工学博士, 東京農工大学

光化学、有機光エレクトロニクス、分子フォトニクス

Manufacturing technology (mechanical, electrical/electronic, chemical engineering), Electronic devices and equipment

Nanotechnology/Materials, Organic functional materials

Nanotechnology/Materials, Functional solid-state chemistry

Nanotechnology/Materials, Basic physical chemistry

Jun. 2021 - Present
The University of Electro-Communications, Graduate School of Informatics and Engineering, School of Informatics and Engineering Department of Engineering Science, Cluster III(Fundamental Science and Engineering), Associate Professor

01 Jun. 2021
The University of Electro-Communications, Department of Engineering Science, Associate Professor

01 Jan. 2018 - 31 May 2021
The University of Electro-Communications, Department of Engineering Science, Assistant Professor

Jan. 2018 - May 2021
The University of Electro-Communications, Graduate School of Informatics and Engineering, School of Informatics and Engineering Department of Engineering Science, Cluster III(Fundamental Science and Engineering), Assistant Professor

01 Apr. 2016 - 31 Dec. 2017
Tokyo Institute of Technology, Department of Materials Science, Assistant Professor

01 Sep. 2012 - 31 Mar. 2016
Tokyo Institute of Technology, Department of Organic and Polymeric Materials, Assistant Professor

01 Sep. 2012 - 31 Mar. 2016
東京工業大学 有機・高分子物質専攻, 助教

01 Apr. 2012 - 31 Aug. 2012
Kyushu University, Center for Organic Photonics and Electronics Research (OPERA), Research Assistant Professor

01 Apr. 2012 - 31 Aug. 2012
同, 特プロ助教

01 Apr. 2010 - 31 Mar. 2012
Kyushu University, Center for Organic Photonics and Electronics Research (OPERA), Research Assistant Professor

01 Apr. 2010 - 31 Mar. 2012
九州大学 最先端有機光エレクトロニクス研究センター, 特任助教

01 Apr. 2009 - 31 Mar. 2010
Kyushu University, Center for Future Chemistry, Post Doctral Fellow

01 Apr. 2004 - 30 Sep. 2006
株式会社フジクラ, 材料技術研究所

01 Apr. 2006 - 31 Mar. 2009
東京農工大学, 工学府, 応用化学専攻

01 Apr. 2002 - 31 Mar. 2004
東京農工大学, 工学研究科, 応用化学専攻

01 Apr. 1998 - 31 Mar. 2002
東京農工大学, 工学部, 応用化学科

Apr. 2024 - Present
日本化学会関東支部幹事

Jan. 2023 - Dec. 2023
Guest Editor in PNAS, https://www.pnas.org/guest-editor/acknowledgments#section-h

Apr. 2022 - Mar. 2023
光化学若手の会 世話人代表

Jul. 2021 - Jun. 2022
Guest Editor of Frontiers in Chemistry, Frontiers, Others

Sep. 2021 - Mar. 2022
第102回春季年会(2022)の第10回ルミネッセンス化学アンサンブル: 未来のサイエンスに向けた多様な励起化学企画委員

Jan. 2016 - Jun. 2016
有機EL討論会実行委員, 有機EL討論会実行委員, Others

Apr. 2023
Chemical Society Japan
Photo-Induced Triplet Depletion Allowing Higher-Resolution Afterglow
CSJ Student Presentation Award 2023, Kikuya Hayashi

Apr. 2023
The Royal Society of Chemistry
2023 Pioneering Investigator in Chemical Communications, Shuzo Hirata

Jan. 2023
American Chemical Society
2023 Early-Career and Emerging Researcher in The Journal of Physical Chemistry, Shuzo Hirata

Apr. 2019
平成31年度科学技術分野の文部科学大臣表彰 若手科学者賞, 平田修造

Nov. 2018
The Royal Society of Chemistry
2018 Emerging Investigator in Journal of Materials Chemistry C, Shuzo Hirata
Official journal

Sep. 2017
Japanese Photochemistry Association
17th The Japanese Photochemistry Association Award for Young Scientist, Shuzo Hirata

Mar. 2016
Chemical Society Japan
65th Chemical Society Japan (CSJ) Award for Young Chemists, Shuzo Hirata

Apr. 2015
日本化学会
日本化学会第95回春季年会優秀講演賞（学術）, Shuzo Hirata

Mar. 2015
Chemical Society Japan
29th Young Scholar Lectures of Chemical Society Japan (CSJ), Shuzo Hirata

Oct. 2013
2013年度化学･生物素材研究開発奨励賞, 平田修造

May 2013
第2回新化学技術研究奨励賞, 平田修造

Mar. 2011
2010年度(秋季)応用物理学会講演奨励賞, 平田修造

May 2010
日本化学会第90回春季年会講演奨励賞（産業）, 平田修造

May 2010
日本化学会第90回春季年会優秀講演賞（学術）, 平田修造

Jun. 2009
Pan-Pacific Imaging Conference '08コニカミノルタ研究奨励賞, 渡辺敏行、平田修造

May 2006
日本化学会第86回春季年会講演奨励賞（産業）, 平田修造

Synchronizing the nπ* Transition Dipole in a Benzoyl-Linked N-Fused Ring for Highly Efficient Yellow Afterglow
Bahadur Sk; Riku Shimura; Kazuki Fujita; Shuzo Hirata
Last, The Journal of Physical Chemistry Letters, American Chemical Society (ACS), 3904-3910, 10 Apr. 2025, Peer-reviwed
Scientific journal

Oxygen quantification based on the persistent phosphorescence lifetime of host–guest nanocrystals
Riku Shimura; Kikuya Hayashi; Sakuya Ueda; Rana Tsuru; Shuzo Hirata
Last, ACS Materials Letters, in press, Apr. 2025, Peer-reviwed
Scientific journal, English

Selective lower-occupied through-bond interactions for efficient organic phosphorescence enabling high-resolution long-wavelength afterglow
Rajashekhar K. Mulimani; Sakuya Ueda; Ryo Miyashita; Rana Tsuru; Kikuya Hayashi; Riku Shimura; Bahadur Sk; Shinji Matsuda; Shuzo Hirata
Last, Advanced Materials, in press, Apr. 2025, Peer-reviwed
Scientific journal, English

Deciphering carbon–sulfur rotational distribution in a crystalline host for enhanced red persistent organic phosphorescence
Sakuya Ueda; Kazuki Fujita; Bahadur Sk; Shuzo Hirata
Last, Journal of Materials Chemistry C, Royal Society of Chemistry (RSC), 2025, Peer-reviwed, A collaborative synthesis and computational approach is used to decipher confined carbon–sulfur rotational distribution in a crystalline host for enhanced red persistent phosphorescence.
Scientific journal

Symmetry-Breaking Triplet Excited State Enhances Red Afterglow Enabling Ubiquitous Afterglow Readout
Bahadur Sk; Shuzo Hirata
Last, Advanced Science, 11, 14, 2308897, 04 Feb. 2024, Peer-reviwed, Molecular vibrations are often factors that deactivate luminescence. However, if there are molecular motion elements that enhance luminescence, it may be possible to utilize molecular movement as a design guideline to enhance luminescence. Here, the authors report a large contribution of symmetry-breaking molecular motion that enhances red persistent room-temperature phosphorescence (RTP) in donor-π-donor conjugated chromophores. The deuterated form of the donor-π-donor chromophore exhibits efficient red persistent RTP with a yield of 21% and a lifetime of 1.6 s. A dynamic calculation of the phosphorescence rate constant (kp) indicates that the symmetry-breaking movement has a crucial role in selectively facilitating kp without increasing nonradiative transition from the lowest triplet excited state. Molecules exhibiting efficient red persistent RTP enable long-wavelength excitation, indicating the suitability of observing afterglow readout in a bright indoor environment with a white-light-emitting diode flashlight, greatly expanding the range of anti-counterfeiting applications that use afterglow.
Scientific journal

High‐Resolution Afterglow Patterning Using Cooperative Vapo‐ and Photo‐Stimulation
Kikuya Hayashi; Shuzo Hirata
Last, Small, Wiley, 20, 16, 2308103, 28 Nov. 2023, Peer-reviwed, Abstract

Bright afterglow room‐temperature phosphorescence (RTP) soon after ceasing excitation is a promising technique for greatly increasing anti‐counterfeiting capabilities. The development of a process for rapid high‐resolution afterglow patterning of crystalline materials can improve both high‐speed fabrication of anti‐counterfeiting afterglow media and stable afterglow readout compared with those achieved with amorphous materials. Here, the high‐resolution afterglow patterning of crystalline materials via cooperative organic vapo‐ and photo‐stimulation is reported. A single crystal of (S)‐(−)−2,2’‐bis(diphenylphosphino)−5,5’,6,6’,7,7’8,8’‐octahydro‐1,1’‐binaphthyl [ (S)‐H₈‐BINAP] doped with (S)‐(−)−2,2’‐bis(diphenylphosphino)−1,1’‐binaphthyl [ (S)‐BINAP] shows green afterglow RTP. Crystals of (S)‐BINAP‐doped (S)‐H₈‐BINAP changed to an amorphous state with no afterglow capability on weak continuous photoirradiation under dichloromethane (DCM) vapor. Photoirradiation induced oxidation of the (S)‐H₈‐BINAP host molecule in the crystal. The oxidized (S)‐H₈‐BINAP forms on the crystal surface strongly interacted with DCM molecules, which induces melting of the (S)‐BINAP‐doped (S)‐H₈‐BINAP crystal and trigger formation of an amorphous state without an afterglow capability. High‐resolution afterglow patterning of the crystalline film is rapidly achieved by using cooperative organic vapo‐ and photo‐stimulation. In addition to the benefit of rapid afterglow patterning, the formed afterglow images of the crystalline film can be repeatedly read out under ambient conditions without DCM vapor.
Scientific journal

Continuous Condensed Triplet Accumulation for Irradiance‐Induced Anticounterfeit Afterglow
Ende Hopsah Badriyah; Kikuya Hayashi; Bahadur Sk; Rina Takano; Takayuki Ishida; Shuzo Hirata
Last, Advanced Science, Wiley, 10, 2304374, 28 Oct. 2023, Peer-reviwed, Abstract

Afterglow room‐temperature emission that is independent of autofluorescence after ceasing excitation is a promising technology for state‐of‐the‐art bioimaging and security devices. However, the low brightness of the afterglow emission is a current limitation for using such materials in a variety of applications. Herein, the continuous formation of condensed triplet excitons for brighter afterglow room‐temperature phosphorescence is reported. (S)‐(‐)‐2,2′‐Bis(diphenylphosphino)‐1,1′‐binaphthyl ((S)‐BINAP) incorporated in a crystalline host lattice showed bright green afterglow room‐temperature phosphorescence under strong excitation. The small triplet–triplet absorption cross‐section of (S)‐BINAP in the whole range of visible wavelengths greatly suppressed the deactivation caused by Förster resonance energy transfer from excited states of (S)‐BINAP to the accumulated triplet excitons of (S)‐BINAP under strong continuous excitation. The steady–state concentration of the triplet excitons for (S)‐BINAP reached 2.3 × 10⁻² M, producing a bright afterglow. Owing to the brighter afterglow, afterglow detection using individual particles with sizes approaching the diffraction limit in aqueous conditions and irradiance‐dependent anticounterfeiting can be achieved.
Scientific journal

Photoinduced Triplet Depletion Allowing Higher-Resolution Afterglow
Kikuya Hayashi; Keiki Fukumoto; Shuzo Hirata
Last, ACS Materials Letters, 5, 1649-1655, May 2023, Peer-reviwed
Scientific journal

Förster resonance energy transfer involving the triplet state
Bahadur Sk; Shuzo Hirata
Last, Chemical Communications, 59, 6643-6659 (Invited Future Article), Apr. 2023, Peer-reviwed, Invited
Scientific journal, English

Role of Carbonyl Distortions Facilitating Persistent Room-Temperature Phosphorescence
Shuzo Hirata*, Takuya Kamatsuki
Lead, The Journal of Physical Chemistry C, 127, 7, 3861-3871 (Invited Article), Jan. 2023, Peer-reviwed, Invited, False
Scientific journal, English

Selective Triplet-Singlet Förster-Resonance Energy Transfer for Bright Red Afterglow Emission
Bahadur Sk; Rana Tsuru; Kikuya Hayashi; Shuzo Hirata
Last, Advanced Functional Materials, 33, 11, 2211604, Dec. 2022, Peer-reviwed
Scientific journal, English

Enhanced Red Persistent Room-Temperature Phosphorescence Induced by Orthogonal Structure Disruption during Electronic Relaxation
Kei Fukasawa; Yuma Sugawara; Rana Tsuru; Takashi Yamashita; Shuzo Hirata
Last, The Journal of Physical Chemistry Letters, 13, 33, 7788-7796 (Invited Article), Aug. 2022, Peer-reviwed, Invited
Scientific journal, English

Editorial: Metal-Free Room-Temperature Phosphorescence
Shuzo Hirata; Sebastian Reineke; Abhijit Patra; Wan Zhang Yuan
Lead, Frontiers in Chemistry, 10, 1025674, Aug. 2022, Peer-reviwed, Invited
Scientific journal, English

A Rational Key of Triplet Afterglow Sensitizer Allowing Bright Long-Wavelength Afterglow Room-Temperature Emission
Kikuya Hayashi; Kei Fukasawa; Takashi Yamashita; Shuzo Hirata
Last, Chemistry of Materials (Supplementary Cover), 34, 1627-1637, Jan. 2022, Peer-reviwed
Scientific journal, English

Molecular physics of persistent room-temperature phosphorescence and long-lived triplet excitons
Shuzo Hirata
Lead, Applied Physics Reivews, 9, 011304 (Invited Article), Jan. 2022, Peer-reviwed, Invited
Scientific journal, English

Thermo-Reversible Persistent Phosphorescence Modulation Reveals the Large Contribution Made by Rigidity to the Suppression of Endothermic Intermolecular Triplet Quenching
Tomoya Kusama; Shuzo Hirata
Last, Frontiers in Chemistry, 7, 788577, Oct. 2021, Peer-reviwed
Scientific journal, English

高輝度長寿命室温りん光の高解像空間変調媒体への応用
平田修造
化学工業, 株式会社化学工業社, 72, 6, 357-362, Jun. 2021, Invited
Research society, Japanese

Key of Suppressed Triplet Nonradiative Transition-Dependent Chemical Backbone for Spatial Self-Tunable Afterglow
Indranil Bhattacharjee; Kikuya Hayashi; Shuzo Hirata
Last, JACS Au (Front Cover Picture), 1, 945-954, May 2021, Peer-reviwed
Scientific journal, English

Vibrational Radiationless Transition from Triplet States of Chromophores at Room Temperature
Shuzo Hirata; Indranil Bhattacharjee
Lead, The Journal of Physical Chemistry A, 125, 3, 885-894, Jan. 2021, Peer-reviwed
Scientific journal, English

Chiral Approach to Investigate Mechanism of Highly Efficient Thermally Activated Delayed Fluorescence
Kikuya Hayashi; Arimasa Matsumoto; Shuzo Hirata
Last, Chemical Communications, Royal Society of Chemistry (RSC), 57, 14, 1738-1741, Jan. 2021, Peer-reviwed,

Cancellation of the Cotton effect depending on vibrations of a chiral orthogonal donor–acceptor structure identifies a mechanism of highly efficient delayed fluorescence.

Scientific journal, English

Phosphorescence Quenching of Heavy-Atom-Free Dopant Chromophores Triggered by Thermally Activated Triplet Exciton Diffusion of a Conjugated Crystalline Host
Shuzo Hirata; Hyuman Hara; Indranil Bhattacharjee
Lead, JOURNAL OF PHYSICAL CHEMISTRY C, AMER CHEMICAL SOC, 124, 45, 25121-25132, Nov. 2020, Peer-reviwed, Persistent room-temperature phosphorescence (pRTP) from aggregated molecular crystalline materials is important for stable high-resolution afterglow imaging. However, an unclear understanding concerning the deactivation mechanism from the lowest triplet excited state (T-1) precludes the development of highly efficient pRTP. Here, we report the reasons for the presence and absence of pRTP from a heavy-atom-free conjugated dopant in heavy-atom-free conjugated molecular crystals. N,N-di(9H-fluoren-2-yl)phenanthrene-3-amine (DFAP) was separately doped into fluorene crystals and (S)-2,2'-bis(diphenylphosphino)-5,5',6,6',7,7',8,8'-octahydro-1,1'-binaphthalene ((S)-H-8-BINAP) crystals. DFAP doped in fluorene crystals with stronger intermolecular interactions did not generate RTP, while DFAP doped in (S)-H-8-BINAP crystals with weaker intermolecular interactions showed strong pRTP. The pRTP of DFAP doped in (S)-H-8-BINAP crystals is explained by the deep confinement of the T-1 of DFAP in the (S)-H-8-BINAP crystals with a large T-1 energy. The absence of RTP from DFAP doped in fluorene crystals is explained by the temperature dependence of phosphorescence and quantum calculations, which suggest that deactivation is mainly caused by quenching after diffusion of triplet excitons of the host crystals. The temperature dependence of the triplet-triplet annihilation-based delayed fluorescence of the fluorene crystalline host confirms that the triplet diffusion of the fluorene crystalline host deactivates the triplet excitons of DFAP.
Scientific journal, English

The Substituent-Induced Symmetry-Forbidden Electronic Transition Allows Significant Optical Limiting under Weak Sky-Blue Irradiance
Takuya Kamatsuki; Indranil Bhattacharjee; Shuzo Hirata
Last, JOURNAL OF PHYSICAL CHEMISTRY LETTERS, AMER CHEMICAL SOC, 11, 20, 8675-8681, Oct. 2020, Peer-reviwed, We report a novel material containing a rare metal-free dopant chromophore with controlled electronic symmetry, which exhibits strong optical limiting (OL) capabilities under weak, continuous, sky-blue irradiance. Electron-donating substituents at positions C2 and C7 of pyrene allow significant triplet generation because of the symmetrically forbidden transition between the ground state and the lowest singlet excited state, which leads to accumulation of triplet excitons in the dopant chromophore. This also leads to a small ground state absorption coefficient and induces greater absorption of sky-blue wavelengths when triplet excitons of the chromophore accumulate. Consequently, molecular glass doped with the designed chromophore displays stronger OL characteristics compared with those of the rare element-containing glass that previously demonstrated the greatest OL performance under continuous sky-blue irradiance at sunlight power levels. The described approach to developing cost-effective, state-of-the-art OL materials is crucial for nonlinear optical applications working at a large scale under sunlight or room lights.
Scientific journal, English

Energy localization vs. charge funneling in aggregates of CsPbBr(3 )perovskite nanocrystals
Dharmendar Kumar Sharma; Shuzo Hirata; Martin Vacha
JOURNAL OF LUMINESCENCE, ELSEVIER, 222, 117119, Jun. 2020, Peer-reviwed, We studied photoluminescence (PL) and electroluminescence (EL) on single aggregates composed of tens to hundreds of nanocrystals (NCs) of the halide perovskite CsPbBr3. Energy landscape of the aggregate caused by size distribution of the NCs leads to funneling of charges towards and EL from the largest NC. This phenomenon results in pronounced blinking of the aggregate EL. In PL, on the other hand, the absorbed light energy is localized and reemitted on individual NCs, without significant redistribution by energy/exciton transfer. As a result the PL of individual aggregates does not show any blinking. We further investigated the effect of externally applied de voltage on PL of the aggregates in a capacitance-like device and observed an intriguing phenomenon of large oscillations of PL intensity that occur with a period of seconds and are correlated between different aggregates across micrometer distances.
Scientific journal, English

Highly Efficient Persistent Room‐Temperature Phosphorescence from Heavy Atom‐Free Molecules Triggered by Hidden Long Phosphorescent Antenna
Indranil Bhattacharjee; Shuzo Hirata
Last, Advanced Materials, 32, 2001348, Jun. 2020, Peer-reviwed
Scientific journal, English

Effect of the Tris(trimethylsilyl)silyl Group on the Fluorescence and Triplet Yields of Oligothiophenes
Shuzo Hirata; Masaki Nishio; Hikaru Uchida; Tsukasa Usuki; Toyotaka Nakae; Mariko Miyachi; Yoshinori Yamanoi; Hiroshi Nishihara
Lead, JOURNAL OF PHYSICAL CHEMISTRY C, AMER CHEMICAL SOC, 124, 5, 3277-3286, Feb. 2020, Peer-reviwed, The origin of the large difference of room-temperature fluorescence yields (Phi(f)-(RT)) among tris(trimethylsilyl)silylated oligothiophene derivatives was investigated. Tris(trimethylsilyOsilylated thiophene (1) and tris(trimethylsilyl)-silylated terthiophene (3) show low fluorescence yields while that of tris-(trimethylsilyl)silylated bithiophene (2) is high. Nanosecond transient absorption measurements for 2 and 3 verified that the large difference between their intersystem crossing (ISC) rates from the lowest singlet excited state (S-1) causes the large difference in Phi(f)(DOT). Quantum calculations indicated that the Si-Si sigma bond of (Me3Si)(3)Si, corresponding to the highest occupied molecular orbital (HOMO), is closely involved in the ISC from S-1. The planar conjugated core having much higher or comparable HOMO energy relative to the (Me3Si)(3)Si substituent, such as 1 and 3, induces large spin-orbit coupling (SOC) between S-1 and the second-order triplet excited state (T-2), resulting in fast ISC from 5, leading to a small Phi(f)(RT). However, a planar conjugated core having slightly higher HOMO energy than that of the (Me3Si)(3)Si substituent, such as 2, minimizes SOC between S-1 and T-2, resulting in slow ISC from S-1 leading to a large Phi(f)(DOT). Thus, the relationship between the HOMO level of the (Me3Si)(3)Si substituent and that of the planar conjugated core is key to controlling the ISC from S-1.
Scientific journal, English

Single-particle electroluminescence of CsPbBr3 perovskite nanocrystals reveals particle-selective recombination and blinking as key efficiency factors
Dharmendar Kumar Sharma; Shuzo Hirata; Martin Vacha
NATURE COMMUNICATIONS, NATURE PUBLISHING GROUP, 10, 4499, Oct. 2019, Peer-reviwed, Halide perovskites nanocrystals (NCs) are being explored as promising materials for optoelectronic applications, such as light-emitting devices or lasers. However, electroluminescence devices prepared from such NCs have long suffered from low efficiency and there has been no systematic study on the nanoscale origin of the poor efficiencies. Here, we use single-particle spectroscopy to compare electroluminescence and photoluminescence on the level of individual NCs of the perovskite CsPbBr3. The NCs form aggregates in a conducting matrix used as an emission layer in an electroluminescence device. In electroluminescence, only a small fraction of the NCs within the aggregate is emitting as a result of efficient charge migration, accumulation and selective recombination on larger NCs, leading to pronounced blinking and decreased efficiency. Under the condition of comparable excitation rates in both electroluminescence and photoluminescence, the intrinsic quantum yield in electroluminescence is on average 0.36 of that in photoluminescence.
Scientific journal, English

Roles of Localized Electronic Structures Caused by pi Degeneracy Due to Highly Symmetric Heavy Atom-Free Conjugated Molecular Crystals Leading to Efficient Persistent Room-Temperature Phosphorescence
Shuzo Hirata
Lead, ADVANCED SCIENCE, WILEY, 6, 14, 1900410, Jul. 2019, Peer-reviwed, Conjugated molecular crystals with persistent room-temperature phosphorescence (RTP) are promising materials for sensing, security, and bioimaging applications. However, the electronic structures that lead to efficient persistent RTP are still unclear. Here, the electronic structures of tetraphenylmethane (C(C6H5)(4)), tetraphenylsilane (Si(C6H5)(4)), and tetraphenylgermane (Ge(C6H5)(4)) showing blue-green persistent RTP under ambient conditions are investigated. The persistent RTP of the crystals originates from minimization of triplet exciton quenching at room temperature not suppression of molecular vibrations. Localization of the highest occupied molecular orbitals (HOMOs) of the steric and highly symmetric conjugated crystal structures decreases the overlap of intermolecular HOMOs, minimizing triplet exciton migration, which accelerates defect quenching of triplet excitons. The localization of the HOMOs over the highly symmetric conjugated structures also induces moderate charge-transfer characteristics between high-order singlet excited states (S-m) and the ground state (S-0). The combination of the moderate charge-transfer characteristics of the S-m-S-0 transition and local-excited state characteristics between the lowest excited triplet state and S-0 accelerates the phosphorescence rate independent of the vibration-based nonradiative decay rate from the triplet state at room temperature. Thus, the decrease of triplet quenching and increase of phosphorescence rate caused by the HOMO localization contribute to the efficient persistent RTP of Ge(C6H5)(4) crystals.
Scientific journal, English

Suppressed Triplet Exciton Diffusion Due to Small Orbital Overlap as a Key Design Factor for Ultralong-Lived Room-Temperature Phosphorescence in Molecular Crystals
Kaishi Narushima; Yasuhiro Kiyota; Takehiko Mori; Shuzo Hirata; Martin Vacha
Corresponding, ADVANCED MATERIALS, WILEY-V C H VERLAG GMBH, 31, 10, 1807268, Mar. 2019, Peer-reviwed, Persistent room-temperature phosphorescence (RTP) under ambient conditions is attracting attention due to its strong potential for applications in bioimaging, sensing, or optical recording. Molecular packing leading to a rigid crystalline structure that minimizes nonradiative pathways from triplet state is often investigated for efficient RTP. However, for complex conjugated systems a key strategy to suppress the nonradiative deactivation is not found yet. Here, the origin of small rates of a nonradiative decay process from triplet states of conjugated molecular crystals showing RTP is reported. Optical microscopy analysis showed that, despite a favorable molecular stacking, an aromatic crystal with strong RTP is characterized by small diffusion length and small values of the diffusion coefficient of triplet excitons. Quantum chemical calculations reveal a large overlap between the lowest unoccupied molecular orbitals but very small overlap between the highest occupied molecular orbitals (HOMOs). Inefficient electron exchange caused by the small overlap of HOMOs prevents triplet excitons from diffusing over long distances and consequently from quenching at defect sites inside the crystal or at the crystal surface. These results will allow design of comprehensive molecular structures to obtain molecular solids with more efficient RTP.
Scientific journal, English

A colorless semi-aromatic polyimide derived from a sterically hindered bromine-substituted dianhydride exhibiting dual fluorescence and phosphorescence emission
Kenta Kanosue; Shuzo Hirata; Martin Vacha; Ramunas Augulis; Vidmantas Gulbinas; Ryohei Ishige; Shinji Ando
MATERIALS CHEMISTRY FRONTIERS, ROYAL SOC CHEMISTRY, 3, 1, 39-49, Jan. 2019, Peer-reviwed, Colorless, transparent, and environmentally stable polymer films with large luminescence Stokes shift are in demand for down-conversion of solar UV radiation. To develop such a polymer film that exhibits phosphorescence at room-temperature with a large Stokes shift and excellent thermal stability, a semi-aromatic polyimide (DBrBP-PI) was newly synthesized using a biphenyltetracarboxylic dianhydride substituted with two bromine (Br) atoms. Thin films of DBrBP-PI were completely colorless because of effective suppression of the aggregation of the PI chains due to the steric effects of the Br-substituted dianhydride structure. The PI films exhibited bright green phosphorescence at 512 nm (phi = 0.02) with a very large Stokes shift of 12215 cm(-1) as well as prompt blue fluorescence at around 408 nm when excited at 315 nm at 298 K. The glass transition and the 5 wt% loss temperatures of DBrBP-PI were 325 degrees C and 427 degrees C, respectively. The phosphoresce intensity of the DBrBP-PI film was significantly enhanced under vacuum (phi = 0.22) and at low temperatures (phi = 0.76 at 77 K) owing to suppression of triplet state quenching by atmospheric oxygen and dumping of the molecular motions of the PI chains in the solid film. The suggested material design concept shows a way towards creation of stable and efficient down-converters for UV radiation.
Scientific journal, English

Stark Effect and Environment-Induced Modulation of Emission in Single Halide Perovskite Nanocrystals
Dharmendar Kumar Sharma; Shuzo Hirata; Vasudevanpillai Biju; Martin Vacha
ACS NANO, AMER CHEMICAL SOC, 13, 1, 624-632, Jan. 2019, Peer-reviwed, Organic-inorganic halide perovskites have emerged as promising materials for next-generation solar cells. In nanostructured form also, these materials are excellent candidates for optoelectronic applications such as lasers and light-emitting diodes for displays and lighting. While great progress has been achieved so far in optimizing the intrinsic photophysical properties of perovskite nanocrystals (NCs), in working optoelectronic devices, external factors, such as the effects of conducting environment and the applied electric field on exciton generation and photon emission, have been largely unexplored. Here, we use NCs of the all-inorganic perovskite CsPbBr3 dispersed polyvinyl carbazole, a hole-conductor, and in poly(methyl methacrylate), an insulator, to examine the effects of applied electric field and conductivity of the matrix on the perovskite photophysics at the single-particle level. We found that the conducting environment causes a significant decrease of photoluminescence (PL) brightness of individual NCs due the appearance of intermediate-intensity emitting states with significantly shortened lifetime. Applied electric field has a similar effect and, in addition, causes a nonlinear spectral shift of the PL maxima, a combination of linear and quadratic Stark effects caused by environment-induced polarity and field-related polarizability. The environment and electric-field effects are explained by ionization of the NCs through hole transfer and emission of the resulting negatively charged excitons.
Scientific journal, English

Wavelength-Tunable Band-Edge Photoluminescence of Nonstoichiometric Ag-In-S Nanoparticles via Ga3+ Doping
Tatsuya Kameyama; Marino Kishi; Chie Miyamae; Dharmendar Kumar Sharma; Shuzo Hirata; Takahisa Yamamoto; Taro Uematsu; Martin Vacha; Susumu Kuwabata; Tsukasa Torimoto
ACS APPLIED MATERIALS & INTERFACES, AMER CHEMICAL SOC, 10, 49, 42844-42855, Dec. 2018, Peer-reviwed, The nonstoichiometry of semiconductor I-III-VI semiconductor nanoparticles, especially the ratio of group Ito group III elements, has been utilized to control their physicochemical properties. We report the solution-phase synthesis of non-stoichiometric Ag-In-S and Ag-In-Ga-S nanoparticles and results of the investigation of their photoluminescence (PL) properties in relation to their chemical compositions. While stoichiometric AgInS2 nanoparticles simply exhibited only a broad PL band originating from defect sites in the particles, a narrow band edge PL peak newly appeared with a decrease in the Ag fraction in the nonstoichiometric Ag-In-S nano-particles. The relative PL intensity of this band edge emission with respect to the defect-site emission was optimal at a Ag/(Ag + In) value of ca. 0.4. The peak wavelength of the band edge emission was tunable from 610 to 500 nm by increased doping with Ga3+ into Ag-In-S nanoparticles due to an increase of the energy gap. Furthermore, surface coating of Ga3+-doped Ag-In-S nanoparticles, that is, Ag-In-Ga-S nanoparticles, with a GaSx shell drastically and selectively suppressed the broad defect-site PL peak and, at the same time, led to an increase in the PL quantum yield (QY) of the band edge emission peak. The optimal PL QY was 28% for Ag-In-Ga-S@GaSx core-shell particles, with green band-edge emission at 530 nm and a full width at half-maximum of 181 meV (41 nm). The observed wavelength tunability of the band-edge PL peak will facilitate possible use of these toxic-element-free I-III-VI-based nanoparticles in a wide area of applications.
Scientific journal, English

Efficient triplet-triplet annihilation upconversion in binary crystalline solids fabricated via solution casting and operated in air (vol 4, pg 83, 2017)
Kenji Kamada; Yusuke Sakagami; Toshiko Mizokuro; Yutaka Fujiwara; Kenji Kobayashi; Kaishi Narushima; Shuzo Hirata; Martin Vacha
MATERIALS HORIZONS, ROYAL SOC CHEMISTRY, 5, 6, 1219-1219, Nov. 2018, Peer-reviwed
English

Ultralong-lived room temperature triplet excitons: molecular persistent room temperature phosphorescence and nonlinear optical characteristics with continuous irradiation
Shuzo Hirata
Lead, JOURNAL OF MATERIALS CHEMISTRY C, ROYAL SOC CHEMISTRY, 6, 44, 11785-11794, Nov. 2018, Peer-reviwed, Invited, Heavy atom-free conjugated molecules tend to display triplet exciton lifetimes longer than one second only at liquid nitrogen temperature because nonradiative deactivation of the triplet state is usually rapid at room temperature (RT). This review summarizes recent progress of molecular materials with long triplet exciton lifetimes at RT. Recent careful photophysical analyses indicated that the fast nonradiative deactivation of the triplet state of heavy atom-free conjugated molecular guests in solid hosts with large triplet energy was caused by not intramolecular vibrations of the guests but endothermic energy transfer from the guests to the host and quenching by oxygen in the host. Minimization of both energy transfer and quenching using a highly rigid molecular host realized ultralong-lived RT triplet excitons for many heavy atom-free conjugated structures. The discovery of such host-guest materials triggered the emergence of several kinds of molecular materials with ultralong-lived RT triplet excitons. These materials showed novel functions like nonlinear absorption characteristics and persistent RT phosphorescence. A variety of new applications using such molecular materials have been demonstrated in the past five years.
Scientific journal, English

Identification of Short- and Long-Wavelength Emitting Chlorophylls in Cyanobacterial Photosystem I by Plasmon-Enhanced Single-Particle Spectroscopy at Room Temperature
Soya Hatazaki; Dharmendar Kumar Sharma; Shuzo Hirata; Keiji Nose; Tomokazu Iyoda; Adrian Koelsch; Heiko Lokstein; Martin Vacha
JOURNAL OF PHYSICAL CHEMISTRY LETTERS, AMER CHEMICAL SOC, 9, 22, 6669-6675, Nov. 2018, Peer-reviwed, A peculiarity of cyanobacterial Photosystem I (PSI) is the presence of so-called red chlorophylls absorbing at wavelengths longer than the reaction center P700. The origin and function of these chlorophylls have been debated in literature, but so far no consensus has been reached on either question. Here, we use plasmon-enhanced single particle fluorescence spectroscopy to elucidate the origin of both short- and long-wavelength emitting species in monomeric PSI from Thermosynechococcus elongatus at room temperature. Polarized fluorescence spectra of single PSI complexes reveal a phase shift in the modulation of the short-wavelength (687 nm) and long-wavelength (717 nm) peaks. Numerical simulations show that this phase shift reflects a spatial angle of 15 between the transition dipole moments of the two forms. Quantum chemical calculations, together with reported Xray structural and spectroscopic data, were used to assign the chlorophyll a monomer A3 as a candidate for the short-wavelength emitter and the B31-B32 chlorophyll dimer as a candidate for the long-wavelength emitter.
Scientific journal, English

Intrinsic Analysis of Radiative and Room-Temperature Nonradiative Processes Based on Triplet State Intramolecular Vibrations of Heavy Atom-Free Conjugated Molecules toward Efficient Persistent Room-Temperature Phosphorescence
Shuzo Hirata
Lead, JOURNAL OF PHYSICAL CHEMISTRY LETTERS, AMER CHEMICAL SOC, 9, 15, 4251-4259, Aug. 2018, Peer-reviwed, The radiative rate (k(p)) of the lowest triplet excited state (T-1) and the nonradiative rate based on intramolecular vibrations at room temperature [k(nr)(RT)] from T-1 for heavy atom-free conjugated structures are determined by considering the triplet yield and quenching rate from T-1. Donor substitution did not strongly influence k(nr)(RT) but greatly enhanced k(p). The k(nr)(RT) values were comparable between donor-substituted molecules and nonsubstituted molecules, which we explain by similar vibrational spin orbit coupling (SOC) related to the transition from T-1 to the ground state (S-o). We attribute the enhancement of k(p) induced by donor substitution to the appearance of a large SOC between high-order singlet excited states (S-m) and T-1 together with the large transition dipole moments of the S-m-S-o transitions. Knowledge of this mechanism is important for developing future efficient persistent room-temperature phosphorescence from doped aromatic materials and aromatic crystals.
Scientific journal, English

Narrow band-edge photoluminescence from AglnS(2) semiconductor nanoparticles by the formation of amorphous III-VI semiconductor shells
Taro Uematsu; Kazutaka Wajima; Dharmendar Kumar Sharma; Shuzo Hirata; Takahisa Yamamoto; Tatsuya Kameyama; Martin Vacha; Tsukasa Torimoto; Susumu Kuwabata
NPG ASIA MATERIALS, NATURE PUBLISHING GROUP, 10, 713-726, Aug. 2018, Peer-reviwed, Nanoparticles of I-III-VI semiconductors are promising candidates for novel non-toxic fluorescent materials. However, removal of defect levels responsible for their broad-band emission has not been successful to date. The present study demonstrates, for the first time, the coating of core AglnS(2) nanoparticles-one of the I-III-VI group semiconductors with a bandgap in the visible region-with III-VI group semiconductors. The AglnS(2)/InSx and AglnS(2)/GaSx (x = 0.8-1.5) core/shell structures generate intense narrow-band photoluminescence originating from a band-edge transition at a wavelength shorter than that of the original defect emission. Microscopic analyses reveal that the GaSx shell has an amorphous nature, which is unexpected for typical shell materials such as crystalline lattice-matching ZnS. Single-particle spectroscopy shows that the average linewidth of the band-edge photoluminescence is as small as 80.0 meV (or 24 nm), which is comparable with that of industry-standard II-VI semiconductor quantum dots. In terms of photoluminescence quantum yield, a value of 56% with nearly single-band emission has been achieved as a result of several modifications to the reaction conditions and post-treatment to the core/shell nanoparticles. This work indicates the increasing potential of AglnS(2) nanoparticles for use as practical cadmium-free quantum dots.
Scientific journal, English

Large refractive index variations induced by accumulating triplet excitons under photoexcitation at low power
Tomoe Hori; Kenro Totani; Shuzo Hirata; Toshiyuki Watanabe
CHEMICAL PHYSICS LETTERS, ELSEVIER SCIENCE BV, 704, 5-10, Jul. 2018, Peer-reviwed, Herein, we present a method for the modification of the refractive index (n), based on employing an organic molecule with a long triplet excited-state lifetime. A host-guest material composed of a cyclic aromatic as the guest and an amorphous steroidal compound as the host was used to modulate n. The guest material exhibited a triplet lifetime longer than 1 s, and a high-density triplet excited-state population was obtained upon excitation with blue-violet light. The refractive index could be changed by 0.002, even when using a relatively low excitation power level of 100 mW cm(2). (C) 2018 Elsevier B.V. All rights reserved.
Scientific journal, English

Excited State Behavior of Single Strand and Bulk P3HT in Contact with a Au-Nanowire Array
Mengdi Liu; Shuzo Hirata; Tomokazu Iyoda; Martin Vacha; Piotr Piotrowiak
JOURNAL OF PHYSICAL CHEMISTRY C, AMER CHEMICAL SOC, 122, 14, 7925-7933, Apr. 2018, Peer-reviwed, Pump-probe transient absorption and single molecule fluorescence microscopy reveal multifaceted excited state behavior of regioregular (RR) P3HT interacting with a hexagonal array of Au nanowires. An average 5-fold increase of fluorescence intensity has been detected for single strands of P3HT in the presence of the nanowire array, with the strongest emitters exceeding the brightness of their counterparts on glass by a factor of 40. The single molecule trajectories show that the same polymer strand is capable of exhibiting a range of enhancement levels. The "off" periods on the Au substrate are exceptionally long and erratic. This behavior is attributed to sporadic electron transfer events between the strand and the metal. Bulk P3HT deposited on the same Au-nanowire array shows a dramatic reduction of the yield and lifetime of singlet excitons in comparison with the glass support, indicating that the proximity of the metal greatly accelerates both exciton dissociation and charge recombination. Interestingly, a large increase of the triplet exciton population is observed in the presence of the metal, indicating a much faster loss of the spin spin correlation. The bulk P3HT results suggest that the large fluorescence enhancement observed in the single molecule experiments occurs only for a few emitters which have been fortuitously placed at the optimum distance and orientation with respect to the metal.
Scientific journal, English

Intrachain Aggregates as the Origin of Green Emission in Polyfluorene Studied on Ensemble and Single-Chain Level
Tomonori Nakamura; Dharmendar Kumar Sharma; Shuzo Hirata; Martin Vacha
JOURNAL OF PHYSICAL CHEMISTRY C, AMER CHEMICAL SOC, 122, 15, 8137-8146, Apr. 2018, Peer-reviwed, Polyfluorenes are conjugated polymers that show strong blue emission and as such have been explored for potential applications in light-emitting devices. However, heat treatment, prolonged exposure to air, or extended operation in electro-luminescent devices can lead to an appearance of parasitic green emission that degrades the material performance. This phenomenon has been extensively studied over the past two decades, and two main and conflicting explanations, i.e., oxidation and formation of fluorenone species on the one hand and inter- or intrachain aggregation on the other, have been put forward. There is abundant experimental evidence to support either of these theories, and the question is far from settled. Here, we aim at getting deeper insight into the problem of the green emission origin using single-molecule spectroscopy performed on individual chains of poly(9,9-di-n-octylfluorene) (PFO) to resolve the green emission band and reveal its spectral and temporal heterogeneity. We disperse single PFO chains in solid thin-film matrices of polystyrene (PS) and poly(methyl methacrylate), as well as in solutions of cyclohexane, toluene, or PS/toluene, to simulate good and poor-solvent environments and environments with different permeabilities and diffusions of oxygen, to systematically study the effects of intrachain aggregation as well as oxidation on the appearance and characteristics of the green band. The studies are complemented by direct measurement of individual chain conformation by atomic force microscopy and by bulk measurements of photoluminescence (PL) lifetimes and quantum yield. The single-molecule results reveal two PL spectral forms in the region of the green emission, a vibrationally resolved type located around 500 nm and broad structureless type located toward lower energies, none of them sensitive to the presence of oxygen. These two types are characterized by different lifetimes of 1.4 and 5.1 ns, respectively, and their oscillator strengths are 2 orders of magnitude smaller compared to those of the blue emission band. These results point to two different optical transitions comprising the green band, and these have been assigned to the emission of H-aggregates and charge transfer or indirectly excited excimer states, respectively.
Scientific journal, English

Single-molecule studies beyond optical imaging: Multi-parameter single-molecule spectroscopy
Martin Vacha; Dharmendar Kumar Sharma; Shuzo Hirata
JOURNAL OF PHOTOCHEMISTRY AND PHOTOBIOLOGY C-PHOTOCHEMISTRY REVIEWS, ELSEVIER SCIENCE BV, 34, 121-136, Mar. 2018, Peer-reviwed, Invited, Single molecule spectroscopy has undergone a remarkable development in the past few decades, and its ability to unmask the unique features of individual molecules has found increasing use in research of soft matter and polymers, in chemistry, as well as in biophysics and biology. In this concise review we bring an overview of the synergy effects that result from combinations of single-molecule and single particle fluorescence spectroscopy with other techniques, such as electron microscopy and scanning probe microscopy, or with external-field effects including hydrostatic pressure and electric and magnetic fields. (C) 2017 Elsevier B.V. All rights reserved.
Scientific journal, English

Macrocyclic poly(p-phenylenevinylene)s by ring expansion metathesis polymerisation and their characterisation by single-molecule spectroscopy
Benjamin John Lidster; Shuzo Hirata; Shoki Matsuda; Takuya Yamamoto; Venukrishnan Komanduri; Dharam Raj Kumar; Yasuyuki Tezuka; Martin Vacha; Michael L. Turner
CHEMICAL SCIENCE, ROYAL SOC CHEMISTRY, 9, 11, 2934-2941, Mar. 2018, Peer-reviwed, Ring expansion metathesis polymerisation (REMP) has proven to be a viable approach to prepare high purity cyclic polymers. Macrocyclic polymers with a fully conjugated defect free backbone are of particular interest as these polymers have no end groups that can act as charge traps. In this work soluble macrocyclic poly(p-phenylenevinylene)s (cPPVs) have been prepared directly via the REMP of substituted paracyclophanedienes. Single-molecule spectroscopy of the two topological forms of PPV i.e., linear (lPPV) and cyclic (cPPV) revealed that lPPV exists in an extended conformation whereas the cPPV adopts a restricted ring-like conformation. Despite such large differences in the chain conformation, the spectral properties of the two compounds are unexpectedly very similar, and are dominated by torsional deformations in relatively short conjugated segments.
Scientific journal, English

Plasmon Enhancement of Triplet Exciton Diffusion Revealed by Nanoscale Imaging of Photochemical Fluorescence Upconversion
Lukasz Bujak; Kaishi Narushima; Dharmendar Kumar Sharma; Shuzo Hirata; Martin Vacha
JOURNAL OF PHYSICAL CHEMISTRY C, AMER CHEMICAL SOC, 121, 45, 25479-25486, Nov. 2017, Peer-reviwed, Photon upconversion based on the process of triplet triplet annihilation in a system of organic donor and acceptor molecules has been attracting increasing attention because it can potentially lead to improved efficiency of light energy conversion devices working under sunlight irradiation. Here we aim to gain insight into the effect of localized plasmons of metal nanostructures on the individual photophysical steps involved in the upconversion mechanism. We present an optical microscopy study of the photophysical properties of plasmonic hybrid nanostructures composed of silver nanowires combined with an upconversion system consisting of platinum octaethylporphyrin donor molecules and 9,10-diphenylanthracene acceptor molecules dispersed in poly(methyl methacrylate) thin film. Using an image-splitting technique, we simultaneously record upconversion and phosphorescence microscopy images and analyze the results to decouple the individual photophysical events. In addition to moderate intensity enhancement on the nanowires, the upconversion emission intensity can be enhanced up to 15-fold in the vicinity of hotspots formed by the silver nanowire junctions, compared with a 4-5-fold enhancement of phosphorescence in the same locations. Furthermore, whereas the phosphorescence enhancement is localized in the hotspots, the upconversion emission is enhanced along micrometer distances on the top of the nanowires. These findings are interpreted in terms of plasmon enhancement of Dexter-type energy transfer between the triplet states of the donor and acceptor as well as between the triplet states of the acceptor molecules. The latter gives rise to the apparent long-distance propagation of the triplet excitons along the nanowires.
Scientific journal, English

Recent Advances in Materials with Room-Temperature Phosphorescence: Photophysics for Triplet Exciton Stabilization
Shuzo Hirata
Lead, ADVANCED OPTICAL MATERIALS, WILEY-V C H VERLAG GMBH, 5, 17, 1700116, Sep. 2017, Peer-reviwed, Room-temperature phosphorescence (RTP), which has a much longer emission lifetime than fluorescence, often enables unique material characteristics and fabrication of state-of-the-art optoelectronic devices that cannot be realized using conventional fluorescent materials. The triplet exciton characteristics related to the appearance of efficient RTP also often provide intrinsic intra-and inter-molecular physical information about the materials. This article reviews recently reported aromatic materials that present RTP characteristics. Various aromatic materials with RTP characteristics are classified in terms of their radiative rates and radiationless rates from the lowest triplet excited state (T1) while taking the presence and absence of heavy atoms and charge transfer characteristics at T1 into consideration. Statistical arrangements based on physical factors of RTP materials indicate that the recent appearance of RTP in various metal-free aromatic structures is related to a large reduction in quenching caused by strong intermolecular interaction between the aromatics and the surrounding materials; additionally, intrinsic factors of the aromatics including the radiative rate and the nonradiative rate caused by intramolecular vibration are still not well controlled. Intrinsic control of these rates is important for overall control of the RTP yield and lifetime for potential material applications. Finally, recent applications using the RTP characteristics are highlighted.
Scientific journal, English

Large Reverse Saturable Absorption at the Sunlight Power Level Using the Ultralong Lifetime of Triplet Excitons
Shuzo Hirata; Martin Vacha
Lead, JOURNAL OF PHYSICAL CHEMISTRY LETTERS, AMER CHEMICAL SOC, 8, 15, 3683-3689, Aug. 2017, Peer-reviwed, Large reverse saturable absorption (RSA) at the sunlight power level was observed from a host guest amorphous material composed of d(12)-coronene as a guest and beta-estradiol as a rigid amorphous host. The large highly symmetric two-dimensional (2D) aromatic structure of d(12)-coronene doped into the rigid host causes ultralong triplet lifetime as well as high triplet yield, serving efficient accumulation of the triplet excitons of d(12)-coronene under weak excitation light. The high absorption coefficient of the triplet state (sigma(34)) compared with that of the ground state (sigma(01)) for d(12)-coronene is also caused by the highly symmetric 2D aromatic structure. The efficient accumulation of the triplet excitons and high sigma(34) - sigma(01) led to an onset of the RSA characteristics under irradiance below 10(-1) mW cm(-2). A film of the amorphous material showed a large decrease of transmittance from 66% at 0.02 mW cm(-2) to 24% at 50 mW cm(-2) for continuous light at 405 nm.
Scientific journal, English

Nanoscale triplet exciton diffusion via imaging of up-conversion emission from single hybrid nanoparticles in molecular crystals
Kaishi Narushima; Shuzo Hirata; Martin Vacha
Corresponding, NANOSCALE, ROYAL SOC CHEMISTRY, 9, 30, 10653-10661, Aug. 2017, Peer-reviwed, Up-conversion materials composed of donor and acceptor molecules which convert low energy photons into higher energy ones by triplet-triplet annihilation can improve the sensitivity of photocatalysts or the efficiency of solar cells. The use of crystalline materials can lead to a decrease in the up-conversion threshold intensity due to increased diffusion length L-T of triplet excitons. Here, we demonstrate direct microscopic imaging of triplet exciton diffusion in polycrystalline films. The generation of high local density of triplet states is achieved by functionalizing alumina nanospheres with donor molecules and dispersing them in the acceptor films. Diffusion of the triplet excitons and up-converted emission are reflected in enlarged microscopic images of the nanoparticles. Analysis provides the average L-T values of 491 nm for the acceptor of polycrystalline anthracene and 172 nm for polycrystalline 9,10-diphenylanthracene, and reveals large distributions of the diffusion characteristics. These average values are more than an order of magnitude larger than L-T obtained by a conventional method, and highlight the need for accurate nanoscale characterization of the up-conversion materials.
Scientific journal, English

White Afterglow Room-Temperature Emission from an Isolated Single Aromatic Unit under Ambient Condition
Shuzo Hirata; Martin Vacha
Lead, ADVANCED OPTICAL MATERIALS, WILEY-V C H VERLAG GMBH, 5, 5, Mar. 2017, Peer-reviwed, Single aromatic structures generally do not generate emission with a white afterglow (i.e., a lifetime longer than 1 s). This study shows white afterglow room-temperature (RT) emission from an isolated single aromatic structure doped into a rigid amorphous matrix in air. 2,5,8,11,14,17-Hexa(4-(2-ethylhexyl-)-hexa-peri-hexabenzocoronene (6EhHBC) doped into beta-estradiol shows blue-green thermally activated delayed fluorescence (TADF), as well as red phosphorescence with a lifetime of 3.9 s, at RT in air. The energy difference between the lowest singlet excited state and the lowest triplet excited state (Delta E-ST) of 6EhHBC is reduced to below 0.5 eV because of the effective separation between the two molecular orbitals related to fluorescence caused by the large 2D symmetric extension of the planar aromatic cyclic structures. The long-lived RT triplet state of 6EhHBC in the rigid host matrix enables an efficient TADF with Delta E-ST approximate to 0.5 eV at RT, as well as a red afterglow RT phosphorescence, leading to white afterglow RT emission.
Scientific journal, English

Influence of Zn on the photoluminescence of colloidal (AgIn)(x)Zn2(1-x) S-2 nanocrystals
Dharmendar Kumar Sharma; Shuzo Hirata; Lukasz Bujak; Vasudevanpillai Biju; Tatsuya Kameyama; Marino Kishi; Tsukasa Torimoto; Martin Vacha
PHYSICAL CHEMISTRY CHEMICAL PHYSICS, ROYAL SOC CHEMISTRY, 19, 5, 3963-3969, Feb. 2017, Peer-reviwed, We study the effect of Zn on the photophysical properties of a family of group I-III-VI nanocrystals (NCs), namely in solid solutions of (AgIn)(x)Zn2(1-x)S2 (ZAIS). We focus on the comparison of the photo-luminescence (PL) properties of ZAIS NCs of comparable sizes and different amounts of Zn. This approach helps us to decouple the effects of size and varying chemical composition of the NCs which both influence the PL properties. We show that in the presence of Zn new radiative centers are generated which improve the NC quality in terms of PL quantum yield. However, an amount of Zn beyond a particular limit places the radiative recombination centers close to each other, leading to undesired interactions among charge carriers and non-radiative transitions. Proximity between the energy levels of these radiative centers and the conduction band leads to non-radiative localized-delocalized transitions, as evidenced from temperature dependent absorption, PL and lifetime measurements.
Scientific journal, English

Photo-Functional Materials with Ultralong Exciton Lifetime Using Super Rigid Molecular Hosts
HIRATA SHUZOU
Sen'i Gakkaishi, The Society of Fiber Science and Technology, Japan, 73, 9, P-336-P-341, 2017
Japanese

Efficient triplet-triplet annihilation upconversion in binary crystalline solids fabricated: Via solution casting and operated in air
Kenji Kamada; Yusuke Sakagami; Toshiko Mizokuro; Yutaka Fujiwara; Kenji Kobayashi; Kaishi Narushima; Shuzo Hirata; Martin Vacha
Materials Horizons, Royal Society of Chemistry, 4, 1, 83-87, 01 Jan. 2017, Peer-reviwed, Binary crystalline solids consisting of a sensitizer (Pt-octaethylporphyrin) and an emitter (9,10-diphenylanthracene (DPA) or its alkyl-strapped derivative (C7-sDPA)) were fabricated by solution casting under rapid drying conditions and found to show efficient triplet-triplet annihilation upconversion by the suppression of component segregation. Microspectroscopic studies of individual crystalline particles of the binary solids revealed threshold intensities as low as 5 mW cm-2, close to solar levels, and UC quantum yields of 20% were possible when using C7-sDPA as an emitter, even in air.
Scientific journal, English

Selective turn-on and modulation of resonant energy transfer in single plasmonic hybrid nanostructures
Lukasz Bujak; Tatsuya Ishii; Dharmendar Kumar Sharma; Shuzo Hirata; Martin Vacha
NANOSCALE, ROYAL SOC CHEMISTRY, 9, 4, 1511-1519, Jan. 2017, Peer-reviwed, Forster resonant energy transfer (FRET) is a nonradiative process by which the energy of light absorbed by a donor molecule is transferred to an acceptor molecule over a distance of several nanometers. FRET plays a crucial role in photosynthesis and nature-inspired artificial light-harvesting systems that are being explored for use in energy conversion applications. Localized plasmons of metal nanoparticles can potentially lead to a significant increase of FRET efficiency and effective donor-acceptor distance. Here, we prepare hybrid nanostructures composed of a gold nanorod and donor and acceptor molecules covalently attached to its surface, and study them on the level of a single nanoparticle by simultaneous dark-field scattering, fluorescence imaging and spectroscopy. The single-particle approach enables selective excitation of the longitudinal plasmon of the gold nanorod by polarization of the excitation light. The emission intensity of the acceptor molecules can be controllably and reversibly modulated over a wide range by the polarization angle, thus enabling a selective turn-on of the FRET process and control over the emission color of the hybrid nanostructure. Numerical simulations show that the interactions of the donor and acceptor molecules with the plasmon lead to an increase of the energy transfer efficiency by a factor of similar to 65. These findings represent the concept of a novel colour switching approach and could pave the way for innovative applications in optoelectronics and nanophotonics.
Scientific journal, English

Efficient triplet-triplet annihilation upconversion in binary crystalline solids fabricated via solution casting and operated in air
Kenji Kamada; Yusuke Sakagami; Toshiko Mizokuro; Yutaka Fujiwara; Kenji Kobayashi; Kaishi Narushima; Shuzo Hirata; Martin Vacha
MATERIALS HORIZONS, ROYAL SOC CHEMISTRY, 4, 1, 83-87, Jan. 2017, Peer-reviwed, Binary crystalline solids consisting of a sensitizer (Pt-octaethylporphyrin) and an emitter (9,10-diphenylanthracene (DPA) or its alkyl-strapped derivative (C7-sDPA)) were fabricated by solution casting under rapid drying conditions and found to show efficient triplet-triplet annihilation upconversion by the suppression of component segregation. Microspectroscopic studies of individual crystalline particles of the binary solids revealed threshold intensities as low as 5 mW cm(-2), close to solar levels, and UC quantum yields of 20% were possible when using C7-sDPA as an emitter, even in air.
Scientific journal, English

分子性室温りん光と三重項の光物理化学
平田修造
光化学協会誌, 光化学協会, 47, 2, 84-91, Sep. 2016, Invited
Research society, Japanese

Circularly Polarized Persistent Room-Temperature Phosphorescence from Metal-Free Chiral Aromatics in Air
Shuzo Hirata; Martin Vacha
Lead, JOURNAL OF PHYSICAL CHEMISTRY LETTERS, AMER CHEMICAL SOC, 7, 8, 1539-1545, Apr. 2016, Peer-reviwed, Circularly polarized room-temperature phosphorescence (RTP) with persistent emission characteristics was observed from metal-free chiral binaphthyl structures. Enantiomers of the binaphthyl compounds doped into an amorphous hydroxylated steroid matrix produced blue fluorescence and yellow persistent RTP in air. The lifetime and quantum yield of the yellow persistent RTP were 0.67 s and 2.3%, respectively. The dissymmetry factors of circular dichroism (CD) in the first absorption band, circularly polarized fluorescence (CPF), and circularly polarized persistent RTP were vertical bar 1.1 x 10(-3)vertical bar, vertical bar 4.5 x 10(-4)vertical bar, and vertical bar 2.3 x 10(-3)vertical bar, respectively. A comparison between the experimental data and calculations by time-dependent density functional theory for transient CD spectra confirmed that the binaphthyl conformations in the lowest singlet excited state (S-1) and the lowest triplet state (T-1) were different. The large difference in the dissymmetry factors for the CPF and the circularly polarized persistent RTP was likely caused by this conformational change between S-1 and T-1.
Scientific journal, English

Large Transmittance Change Induced by Exciton Accumulation under Weak Continuous Photoexcitation
Shuzo Hirata; Martin Vacha
Lead, ADVANCED OPTICAL MATERIALS, WILEY-V C H VERLAG GMBH, 4, 2, 297-305, Feb. 2016, Peer-reviwed, Excited-state absorption of materials is caused by instantaneous accumulation of excitons when irradiated with a high-intensity laser pulse. If excitons can be accumulated by irradiation with weak continuous incoherent light at room temperature (RT) in air, then excited-state absorption can be obtained over a large area, which is potentially useful for a variety of optical applications. Here, photoresponsive transmittance control using long-lived RT triplet excitons is demonstrated. Host-guest glass films composed of a secondary amino-substituted deuterated aromatic carbon material as a guest and an amorphous hydroxyl steroidal compound as a host form guest-based triplet excitons with an RT lifetime of longer than 1 s upon photoexcitation and the triplet excitons of the guest exhibit a large absorption coefficient over the whole visible region. Efficient accumulation of the triplet excitons of the guest triggered by photoexcitation causes a large decrease in the transmittance of the host-guest films. The transmittance of one of the host-guest films decreases from 98% to 30% over the whole visible range and from 92% to 13% at the wavelength of maximum triplet-triplet absorption of the guest as the power of UV photoexcitation is increased from 10(-1) to 10(3) mW cm(-2).
Scientific journal, English

Single-particle spectroscopy of I-III-VI semiconductor nanocrystals: spectral diffusion and suppression of blinking by two-color excitation
Dharmendar Kumar Sharma; Shuzo Hirata; Lukasz Bujak; Vasudevanpillai Biju; Tatsuya Kameyama; Marino Kishi; Tsukasa Torimoto; Martin Vacha
NANOSCALE, ROYAL SOC CHEMISTRY, 8, 28, 13687-13694, 2016, Peer-reviwed, Ternary I-III-VI semiconductor nanocrystals have been explored as non-toxic alternatives to II-VI semiconductors for optoelectronic and sensing applications, but large photoluminescence spectral width and moderate brightness restrict their practical use. Here, using single-particle photoluminescence spectroscopy on nanocrystals of (AgIn)(x)Zn2(1-x)S2 we show that the photoluminescence band is inhomogeneously broadened and that size distribution is the dominant factor in the broadening. The residual homogeneous linewidth of individual nanocrystals reaches up to 75% of the ensemble spectral width. Single nanocrystals undergo spectral diffusion which also contributes to the inhomogeneous band. Excitation with two lasers with energies above and below the bandgap reveals coexistence of two emitting donor states within one particle. Spectral diffusion in such particles is due to temporal activation and deactivation of one such state. Filling of a trap state with a lower-energy laser enables optical modulation of photoluminescence intermittency (blinking) and leads to an almost two-fold increase in brightness.
Scientific journal, English

Photoreversible On-Off Recording of Persistent Room-Temperature Phosphorescence
Yuki Katsurada; Shuzo Hirata; Kenro Totani; Toshiyuki Watanabe; Martin Vacha
Corresponding, ADVANCED OPTICAL MATERIALS, WILEY-V C H VERLAG GMBH, 3, 12, 1726-1737, Dec. 2015, Peer-reviwed, Photoreversible on-off recording of red persistent room-temperature phosphorescence (RTP) is demonstrated. Host-guest materials composed of a persistent phosphorescent guest (D), a photochromic guest (A), and an amorphous steroidal host show red persistent RTP with a lifetime longer than 1 s based on D. The red persistent RTP function is erased by ultraviolet irradiation and recovered by irradiation with green light. The reversible photocyclization and decyclization of A allows and prevents dual dipole-dipole energy transfer from the singlet and triplet states of D to the ground state of A, respectively. The occurrence and lack of dual dipole-dipole energy transfer trigger the deactivation and activation of red persistent RTP from D, respectively. In samples labeled by the recording material, the RTP function of a specific target can be selectively activated using green light irradiation and the movement of the target can be detected as red persistent emission signal without interference from the movement of other persistent phosphorescent species as well as excitation light scattering.
Scientific journal, English

Super-resolution localization microscopy reveals nanoscale dynamics of polymers and soft matter
Shuzo Hirata; Syoji Ito; Martin Vacha; Hiroshi Miyasaka
Kobunshi, 64, 9, 575-577, Sep. 2015, Super-resolved astigmatic microscopy allows 3D spatial localization of individual molecules of fluorescent dyes with nanometer accuracy. Apart from imaging, such localization has found applications in the study of nanometer-scale physical properties of polymers and complex soft matter. Here, we introduce the principle of the astigmatic imaging and present examples of its use in the study of polymers and liquid crystals. Study of relaxation dynamics across thin polymer films shows that the effect of substrate is dominant over the surface effect in determining the thin film properties below the glass transition temperature. Monitoring of diffusion in nematic liquid crystals reveals position-dependent changes in tilt angle, confined diffusion close to the liquid crystal cell wall and reorientation of the liquid crystal director close to a nanoparticle. Study of diffusion in polymer films above the glass transition shows that the film substrate causes considerable slow-down in the diffusion and that this effect extends up to 200 nm into the bulk of the film.
Scientific journal

Material degradation of liquid organic semiconductors analyzed by nuclear magnetic resonance spectroscopy
Tatsuya Fukushima; Junichi Yamamoto; Masashi Fukuchi; Shuzo Hirata; Heo Hyo Jung; Osamu Hirata; Yuki Shibano; Chihaya Adachi; Hironori Kaji
AIP ADVANCES, AMER INST PHYSICS, 5, 8, Aug. 2015, Peer-reviwed, Liquid organic light-emitting diodes (liquid OLEDs) are unique devices consisting only of liquid organic semiconductors in the active layer, and the device performances have been investigated recently. However, the device degradation, especially, the origin has been unknown. In this study, we show that material degradation occurs in liquid OLEDs, whose active layer is composed of carbazole with an ethylene glycol chain. Nuclear magnetic resonance (NMR) experiments clearly exhibit that the dimerization reaction of carbazole moiety occurs in the liquid OLEDs during driving the devices. In contrast, cleavages of the ethylene glycol chain are not detected within experimental error. The dimerization reaction is considered to be related to the device degradation. (C) 2015 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution 3.0 Unported License.
Scientific journal, English

Position-Dependent Three-Dimensional Diffusion in Nematic Liquid Crystal Monitored by Single-Particle Fluorescence Localization and Tracking
Seonik Lee; Koushi Noda; Shuzo Hirata; Martin Vacha
Journal of Physical Chemistry Letters, AMER CHEMICAL SOC, 6, 8, 1403-1407, Apr. 2015, Peer-reviwed, Anisotropic mass diffusion in liquid crystals (LCs) is important from the point of both basic LC physics and their applications in optoelectronic devices. We use super-resolution fluorescence microscopy with astigmatic imaging to track 3D diffusion of quantum dots (QDs) in an ordered nematic LC. The method allowed us to evaluate the diffusion coefficients independently along the three spatial axes as well as to determine the absolute position of the QD with respect to the cell wall. We found variations of the diffusion coefficient along the different directions across the cell thickness and explained these as being due to changes of a tilt angle of the LC director. Close to the surface, the diffusion is slowed down due to the confinement effect of the cell wall. Overall, the QD diffusion is much slower than expected for a corresponding particle size. This phenomenon is suggested to originate from reorientation of the LC director in the vicinity of the particle.
Scientific journal, English

Highly efficient blue electroluminescence based on thermally activated delayed fluorescence
Shuzo Hirata; Yumi Sakai; Kensuke Masui; Hiroyuki Tanaka; Sae Youn Lee; Hiroko Nomura; Nozomi Nakamura; Mao Yasumatsu; Hajime Nakanotani; Qisheng Zhang; Katsuyuki Shizu; Hiroshi Miyazaki; Chihaya Adachi
Lead, NATURE MATERIALS, NATURE PUBLISHING GROUP, 14, 3, 330-336, Mar. 2015, Peer-reviwed, Organic compounds that exhibit highly efficient, stable blue emission are required to realize inexpensive organic light-emitting diodes for future displays and lighting applications. Here, we define the design rules for increasing the electroluminescence efficiency of blue-emitting organic molecules that exhibit thermally activated delayed fluorescence. We show that a large delocalization of the highest occupied molecular orbital and lowest unoccupied molecular orbital in these charge-transfer compounds enhances the rate of radiative decay considerably by inducing a large oscillator strength even when there is a small overlap between the two wavefunctions. A compound based on our design principles exhibited a high rate of fluorescence decay and efficient up-conversion of triplet excitons into singlet excited states, leading to both photoluminescence and internal electroluminescence quantum yields of nearly 100%.
Scientific journal, English

Meta-linking strategy for thermally activated delayed fluorescence emitters with a small singlet-triplet energy gap
Katsuyuki Shizu; Yumi Sakai; Hiroyuki Tanaka; Shuzo Hirata; Chihaya Adachi; Hironori Kaji
ITE Transactions on Media Technology and Applications, Institute of Image Information and Television Engineers, 3, 2, 108-113, 2015, Peer-reviwed, Thermally activated delayed fluorescence (TADF) emitters have recently attracted considerable attention as dopants for organic light-emitting diodes (OLEDs), and are considered promising alternatives to fluorescent and phosphorescent dopants. TADF emitters require a small singlet-triplet energy gap (?EST). This study presents a molecular design strategy to achieve a small ?EST. An electroluminescent dopant containing two electron-donating carbazolyl groups and an electron-accepting triphenyltriazine, m-bisCzTRZ, was prepared. The electron-donating moieties were introduced at the meta positions of the two phenyl rings in triphenyltriazine. Transient photoluminescence decay measurements confirmed that m-bisCzTRZ emitted blue TADF in a solid-state host layer and thus it showed promise as a blue dopant. The experimental ?EST value for m-bisCzTRZ was small (0.09 eV), as determined from fluorescence and phosphorescence spectra of a mbisCzTRZ- doped host. These observations suggested that the use of meta-linked electron-donating and electronaccepting units could be a useful strategy to obtain TADF emitters.
Scientific journal, English

Long-lived Triplet Excitons Allowed by Intermolecular Hydrogen Bonding in Amorphous Matrix
Yuichiro Tsubomoto; Shuzo Hirata; Kenro Totani; Martin Vacha; Toshiyuki Watanabe
Corresponding, JOURNAL OF PHOTOPOLYMER SCIENCE AND TECHNOLOGY, TECHNICAL ASSOC PHOTOPOLYMERS,JAPAN, 28, 4, 573-577, 2015, Peer-reviwed, A purely organic guest material with a long triplet excited state lifetime (tau > 1 s) was doped into two different pi-conjugated amorphous hosts with similar glass transition temperatures (T-g). The phosphorescence quenching behavior of the guest material was investigated under vacuum conditions. When doped into a host that did not exhibit intermolecular hydrogen bonding, the tau of the guest decreased significantly at temperatures below the T-g of the host. Conversely, when doped into a host that did exhibit intermolecular hydrogen bonding, the tau remained almost unaffected at temperatures below the T-g of the host. The diffusion coefficient of oxygen, which was largely removed from the host materials under vacuum, was similar for both host materials. These results indicated that weak thermal diffusional motion of a host material intrinsically quenches long-lived triplet excitons of purely organic guest materials.
Scientific journal, English

Thermally activated delayed fluorescence with circularly polarized luminescence characteristics
Takuro Imagawa; Shuzo Hirata; Kenro Totani; Toshiyuki Watanabe; Martin Vacha
Corresponding, CHEMICAL COMMUNICATIONS, ROYAL SOC CHEMISTRY, 51, 68, 13268-13271, 2015, Peer-reviwed, A metal-free aromatic compound with a chiral carbon sandwiched between a donor moiety and an acceptor moiety was designed. Under thermally activated delayed fluorescence, the compound displayed a photoluminescence quantum yield of 26%, and showed circularly polarized luminescence with a dissymmetry factor of 10(-3).
Scientific journal, English

Large reverse saturable absorption under weak continuous incoherent light
Shuzo Hirata; Kenro Totani; Takashi Yamashita; Chihaya Adachi; Martin Vacha
Lead, NATURE MATERIALS, NATURE PUBLISHING GROUP, 13, 10, 938-946, Oct. 2014, Peer-reviwed, In materials showing reverse saturable absorption (RSA), the optical absorbance increases as the power of the light incident on them increases. To date, RSA has only been observed when very intense light sources, such as short-pulse lasers, are used. Here, we show that hydroxyl steroidal matrices embedding properly designed aromatic molecules as acceptors and transition-metal complexes as donors exhibit high RSA on exposure to weak incoherent light at room temperature and in air. Accumulation by photosensitization of long-lived room-temperature triplet excitons in acceptors with a large triplettriplet absorption coefficient allows a nonlinear increase in absorbance also under low-power irradiation conditions. As a consequence, continuous exposure to weak light significantly decreases the transmittance of thin films fabricated with these compounds. These optical limiting properties may be used to protect eyes and light sensors from exposure to intense radiation generated by incoherent sources and for other light-absorption applications that have not been realized with conventional RSA materials.
Scientific journal, English

Circularly polarized luminescence from individual microstructures of conjugated polymer aggregates with solvent-induced chirality
Kenta Katayama; Shuzo Hirata; Martin Vacha
PHYSICAL CHEMISTRY CHEMICAL PHYSICS, ROYAL SOC CHEMISTRY, 16, 33, 17983-17987, Sep. 2014, Peer-reviwed, We report a microscopic study of circularly polarized luminescence (CPL) from R and S isomers of aggregates of the conjugated polymer F8BT, a copolymer containing fluorene and thiophene monomer units. Chirality in the aggregates is induced by addition of either (R)- or (S)-limonene during aggregation in solution. Solid-state samples are prepared either by drop-casting or spin-coating of the aggregate solution. CPL dissymmetry parameter g measured for individual aggregate microstructures shows a broad distribution of values ranging from positive to negative even for the same isomer. The difference in the centers of the g distribution between the R and S isomers reflects the intrinsic CPL from the chiral aggregates, and is found to depend on the size of the aggregate structures. On the other hand, the large widths of the distributions are ascribed to an optical effect arising from phase retardation along the optical path of the CPL inside the sample.
Scientific journal, English

Single-molecule electroluminescence and photoluminescence of polyfluorene unveils the photophysics behind the green emission band
Yoshihiro Honmou; Shuzo Hirata; Hideaki Komiyama; Junya Hiyoshi; Susumu Kawauchi; Tomokazu Iyoda; Martin Vacha
NATURE COMMUNICATIONS, NATURE PUBLISHING GROUP, 5, 938-946, Aug. 2014, Peer-reviwed, Optoelectronic properties of polyfluorene, a blue light-emitting organic semiconductor, are often degraded by the presence of green emission that originates mainly from oxidation of the polymer. Here, we use single-molecule electroluminescence (EL) and photoluminescence (PL) spectroscopy on polyfluorene chains confined in vertical cylinders of a phase-separated block copolymer to spectrally resolve the green band and investigate in detail the photophysical processes responsible for its appearance. In both EL and PL, a substantial fraction of polyfluorene chains shows spectrally stable green emission which is ascribed to a keto defect. In addition, in EL, we observe a new type of vibrationally resolved spectra distributed over a wide range of frequencies and showing strong spectral dynamics. Based on quantum chemical calculations, this type is proposed to originate from charge-assisted formation and stabilization of ground-state aggregates. The results are expected to have broad implications in the fields of photophysics and material design of polyfluorene materials.
Scientific journal, English

Bacteriochlorophyll Aggregates Self-Assembled on Functionalized Gold Nanorod Cores as Mimics of Photosynthetic Chlorosomal Antennae: A Single Molecule Study
Shu Furumaki; Frantisek Vacha; Shuzo Hirata; Martin Vacha
ACS NANO, AMER CHEMICAL SOC, 8, 3, 2176-2182, Mar. 2014, Peer-reviwed, We prepare artificial aggregates that mimic the structure and function of natural chlorosomal light harvesting complexes of green photosynthetic bacteria. Gold nanorods functionalized with hydroxyl groups and immobilized on a substrate serve as cores for the growth of bacteriochlorophyll (BChl) aggregates from a buffer solution. The BChl pigments form large self-assembled aggregate particles with sizes more than twice that of natural chlorosomes. The size is controllable by the aggregation time. The aggregates are characterized on a single-particle level by atomic force microscopy, electron microscopy, and single-molecule spectroscopy. The absorption and fluorescence spectral properties which reflect the molecular level arrangement of the BChl aggregates closely resemble those of the natural chlorosomes of the photosynthetic bacterium Chlorobaculum tepidum. On the other hand, the results of linear dichroism and circular dichroism are different from those of the chlorosomes and indicate a different mesoscopic structure for the artificial aggregates. These results emphasize the structural role played by the baseplate pigment protein complex in natural chlorosomes.
Scientific journal, English

Relationship between room temperature phosphorescence and deuteration position in a purely aromatic compound
S. Hirata; K. Totani; T. Watanabe; H. Kaji; M. Vacha
Lead, CHEMICAL PHYSICS LETTERS, ELSEVIER SCIENCE BV, 591, 119-125, Jan. 2014, Peer-reviwed, The development of organometallic and purely organic compounds showing room temperature phosphorescence (RTP) has several promising applications. We report a relationship between the phosphorescence characteristics and deuteration position in a purely organic aromatic compound. Hydrogen-deuterium exchange at the carbons where the lowest unoccupied molecular orbital is located is the most effective method to enhance the RTP lifetime and quantum yield. The increase in RTP lifetime comes from a decrease in the Franck-Condon factor while the enhancement of RTP yield is caused by an increase in intersystem crossing from the lowest singlet excited state to the lowest triplet excited state. (C) 2013 Elsevier B.V. All rights reserved.
Scientific journal, English

Mechanical Manipulation of Photophysical Properties of Single Conjugated Polymer Nanoparticles
Hiroyuki Kobayashi; Shuzo Hirata; Martin Vacha
JOURNAL OF PHYSICAL CHEMISTRY LETTERS, AMER CHEMICAL SOC, 4, 15, 2591-2596, Aug. 2013, Peer-reviwed, Results on simultaneous atomic force microscopy (AFM) and fluorescence microspectroscopy on single nanopartides of the conjugated polymer poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV) are presented. Single particle fluorescence spectra and defocused images confirm that the particles are composed of large numbers of randomly oriented conjugated segments (chromophores) with a wide distribution of the segment lengths. Mechanical contact of the particle surface with a sharp tip of the AFM probe causes reversible modification of the particle fluorescence intensity and spectra. The majority of the partides show an increase of fluorescence intensity and blue spectral shift upon contact with the tip. The fluorescence increase is correlated with the particle size and is most pronounced for the smallest particles. The phenomena are interpreted in terms of local disturbance of the MEH-PPV chain conformation by the probe tip.
Scientific journal, English

Efficient Persistent Room Temperature Phosphorescence in Organic Amorphous Materials under Ambient Conditions
Shuzo Hirata; Kenro Totani; Junxiang Zhang; Takashi Yamashita; Hironori Kaji; Seth R. Marder; Toshiyuki Watanabe; Chihaya Adachi
Lead, ADVANCED FUNCTIONAL MATERIALS, WILEY-V C H VERLAG GMBH, 23, 27, 3386-3397, Jul. 2013, Peer-reviwed, Persistent emission with a long lifetime (>1 s) from organic materials can only be observed at a low temperature, because of the significant nonradiative deactivation pathway that occurs at room-temperature (RT). If organic materials with persistent RT emission in air could be developed, they could potentially be utilized for a variety of applications. Here, organic host-guest materials with efficient persistent RT phosphorescence (RTP) are developed by minimizing the nonradiative deactivation pathway of triplet excitons. The nonradiative deactivation pathway is dependent on both nonradiative deactivation of the guest and quenching by diffusional motion of the host. The rigidity and oxygen barrier properties of the steroidal compound used as the host suppressed the quenching, and the aromatic hydrocarbon used as the guest is highly deuterated to minimize nonradiative deactivation of the guest. Red-green-blue persistent RTP with a lifetime >1 s and a quantum yield >10% in air is realized for a pure organic material.
Scientific journal, English

Reversible Thermal Recording Media Using Time-Dependent Persistent Room Temperature Phosphorescence
Shuzo Hirata; Kenro Totani; Hironori Kaji; Martin Vacha; Toshiyuki Watanabe; Chihaya Adachi
Lead, ADVANCED OPTICAL MATERIALS, WILEY-V C H VERLAG GMBH, 1, 6, 438-442, Jun. 2013, Peer-reviwed
Scientific journal, English

Energy Transfer: Thermoresponsive Persistent Phosphorescent Color Change Using Efficient Thermally Activated Reverse Energy Transfer with a Large Energy Difference (Advanced Optical Materials 4/2013)
Kenro Totani; Yuya Okada; Shuzo Hirata; Martin Vacha; Toshiyuki Watanabe
Advanced Optical Materials, 1, 4, 282-282, Apr. 2013, Peer-reviwed, K. Totani, S. Hirata, and co-workers report on page 283 the efficient thermally activated reverse energy transfer from the lower excited state of a donor to the higher excited state of an acceptor when the energy difference between the two excited states is 0.4 eV. This energy transfer results in a temperaturedependent color change with persistent phosphorescence. © 2013 WILEY-VCH Verlag GmbH &
Co. KGaA, Weinheim.
Scientific journal, English

Thermoresponsive Persistent Phosphorescent Color Change Using Efficient Thermally Activated Reverse Energy Transfer with a Large Energy Difference
Kenro Totani; Yuya Okada; Shuzo Hirata; Martin Vacha; Toshiyuki Watanabe
Corresponding, ADVANCED OPTICAL MATERIALS, WILEY-V C H VERLAG GMBH, 1, 4, 283-288, Apr. 2013, Peer-reviwed, Temperature-dependent changes of the color of persistent (>
0.3 s) phosphorescence are observed from a host-guest material containing donor and acceptor guests. Efficient thermally activated triplet-triplet reverse energy transfer is realized because of slow nonradiative decay of the donor at high temperature. © 2013 WILEY-VCH Verlag GmbH &
Co. KGaA, Weinheim.
Scientific journal, English

Efficient Persistent Room Temperature Phosphorescence in Organic Materials
Shuzo Hirata; Chihaya Adachi; Toshiyuki Watanabe; Kenro Totani
Lead, KOBUNSHI RONBUNSHU, SOC POLYMER SCIENCE JAPAN, 70, 11, 623-636, 2013, Peer-reviwed, It has been well-recognized that phosphorescence lasting longer than one second in organic materials is only observable in the frozen state at 77 K under inert conditions. This is because of several factors: Thermally activated vibrational motion of molecules, the diffusion processes between host and guest compounds and the existence of oxygen. All of these factors significantly quench the excited stable triplet states at room temperature. Here we demonstrate a design concept of organic materials showing efficient persistent room temperature phosphorescence (RTP) by suppressing non-radiative processes of the excited triplet states. We used a host-guest system composed of a secondary amino-substituted aromatic deuterated carbon and a hydroxy steroid compound as guest and host, respectively. In these materials, efficient persistent RTP was observed, since the non-radiative process at the lowest excited triplet state of the guest compound is significantly suppressed. Quantum efficiency of persistent RTP was more than 0.1 and phosphorescence lifetime was longer than 1 s for RUB colors.
Scientific journal, Japanese

Reversible Coloration Enhanced by Electrochemical Deposition of an Ultrathin Zinc Layer onto an Anodic Nanoporous Alumina Layer
Shuzo Hirata; Toshiro Tsuji; Yoshimine Kato; Chihaya Adachi
Lead, ADVANCED FUNCTIONAL MATERIALS, WILEY-V C H VERLAG GMBH, 22, 20, 4195-4201, Oct. 2012, Peer-reviwed, A productive method is introduced to realize large area color electronic paper (e-paper) with high UV resistance, heat resistance, and good significant bending properties using a color change triggered by reversible electronic change in the device structure. Reversible coloration and decoloration triggered by electrochemical deposition and desorption, respectively, of an ultra-thin zinc (Zn) layer on a thin transparent conductive layer coated on anodic nanoporous alumina has been developed. The deposition of the ultra-thin Zn layer triggers the formation of destructive interference, which leads to coloration. Yellow, magenta, and cyan colors were obtained in the colored state by increasing the NP-Al2O3 layer thickness, based on Bragg diffraction theory. Reflectance of more than 70% and contrast values of more than 7 were obtained, which are nearly equivalent to those of previous e-papers. The color images in these devices also showed high UV resistance, heat resistance, and repeated significant bending endurance. The devices can be fabricated with large areas using low-cost manufacturing processes such as anodic oxidation, and use abundantly available materials. Our proposed device provides low-cost and flexible large area color e-paper for outdoor use.
Scientific journal, English

Uniform and refreshable liquid electroluminescent device with a back side reservoir
Chang-Hoon Shim; Shuzo Hirata; Juro Oshima; Tomohiko Edura; Reiji Hattori; Chihaya Adachi
APPLIED PHYSICS LETTERS, AMER INST PHYSICS, 101, 11, 283-288, Sep. 2012, Peer-reviwed, We fabricated a refreshable organic light-emitting diode with a liquid emitting layer. This device has a mesh-structured cathode and a liquid reservoir in the back side of the cathode for easy convection of the liquid emitter. The small uniform gap between the electrodes was fabricated by means of micro-electro-mechanical systems (MEMS) processing. Although the device luminance decreased because of decomposition of the liquid emitters under the drive current, the decreased emission was quickly recovered to the initial state by convectional replacement of the decomposed emitters with fresh emitters through the holes of the mesh cathode. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4749791]
Scientific journal, English

Liquid Carbazole Substituted with a Poly(ethylene oxide) Group and Its Application for Liquid Organic Light-emitting Diodes
Korefumi Kubota; Shuzo Hirata; Yuki Shibano; Osamu Hirata; Masayuki Yahiro; Chihaya Adachi
CHEMISTRY LETTERS, CHEMICAL SOC JAPAN, 41, 9, 934-936, Sep. 2012, Peer-reviwed, We report efficient carrier injection characteristics in liquid organic light-emitting diodes (OLEDs). The use of a liquid carbazole substituted with a poly(ethylene oxide) (PEO) chain provided a substantial improvement in carrier injection compared to devices constructed with carbazoles without PEO units. The external electroluminescence quantum efficiency (Phi(EL).) of an OLED with the liquid carbazole as an emitting layer resulted in Phi(EL) = 0.75%, 25 times higher Phi(EL) than that of our previous liquid OLED without electrolyte.
Scientific journal, English

Design of Efficient Thermally Activated Delayed Fluorescence Materials for Pure Blue Organic Light Emitting Diodes
Qisheng Zhang; Jie Li; Katsuyuki Shizu; Shuping Huang; Shuzo Hirata; Hiroshi Miyazaki; Chihaya Adachi
JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, AMER CHEMICAL SOC, 134, 36, 14706-14709, Sep. 2012, Peer-reviwed, Efficient thermally activated delayed fluorescence (TADF) has been characterized for a carbazole/sulfone derivative in both solutions and doped films. A pure blue organic light emitting diode (OLED) based on this compound demonstrates a very high external quantum efficiency (EQE) of nearly 10% at low current density. Because TADF only occurs in a bipolar system where donor and acceptor centered (3)pi pi* states are close to or higher than the triplet intramolecular charge transfer (3CT) state, control of the pi-conjugation length of both donor and acceptor is considered to be as important as breaking the pi-conjugation between them in blue TADF material design.
Scientific journal, English

Improved Device Lifetime of Organic Light Emitting Diodes with an Electrochemically Stable pi-Conjugated Liquid Host in the Liquid Emitting Layer
Shuzo Hirata; Hyo Jung Heo; Yuki Shibano; Osamu Hirata; Masayuki Yahiro; Chihaya Adachi
Lead, JAPANESE JOURNAL OF APPLIED PHYSICS, JAPAN SOC APPLIED PHYSICS, 51, 4, 14706-14709, Apr. 2012, Peer-reviwed, The device lifetimes of organic light emitting diodes with a liquid emitting layer (liquid OLEDs) were improved by proper combination of host and guest molecules in the liquid emitting layer. The device lifetime strongly depends on the electrochemical stability of radical cations in the liquid emitting layer. The electrochemical stability of the liquid host materials was achieved by the dimerization of the alkyl-substituted carbazole 9,9'-{2[2-(2-methoxyethoxy)ethoxy]ethyl}-3,3'-bis(9H-carbazole) [ (TEGCz)(2)]. The use of a guest compound with its highest occupied molecular orbital level higher in energy than that of (TEGCz)(2) is a critical factor for realizing stable electroluminescence performance. A liquid OLED with proper combination of the guest and host materials showed an improved device lifetime of longer than 1 h, which is 100 times longer than that of our previous reports. (C) 2012 The Japan Society of Applied Physics
Scientific journal, English

Self-refreshable lighting device using liquid oled material
Chang-Hoon Shim; Shuzo Hirata; Juro Oshima; Tomohiko Edura; Reiji Hattori; Chihaya Adachi
Digest of Technical Papers - SID International Symposium, Blackwell Publishing Ltd, 43, 1, 1542-1543, 2012, We made a self-refreshable lighting device using liquid OLED which can emit light in the liquid state. This device has a mesh-structure cathode made by means of MEMS processes and a liquid reservoir in the backside of the cathode. Although luminance decreased as the light emitting, the degraded emitting material was refreshed by natural replacement from the reservoir in the backside.
International conference proceedings, English

MICROFLUIDIC ORGANIC LIGHT EMITTING DIODE (OLED) USING LIQUID ORGANIC SEMICONDUCTORS
T. Kasahara; J. Mizuno; S. Hirata; T. Edura; S. Matsunami; C. Adachi; S. Shoji
2012 IEEE 25TH INTERNATIONAL CONFERENCE ON MICRO ELECTRO MECHANICAL SYSTEMS (MEMS), IEEE, 1069-1072, 2012, Peer-reviwed, We propose a first prototype of the microfluidic organic light emitting diode (OLED). A matrix of 3x3 OLED array was fabricated in the SU-8 microchannels sandwiched by the indium tin oxide (ITO) anode and cathode. The liquid organic semiconductors were employed for the light emitters and were injected into the microchannels. The electroluminescence was obtained in the microchannels under the optimized applied voltage. The current density of 2.11 mA/cm(2) was measured at 60 V. Since flesh liquid organic semiconductors are continuously supplied to the emitting layer, long-term stable electroluminescence is expected by the proposed OLED.
International conference proceedings, English

Improvement of Electroluminescence Performance of Organic Light-Emitting Diodes with a Liquid-Emitting Layer by Introduction of Electrolyte and a Hole-Blocking Layer
Shuzo Hirata; Korefumi Kubota; Heo Hyo Jung; Osamu Hirata; Kenichi Goushi; Masayuki Yahiro; Chihaya Adachi
Lead, ADVANCED MATERIALS, WILEY-V C H VERLAG GMBH, 23, 7, 889-+, Feb. 2011, Peer-reviwed, Organic light-emitting diodes containing a liquid-emitting layer that exhibit improved external electroluminescence quantum efficiency (Phi(EL)) and maximum luminance are presented. Doping the liquid-emitting layer with an electrolyte significantly decreases the turn-on voltage for electroluminescence. Insertion of a TiO2 hole-blocking layer between the liquid-emitting layer and indium tin oxide cathode improves Phi(EL).
Scientific journal, English

Enhanced figure of merit of a porous thin film of bismuth antimony telluride
Makoto Kashiwagi; Shuzo Hirata; Kentaro Harada; Yanqiong Zheng; Koji Miyazaki; Masayuki Yahiro; Chihaya Adachi
APPLIED PHYSICS LETTERS, AMER INST PHYSICS, 98, 2, 14706-14709, Jan. 2011, Peer-reviwed, A porous thin film of Bi0.4Te3Sb1.6 with an enhanced figure of merit of 1.8 at room temperature was fabricated by flash evaporation on an alumina substrate containing hexagonally arranged nanopores with an average diameter of 20 nm, separated by an average distance of 50 nm. The thermal conductivity was significantly reduced compared with standard Bi0.4Te3Sb1.6 films to 0.25 W/(m.K) with no major decrease in either the electrical conductivity (398 S/cm) or the Seebeck coefficient (198 mu V/K). The reduction in thermal conductivity was rationalized using a model for the full distribution of the phonon mean free path in the film. (c) 2011 American Institute of Physics. [doi:10.1063/1.3543852]
Scientific journal, English

Investigation of Quenching Mechanism in Thermoreversible Fluorescent Recording Materials of Fluorescence Using Thermochromic Fluorescence Resonance Energy Transfer
Shuzo Hirata; Martin Vacha; Toshiyuki Watanabe
Lead, JAPANESE JOURNAL OF APPLIED PHYSICS, JAPAN SOC APPLIED PHYSICS, 49, 5, 889-+, May 2010, Peer-reviwed, We demonstrated reversible thermosensitive recording of a fluorescent image (TRF) using a low-molecular-weight mixture consisting of a fluorescent dye, a fluoran dye, a developer, and a reversible matrix. In this material, reversible thermoresponsive disorder-crystal transition triggers a cyclical colorless-color change of a fluoran dye, which induces on-off switching of fluorescence resonance energy transfer (FRET) from a fluorescent dye to a fluoran dye. On-off switching of fluorescence is induced by heat-promoted off-on switching of FRET. Modulation of fluorescence is held at room temperature by utilizing thermal hysteresis, and nondestructive readout of the fluorescent image is accomplished in the presence of excitation light. Here, we investigate the on-off switching mechanism of fluorescence in this recording material. We analyzed the theoretical factor of emission quenching in the erasing state by comparing the theoretical overlap integral Omega between fluorescent dyes and fluoran dyes on the basis of the FRET theory with experimental emission contrast for various combinations of fluorescent dyes and fluoran dyes. It was proved that fluorescence on-off switching occurs mainly by concentration quenching due to the aggregation of fluorescent dyes and FRET from isolated fluorescent dyes to colored fluoran dyes. The key issue to obtain both high-contrast fluorescence and high fluorescence quantum yield is to control these two factors. (C) 2010 The Japan Society of Applied Physics
Scientific journal, English

高輝度有機蓄光材料と感熱型蓄光記録素子の開発
渡辺敏行; 平田修造
WEBジャーナル, 99, 29-33, Apr. 2009, Peer-reviwed
Scientific journal, Japanese

Reversible Fluorescent On-Off Recording in a Highly Transparent Polymeric Material Utilizing Fluorescent Resonance Energy Transfer (FRET) Induced by Heat Treatment
Shuzo Hirata; Kwang-Sup Lee; Toshiyuki Watanabe
Lead, ADVANCED FUNCTIONAL MATERIALS, WILEY-V C H VERLAG GMBH, 18, 19, 2869-2879, Oct. 2008, Peer-reviwed, One productive technique for ultrahigh resolution readout of tiny regions is the measurement of the fluorescence signal of materials. A transparent polymeric materials whose fluorescence quantum yield is changed and recorded by thermally controlling the aggregation of fluoran dyes and developers with long alkyl chains has been developed. The recording medium can be fabricated easily by casting or coating recording materials. Fluorescence is observed after annealing at 363 K for about twelve seconds and then cooling to room temperature (RT), and quenched by annealing at 423 K for a few seconds and then quenching to RT. Nondestructive readout by excitation light with a fluorescent contrast of above 10 is achieved using red, green, and blue fluorescent dyes. Fluorescence on-off switching is induced by fluorescent resonance energy transfer (FRET) from a fluorescent dye to a colored fluoran dye in the recording material. Fluorescence was uniformly quenched in the visible region after erasing. Since the recording materials allow the penetration of laser light due to the presence of crystals smaller than the wavelength range of visible light in both the emission and quenching states, nondestructive readout of the fluorescent signal by two-photon absorption is accomplished. This work provides an important stepping-stone for achieving rewritable-type near-field optical storage or multilayer recording.
Scientific journal, English

Reversible thermoresponsive on-off recording of fluorescence and long lived room temperature phosphorescence in organic materials /Next-generation advanced materials for security technology
S. Hirata; T. Watanabe
Lead, Proceeding of Pan-Pacific Imaging Conference, 1069-1072, Jun. 2008
International conference proceedings, English

Reversible thermoresponsive recording of fluorescent images (TRF)
Shuzo Hirata; Toshiyuki Watanabe
Lead, ADVANCED MATERIALS, WILEY-V C H VERLAG GMBH, 18, 20, 2725-+, Oct. 2006, Peer-reviwed, Nondestructive readout by an excitation light with high fluorescence contrast has been achieved using red, green, and blue fluorescent dyes (see figure). Reversible thermoresponsive recording of fluorescent images (TRF) using a molecularly doped matrix made up of a fluorescent dye, a leuco dye, and a developer is reported.
Scientific journal, English

ホストゲスト有機分子結晶からの 高輝度室温りん光と高解像アフターグロー
平田修造
Lead, Mar. 2024, 超分子アニュアルレビュー (公益社団法人 高分子学会 超分子研究会), 44, Japanese, Invited, Introduction other

明るい環境下でも視認可能な高輝度蓄光分子
平田修造
株式会社加工技術研究会, Dec. 2020, コンバーテック, 573, 48, 91-94, Japanese, Introduction commerce magazine

高解像蓄光イメージングを可能にする高輝度長寿命室温りん光分子
平田修造
株式会社オプトロニクス社, Nov. 2020, OPTRONICS, 467, 11, 200-204, Japanese, Introduction commerce magazine

Role of Suppressed Triplet Exciton Diffusion of pi-Aggregated Molecular Materials for Ultralong-Lived Room Temperature Phosphorescence
Shuzo Hirata
SOC FIBER SCIENCE TECHNOLOGY, May 2019, SEN-I GAKKAISHI, 75, 5, P253-P257, Japanese, 0037-9875, WOS:000474324000005

超剛直有機媒体による芳香族分子の励起子蓄積機能を利用した光機能性材料
平田修造
繊維学会, Oct. 2017, 繊維学会紙, 79, 3, 336-341, Japanese, Invited, Introduction commerce magazine

High-throughput virtual screening
Shuzo Hirata; Katsuyuki Shizu
NATURE PUBLISHING GROUP, Oct. 2016, NATURE MATERIALS, 15, 10, 1056-1057, English, Peer-reviwed, Invited, Introduction commerce magazine, 1476-1122, 1476-4660, WOS:000384677100005

Large nonlinear absorption under weak continuous incoherent light
平田 修造
コスメトロジー研究振興財団, 2016, コスメトロジー研究報告, 24, 43-52, Japanese, 2188-563X, 40020954778, AA11571370

室温長寿命励起子を利用した光機能材料の創製
平田修造
日本化学会, Nov. 2015, 化学と工業11月号, 575-577, Japanese, Invited, Introduction commerce magazine

非点収差を用いた高分子の三次元ダイナミックス評価
平田修造; 伊都庄司; バッハマーティン; 宮坂博
高分子学会, Sep. 2015, 高分子, 575-577, Japanese, Invited, Introduction commerce magazine

長い励起状態を利用した光機能性材料
平田修造
シーエムシー出版, Apr. 2015, 月刊機能材料, 35, 4, 41-48, Japanese, Invited, Introduction commerce magazine, 0286-4835, 40021171742, AN00360069

Degradation of liquid organic semiconductors analyzed by nuclear magnetic resonance
Junichi Yamamoto; Masashi Fukuchi; ○Tatsuya Fukushima; Shuzo Hirata; Heo Hyo Jung; Osamu Hirata; Yuki Shibano; Chihaya Adachi; Hironori Kaji
Sep. 2012, International Conference on Electroluminescence & Organic Optoelectronics, Fukuoka, Japan, English, Peer-reviwed

背面貯蔵型液体ELデバイス
SHIM Chang-Hoon; SHIM Chang-Hoon; 平田修造; 大島寿郎; 大島寿郎; 江面知彦; 服部励治; 服部励治; 安達千波矢
2012, 応用物理学関係連合講演会講演予稿集(CD-ROM), 59th, 201202293383784454

液体有機半導体における材料劣化のNMR解析
山本順一; 福地将志; 福島達也; 平田修造; ホ ヒョジョン; 平田修; 柴野佑紀; 安達千波矢; 梶弘典
Nov. 2011, 有機EL討論会 第13回例会，大阪, Japanese, Peer-reviwed

Material degradations in liquid organic semiconductors analyzed by solution NMR
Junichi Yamamoto; Masashi Fukuchi; Tatsuya Fukushima; Shuzo Hirata; Heo Hyo Jung; Osamu Hirata; Yuki Shibano; Chihaya Adachi; Hironori Kaji
Nov. 2011, Asian Conference on Organic Electronics, Taipei, Taiwan, English, Peer-reviwed

Long-lived Phosphorescent Color Change with Temperature Increase : Inter-molecular thermally activated triplet-triplet energy transfer
TOTANI Kenro; OKADA Yuya; HIRATA Shuzo; WATANABE Toshiyuki
A significant long-lived phosphorescent color change with temperature increase using efficient inter-molecular thermally activated energy transfer was observed. The materials are a host-guest compound composed of secondary amino substituted aromatic carbons as a guest, phosphorescent iridium complex as a guest, and amorphous steroid compound as a host matrix. The phosphorescent color was gradually changed with increasing temperature from red in low temperature region at 77 K to green in room temperature region at 300 K. The red color was originated from aromatic carbons and the green color was originated from iridium complex, resulting from thermally activated energy transfer with temperature increase., The Institute of Electronics, Information and Communication Engineers, 11 Oct. 2011, Technical report of IEICE. OME, 111, 236, 7-8, Japanese, 110008900295, AN10013334

NMRによる有機EL分子の配向および劣化解析
梶弘典; 福島達也; 福地将志; 山本順一; 藤村昴; 八尋正幸; 平田修造; HEO Hyo Jung; 平田修; 柴野佑紀; 安達千波矢
11 Mar. 2011, 日本化学会講演予稿集, 91st, 1, 5, Japanese, 0285-7626, 201102221984915760

NMRによる液体有機半導体の劣化解析
山本順一; 福島達也; 福地将志; 平田修造; HEO Hyo Jung; 平田修; 柴野佑紀; 安達千波矢; 梶弘典
09 Mar. 2011, 応用物理学関係連合講演会講演予稿集(CD-ROM), 58th, ROMBUNNO.26P-BD-2, Japanese, 201102273763414651

MNM-4A-5 Thermoelectric thin film deposition on a porous alumina
KASHIWAGI Makoto; Zheng Yanqiong; HIRATA Shuzo; HARADA Kentaro; MIYAZAKI Koji; YAHIRO Masayuki; ADACHI Chihaya
A nano-porous thin film of p-type Bismuth-Telluride with an enhanced figure of merit of 1.8 at room temperature was fabricated by flash evaporation on an alumina substrate containing hexagonally arranged nano-pores with an average diameter of 20 nm, separated by an average of 50 nm. The thermal conductivity was significantly reduced compared with standard Bismuth-Telluride films to 0.25 [W/(m・k)] with no major decrease in either the electrical conductivity (398 [S/cm]) or the Seebeck coefficient (198 [μV/K]). The reduction in thermal conductivity was roughly explained using a full distribution model of the phonon mean free path, The Japan Society of Mechanical Engineers, 12 Oct. 2010, マイクロ・ナノ工学シンポジウム, 2010, 2, 179-180, Japanese, 110008743277, AA12456946

Material's design concept for organic highly efficient long lived room temperature phosphorescence by decreasing nonradiative process at excited triplet state
TOTANI Kenro; HIRATA Shuzo; WATANABE Toshiyuki; ADACHI Chihaya
Long lived room temperature phosphorescence (LL-RTP) is not observed under the atmosphere in organic materials since active thermal motion of dye and matrix quenches a long exited triplet state of dyes at RT and oxygen accelerates electron quenching in an excited triplet state of dyes due to triplet-triplet energy transfer from a dye to oxygen. Therefore, it has been reported that long excited lifetime more than second order and efficient long lived phosphorescence are usually observed when some organic dyes dispersed into matrix is frozen to 77 K. Here we report that aromatic carbons substituted with strong electron donors dispersed homogeneously into amorphous steroid compounds show highly efficient LL-RTP under the atmosphere., The Institute of Electronics, Information and Communication Engineers, 20 May 2010, IEICE technical report, 110, 59, 51-53, Japanese, 0913-5685, 110008001569, AN10013334

【96】常温有機蓄光体の開発とデバイスへの応用展開
平田 修造; 戸谷 健朗; Junzhang Zhang; 山下 俊; 渡辺 敏行; Seth Richard Marder; 梶 弘典; 安達 千波矢
12 Nov. 2009, 有機EL討論会 第9回例会 ,京都大学 宇治キャンパス おうばくプラザ, Japanese, Peer-reviwed

【67】熱による有機化合物の凝集変化を利用した蛍光や蓄光情報の可逆的なOn-Off 記録特性
平田修造; 渡辺敏行; 梶弘典
20 Jun. 2008, 繊維学会 平成20年度年次大会 ,東京, Japanese, Peer-reviwed

Reversible thermoresponsive on-off recording of strong long lived room temperature phosphorescence in organic materials under atmosphere
Hirata S; Sesei T; Kaji H; Yamashita T; Watanabe T
18 May 2008, International Conference on Organic Photonics and Electronics 2008 (ICOPE2008) ,Santa Fe, New Mexico, USA, English, Peer-reviwed

【59】感熱記録による有機材料の常温蓄光機能および蛍光機能のOn-Off制御
平田修造; 瀬々井巌士; 梶弘典; 山下隆志; 渡辺敏行
27 Mar. 2008, 日本化学会第88回春季年会 アドバンスト・テクノロジー・プログラム(ATP) シンポジウム ,東京, Japanese, Peer-reviwed

感熱型蛍光記録材料
渡辺敏行; 平田修造
2008, 工業材料, 56, 1, 82-83

感熱型蛍光記録材料
渡辺敏行; 平田修造
日刊工業新聞, Jan. 2008, 工業材料, 1, 83-84, Japanese, Invited, Introduction commerce magazine

Migration-proof membrane circuits for fine-pitch connector
S. Hirata; A. Ono; Y. Kurosawa; Y. Oyama; M. Chiba
Oct. 2006, Fujukura Technical Review, 36, 25-29, English, Technical report

Single-Molecule Level Study and Control of Collective Photosynergetic Responses in Molecules and Molecular Aggregates; Photoresponse in Molecular Complexes and Related Systems
Martin Vacha; Shuzo Hirata
Scholarly book, English, Joint work, Springer, Singapore, Sep. 2020

環状高分子の合成と機能発現
平田修造; バッハマーティン
Scholarly book, Japanese, Joint work, 第5章 単一分子分光法による環状共役高分子の コンフォメーションおよび励起状態の解析, シーエムシー出版, Nov. 2018

先端有機半導体デバイス―基礎からデバイス物性まで
平田修造
Dictionary or encycropedia, Japanese, Joint work, 常温りん光, オーム社, Jan. 2015

光化学の事典
平田修造
Dictionary or encycropedia, Japanese, Joint work, 第2章, 2項, 長寿命発光-遅延発光の原理, 朝倉書店, 2014

導電性ポリマー材の高機能化と用途開発最前線
平田修造; 羽渕聡志; バッハマーティン
General book, Japanese, Joint work, 第2章, 第2節, 共役系高分子のコンフォメーションと光物性, シーエムシー出版, 2014

有機光半導体デバイスの物性
平田修造
General book, Japanese, Joint work, 電荷再結合領域(pp.107-109), 励起子相互作用(pp.109-117), 金属非含有型常温りん光材料(pp.269-273), 講談社, 2012

CSJ Current Review 07, 高分子と光が織りなす新機能・新物性
渡辺敏行; 平田修造
General book, Japanese, Joint work, 感熱型蛍光記録材料, Part II、Chapter 10, 日本化学会, 2011

Microparticulation of molecular crystals to enhance oxygen sensing capability based on long-lived phosphorescence lifetime
Riku Shimura; Kikuya Hayashi; Shuzo Hirata
Japanese, The 105th CSJ Annual Meeting
29 Mar. 2025
26 Mar. 2025- 29 Mar. 2025

Role of through-space interaction for enhancing long-wavelength organic phosphorescence
Ryo Miyashita; Rajashekhar Kashipati Mulimani; Shuzo Hirata
Oral presentation, Japanese, The 105th CSJ Annual Meeting
29 Mar. 2025
26 Mar. 2025- 29 Mar. 2025

Host-induced site-selective vibrational suppression of a π-molecule revealed by extensive phosphorescence analysis
Rana Tsuru; Sakuya Ueda; Shuzo Hirata
Oral presentation, Japanese, The 105th CSJ Annual Meeting
29 Mar. 2025
26 Mar. 2025- 29 Mar. 2025

Enhanced red persistent room-temperature phosphorescence using a phenylthio substituent
Sakuya Ueda; Kazuki Fujita; Bahadur Sk; Shuzo Hirata
Oral presentation, Japanese, The 105th CSJ Annual Meeting
26 Mar. 2025
26 Mar. 2025- 29 Mar. 2025

Predicted Organic Phosphorescence Performance Considering Molecular Vibrations
Shuzo Hirata
Invited oral presentation, English, 12th Singapore International Chemical Conference (SICC-12), Invited
11 Dec. 2024
09 Dec. 2024- 13 Dec. 2024

Enhanced red persistent room-temperature phosphorescence using a phenylthio substituent
Sakuya UEDA; Bahadur SK; Shuzo HIRATA
Poster presentation, English, Annual Meeting on Photochemistry 2024
05 Sep. 2024
03 Sep. 2024- 05 Sep. 2024

Efficient red persistent room temperature phosphorescence from a selenium substituted aromatic carbon
Kikuya HAYASHI; Rajashekhar; MULIMANI KASHIPATI; Rana TSURU; Sakuya UEDA; Shuzo HIRATA
Oral presentation, English, Annual Meeting on Photochemistry 2024
05 Sep. 2024
03 Sep. 2024- 05 Sep. 2024

Synchronized Twosome in Benzoyl Linked N-Fused Ring for Highly Efficient Yellow Afterglow
Bahadur Sk; Shuzo Hirata
Oral presentation, English, Annual Meeting on Photochemistry 2024
05 Sep. 2024
03 Sep. 2024- 05 Sep. 2024

Role of multiple sulfur bridged substitutions for facilitating red persistent room-temperature phosphorescence
Rajashekhar Kashipati MULIMANI; Shuzo HIRATA
Poster presentation, English, Annual Meeting on Photochemistry 2024
03 Sep. 2024
03 Sep. 2024- 05 Sep. 2024

High-resolution oxygen sensing using persistent room-temperature phosphorescence from individual nanoparticles
Riku SHIMURA; Kikuya HAYASHI; Shuzo HIRATA
English, Annual Meeting on Photochemistry 2024
03 Sep. 2024
03 Sep. 2024- 05 Sep. 2024

Molecular Vibrations and Distortions Facilitating Persistent Room-Temperature Phosphorescence
Shuzo Hirata
Oral presentation, English, 29th PhotoIUPAC, Peer-reviewed
16 Jul. 2024
14 Jul. 2024- 19 Jul. 2024

High-Resolution Afterglow Modulation Using Efficient Persistent Room-Temperature Phosphorescence Materials
Shuzo Hirata
Invited oral presentation, English, OPTICS & PHOTONICS International Congress 2024, Invited
26 Apr. 2024
22 Apr. 2024- 26 Apr. 2024

Photoinduced Triplet Depletion Allowing Higher-Resolution Afterglow
Kikuya Hayashi; Shuzo Hirata
Oral presentation, English, SPIE Photonics Europe 2024, Peer-reviewed
09 Apr. 2024
07 Apr. 2024- 11 Apr. 2024

Challenge to improve the brightness of persistent room temperature phosphorescence for high-resolution autofluorescence-free imaging
Shuzo Hirata
Invited oral presentation, English, SPIE Photonics Europe 2024, Invited
09 Apr. 2024
07 Apr. 2024- 11 Apr. 2024

Photoinduced Triplet Depletion Allowing Higher-Resolution Afterglow
Kikuya Hayashi; Shuzo Hirata
Oral presentation, English, SPIE Photonics West 2024, Peer-reviewed
30 Jan. 2024

High-resolution afterglow imaging using efficient long-lived room-temperature phosphorescence
Shuzo Hirata
Invited oral presentation, English, SPIE Photonics West 2024, Invited, Peer-reviewed
30 Jan. 2024

協働刺激による高スピードアフターグロー光パターニングと 高解像アフターグロー読み出し
平田 修造; 林 希久也
Invited oral presentation, Japanese, 第72回高分子討論会, Invited
26 Sep. 2023

High-resolution afterglow patterning using cooperative vapo- and photo-chemical reactions
Kikuya Hayashi; Shuzo Hirata
Oral presentation, English, 2023年光化学討論会, Peer-reviewed
06 Sep. 2023

高輝度アフターグロー発光に向けた高濃度三重項蓄積挙動
平田 修造; Badriyah Ende Hopsah; 林 希久也; Sk Bahadur
Oral presentation, Japanese, 2023年光化学討論会, Peer-reviewed
05 Sep. 2023

Role of molecular vibrations and distortions facilitating persistent room-temperature phosphorescence
Shuzo Hirata
Invited oral presentation, English, CEMS Topical Meeting on Chemistry of pi-Conjugated Materials, Invited
31 Jul. 2023

Symmetry-breaking triplet excited state allowing enhanced red afterglow room-temperature phosphorescence
Bahadur Sk; Shuzo Hirata
Oral presentation, English, The 31st International Conference on Photochemistry (ICP2023), Peer-reviewed
25 Jul. 2023

Triplet Quenching Mechanism of Chromophores in Insulating Polymers
Takuya Kamatsuki; Shuzo Hirata
Oral presentation, Japanese, The 103rd CSJ Annual Meeting
22 Mar. 2023
22 Mar. 2023- 25 Mar. 2023

Photo-Induced Triplet Depletion Allowing Higher-Resolution Afterglow
Kikuya Hiyashi; Keiki Fukumoto; Shuzo Hirata
Oral presentation, English, 日本化学会第103回春季年会
22 Mar. 2023
22 Mar. 2023- 25 Mar. 2023

Excited state science of N-fused ring allowing selective and efficient triplet-singlet resonance energy transfer for bright red afterglow emission
Bahadur Sk; Shuzo Hirata
Oral presentation, English, Annual Meeting on Photochemistry 2022
13 Sep. 2022

計算科学を活用した戦略的長波長長寿命室温りん光材料の開発
平田修造
Invited oral presentation, Japanese, 第71回高分子討論会, Invited, Domestic conference
05 Sep. 2022

分子固体ホストの相状態の違いを利用した分子間熱活性三重項消光因子の考察
草間 智也; 平田 修造
Oral presentation, Japanese, 日本化学会 第102春季年会, Domestic conference
25 Mar. 2022

Key factor facilitating triplet-singlet resonance energy transfer for efficient red afterglow emission
Kikuya Hayashi; Kei Fukasawa; Takashi Yamashita; Shuzo Hirata
Oral presentation, English, Web Annual Meeting on Photochemistry 2021, Domestic conference
14 Sep. 2021

蓄光ナノイメージングを可能にする高輝度残光型室温りん光分子の開発
平田修造
Invited oral presentation, Japanese, 第69回高分子討論会, Domestic conference
16 Sep. 2020

実験と理論の協働によるπ共役系凝集体における三重項失活メカニズムの考察
平田修造
Invited oral presentation, Japanese, 第69回高分子討論会, Invited, Domestic conference
16 Sep. 2020

ドナーアクセプター直交型キラル分子を利用した高効率熱活性化遅延蛍光発生要因の考察
林希久也; 松本有正; 平田修造
Oral presentation, Japanese, 2020年web光化学討論会, Domestic conference
11 Sep. 2020

Highly Efficient Persistent Room Temperature Phosphorescence From Heavy Atom Free Molecules Triggered By Hidden Long Phosphorescent Antenna
Indranil Bhattacharjee; Shuzo Hirata
Oral presentation, English, Web Annual Meeting on Photochemistry 2020, Domestic conference
11 Sep. 2020

The effect of the lowest singlet excited state lifetime on up-conversion emission via stepwise two-photon absorption
Kentaro Yomogita; Shuzo Hirata
Poster presentation, English, Web Annual Meeting on Photochemistry 2020, Domestic conference
09 Sep. 2020

高次励起状態の電子構造制御による高輝度且つ高効率な長寿命室温りん光の抽出
平田修造
Invited oral presentation, Japanese, 第三回“光”機到来！Qコロキウム
06 Jul. 2020

Intrinsic analysis of transition processes from the lowest excited triplet state of heavy atom-free molecules with persistent room-temperature phosphorescence
Shuzo Hirata
Invited oral presentation, English, SPIE Photonics Europe, Digital Forum, Invited, International conference
29 Mar. 2020

置換基誘起の対称禁制遷移分子を用いた弱連続青色光下での大きな光制限効果
釜付卓弥; Bhattacharjee Indranil; 平田修造
Oral presentation, Japanese, Domestic conference
19 Mar. 2020

Intrinsic analysis of transition processes from the lowest excited triplet state of heavy atom-free conjugated molecular crystals with persistent room temperature phosphorescence
Shuzo Hirata
Invited oral presentation, English, 2019 MRS Fall Meeting, Boston, USA, Invited, Boston, USA, International conference
03 Dec. 2019

Donor-acceptor molecules showing photon upconversion emission by stepwise two photon absorption
YOMOGITA Kentaro; ZHANG Junxiang; MIZUTANI Ryota; VAHCA Martin; KAMADA Kenji; MARDER Seth; HIRATA Shuzo
Oral presentation, English, Annual Meeting on Photochemistry 2019, Domestic conference
04 Sep. 2019

分散系および凝集系における重原子フリー分子の三重項励起状態
平田修造
Invited oral presentation, Japanese, 141 M&BE 新分野開拓研究会「有機半導体制御技術の最新動向～分子配向・電荷・励起子～」, Domestic conference
28 Aug. 2019

Analysis of Triplet State in Conjugated Molecular Crystals toward Persistent Room Temperature Phosphorescence from Soft Crystals
Shuzo Hirata
Invited oral presentation, English, The 2nd International Symposium of Soft Crystals, Chiba, Japan, Invited, International conference
13 Jul. 2019

Exciton management for unique molecular emission characteristics
Shuzo Hirata
Invited oral presentation, English, The 36th International Conference of Photopolymer Science and Technology (ICPST-36), Chiba, Japan, Invited, International conference
25 Jun. 2019

Molecular Materials with Ultralong-Lived Room Temperature Triplet Excitons
Shuzo Hirata
Invited oral presentation, English, 2019 International Seminar on Polymer Photochemistry (2019 ISPP), Guangzhou, China, Invited, International conference
09 May 2019

高効率分子蓄光に向けた三重項からの輻射と非輻射過程の解析
平田
Oral presentation, Japanese, 日本化学会第99回春季年会 特別企画 ルミネッセンス化学アンサンブル：発光の未来を探る, Domestic conference
Mar. 2019

遷移双極子が小さい光学活性分子材料：円偏光遅延蛍光と円偏光室温蓄光
平田修造
Invited oral presentation, Japanese, 千葉大学分子キラリティーセンター定例研究会, Invited, Domestic conference
Jan. 2019

分散系共役分子および凝集系共役分子結晶の室温長寿命三重項励起子のサイエンスと機能
平田修造
Invited oral presentation, Japanese, PHyM若手フォーラム, Invited, Domestic conference
Nov. 2018

Intrinsic analysis of radiative process, intramolecular vibrational room-temperature nonradiative process, and quenching process from triplet state for heavy atom-free conjugated structures
Shuzo Hirata
Invited oral presentation, English, Annual Meeting on Photochemistry on 2018, Invited, Domestic conference
07 Sep. 2018

Intrinsic Analysis between Radiative Process and Room-Temperature Nonradiative Process based on Intramolecular Vibrations from Triplet State of Heavy Atom-free Aromatics toward Efficient Persistent Room-temperature Phosphorescence
Shuzo Hirata
Invited oral presentation, English, 2018 International Seminar on Advanced Materials Research 2018 ISAMR, Shanghai, China, Invited, International conference
Aug. 2018

Molecular Materials with Ultralong-lived Room-temperature Triplet Excitons
Shuzo Hirata
Invited oral presentation, English, Seminor in Key Laboratory of Advanced Display and System Applications (Shanghai University)
Aug. 2018

振動状態を考慮に入れたスピン禁制から見えてくる共役分子の三重項からの輻射・非輻射過程の本質
平田修造
Invited oral presentation, Japanese, 学振142委員会ABC合同部会, Invited, Domestic conference
Jul. 2018

分子発光材料の設計指針と現状
平田修造
Public discourse, Japanese, 新学術領域高次複合光応答分子システムの開拓と学理の構築, Domestic conference
Jan. 2018

Photofunctional materials using long-lived room-temperature triplet excitons
Shuzo Hirata
Invited oral presentation, English, Royal Society of Chemistry Symposia on Electronic and Photonic Materials, Tsukuba, Japan, Invited, International conference
Nov. 2017

Extraction of Unique Emission and Absorption Characteristics by Stabilization of Triplet Excitons
Shuzo Hirata
Invited oral presentation, English, The 97th CSJ Annual Meeting, Asian International Symposium- Photochemistry, Invited, Domestic conference
Mar. 2017

励起三重項を経由したルミネッセンスの科学と応用
平田修造
Invited oral presentation, Japanese, シンポジウム超短パルスレーザーと機能性材料, Invited, Domestic conference
Oct. 2016

White afterglow room temperature emission from isolated aromatic unit in air
Shuzo Hirata
Invited oral presentation, English, 2016 International Symposium on Integrated Molecular / Materials Science & Engineering (IMSE 2016), Qingdao, China, International conference
Oct. 2016

非共役系有機媒体の超剛直性を利用した芳香族分子の新規光機能
平田修造
Invited oral presentation, Japanese, 平成28年度繊維学会秋季研究発表会, Domestic conference
Sep. 2016

Large reverse saturable absorption under weak continuous incoherent light
Shuzo Hirata
Oral presentation, English, MRS Spring Meeting, Arizona, USA, International conference
Mar. 2016

スーパーハードな環境下での芳香族化合物からの新規光機能の開拓
平田修造
Invited oral presentation, Japanese, 第96回日本化学会春季年会, Invited, Domestic conference
Mar. 2016

Large reverse saturable absorption under weak continuous incoherent light
Shuzo Hirata
Invited oral presentation, English, The 32nd International Conference of Photopolymer Science and Technology, Chiba, Japan, Invited, International conference
Jun. 2015

室温長寿命励起子を用いた光機能性材料の開発
平田修造
Invited oral presentation, Japanese, 第95回日本化学会春季年会, Invited, Domestic conference
Mar. 2015

室温長寿命励起子を利用した非コヒーレント光に応答する非線形吸収材料の開発
平田修造
Invited oral presentation, Japanese, 高分子同友会, Invited, Domestic conference
Feb. 2015

Novel organic emitting materials for electronics and optics applications
Shuzo Hirata
Invited oral presentation, English, PITTCON CONFERENCE & EXPO 2012, JAPAN SYMPOSIUM, The State-of-the-Art Technologies, Florida, USA, Invited, International conference
Mar. 2012

Improvement of electroluminescence performance of organic light emitting diodes with a liquid emitting layer
Shuzo Hirata; Chihaya Adachi
Invited oral presentation, English, 2nd Asian Conference on Organic Electronics (A-COE 2010), Seoul, Korea, Invited, International conference
Dec. 2010

物理化学II
The University of Electro-Communications

物理化学II
電気通信大学

基礎物理化学
The University of Electro-Communications

基礎物理化学
電気通信大学

現代有機化学論
京都大学大学院

現代有機化学論
京都大学大学院

サステーナビリティー化学
東京工科大学

サステーナビリティー化学
東京工科大学

現代化学
The University of Electro-Communications

化学生命工学実験第一
The University of Electro-Communications

化学生命工学実験第一
The University of Electro-Communications

化学生命工学実験第一
電気通信大学

固体物性化学特論
The University of Electro-Communications

固体物性化学特論
電気通信大学

現代化学
The University of Electro-Communications

現代化学
電気通信大学

日本化学会

応用物理学会

光化学協会

高分子学会

アメリカ化学会

高度π分子体の３重項エンジニアリング
平田修造、福本恵紀
学術変革領域研究(A)計画班, Principal investigator, 25H01253
Apr. 2025 - Mar. 2030

生体内の高解像蓄光イメージング技術の創生(フェーズ2)
平田修造
JST, 創発的研究支援事業, 電気通信大学, Principal investigator
Apr. 2024 - Mar. 2028

りん光増強分子フレキシブル要素の抽出と赤色長寿命室温りん光への応用
Shuzo Hirata
日本学術振興会, 科学研究費助成事業, 電気通信大学, 基盤研究(B), Principal investigator, 24K01567
Apr. 2024 - Mar. 2027

分子固体の室温での三重項失活速度の推定法の確立
平田 修造
日本学術振興会, 科学研究費助成事業, 電気通信大学, 基盤研究(B), 本研究では、分子固体の室温での三重項失活速度の推定法の確立を目的としている。三重項失活速度の推定法を正しく推定するためには、材料の三重項からの輻射速度(kp)、三重項からの非放射遷移速度（knr）、および三重項からの分子間電子移動を経由した失活速度（kq）の3つを少なくとも定量的に議論し、推定可能な計算法を見出すことが必要となる。 本年度までに、knrに関しては20のさまざまな種類の有機分子や錯体に関して、室温エネルギーでの全振動による分子配座変化を考慮したスピン軌道相互作用を計算することで、実験値との良好な相関が取れることを確認している。この手法を用いると、さまざまな分子のknrが推定可能となることを学術論文で報告した。 kpの推定に関しては、これまで計算量コストの問題から、室温の熱による振動や室温の熱によって統計的に生まれる配座変化が考慮された計算は行われてこなかった。本年度は、その計算法に切り込み、室温の熱による振動や室温の熱によって統計的に生まれる配座変化によりknrが増強されずにkpのみが増強される分子群が存在することを明らかにした。knrが増強されずにkpのみが増強される分子群のサイエンスとして、ヘテロアトムの共役系の面外振動が誘起する系を学術論文で報告し、分子の対象性が崩れる系は学術論文の投稿準備中である。これら論文の中で、全振動考慮型のkp計算法とキーとなる振動のみを変動させるkp計算法を提案した。 またkq に関しては、さまざまなゲスト分子を絶縁ホスト分子に分散した材料を評価する中で、ホスト分子の動きとゲスト分子のT1とS0間のスピン軌道相互作用の両者がかかわる失活モードが存在することを統計的に明らかにし、学会で発表している。, 21H02011
Apr. 2021 - Mar. 2024

生体内の高解像蓄光イメージング技術の創生(フェーズ1)
平田修造
JST, 創発的研究支援事業
Apr. 2021 - Mar. 2024

Photoinduced Triplet Depletion for Super-Resolution Afterglow Imaging
Hirata Shuzo
Japan Society for the Promotion of Science, Grants-in-Aid for Scientific Research, The University of Electro-Communications, Grant-in-Aid for Challenging Research (Exploratory), Afterglow emission allows imaging independent of autofluorescence under ambient conditions. Although higher resolution afterglow is crucial for increasing quality of the autofluorescence-free emission imaging, increase of excitation intensity to allow brighter afterglow emission induces a decrease of the resolution of afterglow images. Therefore, procedure and mechanism of materials to allow afterglow imaging with more higher-resolution capability is neccesary. Here, we report photoinduced triplet depletion and improved resolution of bright afterglow emission using depletion. Triplet excitons accumulated in a solid material by excitation were depleted under irradiation with a depletion beam with a longer wavelength than the absorption wavelength of the material. A higher-resolution afterglow image was observed by simultaneously focusing a donut-shaped depletion beam and an excitation beam., 21K18928
Jul. 2021 - Mar. 2023

残光機能や散乱機能を可逆的に制御可能なソフトクリスタルの構築
平田修造
01 Apr. 2020 - 31 Mar. 2022

先進的な発光特性を示す材料に関する研究
01 Apr. 2018 - 31 Mar. 2021

高次励起状態から発光する分子設計と光エネルギー材料への応用
平田修造
Japan Society for the Promotion of Science, Grants-in-Aid for Scientific Research, The University of Electro-Communications, Grant-in-Aid for Scientific Research (B), Electronic structures relating to the high order singlet excited state (Sn) have not been considered to control excitons. Here we enhance photon up-conversion characteristics via two-photon absorption and persistent room-temperature phosphorescence (RTP) characteristics by controlling the electronic structures relating to Sn. The effective separation between electronic structures relating to Sn and that relating to the lowest singlet excited state led to more fluorescence from Sn to allow enhanced photon-up conversion intensity after stepwise two-photon absorption. The enhancement of the transition dipole moment between Sn and the ground state by controlling the Sn electronic structure increases the rate constant of phosphorescence without largely increasing the rate constant of nonradiative transition from the lowest triplet excited state, resulting in a large increase of RTP yield with keeping long RTP lifetime., 18H02046
Apr. 2018 - Mar. 2021

化合物半導体ナノ粒子の光物性評価
平田修造
01 Oct. 2018 - 30 Sep. 2020

ソフトキラル分子結晶による刺激応答性室温円偏光蓄光材料の創生
01 Apr. 2018 - 31 Mar. 2020

従来の分子光励起応答の制約を打破する革新的な分子励起サイエンスに関する研究
文部科学省卓越研究員事業
01 Jan. 2018 - 31 Mar. 2019

高発光量子収率と高2色性を示す円偏光発光型熱活性化遅延蛍光材料の開発と高性能表示素子への応用
平田修造
JST, 地域産学バリュープログラム
01 Sep. 2017 - 31 Mar. 2019

先進的有機機能性材料に関する研究
平田修造
文部科学省, 平成２９年度科学技術人材育成費補助事業「卓越研究員事業」助成金, Principal investigator
Jan. 2018 - Mar. 2019

Science of zero oscillator strength for circularly polarized luminescence and their application for light emitting diodes
Hirata Shuzo
Japan Society for the Promotion of Science, Grants-in-Aid for Scientific Research, The University of Electro-Communications, Grant-in-Aid for Challenging Research (Exploratory), Novel chiral conjugated molecules with significant small oscillator strength for fluorescence (F) were synthesized. The chiral molecules that a chiral carbon is located between the highest occupied molecular orbital and the lowest unoccupied molecular orbital showed circularly polarized luminescence with absolute value of dissymmetry factor (|g|) of 10-3 when they were doped in solutions or solid films. On the other hand, |g| of the molecules largely increased up to 5×10-2 in their crystalline thin films. Emission yield (ΦPL) of the molecules did not decrease between doped condition and aggregated crystalline state because of no large Davydov splitting due to the significant small F value. One of the chiral molecules showed large ΦPL as well as large |g| in crystalline state., 17K19152
Jun. 2017 - Mar. 2019

Molecular-level study and control of cooperative photoresponse of molecular complexes
VACHA Martin
Japan Society for the Promotion of Science, Grants-in-Aid for Scientific Research, Tokyo Institute of Technology, Grant-in-Aid for Scientific Research on Innovative Areas (Research in a proposed research area), Using single-molecule spectroscopy we studied and controlled the photoresponse of molecular complexes, such as aggregates, molecular crystals and conjugated polymers, as well as their semiconducting counterparts, such as quantum dots, and hybrid systems composed of noble metal nanoparticles and organic dyes. The results include conformational and spectroscopic characterization of poly(phenylene vinylene) and polyfluorene conjugated polymers, origin and suppression of defect emission and characterization of band-edge emission in I-III-IV semiconductor quantum dots, characterization of blinking, emission quantum efficiency and electroluminescence in halide perovskite nanocrystals, effect of enhancement of resonant energy transfer between organic dyes by localized plasmons and study of triplet exciton diffusion, phosphorescence and of triple-triplet annihilation and photon upconversion in molecular solids., 26107014
Jul. 2014 - Mar. 2019

先進的有機機能性材料に関する研究
平田修造
研究助成, Principal investigator
Jun. 2017 - Dec. 2017

非晶材料中における分子運動性と三重項励起子の寿命の関係に関する研究
平田修造
京都大学化学研究所, 共同設備利用費, Principal investigator
Apr. 2016 - Mar. 2017

Highly efficient circularly polarized organic luminogens with a large dissymmetry factor of circularly polarized luminescence characteristics
Hirata Shuzo
Japan Society for the Promotion of Science, Grants-in-Aid for Scientific Research, Tokyo Institute of Technology, Grant-in-Aid for Challenging Exploratory Research, Three kinds of metal-free aromatic compounds (CPDF1-3) with a chiral carbon sandwiched between a donor moiety and an acceptor moiety were designed. They showed thermally activated delayed fluorescence (TADF) as well as circularly polarized luminescence (CPL) characteristics. (R)-CPDF3 and (S)-CPDF3 showed CPL with a dissymmetry factor of 4×10-4 in toluene solution. CPDF3 doped into π-conjugated host with large energy of the lowest triplet excited state displayed a photoluminescence quantum yield of 99%. An electroluminescence (EL) device having a 30 wt% CPDF3 doped π-conjugated host as an emitting layer showed an external EL quantum yield of 9.5%. With increasing the concentration of (R)-CPDF3 and (S)-CPDF3 in the emitting layer, intermolecular charge transfer transition largely contributed to TADF, causing a disappearance of CPL characteristics from the devices., 26620165
Apr. 2014 - Mar. 2017

Large reverse saturable absorption at sunlight power level using ultralong lifetime of triplet excitons
Hirata Shuzo
Japan Society for the Promotion of Science, Grants-in-Aid for Scientific Research, Tokyo Institute of Technology, Grant-in-Aid for Young Scientists (A), Large reverse saturable absorption (RSA) at sunlight power level was observed from a host-guest amorphous material composed of d12-coronene as a guest and β-estradiol as a rigid amorphous host. Large highly symmetric two dimensional (2D) aromatic structure of d12-coronene doped into the rigid host causes ultralong triplet lifetime as well as high triplet yield, serving efficient accumulation of the triplet excitons of d12-coronene under weak excitation light. The high absorption coefficient of the triplet state (σ34) compared with that of the ground state (σ01) for d12-coronene is also caused by the highly symmetric 2D aromatic structure. The efficient accumulation of the triplet excitons and high σ34/σ01 led to an onset of the RSA characteristics under irradiance below 10-1 mW cm-2. An film of the amorphous material showed a large decrease of transmittance from 66% at 0.02 mW cm-2 to 24% at 50 mW cm-2 for continuous light at 405 nm., 26708010
Apr. 2014 - Mar. 2017

ナノ空間場を用いた10 mW/cm2で最大効率を示すフォトンアップコンバージョン材料への挑戦
平田修造
野口遵研究所, 研究助成, Principal investigator
Apr. 2015 - Mar. 2016

10 mW/cm2以下の非コヒーレント光照射で大きな非線形吸収を示す材料への挑戦
平田修造
住友財団, 研究助成, Principal investigator
Apr. 2014 - Sep. 2015

低パワーの非コヒーレント光による高効率エネルギーアップコンバージョン
平田修造
矢崎科学技術振興記念財団, 研究助成, Principal investigator
Apr. 2014 - Mar. 2015

明るい環境でより鮮やかに着色する有機材料の開発
平田修造
コスメトロジー研究振興財団, 研究助成, Principal investigator
Apr. 2014 - Mar. 2015

生体内の高コントラスト動的イメージングにむけた時間分解発光ラベルの開発
平田修造
一般財団法人バイオインダストリー協会, 研究助成, Principal investigator
Oct. 2013 - Sep. 2014

メタルフリーの低閾値非線形吸収材料の開発
平田修造
新化学技術推進協会, 研究助成, Principal investigator
May 2013 - Apr. 2014

低パワーの非コヒーレント光に応答する非線形吸収材料の開発
平田修造
東京工業大学, 新任助教助成, Principal investigator
Aug. 2013 - Mar. 2014

Stretching Organic Solar Cells using a Gel Composed of Conjugated Liquids and a Polymer Matrix
HIRATA shuzo
Japan Society for the Promotion of Science, Grants-in-Aid for Scientific Research, Tokyo Institute of Technology, Grant-in-Aid for Challenging Exploratory Research, We fabricated solar cells whose active layer is constructed from a gel material composed of conjugated liquid molecules and a polymer matrix. Elastic modulus and strain of the gel materials were 0.01 times less than and 100 times larger than those of conventional solid conjugated polymers, respectively. Power conversion efficiency of the solar cells containing the gel layer as an active layer was 0.01% when they were not stretched. The power conversion efficiency of a solar cell using conventional conjugated polymer as an active layer decreases when the device was stretched to 20%. On the other hand, the decrease of power efficiency was not observed in the devices using the gels as an active layer., 24655175
Apr. 2012 - Mar. 2014

低パワー非コヒーレント光による有機非線形吸収の実現と調光材料への応用
平田修造
Japan Society for the Promotion of Science, Grants-in-Aid for Scientific Research, Kyushu University, Grant-in-Aid for Young Scientists (B), Principal investigator, We developed an organic RSA material that displays a large decrease in transmittance upon exposure to weak incoherent light, such as that from light emitting diodes(LEDs), at room temperature(RT) in air. To minimize threshold of transmittance decrease(Fth) and obtain a large decrease in transmittance, two kinds of guest compounds dispersed in an amorphous steroidal host matrix were used. One guest compound is a metal complex used as a donor for photosensitization and the other is a deuterated aromatic deuterated carbon that behaves as an acceptor to allow efficient accumulation of the Ti state. The accumulation of long-lived RT triplet excitons of the acceptor with a large triplet-triplet absorption coefficient by photosensitization of the donor allowed a drastic decrease in the power threshold to be realized., 22750132
Apr. 2010 - Mar. 2012

2022年光化学討論会 男女共同参画・若手研究者交流ランチョンシンポジウム
Presenter