| Nakanotani Hajime | Last modified date：2024.04.19 |
Associate Professor /
Department of Applied Chemistry /
Faculty of Engineering
Papers
| 1. | Kohata, Shintaro; Nakanotani, Hajime; Adachi, Chihaya, Modulation of Intersystem Crossing Rate Induced by Singlet-triplet Energy Level Alignment in 1,2,3,5-Tetrakis(carbazol-9-yl)-4,6-dicyanobenzene Single Crystals, CHEMISTRY LETTERS, 10.1246/cl.220304, 51, 10, 989-992, 2022.10. |
| 2. | Thanh Ba Nguyen, Hajime Nakanotani, Chihaya Adachi, An Overlooked Charge-Transfer Interaction in the Interfacial Triplet-Triplet Upconversion Process in Blue Organic Light-Emitting Diodes, ADVANCED OPTICAL MATERIALS, 10.1002/adom.202200704, 10, 18, 2022.09. |
| 3. | Masaki Tanaka, Morgan Auffray, Hajime Nakanotani & Chihaya Adachi , Spontaneous formation of metastable orientation with well-organized permanent dipole moment in organic glassy films, NATURE MATERIALS, 10.1038/s41563-022-01265-7, 21, 7, 819-+, 2022.07, The performance of organic optoelectronic and energy-harvesting devices is largely determined by the molecular orientation and resultant permanent dipole moment, yet this property is difficult to control during film preparation. Here, we demonstrate the active control of dipole direction—that is, vector direction and magnitude—in organic glassy films by physical vapour depo- sition. An organic glassy film with metastable permanent dipole moment orientation can be obtained by utilizing the small surface free energy of a trifluoromethyl unit and intramolecular permanent dipole moment induced by functional groups. The proposed molecular design rule could pave a way toward the formation of spontaneously polarized organic glassy films, leading to improvement in the performance of organic molecular devices.. |
| 4. | Yuuhi Ueda, Hajime Nakanotani, Takuya Hosokai, Yuya Tanaka, Hokuto Hamada, Hisao Ishii, Shuhei Santo, Chihaya Adachi, Role of Spontaneous Orientational Polarization in Organic Donor–Acceptor Blends for Exciton Binding, Advanced Optical Materials, 10.1002/adom.202000896, 8, 2020.10, Electron–hole pairs at the interface between electron-donating and electron-accepting molecules form charge-transfer excitons (CTEs) via Coulomb attraction. Generally, the attraction energy of the CTE is weaker than that of the Frenkel exciton because of spatial separation of the charge pair; thus, the binding of the CTE is expected to be sensitive to an electric field. Here, the shielding of the binding energy of the CTEs by an internal electric field induced by spontaneous orientation polarization (SOP) of the solid-state donor–acceptor blend film is reported. When the blend film forms a large SOP, the photogenerated CTEs spontaneously dissociate without an external electric field, resulting in carrier diffusion and carrier lifetimes that are in the milliseconds or longer. In the absence of a large SOP, the CTEs preferentially form exciplexes that quickly release their energy as light rather than dissociation. Hence, the control of SOP in the donor–acceptor blend films can provide new insights into exciton binding and facilitate the development of tailored high-performance organic semiconductor devices.. |
| 5. | Youichi Tsuchiya, Keita Tsuji, Ko Inada, Fatima Bencheikh, Yan Geng, H. Shaun Kwak, Thomas J.L. Mustard, Mathew D. Halls, Hajime Nakanotani, Chihaya Adachi, Molecular Design Based on Donor-Weak Donor Scaffold for Blue Thermally-Activated Delayed Fluorescence Designed by Combinatorial DFT Calculations, Frontiers in Chemistry, 10.3389/fchem.2020.00403, 8, 2020.05, Quantum chemical calculations are necessary to develop advanced emitter materials showing thermally-activated delayed fluorescence (TADF) for organic light-emitting diodes (OLEDs). However, calculation costs become problematic when more accurate functionals were used, therefore it is judicious to use a multimethod approach for efficiency. Here we employed combinatorial chemistry in silico to develop the deep blue TADF materials with a new concept of homo-junction design. The homo-junction materials containing TADF candidates designed by calculation were synthesized and analyzed. We found that these materials showed the emission from charge transfer (CT) state, and the clear delayed emission was provided in solid state. Because the homo-junction TADF materials showed three exponential decayed emission in solid state, we employed novel four-state kinetic analysis.. |
| 6. | Ru Feng, Narumi Sato, Mayuka Nomura, Akinori Saeki, Hajime Nakanotani, Chihaya Adachi, Takuma Yasuda, Hiroyuki Furuta, Soji Shimizu, Near-infrared absorbing pyrrolopyrrole aza-BODIPY-based donor-acceptor polymers with reasonable photoresponse, Journal of Materials Chemistry C, 10.1039/d0tc01487g, 8, 26, 8770-8776, 2020.07, Designing near-infrared (NIR) absorbing donor-acceptor (D-A) polymers with photoresponse beyond 900 nm has remained a challenge in the area of organic photovoltaics (OPV) owing to the limited kinds of strong electron acceptors. Here we present the use of pyrrolopyrrole aza-BODIPY (PPAB) as a new acceptor group in D-A polymers in place of a conventional diketopyrrolopyrrole acceptor to achieve power conversion efficiencies up to 2.27% despite the ultra-small bandgap of 1.08 eV. The small photon energy loss of the PPAB-based D-A polymer and moderately high short-circuit current of 8.52 mA cm-2 arising from the panchromatic visible/NIR absorption guarantee PPAB as a potential building block of D-A polymers for NIR photovoltaics. This journal is. |
| 7. | Lin Song Cui, Alexander J. Gillett, Shou Feng Zhang, Hao Ye, Yuan Liu, Xian Kai Chen, Ze Sen Lin, Emrys W. Evans, William K. Myers, Tanya K. Ronson, Hajime Nakanotani, Sebastian Reineke, Jean Luc Bredas, Chihaya Adachi, Richard H. Friend, Fast spin-flip enables efficient and stable organic electroluminescence from charge-transfer states, Nature Photonics, 10.1038/s41566-020-0668-z, 14, 10, 636-642, 2020.10. |
| 8. | Jong Uk Kim, In Seob Park, Chin Yiu Chan, Masaki Tanaka, Youichi Tsuchiya, Hajime Nakanotani, Chihaya Adachi, Nanosecond-time-scale delayed fluorescence molecule for deep-blue OLEDs with small efficiency rolloff, Nature communications, 10.1038/s41467-020-15558-5, 11, 1, 2020.04. |
| 9. | M. Tanaka, R. Nagata, H. Nakanotani, C. Adachi, Understanding degradation of organic light-emitting diodes from magnetic field effects, communications materials, https://doi.org/10.1038/s43246-020-0019-0, 1, 2020.04, [URL]. |
| 10. | Thanh Ba Nguyen, Hajime Nakanotani, Takuji Hatakeyama, Chihaya Adachi, The Role of Reverse Intersystem Crossing Using a TADF-Type Acceptor Molecule on the Device Stability of Exciplex-Based Organic Light-Emitting Diodes, Advanced Materials, 10.1002/adma.201906614, 32, 9, 2020.01, Exciplex system exhibiting thermally activated delayed fluorescence (TADF) holds a considerable potential to improve organic light‐emitting diode (OLED) performances. However, the operational lifetime of current exciplex‐based devices, unfortunately, falls far behind the requirement for commercialization. Herein, rationally choosing a TADF‐type electron acceptor molecule is reported as a new strategy to enhance OLEDs' operating lifetime. A comprehensive study of the exciplex system containing 9,9′,9′′‐triphenyl‐9H,9′H,9′′H‐3,3′:6′,3′′‐tercarbazole (Tris‐PCz) and triazine (TRZ) derivatives clarifies the relationship between unwanted carrier recombination on acceptor molecules, TADF property of acceptors, and the device degradation event. By employing a proposed “exciton recycling” strategy, a threefold increased operational lifetime can be achieved while still maintaining high‐performance OLED properties. In particular, a stable blue OLED that employs this strategy is successfully demonstrated. This research provides an important step for exciplex‐based devices toward the significant improvement of operational stability.. |
| 11. | Umamahesh Balijapalli, Masaki Tanaka, Morgan Auffray, Chin Yiu Chan, Yi Ting Lee, Youichi Tsuchiya, Hajime Nakanotani, Chihaya Adachi, Utilization of Multi-Heterodonors in Thermally Activated Delayed Fluorescence Molecules and Their High Performance Bluish-Green Organic Light-Emitting Diodes, ACS Applied Materials and Interfaces, 10.1021/acsami.9b20020, 12, 8, 9498-9506, 2020.02. |
| 12. | Masaki Tanaka, Hiroki Noda, Hajime Nakanotani, Chihaya Adachi, Molecular orientation of disk-shaped small molecules exhibiting thermally activated delayed fluorescence in host-guest films, Applied Physics Letters, 10.1063/1.5140210, 116, 2, 2020.01. |
| 13. | Naoto Notsuka, Hajime Nakanotani, Hiroki Noda, Kenichi Goushi, Chihaya Adachi, Observation of Nonradiative Deactivation Behavior from Singlet and Triplet States of Thermally Activated Delayed Fluorescence Emitters in Solution, Journal of Physical Chemistry Letters, 10.1021/acs.jpclett.9b03302, 11, 2, 562-566, 2020.01. |
| 14. | Takahiko Yamanaka, Hajime Nakanotani, Chihaya Adachi, Slow recombination of spontaneously dissociated organic fluorophore excitons, Nature communications, 10.1038/s41467-019-13736-8, 10, 1, 2019.12, The harvesting of excitons as luminescence by organic fluorophores forms the basis of light-emitting applications. Although high photoluminescence quantum yield is essential for efficient light emission, concentration-dependent quenching of the emissive exciton is generally observed. Here we demonstrate generation and accumulation of concentration-dependent “long-lived” (i.e., over 1 h) photo-generated carriers and the successive release of their energy as electroluminescence in a solid-state film containing a polar fluorophore. While fluorophore excitons are generally believed to be stable because of their high exciton binding energies, our observations show that some of the excitons undergo spontaneous exciton dissociation in a solid-state film by spontaneous orientation polarization even without an external electric field. These results lead to the reconsideration of the meaning of “luminescence quantum yield” for the solid films containing polar organic molecules because it can differ for optical and electrical excitation.. |
| 15. | Hiroki Noda, Xian Kai Chen, Hajime Nakanotani, Takuya Hosokai, Momoka Miyajima, Naoto Notsuka, Yuuki Kashima, Jean Luc Brédas, Chihaya Adachi, Critical role of intermediate electronic states for spin-flip processes in charge-transfer-type organic molecules with multiple donors and acceptors, Nature Materials, 10.1038/s41563-019-0465-6, 18, 10, 1084-1090, 2019.10, Spin-flip in purely organic molecular systems is often described as a forbidden process; however, it is commonly observed and utilized to harvest triplet excitons in a wide variety of organic material-based applications. Although the initial and final electronic states of spin-flip between the lowest singlet and lowest triplet excited state are self-evident, the exact process and the role of intermediate states through which spin-flip occurs are still far from being comprehensively determined. Here, via experimental photo-physical investigations in solution combined with first-principles quantum-mechanical calculations, we show that efficient spin-flip in multiple donor–acceptor charge-transfer-type organic molecular systems involves the critical role of an intermediate triplet excited state that corresponds to a partial molecular structure of the system. Our proposed mechanism unifies the understanding of the intersystem crossing mechanism in a wide variety of charge-transfer-type molecular systems, opening the way to greater control over spin-flip rates.. |
| 16. | T. Hosokai, Hajime Nakanotani, S. Santou, H. Noda, Y. Nakayama, Chihaya Adachi, TADF activation by solvent freezing The role of nonradiative triplet decay and spin-orbit coupling in carbazole benzonitrile derivatives, Synthetic Metals, 10.1016/j.synthmet.2019.04.005, 252, 62-68, 2019.06. |
| 17. | Masaki Tanaka, Hiroki Noda, Hajime Nakanotani, Chihaya Adachi, Effect of Carrier Balance on Device Degradation of Organic Light-Emitting Diodes Based on Thermally Activated Delayed Fluorescence Emitters, Advanced Electronic Materials, 10.1002/aelm.201800708, 5, 5, 2019.05. |
| 18. | Brett Yurash, Hajime Nakanotani, Yoann Olivier, David Beljonne, Chihaya Adachi, Thuc Quyen Nguyen, Photoluminescence Quenching Probes Spin Conversion and Exciton Dynamics in Thermally Activated Delayed Fluorescence Materials, Advanced Materials, 10.1002/adma.201804490, 31, 21, 2019.05. |
| 19. | Masaki Saigo, Kiyoshi Miyata, Sei'Ichi Tanaka, Hajime Nakanotani, Chihaya Adachi, Ken Onda, Suppression of Structural Change upon S 1 -T 1 Conversion Assists the Thermally Activated Delayed Fluorescence Process in Carbazole-Benzonitrile Derivatives, Journal of Physical Chemistry Letters, 10.1021/acs.jpclett.9b00810, 10, 10, 2475-2480, 2019.05, Thermally activated delayed fluorescence (TADF) molecules are gathering attention for their potential to boost the efficiency of organic light-emitting diodes without precious metals. Minimizing the energy difference between the S 1 and T 1 states (ΔE ST ) is a fundamental strategy to accelerate reverse intersystem crossing (RISC). However, the lack of microscopic understanding of the process prevents adequate design strategies for efficient TADF materials. Here, we focused on four carbazole-benzonitrile (Cz-BN) derivatives that possess identical ΔE ST but distinct TADF activities. We systematically compared their geometrical dynamics upon photoexcitation using time-resolved infrared (TR-IR) vibrational spectroscopy in conjunction with quantum chemical calculations. We found that the most TADF-active molecule, 4CzBN, shows little structural change after photoexcitation, while the TADF-inactive molecules show relatively large deformation upon S 1 -T 1 conversion. This implies that the suppression of structural deformation is critical for minimizing the activation energy barrier for RISC in cases of the Cz-BN derivatives.. |
| 20. | Hiroki Noda, Hajime Nakanotani, Chihaya Adachi, Highly efficient thermally activated delayed fluorescence with slow reverse intersystem crossing, Chemistry Letters, 10.1246/cl.180813, 48, 2, 126-129, 2019.01. |
| 21. | Youichi Tsuchiya, Koudai Ikesue, Hajime Nakanotani, Chihaya Adachi, Photostable and highly emissive glassy organic dots exhibiting thermally activated delayed fluorescence, Chemical Communications, 10.1039/c9cc01420a, 55, 36, 5215-5218, 2019.01. |
| 22. | Jong Uk Kim, Michael Y. Wong, Shiv Kumar, Oliver G. Hayes, Finlay Duncan, Chin Yiu Chan, Ben Yiu Wing Wong, Hao Ye, Lin Song Cui, Hajime Nakanotani, Eli Zysman-Colman, Chihaya Adachi, High-triplet-energy Bipolar Host Materials Based on Phosphine Oxide Derivatives for Efficient Sky-blue Thermally Activated Delayed Fluorescence Organic Light-emitting Diodes with Reduced Roll-off, Chemistry Letters, 10.1246/cl.190412, 48, 10, 1225-1228, 2019.01, We designed and synthesized two new ambipolar host materials, namely CzPO and Cz3PO. Combining CzPO and Cz3PO with CzTRZ2 as the emitter resulted in improved maximum external quantum efficiencies of 13.1% and 13.2%, respectively, together with small efficiency roll-offs, while the device based on bis[2-(diphenylphosphino)phenyl]ether oxide (DPEPO) as host showed a much more pronounced efficiency roll-off.. |
| 23. | Chin Yiu Chan, Masaki Tanaka, Hajime Nakanotani, Chihaya Adachi, Efficient and stable sky-blue delayed fluorescence organic light-emitting diodes with CIEy below 0.4, Nature communications, 10.1038/s41467-018-07482-6, 9, 1, 2018.12, Organic light-emitting diodes utilizing thermally activated delayed fluorescence is a potential solution for achieving stable blue devices. Sky-blue devices (CIEy 15%) at 1000 cd m−2 based on either delayed fluorescence or phosphorescence are still limited and very hard to achieve simultaneously. Here, we report the design and synthesis of a new thermally activated delayed fluorescence emitter, 3Ph2CzCzBN. A sky-blue device based on 3Ph2CzCzBN exhibits a high external quantum efficiency of 16.6% at 1000 cd m−2. The device shows a sky-blue electroluminescence of 482 nm and achieves Commission Internationale de l’ Eclairage coordinates of (0.17, 0.36). The sky-blue device exhibits a superb LT90 of 38 h. This is the first demonstration of high-efficiency and stable sky-blue devices (CIEy |
| 24. | Masashi Mamada, Guojian Tian, Hajime Nakanotani, Jianhua Su, Chihaya Adachi, The Importance of Excited-State Energy Alignment for Efficient Exciplex Systems Based on a Study of Phenylpyridinato Boron Derivatives, Angewandte Chemie - International Edition, 10.1002/anie.201804218, 57, 38, 12380-12384, 2018.09, Understanding excited-state dynamics is critical for improving the photoluminescence (PL) efficiency of exciplexes. A series of exciplexes based on conventional hole-transporting materials as donor and newly developed phenylpyridinato boron derivatives as acceptor were investigated. High PL efficiencies were achieved in only some combinations, and a large difference in performance among combinations provided insight into nonradiative processes in exciplex systems. Furthermore, the triplet local excited states (3LE) of each donor and acceptor were found play an important role in triplet exciplex harvesting. Significant contributions from triplets were clearly observed when the charge-transfer excited states (1CT and 3CT) and 3LE were ideally aligned. We also demonstrated fine control of relative energy alignment via the concentration to improve the PL efficiency.. |
| 25. | Ryo Nagata, Hajime Nakanotani, William J. Potscavage, Chihaya Adachi, Exploiting Singlet Fission in Organic Light-Emitting Diodes, Advanced Materials, 10.1002/adma.201801484, 30, 33, 2018.08, Harvesting of both triplets and singlets yields electroluminescence quantum efficiencies of nearly 100% in organic light-emitting diodes (OLEDs), but the production efficiency of excitons that can undergo radiative decay is theoretically limited to 100% of the electron–hole pairs. Here, breaking of this limit by exploiting singlet fission in an OLED is reported. Based on the dependence of electroluminescence intensity on an applied magnetic field, it is confirmed that triplets produced by singlet fission in a rubrene host matrix are emitted as near-infrared (NIR) electroluminescence by erbium(III) tris(8-hydroxyquinoline) (ErQ3) after excitonic energy transfer from the “dark” triplet state of rubrene to an “emissive” state of ErQ3, leading to NIR electroluminescence with an overall exciton production efficiency of 100.8%. This demonstration clearly indicates that the harvesting of triplets produced by singlet fission as electroluminescence is possible even under electrical excitation, leading to an enhancement of the quantum efficiency of the OLEDs. Electroluminescence employing singlet fission provides a route toward developing high-intensity NIR light sources, which are of particular interest for sensing, optical communications, and medical applications.. |
| 26. | Takuya Hosokai, Hiroki Noda, Hajime Nakanotani, Takanori Nawata, Yasuo Nakayama, Hiroyuki Matsuzaki, Chihaya Adachi, Solvent-dependent investigation of carbazole benzonitrile derivatives Does the le3 - CT1 energy gap facilitate thermally activated delayed fluorescence?, Journal of Photonics for Energy, 10.1117/1.JPE.8.032102, 8, 3, 2018.07, The photophysical properties of six types of carbazole benzonitrile (CzBN) derivatives are investigated in different solvents to examine the thermally activated delayed fluorescence (TADF) activation via reducing the energy gap between the singlet charge-transfer and triplet locally excited states, ΔEST(LE). Relative to the ΔEST(LE) values for the CzBN derivatives in the low polarity solvent toluene (ϵ∼2), a reduction of ΔEST(LE) for the CzBN derivatives in the polar solvent acetonitrile (ϵ∼37) was confirmed while maintaining fairly constant ΔEST values. Notably, TADF activation was observed in acetonitrile for some CzBN derivatives that are TADF inactive in toluene. A numerical analysis of various rate constants revealed the cause of TADF activation as an increase in the reverse intersystem crossing rate and a suppression of the non-radiative decay rate of the triplet states. The positive effect of ΔEST(LE) was limited, however, as an excessive decrease in ΔEST(LE) facilitates the nonradiative deactivation of the triplet states, leading to a loss of the TADF efficiency. This paper shows that ΔEST(LE) provides a measure of TADF activation and that appropriate regulation of ΔEST(LE) is required to achieve high TADF efficiency.. |
| 27. | Yuri Hasegawa, Hayato Minami, Satoru Kanada, Yoichi Yamada, Masahiro Sasaki, Takuya Hosokai, Hajime Nakanotani, Chihaya Adachi, Well-ordered films of disk-shaped thermally activated delayed fluorescence molecules, Journal of Photonics for Energy, 10.1117/1.JPE.8.032110, 8, 3, 2018.07, We fabricated well-ordered, crystalline mono- And multilayers of disk-shaped thermally activated delayed fluorescence (TADF) molecules such as 4CzIPN, 2CzPN, and 5CzBN. The slow deposition of these molecules on flat substrates such as Ag(111) at room temperature resulted in the formation of well-ordered and homogeneous monolayers. Moreover, the multilayer of the 4CzIPN was also found to be well-ordered and flat when deposited on highly oriented pyrolytic graphite (HOPG). The electronic states of the crystalline monolayer and multilayer of 4CzIPN were found to be nearly the same, suggesting that the electronic states of both layers are not altered significantly by adsorption on substrates. Indeed, we also confirmed the delayed fluorescence from the crystalline multilayer of 4CzIPN on the HOPG substrate even in an ambient condition. These results show promising applications of crystalline films of disk-shaped TADF-molecules such as 4CzIPN for organic light-emitting diodes devices with high outcoupling efficiency.. |
| 28. | Hiroki Noda, Hajime Nakanotani, Chihaya Adachi, Excited state engineering for efficient reverse intersystem crossing, Science Advances, 10.1126/sciadv.aao6910, 4, 6, 2018.06, Reverse intersystem crossing (RISC) from the triplet to singlet excited state is an attractive route to harvesting electrically generated triplet excitons as light, leading to highly efficient organic light-emitting diodes (OLEDs). An ideal electroluminescence efficiency of 100% can be achieved using RISC, but device lifetime and suppression of efficiency roll-off still need further improvement. We establish molecular design rules to enhance not only the RISC rate constant but also operational stability under electrical excitation. We show that the introduction of a second type of electron-donating unit in an initially donor-acceptor system induces effective mixing between charge transfer and locally excited triplet states, resulting in acceleration of the RISC rate while maintaining high photoluminescence quantum yield. OLEDs using our designed sky-blue emitter achieved a nearly 100% exciton production efficiency and exhibited not only low efficiency roll-off but also a marked improvement in operational stability.. |
| 29. | Chin Yiu Chan, Lin Song Cui, Jong Uk Kim, Hajime Nakanotani, Chihaya Adachi, Rational Molecular Design for Deep-Blue Thermally Activated Delayed Fluorescence Emitters, Advanced Functional Materials, 10.1002/adfm.201706023, 28, 11, 2018.03, By simple modification of the functional groups on the donor unit, the thermally activated delayed fluorescence (TADF) properties of emitters can easily be manipulated. A series of deep blue to blue emissive TADF derivatives is developed, capable of deep-blue emissions from 403 to 460 nm in toluene. Deep-blue organic light-emitting diodes (OLEDs) based on this series of TADF emitters are fabricated, resulting in an electroluminescence peak at 428 nm and a high external quantum efficiency of up to 10.3%. One deep-blue OLED has achieved the commission internationale de l'eclairage (CIE) coordinates of (0.156, 0.063), which is among the best reported TADF performances for deep-blue OLEDs with CIEy |
| 30. | Y. Hasegawa, Y. Yamada, M. Sasaki, T. Hosokai, Hajime Nakanotani, Chihaya Adachi, Well-Ordered 4CzIPN ((4s,6s)-2,4,5,6-Tetra(9-H-carbazol-9-yl)isophthalonitrile) Layers Molecular Orientation, Electronic Structure, and Angular Distribution of Photoluminescence, Journal of Physical Chemistry Letters, 10.1021/acs.jpclett.7b03232, 9, 4, 863-867, 2018.02, We fabricated a well-ordered homogeneous monolayer of disk-shaped, carbazolyl dicyanobenzene (CDCB)-based thermally activated delayed fluorescence (TADF) molecule, i.e., 4CzIPN((4s,6s)-2,4,5,6-tetra(9Hcarbazol-9-yl)isophthalonitrile) at room temperature on flat Ag(111), Au(111), and Cu(111) surfaces. The second layer of the 4CzIPN was also found to be well ordered. The electronic states of the well-ordered monolayer and multilayer of 4CzIPN were found to be nearly unchanged from that of the isolated molecule calculated by the density functional theory (DFT), suggesting that the ordered layers retain the TADF properties. Indeed, we demonstrated the delayed fluorescence and the nearly perfect in-plane alignment of the transition dipole moment of a 4CzIPN thin film on glass substrate even in an ambient condition. These results indicate that the well-ordered films of the disc-shaped carbazole-based TADF molecules could potentially be utilized in organic light-emitting diode (OLED) devices with high light outcoupling efficiency.. |
| 31. | Masayuki Yokoyama, Ko Inada, Youichi Tsuchiya, Hajime Nakanotani, Chihaya Adachi, Trifluoromethane modification of thermally activated delayed fluorescence molecules for high-efficiency blue organic light-emitting diodes, Chemical Communications, 10.1039/c8cc03425g, 54, 59, 8261-8264, 2018.01, Highly efficient blue and green thermally activated delayed fluorescence (TADF) molecules bearing trifluoromethane-modified carbazole groups were developed. The trifluoromethane groups on carbazole induced blue-shifted emission and improved the photoluminescence quantum yield. The photostability of the TADF molecules was strongly related to the modification position of trifluoromethane on carbazole.. |
| 32. | Yan Geng, Anthony D'Aleo, Ko Inada, Lin Song Cui, Jong Uk Kim, Hajime Nakanotani, Chihaya Adachi, Donor–σ–Acceptor Motifs Thermally Activated Delayed Fluorescence Emitters with Dual Upconversion, Angewandte Chemie - International Edition, 10.1002/anie.201708876, 56, 52, 16536-16540, 2017.12, A family of organic emitters with a donor–σ–acceptor (D-σ-A) motif is presented. Owing to the weakly coupled D-σ-A intramolecular charge-transfer state, a transition from the localized excited triplet state (3LE) and charge-transfer triplet state (3CT) to the charge-transfer singlet state (1CT) occurred with a small activation energy and high photoluminescence quantum efficiency. Two thermally activated delayed fluorescence (TADF) components were identified, one of which has a very short lifetime of 200–400 ns and the other a longer TADF lifetime of the order of microseconds. In particular, the two D-σ-A materials presented strong blue emission with TADF properties in toluene. These results will shed light on the molecular design of new TADF emitters with short delayed lifetimes.. |
| 33. | Lin Song Cui, Shi Bin Ruan, Fatima Bencheikh, Ryo Nagata, Lei Zhang, Ko Inada, Hajime Nakanotani, Liang Sheng Liao, Chihaya Adachi, Long-lived efficient delayed fluorescence organic light-emitting diodes using n-type hosts, Nature Communications, 10.1038/s41467-017-02419-x, 8, 1, 2017.12, Organic light-emitting diodes have become a mainstream display technology because of their desirable features. Third-generation electroluminescent devices that emit light through a mechanism called thermally activated delayed fluorescence are currently garnering much attention. However, unsatisfactory device stability is still an unresolved issue in this field. Here we demonstrate that electron-transporting n-type hosts, which typically include an acceptor moiety in their chemical structure, have the intrinsic ability to balance the charge fluxes and broaden the recombination zone in delayed fluorescence organic electroluminescent devices, while at the same time preventing the formation of high-energy excitons. The n-type hosts lengthen the lifetimes of green and blue delayed fluorescence devices by > 30 and 1000 times, respectively. Our results indicate that n-type hosts are suitable to realize stable delayed fluorescence organic electroluminescent devices.. |
| 34. | Jong Uk Kim, Saripally Sudhaker Reddy, Lin Song Cui, Hiroko Nomura, Sunbin Hwang, Dae Hyeon Kim, Hajime Nakanotani, Sung Ho Jin, Chihaya Adachi, Thermally activated delayed fluorescence of Bis(9,9-dimethyl-9,10-dihydroacridine) dibenzo[b,d]thiophene 5,5-dioxide derivatives for organic light-emitting diodes, Journal of Luminescence, 10.1016/j.jlumin.2017.06.006, 190, 485-491, 2017.10, Two luminescent dibenzo[b,d]thiophene 5,5-dioxide derivatives combined with 9,9-dimethyl-9,10-dihydroacridine were synthesized and the appearance of thermally activated delayed fluorescence was confirmed. Both 3,7- and 2,8-bis(9,9-dimethyl-9,10-dihydroacridine)dibenzo[b,d]thiophene 5,5-dioxide (3ASOA) and (4ASOA) showed prompt and delayed fluorescence with high total photoluminescence (PL) quantum efficiencies of 72% and 88% in their doped films, respectively. The maximum external electroluminescence (EL) efficiencies of 13.8% in 4ASOA and 10.4% in 3ASOA were obtained. Further, 4ASOA showed slightly relaxed rolloff behavior, indicating that 2,8-substitution of the donors appreciably improved both PL and EL characteristics.. |
| 35. | Masashi Mamada, Ko Inada, Takeshi Komino, William J Potscavage, Hajime Nakanotani, Chihaya Adachi, Highly Efficient Thermally Activated Delayed Fluorescence from an Excited-State Intramolecular Proton Transfer System, ACS Central Science, 10.1021/acscentsci.7b00183, 3, 7, 769-777, 2017.07, Thermally activated delayed fluorescence (TADF) materials have shown great potential for highly efficient organic light-emitting diodes (OLEDs). While the current molecular design of TADF materials primarily focuses on combining donor and acceptor units, we present a novel system based on the use of excited-state intramolecular proton transfer (ESIPT) to achieve efficient TADF without relying on the well-established donor-acceptor scheme. In an appropriately designed acridone-based compound with intramolecular hydrogen bonding, ESIPT leads to separation of the highest occupied and lowest unoccupied molecular orbitals, resulting in TADF emission with a photoluminescence quantum yield of nearly 60%. High external electroluminescence quantum efficiencies of up to 14% in OLEDs using this emitter prove that efficient triplet harvesting is possible with ESIPT-based TADF materials. This work will expand and accelerate the development of a wide variety of TADF materials for high performance OLEDs.. |
| 36. | Takahiko Yamanaka, Hajime Nakanotani, Shigeo Hara, Toru Hirohata, Chihaya Adachi, Near-infrared organic light-emitting diodes for biosensing with high operating stability, Applied Physics Express, 10.7567/APEX.10.074101, 10, 7, 2017.07, We demonstrate highly stable NIR organic light-emitting diodes (OLEDs) based on a system using excitonic energy transfer from thermally activated delay fluorescence molecules to NIR fluorophores. The NIR OLEDs showed an electroluminescence peak at 780nm and robust operational stability with 2% loss of the initial radiant flux after 1000h under a constant current density of 10mA/cm2. The variation of hemoglobin oxygen saturation can be detected using the NIR OLEDs as a light source.. |
| 37. | Hajime Nakanotani, Taro Furukawa, Takuya Hosokai, Takuji Hatakeyama, Chihaya Adachi, Light Amplification in Molecules Exhibiting Thermally Activated Delayed Fluorescence, Advanced Optical Materials, 10.1002/adom.201700051, 5, 12, 2017.06, To reduce the threshold current density and move closer toward the realization of future current-injection organic semiconductor lasers, the harvesting of triplet excitons is anticipated because 75% excitons are directly formed as triplet excited states under electrical excitation according to spin statics. However, the observation of light amplification in pure phosphorescent or thermally activated delayed fluorescence (TADF) materials has nor yet been reported even under optical excitation. Herein, light amplification was observed in the TADF emitter 9-([1,1′-biphenyl]-3-yl)-N,N,5,11-tetraphenyl-5,9-dihydro-5,9-diaza-13b-boranaphtho[3,2,1-de]anthracen-3-amine (DABNA-2). It is found that DABNA-2 possesses not only a large stimulated emission cross-section but also a favorable window for light amplification. These results indicate that TADF emitters can form a new category of laser dyes and are important candidates for the realization of an organic semiconductor laser.. |
| 38. | Takuya Hosokai, Hiroyuki Matsuzaki, Hajime Nakanotani, Katsumi Tokumaru, Tetsuo Tsutsui, Akihiro Furube, Keirou Nasu, Hiroko Nomura, Masayuki Yahiro, Chihaya Adachi, Evidence and mechanism of efficient thermally activated delayed fluorescence promoted by delocalized excited states, Science advances, 10.1126/sciadv.1603282, 3, 5, 2017.05. |
| 39. | Ryo Nagata, Nakanotani Hajime, CHIHAYA ADACHI, Near-Infrared Electrophosphorescence up to 1.1 mu m using a Thermally Activated Delayed Fluorescence Molecule as Triplet Sensitizer, ADVANCED MATERIALS, 10.1002/adma.201604265, 29, 5, 2017.02. |
| 40. | Lin-Song Cui, Hiroko Nomura, Yan Geng, Uk Jong, Nakanotani Hajime, CHIHAYA ADACHI, Controlling Singlet-Triplet Energy Splitting for Deep-Blue Thermally Activated Delayed Fluorescence Emitters, ANGEWANDTE CHEMIE-INTERNATIONAL EDITION, 10.1002/anie.201609459, 56, 6, 1571-1575, 2017.02. |
| 41. | Yan Geng, Lin Song Cui, Jong Uk Kim, Hajime Nakanotani, Chihaya Adachi, Molecular design for blue thermal activated delayed fluorescence materials Substitution position effect, Chemistry Letters, 10.1246/cl.170587, 46, 10, 1490-1492, 2017.01, Three emitters having a donor-phenyl-acceptor structure are considered as thermally activated delayed fluorescence (TADF) materials. They present different triplet excited-state energies depending on the substitution positions. Consequently, two materials exhibit blue emission with TADF properties. The OLEDs based on o-CzXTN provided a maximum EQE as high as 10.6%.. |
| 42. | Yuya Tanaka, Takehiro Takahashi, Junichi Nishide, Yasuhide Hiraga, Nakanotani Hajime, CHIHAYA ADACHI, Application of wide-energy-gap material 3,4-di(9H-carbazol-9-yl)benzonitrile in organic light-emitting diodes, THIN SOLID FILMS, 10.1016/j.tsf.2016.11.016, 619, 120-124, 2016.11. |
| 43. | Hin-Wai Mo, Youichi Tsuchiya, Yan Geng, Takehiro Sagawa, Chika Kikuchi, Fuyuki Ito, Nakanotani Hajime, CHIHAYA ADACHI, Color Tuning of Avobenzone Boron Difluoride as an Emitter to Achieve Full-Color Emission, ADVANCED FUNCTIONAL MATERIALS, 10.1002/adfm.201601257, 26, 37, 6703-6710, 2016.10. |
| 44. | Masatoshi Ishida, Toshihiro Omagari, Ryuji Hirosawa, Keisuke Jono, Young Mo Sung, Yuhsuke Yasutake, Hidemitsu Uno, Motoki Toganoh, Nakanotani Hajime, Susumu Fukatsu, Dongho Kim, Hiroyuki Furuta, Boron Difluoride Complexes of Expanded N-Confused Calix[n]phyrins That Demonstrate Unique Luminescent and Lasing Properties, Angew.Chem. Int. Ed., 10.1002/anie.201606246, 55, 12045-12049, 2016.09. |
| 45. | Lin-Song Cui, Jong Uk Kim, Hiroko Nomura, Nakanotani Hajime, CHIHAYA ADACHI, Benzimidazobenzothiazole-based Bipolar Hosts to Harvest Nearly All of the Excitons from Blue Delayed Fluorescence and Phosphorescent Organic Light-Emitting Diodes, Angewandte Chemie International Edition, 10.1002/anie.201601136, 2016.05. |
| 46. | Hiroya Arai, Nakanotani Hajime, CHIHAYA ADACHI, Magnesium-gold binary alloy for organic light-emitting diodes with high corrosion resistance, Journal of Vacuum Science and Technology, 2016.05. |
| 47. | Shuho Tanimoto, Takatsugu Suzuki, Nakanotani Hajime, CHIHAYA ADACHI, Thermally activated delayed fluorescence from pentacarbazorylbenzonitrile, Chem. Lett., 10.1246/cl.160290, 2016.04. |
| 48. | Nakanotani Hajime, Taro Furukawa, Kei Morimoto, CHIHAYA ADACHI, Long-range coupling of electron-hole pairs in spatially separated organic donor-acceptor layers, Science Advances , 10.1126/sciadv.1501470, 2016.03, Understanding exciton behaviour in organic semiconductor molecules is crucial for the development of organic semiconductor-based excitonic devices like organic light-emitting diodes and organic solar cells, and the tightly bound electron–hole pair forming an exciton is normally assumed to be localized on an organic semiconducting molecule. Here we report the observation of long-range coupling of electron–hole pairs in spatially separated electron-donating and -accepting molecules across a 10-nm-thick spacer layer. We found that the exciton energy can be tuned over 100 meV and the fraction of delayed fluorescence can be increased by adjusting the spacer layer thickness. Furthermore, increasing the spacer layer thickness produced an organic light-emitting diode with an electroluminescence efficiency nearly eight times higher than that of a device without a spacer layer. Our results demonstrate the first example of a long-range coupled charge-transfer state between electron-donating and -accepting molecules in a working device.. |
| 49. | Takahiro Higuchi, Hajime Nakanotani, Chihaya Adachi, High-Efficiency White Organic Light-Emitting Diodes Based on a Blue Thermally Activated Delayed Fluorescent Emitter Combined with Green and Red Fluorescent Emitters, ADVANCED MATERIALS, 10.1002/adma.201404967, 27, 12, 2019-2023, 2015.03, A new device architecture for highly efficient white OLEDs using a molecule exhibiting blue thermally activated delayed fluorescence as a common source of singlet excitons for molecules emitting red and green light based on conventional fluorescence is proposed. The device with an optimum combination of materials shows a maximum external quantum efficiency of over 12% without using phosphorescent emitters.. |
| 50. | Munetomo Inoue, Toshinori Matsushima, Nakanotani Hajime, Chihaya Adachi, Introduction of oxygen into organic thin films with the aim of suppressing singlet-triplet annihilation, Chem. Phys. Lett., 10.1016/j.cplett.2015.02.010, 624, 43-46, 2015.03. |
| 51. | Shuzo Hirata, Yumi Sakai, Kensuke Masui, Hiroyuki Tanaka, Lee Sae Youn, Nomura Hiroko, Nakamura Nozomi, Yasumatsu Mao, Hajime Nakanotani, Zhang Qisheng, Shizu Katsuyuki, Miyazaki Hiroshi, Chihaya Adachi, Highly efficient blue electroluminescence based on thermally activated delayed fluorescence, NATURE MATERIALS, 10.1038/NMAT4154, 14, 3, 330-336, 2015.03. |
| 52. | Kohei Hayashi, Nakanotani Hajime, Munetomo Inoue, Kou Yoshida, Mikhnenko, Oleksandr, Thuc-Quyen Nguyen, Chihaya Adachi, Suppression of roll-off characteristics of organic light-emitting diodes by narrowing current injection/transport area to 50 nm, Appl. Phys. Lett., 10.1063/1.4913461, 106, 9, 2015.03. |
| 53. | Jiyoung Lee, Katsuyuki Shizu, Hiroyuki Tanaka, Hajime Nakanotani, Takuma Yasuda, Hironori Kaji, Chihaya Adachi, Controlled emission color and singlet-triplet energy gap of dihydrophenazine-based thermally activated delayed fluorescence emitters, J. Mater. Chem. C, 10.1039/C4TC02530J, 3, 2175-2181, 2015.01. |
| 54. | Taro Furukawa, Hajime Nakanotani, Chihaya Adachi, Dual enhancement of electroluminescence efficiency and operational stability by rapid upconversion of triplet excitons in OLEDs, SCIENTIFIC REPORTS, 10.1038/srep08429, 5, 8429, 2015.02, Recently, triplet harvesting via a thermally activated delayed fluorescence (TADF) process has been established as a realistic route for obtaining ultimate internal electroluminescence (EL) quantum efficiency in organic light-emitting diodes (OLEDs). However, the possibility that the rather long transient lifetime of the triplet excited states would reduce operational stability due to an increased chance for unwarranted chemical reactions has been a concern. Herein, we demonstrate dual enhancement of EL efficiency and operational stability in OLEDs by employing a TADF molecule as an assistant dopant and a fluorescent molecule as an end emitter. The proper combination of assistant dopant and emitter molecules realized a “one-way” rapid Förster energy transfer of singlet excitons from TADF molecules to fluorescent emitters, reducing the number of cycles of intersystem crossing (ISC) and reverse ISC in the TADF molecules and resulting in a significant enhancement of operational stability compared to OLEDs with a TADF molecule as the end emitter. In addition, we found that the presence of this rapid energy transfer significantly suppresses singlet-triplet annihilation. Using this finely-tuned rapid triplet-exciton upconversion scheme, OLED performance and lifetime was greatly improved.. |
| 55. | Shuzo Hirata, Yumi Sakai, Kensuke Masui, Hiroyuki Tanaka, Sae Youn Lee, Hiroko Nomura, Nozomi Nakamura, Mao Yasumatsu, Hajime Nakanotani, Qisheng Zhang, Katsuyuki Shizu, Hiroshi Miyazaki, Chihaya Adachi, Highly efficient blue electroluminescence based on thermally activated delayed fluorescence, Nature Materials, 10.1038/nmat4154, 14, 3, 330-336, 2015.01, Organic compounds that exhibit highly efficient, stable blue emission are required to realize inexpensive organic light-emitting diodes for future displays and lighting applications. Here, we define the design rules for increasing the electroluminescence efficiency of blue-emitting organic molecules that exhibit thermally activated delayed fluorescence. We show that a large delocalization of the highest occupied molecular orbital and lowest unoccupied molecular orbital in these charge-transfer compounds enhances the rate of radiative decay considerably by inducing a large oscillator strength even when there is a small overlap between the two wavefunctions. A compound based on our design principles exhibited a high rate of fluorescence decay and efficient up-conversion of triplet excitons into singlet excited states, leading to both photoluminescence and internal electroluminescence quantum yields of nearly 100%.. |
| 56. | Hajime Nakanotani, Takahiro Higuchi, Taro Furukawa, Kensuke Masui, Kei Morimoto, Masaki Numata, Hiroyuki Tanaka, Yuta Sagara, Takuma Yasuda, CHIHAYA ADACHI, High-efficiency organic light-emitting diodes with fluorescent emitters, NATURE COMMUNICATIONS, 10.1038/ncomms5016, 5, 2014.05, Fluorescence-based organic light-emitting diodes have continued to attract interest because of their long operational lifetimes, high colour purity of electroluminescence and potential to be manufactured at low cost in next-generation full-colour display and lighting applications. In fluorescent molecules, however, the exciton production efficiency is limited to 25% due to the deactivation of triplet excitons. Here we report fluorescence-based organic light-emitting diodes that realize external quantum efficiencies as high as 13.4–18% for blue, green, yellow and red emission, indicating that the exciton production efficiency reached nearly 100%. The high performance is enabled by utilization of thermally activated delayed fluorescence molecules as assistant dopants that permit efficient transfer of all electrically generated singlet and triplet excitons from the assistant dopants to the fluorescent emitters. Organic light-emitting diodes employing this exciton harvesting process provide freedom for the selection of emitters from a wide variety of conventional fluorescent molecules.. |
| 57. | Kensuke Masui, Hajime Nakanotani, Chihaya Adachi, Analysis of exciton annihilation in high-efficiency sky-blue organic light-emitting diodes with thermally activated delayed fluorescence, ORGANIC ELECTRONICS, 10.1016/j.orgel.2013.07.010, 14, 11, 2721-2726, 2013.11. |
| 58. | Nakanotani, Hajime; Masui, Kensuke; Nishide, Junichi; Shibata, Takumi; Adachi, Chihaya, Promising operational stability of high-efficiency organic light-emitting diodes based on thermally activated delayed fluorescence, SCIENTIFIC REPORTS, 10.1038/srep02127, 3, 2013.07. |
| 59. | Hajime Nakanotani, Chihaya Adachi, Amplified Spontaneous Emission and Electroluminescence from Thiophene/Phenylene Co-Oligomer-Doped p-bis(p-Styrylstyryl)Benzene Crystals, ADVANCED OPTICAL MATERIALS, 10.1002/adom.201200066, 1, 6, 422-427, 2013.06. |
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