Search

Your search keyword '"Nakao, Kohei"' showing total 113 results
Start Over Author "Nakao, Kohei"
113 results on '"Nakao, Kohei"'

2. A water-soluble luminescent tris(2,4,6-trichlorophenyl)methyl radical-carbazole dyad.

Author

Anraku, Kosuke, Matsuda, Kenshiro, Miyata, Satoshi, Ishii, Hikaru, Hosokai, Takuya, Okada, Satoshi, Nakamura, Kazuhiro, Nakao, Kohei, and Albrecht, Ken

Abstract

Organic luminescent radicals are a new class of materials with potential applications not only in light-emitting devices but also in the biochemistry field. New tris(2,4,6-trichlorophenyl)methyl (TTM) radicals with alkoxy-substituted carbazole donors were synthesized and characterized. PEG-substituted carbazole-TTM was found to be water-soluble. The water-soluble TTM radical aqueous solution showed fluorescence at 777 nm and the ability to shorten the longitudinal relaxation time (T1) of water. The concept of water-soluble luminescent radicals is expected to be used to develop a potential fluorescence and MR dual-use imaging moiety. [ABSTRACT FROM AUTHOR]

Published
2024
Full Text
View/download PDF

8. Thermally activated delayed fluorescence carbazole‐triazine dendrimer with bulky substituents.

Author

Ikebe, Hiroki, Nakao, Kohei, Hisamura, Eri, Furukori, Minori, Nakayama, Yasuo, Hosokai, Takuya, Yang, Minlang, Liu, Guanting, Yasuda, Takuma, and Albrecht, Ken

Subjects
DELAYED fluorescence, CARBAZOLE, TRIAZINES
Abstract

Carbazole‐triazine dendrimers with a bulky terminal substituent were synthesized, and the thermally activated delayed fluorescence (TADF) property was investigated. Compared to unsubstituted carbazole dendrimers, dendrimers with bulky terminal substituents showed comparable to better photoluminescence quantum yields (PLQY) in neat films. Phenylfluorene (PF)‐substituted dendrimers showed the highest PLQY of 81%, a small ΔEst of 0.06 eV, and the fastest reverse intersystem crossing (RISC) rate of ∼1 × 105 s−1 compared to other dendrimers. Phosphorescence measurements of dendrimers and dendrons (fragments) indicate that the close proximity of the triplet energy of phenylfluorene‐substituted carbazole dendrons (3LE) to that of phenylfluorene‐substituted dendrimers (1CT, 3CT) contributes to RISC promotion and improves TADF efficiency. Terminal modification fine‐tunes the energy level and suppresses intermolecular interactions, and this study provides a guideline for designing efficient solution‐processable and non‐doped TADF materials. [ABSTRACT FROM AUTHOR]

Published
2024
Full Text
View/download PDF

12. Carbazole‐Dendronized Luminescent Radicals

Author

Xiaotian, Rui, primary, Ota, Wataru, additional, Sato, Tohru, additional, Furukori, Minori, additional, Nakayama, Yasuo, additional, Hosokai, Takuya, additional, Hisamura, Eri, additional, Nakamura, Kazuhiro, additional, Matsuda, Kenshiro, additional, Nakao, Kohei, additional, Monkman, Andrew, additional, and Albrecht, Ken, additional

Published
2023
Full Text
View/download PDF

13. Highly Luminescent Aluminum Complex with β-Diketone Ligands Exhibiting Near-Unity Photoluminescence Quantum Yield, Thermally Activated Delayed Fluorescence, and Rapid Radiative Decay Rate Properties in Solution-Processed Organic Light-Emitting Devices

Author

Matsuya, Misaki, primary, Sasabe, Hisahiro, additional, Sumikoshi, Shunsuke, additional, Hoshi, Keigo, additional, Nakao, Kohei, additional, Kumada, Kengo, additional, Sugiyama, Ryo, additional, Sato, Ryoma, additional, and Kido, Junji, additional

Published
2023
Full Text
View/download PDF

19. Highly Luminescent Aluminum Complex with ß-Diketone Ligands Exhibiting Near-Unity Photoluminescence Quantum Yield, Thermally Activated Delayed Fluorescence, and Rapid Radiative Decay Rate Properties in Solution-Processed Organic Light-Emitting Devices

Author

Matsuya, Misaki, Sasabe, Hisahiro, Sumikoshi, Shunsuke, Hoshi, Keigo, Nakao, Kohei, Kumada, Kengo, Sugiyama, Ryo, Sato, Ryoma, and Kido, Junji

Abstract

A highly luminescent mononuclear Al complex with ß-diketone ligands exhibiting superior thermally activated delayed fluorescence (TADF) properties was developed in this work. The complex showed yellow emission with promising photofunctions, including a near-unity photoluminescence quantum yield (PLQY), a rapid radiative decay rate, and a short delayed fluorescence lifetime in the solid state. When applied in a solution-processed organic light-emitting device, an external quantum efficiency (EQE) exceeding 18% and a low turn-on voltage of 2.9 V at 1 cd/m2were obtained, surpassing those of the corresponding ß-diketone ligand. Metal complexation with Al generated unique electronic structures that significantly strengthened the photofunctions of the original ß-diketone ligand in the solid state.Highly luminescent aluminum complexes with ß-diketone ligands exhibiting a near-unity photoluminescent quantum yield (PLQY) and delayed fluorescence properties were developed. The complexes showed significantly strengthened photofunctions, such as improved PLQY, short delayed lifetime, and rapid radiative decay, compared with those of the corresponding ligands.

Published
2023
Full Text
View/download PDF

42. Unique Solid-State Emission Behavior of Aromatic Difluoroboronated β-Diketones as an Emitter in Organic Light-Emitting Devices.

Author

Sasabe, Hisahiro, Sasaki, Kanako, Mamiya, Michitaka, Suwa, Yurie, Watanabe, Taiki, Onuma, Natsuki, Nakao, Kohei, Yamaji, Minoru, and Kido, Junji

Subjects
SOLID state electronics, KETONES, ORGANIC light emitting diodes, CARBAZOLE derivatives, DELAYED fluorescence
Abstract

Aromatic difluoroboronated β-diketone ( BF2DK) derivatives are a widely known class of luminescent organic materials that exhibit high photoluminescent quantum efficiency and unique aggregation-dependent fluorescence behavior. However, there have been only a few reports on their use in solid-state electronic devices, such as organic light-emitting devices (OLEDs). Herein, we investigated the solid-state properties and OLED performance of a series of π-extended BF2DK derivatives that have previously been shown to exhibit intense fluorescence in the solution state. The BF2DK derivatives formed exciplexes with a carbazole derivative and exhibited thermally activated delayed fluorescence (TADF) behavior to give orange electroluminescence with a peak external quantum efficiency of 10 % that apparently exceeds the theoretical efficiency limit of conventional fluorescent OLEDs (7.5 %), assuming a light out-coupling factor of 30 %. [ABSTRACT FROM AUTHOR]

Published
2017
Full Text
View/download PDF

44. Highly Luminescent π-Conjugated Terpyridine Derivatives Exhibiting Thermally Activated Delayed Fluorescence.

Author

Sasabe, Hisahiro, Hayasaka, Yuya, Komatsu, Ryutaro, Nakao, Kohei, and Kido, Junji

Subjects
DELAYED fluorescence, CHEMICAL derivatives, PHOSPHORS, ORGANIC light emitting diodes, QUANTUM efficiency, QUANTUM chemistry, OXIDATIVE coupling, METAL ions
Abstract

Typically, luminescent π-conjugated 2,2′:6′,2′′-terpyridine (tpy) derivatives are versatile components for tridentate metal ligands, supramolecular materials, two-photon absorption bioimaging probes, fluorescent ion sensors, and organic light-emitting devices. However, a limited number of luminescent tpy materials, other than metal complexes, have been reported. This study introduces a series of π-conjugated tpy derivatives that exhibit strong thermally activated delayed fluorescence (TADF). We have observed that a blue tpy emitter outperforms conventional fluorescent emitters. Additionally, a green tpy emitter has exhibited a performance that is almost comparable to that of its green phosphorescent counterparts, realizing an external quantum efficiency close to 25 % and a power efficiency exceeding 80 lm W−1 with an exceptionally low efficiency roll-off. This study demonstrates the first example of highly luminescent tpy-based TADF emitters. [ABSTRACT FROM AUTHOR]

Published
2017
Full Text
View/download PDF

47. Magnetic Properties of Ru-rich RuFeCr Z ( Z=Si, Ge).

Author

Hiroi, Masahiko, Nakashima, Shingo, Nakao, Kohei, Rokkaku, Tsugumi, Ito, Masakazu, Shigeta, Iduru, Manaka, Hirotaka, and Terada, Norio

Subjects
MAGNETIC properties, MAGNETIC susceptibility, TEMPERATURE measurements, MAGNETIZATION, SPIN glasses
Abstract

The properties of Heusler compounds RuFeCrGe are investigated and compared with those of RuFeCrSi. RuCrGe is confirmed to exhibit an antiferromagnetic transition with Neél temperature 13 K by magnetic susceptibility and specific heat measurements. When Fe is substituted for Ru, a peak in the magnetic susceptibility is observed, and in the lower temperature region irreversibility between temperature dependences of magnetization for zero-field-cooling and field-cooling conditions is found. Nevertheless, in specific heat of RuFeCrGe, there is no anomaly to indicate phase transition. The specific heat is almost identical to that for RuFeCrSi. The above results demonstrate that the magnetic states in the low temperature region of Fe-substituted samples are spin-glass-like states. Slight substitution of Fe for Ru destroys the long-range-order and lead to peculiar spin-glass-like states. [ABSTRACT FROM AUTHOR]

Published
2011
Full Text
View/download PDF

48. Light-Blue Thermally Activated Delayed Fluorescent Emitters Realizing a High External Quantum Efficiency of 25%.

Author

Komatsu, Ryutaro, Sasabe, Hisahiro, Seino, Yuki, Nakao, Kohei, and Kido, Junji

Subjects
QUANTUM efficiency, FLUORESCENCE, ORGANIC light emitting diodes
Abstract

Thermally activated delayed fluorescent (TADF) emitters are one of the most promising candidates for low-cost and high efficiency organic light-emitting devices (OLEDs) to realize 100% of internal quantum efficiency. In this paper, we developed a series of TADF emitters, 2-functionalized-4,6-bis[4-(9,9-dimethyl-9,10-dihydroacridine)phenyl]pyrimidine called Ac-RPM. The optimized device realized a extremely high efficiency of 62 lm W-1, a high external quantum efficiency of 25%, light-blue emissions with the Commission Internationale de l'Eclairage chromaticity coordinates of (0.19, 0.37) and a low turn-on voltage of <3.0 V. [ABSTRACT FROM AUTHOR]

Published
2016
Full Text
View/download PDF

49. Inside Back Cover: Highly Luminescent π-Conjugated Terpyridine Derivatives Exhibiting Thermally Activated Delayed Fluorescence (Chem. Eur. J. 1/2017).

Author

Sasabe, Hisahiro, Hayasaka, Yuya, Komatsu, Ryutaro, Nakao, Kohei, and Kido, Junji

Subjects
CHEMISTRY periodicals, LUMINESCENCE, FLUORESCENCE
Abstract

A series of terpyridine/acridine conjugates exhibits strong blue‐to‐green emission and thermally activated delayed fluorescence (TADF) character in the solid state. An organic light‐emitting device with a green emissive terpyridine/acridine conjugate showed an external quantum efficiency of approximately 25%, a power efficiency of over 80 lm W−1, and an exceptionally low‐efficiency roll‐off. More information can be found in the Full Paper by H. Sasabe and J. Kido et al. on page 114 ff. [ABSTRACT FROM AUTHOR]

Published
2017
Full Text
View/download PDF

Catalog

Books, media, physical & digital resources
See catalog results