2012年にNatureに発表後、世界を先導して開発を進めてきた熱活性化遅延蛍光（TADF)の科学技術が高く評価された。本研究成果が、物理の根幹に係わる学理の開拓に繋がっていることを実証している。

有機発光ダイオード（有機 EL, OLED）は、スマートフォンやタブレット端末の小型ディスプレイから大型 TV の画面に至るまで幅広い先端電子デバイスにおいて実用化が進んでいる。1990 年代後半から、第二世代の発光分子として白金やイリジウム等を含有する有機金属錯体の研究が盛んに行われ実用化に至っているが、分子設計の自由度の低さや高コスト、更には希少資源などの問題を抱えていた。
これに対して、熱活性化遅延蛍光（TADF）に着目し、緻密な量子化学計算と巧みな分子設計によって、100%の内部量子効率を単純な芳香族化合物によって実現した。高効率の TADF を実現するために、励起一重項エネルギーと励起三重項エネルギーの差が小さい（100 meV 以下）化合物を設計して、通常ではスピン状態が異なるために遷移確率の低い励起三重項状態から励起一重項状態への遷移を熱的に可能とした（変換効率 100%）。この新規分子を発光層に用いた OLED において、電流励起によって得られた励起三重項状態を励起一重項状態に変換することによって、100%の内部量子効率を有する OLED を実現している。TADF 分子は比較的単純な芳香族化合物であることから、世界的にも多くの研究が追随された（論文の引用回数の多さが物語っている）。
また、従来開発が困難であった青色発光 TADF 分子の開発にも成功しており、さらに、TADF の派生技術として１時間以上の連続発光が可能な有機蓄光現象など、有機電荷移動（CT）状態の精密制御によって新基軸の開拓に繋がっている。
以上のように、理論に基づいた分子設計によって実用可能なエレクトロニクス材料を創出しており、学術的にも工業的にも高いレベルであると判断される。特に、有機CT 状態の精密制御がデバイス性能の向上に重要であることを体系的に明らかにしたことは、有機デバイス分野の発展に大きく貢献した。Nature およびその姉妹誌に掲載された論文の引用数（TADF の論文は 5000 件）（総論文の引用数は 75571 件）は群を抜いており、376 件の特許出願も注目に値する。また、実用化に関しては、九大発のベンチャー（（株）Kyulux）が設立され、世界初の TADF 材料を用いた OLED パネルが台湾の企業（WiseChip 社）から上市され、実用化に至っている。

革新的な材料創成による有機発光デバイスの高性能化

有機発光ダイオード（Organic Light-Emitting Diode: OLED，あるいは，有機EL）は，1990年代後半からカーナビゲーション用ディスプレイとしての製品化が始まり，2010年代からスマートフォン，大型テレビ，医療機器，車載パネル，照明パネル等，産業的に大きな広がりを示している。1980年代後半の黎明期から現在に至るまで一貫してOLEDの研究に取り組み，OLEDの設計指針を示し，新規発光材料を設計・合成することで，当該分野を先導する革新的な成果を挙げた。

OLEDの発光原理は，蛍光（第1世代），燐光（第2世代），熱活性化遅延蛍光（TADF）（第3世代）である。全ての世代で，重要な役割を果たした。第1世代のOLEDは当初，電子輸送層・発光層／正孔輸送層の二層構造であったが，電子輸送層／発光層／正孔輸送層なるダブルヘテロ構造により高効率化を実現した。ダブルヘテロ構造はその後のOLEDの基本構造となった。

第1世代の蛍光OLEDの内部量子効率は25%程度であったが，燐光材料を発光層に用いたダブルヘテロ構造OLEDにより，内部量子効率が100%となること実証し，第2世代燐光OLEDの有用性を示した。この後，TADFを発現する分子群を設計・合成し，燐光材料とは異なるレアメタルを含有しない比較的単純な芳香族化合物でありながら内部量子効率100%の第3世代TADF OLEDを実現した。究極のOLED発光材料としての地位を確立し，多数の研究活動を触発している。さらに，TADF材料に蛍光材料を添加した第4世代OLEDにおいて，TADF材料と同等な内部量子効率を有する高色純度を実現している。

また、TADF OLEDに関する100件を超える特許出願を行い，それをもとに2015年に九州大学発ベンチャーである(株) Kyulux を設立している。

2012年にNatureに発表後、世界を先導して開発を進めてきた熱活性化遅延蛍光（TADF)の科学技術が高く評価された。特に今年度は物理分野での選定であり、本研究成果が、物理の根幹に係わる学理の開拓に繋がっていることを実証している。

2012年にNatureに発表後、世界を先導して開発を進めてきた熱活性化遅延蛍光（TADF)の科学技術が高く評価された。特に今年度は物理分野での選定であり、本研究成果が、物理の根幹に係わる学理の開拓に繋がっていることを実証している。

2012年にNatureに発表後、世界を先導して開発を進めてきた熱活性化遅延蛍光（TADF)の科学技術が高く評価された。

2012年にNature誌に発表し、その後、世界を先導して研究開発を進めてきた熱活性化遅延蛍光（TADF)の研究成果が基礎学術の視点（化学の新しい学理の開拓）から広く認められた。

2012年にNature誌に発表し、その後、世界を先導して研究開発を進めてきた熱活性化遅延蛍光（TADF)の研究成果が広く認められたことを意味している。

100％の三重項励起子の励起一重項状態への遷移が実現された。これにより、100％の電流ー光変換を実現する高効率有機EL素子の実現のみならず、分子励起子のスピン状態の基礎的な理解が進み、分子物性物理学にも大きな貢献を果たした。

作業中

【受賞コメント】TADFは骨格を限定せず、有機材料設計の無限の可能性を生かした分子設計が可能であるため、RGB全ての色において、高効率な材料の創出が可能となります。今後、有機ELの新しいアプリケーションが各企業から販売され身近なものになるに伴って、TADF材料が世界中で使われ、有機ELの世界的普及に貢献できることを願っております。

担当区分：責任著者   記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Angewandte Chemie - International Edition  

The pursuit of highly efficient thermally activated delayed fluorescence (TADF) emitters with two-photon absorption (2PA) character is hampered by the concurrent achievement of a small singlet-triplet energy gap (ΔEST) and high photoluminescence quantum yield (ΦPL). Here, by introducing a terephthalonitrile unit into a sterically crowded donor-π-donor structure, inducing a hybrid electronic excitation character, we designed unique TADF emitters possessing 2PA ability. This rational molecular design was achieved through a main π-conjugated donor-acceptor-donor backbone in line with locally excited feature renders a large oscillator strength and transition dipole moment, maintaining a high 2PA cross-section value. The ancillary N-donor-acceptor-donor with charge transfer character highly balances the TADF phenomenon by minimizing ΔEST. A near-unity ΦPL value with a large radiative decay rate over an order of magnitude higher than the intersystem crossing rate and a high horizontal orientation ratio of 0.95 were simultaneously attained for TPCz2NP. The organic light-emitting diodes fabricated with this material exhibit a high maximum external quantum efficiency of 25.4 % with an elevated 2PA cross-section (σ2) value up to 143 GM at 850 nm. These findings offer a venue for designing high-performance TADF emitters with exceptional performance inclusive of 2PA properties, expanding for future functional material design.

DOI： 10.1002/anie.202420417

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Journal of Physical Chemistry C  

We have examined the structural and electron transport properties of a swallow-tailed N,N’-bis(1-heptyloctyl)-perylene-3,4:9,10-bis(dicarboximide) (PDI-C8,7) in thin films. A comprehensive analysis of material with the use of X-ray scattering methods evidenced the appearance of a new soft-crystalline mesophase that was induced by thermal processing of the swallow-tail PDI derivative. By combining electrical measurements with grazing-incidence wide-angle X-ray scattering (GIWAXS), we show that these morphological changes of thin films boost their charge transport in the organic field-effect transistor (OFET) configuration. The systematic device engineering of OFETs, including device architecture, thermal history, and preparation method of the active layer, resulted in a significant improvement in the electron field-effect mobility and the related performance parameters. In particular, the results demonstrate a strong improvement in the charge transport of PDI-C8,7 films in their soft-crystalline phase, which originates from the N-substitution by swallow-tails. In addition, our study demonstrates that the melt-processing route, a solvent-free and vacuum-free method for the fabrication of organic thin films, represents an efficient strategy for the fabrication of high-performance air-stable n-type OFETs.

DOI： 10.1021/acs.jpcc.4c06222

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記述言語：英語   出版者・発行元：Chemistry - A European Journal  

Organic vapochromic materials which undergo a drastic change in their photophysical properties upon exposure to vapors or gases are attracting growing scientific attention because of their low price and wide range of possible applications. In this work, luminescence vapochromism of carbazole-pyridinium-based organic salts with a general structure of (CzPy)X (CzPy+=2,3-di(9H-carbazol-9-yl)pyridinium ion; X=Cl, Br or I) is reported. It was found that (CzPy)X compounds form J-aggregates, which rearranged back to monomeric form upon exposure to methanol, ethanol, acetone, and water vapors. In contrast, acetonitrile was found to promote the J-aggregation in (CzPy)X compounds by occupying the voids in their crystal lattice and pushing cations closer together. It was further demonstrated that the efficiency of J-aggregation in (CzPy)X compounds depends on the size of the anion, which was employed to realize dynamic luminescence vapochromism, with vapochromic response times ranging from a couple of minutes in (CzPy)Cl to more than an hour in (CzPy)I. In addition, (CzPy)X compounds exhibited high melting points of about 250 °C and excellent thermal stability. (CzPy)Cl and (CzPy)Br have also shown good photoluminescence quantum yields at room temperature in a solid state.

DOI： 10.1002/chem.202402777

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担当区分：責任著者   記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Wiley  

Photon‐upconversion (PUC) processes in organic molecular systems, such as triplet‐triplet upconversion and hot‐band absorption, are promising technologies for future energy harvesting. Although these processes can generate high‐energy excitons compared to excitation energy, a PUC process with a high yield and no energy loss has not been established and, therefore, is highly desired. Here, we propose an alternative PUC mechanism that uses reverse intersystem crossing on thermally activated delayed fluorescence (TADF) molecules. This process combines a triplet sensitizer and a TADF molecule, generating a triplet in the former and transferring it to the latter. Specifically, the triplet energy transfer from Ir(ppy)3 (sensitizer) to CzBSe (TADF) results in anti‐Stokes emission with an anti‐Stokes energy of 0.18 eV. We found that the triplet energy transfer rate strongly depends on the triplet radiative decay rate of TADF molecules and the difference in Gibbs energy between the energy acceptor and donor. Our findings will contribute to understanding triplet energy transfer dynamics in organic energy donor‐acceptor systems and will lead to various applications, such as future optical cooling systems.

DOI： 10.1002/anie.202419323

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担当区分：責任著者   記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Advanced Materials  

Two-dimensional perovskites containing an organic fluorophore can be a unique emitter for light-emitting diodes (LEDs). However, external quantum efficiencies (EQEs) of fluorophore-containing perovskite LEDs reported thus far are still very low. In this study, these are able to boost the EQE to ≈10% by choosing an organic fluorophore with appropriate energy levels for the perovskite structure organization. In the fluorophore-containing perovskite LEDs, carrier transport and exciton formation take place in the perovskite's metal halide framework, thereby avoiding the direct formation of nonradiative triplet excitons on the organic fluorophores. Subsequently, the bright triplet excitons formed in the metal halide framework are transferred to form the radiative singlet states of the organic fluorophores, leading to efficient electroluminescence (EL) from the organic fluorophores regularly dispersed inside the perovskite structure. Unexpectedly higher light-outcoupling efficiency, which is caused by the light scattering in the polycrystalline perovskite layer, will be another reason for efficient EL. These findings will contribute toward the fabrication of LED-based products with high performance at a low cost.

DOI： 10.1002/adma.202408775

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担当区分：責任著者   掲載種別：研究論文（学術雑誌）   出版者・発行元：Advanced Optical Materials  

Electron donor and acceptor interactions are the fundamentals for the emergence of optoelectronic functions in most organic devices. In particular, exciplexes, which hold the possibility to utilize dark triplets, are widely investigated in organic light-emitting diodes. However, the relatively low radiative decay rate with a low photoluminescence quantum yield poses further advanced challenges. Traditionally, it is well recognized that exciplexes are formed through a charge transfer process, i.e., direct electron transfer, by photoexciting either a donor or an acceptor component. In this study, the focus is on a long-range exciplex system where tris(4-carbazoyl-9-ylphenyl)amine (TCTA) and 2,4,6-tris[3-(diphenylphosphinyl)phenyl]−1,3,5-triazine (PO-T2T) serve as the donor and acceptor, respectively. Moreover, 1,2-bis(triphenylsilyl) benzene (UGH2) and bis[2-(diphenylphosphino)phenyl]ether oxide (DPEPO), having a wide energy gap and a high triplet energy level, are employed as the double insulating layer to suppressing direct electron transfer between the donor and acceptor. The indirect through-space exciplex formation is demonstrated by the simultaneous excitation of both donor and acceptor layers optically and electrically, providing a new route for exciplex formation.

DOI： 10.1002/adom.202401237

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その他リンク： https://onlinelibrary.wiley.com/doi/pdf/10.1002/adom.202401237

担当区分：責任著者   記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Nature Communications  

We propose an organic thermoelectric device having a new power generation mechanism that extracts small-scale thermal energy, i.e., a few tens of millielectronvolts, at room temperature without a temperature gradient. We demonstrate a new operating mechanism based on an organic thermoelectric power generation architecture that uses the charge separation capabilities of organic charge transfer (CT) interfaces composed of copper (II) phthalocyanine and copper (II) 1,2,3,4,8,9,10,11,15,16,17,18,22,23,24,25-hexadecafluoro-29H,31H-phthalocyanine as the donor and acceptor, respectively. With the optimized device architecture, values of open-circuit voltage VOC of 384 mV, short-circuit current density JSC of 1.1 μA/cm2, and maximum output Pmax of 94 nW/cm2 are obtained. The temperature characteristics of the thermoelectric properties yield activation energy values of approximately 20–60 meV, confirming the low-level thermal energy’s contribution to the power generation mechanism. Furthermore, from surface potential analysis using a Kelvin probe, we confirm that charges are generated at the CT interface, and the electrons and holes are diffused to the counter-electrodes with the aid of Fermi-level alignment between adjacent layers.

DOI： 10.1038/s41467-024-52047-5

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その他リンク： https://www.nature.com/articles/s41467-024-52047-5

担当区分：責任著者   記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Communications Chemistry  

Thermally activated delayed fluorescence (TADF) is a promising mechanism for harvesting triplet excitons in organic light-emitting diodes (OLEDs). The donor–acceptor (D–A) design is the most conventional strategy for developing efficient TADF emitters. A subsequently emerged approach, known as the multiple resonance (MR) effect, also employs electron-donating and electron-withdrawing functional groups. Thus, developing TADF materials has traditionally relied on ingenuity in selecting and combining two functional units. Here, we have realized a TADF molecule by utilizing only a carbazole donor moiety. This molecule is an unusual example in the family of TADF materials and offers better insight into the electronic structures in the excited states for luminescent materials. (Figure presented.)

DOI： 10.1038/s42004-024-01301-4

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その他リンク： https://www.nature.com/articles/s42004-024-01301-4

掲載種別：研究論文（学術雑誌）   出版者・発行元：ACS Photonics  

Exciton polaritons are collective matter-light excitations that can be spaced up to 1 eV away from the bare molecular excited states. This hints at their potential to modify molecular emission processes. In the vast majority of cases, however, the observed emission rates from exciton polaritons remain nearly unchanged from those of the bare molecule and can be explained through radiative pumping of polaritons by dark molecular excited states. In this study, we observe a reduction in the prompt and delayed emission rates from exciton polaritons in a microcavity containing molecules that show multiresonance thermally activated delayed fluorescence. We find that most of our experimental observations are due to the existence of molecular configurations supporting excimers in the film. In the presence of strong coupling, polariton emission at the excimer energy shows the same kinetics observed at the monomer energy. Using a semiclassical model to describe the polariton kinetics, we find that this can be explained by the transfer of polaritons initially populated by the monomers to the dark states, followed by re-emission at lower energies. At the lowest temperatures, the longest-lived component of the delayed emission lifetime still cannot be understood via this mechanism.

DOI： 10.1021/acsphotonics.4c00488

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担当区分：責任著者   掲載種別：研究論文（学術雑誌）   出版者・発行元：Japanese Journal of Applied Physics, Part 1: Regular Papers and Short Notes and Review Papers  

Luminescent lanthanide ions incorporated in sodium yttrium fluoride nanocrystals are promising as new luminescent materials in optoelectronics and bioimaging since the nonradiative transition is significantly suppressed due to the absence of high-energy vibrational modes. To prepare optically and electrically active nanocrystals, we explored organic ligands that allow efficient triplet energy transfer to Eu3+ incorporated into nanocrystals, resulting in an efficient photosensitization effect in colloidal solutions and films. Further, we applied these emitting nanocrystals to light-emitting devices and observed the electroluminescence.

DOI： 10.35848/1347-4065/ad760d

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その他リンク： https://iopscience.iop.org/article/10.35848/1347-4065/ad760d/pdf

担当区分：責任著者   掲載種別：研究論文（学術雑誌）   出版者・発行元：Advanced Functional Materials  

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.

DOI： 10.1002/adfm.202402287

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担当区分：責任著者   掲載種別：研究論文（学術雑誌）   出版者・発行元：Advanced Functional Materials  

While metal-organic frameworks (MOFs) and covalent organic frameworks (COFs) have been widely investigated as porous conductive materials, the research on the electrical properties of HOF materials has been limited. Moreover, the electrical conductivity of HOF materials is typically several orders of magnitude lower than that of MOFs and COFs. In this work, a HOF material based on naphthalene diimide is designed and achieved a remarkable electrical conductivity of 2.9 × 10−2 S cm−1 after hydrazine doping, which represents the highest value reported in the HOF system to date. In addition, this material exhibits a reversible change of its electrical conductivity under exposure to ammonia which is promising for gas-sensor applications. The demonstration reveals a new dimension of HOFs as conductive materials and opens up possibilities for new HOF-based devices.

DOI： 10.1002/adfm.202409299

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担当区分：責任著者   記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Physical Chemistry Chemical Physics  

Two novel deep-blue multi-resonance thermally activated delayed fluorescence (MR-TADF) emitters, 1B-CzCrs and 2B-CzCrs, containing a fused carbazole unit were synthesized. The carbazole contributed to the emergence of TADF in these small molecules. Particularly, organic light-emitting diodes with 1B-CzCrs doped in the mCP host achieve a maximum external quantum efficiency of 12.8% at CIE coordinates of (0.146, 0.062).

DOI： 10.1039/d4cp02664k

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担当区分：責任著者   掲載種別：研究論文（学術雑誌）   出版者・発行元：Chemical Physics Letters  

Exciplexes are crucial in organic optoelectronic devices since well-elaborated charge-transfer (CT) complexes exhibit unique exciton generation behavior. Thus, understanding the CT energy structures with exciton dynamics depending on donor–acceptor separation distances is essential for extracting their full potential. In this study, we investigated a long-range exciplex behavior between the electron donor of tris(4-carbazoyl-9-ylphenyl)amine (TCTA) and the electron acceptor of 2,4,6-tris[3-(diphenylphosphinyl)phenyl]-1,3,5-triazine (PO-T2T) by finely controlling their distance with 1,4-bis(triphenylsilyl)benzene (UGH-2) as a spacer layer. We report the characteristic exciplex photophysical kinetic behavior with time-dependent dynamics in terms of the donor–acceptor distance associated with the singlet–triplet energy gap and activation energy variation.

DOI： 10.1016/j.cplett.2024.141390

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担当区分：責任著者   掲載種別：研究論文（学術雑誌）   出版者・発行元：Solar RRL  

Halide perovskites are promising as the light absorbers of solar cells with efficient solar power conversion. However, why the degradation of perovskite solar cells (PSCs), especially at high temperatures, happens has not been completely understood to date. Herein, it is shown that evaporation of 4-tert-butylpyridine (4-tBP) from the hole transport layer (HTL) of 2,2',7,7'-tetrakis(N,N-di-p-methoxyphenylamino)-9,9'-spirobifluorene (spiro-OMeTAD) is one of possible degradation mechanisms in PSCs at a high temperature of 85 °C. In fresh PSCs, the chemical doping of the spiro-OMeTAD HTL with lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) is not so efficient because of the formation of a LiTFSI:4-tBP complex in the HTL. When PSCs are placed at 85 °C, 4-tBP gradually evaporates from the HTL, resulting in the dissociation of the LiTFSI:4-tBP complex. This 4-tBP evaporation enhances the chemical doping of spiro-OMeTAD by LiTFSI and makes the hole transport level of the spiro-OMeTAD HTL deeper, thereby impeding hole extraction at the perovskite/spiro-OMeTAD/Au interfaces. Herein, the 4-tBP evaporation by covering PSCs with a fluoro-polymer CYTOP layer, significantly improving the high-temperature durability of PSCs, is suppressed. The basic understanding obtained in this study would help promote the spread of more thermally durable PSC products in the future.

DOI： 10.1002/solr.202400342

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その他リンク： https://onlinelibrary.wiley.com/doi/pdf/10.1002/solr.202400342

担当区分：責任著者   記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Nature Communications  

The orientation of a permanent dipole moment during vacuum deposition results in the occurrence of spontaneous orientation polarization (SOP). Previous studies reported that the presence of SOP in organic light-emitting diodes (OLEDs) lowers electroluminescence efficiency because electrically generated excitons are seriously quenched by SOP-induced accumulated charges. Thus, the SOP in a host:guest-based emission layer (EML) should be finely controlled. In this study, we demonstrate the positive effect of dipole-dipole interactions between polar host and polar emitter molecules on the OLED performance. We found that a small-sized polar host molecule that possesses both high molecular diffusivities and moderate permanent dipole moment, well cancels out the polarization formed by the SOP of the emitter molecules in the EML without a disturbance of the emitter molecules’ intrinsic orientation, leading to high-performance of OLEDs. Our molecular design strategy will allow emitter molecules to pull out the full potential of the EMLs in OLEDs.

DOI： 10.1038/s41467-024-50326-9

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その他リンク： https://www.nature.com/articles/s41467-024-50326-9

担当区分：責任著者   掲載種別：研究論文（学術雑誌）   出版者・発行元：Advanced Optical Materials  

Near-infrared organic light-emitting diodes (NIR-OLEDs) possess substantial potential for future valuable applications, such as a light source for sensing applications. However, the low photoluminescence quantum yield (PLQY) of NIR-emitting molecules represents a significant impediment to these applications. In this study, the impact of the deuteration of both of host (mCP-d20: 1,3-Dicarbazole-benzene-d20) and guest (BBT-TPA-d28: 4,8-bis[4-(N,N-diphenylamino)phenyl]benzo[1,2-c:4,5-c']bis[1,2,5]thiadiazole-d28) on NIR PL properties in the host–guest codeposited film is reported. The 1 wt%-BBT-TPA-d28:mCP-d20 codeposited film exhibited PLQY of 15 ± 2% with an emission peak wavelength at ≈900 nm, which is about three times higher than that of the film composed of undeuterated molecules. Importantly, the deuteration of only the host or guest does not yield the PLQY up to 15%, underlining the importance of the deuteration of both host and guest molecules in suppressing nonradiative decay processes. The NIR-OLED with the deuterated codeposited film as an emissive layer demonstrates a maximum external electroluminescence quantum efficiency of 2.3 ± 0.2%.

DOI： 10.1002/adom.202400932

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担当区分：責任著者   記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Advanced Materials  

Hexacarbazolylbenzene (6CzPh), which is benzene substituted by six carbazole rings, is a simple and attractive compound. Despite the success of a wide variety of carbazole derivatives in organic light-emitting diodes (OLEDs), 6CzPh has not received attention so far. Here, excellent performances of 6CzPh are revealed as a host material in OLEDs regarding conventional host materials. Various strategies are implemented to improve the performance of OLEDs, e.g., triplet utilization by thermally activated delayed fluorescence (TADF) and phosphorescence emitters for maximizing internal quantum efficiency, and molecular orientation control for increasing outcoupling efficiency. The present host material is suited for both criteria. Robustness of the structure and sufficiently high triplet energy enables a high external quantum efficiency with a long device lifetime. Besides, the host material boosts the horizontal molecular orientations of several guest emitters. It is noteworthy that disk-shaped 4CzIPN marks the complete horizontal molecular orientations (Θh = 100%, S = −0.50). These results provide an effective way of improving efficiencies without sacrificing device durability for future OLEDs.

DOI： 10.1002/adma.202402275

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担当区分：責任著者   記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：ACS Nano  

The spatial distribution and electronic properties of the frontier molecular orbitals (FMOs) in a thermally activated delayed fluorescence (TADF) molecule contribute significantly to the TADF properties, and thus, a detailed understanding and sophisticated control of the FMOs are fundamental to the design of TADF molecules. However, for multiple-resonance (MR)-TADF molecules that achieve spatial separation of FMOs by the MR effect, the distinctive distribution of these molecular orbitals poses significant challenges for conventional computational analysis and ensemble averaging methods to elucidate the FMOs’ separation and the precise mechanism of luminescence. Therefore, the visualization and analysis of electronic states with the specific energy level of a single MR-TADF molecule will provide a deeper understanding of the TADF mechanism. Here, scanning tunneling microscopy/spectroscopy (STM/STS) was used to investigate the electronic states of the DABNA-1 molecule at the atomic scale. FMOs’ visualization and local density of states analysis of the DABNA-1 molecule clearly show that MR-TADF molecules also have well-separated FMOs according to the internal heteroatom arrangement, providing insights that complement existing theoretical prediction methods.

DOI： 10.1021/acsnano.4c04813

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担当区分：責任著者   掲載種別：研究論文（学術雑誌）   出版者・発行元：Journal of Physical Chemistry C  

In recent years, halide perovskite materials have made significant progress in optically pumped lasing. Among many reported perovskites, 1-naphthylmethylamine (NMA)-based quasi-two-dimensional (quasi-2D) perovskite films are promising as a gain medium for low-threshold optical lasing. However, their optical laser thresholds are still high for the realization of electrically pumped lasing. To explore the possibility of reducing the thresholds, we investigate temperature-dependent laser characteristics of NMA-based quasi-2D perovskite films fabricated on top of a circularly shaped distributed feedback resonator. Although the laser threshold of these films is already low (∼2 μJ cm-2) at room temperature (298 K), their threshold is further reduced by ∼1/200 to ∼0.01 μJ cm-2 as the film temperatures go down to 73 K. From the optical threshold at 73 K, the threshold current density required for the electrical lasing is estimated at a very low value of ∼3.4 A cm-2. However, the optical laser threshold and estimated current threshold are, respectively, increased to ∼6 μJ cm-2 and ∼2.04 kA cm-2 because of the presence of an optical loss in actual devices with a metal electrode. Therefore, future optimization of device architectures to reduce the optical loss is crucial to realizing the electrical lasing.

DOI： 10.1021/acs.jpcc.4c01763

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担当区分：責任著者   記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Journal of the American Chemical Society  

Efficient red-green-blue primary luminescence with an extraordinarily narrow band and durability is crucial for advanced display applications. Recently, the emergence of multiple-resonance (MR) from short-range atomic interactions has been shown to induce extremely narrow spectral widths in pure organic emitters. However, achieving wide-range color tuning without compromising color purity remains a persistent challenge for MR emitters. Herein, the concept of electronic donor/acceptor “core-shell” modulation is proposed within a boron/nitrogen (B/N) MR skeleton, enabling the rational utilization of intramolecular charge transfer to facilitate wavelength shift. The dense B atoms localized at the center of the molecule effectively compress the electron density and stabilize the lowest unoccupied molecular orbital wave function. This electron-withdrawing core is embedded with peripheral electron-donating atoms. Consequently, doping a single B atom into a deep-blue MR framework led to a profound bathochromic shift from 447 to 624 nm (∼0.8 eV) while maintaining a narrow spectral width of 0.10 eV in this pure-red emitter. Notably, organic light-emitting diodes assisted by thermally activated delayed fluorescence molecules achieved superb electroluminescent stability, with an LT99 (99% of the initial luminance) exceeding 400 h at an initial luminance of 1000 cd m-2, approaching commercial-level performance without the assistance of phosphors.

DOI： 10.1021/jacs.4c02598

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担当区分：責任著者   記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：ACS Applied Materials and Interfaces  

The spontaneous orientation polarization (SOP) of a permanent dipole moment of the molecule induces a giant surface potential (GSP) in an organic semiconductor film, and GSP is expected to be a crucial parameter for understanding the operational mechanism of organic light-emitting diodes (OLEDs). This study demonstrates that the voltage-dependent migration of a carrier recombination zone induced by a polar electron transporting layer (ETL) having a positive SOP causes a decline in the overall performance of the OLED in triplet-triplet upconversion (TTU) based on OLEDs. Specifically, the TTU efficiency in an OLED with 2,2′,2″-(1,3,5-benzinetriyl)-tris(1-phenyl-1-H-benzimidazole) (TPBi) as the ETL decreased by 20% due to the reduction of electrically generated triplet exciton density. This decrease resulted in a lower external electroluminescence (EL) quantum efficiency (EQE) of 5.4% at 1 mA cm-2, while the OLED with a nonpolar ETL resulted in an EQE of around 8.1% at 1 mA cm-2. We confirmed a shift in the recombination zone from the current density dependence of the EL spectra in the OLEDs. Our results indicate that the fixed carrier recombination zone near a hole transport layer and an emitting layer (HTL/EML) strongly enhanced the TTU process, while the polar EML/ETL interface induced the migration of the recombination zone depending on voltage, resulting in the decrease of triplet exciton density.

DOI： 10.1021/acsami.4c02821

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担当区分：責任著者   記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Advanced Materials  

Narrowband emissive multiresonant thermally activated delayed fluorescence (MR-TADF) emitters are a promising solution to achieve the current industry-targeted color standard, Rec. BT.2020-2, for blue color without using optical filters, aiming for high-efficiency organic light-emitting diodes (OLEDs). However, their long triplet lifetimes, largely affected by their slow reverse intersystem crossing rates, adversely affect device stability. In this study, a helical MR-TADF emitter (f-DOABNA) is designed and synthesized. Owing to its π-delocalized structure, f-DOABNA possesses a small singlet-triplet gap, ΔEST, and displays simultaneously an exceptionally faster reverse intersystem crossing rate constant, kRISC, of up to 2 × 106 s−1 and a very high photoluminescence quantum yield, ΦPL, of over 90% in both solution and doped films. The OLED with f-DOABNA as the emitter achieved a narrow deep-blue emission at 445 nm (full width at half-maximum of 24 nm) associated with Commission Internationale de l'Éclairage (CIE) coordinates of (0.150, 0.041), and showed a high maximum external quantum efficiency, EQEmax, of ≈20%.

DOI： 10.1002/adma.202402289

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担当区分：責任著者   記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Nature Communications  

Manipulating dynamic behaviours of charge carriers and excitons in organic light-emitting diodes (OLEDs) is essential to simultaneously achieve high colour purity and superior operational lifetime. In this work, a comprehensive transient electroluminescence investigation reveals that incorporating a thermally activated delayed fluorescence assistant molecule with a deep lowest unoccupied molecular orbital into a bipolar host matrix effectively traps the injected electrons. Meanwhile, the behaviours of hole injection and transport are still dominantly governed by host molecules. Thus, the recombination zone notably shifts toward the interface between the emissive layer (EML) and the electron-transporting layer (ETL). To mitigate the interfacial carrier accumulation and exciton quenching, this bipolar host matrix could serve as a non-barrier functional spacer between EML/ETL, enabling the distribution of recombination zone away from this interface. Consequently, the optimized OLED exhibits a low driving voltage, promising device stability (95% of the initial luminance of 1000 cd m−2, LT95 > 430 h), and a high Commission Internationale de L’Éclairage y coordinate of 0.69. This indicates that managing the excitons through rational energy level alignment holds the potential for simultaneously satisfying Rec.2020 standard and achieving commercial-level stability.

DOI： 10.1038/s41467-024-48659-6

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その他リンク： https://www.nature.com/articles/s41467-024-48659-6

担当区分：責任著者   記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Science  

Contemporary materials discovery requires intricate sequences of synthesis, formulation, and characterization that often span multiple locations with specialized expertise or instrumentation. To accelerate these workflows, we present a cloud-based strategy that enabled delocalized and asynchronous design-make-test-analyze cycles. We showcased this approach through the exploration of molecular gain materials for organic solid-state lasers as a frontier application in molecular optoelectronics. Distributed robotic synthesis and in-line property characterization, orchestrated by a cloud-based artificial intelligence experiment planner, resulted in the discovery of 21 new state-of-the-art materials. Gram-scale synthesis ultimately allowed for the verification of best-in-class stimulated emission in a thin-film device. Demonstrating the asynchronous integration of five laboratories across the globe, this workflow provides a blueprint for delocalizing-and democratizing-scientific discovery.

DOI： 10.1126/science.adk9227

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出版者・発行元：Nature Photonics  

Perovskite light-emitting diodes (LEDs) show promises for next-generation displays owing to their excellent luminescent properties and low cost. Despite substantial progress with green- and red-emitting devices, the development of efficient blue perovskite LEDs has lagged behind. Here we demonstrate efficient blue perovskite LEDs based on a mixed two-dimensional–three-dimensional perovskite and a multifunctional ionic additive that enables control over the reduced-dimensional phases, non-radiative recombination channels and spectral stability. We report a series of devices that emit efficient electroluminescence from mixed bromide/chloride quasi-three-dimensional regions, with external quantum efficiencies of up to 21.4% (at a luminance of 22 cd m–2 and emission peak at 483 nm), 13.2% (at a luminance of 2.0 cd m–2 and emission peak at 474 nm) and 7.3% (at a luminance of 6 cd m–2 and emission peak at 464 nm). Devices show a nearly 30-fold increase in operational stability compared with control LEDs, with a half-lifetime of 129 min at an initial luminance of 100 cd m–2. Our findings demonstrate the performance of blue perovskite LEDs close to that of state-of-the-art blue organic LEDs and inorganic quantum dot LEDs and provide a new approach to design multifunctional molecules to boost the performance of perovskite optoelectronic devices.

DOI： 10.1038/s41566-024-01382-6

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担当区分：責任著者   掲載種別：研究論文（学術雑誌）   出版者・発行元：Journal of Materials Chemistry C  

A bio-tissue-inspired random laser (RL) has been successfully demonstrated using a dye-covered silk fibroin replica film (DC-SFRF) fabricated through soft lithography of a cicada's wing. Thanks to the increased light scattering between the nanopapillate structures of the DC-SFRF, the RL exhibits a lower lasing threshold, higher slope efficiency, and broader angular emission compared to those of the dye-covered silk fibroin film (DC-SFF). The low spatial coherence NIR RL can also serve as a suitable light source in bio-diagnosis to generate a low speckle noise image with a contrast of approximately 0.040. By employing flexible PET as a substrate, we have demonstrated the flexibility of the near-infrared random laser (NIR RL) through the application of mechanical stress to alter the distribution of nanopapillate structures on the surface of the replica film. As the curvature increases, the DC-SFRF RL exhibits a blue shift of 13.3 nm in the emission spectrum and a further reduction in the speckle contrast to 0.031.

DOI： 10.1039/d3tc03576j

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担当区分：責任著者   記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Nature Communications  

To fulfill ultra-high-definition display, efficient and bright green organic light-emitting diodes with Commission Internationale de l’Éclairage y-coordinate ≥ 0.7 are required. Although there are some preceding reports of highly efficient devices based on pure-green multi-resonance emitters, the efficiency rolloff and device stabilities for those pure-green devices are still unsatisfactory. Herein, we report the rational design of two pure-green multi-resonance emitters for achieving highly stable and efficient pure-green devices with CIEx,ys that are close to the NTSC and BT. 2020 standards. In this study, our thermally activated delayed fluorescence OLEDs based on two pure-green multi-resonance emitters result in CIEy up to 0.74. In hyperfluorescent device architecture, the CIExs further meet the x-coordinate requirements, i.e., NTSC (0.21) and BT. 2020 (0.17), while keeping their CIEys ~ 0.7. Most importantly, hyperfluorescent devices display the high maximum external quantum efficiencies of over 25% and maximum luminance of over 105 cd m−2 with suppressed rolloffs (external quantum efficiency of ~20% at 104 cd m−2) and long device stabilities with LT95s of ~ 600 h.

DOI： 10.1038/s41467-024-47482-3

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その他リンク： https://www.nature.com/articles/s41467-024-47482-3

担当区分：責任著者   掲載種別：研究論文（学術雑誌）   出版者・発行元：Solar RRL  

Perovskite solar cells (PSCs) have undergone an unprecedentedly rapid development in both power conversion efficiency (PCE) and operational durability. However, a number of unknown challenges remain before PSC products are ready to launch. Herein, it is demonstrated that the vacuum deposition of gold (Au) onto the organic hole-transport layer (HTL) results in Au penetration into the perovskite layer. This Au penetration proves to be a limiting factor in PCE due to detrimental carrier recombination caused by the penetrated Au component inside the perovskite light absorber. To mitigate this issue, a thin molybdenum oxide (MoOx) interlayer between the organic HTL and the Au electrode is introduced, effectively reducing the Au penetration and suppressing the carrier recombination. Consequently, this MoOx introduction increases PCEs from ≈16.9% to ≈19.6% by ≈2.7%. Furthermore, using the MoOx interlayer improves the long-term durability of PSCs. These findings are crucial in elucidating a basic mechanism that limits PCE and in advancing the fabrication of PSC products with even higher performance.

DOI： 10.1002/solr.202400029

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担当区分：責任著者   掲載種別：研究論文（学術雑誌）   出版者・発行元：Chemistry Letters  

In recent decades, various types of aryl-substituted 1,3,5-triazine derivatives have been applied in many research fields, including biomedical chemistry, non-linear optics, and organic electronics. However, the substituent scope for 4,6-diaryl-1,3,5-triazines (DAr-TRZs) remains limited. Here, we present our work on the synthesis of 2-amino- and 2-bromo-DAr-TRZ derivatives bearing electron-withdrawing groups on the aryl rings. Our synthetic methods successfully provided trifluoromethyl-, nitrile-, and nitro-substituted DAr-TRZs. These will expand the structural diversity of conventional triazine-based functional materials.

DOI： 10.1093/chemle/upae059

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その他リンク： https://academic.oup.com/chemlett/article-pdf/53/4/upae059/57335721/upae059.pdf

記述言語：その他   掲載種別：研究論文（学術雑誌）  

Abstract

Despite significant progress made over the past decade in thermally activated delayed fluorescence (TADF) molecules as a material paradigm for enhancing the performance of organic light-emitting diodes, the underlying spin-flip mechanism in these charge-transfer (CT)-type molecular systems remains an enigma, even since its initial report in 2012. While the initial and final electronic states involved in spin-flip between the lowest singlet and lowest triplet excited states are well understood, the exact dynamic processes and the role of intermediate high-lying triplet (T) states are still not fully comprehended. In this context, we propose a comprehensive model to describe the spin-flip processes applicable for a typical CT-type molecule, revealing the origin of the high-lying T state in a partial molecular framework in CT-type molecules. This work provides experimental and theoretical insights into the understanding of intersystem crossing for CT-type molecules, facilitating more precise control over spin-flip rates and thus advancing toward developing the next-generation platform for purely organic luminescent candidates.

DOI： 10.1038/s41467-024-46406-5

記述言語：英語   出版者・発行元：Chemical Communications  

Herein, we report the first example of chiral donor-acceptor cage DA-2 displaying efficient circularly polarized thermally activated delayed fluorescence (CP-TADF) with |glum| values up to 2.1 × 10−3 and PLQY of 32%. A small ΔEST of 0.051 eV and quasi-parallel (θ = 6°) transition electric and magnetic dipole moments were realized from the through-space charge transfer interaction between the parallelly aligned donor and acceptor in DA-2. This D-A cage configuration has provided a novel design strategy for discovering potential efficient CP-TADF emitters.

DOI： 10.1039/d3cc05136f

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記述言語：その他   掲載種別：研究論文（学術雑誌）  

Organic light-emitting diodes (OLEDs) that efficiently emit near-infrared (NIR) light and consume little power will create valuable applications for OLEDs beyond just displays. Here, we report such a NIR-OLED with high operational stability that can be used as a light source for three-dimensional sensing of object’s surfaces. Using a narrow-energy-gap material as a host for producing NIR hyperfluorescence system, we fabricated a NIR-OLED exhibiting intense emission at 930 nm with a high external electroluminescence quantum efficiency of more than 1% at a current density of 100 milliamperes per square meter without any degradation even after more than 300 hours of operation. The NIR-OLEDs were integrated with dense complementary metal-oxide semiconductor circuits to make a micro-NIR-OLED projector (0.21 inch, 230,400 pixels). By actively driving the projector on a pixel by pixel and projecting their emission onto objects, we successfully scanned and sensed the surfaces in three dimensions with invisible NIR.

DOI： 10.1126/sciadv.adj6583

記述言語：その他   掲載種別：研究論文（学術雑誌）  

Abstract

Advanced organoboron dyes, incorporating tetra‐boron difluoride (tetra‐BF₂) moieties, are developed, demonstrating efficient electrochemiluminescence (ECL) emissions in the green to orange regions through direct ion annihilation. By introducing diverse alkyl modifications in the molecules, luminescence color tuning is achieved via alterations in conjugation and bending angle. A photoluminescence quantum yield of 100% in dilute solutions is successfully achieved. Notably, the introduction of alkyl groups to the methine side stabilizes the radical ionic state, resulting in a high ECL efficiency of 74% through an efficient radical‐ion annihilation pathway. The key factor is that the energy of the annihilation reaction exceeds the S₁ energy required for luminescence. Spin density calculations further elucidate the substituent effects on the radical ions of complexes. Moreover, the lasing properties of these materials in the solution‐processed blend films are investigated, revealing a low amplified spontaneous emission (ASE) threshold (E_th) of 6.40 ± 0.24 µJ cm⁻², which is notably lower among organic laser materials. This is attributed to their large Stokes shifts and high quantum yield. The excellent ECL and ASE performances establish these materials as a valuable addition to the existing library of organoboron dyes, offering fresh insights into the development of organic solid‐state lasers.

DOI： 10.1002/adom.202302803

記述言語：その他   掲載種別：研究論文（学術雑誌）  

Abstract

Organic light-emitting diodes (OLEDs) exploiting simple binary emissive layers (EMLs) blending only emitters and hosts have natural advantages in low-cost commercialization. However, previously reported OLEDs based on binary EMLs hardly simultaneously achieved desired comprehensive performances, e.g., high efficiency, low efficiency roll-off, narrow emission bands, and high operation stability. Here, we report a molecular-design strategy. Such a strategy leads to a fast reverse intersystem crossing rate in our designed emitter h-BNCO-1 of 1.79×10⁵ s⁻¹. An OLED exploiting a binary EML with h-BNCO-1 achieves ultrapure emission, a maximum external quantum efficiency of over 40% and a mild roll-off of 14% at 1000 cd·m⁻². Moreover, h-BNCO-1 also exhibits promising operational stability in an alternative OLED exploiting a compact binary EML (the lifetime reaching 95% of the initial luminance at 1000 cd m⁻² is ~ 137 h). Here, our work has thus provided a molecular-design strategy for OLEDs with promising comprehensive performance.

DOI： 10.1038/s41467-024-44981-1

記述言語：その他   掲載種別：研究論文（学術雑誌）  

Abstract

Although thermally activated delayed fluorescence (TADF) based organic light‐emitting diodes (OLEDs) continue to achieve high efficiencies, their device stability still does not necessarily meet industrial standards. To improve device stability, careful design of a stable host material is crucial. Herein, with reference to a common p‐type host material, 3,3′‐di(9H‐carbazol‐9‐yl)‐1,1′‐biphenyl (mCBP), three novel host materials based on a pyridine unit, mCBP‐1N, CzPyPhCz, and CzPyBF, are systematically designed to improve the stabilities efficiently. The green and blue TADF OLEDs are fabricated with these three new hosts. The maximum external quantum efficiencies (EQE_maxs) of green OLEDs are 20.3 % and 14.0% for CzPyBF and mCBP hosts, respectively. Further, high EQEs of 19.2% and 12.9% are maintained even at 1000 cd m⁻². Most importantly, the device lifetime of the CzPyBF host can achieve LT₉₅ of 62.7 h, which is 2.5 times longer than that of mCBP. Also, lower turn‐on voltages are achieved by using CzPyPhCz in blue and green devices. With host engineering, the TADF OLEDs are simultaneously improved with lower turn‐on voltages, higher EQEs, and longer device lifetimes.

DOI： 10.1002/adom.202302971

記述言語：その他   掲載種別：研究論文（学術雑誌）  

DOI： 10.1021/acs.jpcc.3c06330

DOI： 10.1002/adom.202470007

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記述言語：その他   掲載種別：研究論文（学術雑誌）   出版者・発行元：Journal of Materials Chemistry C  

Optically generated carriers are pinned at the organic/organic interface if the two organic layers have a large polarization difference, underlining that the combination of polar molecules is crucial to extend the carrier lifetime.

DOI： 10.1039/d3tc03979j

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記述言語：その他   掲載種別：研究論文（学術雑誌）  

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.

DOI： 10.1002/anie.202315210

記述言語：その他   掲載種別：研究論文（学術雑誌）  

DOI： 10.1016/j.cplett.2023.140915

記述言語：その他   掲載種別：研究論文（学術雑誌）  

9-[1,4]Benzoxaborino[2,3,4-kl]phenoxaborine-7-yl-1,3,6,8-tetramethyl-9H-carbazole, a donor–acceptor linked TADF molecule with a very short delay lifetime of 750 ns, exhibits a peculiar thermal behavior similar to that of negative gap materials.

DOI： 10.1039/d3fd00151b

記述言語：その他   掲載種別：研究論文（学術雑誌）  

DOI： 10.1021/acs.jpcc.3c06465

記述言語：その他   掲載種別：研究論文（学術雑誌）  

The effect of excited-state intramolecular proton-transfer (ESIPT) laser material rigidity on photophysical properties and amplified spontaneous emission (ASE) thresholds (EASEth) is studied.

DOI： 10.1039/d3tc02707d

記述言語：その他   掲載種別：研究論文（学術雑誌）  

In this work, we demonstrate that the permeability of a SiNx thin film (prepared by plasma-enhanced chemical vapor deposition) to water and oxygen is closely related to the deposition pressure. By dynamic secondary ion mass spectrometry, we confirmed that water penetration occurs into the SiNx film only in the oxidized layer. Furthermore, positron annihilation lifetime spectroscopy indicated that a SiNx film with a lower deposition pressure provides a smaller pore (free volume hole) radius, which is more effective in terms of blocking ambient molecular diffusion or penetration. The SiNx films were also applied as an encapsulation layer for organic light-emitting diodes; SiNx films with a lower deposition pressure exhibited higher encapsulation properties.

DOI： 10.1116/6.0003050

記述言語：その他   掲載種別：研究論文（学術雑誌）  

Abstract

It is well known that triplet–triplet annihilation upconversion (TTU) can enhance electroluminescence (EL) efficiency by converting two low‐energy triplet excitons into one high‐energy singlet exciton. However, conventional intermolecular TTU requires high doping concentration to activate, limiting device architecture. Here, six dimer molecules comprised of two anthracene units connected by a spacer unit are investigated, which have a possibility of the intramolecular TTU process. As a result, two dimer molecules show high TTU efficiencies close to the theoretical maximum even in dispersed, diluted conditions. By comparing these molecular conformations, a correlation is found between the dimer structures of two anthracene units and the TTU activity in the diluted condition, i.e., the 3D molecular structure with the exciton utilizing efficiency.

DOI： 10.1002/adom.202301924

記述言語：その他   掲載種別：研究論文（学術雑誌）  

<p lang="en"><p>Hybrid Locally-excited and Charge-Transfer (HLCT) materials have garnered significant attention for their high exciton utilization efficiency in organic light-emitting diodes (OLEDs). However, conventional HLCT materials suffer from broad emission, which limits their applications. In this study, we report a narrowband HLCT emitter, namely 10-(dimesitylboranyl)-8,8,12,12-tetraphenyl-8,12-dihydrobenzo[9,1]quinolizino[3,4,5,6,7-klmn]phenoxazine (PXZ-DL), incorporated by double-locked intramolecular connection. PXZ-DL exhibits a narrow emission spectrum with a small full width at half-maximum (FWHM) of 35 nm and 47 nm in solution and as an OLED emitter, respectively. Moreover, PXZ-DL demonstrates a high photoluminescence quantum yield of 100&#37; and an external quantum efficiency of 8.0&#37;. Additionally, PXZ-DL demonstrates excellent performance in amplified spontaneous emission with a low threshold of 5.7 ��J cm^-2 and a narrow FWHM of 11 nm. The intramolecular lock strategy offers a promising approach for the development of HLCT materials with high color purity.</p></p>

DOI： 10.59717/j.xinn-mater.2023.100026

記述言語：その他   掲載種別：研究論文（学術雑誌）  

DOI： 10.1016/j.cej.2023.144516

記述言語：その他   掲載種別：研究論文（学術雑誌）  

Abstract

Photon‐upconversion in organic molecular systems is one of the promising technologies for future energy harvesting systems because these systems can generate excitons that possess higher energy than excitation energy. The photon‐upconversion caused by absorbing ambient heat as additional energy is particularly interesting because it could ideally provide a light‐driving cooling system. However, only a few organic molecular systems have been reported. Here, we report the anti‐Stokes photoluminescence (ASPL) derived from hot‐band absorption in a series of multi‐resonance‐type thermally‐activated delayed fluorescence (MR‐TADF) molecules. The MR‐TADF molecules exhibited an anti‐Stokes shift of approximately 0.1 eV with a high PL quantum yield in the solution state. The anti‐Stokes shift corresponded well to the 1–0 vibration transition from the ground state to the excited singlet state, and we further evaluated a correlation between the activation energy for the ASPL intensity and the TADF process. Our demonstration underlines that MR‐TADF molecules have become a novel class of ASPL materials for various future applications, such as light‐driving cooling systems.

DOI： 10.1002/anie.202312326

記述言語：その他   掲載種別：研究論文（学術雑誌）  

DOI： 10.1021/acsmaterialslett.3c00509

記述言語：その他   掲載種別：研究論文（学術雑誌）  

Abstract

Films of the quasi‐2D perovskite based on 1‐naphthylmethylamine (NMA) are promising as the gain medium for optically pumped lasing and future electrically pumped lasing because of its low lasing threshold and small electroluminescence efficiency rolloff. However, reasons for the low threshold and small efficiency rolloff are still unclear. Therefore, exciton dynamics are investigated in NMA‐based quasi‐2D perovskite films. It is found that quenching of bright excitons by other excitons or charge carriers is unlikely in NMA‐based quasi‐2D perovskite films, which is one reason for the low lasing threshold and small efficiency rolloff. Moreover, thermally stimulated current measurements reveal that the defect levels inside the band gap of the NMA‐based quasi‐2D perovskite are shallow, with a depth of ≈0.3 eV, causing a decrease in nonradiative exciton recombination through the defects. Therefore, population inversion can be easily achieved, leading to the low lasing threshold as well. For fabrication of NMA‐based quasi‐2D perovskite laser devices with even lower lasing thresholds, a circular‐shaped optical resonator, and small‐molecule‐based defect passivation are used. Optically pumped lasing can be obtained from these devices, with a threshold of ≈1 µJ cm⁻², which is one of the lowest values ever reported in any perovskite lasers.

DOI： 10.1002/adfm.202301794

記述言語：英語   出版者・発行元：Journal of Physical Chemistry Letters  

Reverse intersystem crossing (RISC) in purely organic molecules has become an attractive research topic since the demonstration of high efficiencies in organic light-emitting diodes using thermally activated delayed fluorescence (TADF). Although the intermolecular interactions have a significant impact on the exciton dynamics, it is generally difficult to identify the quantitative relationship associated with a specific factor. In this work, we used a clathrate crystal with TADF and H2O molecules to evaluate the effect of hydrogen bonding while maintaining molecular conformations and other intermolecular interactions. The hydrogen bonding shifted the charge transfer excited states to lower energies, resulting in superior TADF properties. Although the increase in the RISC rate is considered to enhance the stabilities of TADF molecules, photostability analysis revealed nearly the same degradation speed despite the 3 times faster RISC rate.

DOI： 10.1021/acs.jpclett.3c00915

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記述言語：その他   掲載種別：研究論文（学術雑誌）  

After remarkable progress over the past decades, perovskite solar cells (PSCs) currently exhibit efficient solar power conversion efficiency. However, the environmental instability of perovskite materials and devices is still a serious issue, impeding the future commercialization of this technology. Herein, why PSCs degrade in air is investigated and it is found that one of the critical reasons for the air‐induced PSC degradation is the doping of the 2,2′,7,7′‐tetrakis(N,N‐di‐p‐methoxyphenylamine)‐9,9′‐spirobi‐fluorene (spiro‐OMeTAD) hole‐transport layer with oxygen. Photoelectron yield spectroscopy reveals that the hole‐transport level of the spiro‐OMeTAD layer becomes deeper by oxygen doping, increasing an energy barrier for hole extraction. In other words, decreased hole extraction at the perovskite/spiro‐OMeTAD interface induces the degradation of PSCs in air. However, this oxygen‐induced degradation of PSCs is reversible to some extent by storing PSCs in a vacuum to remove oxygen. In contrast, no detectable degradation of the perovskite light absorber is observed after ≈600 h of air exposure from the results of morphological and structural characterizations. These aspects provide a deeper understanding of PSCs degradation, giving insight into improving long‐term durability in air in the future.

DOI： 10.1002/solr.202300127

記述言語：その他   掲載種別：研究論文（学術雑誌）   出版者・発行元：Scientific Reports  

Abstract

A considerable variety of donor–acceptor (D–A) combinations offers the potential for realizing highly efficient thermally activated delayed fluorescence (TADF) materials. Multiple D–A type compounds are one of the promising families of TADF materials in terms of stability as well as efficiencies. However, those emitters are always composed of carbazole-based donors despite a wide choice of moieties used in linearly linked single D–A molecules. Herein, we developed a multiple D–A type TADF compound with two distinct donor units of 9,10-dihydro-9,9-dimethylacridine (DMAC) and carbazole as the hetero-donor design. The new emitter exhibits high photoluminescence quantum yield (PLQY) in various conditions including polar media blend and high concentrations. Organic light-emitting diodes (OLEDs) showed a reasonably high external quantum efficiency (EQE). In addition, we revealed that the multiple-D–A type molecules showed better photostability than the single D–A type molecules, while the operational stability in OLEDs involves dominant other factors.

DOI： 10.1038/s41598-023-34623-9

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その他リンク： https://www.nature.com/articles/s41598-023-34623-9

記述言語：その他   掲載種別：研究論文（学術雑誌）  

DOI： 10.1002/adma.202211873

記述言語：その他   掲載種別：研究論文（学術雑誌）  

N,N-di(4-methoxyphenyl)amino-9,9′-spirobifluorene (spiro-OMeTAD) is a widely used hole transport layer (HTL) material for emerging lead halide hybrid perovskite solar cells (PSCs). Finding alternative HTL materials is required for the future development of more efficient and stable PSCs. Here, we developed a new HTL material of N2,N2,N,7N7-tetrakis(4-methoxyphenyl)benzo[b]benzo[4,5]thieno[2,3-d]thiophene-2,7-diamine (TBTD). Chemically doped TBTD provided better hole extraction in PSCs than chemically doped spiro-OMeTAD due to higher electrical conductivity and a more suitable hole transport energy level. Thus, PSCs with the TBTD HTL showed higher power conversion efficiency (∼21&#37;) than spiro-OMeTAD HTL (∼19&#37;). The operational stability of TBTD-based PSCs was similar to that of spiro-OMeTAD-based PSCs. The findings discussed in this study will aid in the future development of high-performance PSCs.

DOI： 10.1063/5.0150066

記述言語：その他   掲載種別：研究論文（学術雑誌）  

DOI： 10.1021/acsami.3c02855

記述言語：その他   掲載種別：研究論文（学術雑誌）  

Highly efficient light harvesting of a Eu(iii) complex in a host–guest film by triplet sensitization
Very high photoluminescence intensity of a Eu(iii) complex is achieved using a host–guest system. The intensity is 400 times larger than that of the Eu(iii) complex itself.

DOI： 10.1039/D3SC01817B

記述言語：その他   掲載種別：研究論文（学術雑誌）  

Two newly developed carboynyl-based multi-resonant TADF show bright green-yellow emission. These were used as emitters in both OLEDs, and LECs.

DOI： 10.1039/d3tc00641g

記述言語：その他   掲載種別：研究論文（学術雑誌）  

DOI： 10.1021/acs.orglett.3c00848

記述言語：その他   掲載種別：研究論文（学術雑誌）  

DOI： 10.1021/acsmaterialslett.3c00310

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Journal of Physical Chemistry Letters  

Continuous-wave (CW) lasing in quasi-two-dimensional (2D) perovskite-based distributed feedback cavities has been achieved at room temperature; however, CW microcavity lasers comprising distributed Bragg reflectors (DBRs) have rarely been prepared using solution-processed quasi-2D perovskite films because the roughness of perovskite films significantly increases intersurface scattering loss in the microcavity. Herein, high-quality spin-coated quasi-2D perovskite gain films were prepared using an antisolvent to reduce roughness. The highly reflective top DBR mirrors were deposited via room-temperature e-beam evaporation to protect the perovskite gain layer. Lasing emission of the prepared quasi-2D perovskite microcavity lasers under CW optical pumping was clearly observed at room temperature, featuring a low threshold of ∼1.4 W cm-2 and beam divergence of ∼3.5°. It was concluded that these lasers originated from weakly coupled excitons. These results elucidate the importance of controlling the roughness of quasi-2D films to achieve CW lasing, thus facilitating the design of electrically pumped perovskite microcavity lasers.

DOI： 10.1021/acs.jpclett.3c00279

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記述言語：その他   掲載種別：研究論文（学術雑誌）  

DOI： 10.1002/adma.202211160

記述言語：その他   掲載種別：研究論文（学術雑誌）  

DOI： 10.1002/adom.202202734

記述言語：その他   掲載種別：研究論文（学術雑誌）  

DOI： 10.1002/slct.202300274

記述言語：その他   掲載種別：研究論文（学術雑誌）  

DOI： 10.1002/adom.202202666

記述言語：その他   掲載種別：研究論文（学術雑誌）  

DOI： 10.1038/s41566-022-01106-8

記述言語：その他   掲載種別：研究論文（学術雑誌）  

DOI： 10.1002/adma.202210335

記述言語：その他   掲載種別：研究論文（学術雑誌）  

DOI： 10.1002/anie.202217377

記述言語：その他   掲載種別：研究論文（学術雑誌）  

DOI： 10.1016/j.cplett.2022.140155

記述言語：その他   掲載種別：研究論文（学術雑誌）  

DOI： 10.1002/adma.202207070

記述言語：その他   掲載種別：研究論文（学術雑誌）  

The defects in the light-harvesting perovskite absorber layer play a key role in limiting power conversion efficiencies (PCEs) and long-term stability of lead halide perovskite solar cells (PSCs). Although organic ammonium halides have been used for defect passivation in high-performance PSCs, the stability issue is still a challenge. Herein, we develop a novel material of pyridine-carbazole (Py-Cz) to passivate defects via coordination bonding. With this passivation, the photoluminescence intensity of perovskite films was increased. In addition, the formation of under-coordinated Pb2+defects in perovskite films was reduced significantly, enabling high-performance and long-term stable PSCs. Three different sets of PSCs were constructed, namely, without passivation, with phenethylammonium iodide (PEAI) (commonly used for passivation), and with Py-Cz passivation. Remarkably, the PSCs fabricated using the Py-Cz passivation not only achieved PCEs of over 20&#37; but also retained 85&#37; of their initial performances over more than 5000 h. In contrast, the PSCs without or with PEAI passivation degraded quickly during the long-term operational stability test under light illumination. This method opens up a new opportunity to develop highly efficient and operationally stable PSCs.

DOI： 10.1021/acsaem.2c03364

記述言語：その他   掲載種別：研究論文（学術雑誌）  

DOI： 10.1021/jacs.2c10946

記述言語：その他   掲載種別：研究論文（学術雑誌）  

Trifluoromethylated thermally activated delayed fluorescent molecule 4[Cz(CF₃)₂]IPN has been demonstrated as a versatile photocatalyst that facilitates radical reactions via electron transfer and dearomative cycloaddition via energy transfer.

DOI： 10.1039/d2ob02055f

記述言語：その他   掲載種別：研究論文（学術雑誌）  

A low lasing threshold of up to 0.27 μJ cm⁻¹ was achieved by using TADF materials. Advanced light amplification architectures composed of dual DABNA derivatives were also demonstrated.

DOI： 10.1039/d2qm01040b

記述言語：その他   掲載種別：研究論文（学術雑誌）  

The control of laser emission angles in laser devices is essential for many optoelectronic and photonic applications such as optical sensing and displays. In this context, we studied the light diffraction pattern of laser beams in a one-dimensional sampled distributed feedback resonator having organic gain media. The gratings consist of the repetition of supercells having a mixed-order sampled grating in which 1st-order gratings surround a 2nd-order grating. The experimental results showed that the diffraction angles of the laser beams are quite diverse depending on the supercell structures. We demonstrate that the interval of the diffraction angle (θ) of the laser beams is inversely proportional to the length of the supercell experimentally and theoretically. By tuning the length of supercells as well as the length of 1st-order and 2nd-order regions, the interval θ was tuned from 0.1° to 43° with the different arc emission patterns. With the reduction of θ, i.e., the longer 1st-order region, a significant decrease in the laser threshold was obtained, resulting in the lowest lasing threshold of 2.5 ± 0.1  μJ/cm² with ∼3.5 ns of a long pulse width excitation source.

DOI： 10.1063/5.0123476

記述言語：その他   掲載種別：研究論文（学術雑誌）  

DOI： 10.1103/physrevapplied.18.054082

記述言語：その他   掲載種別：研究論文（学術雑誌）  

In this study, we developed two thermally activated delayed fluorescence (TADF) emitters, ICzCN and ICzCYP, to apply to organic light-emitting diodes (OLEDs). These emitters involve indolocarbazole (ICz) donor units and nicotinonitrile acceptor units with a twisted donor-acceptor-donor (D-A-D) structure for small singlet (S1) and triplet (T1) state energy gap (ΔEST) to enable efficient exciton transfer from the T1 to the S1 state. Depending on the position of the cyano-substituent, ICzCN has a symmetric structure by introducing donor units at the 3,5-position of isonicotinonitrile, and ICzCYP has an asymmetric structure by introducing donor units at the 2,6-position of nicotinonitrile. These emitters have different properties, such as the maximum luminance (Lmax) value. The Lmax of ICzCN reached over 10000 cd m−2. The external quantum efficiency (ηext) was 14.8&#37; for ICzCN and 14.9&#37; for ICzCYP, and both achieved a low turn-on voltage (Von) of less than 3.4 eV.

DOI： 10.3390/molecules27238274

記述言語：その他   掲載種別：研究論文（学術雑誌）  

DOI： 10.1021/acsenergylett.2c02471

記述言語：その他   掲載種別：研究論文（学術雑誌）  

DOI： 10.1246/cl.220304

記述言語：その他   掲載種別：研究論文（学術雑誌）  

There has been increasing interest in blue organic light-emitting diodes based on thermally activated delayed fluorescence (TADF). The construction of a fully optimized device architecture is crucial in accordance with developing high-performance materials because highly efficient electroluminescence cannot be realized without balancing both carrier injection and transport with decreasing several exciton loss processes. Thus, the detailed mechanism of carrier injection, transport, and recombination in emitting layers has to be clarified. In this study, various device architectures for a recently emerged blue TADF molecular system based on multiple donors and acceptors were systematically investigated, especially by focusing on the interlayers. This work also aims to offer guidelines for improving device stabilities. Our findings clarify the role of each layer, providing in-depth insight into device design and the selection of proper materials for each constituted layer.

DOI： 10.1063/5.0100373

記述言語：その他   掲載種別：研究論文（学術雑誌）   出版者・発行元：Chemical Communications  

The convenient melt-blending method for DSC measurement provides the reliable glass transition temperature (T_g) of the materials which are hard to measure by the standard DSC measurement, e.g., organic semiconductors.

DOI： 10.1039/d2cc01467j

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記述言語：その他   掲載種別：研究論文（学術雑誌）  

DOI： 10.1002/adom.202200704

記述言語：その他   掲載種別：研究論文（学術雑誌）  

We studied the photophysical and electroluminescent (EL) characteristics of a series of azaborine derivatives having a pair of boron and nitrogen aimed at the multi-resonance (MR) effect. The computational study with the STEOM-DLPNO-CCSD method clarified that the combination of a BN ring-fusion and a terminal carbazole enhanced the MR effect and spin-orbit coupling matrix element (SOCME), simultaneously. Also, we clarified that the second triplet excited state (T₂) plays an important role in efficient MR-based thermally activated delayed fluorescence (TADF). Furthermore, we obtained a blue–violet OLED with an external EL quantum efficiency (EQE) of 9.1&#37;, implying the presence of a pronounced nonradiative decay path from the lowest triplet excited state (T₁).

DOI： 10.3389/fchem.2022.990918

記述言語：その他   掲載種別：研究論文（学術雑誌）  

DOI： 10.1002/adom.202200682

記述言語：英語   出版者・発行元：Frontiers in Chemistry  

DOI： 10.3389/fchem.2022.973254

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記述言語：その他   掲載種別：研究論文（学術雑誌）  

DOI： 10.1002/adfm.202204352

記述言語：その他   掲載種別：研究論文（学術雑誌）  

DOI： 10.1002/adfm.202205967

記述言語：日本語   出版者・発行元：公益社団法人 応用物理学会  

DOI： 10.11470/oubutsu.91.7_386

CiNii Research

記述言語：その他   掲載種別：研究論文（学術雑誌）  

Two new deep-blue narrowband multi-resonant emitters, 1B-DTACrs and 2B-DTACrs, one of which shows TADF, based on boron, nitrogen, and oxygen doped nanographenes are reported.

DOI： 10.1039/d2cc03347j

記述言語：その他   掲載種別：研究論文（学術雑誌）  

Abstract

In this study, electron and hole injection, and transport in semi-transparent organic light-emitting diodes, including dielectric/metal/dielectric (DMD) electrodes, were investigated. The DMD electrode was modified by incorporating a 5 nm-thick Cs:MoOx layer and a 10 nm-thick 1,4,5,8,9,11-hexaazatriphenylene hexacarbonitrile (HATCN) layer to improve the electron and hole injection in standard and inverse structures, respectively. The inverse structure showed a reasonably good and stable external quantum efficiency due to the well-balanced carrier densities at both low and high voltages which was confirmed by an electrical simulation study. Also, the peak position of the hole and electron recombination rate in the inverse structure was located on the ITO side, which is beneficial for reducing exciton quenching and photon absorption by metallic electrodes.

DOI： 10.35848/1347-4065/ac7e96

記述言語：英語   掲載種別：研究論文（学術雑誌）  

This work reports a new acceptor for constructing donor-acceptor type (D-A type) blue thermally activated delayed fluorescence (TADF) emitters with narrowed charge-transfer (CT) emissions. A new acceptor core, carbazole-2-carbonitrile (CCN), is formed by the fusion of carbazole and benzonitrile. Three D-A type TADF emitters based on the CCN acceptor, namely 3CzCCN, 3MeCzCCN, and 3PhCzCCN, have been successfully synthesized and characterized. These emitters show deep-blue emissions from 439 to 457 nm with high photoluminescence quantum yields of up to 85&#37; in degassed toluene solutions. Interestingly, all CCN-based deep-blue TADF emitters result in narrow CT emissions with full-width at half-maximums (FWHMs) of less than 50 nm in toluene solutions, which are pretty narrower compared with those of typical D-A type TADF emitters. Devices based on these emitters show high maximum external quantum efficiencies of up to 17.5&#37;.

DOI： 10.1039/d2sc02478k

記述言語：その他   掲載種別：研究論文（学術雑誌）  

Abstract

We investigated the impact of various excitonic and photonic losses on the lasing threshold and slope efficiency of organic semiconductor lasers (OSLs) under optical and electrical excitations. The rate equations are solved numerically using the Euler method for an OSL and an organic semiconductor laser diode, including 4,4′-bis[(N-carbazole)styryl]biphenyl (BSB-Cz) as a gain medium. The results showed that the loss mechanisms that affect the exciton and photon densities cause an increase in the laser threshold and a decrease in the slope efficiency. Further, we demonstrated that by using a thermally activated delayed fluorescence (TADF) emitter as a gain medium, the triplet excitons could be harvested by increasing the reverse intersystem crossing rate (k_RISC), resulting in an appreciable decrease of the laser threshold and an increase of the slope efficiency. Accordingly, the TADF emitters with a fast k_RISC are expected to significantly reduce the current density required for electrical excitation.

DOI： 10.35848/1347-4065/ac759d

記述言語：その他   掲載種別：研究論文（学術雑誌）  

A solvent-dependent access to E vs. Z-allylic amines was achieved via decarboxylative vinylation of amino acids. Detailed experimental studies have been conducted to understand the role of the solvent in the reactivity and stereoselectivity of the vinylation reactions.

DOI： 10.1039/d2sc02090d

記述言語：その他   掲載種別：研究論文（学術雑誌）  

DOI： 10.1038/s41563-022-01265-7

記述言語：その他   掲載種別：研究論文（学術雑誌）  

DOI： 10.1002/adma.202201409

記述言語：その他   掲載種別：研究論文（学術雑誌）  

We compare the effect of donor strength on the optoelectronic properties of thermally activated delayed fluorescence poly(dendrimer)s and their dendrimer analogues.

DOI： 10.1039/d1tc05151b

記述言語：英語  

DOI： 10.1002/adpr.202200003

記述言語：英語  

DOI： 10.1039/D2TC01324J

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Clarification of the role of the spin state that initiates exciton dissociation is critical to attaining a fundamental understanding of the mechanism of organic photovoltaics. Although an excited spin-triplet state with an energy lower than that of excited spin-singlet state is disadvantageous in exciton dissociation, a small electron exchange integral results in small singlet-triplet energy splitting in some material systems. This energy splitting leads to a nearly isoenergetic alignment of both excited states, raising a question about the role of excited spin states in exciton dissociation. Herein, we show that the spin-triplet rather than the spin-singlet plays a critical role in the exciton dissociation that leads to the formation of free carriers. This result indicates that the spin-triplet inherently acts as an intermediate, leading to exciton dissociation. Thus, our demonstration provides a fundamental understanding of the role of excited spin states of organic molecular systems in photoinduced charge-carrier generation.

DOI： 10.1126/sciadv.abj9188

記述言語：英語  

DOI： 10.1002/marc.202200118

記述言語：英語  

DOI： 10.1002/marc.202200115

記述言語：英語   掲載種別：研究論文（学術雑誌）  

The limitation of lasing duration less than nanosecond order has been a major problem for realizing organic solid-state continues-wave (CW) lasers and organic semiconductor laser diodes. Triplets accumulation under CW excitation has been well recognized as a critical inhibiting factor. To overcome this issue, the utilization of thermally activated delayed fluorescence (TADF) emitters is a promising mechanism because of efficient reverse intersystem crossing. Herein, we model the triplet accumulation processes under lasing and propose the active utilization of TADF for lasing based on our simulation analysis. We used the rate constants experimentally determined from the optical properties of a boron difluoride curcuminoid fluorophore showing both TADF and lasing. We demonstrate that the intersystem crossing efficiency is gradually increased after the convergence of relaxation oscillation, i.e., terminating laser oscillation. In addition, we found that when the reverse intersystem crossing rate is close to the intersystem crossing rate, CW lasing becomes dominant.

DOI： 10.1021/acs.jpclett.1c03983

記述言語：英語   出版者・発行元：Chemistry - A European Journal  

Charge-transfer emitters are attractive due to their color tunability and potentially high photoluminescence quantum yields (PLQYs). We herein present tetraaminospirenes as donor moieties, which, in combination with a variety of acceptors, furnished 12 charge-transfer emitters with a range of emission colors and PLQYs of up to 99 %. The spatial separation of their frontier molecular orbitals was obtained through careful structural design, and two DA structures were confirmed by X-ray crystallography. A range of photophysical measurements supported by DFT calculations shed light on the optoelectronic properties of this new family of spiro-NN-donor-acceptor dyes.

DOI： 10.1002/chem.202104150

Web of Science

Scopus

PubMed

記述言語：その他   掲載種別：研究論文（学術雑誌）  

DOI： 10.1246/bcsj.20210323

記述言語：英語  

DOI： 10.1109/JPHOT.2022.3146365

記述言語：英語  

DOI： 10.1038/s41467-021-27739-x

記述言語：英語  

DOI： 10.1002/anie.202201886

出版者・発行元：Proceedings of the International Display Workshops  

We report first time the emission zone profile, the spatial distribution of the emission intensity along the direction of the applied bias, of a quantum dot light-emitting diode. The emission zone profile is correlated with the balance of n- and p-type currents in a diode, and the device efficiency and its roll-off behavior strongly depend on whether the emission peak is preferably distributed or concentrated at a specific interface. The emission zone profiling can thus provide us with clues for improving the performance of organic–quantum dots hybrid devices.

Scopus

出版者・発行元：Digest of Technical Papers - SID International Symposium  

By utilizing time-of-flight secondary ion mass spectrometry (TOF-SIMS), the degradation processes of quantum dot core components and the surface ligands were studied. Intentionally degraded QLED samples were prepared, and the TOF-SIMS mass composition signals of each layer within the QLEDs are estimated. The result of the analysis gives possible structural information of the degraded species induced in the device, providing useful insights for further developments of highly efficientR/G/B quantum dotmaterials.

DOI： 10.1002/sdtp.15815

Scopus

出版者・発行元：Proceedings of SPIE - The International Society for Optical Engineering  

Organic light-emitting diodes (OLEDs) are a promising light-emitting technology useful for various display applications1,2. Despite great progress in this field3-12, there is an ongoing challenge to realize high performance blue OLEDs with efficiency, good color purity, and device lifetime. Here, we report pure-blue (CIEx,y color coordinates of [0.13, 0.16]) OLEDs with high-efficiency (external quantum efficiency of 32 % at 1000 cd m-2), narrow-emission (full width half maximum of 19 nm), and good stability (LT95 of 18 hours at an initial luminance of 1000 cd m-2). The design is based on a two-unit stacked tandem hyperfluorescence (HF)-OLED with an improved singlet-excited energy transfer process from a sky-blue TADF assistant dopant (AD) (HDT-1) to a pure-blue terminal emitter (TE) (v-DABNA). Furthermore, the effect of dopant concentration of terminal emitter on the device performance of hyperfluorescence OLEDs is studied. Device shows a better color purity when dopant concentration is increased. On the other hand, new hyperfluorescence OLEDs have been fabricated, in which device stability has been extended with a new molecular design of TE.

DOI： 10.1117/12.2632333

Web of Science

Scopus

出版者・発行元：Proceedings of SPIE - The International Society for Optical Engineering  

In this study, we developed highly efficient pixelated near-infrared organic light-emitting diodes (NIR-OLEDs) featuring self-emission and small form factor, which are expected to expand applications of light sensing. To realize new NIROLEDs in which active-matrix drive is possible by multiple fine pixels, we established a highly efficient NIR-OLED material and top-emitting NIR-OLEDs with fine pixels. Excellent characteristics including pixel pitch of 7.8 μm, peak wavelength of more than 900 nm, and external quantum efficiency of approximately 1% were successfully demonstrated. In addition, we confirmed the feasibility of highly efficient NIR-OLEDs with fine pixels, which is expected to contribute toward miniaturized sensing light sources with low power consumption, and hence improved value.

DOI： 10.1117/12.2608387

Web of Science

Scopus

記述言語：その他   掲載種別：研究論文（学術雑誌）  

DOI： 10.1021/acsaem.1c03213

記述言語：英語  

DOI： 10.11370/isj.60.615

記述言語：英語  

DOI： 10.1039/D1TC04937B

記述言語：その他   掲載種別：研究論文（学術雑誌）  

Abstract

Photostimulated luminescence allows energy or data to be stored and released using electromagnetic waves as both the input and output, and has attracted considerable interest in the fields of biomedical and information technologies. However, this phenomenon is mostly limited to solid inorganic materials. Here, we report photostimulated luminescence from purely organic blend films, composed of electron donor, acceptor, and trap/emitter molecules. Charges in the films are accumulated as radical ions by ultraviolet light irradiation and then extracted by near-infrared light irradiation. Even after storage in the dark for one week they produce visible light with good repeatability, color tunability, and are responsive to weak external magnetic fields. These findings might broadly impact existing applications and provide new prospects for innovative flexible devices.

DOI： 10.1038/s43246-021-00178-3

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Abstract

Fast emission and high color purity are essential characteristics of modern opto-electronic devices, such as organic light emitting diodes (OLEDs). These properties are currently not met by the latest generation of thermally activated delayed fluorescence (TADF) emitters. Here, we present an approach, called “hot exciplexes” that enables access to both attributes at the same time. Hot exciplexes are produced by coupling facing donor and acceptor moieties to an anthracene bridge, yielding an exciplex with large T₁ to T₂ spacing. The hot exciplex model is investigated using optical spectroscopy and quantum chemical simulations. Reverse intersystem crossing is found to occur preferentially from the T₃ to the S₁ state within only a few nanoseconds. Application and practicality of the model are shown by fabrication of organic light-emitting diodes with up to 32 &#37; hot exciplex contribution and low efficiency roll-off.

DOI： 10.1038/s41467-021-26439-w

記述言語：英語  

DOI： 10.1002/anie.202112794

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Highly efficient organic light-emitting diodes (OLEDs) with the concurrent achievement of high external electroluminescence quantum efficiency (EQE) and low light amplification thresholds under optical excitation have been considered as a crucial evolution towards the development of high-performance electrically pumped organic semiconductor laser diodes. Herein, a series of 2,6-dicarbonitrile-diphenyl-1 lambda(5)-phosphinine (DCNP) based donor (D)-acceptor (A) type dyes with different electron-withdrawing and donating moieties have been designed and characterized. The well-manipulated D-A strength with tunable optical properties guaranteed the low amplified spontaneous emission (ASE) thresholds of below 10 mu J cm(-2) and furnished a wide-range color-tuning capability in the visible region (485-595 nm). Furthermore, employing a thermally-activated delayed fluorescence (TADF) molecule as a triplet harvester boosted the performance of OLEDs based on mDMCz that exhibits an exceptional EQE value of 18.4&#37; which is an eightfold enhancement as compared with that of standard fluorescence OLEDs. Also, the TADF-assistant fluorescence (TAF) system enables a reduction of the ASE threshold to 3 mu J cm(-2) and excellent ASE stability. These results provide a rational design strategy to construct color-tunable lasing dyes with reduced ASE thresholds and clarify their potentiality as the fluorescent dopant in the TAF system to utilize up-converted triplet excitons via efficient energy transfer.

DOI： 10.1002/adom.202101122

記述言語：英語   掲載種別：研究論文（学術雑誌）  

As in many fields, the most exciting endeavors in photon upconversion research focus on increasing the efficiency (upconversion quantum yield) and performance (anti-Stokes shift) while diminishing the cost of production. In this vein, studies employing metal-free thermally activated delayed fluorescence (TADF) sensitizers have garnered increased interest. Here, for the first time, the strategy of ternary photon upconversion is utilized with the TADF sensitizer 2,4,5,6-tetrakis(carbazol-9-yl)isophthalonitrile (4CzIPN), resulting in a doubling of the upconversion quantum yield in comparison to the binary system employing p-terphenyl as the emitter. In this ternary blend, the sensitizer 4CzIPN is paired with an intermediate acceptor, 1-methylnaphthalene, in addition to the emitter molecule, p-terphenyl, yielding a normalized upconversion quantum yield of 7.6&#37; while maintaining the 0.83 eV anti-Stokes shift. These results illustrate the potential benefits of utilizing this strategy of energy-funneling, previously used only with heavy-metal based sensitizers, to increase the performance of these photon upconversion systems.

DOI： 10.1002/adma.202103976

記述言語：英語  

DOI： 10.1002/adom.202102034

記述言語：英語  

DOI： 10.1002/adom.202101789

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Organic long-persistent-luminescent (OLPL) materials demonstrating hour-long photoluminescence have practical advantages in applications owing to their flexible design and easy processability. However, the energy absorbed in these materials is typically stored in an intermediate charge-separated state that is unstable when exposed to oxygen, thus preventing persistent luminescence in air unless oxygen penetration is suppressed through crystallization. Moreover, OLPL materials usually require ultraviolet excitation. Here we overcome such limitations and demonstrate amorphous OLPL systems that can be excited by radiation up to 600 nm and exhibit persistent luminescence in air. By adding cationic photoredox catalysts as electron-accepting dopants in a neutral electron-donor host, stable charge-separated states are generated by hole diffusion in these blends. Furthermore, the addition of hole-trapping molecules extends the photoluminescence lifetime. By using a p-type host less reactive to oxygen and tuning the donor-acceptor energy gap, our amorphous blends exhibit persistent luminescence stimulated by visible light even in air, expanding the applicability of OLPL materials.

DOI： 10.1038/s41563-021-01150-9

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Achieving continuous-wave (CW) lasing in organic semiconductors is known to be a difficult task because long-lived triplets quench radiative singlets via singlet-triplet annihilation (STA). To avoid STA and operate organic lasers in CW or long-pulse photoexcitation, the triplets need to be removed from an organic laser gain medium. However, this triplet removal leads to a loss of excitons. In addition to removing the detrimental triplets, here it is reported a triplet recycling process, which includes triplet scavenging and successive triplet upconversion via triplet-triplet annihilation (TTA) to regenerate emissive singlet excitons in a laser medium. An anthracene derivative of 9-(1-naphthalenyl)-10-(4-(2-naphthalenyl)phenyl)anthracene (NaNaP-A) and a laser dye of 4,4 '-bis[4-(diphenylamino)styryl]biphenyl (BDAVBi) are used as the triplet recycling sensitizer and the emitting laser dye, respectively. In this laser system, NaNaP-A can efficiently scavenge the triplets formed on BDAVBi because the triplet level is deeper for NaNaP-A than for BDAVBi, and then NaNaP-A successively recycles the triplets into the BDAVBi's singlet state via TTA. The TTA compensates and overcomes the STA in this laser system. Hence, these laser devices can be operated with long pulse widths of up to 10 ms. This unique triplet recycling behavior is confirmed by transient photoluminescence (PL) and electroluminescence (EL) studies.

DOI： 10.1002/adom.202101302

記述言語：その他  

DOI： 10.1021/acs.jpca.1c04056

記述言語：英語  

DOI： 10.1002/anie.202108943

記述言語：その他   掲載種別：研究論文（学術雑誌）  

DOI： 10.1002/adom.202101048

記述言語：その他   掲載種別：研究論文（学術雑誌）  

DOI： 10.1002/adfm.202104529

記述言語：その他   掲載種別：研究論文（学術雑誌）  

DOI： 10.1021/acs.jpclett.1c02140

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1002/ange.202108413

記述言語：その他  

DOI： 10.1002/9781119146131.ch12

記述言語：英語  

DOI： 10.1021/acsami.1c06148

記述言語：その他  

DOI： 10.1002/anie.202106570

記述言語：その他   掲載種別：研究論文（学術雑誌）  

DOI： 10.1002/aelm.202100486

記述言語：その他   掲載種別：研究論文（学術雑誌）  

DOI： 10.1002/anie.202106490

記述言語：その他   掲載種別：研究論文（学術雑誌）  

This paper proposes a novel conceptual system of optical wireless power transfer (OWPT) between objects, which is different from the existing OWPT systems such that a single device—an optical transceiver—is employed. This optical transceiver, which is capable of both absorbing and emitting light, is fabricated from a metal halide perovskite known for its superior features that can help significantly reduce the whole system size and cost. The proposed system contributes to realizing a thing-to-thing OWPT network, in which surfaces of objects/things are covered by perovskite transceivers (fully or partially), enabling them to wirelessly charge or discharge from the others.

DOI： 10.3389/fenrg.2021.679125

記述言語：その他   掲載種別：研究論文（学術雑誌）  

DOI： 10.1063/5.0051527

記述言語：その他   掲載種別：研究論文（学術雑誌）  

Solid-state films exhibiting thermally activated delayed fluorescence (TADF) can offer high internal electroluminescence (EL) quantum efficiency, even in a simplified device structure. However, the exciton dynamics in solid-state TADF films, particularly for the unexpected exciton loss processes such as concentration quenching, have not yet been clarified. The dynamics of photoexcited electrons in the TADF process of a 2,4,5,6-Tetra (9H-carbazol-9-yl) isophthalonitrile (4CzIPN) solid film are observed via time-resolved photoelectron emission microscopy (TR-PEEM) and the results are compared with the conventional time-resolved photoluminescence (TR-PL) technique. The initial decay process of the photoexcited electrons probed via TR-PEEM is thoroughly traced in the TR-PL signal, while unusual long-lived electrons are detected only through the use of TR-PEEM. These results indicate that the excitons of 4CzIPN spontaneously dissociate into free carriers within the exciton lifetime, which seems to be a common process that contributes to the exciton loss in polar organic solids.

DOI： 10.1002/adom.202100619

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Organic long-persistent luminescent systems (OLPLs) exhibiting long-lasting emission after photoexcitation consist of organic electron donors and acceptors, that are widely used in organic light-emitting diodes (OLEDs). Although OLPLs and OLEDs include very similar excitonic processes, long-lasting emission has never been observed in OLEDs. This study confirms the presence of long-persistent luminescence (LPL) under electrical excitation.

DOI： 10.1002/adma.202008844

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Glow-in-the-dark materials can store absorbed photon energy and emit light for long periods of time. While inorganic long-persistent luminescence (LPL) materials are crystalline and often require rare metals, organic LPL (OLPL) materials are flexible and require no rare metals. The emission process of OLPL systems consists of photoinduced charge separation, charge accumulation, and emission from charge recombination. Although emission processes of OLPL systems have been investigated, the charge separation and accumulation processes remain enigmatic. In this study, we investigated the charge carrier dynamics of a binary OLPL system comprising of electron donors and acceptors. We confirmed the presence of thermal activation processes, thermally activated delayed fluorescence and thermoluminescence in the OLPL system.

DOI： 10.1039/d0nr09227d

記述言語：その他   掲載種別：研究論文（学術雑誌）  

DOI： 10.1002/ange.202016089

記述言語：その他   掲載種別：研究論文（学術雑誌）  

DOI： 10.1002/chem.202100936

記述言語：その他  

DOI： 10.1039/D0MA00756K

記述言語：英語   掲載種別：研究論文（学術雑誌）  

A tetracene dimer, 5,5'-bitetracene (55BT), has successfully been synthesized for the first time and its structure was confirmed by X-ray single crystal analysis. The electrochemical and optical properties of 55BT were investigated and compared to those of tetracene. Although the photoluminescence quantum yield of 55BT was slightly higher than that of tetracene, the results of the transient absorption spectroscopy suggested triplet formation by singlet fission in solution.

DOI： 10.1246/cl.200909

記述言語：その他   掲載種別：研究論文（学術雑誌）  

DOI： 10.1002/anie.202016089

記述言語：その他   掲載種別：研究論文（学術雑誌）  

DOI： 10.1002/adfm.202009488

記述言語：その他   掲載種別：研究論文（学術雑誌）  

DOI： 10.1002/aelm.202001090

記述言語：その他   掲載種別：研究論文（学術雑誌）  

DOI： 10.1002/smsc.202000057

記述言語：その他   掲載種別：研究論文（学術雑誌）  

DOI： 10.1002/anie.202014319

記述言語：その他   掲載種別：研究論文（学術雑誌）  

<p>Simultaneous fast energy funnelling between the neighbouring sheets and slower carrier and exciton in-plane diffusion revealed in quasi-2D perovskites.</p>

DOI： 10.1039/d1tc00422k

記述言語：英語   掲載種別：研究論文（学術雑誌）  

With the aim of achieving high-performance thermally activated delayed fluorescence, a series of trioxoazatriangulene derivatives are systematically developed by modifying the donor substituents. The emission colors are shifted from green to greenish-yellow and to yellow with rather broad spectral widths of 70-95 nm by introducing carbazole, triphenylamine, or diphenylamine donor units, indicating that each emission originates from a charge-transfer transition. On the other hand, the trioxoazatriangulene modified with three diphenylamines shows orange emission with a narrow emission spectrum (45 nm), suggesting that the transition mainly originates from a multiple resonance effect.

DOI： 10.1002/adom.202002174

記述言語：その他   掲載種別：研究論文（学術雑誌）  

DOI： 10.1038/s41566-020-00745-z

記述言語：その他   掲載種別：研究論文（学術雑誌）  

A bright near-infrared (NIR) fluorescent molecule was developed based on the donor–acceptor–donor (D–A–D) approach using an aza-BODIPY analog called pyrrolopyrrole aza-BODIPY (PPAB) as an electron-accepting chromophore. Directly introducing electron-donating triphenylamine (TPA) to develop a D–A–D structure caused redshifts of absorption and emission of PPAB into the NIR region with an enhanced fluorescence brightness of up to 5.2×104 m−1 cm−1, whereas inserting a phenylene linker between the TPA donor and the PPAB acceptor induced solvatochromic behavior in emission. Transient absorption spectra and theoretical calculations revealed the presence of a highly emissive hybridized locally excited and charge-transfer state in the former case and the contribution of the dark charge-separated state to the excited state in the latter case. The bright D–A–D PPAB as a novel emitter resulted in a NIR electroluminescence with a high external quantum efficiency of 3.7 &#37; and a low amplified spontaneous emission threshold of ca. 80 μJ cm−2, indicating the high potential for NIR optoelectronic applications.

DOI： 10.1002/chem.202005360

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Continuous-wave (CW) lasing is still difficult to realize in organic laser dyes, one reason being the thermal degradation caused by intense photoexcitation. A decrease in laser threshold suppresses the thermal degradation and, therefore, leads to long-lasting lasing from organic laser dyes. Here, we show that it is possible to decrease the laser thresholds by combining the organic laser dye 4,4-bis[(N-carbazole)styryl]biphenyl, which has a small spectral overlap between the laser emission and the excited-state triplet absorption, with two-dimensional (2D) distributed-feedback (DFB) gratings. We used second-order 2D cross double and square lattice DFB gratings, which offer light feedback in two orthogonal directions, and second-order and mixed-order circular DFB gratings, which offer light feedback in radial directions. Among these grating structures, the mixed-order circular DFB grating structure led to the lowest lasing threshold of similar to 0.015 mu J cm(-2) under short-pulse photoexcitation because of the excellent optical feedback. Moreover, a low average-power threshold of 10 W cm(-2) (a peak-power threshold of 1 kW cm-2) was obtained when laser devices with this grating structure were operated under 1 s of long-pulse photoexcitation with a repetition rate of 0.01 Hz. Additionally, using the mixed-order circular DFB grating structure improved the laser stability under CW photoexcitation since shorter exciton lifetimes in the optical resonator suppress the chemical decomposition. These results demonstrate the importance of choosing an optical resonator structure for improving organic laser performance.

DOI： 10.1021/acsphotonics.0c01728

記述言語：その他   掲載種別：研究論文（学術雑誌）  

DOI： 10.1002/ejoc.202100086

記述言語：英語   掲載種別：研究論文（学術雑誌）  

The development of near-infrared (NIR) light sources has attracted much interest due to their attractive applications, such as biosensing and light detection and ranging (LiDAR). In particular, organic semiconductor laser diodes with NIR emission are emerging as a next generation technology. However, organic NIR emitters have generally suffered from a low quantum yield, which has resulted in only a few examples of organic solid-state NIR lasers. In this study, the authors demonstrate a highly efficient NIR emitter based on a boron difluoride curcuminoid structure, which shows a high photoluminescence (PL) quantum yield (phi(PL)) at >700 nm and a high fluorescence radiative rate constant in a solid-state film. Amplified spontaneous emission and lasing occurs at >800 nm with very low thresholds. The large redshift of the stimulated emission is attributed to the transition from the lowest excited state to the different vibrational levels of the ground state owing to the overlap between the emission and the singlet-singlet excited-state absorption.

DOI： 10.1002/adom.202001947

記述言語：その他   掲載種別：研究論文（学術雑誌）  

<p>The introduction of naphthalene units into a stilbene structure improves not only the PL quantum yield but also stability. The emission wavelength is redshifted upon π-extension, resulting in the realization of excellent green laser dyes.</p>

DOI： 10.1039/d0tc05387b

記述言語：英語  

DOI： 10.1021/acsami.1c07859

記述言語：その他   掲載種別：研究論文（学術雑誌）  

<p>Highly stable <italic>peri</italic>-tetracene analogues with a high degree of singlet biradical character were synthesized in a very simple route, and their crystal structures and semiconducting properties were investigated.</p>

DOI： 10.1039/d0sc04699j

記述言語：その他   掲載種別：研究論文（学術雑誌）  

DOI： 10.1246/cl.200915

記述言語：英語   掲載種別：研究論文（学術雑誌）  

<title>Abstract</title>
Large external quantum efficiency rolloff at high current densities in organic light-emitting diodes (OLEDs) is frequently caused by the quenching of radiative singlet excitons by long-lived triplet excitons [singlet–triplet annihilation (STA)]. In this study, we adopted a triplet scavenging strategy to overcome the aforementioned STA issue. To construct a model system for the triplet scavenging, we selected 2,6-dicyano-1,1-diphenyl-λ⁵σ⁴-phosphinine (DCNP) as the emitter and 4,4′-bis[(<italic>N</italic>-carbazole)styryl]biphenyl (BSBCz) as the host material by considering their singlet and triplet energy levels. In this system, the DCNP’s triplets are effectively scavenged by BSBCz while the DCNP’s singlets are intact, resulting in the suppressed STA under electrical excitation. Therefore, OLEDs with a 1 wt.&#37;-DCNP-doped BSBCz emitting layer demonstrated the greatly suppressed efficiency rolloff even at higher current densities. This finding favourably provides the advanced light-emitting performance for OLEDs and organic semiconductor laser diodes from the aspect of the suppressed efficiency rolloff.

DOI： 10.1038/s41467-020-18292-0

記述言語：その他   掲載種別：研究論文（学術雑誌）  

DOI： 10.1021/acsmaterialslett.0c00421

記述言語：その他   掲載種別：研究論文（学術雑誌）  

DOI： 10.1021/acs.jpcc.0c09241

記述言語：その他   掲載種別：研究論文（学術雑誌）  

<title>Abstract</title>
Triplet excitons have been identified as the major obstacle to the realisation of organic laser diodes, as accumulation of triplet excitons leads to significant losses under continuous wave (CW) operation and/or electrical excitation. Here, we report the design and synthesis of a solid-state organic triplet quencher, as well as in-depth studies of its dispersion into a solution processable bis-stilbene-based laser dye. By blending the laser dye with 20 wt&#37; of the quencher, negligible effects on the ASE thresholds, but a complete suppression of singlet–triplet annihilation (STA) and a 20-fold increase in excited-state photostability of the laser dye under CW excitation, were achieved. We used small-area OLEDs (0.2 mm²) to demonstrate efficient STA suppression by the quencher in the nanosecond range, supported by simulations to provide insights into the observed STA quenching under electrical excitation. The results demonstrate excellent triplet quenching ability under both optical and electrical excitations in the nanosecond range, coupled with excellent solution processability.

DOI： 10.1038/s41467-020-19443-z

記述言語：その他   掲載種別：研究論文（学術雑誌）  

DOI： 10.1021/acs.macromol.0c02235

記述言語：その他   掲載種別：研究論文（学術雑誌）  

DOI： 10.1038/s41467-019-14035-y

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1021/acsomega.0c04809

記述言語：英語   掲載種別：研究論文（学術雑誌）  

<p>Biradicaloid HDIP derivatives show that the Δ<italic>E</italic>_S–T gap does not follow the reverse trend of the biradical character but depends more on the delocalization of the radical centres at the outer rings.</p>

DOI： 10.1039/d0sc04583g

記述言語：その他   掲載種別：研究論文（学術雑誌）  

DOI： 10.1016/j.cej.2020.127591

記述言語：その他   掲載種別：研究論文（学術雑誌）  

DOI： 10.1063/5.0029608

記述言語：その他   掲載種別：研究論文（学術雑誌）  

DOI： 10.1002/adom.202001234

記述言語：その他   掲載種別：研究論文（学術雑誌）  

DOI： 10.1002/adma.202003911

記述言語：その他   掲載種別：研究論文（学術雑誌）  

Simultaneous achievement of both high electroluminescence efficiency and high operational stability in organic light-emitting diodes (OLEDs) is required for their use in various practical applications. Although OLEDs based on thermally activated delayed fluorescence-Assisted fluorescence (TAF) are considered to possess a promising device architecture to exploit the full potential of OLEDs, the operational stability of such systems still requires further improvement. In this study, a quaternary emission layer consisting of a combination of TAF and mixed-host systems is developed. OLEDs containing this emission layer show improved operational stability through the management of exciton generation processes while maintaining high electroluminescence efficiency. Furthermore, a gradient of the mixed ratio of the co-host matrix is used to optimize the recombination zone profile in the emission layer, leading to 17 times improvement of the operational lifetime compared with that of the corresponding single-host-based device. This research provides a simple and general method to develop highly stable TAF-OLEDs.

DOI： 10.1021/acsami.0c15208

記述言語：英語   掲載種別：研究論文（学術雑誌）  

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.

DOI： 10.1002/adom.202000896

記述言語：その他   掲載種別：研究論文（学術雑誌）  

<p>The phenyl group in blue controls the photochromism of [3<italic>H</italic>]-naphthopyran derivatives by favouring the photoinduced formation of the TT isomer over TC at the photostationary state by steric hindrance.</p>

DOI： 10.1039/d0pp00202j

記述言語：その他   掲載種別：研究論文（学術雑誌）  

DOI： 10.1038/s41566-020-0668-z

記述言語：その他   掲載種別：研究論文（学術雑誌）  

DOI： 10.1063/5.0016052

記述言語：その他   掲載種別：研究論文（学術雑誌）  

DOI： 10.1002/adom.202000784

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Highly efficient and stable blue-green thermally-activated delayed fluorescence (TADF) molecules with trifluoromethyl (CF3) groups were developed. Partial modification with CF3 groups at the appropriate position of the donor moiety improved the luminescence efficiency and excited state stability. OLEDs using modified emitters showed improved EQE and operational lifetime compared with unmodified examples.

DOI： 10.1246/cl.200435

記述言語：その他   掲載種別：研究論文（学術雑誌）  

DOI： 10.1002/solr.202000305

記述言語：その他   掲載種別：研究論文（学術雑誌）  

<p>Suitable intermolecular hydrogen bonding enables the formation of a fixed 3D supramolecular framework and suppresses the exciton nonradiative decays and quenching.</p>

DOI： 10.1039/d0mh00952k

記述言語：その他  

Photostimulated luminescence, which allows energy or data to be stored and released using electromagnetic waves as both the input and output, has attracted considerable interest in the fields of biomedical and informatics technologies, but this phenomenon is mostly limited to solid inorganic materials. Here, we report photostimulated luminescence from purely organic blend films composed of electron donor, acceptor, and trap/emitter molecules. In the films, charges are accumulated as radical ions by ultraviolet light irradiation and then extracted by near infrared light irradiation to produce visible light. Films are capable of multiple cycles (>10 times) of organic photostimulated luminescence, which was still observable from films left in the dark at room temperature for one week after excitation, and emission color could be varied by changing the trap/emitter molecules. These findings will broadly impact existing applications and provide new prospects for innovative flexible devices.

DOI： 10.26434/chemrxiv.12956456

記述言語：その他   掲載種別：研究論文（学術雑誌）  

DOI： 10.1063/5.0023622

記述言語：その他   掲載種別：研究論文（学術雑誌）  

Organic–inorganic lead halide quasi-two-dimensional (2D) perovskites are promising gain media for lasing applications because of their low cost, tunable colour, excellent stability and solution processability1,2,3. Optically pumped continuous-wave (CW) lasing is highly desired for practical applications in high-density integrated optoelectronics devices and constitutes a key step towards electrically pumped lasers4,5,6. However, CW lasing has not yet been realized at room temperature because of the ‘lasing death’ phenomenon (the abrupt termination of lasing under CW optical pumping), the cause of which remains unknown. Here we study lead halide-based quasi-2D perovskite films with different organic cations and observe that long-lived triplet excitons considerably impede population inversion during amplified spontaneous emission and optically pumped pulsed and CW lasing. Our results indicate that singlet–triplet exciton annihilation is a possible intrinsic mechanism causing lasing death. By using a distributed-feedback cavity with a high quality factor and applying triplet management strategies, we achieve stable green quasi-2D perovskite lasers under CW optical pumping in air at room temperature. We expect that our findings will pave the way to the realization of future current-injection perovskite lasers.

DOI： 10.1038/s41586-020-2621-1

記述言語：その他   掲載種別：研究論文（学術雑誌）  

DOI： 10.31635/ccschem.020.202000327

記述言語：その他   掲載種別：研究論文（学術雑誌）  

DOI： 10.1246/cl.200337

記述言語：英語   掲載種別：研究論文（学術雑誌）  

A simple way to control only the surface properties of polymer materials, without changing the bulk properties, has long been desired. The segregation behavior when a component with a tiny amount fed into the matrix is thermodynamically enriched at the surface is one of the candidate methods. This capability was examined herein by focusing on a star-shaped polyhedral oligomeric silsesquioxane (s-POSS), where the central POSS unit is tethered to eight isobutyl-substituted POSS cages as a surface modifier. X-ray photoelectron spectroscopy revealed that the surface of a film of poly(methyl methacrylate) (PMMA) was almost completely covered with POSS units by adding just 5 wt &#37; s-POSS to it. The segregated POSS dramatically altered the physical properties such as molecular motion and the mechanical and dielectric responses at the surface of the PMMA film. These findings make it clear that s-POSS is an excellent surface modifier for glassy polymers.

DOI： 10.1021/acs.langmuir.0c01785

記述言語：その他   掲載種別：研究論文（学術雑誌）  

© The Royal Society of Chemistry. 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&#37; 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

DOI： 10.1039/d0tc01487g

記述言語：その他   掲載種別：研究論文（学術雑誌）  

DOI： 10.1021/acs.jpcc.0c03996

記述言語：その他   掲載種別：研究論文（学術雑誌）  

DOI： 10.1021/acsami.0c06737

記述言語：英語  

DOI： 10.1002/adom.202000554

記述言語：その他   掲載種別：研究論文（学術雑誌）  

DOI： 10.1246/bcsj.20200159

記述言語：英語  

DOI： 10.1002/adfm.202000580

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Quenching of singlets by long-lived triplets is a serious issue for lasing from organic laser dyes, especially under long pulse excitation. As a strategy to scavenge or manage unnecessary triplets, an organic laser dye is dispersed into a host material having high singlet and low triplet energy levels [a large singlet-triplet energy gap (Delta E-ST)]. However, finding such a host material having a triplet scavenging capability is limited. In this study, an organic laser dye, 2,6-dicyano-1,1-diphenyl-lambda(5)sigma(4)-phosphinine (DCNP), having a small Delta E-ST of approximate to 0.44 eV is synthesized, and thus 4-4 '-bis[(N-carbazole)styryl] biphenyl (BSBCz) can be employed as a triplet scavenging host, i.e., the triplets formed on DCNP are easily transferred to BSBCz. A 1 wt&#37;-DCNP-doped BSBCz film is formed on a mixed-order distributed feedback grating, showing lasing with a low threshold value of approximate to 0.86 mu J cm(-2) and a full-width-at-half-maximum value of approximate to 0.5 nm. Because of the suppressed singlet-triplet annihilation, DCNP-based laser devices operating under a continuous-wave regime, with a low threshold of 72 W cm(-2) and a long laser half-lifetime of approximate to 3 min, are demonstrated. These results indicate a possibility of the wider selection of host materials, easing a material design strategy of fabricating high-performance laser devices in future.

DOI： 10.1002/adfm.202001078

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Organic photodetector performance for enhancing the sensing abilities of an organic photoplethysmography sensor was investigated. The optimized organic photodetector with an anode interlayer and a cathode interlayer showed a reverse dark current density of 22 nA cm(-2) at -2 V and an external quantum efficiency of 53.3&#37; at 0 V. This organic photodetector was fabricated monolithically with an organic light-emitting diode on a glass substrate to achieve a reflectance-mode photoplethysmography sensor, demonstrating the impact of organic photodetector device performance on the measured photoplethysmography signal for sensing applications. Furthermore, we estimated the optimal sensor design for circular geometry in terms of device area and distance between the organic light-emitting diode and organic photodetector to maximize the signal-to-noise ratio and lower the power consumption of organic photoplethysmography sensor devices. For the most favorable photoplethysmography sensor design, a signal strength of 130 mV with 600 mu W power consumption was measured.

DOI： 10.1021/acsaelm.0c00082

記述言語：英語   掲載種別：研究論文（学術雑誌）  

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.

DOI： 10.3389/fchem.2020.00403

記述言語：英語  

DOI： 10.1063/5.0007310

記述言語：英語  

DOI： 10.1038/s43246-020-0028-z

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1021/acsami.0c05449

記述言語：英語  

DOI： 10.1002/chem.201905345

記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語  

DOI： 10.1002/adma.201905035

記述言語：英語  

DOI： 10.1021/acs.jpclett.0c00498

記述言語：英語  

DOI： 10.1002/adfm.202001816

記述言語：英語  

DOI： 10.1038/s41467-020-15558-5

記述言語：英語  

DOI： 10.1002/adfm.202000795

記述言語：英語  

DOI： 10.1063/1.5141101

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1038/s43246-020-0019-0

記述言語：英語  

DOI： 10.1016/j.optmat.2019.109636

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Careful harvesting of triplet excitons allows the realization of efficient green-emitting quasi-2D perovskite LEDs.Perovskite light-emitting diodes are promising for next-generation lighting and displays because of their high colour purity and performance(1). Although the management of singlet and triplet excitons is fundamental to the design of efficient organic light-emitting diodes, the nature of how excitons affect performance is still not clear in perovskite(2-4) and quasi-two-dimensional (2D) perovskite-based devices(5-9). Here, we show that triplet excitons are key to efficient emission in green quasi-2D perovskite devices and that quenching of triplets by the organic cation is a major loss path. Employing an organic cation with a high triplet energy level (phenylethylammonium) in a quasi-2D perovskite based on formamidinium lead bromide yields efficient harvesting of triplets. Furthermore, we show that upconversion of triplets to singlets can occur, making 100&#37; harvesting of electrically generated excitons potentially possible. The external quantum and current efficiencies of our green (527 nm) devices reached 12.4&#37; and 52.1 cd A(-1), respectively.

DOI： 10.1038/s41566-019-0545-9

記述言語：英語  

DOI： 10.1021/acsami.9b20020

記述言語：その他   掲載種別：研究論文（学術雑誌）  

© 2019 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim For a better understanding of the exciton decay process in thermally activated delayed fluorescence (TADF) emitters, the intersystem crossing rate, kISC, is one of the important physical constants that have to be determined. Herein, a method to calculate the kISC value from photoluminescence (PL) measurements is reconsidered. The kISC value can be determined at very low temperatures where delayed fluorescence (DF) is completely suppressed, as well as around room temperature where triplet excitons mainly decay into the ground state by emitting DF. However, there is a temperature range where the kISC value cannot be determined accurately because the influences of nonradiative decay paths can be neither ignored nor corrected. For such a temperature range, an alternative approach, which utilizes the temperature dependence of an observed PL decay rate, is presented. In this way, kISC values from 300 to 10 K are determined for thin films of two TADF emitters, i.e., 1,2,3,5-tetrakis(carbazol-9-yl)-4,6-dicyanobenzene and 1,2-bis(carbazol-9-yl)-4,5-dicyanobenzene, which are known as 4CzIPN and 2CzPN, respectively.

DOI： 10.1002/pssa.201900616

記述言語：英語  

In this paper, we report a new molecular architecture for increasing the emission efficiency of nicotinonitrile-derivatives-based donor-acceptor-donor combined thermally activated delayed fluorescence (TADF) emitters with asymmetric molecular architecture. The proposed molecular design facilitates highly effective TADF emission through a relatively small singlet (S₁) and triplet (T₁) energy gap (ΔE_ST ≈ 0.1 eV) and provides an increased reverse intersystem crossing efficiency (Φ_RISC) of up to 86&#37; from T₁ to S₁ states. Organic light-emitting diodes (OLEDs) employing the proposed asymmetric nicotinonitrile derivatives as emitters exhibit external quantum efficiencies (η_ext) of up to 18.5&#37; in greenish-blue and green emissions.

DOI： 10.1016/j.dyepig.2019.107849

記述言語：英語   掲載種別：研究論文（学術雑誌）  

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.

DOI： 10.1002/adma.201906614

記述言語：英語  

DOI： 10.1021/acsmaterialslett.9b00536

記述言語：英語  

DOI： 10.1002/aelm.201901172

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Control of the molecular orientation in a glassy film is a crucial issue, not only for an understanding of the fundamental processes of organic amorphous film formation but also for enhancement of the performance of organic light-emitting diodes (OLEDs) by increasing their light-outcoupling efficiency. In this study, the molecular orientation in codeposited films composed of a host molecule and a disk-shaped emitter that exhibits thermally activated delayed fluorescence is investigated systematically. It is found that the orientation of the transition dipole moment (TDM) of the disk-shaped emitters is strongly dependent on the glass transition temperature and the polarization of the host molecules, and almost perfectly horizontal orientation of the TDM of the disk-shaped emitters can be realized. Our findings clarify the role of the host-guest dipole-dipole interaction in the molecular orientation, and it will enable the expansion of both the molecular design and the material combination rules for high-performance OLEDs.

DOI： 10.1063/1.5140210

記述言語：英語  

In this work, we designed and investigated two TADF molecules, AcCN and PxCN, introducing donor moieties into the 3,5-position of 4-pyridinecarbonitrile acceptor core. These D‒A‒D type compounds exhibit effective utilization of triplet excitons through a reverse intersystem crossing (RISC) process with relatively small singlet-triplet energy splitting (ΔE_ST) values less than 0.1 eV. With their high PL quantum yield (Φ_PL) and sufficient rate constant for RISC process (k_RISC), organic light-emitting diodes (OLEDs) employing AcCN and PxCN as emitters achieve a maximum external quantum efficiency (η_ext) of 20.6&#37; and 15.5&#37;, respectively, with green emissions.

DOI： 10.1016/j.dyepig.2019.107775

記述言語：英語  

DOI： 10.1002/adom.201901670

記述言語：英語  

DOI： 10.1246/cl.190823

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Excited states of emissive organic molecules undergo various kinds of quenching phenomena such as vibration-coupled quenching depending on their environmental conditions. Because bright singlet excitons in purely organic molecules exhibiting thermally activated delayed fluorescence (TADF) can access dark triplet excited states, photogenerated singlet excitons can decay nonradiatively through both singlet and triplet excited states. Here, we investigated nonradiative decay behavior, including internal and external exciton quenching processes, of various types of TADF materials in solution. Under air-saturated conditions, both the lowest singlet and triplet excited states of almost all of the TADF materials showed oxygen quenching. We considered the effect of oxygen quenching for both spin states to develop a method for determination of the triplet contribution to the total photoluminescence quantum yield from the transient photoluminescence profiles. Furthermore, we observed a clear energy gap law for the internal nonradiative processes.

DOI： 10.1021/acs.jpclett.9b03302

記述言語：英語   掲載種別：研究論文（学術雑誌）  

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.

DOI： 10.1038/s41467-019-13736-8

記述言語：英語  

DOI： 10.1038/s41467-019-13289-w

記述言語：英語  

DOI： 10.1063/1.5121485

記述言語：英語  

DOI： 10.1063/1.5127308

記述言語：英語  

DOI： 10.1002/adom.201901150

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Triplet-triplet upconversion, in which two triplet excitons are converted to one singlet exciton, is a well-known approach to exceed the limit of electroluminescence quantum efficiency in conventional fluorescence-based organic light-emitting diodes. Considering the spin multiplicity of triplet pairs, upconversion efficiency is usually limited to 20&#37;. Although this limit can be exceeded when the energy of a triplet pair is lower than that of a second triplet excited state, such as for rubrene, it is generally difficult to engineer the energy levels of higher triplet excited states. Here, we investigate the upconversion efficiency of a series of new anthracene derivatives with different substituents. Some of these derivatives show upconversion efficiencies close to 50&#37; even though the calculated energy levels of the second triplet excited states are lower than twice the lowest triplet energy. A possible upconversion mechanism is proposed based on the molecular structures and quantum chemical calculations.

DOI： 10.1038/s41467-019-13044-1

記述言語：英語  

DOI： 10.1039/C9RA07048F

記述言語：英語  

DOI： 10.1063/1.5113647

記述言語：英語  

DOI： 10.1039/C9TC03548F

記述言語：英語  

DOI： 10.1246/cl.190412

記述言語：英語  

DOI： 10.1063/1.5116411

記述言語：英語  

DOI： 10.1016/j.cclet.2019.08.006

記述言語：英語   掲載種別：研究論文（学術雑誌）  

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.

DOI： 10.1038/s41563-019-0465-6

記述言語：英語  

DOI： 10.1021/acs.jpcc.9b03226

記述言語：英語  

DOI： 10.1038/s41586-019-1435-5

記述言語：英語  

DOI： 10.1002/anie.201906575

記述言語：英語  

DOI： 10.1063/1.5097433

記述言語：英語   掲載種別：研究論文（学術雑誌）  

© 2019 Elsevier B.V. Thermally activated delayed fluorescence (TADF) materials have attracted considerable attentions as a new kind of emitters in organic light-emitting diodes. While it is requisite to minimize an energy difference between the lowest excited triplet state (T 1 ) and lowest excited singlet state (S 1 ), so-called ΔE ST , a deeper understanding of the emission mechanism is desirable to clarify the comprehensive molecular design. In this paper, we present that the TADF ability and efficiency of (rare-)metal free organic molecules are surely influenced by both the nonradiative decay of T 1 and spin-orbit coupling. By investigating a temperature dependent photoluminescence of carbazole benzonitrile derivatives in toluene solutions using a newly developed liquid nitrogen cryostat, we demonstrate the activation of TADF by solvent freezing for room temperature-TADF inactive molecules. Transient photoluminescence measurements of the frozen samples show a significant increase of a lifetime of T 1 , probing the suppression of nonradiative decay path of T 1 . A magnitude of the TADF activation by the solvent freezing is closely related to the degree of spin-orbit coupling of the molecules. The present results emphasize the importance of suppression of nonradiative decay of T 1 and an increase of spin-orbit coupling together with reducing ΔE ST to achieve a high TADF emission efficiency.

DOI： 10.1016/j.synthmet.2019.04.005

記述言語：その他   掲載種別：研究論文（その他学術会議資料等）  

Dopant and non-dopant OLEDs were fabricated for testing four TADF emitters, having EL of blue to greenish blue color. The tetraphenyibenzene (4Ph)-containing emitters have been demonstrated having a higher light outcoupling efficiency for dopant devices and a superior IQEfor the non-dopant devices.

DOI： 10.1002/sdtp.12958

記述言語：英語   掲載種別：研究論文（その他学術会議資料等）  

記述言語：英語  

DOI： 10.1021/acs.jpclett.9b01220

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Fluorescent materials that efficiently convert triplet excitons into singlets through reverse intersystem crossing (RISC) rival the efficiencies of phosphorescent state-of-the-art organic light-emitting diodes. This upconversion process, a phenomenon known as thermally activated delayed fluorescence (TADF), is dictated by the rate of RISC, a material-dependent property that is challenging to determine experimentally. In this work, a new analytical model is developed which unambiguously determines the magnitude of RISC, as well as several other important photophysical parameters such as exciton diffusion coefficients and lengths, all from straightforward time-resolved photoluminescence measurements. From a detailed investigation of five TADF materials, important structure-property relationships are derived and a brominated derivative of 2,4,5,6-tetrakis(carbazol-9-yl)isophthalonitrile that has an exciton diffusion length of over 40 nm and whose excitons interconvert between the singlet and triplet states approximate to 36 times during one lifetime is identified.

DOI： 10.1002/adma.201804490

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Suppression of Structural Change upon S-1-T-1 Conversion Assists the Thermally Activated Delayed Fluorescence Process in Carbazole-Benzonitrile Derivatives
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 (Delta E-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 Delta E-ST but distinct TADF activities. We systematically compared their geometrical dynamics upon photo excitation 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 onversion. 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.

DOI： 10.1021/acs.jpclett.9b00810

記述言語：英語  

DOI： 10.1002/asia.201900401

記述言語：英語  

DOI： 10.1063/1.5089269

記述言語：英語  

DOI： 10.1039/C9SC01821B

記述言語：英語   掲載種別：研究論文（学術雑誌）  

In this study, we investigate the lasing properties of 4,4'-bis[(N-carbazole) styryl] biphenyl thin films under electrical pumping. The electroluminescent devices incorporate a mixed-order distributed feedback SiO2 grating into an organic light-emitting diode structure and emit blue lasing. The results provide an indication of lasing by direct injection of current into an organic thin film through selection of a high-gain organic semiconductor showing clear separation of the lasing wavelength from significant triplet and polaron absorption and design of a proper feedback structure with low losses at high current densities. This study represents an important advance toward a future organic laser diode technology. (C) 2019 The Japan Society of Applied Physics

DOI： 10.7567/1882-0786/ab1b90

記述言語：英語  

DOI： 10.1021/acs.jpcc.9b02288

記述言語：英語  

Two novel thermally activated delayed fluorescence (TADF) emitters, 3-phenylquinolino[3,2,1-de]acridine-5,9-dione (3-PhQAD) and 7-phenylquinolino[3,2,1-de]acridine-5,9-dione (7-PhQAD), were designed and synthesized based on a rigid quinolino[3,2,1-de]acridine-5,9-dione (QAD) framework. With the effective superimposed resonance effect from electron-deficient carbonyls and electron-rich nitrogen atom, both emitters realize significant TADF characteristics with small ΔE _ST s of 0.18 and 0.19 eV, respectively. And, molecular relaxations were dramatically suppressed for both emitters because of their conjugated structure. In the devices, 3-PhQAD realizes superior performance with a maximum external quantum efficiency (EQE) of 19.1&#37; and a narrow full width at half-maximum (FWHM) of 44 nm, whereas a maximum EQE of 18.7&#37; and an extremely narrow FWHM of 34 nm are realized for 7-PhQAD. These superior results reveal that apart from nitrogen and boron-aromatic systems, QAD framework can also act as a TADF matrix with effective resonance effect, and QAD derivatives are ideal candidates to develop TADF emitters with narrow FWHMs for practical applications.

DOI： 10.1021/acsami.8b19635

記述言語：英語  

Doping poly(3,4-ethylenedioxythiophene):poly (styrene sulfonate) (PEDOT:PSS) by polar solvent is a promising approach to decrease the resistivity of pristine PEDOT:PSS film. In this work, properties of doped PEDOT:PSS films by a series of alcohol additives, including ethanol, glycerol, meso-erythritol, xylitol, and D-sorbitol, are comparatively studied for the first time. The absorption spectra, surface morphology, solvent contact angle, hole mobility, work function, and carrier transport properties via Hall measurement of these doped films were systematically investigated to find out the dopant dependent PEDOT:PSS film property. Then these low-resistivity PEDOT:PSS films were applied as the hole transport layer in 20 wt&#37; poly(diketopyrro lopyrrole-terthiophene) (PDPP3T) based bulk heterojunctions (BHJs), and the highest power conversion efficiency (PCE) of 3.74&#37; was achieved for the meso-erythritol doped PEDOT:PSS based BHJ, which is 21&#37; higher than that (3.09&#37;) of the pristine PEDOT:PSS based BHJ. Finally, the performance of all six BHJs is significantly improved by using lithium fluoride instead of bathocuproine, and the PCE for the meso-erythritol doped PEDOT:PSS based BHJ achieves 4.86&#37;. Among these alcohol additives, meso-erythritol and D-sorbitol depict the optimum doping effect. Our results give important guidance to develop alcohol-additive doped PEDOT:PSS films in organic optoelectronic devices.

DOI： 10.1088/1361-6463/ab04dc

記述言語：その他   掲載種別：研究論文（学術雑誌）  

We report the electrochemical properties, and electrogenerated chemiluminescence (ECL) of eight different organometallic complexes of Eu(III) and Tb(III), Eu(dbm) phen, Eu(dbm) bath, Eu(fod) phen, Eu(tta) phen, Tb(acac) phen, Tb(acac) bath, Tb(fod) phen, and Tb(tmhd) bpy in acetonitrile, where phen, bath, and bpy are 1, 10-phenanthroline, bathophenanthroline, 2,2′-bipyridyl, respectively, and the anionic ligands, acac , dbm , fod , and tta are the enolate forms of acetylacetone, dibenzoylmethanate, 6,6,7,7,8,8,8-heptafluoro-2,2-dimethyl-3,5-octanedione, and thenoyltrifluoroacetone, respectively. The electronic states of the neutral and some charged states of the complexes were clarified with density functional theory calculations. The ECL spectra were recorded by using S O as a coreactant, and for all complexes, sharp ECL spectra, which are attributable to the f-f transitions, were observed. On the potential-dependent ECL spectra, broad ECLs, which were originated from the ligands, were also detected. Based on the ECL behavior and the electronic states, the mechanisms of the intraconfigurational ECL were discussed. 3 3 3 3 3 3 3 3 2 8 − − − − 2−

DOI： 10.1002/slct.201900595

記述言語：その他   掲載種別：研究論文（学術雑誌）  

© 2019 Optical Society of America. Encapsulation of fluorescent directives "thermally activated delayed fluorescence" molecules into a zeolitic imidazole frameworks was proposed, and 4CzIPN molecules were successfully encapsulated into ZIF-11 pores by one step process with a loading efficiency of 0.064 of the proportion of 4CzIPN/ZIF-11. Some Spectroscopic studies such as XRD, UV-Vis, FTIR, THz-TDS and time resolved streak measurement, and the suppression of intramolecular vibrational, rotational and librational motions of 4CzIPN molecules were confirmed. Interestingly, the florescence lifetime of 4CzIPN was considerably elongated from 2.37 ns to 14.8 ns, while the phosphorescence lifetime became a little bit short from 2.15 μs to 1.65 μs. The lifetime differences was thought to be due to the suppression of the 4CzIPN molecules' motion by the close ZIF-11 frameworks that affected the reverse intersystem crossing.

DOI： 10.1364/OME.9.001150

記述言語：その他  

Fabrication-method Independence of Organic Long-persistent Luminescence Performance

DOI： 10.1246/cl.180949

記述言語：その他  

A solvent-free and vacuum-free melt-processing method to fabricate organic semiconducting layers with large crystal size for organic electronic applications

DOI： 10.1039/c8tc04834g

記述言語：英語  

DOI： 10.1016/j.optmat.2019.03.012

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Encapsulation of fluorescent directives "thermally activated delayed fluorescence" molecules into a zeolitic imidazole frameworks was proposed, and 4CzIPN molecules were successfully encapsulated into ZIF-11 pores by one step process with a loading efficiency of 0.064 of the proportion of 4CzIPN/ZIF-11. Some Spectroscopic studies such as XRD, UV-Vis, FTIR, THz-TDS and time resolved streak measurement, and the suppression of intramolecular vibrational, rotational and librational motions of 4CzIPN molecules were confirmed. Interestingly, the florescence lifetime of 4CzIPN was considerably elongated from 2.37 ns to 14.8 ns, while the phosphorescence lifetime became a little bit short from 2.15 mu s to 1.65 mu s. The lifetime differences was thought to be due to the suppression of the 4CzIPN molecules' motion by the close ZIF-11 frameworks that affected the reverse intersystem crossing. (C) 2019 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

DOI： 10.1364/OME.9.001150

記述言語：英語   掲載種別：研究論文（学術雑誌）  

© 2019 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim The relatively short device lifetime of blue organic light-emitting diodes (OLEDs) when compared with the lifetimes of green and red OLEDs is one of the crucial problems that must be overcome to enable practical application of these devices to full-color OLED displays. This work focuses on the degradation phenomena of OLEDs that are based on sky-blue thermally activated delayed fluorescence emitters and clarifies the degradation mechanisms based on spectral change of the electroluminescence, which indicates the formation of electromer emission from an electron transport layer. Additionally, it is determined that the change in the carrier balance that occurs during this degradation process can be ascribed to the formation of electron traps.

DOI： 10.1002/aelm.201800708

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Organic nanoparticles (O-dots) with a high photoluminescence quantum yield (94%) and long-lived delayed emission (3.1 μs) originating from thermally activated delayed fluorescence (TADF) were developed as glassy state particles using an oil in water emulsion under high pressure (<20 bar). The TADF glassy O-dots exhibit not only good dispersibility and high photostability in water but also good uptake properties into living cells. The glassy O-dots will open new uses as organic emitters in biological applications.

DOI： 10.1039/c9cc01420a

記述言語：英語  

DOI： 10.1016/j.orgel.2019.01.032

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Abstract

The organic material 4,4′‐bis[(N‐carbazole)styryl]biphenyl (BSBCz) is an excellent gain medium for laser devices. However, BSBCz laser output quickly degrades during photoexcitation, which is an issue that must be overcome before it can be used for practical applications. In this study, the photodegradation mechanisms of BSBCz are investigated with the aim of enhancing its excited‐state stability. The photodegradation of BSBCz is attributed to instability of the triplet excited states that would occasionally decompose into other species. This decomposition reduces absorption and introduces exciton quenchers. Incorporating the triplet managing material 9,10‐di(naphtha‐2‐yl)anthracene (ADN) into BSBCz films greatly improves photoluminescence and amplified spontaneous emission stability because of the effective removal of the unstable triplets by ADN. This triplet managing method makes it possible to increase operational stability for BSBCz‐based organic light‐emitting diodes. Therefore, these results will contribute toward the fabrication of stable optically and electrically pumped organic laser diodes.

DOI： 10.1002/adfm.201807148

記述言語：英語   掲載種別：研究論文（学術雑誌）  

This work investigates the feasibility of using low-dimensional perovskites for electrically driven lasers given the current status of perovskite light-emitting diodes and optically pumped lasers. In our progress toward electrically driven lasers, we performed a variety of measurements on bulk and low-dimensional perovskite films to give a baseline for expectations. This included the measurement of amplified spontaneous emission, lasing, and near-infrared light-emitting diodes operated at low and high current density. We considered power density thresholds needed for amplified spontaneous emission and lasing and compared this to light-emitting diodes operated at high current density to speculate on the future of electrically driven perovskite lasers. We concluded that our current perovskite devices will need current densities of similar to 4 to 10 kA/cm(2) to achieve lasing. Future devices will most significantly benefit from architectures that accommodate higher current, but meaningful reductions in threshold may also come from improved film quality and confinement.

DOI： 10.1021/acsphotonics.8b01413

記述言語：英語   掲載種別：研究論文（学術雑誌）  

We report enhanced near-infrared (NIR) electroluminescence from a Nd ³⁺ -complex with thenoyltrifluoroacetone and 1,10-phenanthroline ligands. The NIR-emitting complex was blended into an exciplex-forming co-host system comprising 2,7-bis(diphenylphosphoryl)-9,9′-spirobifluorene as the electron transport material and 4,4′,4″-tris(carbazol-9-yl)triphenylamine as the hole transport material in solution-processed small molecule organic light-emitting diodes (OLEDs). This binary ambipolar host system favors direct charge trapping and exciton formation on the Nd ³⁺ -complex molecules. Efficient energy transfer from the singlet and triplet exciplexes formed between the host molecules to the Nd ³⁺ ions contributes to the enhanced luminescence efficiency. The photoluminescence quantum yield of this blend is 1.2%, and the optimized OLED shows a maximum electroluminescence external quantum efficiency of 0.034%. The device also exhibits a low efficiency roll-off of only 12% over a current density range of 100 mA/cm ² , due to the reduced triplet-polaron annihilation.

DOI： 10.1063/1.5054721

記述言語：英語   掲載種別：研究論文（学術雑誌）  

The development of single-component organic dual light-emitting molecules is of interest for a range of applications including white organic light-emitting diodes. Herein, a new thermally-activated delayed fluorescent molecule containing 4,6-bis-phenyl phenothiazine as donor units and 2-thiophene-1,3,5-triazine as acceptor unit was synthesized using a simple cost-effective method. This compound shows two stable molecular conformations due to the presence of the phenothiazine units in its molecular structure. These conformers exhibit different photophysical properties in both solution and thin films. The electroluminescence properties of this novel emitter were then examined in organic light-emitting diodes and the results provide useful insights into the influence of the device architecture on the dual emission characteristics. The experimental results were consistent with the optical simulations and the optimized architecture led to the fabrication of electroluminescent devices with an external quantum efficiency of 11.5% and a maximum luminance value of 10370 cd m ^-2 .

DOI： 10.1039/c8ra10393c

記述言語：英語  

DOI： 10.1038/s41467-018-07482-6

記述言語：英語   掲載種別：研究論文（学術雑誌）  

We report an efficient luminescent molecule exhibiting thermally activated delayed fluorescence with a long-delayed fluorescence lifetime of 0.8 ms. Although the reverse intersystem crossing rate constant is small at 2.1 x 10(3) s(-1), the molecule shows a high photoluminescence quantum yield of 89 +/- 2&#37;, indicating the suppression of nonradiative decay from the triplet state.

DOI： 10.1246/cl.180813

記述言語：英語  

DOI： 10.1038/s41467-018-07482-6

記述言語：英語   掲載種別：研究論文（学術雑誌）  

We report an efficient luminescent molecule exhibiting thermally activated delayed fluorescence with a long-delayed fluorescence lifetime of 0.8 ms. Although the reverse intersystem crossing rate constant is small at 2.1 x 10(3) s(-1), the molecule shows a high photoluminescence quantum yield of 89 +/- 2&#37;, indicating the suppression of nonradiative decay from the triplet state.

DOI： 10.1246/cl.180813

記述言語：英語  

DOI： 10.1002/advs.201801079

記述言語：英語  

DOI： 10.1021/jacs.8b06002

記述言語：英語  

DOI： 10.1002/advs.201801079

記述言語：英語  

DOI： 10.1021/jacs.8b06002

記述言語：その他  

Low ASE Threshold and Efficient Electroluminescence from a Carbazole Derivatized Excited State Intramolecular Proton Transfer (ESIPT) Dye

DOI： 10.1021/acsphotonics.8b00907

記述言語：英語  

【2018-9】Ultrahigh Power Efficiency Thermally Activated Delayed Fluorescent OLEDs by the Strategic Use of Electron‐Transport Materials

DOI： 10.1002/adom.201800376

記述言語：その他  

Organic Long-Persistent Luminescence from a Flexible and Transparent Doped Polymer

DOI： 10.1002/adma.201803713

記述言語：その他  

Wide-Range Tuning and Enhancement of Organic Long-Persistent Luminescence Using Emitter Dopants

DOI： 10.1002/adma.201800365

記述言語：英語   掲載種別：研究論文（学術雑誌）  

The development of host materials with high performance is essential for fabrication of efficient and stable organic light-emitting diodes (OLEDs). Although host materials used in OLEDs are typically organics, in this study, it is shown that the organic-inorganic perovskite CH3NH3PbCl3 (MAPbCl(3)) can be used as a host layer for OLEDs. Vacuum-evaporated MAPbCl(3) films have a wide band gap of about 3 eV and very high and relatively balanced hole and electron mobilities, which are suitable for the host material. Photoluminescence and electroluminescence take place through energy transfer from MAPbCl(3) to an organic emitter in films. Incorporation of an MAPbCl(3) host layer into OLEDs leads to a reduction of driving voltage and enhancement of external quantum efficiency as compared to devices with a conventional organic host layer. Additionally, OLEDs with an MAPbCl(3) host layer demonstrate very good operational stability under continuous current operation. These results can be extensively applied to organic- and perovskite-based optoelectronics.

DOI： 10.1002/adma.201802662

記述言語：英語   掲載種別：研究論文（学術雑誌）  

We developed a novel naphthalene derivative to function as a wide-energy-gap liquid organic semiconductor (LOS) host material for the limited range of liquid deep-blue light-emitting materials that have been developed to date. The naphthalene derivative 1-naphthaleneacetic acid 2-ethylhexyl ester (NLQ), which shows a low viscosity of 20 mPa·s at 25 °C, was synthesized as a LOS by introducing an ethylhexyl group into naphthalene. We doped 9,10-diphenylanthracene (DPA) into NLQ as a guest deep-blue dye. The highest occupied molecular orbital (HOMO) energy level of NLQ was estimated to be − 6.40 eV from photoelectron spectroscopy measurements in air. The energy gap of NLQ was estimated to be 4.08 eV from its absorption spectrum, indicating that NLQ has the widest energy gap of any such host material to date. The lowest unoccupied molecular orbital energy level of NLQ was calculated to be − 2.31 eV. Deep-blue electroluminescence emission in a liquid state was obtained by doping DPA into NLQ. Light emission could be achieved by a combination of Förster resonance energy transfer and direct recombination of trapped holes and electrons because the energy gap of DPA is straddled by the wider energy gap of NLQ.

DOI： 10.1016/j.jlumin.2018.03.072

記述言語：英語  

DOI： 10.1021/acs.chemmater.8b02247

記述言語：その他   掲載種別：研究論文（学術雑誌）  

© 2018 Author(s). Triplet-triplet annihilation (TTA) will change the ratio between fluorescence and phosphorescence in the photoluminescence spectrum of a thermally activated delayed fluorescence emitter at very low temperature. Using the resultant spectral blueshift, this study investigated the nature of TTA in 1,2,3,5-tetrakis(carbazol-9-yl)-4,6-dicyanobenzene (4CzIPN) doped in a host material. The spectral blueshift is not caused by singlet-triplet annihilation and the emitter saturation effect and is less influenced by the emitter aggregates, particularly for the case of a lower doping concentration. Using these features, it is possible to focus on TTA. For 4CzIPN, the spectral blueshift due to TTA is recognized even in samples with the doping concentration as low as 1 wt. &#37;.

DOI： 10.1063/1.5025870

記述言語：英語   掲載種別：研究論文（学術雑誌）  

The development of host materials with high performance is essential for fabrication of efficient and stable organic light-emitting diodes (OLEDs). Although host materials used in OLEDs are typically organics, in this study, it is shown that the organic-inorganic perovskite CH3NH3PbCl3 (MAPbCl(3)) can be used as a host layer for OLEDs. Vacuum-evaporated MAPbCl(3) films have a wide band gap of about 3 eV and very high and relatively balanced hole and electron mobilities, which are suitable for the host material. Photoluminescence and electroluminescence take place through energy transfer from MAPbCl(3) to an organic emitter in films. Incorporation of an MAPbCl(3) host layer into OLEDs leads to a reduction of driving voltage and enhancement of external quantum efficiency as compared to devices with a conventional organic host layer. Additionally, OLEDs with an MAPbCl(3) host layer demonstrate very good operational stability under continuous current operation. These results can be extensively applied to organic- and perovskite-based optoelectronics.

DOI： 10.1002/adma.201802662

記述言語：その他  

Low Amplified Spontaneous Emission Threshold from Organic Dyes Based on Bis-stilbene

DOI： 10.1002/adfm.201802130

記述言語：英語  

DOI： 10.1021/acs.chemmater.8b02247

記述言語：その他  

Vacuum chamber considerations for improved organic light-emitting diode lifetime

DOI： 10.1063/1.5047542

記述言語：英語   掲載種別：研究論文（学術雑誌）  

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. (C) 2018 Society of Photo-Optical Instrumentation Engineers (SPIE)

DOI： 10.1117/1.JPE.8.032110

記述言語：英語   掲載種別：研究論文（学術雑誌）  

© 2018 Society of Photo-Optical Instrumentation Engineers (SPIE). A four-level model consisting of a higher triplet excited state (T2), the lowest singlet and triplet excited states (S1 and T1), and the ground state was previously used to understand emission properties of a thermally activated delayed fluorescence (TADF) emitter, 1,2,3,5-tetrakis(carbazol-9-yl)-4,6-dicyanobenzene (4CzIPN). In this report, we discuss the four-level model in more detail and apply to the other two TADF emitters, i.e., 1,2,4,5-tetrakis(carbazol-9-yl)-3,6-dicyanobenzene (4CzTPN) and 1,2-bis(carbazol-9-yl)-4,5-dicyanobenzene (2CzPN), in order to determine their excited-state structures. It is suggested that in all the emitters T2 lies between S1 and T1 and play an essential role in the emitting process. In 4CzTPN, phosphorescence from T2 is clearly observed around 100 K as in 4CzIPN. Compared to the other two emitters, 2CzPN has a wider energy gap between S1 and T1 so that delayed fluorescence at room temperature is thought to be mixed with phosphorescence. Because of this mixing, the spectrum characteristic of phosphorescence from T2 in 2CzPN cannot be identified.

DOI： 10.1117/1.JPE.8.032104

記述言語：その他  

The Importance of Excited-State Energy Alignment for Efficient Exciplex Systems Based on a Study of Phenylpyridinato Boron Derivatives.

DOI： 10.1002/anie.201804218

記述言語：英語   掲載種別：研究論文（学術雑誌）  

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.

DOI： 10.1117/1.JPE.8.032102

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Carrier mobility is one of the crucial parameters determining the electronic device performance. We apply the light-induced transient grating technique to measure independently the carrier diffusion coefficient and lifetime, and to reveal the impact of additives on carrier transport properties in wet-cast CH3NH3PbI3 (MAPbI3) perovskite films. We use the high excitation regime, where diffusion length of carriers is controlled purely by carrier diffusion and not by the lifetime. We demonstrate a four-fold increase in diffusion coefficient due to the reduction of localization center density by additives
however, the density dependence analysis shows the dominance of localization-limited diffusion regime. The presented approach allows us to estimate the limits of technological improvement - carrier diffusion coefficient in wet-cast layers can be expected to be enhanced by up to one order of magnitude.

DOI： 10.1021/acs.jpclett.8b01155

記述言語：その他  

Simultaneous Edge-on to Face-on Reorientation and 1D Alignment of Small pi-Conjugated Molecules Using Room-Temperature Mechanical Rubbing

DOI： 10.1002/adfm.201707038

記述言語：英語   掲載種別：研究論文（学術雑誌）  

【2018-5】Observation of Spontaneous Orientation Polarization in Evaporated Films of Organic Light-Emitting Diode Materials
The molecular orientation in organic semiconductor films determines device performances. In particular, the spontaneous orientation of a permanent dipole moment (PDM) along the surface normal direction induces a polarization charge at the hetero-interfaces of stacked multilayer devices, and the interface charge dominates the charge accumulation and injection properties. Spontaneous orientation polarization (SOP) has been observed in the "randomly oriented" films of several organic semiconductor materials, and is potentially inherent in many common materials. Herein, we report that 11 additional molecules of organic light-emitting diode materials, including thermally activated delayed fluorescence emitters, and horizontally oriented emitters and electron transporters, exhibit SOP in their evaporated films. The experimental results clearly indicate that SOP frequently occurs in "horizontally oriented" films as well as "randomly oriented" films. The factors contributing to SOP formation are discussed in terms of the figure of merit per PDM. We found that strong intermolecular interactions tend to reduce the figure of merit. Moreover, we suggest the impact of SOP on device performances.

DOI： 10.1016/j.orgel.2018.04.026

記述言語：英語   掲載種別：研究論文（学術雑誌）  

In this study, we investigate the nanoscale effects of photochemically active additives of benzoquinone (BQ), hydroquinone (HQ), and tetracyanoquinodimethane (TCNQ) on grain boundaries in CH3NH3PbI3 solar cells. We employ scanning probe microscopy under light illumination, in particular Kelvin probe force microscopy, to study surface potential changes under laser light illumination. The recently found improvement in the efficiency of BQ added solar cells can be clearly seen in vanishing contact potential differences at grain boundaries under illumination, rendering the material more uniform under solar cell operating conditions. These effects are observed for BQ, but not for HQ and TCNQ. Our findings shed light onto halide perovskite materials and the functional additive design for improved solar cell performance.

DOI： 10.1021/acs.jpcc.8b00804

記述言語：英語   掲載種別：研究論文（学術雑誌）  

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&#37;. 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 &lt
0.07.

DOI： 10.1002/adfm.201706023

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Near-infrared organic light-emitting diodes and semiconductor lasers could benefit a variety of applications including night-vision displays, sensors and information-secured displays. Organic dyes can generate electroluminescence efficiently at visible wavelengths, but organic light-emitting diodes are still underperforming in the near-infrared region. Here, we report thermally activated delayed fluorescent organic light-emitting diodes that operate at near-infrared wavelengths with a maximum external quantum efficiency of nearly 10&#37; using a boron difluoride curcuminoid derivative. As well as an effective upconversion from triplet to singlet excited states due to the non-adiabatic coupling effect, this donor-acceptor-donor compound also exhibits efficient amplified spontaneous emission. By controlling the polarity of the active medium, the maximum emission wavelength of the electroluminescence spectrum can be tuned from 700 to 780 nm. This study represents an important advance in near-infrared organic light-emitting diodes and the design of alternative molecular architectures for photonic applications based on thermally activated delayed fluorescence.

DOI： 10.1038/s41566-017-0087-y

記述言語：英語   掲載種別：研究論文（学術雑誌）  

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.

DOI： 10.1021/acs.jpclett.7b03232

記述言語：その他   掲載種別：研究論文（学術雑誌）  

<p>The first metal–organic framework exhibiting thermally activated delayed fluorescence (TADF) was developed.</p>

DOI： 10.1039/c7cc08595h

記述言語：英語  

DOI： 10.1038/s42004-018-0027-x

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Organic single crystals (SCs) expressing long-range periodicity and dense molecular packing are an attractive amplifying medium for the realization of electrically driven organic lasers. However, the amplified spontaneous emission (ASE) threshold (1-10 kW/cm2) of SCs is still significantly higher compared to those of amorphous neat or doped films. The current study addresses this issue by investigating ASE properties of rigid bridging group-containing bifluorene SCs. Introduction of the rigid bridges in bifluorenes enables considerable reduction of nonradiative decay, which, along with enhanced fluorescence quantum yield (72-82&#37;) and short excited state lifetime (1.5-2.5 ns), results in high radiative decay rates (0.5 × 109 s-1) of the SCs, making them highly attractive for lasing applications. The revealed ASE threshold of 400 W/cm2 in acetylene-bridged bifluorene SCs is found to be among the lowest ever reported for organic crystals. Ultrafast transient absorption spectroscopy enabled one to disclose pronounced differences in the excited state dynamics of the studied SCs, pointing out the essential role of radiative traps in achieving a record low ASE threshold. Although the origin of the trap states was not completely unveiled, the obtained results clearly evidence that the crystal doping approach can be successful in achieving extremely low ASE thresholds required for electrically pumped organic laser.

DOI： 10.1021/acsami.7b14702

記述言語：英語   掲載種別：研究論文（学術雑誌）  

We report deep-red amplified spontaneous emission (ASE) from cis-configured squaraine (cis-DCSQ1) under optical pumping. Doping of cis-DCSQ1 into a 4,4′-bis(9-carbazolyl)-2,2′-biphenyl (CBP) host film at an appropriate concentration (0.5 wt &#37; for this system) led to a marked increase of photoluminescence quantum yield because of efficient CBP-to-cis-DCSQ1 Förster resonance energy transfer and suppression of aggregation-caused quenching. Thus, this doped film showed clear ASE with a threshold of around 10 μJ cm-2 and peak wavelength of 687 nm. These results proved that cis-configured squaraine derivatives are promising as gain materials for future applications as deep-red organic lasers.

DOI： 10.1021/acsami.7b15562

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Exciton diffusion is considered to be of prime importance for controlling the recombination zone in organic light emitting devices. This is particularly relevant for organic lasers based on single crystals, where undesirable exciton-exciton annihilation at high concentrations is inevitable. Here, exciton diffusion is studied in bifluorene single crystals specifically designed for organic laser applications, therefore featuring exceptionally low threshold of light amplification. The non-destructive light induced transient grating (LITG) technique capable of simultaneously evaluating the exciton lifetime and diffusion coefficient along different directions of the crystal was employed for this study. Highly anisotropic singlet exciton diffusion with the diffusion coefficient varying from &lt
0.05 up to 0.96 cm2/s (in a perpendicular direction) and the corresponding diffusion lengths changing from &lt
60 up to 300 nm, respectively, was revealed in ethylene-bridged bifluorene crystals. The LITG results on the directionality of exciton diffusion are anticipated to be essential for devising single crystal based organic lasers.

DOI： 10.1063/1.5008376

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Two thermally activated delayed fluorescence (TADF) emitters 9′-(4-(4,6-diphenyl-1,3,5-triazin-2-yl)-2-fluorophenyl)-9′H-9,3′:6′,9′′-tercarbazole (TCTZ-F) and 9′-(4-(4,6-diphenyl-1,3,5-triazin-2-yl)-2,6-difluorophenyl)-9′H-9,3′:6′,9′′-tercarbazole (TCTZ-2F) were synthesized and compared to the previously reported molecule 9′-(4-(4,6-diphenyl-1,3,5-triazin-2-yl)phenyl)-9′H-9,3′:6′,9′′-tercarbazole (TCTZ) to explore the possible effects of the fluorine atom(s) on the molecular conformation, electronic coupling between the donor and acceptor groups, and consequently the photophysical behavior of the emitters. Specifically, the TCTZ-F molecule was calculated to have a smaller dihedral angle than TCTZ-2F and a smaller S₁-T₁ gap than TCTZ, which led it to have the highest photoluminescence quantum yield (PLQY) among this series of compounds. An OLED fabricated with TCTZ-F as the emitter achieved the highest external quantum efficiencies (22.5%) of this series, indicating that fluorination can play a useful role in TADF emitters.

DOI： 10.1039/c8tc01158c

記述言語：英語   掲載種別：研究論文（その他学術会議資料等）  

We evaluated the influence of impurities in the vacuum chamber used for device fabrication on the lifetime ofOLEDs and found a correlation between lifetime and the device fabrication time. Our results suggest that impurities including previously deposited materials and plasticizers from the chamber components impact lifetime and reproducibility.

DOI： 10.1002/sdtp.11560

記述言語：英語   掲載種別：研究論文（学術雑誌）  

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.

DOI： 10.1038/s41467-017-02419-x

記述言語：その他   掲載種別：研究論文（学術雑誌）  

© 2017, The Author(s). The photoluminescence properties of a thermally activated delayed fluorescence emitter, 1,2-bis(carbazol-9-yl)-4,5-dicyanobenzene (2CzPN), doped in a host matrix consisting of 1,3-bis(9-carbazolyl)benzene and a polar inert molecule, camphoric anhydride (CA), in various concentrations have been investigated. It is found that the addition of CA stabilizes only the lowest singlet excited state (S1) of 2CzPN without changing the energy level of the lowest triplet excited state (T1), leading to a reduction in the energy gap between S1and T1. The maximum reduction of energy gap achieved in this work has been determined to be around 65 meV from the shift of the fluorescence spectrum and the temperature dependence of the photoluminescence decay rate.

DOI： 10.1186/s11671-017-2012-1

記述言語：英語   掲載種別：研究論文（学術雑誌）  

In the traditional molecular design of thermally activated delayed fluorescence (TADF) emitters composed of electron-donor and electron-acceptor moieties, achieving a small singlet-triplet energy gap (Delta E-ST) in strongly twisted structures usually translates into a small fluorescence oscillator strength, which can significantly decrease the emission quantum yield and limit efficiency in organic light-emitting diode devices. Here, based on the results of quantum-chemical calculations on TADF emitters composed of carbazole donor and 2,4,6-triphenyl-1,3,5-triazine acceptor moieties, a new strategy is proposed for the molecular design of efficient TADF emitters that combine a small Delta E-ST with a large fluorescence oscillator strength. Since this strategy goes beyond the traditional framework of structurally twisted, charge-transfer type emitters, importantly, it opens the way for coplanar molecules to be efficient TADF emitters. Here, a new emitter, composed of azatriangulene and diphenyltriazine moieties, is theoretically designed, which is coplanar due to intramolecular H-bonding interactions. The synthesis of this hexamethylazatriangulene-triazine (HMAT-TRZ) emitter and its preliminary photophysical characterizations point to HMAT-TRZ as a potential efficient TADF emitter.

DOI： 10.1002/adma.201702767

記述言語：英語   掲載種別：研究論文（学術雑誌）  

The influences of film density and molecular orientation on the carrier conduction and air stability of vacuum-deposited amorphous organic films of N,N'-di(1-naphthyl)-N,N'-diphenyl-(1,1'-biphenyl)-4,4'-diamine (alpha-NPD) were investigated. The substrate temperature (T-sub) during vacuum deposition had different effects on the film density and molecular orientation of alpha-NPD. Film density was a concave function of T-sub; maximum density was attained at T-sub, = 270-300 K. alpha-NPD molecules were randomly oriented at T-sub, = 342 K, and their horizontal orientation on the substrate became dominant as T-sub:, decreased. Hole current and air stability were clearly raised by increasing the film density by 1 to 2&#37;; these effects were, respectively, attributed to carrier hopping between neighboring alpha-NPD molecules and suppressed penetration of oxygen and water. These results imply that increasing film density is more effective to enhance the electrical performance of organic thin-film devices with alpha-NPD films than control of molecular orientation.

DOI： 10.1021/acs.jpclett.7b02808

記述言語：英語   掲載種別：研究論文（学術雑誌）  

A family of organic emitters with a donor-sigma-acceptor (D-sigma-A) motif is presented. Owing to the weakly coupled D-sigma-A intramolecular charge-transfer state, a transition from the localized excited triplet state ((LE)-L-3) and charge-transfer triplet state ((CT)-C-3) to the charge-transfer singlet state ((CT)-C-1) 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-sigma-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.

DOI： 10.1002/anie.201708876

記述言語：英語   掲載種別：研究論文（学術雑誌）  

The optical, structural, and electroluminescent (EL) characteristics of pure quasi-2D CsPb2Br5 were reported. We fabricated continuous, compact, well-crystallized CsPb2Br5 films by centrifugal coating from a colloidal solution containing CsPb2Br5 nanoparticles. The centrifugal-coated CsPb2Br5 films have a photoluminescence quantum yield (PLQY) of similar to 35&#37; because of its low-dimensional structure. Taking advantage of the high PLQY, we fabricated perovskite light-emitting diodes (PeLEDs) with a centrifugal coated CsPb2Br5 emitting layer exhibiting bright green EL, a maximum luminance of 7317 cd m(-2), an and external quantum efficiency of 1.1&#37;. Additionally, the EL color could be changed easily from green to red using a halogen exchange method. The half lifetime of our CsPb2Br5 PeLEDs reached around 6 h under continuous operation at 10 mA cm(-2).

DOI： 10.1021/acs.jpclett.7b02371

記述言語：英語   掲載種別：研究論文（学術雑誌）  

To find some intrinsic relevance between the photovoltaic performance and dielectric properties of diindenoperylene (DIP) mixed heterojunctions (MHJs), this work demonstrates both the photovoltaic performance and dielectric characteristic dependence on the DIP concentration. 5 wt&#37;-DIP MHJ shows relatively higher performance compared to other MHJs with higher DIP ratio over the range of 5 wt&#37;-90 wt&#37;. The dielectric constant of blend layers decreases with the DIP ratio, thus results in larger Coulomb capture radius and exciton binding energy, which suppresses the exciton dissociation in MHJs with high DIP ratio. Then, the dielectric characteristic of capacitance-voltage (C-V) in dark and under illumination as well as of capacitance-frequency (C-f)at dc bias of 1.6 V for the DIP MHJs were measured. The geometric capacitance of the MHJs extracted from the C-V in dark indicates a positive dependence on the DIP concentration. C-V peak height decreases with the DIP concentration from 0 to 60 wt&#37; implies that the hole drift becomes dominated at higher DIP content. The open circuit voltage (V-oc) of all the MHJs shows an identical trend with the normalized built-in potential. In dark condition, depletion width (W) gradually decreases with the DIP concentration from 5 wt&#37; to 60 wt&#37;. W becomes narrower under illumination, ascribed to the increased capacitance from photo-generated charge. The free carrier density (N-D) imposes a negative influence on fill factor of MHJs. The extracted electron mobility by C-f characteristic gradually decreases with the DIP ratio.

DOI： 10.1016/j.synthmet.2017.09.001

記述言語：英語   掲載種別：研究論文（学術雑誌）  

The electrochemical properties and electrogenerated chemiluminescence (ECL) of a borondipyrromethane (BODIPY) derivative, 2,8-bis(4-isopropylphenyl)-difuro[2,3-b][3,2-g]-5,5-difluoro-5-bora-3a,4a-diaza-s-indacene (Derivative 1, Figure) are described. Derivative 1 emitted ECL in the range of 650 similar to 800nm by using tripropylamine (TPA) as a coreactant. In the cyclic voltammogram, Derivative 1 showed a reversible oxidation wave, whereas the reduction wave was irreversible. Energetically, it is likely that triplet-triplet annihilation is the main pathway to emit ECL through the ion annihilation of the radical anions and cations of Derivative 1 whereas the lowest excited singlet state of Derivative 1 is directly produced with TPA. The maximum ECL wavelengths (670nm at 0.01mM) were red-shifted with increasing the concentration of Derivative 1 because of the self-absorption resulted from a small Stokes shift (similar to 10nm). Relative ECL efficiency of Derivative 1 was 0.13 compared to that of a Ru(bpy)(2+)/TPA system.

DOI： 10.1002/slct.201702449

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Long persistent luminescence (LPL) materials - widely commercialized as 'glow-in-the-dark' paints - store excitation energy in excited states that slowly release this energy as light. At present, most LPL materials are based on an inorganic system of strontium aluminium oxide (SrAl 2 O 4) doped with europium and dysprosium, and exhibit emission for more than ten hours. However, this system requires rare elements and temperatures higher than 1,000 degrees Celsius during fabrication, and light scattering by SrAl 2 O 4 powders limits the transparency of LPL paints. Here we show that an organic LPL (OLPL) system of two simple organic molecules that is free from rare elements and easy to fabricate can generate emission that lasts for more than one hour at room temperature. Previous organic systems, which were based on two-photon ionization, required high excitation intensities and low temperatures. By contrast, our OLPL system - which is based on emission from excited complexes (exciplexes) upon the recombination of long-lived charge-separated states - can be excited by a standard white LED light source and generate long emission even at temperatures above 100 degrees Celsius. This OLPL system is transparent, soluble, and potentially flexible and colour-tunable, opening new applications for LPL in large-area and flexible paints, biomarkers, fabrics, and windows. Moreover, the study of long-lived charge separation in this system should advance understanding of a wide variety of organic semiconductor devices.

DOI： 10.1038/nature24010

記述言語：英語   掲載種別：研究論文（学術雑誌）  

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-dimethy1-9,10-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&#37; and 88&#37; in their doped films, respectively. The maximum external electroluminescence (EL) efficiencies of 13.8&#37; in 4ASOA and 10.4&#37; 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.

DOI： 10.1016/j.jlumin.2017.06.006

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Confinement of Long-Lived Triplet Excitons in Organic Semiconducting Host-Guest Systems
Long-lived triplet excitons on organic molecules easily deactivate at room temperature because of the presence of thermally activated nonradiative pathways. This study demonstrates long-lived phosphorescence at room temperature resulting from suppression of the nonradiative deactivation of triplet excitons in conventional organic semiconducting host-guest systems. The nonradiative deactivation pathway strongly depends on the triplet energy gap between the guest emitting molecules and the host matrices. The triplet energy gap required to confine the long-lived triplet excitons (approximate to 0.5 eV) is much larger than that of conventional host-guest systems for phosphorescent emitters. By effectively confining the triplet excitons, this study demonstrates long-lived room-temperature phosphorescence under optical and electrical excitation.

DOI： 10.1002/adfm.201703902

記述言語：英語   掲載種別：研究論文（学術雑誌）  

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&#37;.

DOI： 10.1246/cl.170587

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Metal halide perovskites are attractive materials for the realization of cheap and effective solar cells, thin film transistors, and light emitters. Carrier diffusion at high excitations, however, is poorly addressed in perovskites, even though it governs the diffusion length and determines the efficiency of photonic devices. To fully understand the dependence of diffusion length on carrier density, we performed direct and independent measurements of the carrier diffusion coefficient and recombination rate in several methylammonium lead halide perovskite layers by applying the light-induced transient grating technique. We demonstrate the existence of two distinct carrier diffusion regimes within the density range of 10(18)-10(20) cm(-3). In the perovskite films of high compositional quality, diffusion is governed by a bandlike transport of free carriers. The diffusivity is high (0.28-0.7 cm(2)/s) in these samples, even at low carrier density, and further increases with excitation due to carrier degeneracy. The opposite scenario was observed in disordered perovskite layers, where diffusion is governed by hopping-like transport of localized carriers. The diffusion coefficient in latter layers is small (0.01-0.04 cm(2)/s at low densities) and increases with excitation due to local state filling and carrier delocalization. We show that carrier recombination can be well-described using the nonlinear radiative and nonradiative recombination coefficients that saturate with excitation due to phase space filling at high carrier densities. On the basis of these findings, we provide recommendations for the maximization of carrier diffusion length in different perovskites.

DOI： 10.1021/acs.jpcc.7b04179

記述言語：日本語   掲載種別：研究論文（学術雑誌）  

熱活性型遅延蛍光(TADF)は、三重項励起子を熱励起により一重項励起子に逆項間交差させることで、内部量子効率100&#37;の蛍光発光を可能にする。この分子を用いたデバイスの外部量子効率を向上させるため、配向制御により遷移双極子モーメントを揃えることで、光取出効率を向上させることが重要である。我々は、この分子の配向制御を達成し、さらに配向膜の電子状態が孤立分子と同様であることを示した。

DOI： 10.14886/sssj2008.37.0_3

記述言語：日本語   掲載種別：研究論文（学術雑誌）  

熱活性遅延蛍光分子は、緻密な分子設計によって内部量子効率100&#37;を実現することが知られている。高効率の有機ELデバイス実現のためには、高い内部量子効率の維持が重要であると考える。我々は金属基板上でいくつかのTADF分子について高配向の単分子膜を形成し、STMにより構造解析を行った。また、過渡発光計測の結果、TADF分子の一種である4CzIPNは遅延蛍光の発光効率が膜厚に依存することを見出した。

DOI： 10.14886/sssj2008.37.0_212

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Solution-processable thermally activated delayed fluorescence emitters for application in organic light emitting diodes
Solution-processed organic light emitting diodes (OLEDs) have been fabricated using the thermally activated delayed fluorescence (TADF) emitter, DACT-II, and its soluble derivative, tBu-DACT-II, as emitting dopants. DACT-II reportedly exhibits very high external quantum efficiencies (EQEs) in vacuum-processed OLEDs. The solution-processed DACT-II-based and tBu-DACT-II-based OLEDs exhibited external quantum efficiency exceeding the theoretical upper limit of classical fluorescent OLEDs.

DOI： 10.1002/jsid.598

記述言語：英語   掲載種別：研究論文（学術雑誌）  

The dipole orientation of guest emitters doped into host matrices is usually investigated by angular dependent photoluminescence (PL) measurements, which acquire an out-of-plane PL radiation pattern of the guest-host thin films. The PL radiation patterns generated by these methods are typically analysed by optical simulations, which require expertise to perform and interpret in the simulation. In this paper, we developed a method to calculate an orientational order parameter S without the use of full optical simulations. The PL radiation pattern showed a peak intensity (I-sp) in the emission direction tilted by 40 degrees-60 degrees from the normal of the thin film surface plane, indicating an inherent dipole orientation of the emitter. Thus, we directly correlated I-sp with S. The S - I-sp relation was found to depend on the film thickness (d) and refractive indices of the substrate (n(sub)) and the organic thin film (n(org)). Hence, S can be simply calculated with information of I-sp, d, n(sub), and n(org). We applied our method to thermally activated delayed fluorescence materials, which are known to be highly efficient electroluminescence emitters. We evaluated S and found that the error of this method, compared with an optical simulation, was less than 0.05.

DOI： 10.1038/s41598-017-08708-1

記述言語：英語   掲載種別：研究論文（学術雑誌）  

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&#37; loss of the initial radiant flux after 1000 h under a constant current density of 10mA/cm(2). The variation of hemoglobin oxygen saturation can be detected using the NIR OLEDs as a light source. (C) 2017 The Japan Society of Applied Physics

DOI： 10.7567/APEX.10.074101

記述言語：英語   掲載種別：研究論文（学術雑誌）  

A hemicurcuminoid boron difluoride complex is used as an emitter in organic light-emitting diodes, showing far red/near-infrared electroluminescence with an external quantum efficiency as high as 2.1&#37;. This dye blended in CBP thin films shows amplified spontaneous emission with a threshold of 22 mu J cm(-2) at 750 nm, making this compound attractive for organic semiconductor lasers operating in the near-infrared region.

DOI： 10.1039/c7cc01786c

記述言語：英語   掲載種別：研究論文（学術雑誌）  

The efficiency of organic light emitting diodes (OLEDs) can be improved by controlling the orientation of the transition dipole moment of the emitters. Currently, no effective methods exist for orienting the transition dipole moments in solution processed active layers for OLEDs. We investigate the orientation of the transition dipole moment of small molecular emitters in a host matrix of poly(9,9-dioctylfluorene) (PFO) by means of angle dependent luminescence intensity measurements. The polymer chains of the host orient predominantly in the plane of the film. Fluorescent p-phenylenevinylene oligomers with 6 and 7 repeat units (OPV6, OPV7) are found to also orient preferentially horizontally. The orientation of the emitters can be improved by thermal annealing with up to 90&#37; of transition dipole moments oriented in the plane of the film. The phosphorescent emitter Ir(MDQ)(2)(acac) shows a degree of horizontal orientation in the polymeric host matrix lower than that which is observed for oligomers, but as high as is observed for the same emitter in evaporated layers. A carbazole derivative capable of thermally activated delayed fluorescence shows a small preference for vertical orientation within the polymer host. The strong orientation of OPV6 and OPV7 in the oriented polymer host is rationalized in terms of their high aspect ratios. The use of PFO as host material in host/guest systems allows achieving horizontal orientation of transition dipole moments in solution processed oligomers and small molecular emitters.

DOI： 10.1039/c7tc01568b

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Thermally activated delayed fluorescence (TADF)
[GRAPHIC]
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&#37;. High external electroluminescence quantum efficiencies of up to 14&#37; 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.

DOI： 10.1021/acscentsci.7b00183

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Organo-lead-halide perovskites are promising materials for optoelectronic applications. Perovskite solar cells have reached power conversion efficiencies of over 22&#37;, and perovskite light-emitting diodes have recently achieved over 11&#37; external quantum efficiency. To date, most research on perovskite light-emitting diodes has focused on solution-processed films. There are many advantages of a vapor-based growth process to prepare perovskites, including ease of patterning, ability to batch process, and material compatibility. We investigated an all-vapor perovskite growth process by chemical vapor deposition and demonstrated luminance up to 560 cd/m(2).

DOI： 10.1021/acs.jpclett.7b01093

記述言語：英語   掲載種別：研究論文（その他学術会議資料等）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

We report on the cavity numerical characterization of a second order one-dimensional distributed feedback organic laser. The gain medium containing 6wt. &#37; of 4,4'bis[(N-carbazole) styryl] biphenyl) in a 4,4;-bis[9-dicarbazolyl]-2,2'-biphenyl) host is vacuum deposited to form an organic thin film on a SiO2 grating. The influence of the organic film thickness on the properties of the resonant cavity is investigated through numerical calculations of both the confinement factor Gamma and the Q-factor. The Q-factor is obtained using two methods, one by calculating the eigenmodes of the resonant cavity and the other by calculating the reflection spectrum. It was found that while the Gamma increases with the organic film thickness, the Q-factor shows a non-monotonic function with a maximum value for a thickness of 200 nm. Published by AIP Publishing.

DOI： 10.1063/1.4986504

記述言語：英語  

DOI： 10.1103/PhysRevMaterials.1.075602