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494 results on '"Hatakeyama, Takuji"'

8. Effect of Multiple Acceptor Structures in Electron Transport Materials on Operational Lifetime of Blue Thermally Activated Delayed Fluorescence Organic Light‐Emitting Diodes.

Author

Kiriyama, Shione, Mamada, Masashi, Goushi, Kenichi, Madushani, Bhagya, Hatakeyama, Takuji, and Adachi, Chihaya

Subjects
DELAYED fluorescence, ELECTRON transport, MOLECULAR structure, CHARGE carriers, ORGANIC light emitting diodes, DIODES
Abstract

Recent advances in organic light‐emitting diodes (OLEDs) based on thermally activated delayed fluorescence (TADF)‐assisted fluorescence (TAF) attest to the great promise of this technology in practical use. However, the simultaneous realization of high efficiency and device durability in blue OLEDs remains a significant challenge. Clarification of the degradation mechanisms correlated to molecular structure and device configuration is the key to extending the device lifetime. In this study, electron transport materials incorporating two triazine units in close proximity are adopted to use in hole‐blocking and electron‐transporting layers, resulting in superior device performances. In addition, a modified photodegradation experiment reveals that the degradation origins closely relate to charge carriers. The optimization of the device according to the obtained findings leads to 4.5 times extension in the lifetime of the TAF‐OLED using a multiple resonance emitter. These results also provide guidelines for designing robust electron transport materials for blue OLEDs. [ABSTRACT FROM AUTHOR]

Published
2024
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18. A Rigid Multiple Resonance Thermally Activated Delayed Fluorescence Core Toward Stable Electroluminescence and Lasing.

Author

Tang, Xun, Xie, Mingchen, Lin, Zesen, Mitrofanov, Kirill, Tsagaantsooj, Tuul, Lee, Yi‐Ting, Kabe, Ryota, Sandanayaka, Atula S. D., Matsushima, Toshinori, Hatakeyama, Takuji, and Adachi, Chihaya

Subjects
DELAYED fluorescence, ELECTROLUMINESCENCE, LIGHT emitting diodes, STIMULATED emission, RESONANCE, MOLECULAR conformation, OPTICAL pumping
Abstract

The investigation of organic light‐emitting diodes (OLEDs) and organic laser devices with thermally activated delayed fluorescence (TADF) molecules is emerging due to the potential of harnessing triplets. In this work, a boron/nitrogen multiple‐resonance TADF polycyclic framework fusing carbazole units (CzBNPh) was proposed. CzBNPh exhibited a narrowband emission (<30 nm), a unity photoluminescence quantum yield, and a fast radiative rate. Consequently, CzBNPh demonstrated a low distributed feedback (DFB) lasing threshold of 0.68 μJ cm−2. Furthermore, the stimulated emission zone of CzBNPh was effectively separated from its singlet and triplet absorption, thereby minimizing the singlet‐triplet annihilation under long‐pulsed excitation ranging from 20 μs to 2.5 ms. Significantly, the enhanced rigid molecular conformation, thermal stability, and photo‐stability resulted in improved lasing and electroluminescence stability compared to that of 5,9‐diphenyl‐5,9‐diaza‐13b‐boranaphtho[3,2,1‐de]anthracene (DABNA)‐core. These findings indicate the potential of CzBN‐core as a promising framework for achieving long‐pulsed wave and electrically‐pumped lasing in the future. [ABSTRACT FROM AUTHOR]

Published
2024
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20. Ultra‐Narrowband Blue Multi‐Resonance Thermally Activated Delayed Fluorescence Materials

Author

Oda, Susumu, Kawakami, Bungo, Horiuchi, Masaru, Yamasaki, Yuki, Kawasumi, Ryosuke, Hatakeyama, Takuji, Oda, Susumu, Kawakami, Bungo, Horiuchi, Masaru, Yamasaki, Yuki, Kawasumi, Ryosuke, and Hatakeyama, Takuji

Abstract

Ultra-narrowband blue multi-resonance-induced thermally activated delayed fluorescence (MR-TADF) materials (V-DABNA and V-DABNA-F), consisting of three DABNA subunits possessing phenyl or 2, 6-difluorophenyl substituents on the peripheral nitrogen atoms are synthesized by one-shot triple borylation. Benefiting from the inductive effect of fluorine atoms, the emission maximum of V-DABNA-F (464 nm) is blueshifted from that of the parent V-DABNA (481 nm), while maintaining a small full width at half maximum (FWHM, 16 nm) and a high rate constant for reverse intersystem crossing (6.5 × 10⁵ s⁻¹). The organic light-emitting diodes (OLEDs) using V-DABNA and V-DABNA-F as emitters are fabricated by vapor deposition and exhibit blue emission at 483 and 468 nm with small FWHMs of 17 and 15 nm, corresponding to Commission Internationale d’Éclairage coordinates of (0.09, 0.27) and (0.12, 0.10), respectively. Both devices achieve high external quantum efficiencies of 26.2% and 26.6% at the maximum with minimum efficiency roll-offs of 0.9% and 3.2%, respectively, even at 1000 cd m⁻², which are record-setting values for blue MR-TADF OLEDs.

Published
2023

35. Synthesis and Late‐Stage Diversification of BN‐Embedded Dibenzocorannulenes as Efficient Fluorescence Organic Light‐Emitting Diode Emitters.

Author

Okada, Naoya, Nakatsuka, Soichiro, Kawasumi, Ryosuke, Gotoh, Hajime, Yasuda, Nobuhiro, and Hatakeyama, Takuji

Subjects
LIGHT emitting diodes, ORGANIC light emitting diodes, DELAYED fluorescence, FLUORESCENCE, QUANTUM efficiency, BORYLATION, POLYCYCLIC aromatic hydrocarbons
Abstract

We report the synthesis and late‐stage diversification of a new class of hetero‐buckybowl, BN‐embedded dibenzocorannulenes (B2N2‐DBCs). The synthesis is achieved via one‐shot halogenative borylation, comprising the nitrogen‐directed haloboration of alkyne and an intramolecular bora‐Friedel‐Crafts reaction, which provides BN‐embedded dibenzocorannulene possessing two bromo substituents (B2N2‐DBC‐Br). B2N2‐DBC‐Br undergoes diversification via coupling reactions to provide a variety of arylated derivatives (B2N2‐DBC‐R), exhibiting strong blue fluorescence. An organic light‐emitting diode (OLED) employing one of the derivatives as an emitter exhibited a high external quantum efficiency of 6.6 % and long operational lifetime of 907 h at an initial luminance of 1000 cd m−2, indicating the significant potential for the development of efficient and stable hetero‐buckybowl‐based OLED materials. [ABSTRACT FROM AUTHOR]

Published
2023
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40. Indium-catalyzed 2-alkenylation of 1,3-dicarbonyl compounds with unactivated alkynes

Author

Endo, Kohei, Hatakeyama, Takuji, Nakamura, Masaharu, and Nakamura, Eiichi

Subjects
Indium -- Chemical properties, Carbonyl compounds -- Chemical properties, Acetylene -- Chemical properties, Chemistry
Abstract

An indium catalyzed addition of a 1,3-dicarbonyl compound to a terminal alkyne has provided an efficient synthetic route to 2-alkenyl-1,3-dicarbonyl compounds. The results have suggested that the reaction proceeds via a concerted carbometalation reaction of an indium(III) enolate with the acetylene, where indium-acetylene interaction is important.

Published
2007

48. Multiple Resonance Effect-Based Narrowband TADF Emitters

Author

Hatakeyama, Takuji, primary, Kondo, Yasuihiro, additional, Yoshiura, Kazuki, additional, Kitera, Sayuri, additional, Nishi, Hiroki, additional, Oda, Susumu, additional, Gotoh, Hajime, additional, Sasada, Yasuyuki, additional, and Yanai, Motoki, additional

Published
2020
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