| 1. |
- Deksnys, T., et al.
(författare)
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Synthesis and characterisation of a carbazole-based bipolar exciplex-forming compound for efficient and color-tunable OLEDs
- 2017
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Ingår i: New Journal of Chemistry. - : RSC Publishing. - 1144-0546 .- 1369-9261. ; 41:2, s. 559-568
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Tidskriftsartikel (refereegranskat)abstract
- A new ambipolar fluorophore, 3,6-di(4,4′-dimethoxydiphenylaminyl)-9-(1-naphthyl)carbazole, was synthesized and its physical properties were studied by differential scanning calorimetry, thermogravimetric analysis, UV-vis absorption, luminescence and photoelectron emission spectroscopy, cyclic voltammetry and a time of flight method. The latter technique indicates that the compound demonstrates bipolar semiconducting properties. Using the synthesized compound as an emissive material, a single-layer OLED with an electroluminescence spectrum containing a voltage-dependent electroplex emission band in the region of 550-650 nm was fabricated. Another OLED was fabricated with an additional electron transporting bathophenanthroline layer that forms a direct interface with the layer of 3,6-di(4,4′-dimethoxydiphenylaminyl)-9-(1-naphthyl)carbazole. A strong exciplex-type band in the electroluminescence spectrum of this OLED with an emission maximum at ca. 540 nm was observed. The electroluminescence spectra of both devices were found to be clearly dependent on the applied bias. This effect can be useful for the development of efficient and colour-tunable OLEDs.
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| 2. |
- Gudeika, D., et al.
(författare)
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Flexible diphenylsulfone versus rigid dibenzothiophene-dioxide as acceptor moieties in donor-acceptor-donor TADF emitters for highly efficient OLEDs
- 2020
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Ingår i: Organic electronics. - : Elsevier. - 1566-1199 .- 1878-5530. ; 83
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Tidskriftsartikel (refereegranskat)abstract
- Flexible versus rigid molecular structures of donor-acceptor-donor type compounds are investigated with respect to efficiency of thermally activated delayed fluorescence (TADF) by theoretical and experimental approaches. Three highly efficient TADF emitters based on flexible diphenylsulfone and rigid dibenzothiophene-dioxide as acceptor units and di-tert-butyldimethyldihydroacridine as donor moiety were designed and synthesized. Despite they showed similar singlet-triplet splitting (0.01–0.02 eV) and high photoluminescence quantum yields in appropriate hosts, maximum external quantum efficiencies as different as 24.1 and 15.9/19.4% were obtained for organic light emitting devices based on these emitters with, respectively, flexible and rigid molecular structures. The high efficiency of the light-emitting compounds with the flexible molecular structure could be traced to the bi-configurational nature of the lowest singlet and triplet states resulting in higher spin-orbit coupling than for molecules with rigid structures. All derivatives showed bipolar charge transport character. High device efficiency with electron mobility of 3 × 10−5 cm2V−1s−1 and hole mobility of 1.3 × 10−4 cm2V−1s−1 at the electric field of 5 × 105 Vcm−1 was recorded for the layer of para-disubstituted diphenylsulfone with flexible molecular structure. This TADF emitter showed an excellent performance in the organic light emitting device, exhibiting a maximum current efficiency, power efficiency, and external quantum efficiency of 61.1 cdA-1, 64.0 lmW−1, and 24.1%, respectively.
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| 3. |
- Baryshnikov, Gleb V., et al.
(författare)
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Nine-ring angular fused biscarbazoloanthracene displaying a solid state based excimer emission suitable for OLED application
- 2016
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Ingår i: Journal of Materials Chemistry C. - : Royal Society of Chemistry (RSC). - 2050-7526 .- 2050-7534. ; 4:24, s. 5795-5805
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Tidskriftsartikel (refereegranskat)abstract
- A new biscarbazoloanthracene consisting of nine fused aromatic rings, including two pyrrole units, has been obtained in a straightforward and convergent synthesis. Computational chemistry and conformational analysis revealed that the semiconductor's molecule is not planar, the two carbazole moieties being helical twisted from the plane of the anthracene unit. Photophysical and electrochemical measurements showed that this angular fused heteroacene has a low lying HOMO energy level with a wide band gap despite its extended pi-conjugated molecular framework. Based on its relatively low-lying HOMO level, the semiconductor promises a high environmental stability in comparison to other related linear fused acenes and heteroacenes. The biscarbazoloanthracene has been applied as the light emitting layer in a white light emitting diode (WOLED). It is proposed that the white OLED feature is due to dual light emission properties from the active semiconductor layer being based on both the molecular luminescence of the small molecule and a discrete excimer emission made possible by suitable aggregates in the solid state. Noteworthy, this is the first reported example of such a behavior observed in a small molecule heteroacene rather than an oligomer or a polymer.
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| 4. |
- Ivaniuk, K. B., et al.
(författare)
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New WOLEDs based on pi-extended azatrioxa[8]circulenes
- 2017
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Ingår i: Journal of Materials Chemistry C. - : Royal Society of Chemistry. - 2050-7526 .- 2050-7534. ; 5:17, s. 4123-4128
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Tidskriftsartikel (refereegranskat)abstract
- New stable WOLEDs based on pi-extended azatrioxa[8]circulenes have been fabricated. Combining the own blue emission of the azatrioxa[8] circulenes with the yellow-green emission of the "m-MTDATA:azatrioxa[8]circulene'' exciplex a broad visible region, from 400 to 700 nm, is covered. The so constructed WOLEDs exhibit a luminance exceeding 23 700 cd m(-2) and an external quantum efficiency reaching 3%.
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| 5. |
- Ivaniuk, K., et al.
(författare)
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BaZrO3 perovskite nanoparticles as emissive material for organic/inorganic hybrid light-emitting diodes
- 2017
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Ingår i: Dyes and pigments. - : Elsevier. - 0143-7208 .- 1873-3743. ; 145, s. 399-403
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Tidskriftsartikel (refereegranskat)abstract
- In the present work we have demonstrated double-channel emission from organic exciplexes coupled to inorganic nanoparticles. The process is demonstrated by yellow-green emission in light-emitting diodes based on organic exciplexes hybridized with perovskite-type dispersed BaZrO3 nanoparticles. Such double-channel emission provides a broadening of the electroluminescence spectrum and a resultant yellow-green emission color of the device. We have realized an energy transfer from the exciplexes arranged by the interface between two organic layers and the spherical-shaped BaZrO3 nanoparticles randomly deposited on the organic interface constructed of the tris(4-carbazoyl-9-ylphenyl)amine and 4,7-diphenyl-1,10-phenanthroline molecules. The fabricated device exhibits a current efficiency value of 3.88 C d/A, maximum brightness of 3465 cd/m2 (at 15 V), and external quantum efficiency of about 1.26%. In order to estimate the efficiency of the energy transfer from the exciplex to the BaZrO3 nanoparticles we have applied the Förster model for the dipole-dipole energy transfer accounting for the mutual overlap of the exciplex emission spectrum and the absorption spectrum of the BaZrO3 nanoparticles.
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| 6. |
- Ivaniuk, Khrystyna, et al.
(författare)
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Highly Luminous Sky-Blue Organic Light-Emitting Diodes Based on the Bis[(1,2)(5,6)]indoloanthracene Emissive Layer
- 2016
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Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 120:11, s. 6206-6217
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Tidskriftsartikel (refereegranskat)abstract
- An in-depth analysis of the electro-optical and light-emissive properties was carried out with a new fused heteroacene, the bis[(1,2)(5,6)]indoloanthracene. The compound was synthesized in a straightforward bidirectional manner from 1,4-dibromo-2,5-diodobenzene utilizing a reaction cascade of isomerization and cyclization sequences. Bis[(1,2)(5,6)]indoloanthracene exhibits bright luminescence with high quantum yield in solution as well as in the solid state. By using this novel semiconductor as active layer, an efficient organic light-emitting diode (OLED) has been fabricated for which its emission pattern resembles at least two emitters in a single emissive region originated from the same molecule. One has its origin from the single molecule and is similar to the luminescence spectra in solution, whereas the other functions through the formation of aggregates being similar to the emission pattern found with crystals of bis[(1,2)(5,6)]-indoloanthracene. As a result, bright sky-blue OLEDs with very high luminance exceeding 10 000 cd/m(2) were obtained. Such color pattern and performance have not previously been observed with low molecular weight, electron-rich fused polycyclic aromatic compounds and indicate a promising new class of materials for development.
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