at 2- and 4-positions of carbazole were synthesized by the new synthetic approach. Substitution of electron withdrawing group at 2-position was better than the substitution at 4-position to stabilize energy levels and to improve hole transport properties. However, high glass transition temperature and high quantum efficiency were obtained in the carbazole based host material with substituent at 4-position.
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