Organic light emitting diodes with horizontally oriented thermally activated delayed fluorescence emitters

Kim, D. H.; Inada, Ko; Zhao, Li; Komino, Takeshi; Matsumoto, Naoki; Ribierre, Jean Charles; Adachi, Chihaya

doi:10.1039/c6tc04786f

Cited by 55 publications

(44 citation statements)

References 58 publications

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“…Nearly perfect horizontal orientation can also be achieved through expanding the planarity of the molecular structures. Another TADF emitter, BDQC‐2, was found to exhibit a nearly perfect horizontal orientation in the bis[2‐(diphenylphosphino)phenyl]ether oxide (DPEPO) host due to stronger intermolecular interactions between the guest and host than that in TADF neat films . And since the S0–S4 and S0–S5 transitions is associated with the transition dipoles in the V‐shaped BDQC‐2, BDQC‐2 in neat films tend to be parallel to the substrate plane with the arm of V‐shaped molecule.…”

Section: Tadf Molecular Design Towards Efficient Oleds With Superior mentioning

confidence: 99%

“…Another TADF emitter,B DQC-2, was found to exhibit an early perfect horizontalo rientation in the bis [2-(diphenylphosphino)phenyl]ether oxide (DPEPO) host due to stronger intermolecular interactions between the guest and host than that in TADF neat films. [73] And since the S0-S4 and S0-S5 transitions is associated with the transition dipoles in the V-shaped BDQC-2, BDQC-2 in neat films tend to be parallel to the substrate plane with the arm of V-shaped molecule. As ac onsequence, the doped OLEDsw ith BDQC-2 achieved the EQE max of 15.4 %, about 1.75 times more than the theoretical predictione valuated from the emitting dipole distribution.…”

Section: Tadf Molecules With High Horizontal Dipole Ratiomentioning

confidence: 99%

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Thermally Activated Delayed Fluorescence Materials: Towards Realization of High Efficiency through Strategic Small Molecular Design

Liang

Zheng

2019

Chemistry A European J

195

123

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Thermally activated delayed fluorescence (TADF) is one of the most intriguing and promising discoveries towards realization of highly‐efficient organic light emitting diodes (OLED) utilizing small molecules as emitters. It has the capability of manifesting all excitons generated during the electroluminescent processes, consequently achieving 100 % of internal quantum efficiency. Since the report of the first efficient OLED based on a TADF small molecule in 2012 by Adachi et al., the quest for optimal TADF materials for OLED application has never stopped. Various TADF molecules bearing different design concepts and strategies have been designed and produced, with the aim to boost the overall performances of corresponding OLEDs. In this minireview, the general principles of TADF molecular design based on three basic categories of TADF species: twisted intramolecular charge transfer (TICT), through‐space charge transfer (TSCT) and multi‐resonance induced TADF (MR‐TADF) are discussed in detail. Several key aspects with respect to each category, as well as some effective methods to enhance the efficiency of TADF materials and corresponding OLEDs from the molecular engineering perspectives, are summarized and discussed to exhibit a general landscape of TADF molecular design to a wide variety of scientific researchers within this particular disciplinary area.

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Section: Tadf Molecular Design Towards Efficient Oleds With Superior mentioning

confidence: 99%

Section: Tadf Molecules With High Horizontal Dipole Ratiomentioning

confidence: 99%

Thermally Activated Delayed Fluorescence Materials: Towards Realization of High Efficiency through Strategic Small Molecular Design

Liang

Zheng

2019

Chemistry A European J

195

123

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“…These groups narrow the singlet‐triplet energy gap (Δ E ST ) and thus lead to enhanced efficiency in green and blue TADF emitters. The donors have also shown a tendency for their molecular transition dipole moments to preferentially align in the in‐plane (horizontal) direction relative to the substrate . For example, 2,4‐bis{3‐(9 H ‐carbazol‐9‐yl)‐9 H ‐carbazol‐9‐yl}‐6‐phenyl‐1,3,5‐triazine (CC2TA) which features the carbazolylcarbazole donor shows a preferred horizontal dipole orientation in vacuum‐deposited CC2TA:DPEPO (bis[2‐(diphenylphosphino)phenyl] ether oxide) films .…”

Section: Introductionmentioning

confidence: 99%

Nearly 100% Horizontal Dipole Orientation and Upconversion Efficiency in Blue Thermally Activated Delayed Fluorescent Emitters

Byeon

Kim

Lee

et al. 2018

Advanced Optical Materials

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strong donor. [12][13][14][15] These groups narrow the singlet-triplet energy gap (ΔE ST ) and thus lead to enhanced efficiency in green and blue TADF emitters. The donors have also shown a tendency for their molecular transition dipole moments to preferentially align in the in-plane (horizontal) direction relative to the substrate. [16][17][18] For example, 2,4-bis{3-(9H-carbazol-9-yl)-9H-carbazol-9-yl}-6-phenyl-1,3,5triazine (CC2TA) which features the carbazolylcarbazole donor shows a preferred horizontal dipole orientation in vacuum-deposited CC2TA:DPEPO (bis[2-(diphenylphosphino)phenyl] ether oxide) films. [16,19] Also, dimethylacridine-derived 10-(4-(4,6-diphenyl-1,3,5-triazin-2-yl)phenyl)-9,9-dimethyl-9,10-dihydroacridine (DMAC-TRZ) has also shown horizontal alignment. [20] However, correlations between the molecular structure and the dipole orientation was not established. [21][22][23] Furthermore, the CC2TA emitter showed low external quantum efficiency (EQE) despite its horizontal dipole orientation. [16] Carbazole, biscarbazole, and triscarbazole were adopted as donor units in TADF emitters to study effects of the donor on dipole orientation. We demonstrate that carbazole cannot induce dipole orientation of the TADF emitters, whereas biscarbazole and triscarbazole can. The EQE of OLEDs employing rod-like triscarbazole donor-derived emitters achieve EQE > 30% due to their near-perfect in-plane orientation. The strong donor character of the triscarbazole results in a uniform distribution of the electron density in the highest occupied molecular orbital, and hence a high photoluminescence (PL) quantum yield. Furthermore, the donor structure leads to a relatively short delayed fluorescence lifetime leading to efficient conversion of triplet to singlet excitons. To our knowledge, this work presents the first demonstration of the simultaneous achievement of nearly 100% horizontal dipole orientation and 100% exciton conversion efficiency in TADF-based OLEDs. Results and DiscussionThree carbazole-based compounds studied were: 9-(4-(4,6-diphenyl-1,3,5-triazin-2-yl)phenyl)-9H-carbazole (CzTrz), 9-(4-(4,6-diphenyl-1,3,5-triazin-2-yl) phenyl)-9′-phenyl-9H,9′H-3,3′-bicarbazole (BCzTrz), andThe relationship between anisotropic orientation and molecular structure of thermally activated delayed fluorescent (TADF)-based organic light emitting devices (OLEDs) is studied using TADF emitters with carbazole, biscarbazole, and triscarbazole donor units. The bicarbazole and triscarbazole donors are more effective than the carbazole donor in driving the anisotropic orientation of the TADF molecules. A near-perfect in-plane orientation of the TADF dipole moment is demonstrated using the triscarbazole donor. In addition, the triscarbazole donor based OLED shows high photoluminescence quantum yield and an upconversion efficiency close to 100%. As a consequence, an external quantum efficiency >30% is obtained.

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“…Other ways for tuning the properties of 2,3‐diarylquinoxalines are synthesis of aza‐analogs (pyridopyrazine derivatives) and incorporation of fluorene, phenoxazine or disubstituted carbazole residues into position 6 of quinoxaline scaffold. The derivatives of the latter type with different degrees of planarity exhibit thermally activated delayed fluorescence …”

Section: Introductionmentioning

confidence: 99%

Synthesis and Photophysical Studies of Novel V‐Shaped 2,3‐Bis{5‐aryl‐2‐thienyl}(dibenzo[f,h])quinoxalines

et al. 2020

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A series of novel V‐shaped luminophores containing electron‐withdrawing dibenzo[f,h]quinoxaline core and arylthienyl donor fragments at positions 2 and 3 has been synthesized. The absorption spectra (UV/vis) were recorded in several solvents, whereas emission spectra were recorded in solutions and powders. The solvatochromism as well as halochromism of obtained compounds was also explored. Electronic‐structure calculations using quantum‐chemistry methods were performed to further analyse experimental results. All characteristics were compared with that of 2,3‐bis(arylthienyl)quinoxaline counterparts. The halochromic effect studies showed that upon gradual addition of trifluoroacetic acid (TFA) to the toluene solution of diethylaminophenyl‐substituted dibenzo[f,h]quinoxaline chromophore, absorption and emission changed. Observed band shifts were more distinct in the case of mentioned quinoxaline than for other derivatives. All of the (dibenzo[f,h])quinoxaline chromophores exhibited good sensitivity toward nitro‐containing explosives with high Stern‐Volmer constants up to 57800 M−1, these results are remarkable for such heterocyclic systems.

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Organic light emitting diodes with horizontally oriented thermally activated delayed fluorescence emitters

Abstract: Horizontal orientation of the emission transition dipole of TADF molecules plays a critical role on the light outcoupling efficiency and the performance of TADF organic light-emitting diodes.

Cited by 55 publications

References 58 publications

Thermally Activated Delayed Fluorescence Materials: Towards Realization of High Efficiency through Strategic Small Molecular Design

Thermally Activated Delayed Fluorescence Materials: Towards Realization of High Efficiency through Strategic Small Molecular Design

Nearly 100% Horizontal Dipole Orientation and Upconversion Efficiency in Blue Thermally Activated Delayed Fluorescent Emitters

Synthesis and Photophysical Studies of Novel V‐Shaped 2,3‐Bis{5‐aryl‐2‐thienyl}(dibenzo[f,h])quinoxalines

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