基本情報

所属

• 電子科学研究所　光科学研究部門

職名

• 准教授

学位

• 博士（工学）（2013年03月 京都大学）

ホームページURL

https://sites.google.com/view/kenjihirai/home

科研費研究者番号

• 10754400

J-Global ID

• 201501021836519844

研究キーワード

• 光科学   ナノマテリアル   自己集合   

研究分野

• ナノテク・材料 / 機能物性化学
• ナノテク・材料 / 光工学、光量子科学
• ナノテク・材料 / 無機・錯体化学

担当教育組織

•  学士課程　工学部
•  修士課程　情報科学院
•  博士課程　情報科学院

職歴

• 2022年08月 - 現在 National Yang Ming Chiao Tung University Department of Applied Chemistry Visiting Associate Professor
• 2019年04月 - 現在 北海道大学 大学院情報科学院 情報科学専攻 生体情報工学コース 准教授（兼担）
• 2017年12月 - 現在 北海道大学 電子科学研究所 准教授
• 2018年10月 - 2022年03月 国立研究開発法人科学技術振興機構 さきがけ研究者（兼任）
• 2018年04月 - 2019年03月 北海道大学 大学院情報科学研究科 生命人間情報科学専攻 准教授（兼担）
• 2014年11月 - 2017年11月 北海道大学 大学院理学研究院 特任助教
• 2013年04月 - 2014年10月 独立行政法人日本学術振興会 海外特別研究員
• 2010年04月 - 2013年03月 独立行政法人日本学術振興会 特別研究員（DC1）

学歴

• 2010年04月 - 2013年03月   京都大学   大学院工学研究科合成・生物化学専攻   博士後期課程
• 2008年04月 - 2010年03月   京都大学   大学院工学研究科合成・生物化学専攻   修士課程
• 2004年04月 - 2008年03月   京都大学   工学部   工業化学科

所属学協会

• 錯体化学会   分子科学会   日本化学会   応用物理学会   

研究活動情報

論文

• Mechanical properties of modulative undulating layers in two-dimensional metal–organic frameworks

  Iwai, Yuudai, Kusumoto, Sotaro, Suzuki, Ryo, Tachibana, Masaru, Komatsu, Kazuki, Kikuchi, Takashi, Kawaguchi, Saori, Kadobayashi, Hirokazu, Masubuchi, Yuji, Yamamoto, Yuzuki, Ozawa, Yoshiki, ABE, Masaaki, Hirai, Kenji, Le Ouay, Benjamin, Ohba, Masaaki, Ohtani, Ryo

  Chemistry of Materials 2024年05月 [査読有り][通常論文]
  
• Spatially Heterogeneous Dynamics of droplets formed by arginine-rich dipeptides and poly-A RNA during liquid-liquid phase separation

  Ya Tian, Qiang Zhang, Kenji Hirai, Han Wen, Guilin Feng, Jiangtao Li, Farsai Taemaitree, Tomoko Inose, Kohsuke Kanekura, Hiroshi, Uji-i

  Molecular Crystals and Liquid Crystals 2024年05月 [査読有り][通常論文]
  
• Optical Cavity Design and Functionality for Molecular Strong Coupling

  Kenji Hirai, James Andell Hutchison, Hiroshi Uji-i

  Chemistry – A European Journal 2023年11月08日 [査読有り][招待有り]
   

  Optical cavity/molecule strong coupling offers attractive opportunities to modulate photochemical or photophysical processes. When atoms or molecules are placed in an optical cavity, they can coherently exchange photonic energy with optical cavity vacuum fields, entering the strong coupling interaction regime. Recent work suggests that the thermodynamic and kinetic properties of molecules can be significantly changed by strong coupling, resulting in the emergence of intriguing photochemical and photophysical phenomena. As more and more physico‐chemical systems are studied under strong coupling conditions, optical cavities have also advanced in their sophistication, responsiveness, and (multi)functionality. In this review, we highlight some of these recent developments, particularly focusing on Fabry‐Perot microcavities.
• Visualizing Ribbon‐to‐Ribbon Heterogeneity of Chemically Unzipped Wide Graphene Nanoribbons by Silver Nanowire‐Based Tip‐Enhanced Raman Scattering Microscopy

  Tomoko Inose, Shuichi Toyouchi, Shinnosuke Hara, Shoji Sugioka, Peter Walke, Rikuto Oyabu, Beatrice Fortuni, Wannes Peeters, Yuki Usami, Kenji Hirai, Steven De Feyter, Hiroshi Uji‐i, Yasuhiko Fujita, Hirofumi Tanaka

  Small 2023年08月30日 [査読有り][通常論文]
   

  Abstract Graphene nanoribbons (GNRs), a quasi‐one‐dimensional form of graphene, have gained tremendous attention due to their potential for next‐generation nanoelectronic devices. The chemical unzipping of carbon nanotubes is one of the attractive fabrication methods to obtain single‐layered GNRs (sGNRs) with simple and large‐scale production.  The authors recently found that unzipping from double‐walled carbon nanotubes (DWNTs), rather than single‐ or multi‐walled, results in high‐yield production of crystalline sGNRs. However, details of the resultant GNR structure, as well as the reaction mechanism, are not fully understood due to the necessity of nanoscale spectroscopy. In this regard, silver nanowire‐based tip‐enhanced Raman spectroscopy (TERS) is applied for single GNR analysis and investigated ribbon‐to‐ribbon heterogeneity in terms of defect density and edge structure generated through the unzipping process.  The authors found that sGNRs originated from the inner walls of DWNTs showed lower defect densities than those from the outer walls. Furthermore, TERS spectra of sGNRs exhibit a large variety in graphitic Raman parameters, indicating a large variation in edge structures. This work at the single GNR level reveals, for the first time, ribbon‐to‐ribbon heterogeneity that can never be observed by diffraction‐limited techniques and provides deeper insights into unzipped GNR structure as well as the DWNT unzipping reaction mechanism.
• Light-mediated Covalently Patterned Graphene Substrate for Graphene-Enhanced Raman Scattering (GERS)

  Guilin Feng, Nozomu Suzuki, Qiang Zhang, Jiangrao Li, Tomoko Inose, Farsai Taemaitree, Muhammed Shameem K M, Shuichi Toyouchi, Yasuhiko Fujita, Kenji Hirai, Hiroshi Uji-i

  Chemical Communications 2023年08月 [査読有り][通常論文]
   

  We report covalently patterned graphene with acetic acid as a new potential candidate for graphene-enhanced Raman scattering (GERS). Rhodamine 6G molecule in direct contact with the covalently modified region shows...
• Site-Specific Synthesis of Conductive Graphitic Nanomaterials on a NiFe Thin Film by Localized Laser Irradiation

  Hideki Fujiwara, Seigo Daikokuya, Tatsuki Mirokuin, Kyohei Hayashi, Mizuki Matsuzaka, Yuri Ohashi, Christophe Pin, Hideo Kaiju, Kenji Hirai, Hiroshi Uji-i

  ACS Applied Nano Materials 6 15 13885 - 13893 2023年07月22日 [査読有り][通常論文]
  
• Molecular Chemistry in Cavity Strong Coupling

  Kenji Hirai, James A. Hutchison, Hiroshi Uji-i

  Chemical Reviews 123 13 8099 - 8126 2023年06月30日 [査読有り][招待有り]
  
• SERS Endoscopy for Monitoring Intracellular Drug Dynamics

  Beatrice Fortuni, Monica Ricci, Raffaele Vitale, Tomoko Inose, Qiang Zhang, James Andell Hutchison, Kenji Hirai, Yasuhiko Fujita, Shuichi Toyouchi, Sandra Krzyzowska, Indra Van Zundert, Susana Rocha, Hiroshi Uji-i

  ACS Sensors 8 6 2340 - 2347 2023年05月23日 [査読有り][通常論文]
  
• Selective Detection of Intracellular Drug Metabolism by Metal‐Organic Framework‐Coated Plasmonic Nanowire

  Qiang Zhang, Taku Murasugi, Kotomi Watanabe, Han Wen, Ya Tian, Monica Ricci, Susana Rocha, Tomoko Inose, Hitoshi Kasai, Farsai Taemaitree, Hiroshi Uji‐i, Kenji Hirai, Beatrice Fortuni

  Advanced Optical Materials 2023年05月21日 [査読有り][通常論文]
  
• Liquid-Phase Photo-induced Covalent Modification (PICM) of Single-Layer Graphene by Short-Chain Fatty Acids

  Guilin Feng, Tomoko Inose, Nozomu Suzuki, Han Wen, Farsai Taemaitree, Mathias Wolf, Shuichi Toyouchi, Yasuhiko Fujita, Kenji Hirai, Hiroshi Uji-i

  Nanoscale 15 10 4932 - 4939 2023年 [査読有り][通常論文]
   

  We report an efficient photo-induced covalent modification (PICM) of graphene by short-chain fatty acids (SCFAs) with an alkyl chain at the liquid-solid interface for spatially resolved chemical functionalization of graphene....
• Length-Controllable Gold-Coated Silver Nanowire Probes for High AFM-TERS Scattering Activity

  Han Wen, Jiangtao Li, Qiang Zhang, Tomoko Inose, Wannes Peeters, Beatrice Fortuni, Hitoshi Asakawa, Akito Masuhara, Kenji Hirai, Shuichi Toyouchi, Yasuhiko Fujita, Hiroshi Uji-i

  Nano Letters 23 1615 - 1621 2022年12月09日 [査読有り][通常論文]
  
• Autotuning of Vibrational Strong Coupling for Site-Selective Reactions

  Kenji Hirai, Hiroto Ishikawa, Yasufumi Takahashi, James Andell Hutchison, Hiroshi Uji-i

  Chemistry - A European Journal 28 47 e202201260  2022年06月 [査読有り][通常論文]
   

  Site-selective chemistry opens new paths for the synthesis of technologically important molecules. When a reactant is placed inside a Fabry-Perot (FP) cavity, energy exchange between molecular vibrations and resonant cavity photons results in vibrational strong coupling (VSC). VSC has recently been implicated in modified chemical reactivity at specific reactive sites. However, as a reaction proceeds inside an FP cavity, the refractive index of the reaction solution changes, detuning the cavity mode away from the vibrational mode and weakening the VSC effect. Here we overcome this issue, developing actuatable FP cavities to allow automated tuning of cavity mode energy to maintain maximized VSC during a reaction. As an example, the site-selective reaction of the aldehyde over the ketone in 4-acetylbenzaldehyde is achieved by automated cavity tuning to maintain optimal VSC of the ketone carbonyl stretch during the reaction. A nearly 50% improvement in site-selective reactivity is observed compared to an FP cavity with static mirrors, demonstrating the utility of actuatable FP cavities as microreactors for organic chemistry.
• All-Optical and One-Color Rewritable Chemical Patterning on Pristine Graphene under Water

  Shuichi Toyouchi, Mathias Wolf, Guilin Feng, Yasuhiko Fujita, Beatrice Fortuni, Tomoko Inose, Kenji Hirai, Steven De Feyter, Hiroshi Uji-i

  The Journal of Physical Chemistry Letters 13 17 3796 - 3803 2022年05月05日 [査読有り][通常論文]
  
• Host and guest joining forces: a holistic approach for metal-organic frameworks in nonlinear optics

  Mathias Wolf, Kenji Hirai, Shuichi Toyouchi, Brent Daelemans, Eduard Fron, Hiroshi Uji-i

  Journal of Materials Chemistry C 10 25 9471 - 9477 2022年 [査読有り][通常論文]
   

  Metal–organic frameworks (MOFs) are interesting candidates for nonlinear optics (NLO). Here, it will be demonstrated how combining host and guest emission can greatly improve NLO performance of MOFs by accommodating Li@C₆₀ into MOF-177.
• Gold-coated silver nanowires for long lifetime AFM-TERS probes

  Han Wen, Tomoko Inose, Kenji Hirai, Taiki Akashi, Shoji Sugioka, Jiangtao Li, Wannes Peeters, Eduard Fron, Beatrice Fortuni, Yoshihiko Nakata, Susana Rocha, Shuichi Toyouchi, Yasuhiko Fujita, Hiroshi Uji-i

  Nanoscale 14 14 5439 - 5446 2022年 [査読有り][通常論文]
   

  Au-coated AgNW allows to perform long lifetime TERS activity.
• Li@C60 thin films: characterization and nonlinear optical properties

  Mathias Wolf, Shuichi Toyouchi, Peter Walke, Kazuki Umemoto, Akito Masuhara, Hiroshi Fukumura, Yuta Takano, Michio Yamada, Kenji Hirai, Eduard Fron, Hiroshi Uji-i

  RSC Advances 12 1 389 - 394 2022年 [査読有り][通常論文]
   

  A facile way is shown to obtain thin films of Li@C₆₀ as well as their characterization and nonlinear optical properties. Our results suggest Li@C₆₀ to be a suitable candidate for high-harmonic generation.
• Data science assisted investigation of catalytically active copper hydrate in zeolites for direct oxidation of methane to methanol using H2O2

  Junya Ohyama, Airi Hirayama, Nahoko Kondou, Hiroshi Yoshida, Masato Machida, Shun Nishimura, Kenji Hirai, Itsuki Miyazato, Keisuke Takahashi

  Scientific Reports 11 1 2021年12月 [査読有り][通常論文]
   

  Abstract Dozens of Cu zeolites with MOR, FAU, BEA, FER, CHA and MFI frameworks are tested for direct oxidation of CH₄ to CH₃OH using H₂O₂ as oxidant. To investigate the active structures of the Cu zeolites, 15 structural variables, which describe the features of the zeolite framework and reflect the composition, the surface area and the local structure of the Cu zeolite active site, are collected from the Database of Zeolite Structures of the International Zeolite Association (IZA). Also analytical studies based on inductively coupled plasma-optical emission spectrometry (ICP-OES), X-ray fluorescence (XRF), N₂ adsorption specific surface area measurement and X-ray absorption fine structure (XAFS) spectral measurement are performed. The relationships between catalytic activity and the structural variables are subsequently revealed by data science techniques, specifically, classification using unsupervised and supervised machine learning and data visualization using pairwise correlation. Based on the unveiled relationships and a detailed analysis of the XAFS spectra, the local structures of the Cu zeolites with high activity are proposed.
• Gold-Photodeposited Silver Nanowire Endoscopy for Cytosolic and Nuclear pH Sensing

  Qiang Zhang, Tomoko Inose, Monica Ricci, Jiangtao Li, Ya Tian, Han Wen, Shuichi Toyouchi, Eduard Fron, Anh Thi Ngoc Dao, Hitoshi Kasai, Susana Rocha, Kenji Hirai, Beatrice Fortuni, Hiroshi Uji-i

  ACS Applied Nano Materials 4 9 9886 - 9894 2021年09月07日 [査読有り]
   

  Intracellular pH variations are a crucial indicator of physiological and pathological conditions. As such, cancer is known to have a direct interplay with pH dysregulation. For investigation of the pH alterations in cells, metal nanoparticles have been widely used as surface-enhanced Raman scattering (SERS)-based sensors thanks to their high pH sensitivity. However, these SERS probes allow for detection of the pH exclusively at the acidic compartments of the cells (endolysosomes), where particles are entrapped after their endocytosis. Consequently, the results obtained with metal nanoparticles are limited, and the relationship between the pH values detected in the cells and their physiological conditions remains unclear. Herein, we propose an alternative approach based on gold-deposited silver nanowire endoscopy to study cytosolic and nuclear pH variations with high spatiotemporal resolution and sensitivity. The sensing probe was fabricated by depositing gold nanostructures on silver nanowires (Au-dep AgNWs) via visible-laser-light irradiation and modifying the surface with a pH-responsive Raman reporter (4-mercaptobenzoic acid). The high pH sensitivity was demonstrated by immersing the probe in solutions with different pH values (4.4-9.3). The endoscopic probe was then inserted into either the nucleus or cytosol of a living HeLa cell for site-specific pH sensing. The same experiments were performed after the addition of a hypoxia mimetic agent (CoCl2) and an anticancer drug (cisplatin), individually. Notably, our probe accurately detected specific pH variations upon these treatments over time. Similar pH alterations were not measured in untreated cells. The results reported in this work clearly show that Au-dep AgNW endoscopy is a promising powerful tool for pH-sensing applications in biological systems.
• Selective Crystallization via Vibrational Strong Coupling

  Kenji Hirai, Hiroto Ishikawa, Thibault Chervy, James Andell Hutchison, Hiroshi Uji-i

  Chemical Science 12 36 11986 - 11994 2021年08月10日 [査読有り]
   

  The coupling of (photo)chemical processes to optical cavity vacuum fields is an emerging method for modulating molecular and material properties. Recent reports have shown that strong coupling of the vibrational...

• Controlling polymorphism of metal-organic frameworks

  Kenji Hirai, Atsushi Nagahashi, Taisei Kitagawa, Hiroshi Uji-i

  Metamaterials, Metadevices, and Metasystems 2021 2021年08月01日 [査読有り][招待有り]
  
• Polariton Chemistry in Cavity Vacuum Fields

  Kenji Hirai, Hiroshi Uji-i

  Chemistry Letters 50 4 727 - 732 2021年04月05日 [査読有り][招待有り]
   

  Even without external photon pumping, cavity vacuum fields can be strongly coupled with molecular transitions (electronic excitation and molecular vibration), resulting in the formation of polaritonic states. The energy states of molecular systems are altered under strong coupling, revealing intriguing phenomena, such as improvements in energy/exciton transfer and modulation of chemical reactions. In this review, we highlight recent advances in cavity strong coupling, including exciton strong coupling and vibrational strong coupling, from a chemistry-based viewpoint.
• Adaptive Optical Two-Photon Microscopy for Surface-Profiled Living Biological Specimens

  Kazushi Yamaguchi, Kohei Otomo, Yuichi Kozawa, Motosuke Tsutsumi, Tomoko Inose, Kenji Hirai, Shunichi Sato, Tomomi Nemoto, Hiroshi Uji-i

  ACS Omega 6 1 438 - 447 2020年11月30日 [査読有り]
  
• Pseudo‐Membrane Jackets: Two‐Dimensional Coordination Polymers Achieving Visible Phase Separation in Cell Membrane

  Ryo Ohtani, Kenichi Kawano, Masanao Kinoshita, Saeko Yanaka, Hikaru Watanabe, Kenji Hirai, Shiroh Futaki, Nobuaki Matsumori, Hiroshi Uji‐i, Masaaki Ohba, Koichi Kato, Shinya Hayami

  Angewandte Chemie International Edition 59 41 17931 - 17937 2020年10月05日 [査読有り]
   

  Cell membranes contain lateral systems that consist of various lipid compositions and actin cytoskeleton, providing two-dimensional (2D) platforms for chemical reactions. However, such complex 2D environments have not yet been used as a synthetic platform for artificial 2D nanomaterials. Herein, we demonstrate the direct synthesis of 2D coordination polymers (CPs) at the liquid-cell interface of the plasma membrane of living cells. The coordination-driven self-assembly of networking metal complex lipids produces cyanide-bridged CP layers with metal ions, enabling "pseudo-membrane jackets" that produce long-lived micro-domains with a size of 1-5 μm. The resultant artificial and visible phase separation systems remain stable even in the absence of actin skeletons in cells. Moreover, we show the cell application of the jackets by demonstrating the enhancement of cellular calcium response to ATP.
• Low-Cytotoxic Gold-Coated Silver Nanoflowers for Intracellular pH Sensing

  Qiang Zhang, Han Wen, Kiri Watanabe, Ibuki Kotani, Monica Ricci, Beatrice Fortuni, Anh Thi Ngoc Dao, Akito Masuhara, Kenji Hirai, Hitoshi Kasai, Tomoko Inose, Hiroshi Uji-i

  ACS Applied Nano Materials 3 8 7643 - 7650 2020年08月28日 [査読有り]
   

  Intracellular pH affects many biological processes such as apoptosis, proliferation, endocytosis, and multidrug resistance. In view of this, highly sensitive pH sensing in live cells is essential for understanding biological dynamics. Although surface enhanced Raman scattering (SERS) using noble metal nanoparticles functionalized with acidic ligands has been proposed for highly sensitive intracellular pH sensing, the dependence of SERS pH sensitivity on nanoparticle morphology has been overlooked. The apparent dissociation constant (pK(a)) of acid ligands is known to be sensitive to nanoparticle curvature. Thus, nanoparticle morphology should reflect SERS pH sensitivity. Here, we compared pK a behaviors and SERS pH sensitivities of nearly spherical isotropic and flowerlike anisotropic gold-coated silver nanoparticles (AuAgNPs and AuAgNFs, respectively). We found that the NPs with higher curvature such as AuAgNFs show a narrower pH-sensitive range (pH 5-8) compared to the nearly spherical nanoparticles, providing higher sensitivity to the pH range. Taking advantage of the narrow pH range of AuAgNFs, pH changes are successfully monitored as a function of time in cells treated with and without anticancer drugs, respectively. The results indicate that the pH-sensitive range of SERS-sensing can be tailored by controlling nanoparticle morphology. This tenability is a crucial requirement for pH-sensing applications in various biological systems.
• Recent Progress in Vibropolaritonic Chemistry

  Kenji Hirai, James A. Hutchison, Hiroshi Uji‐i

  ChemPlusChem 85 9 1981 - 1988 2020年08月 [査読有り][招待有り]
   

  Vibrational polaritonic chemistry is emerging as an exciting new sub-field of chemistry, one in which strong interactions with optical cavity vacuum fields are another degree of freedom alongside temperature, solvent, catalyst, and so on to modify thermochemical reactivity. The field stands at a fascinating juncture with experimental works on a variety of organic reactions continuing to blossom, just as many theoretical works appear which diverge significantly in their predictions compared to experiments. The outlook for the field is no doubt an exciting one as it seeks to unify the observed novel optical cavity-induced chemical phenomena with satisfying accompanying physical theory. In this minireview we highlight experimental works on vibrational polaritonic chemistry that have appeared most recently, focusing on the chemistry of the rate-limiting steps to provide mechanistic insight. We hope this review will encourage synthetic chemists to enter the field and we discuss the opportunities and challenges that lie ahead as polaritonic chemistry grows into the future.
• Controlled Fabrication of Optical Signal Input/Output Sites on Plasmonic Nanowires

  Shuichi Toyouchi, Mathias Wolf, Yusuke Nakao, Yasuhiko Fujita, Tomoko Inose, Beatrice Fortuni, Kenji Hirai, Johan Hofkens, Steven De Feyter, James Hutchison, Hiroshi uji-i

  Nano Letters 20 2460 - 2467 2020年03月10日 [査読有り][通常論文]
  
• Modulation of Prins Cyclization by Vibrational Strong Coupling.

  Kenji Hirai, Rie Takeda, James A Hutchison, Hiroshi Uji-I

  Angewandte Chemie (International ed. in English) 59 5332 - 5335 2020年01月22日 [査読有り][通常論文]
   

  Light-molecule strong coupling has emerged within the last decade as an entirely new method to control chemical reactions. A few years ago it was discovered that the chemical reactivity could be altered by vibrational strong coupling (VSC). While the potential of VSC in organic chemistry appears enormous, only a limited number of reactions have been investigated under VSC to date, including solvolysis and deprotection reactions. Here we investigate the effect of VSC on a series of aldehydes and ketones undergoing Prins cyclization, an important synthetic step in pharmaceutical chemistry. We observe a decrease of the second-order rate constant with VSC of the reactant carbonyl stretching groups. We measure an increased activation energy due to VSC, but proportional changes in activation enthalpy and entropy suggest no substantive change in reaction pathway. The addition of common cycloaddition reactions to the stable of VSC-modified chemical reactions is another step towards establishing VSC as a genuine tool for synthetic chemistry.
• Plasmon-Associated Control of Chemical Reaction at Nanometer Scale

  Shuichi Toyouchi, Tomoko Inose, Kenji Hirai, Hiroshi Uji-i

  Photosynergetic Responses in Molecules and Molecular Aggregates 117 - 133 2020年 [査読有り][招待有り]
  
• Label-free visualization of heterogeneities and defects in metal–organic frameworks using nonlinear optics

  Mathias Wolf, Kenji Hirai, Shuichi Toyouchi, Eduard Fron, Wannes Peeters, Steven De Feyter, Hiroshi Uji-i

  Chemical Communications 56 87 13331 - 13334 2020年 [査読有り]
   

  The potential of nonlinear optical microscopy for the label-free visualization of heterogeneities and defects in metal–organic frameworks is demonstrated.

• Multicolour photochromic fluorescence of a fluorophore encapsulated in a metal–organic framework

  Kenji Hirai, Taisei Kitagawa, Hideki Fujiwara, Jenny Pirillo, Yuh Hijikata, Tomoko Inose, Hiroshi Uji-i

  Chemical Communications 56 67 9651 - 9654 2020年 [査読有り][通常論文]
   

  A fluorophore encapsulated in a metal–organic framework showed photochromic multicolour fluorescence.

• Water-mediated polyol synthesis of pencil-like sharp silver nanowires suitable for nonlinear plasmonics.

  Inose T, Toyouchi S, Lu G, Umemoto K, Tezuka Y, Lyu B, Masuhara A, Fron E, Fujita Y, Hirai K, Uji-I H

  Chemical communications (Cambridge, England) 55 77 11630 - 11633 2019年09月 [査読有り][通常論文]
   

  We report a simple method to control the end shape of silver nanowires by adding pure water in the conventional polyol synthesis. The use of 0.2-0.4% (v/v) water in ethylene glycol as a solvent provides pencil-like silver nanowires with sharp ends in a high yield. We have demonstrated remote excitation of SHG on the sharp nanowires, promising a point light source for super resolution microscopy.
• The Rise of Catalyst Informatics: Towards Catalyst Genomics

  Takahashi, K., Takahashi, L., Miyazato, I., Fujima, J., Tanaka, Y., Uno, T., Satoh, H., Ohno, K., Nishida, M., Hirai, K., Ohyama, J., Nguyen, T.N., Nishimura, S., Taniike, T.

  ChemCatChem 11 4 1146 - 1152 2019年 [査読有り][通常論文]
  
• Pyrolysis of Helical Coordination Polymers for Metal-Sulfide-Based Helices with Broadband Chiroptical Activity

  Kenji Hirai, Bongjun Yeom, Kazuki Sada

  ACS NANO 11 6 5309 - 5317 2017年06月 [査読有り][通常論文]
   

  Fabrication of chiroptical materials with broadband response in the visible light region is vital to fully realize their potential applications. One way to achieve broadband chiroptical activity is to fabricate chiral nanostructures from materials that exhibit broadband absorption in the visible light region. However, the compounds used for chiroptical materials have predominantly been limited to materials with narrowband spectral response. Here, we synthesize Ag2S-based nanohelices derived from helical coordination polymers. The right- and left-handed coordination helices used as precursors are prepared from L- and D-glutathione with Ag+ and a small amount of Cu2+. The pyrolysis of the coordination helices yields right- and left-handed helices of Cu0.12Ag1.94S/C, which exhibit chiroptical activity spanning the entire visible light region. Finite element method simulations substantiate that the broadband chiroptical activity is attributed to synergistic broadband light absorption and light scattering. Furthermore, another series of Cu0.10Ag1.90S/C nanohelices are synthesized by choosing the or D-Glu-Cys as starting materials. The pitch length of nanohelicies is controlled by changing the peptides, which alters their chiroptical properties. The pyrolysis of coordination helices enables one to fabricate helical Ag2S-based materials that enable broadband chiroptical activity but have not been explored owing to the lack of synthetic routes.
• Solid-Solution Coordination Polymers as Precursors for ZnxCd1-xS/C Composite Nanowires

  Shinya Tajima, Yoshiki Kuroshima, Tetsuro Katayama, Naoto Tamai, Kazuki Sada, Kenji Hirai

  EUROPEAN JOURNAL OF INORGANIC CHEMISTRY 18 2444 - 2449 2017年05月 [査読有り][通常論文]
   

  The development of synthetic routes to nanomaterials has been motivated by their potential applications in electronics, optics, and catalytic reactions. Solution-based synthesis has relied on organic stabilizers to regulate the crystal growth. Despite the beneficial effect on crystal growth, organic stabilizers attached to the resulting particles reduce the accessibility of reactants and inhibit charge transport, resulting in a lower catalytic activity than expected. In this work we have demonstrated that coordination polymers (CPs) can be used as precursors for photocatalysts without stabilizers. The pyrolysis of CP nanowires of [Cd(l-cysteinate)](n) gave CdS/C nanowires (CdS/C-NWs) that exhibit photocatalytic activity for hydrogen generation superior to CdS nanowires with organic stabilizers (CdS/stb-NWs). Transient absorption spectroscopy showed that CdS/C-NWs provide an active surfaces to facilitate catalytic reactions associated with electron migration. Moreover, Zn-doped CdS nanowires (ZnxCd1-xS/C-NWs) obtained by the pyrolysis of CPs exhibited higher photocatalytic activity than nondoped CdS/C-NWs. The improvement in photocatalytic activity is attributable to the prolonged lifetime of photoexcited electrons. The pyrolysis of CPs provides a facile means to design nanocomposites that realize efficient catalytic reactions associated with facile charge transfer.
• Infrared laser writing of MOFs

  K. Hirai, K. Sada

  CHEMICAL COMMUNICATIONS 53 38 5275 - 5278 2017年05月 [査読有り][通常論文]
   

  An infrared (IR) laser machine is used for the synthesis of metal-organic frameworks (MOFs). Solutions containing metal ions and organic ligands are casted on glass substrates. MOF crystals are formed at the positions the IR laser irradiated, resulting in the patterning of MOFs.
• Nanoparticle Assemblies into Luminescent Dendrites in Shrinking Microdroplets

  Taisuke Kojima, Kenji Hirai, Yunlong Zhou, Priyan Weerappuli, Shuichi Takayama, Nicholas A. Kotov

  LANGMUIR 32 47 12468 - 12475 2016年11月 [査読有り][通常論文]
   

  The self-assembly of nanoparticles (NPs) is essential for emerging dispersion-based energy-conscious technologies. Of particular interest are micro- and macro scale self-organizing superstructures that can bridge 2D/3D processing scales. Here we report the spontaneous assembly of CdTe NPs within an aqueous microdroplet suspended in soybean oil. The gradual diffusion of the water into the surrounding medium results in shrinking of the microdroplet, and a concomitant formation of branched assemblies from CdTe NPs that evolve in size from similar to 50 mu m to similar to 1000 mu m. The fractal dimension of NP assemblies increases from similar to 1.7 to similar to 1.9 during the assembly process. We found that constituents of the soybean oil enter the aqueous solution across the microdroplet interface and affect NP assembly. The obtained NP dendrites can be further altered morphologically by illumination with light that results in the disassembly of the NP dendrites. The use of this microheterogeneous dispersion platform with partially soluble hydrophilic and hydrophobic solvents highlights the sensitivity of the NP assembly process to environment and presents an opportunity to explore droplet-confined NP assembly.
• Gas-generated thermal oxidation of a coordination cluster for an anion-doped mesoporous metal oxide

  Kenji Hirai, Shigehito Isobe, Kazuki Sada

  SCIENTIFIC REPORTS 5 18468  2015年12月 [査読有り][通常論文]
   

  Central in material design of metal oxides is the increase of surface area and control of intrinsic electronic and optical properties, because of potential applications for energy storage, photocatalysis and photovoltaics. Here, we disclose a facile method, inspired by geochemical process, which gives rise to mesoporous anion-doped metal oxides. As a model system, we demonstrate that simple calcination of a multinuclear coordination cluster results in synchronic chemical reactions: thermal oxidation of Ti8O10(4-aminobenzoate)(12) and generation of gases including amino-group fragments. The gas generation during the thermal oxidation of Ti8O10(4-aminobenzoate)(12) creates mesoporosity in TiO2. Concurrently, nitrogen atoms contained in the gases are doped into TiO2, thus leading to the formation of mesoporous N-doped TiO2. The mesoporous N-doped TiO2 can be easily synthesized by calcination of the multinuclear coordination cluster, but shows better photocatalytic activity than the one prepared by a conventional sol-gel method. Owing to an intrinsic designability of coordination compounds, this facile synthetic will be applicable to a wide range of metal oxides and anion dopants.
• Coordination Assembly of Discoid Nanoparticles

  Kenji Hirai, Bongjun Yeom, Shu-Hao Chang, Hang Chi, John F. Mansfield, Byeongdu Lee, Sungsik Lee, Ctirad Uher, Nicholas A. Kotov

  ANGEWANDTE CHEMIE-INTERNATIONAL EDITION 54 31 8966 - 8970 2015年07月 [査読有り][通常論文]
   

  Supramolecular chemistry utilizes coordination bonds to assemble molecular building blocks into a variety of sophisticated constructs. However, traditional coordination assemblies are based on organic compounds that have limited ability to transport charge. Herein, we describe coordination assembly of anisotropic FeS2 pyrite nanoparticles (NPs) that can facilitate charge transport. Zn2+ ions form supramolecular complexes with carboxylate end-groups on NP surface, leading to multiparticle sheets with liquid-crystal-like organization. Conductivity and Hall carrier mobility of the p-type layered semiconductor films with Zn2+ coordination bridging exceed those known for coordination compounds, some by several orders of magnitude. The nanoscale porosity of the assembled sheets combined with fast hole transport leads to high electrocatalytic activity of the NP films. The coordination assembly of NPs embraces the versatility of several types of building blocks and opens a new design space for self-organized materials combining nanoscale and supramolecular structural motifs.
• Diffusion-Coupled Molecular Assembly: Structuring of Coordination Polymers Across Multiple Length Scales

  Kenji Hirai, Julien Reboul, Nobuhiro Morone, John E. Heuser, Shuhei Furukawa, Susumu Kitagawa

  JOURNAL OF THE AMERICAN CHEMICAL SOCIETY 136 42 14966 - 14973 2014年10月 [査読有り][通常論文]
   

  Porous coordination polymers (PCPs) are an intriguing class of molecular-based materials because of the designability of framework scaffolds, pore sizes and pore surface functionalities. Besides the structural designability at the molecular scale, the structuring of PCPs into mesoscopic/macroscopic morphologies has attracted much attention due to the significance for the practical applications. The structuring of PCPs at the mesoscopic/macroscopic scale has been so far demonstrated by the spatial localization of coordination reactions on the surface of templates or at the phase boundaries. However, these methodologies have never been applied to the fabrication of solid-solution or multivariate metalorganic frameworks (MOFs), in which multiple components are homogeneously mixed. Herein, we demonstrate the structuring of a box-type superstructure comprising of a solid-solution PCP by integrating a bidirectional diffusion of multiple organic ligands into molecular assembly. The parent crystals of [Zn2(ndc)(2)(bpy)](n) were placed in the DMF solution of additional organic component of H(2)bdc, and the temperature was rapidly elevated up to 80 degrees C (ndc = 1,4-naphthalenedicarboxylate, bpy = 4,4'-bipyridyl, bdc = 1,4-benzenedicarboxylate). The dissolution of the parent crystals induced the outward diffusion of components; contrariwise, the accumulation of the other organic ligand of H(2)bdc induced the inward diffusion toward the surface of the parent crystals. This bidirectional diffusion of multiple components spatially localized the recrystallization at the surface of cuboid parent crystals; therefore, the nanocrystals of a solid-solution PCP ([Zn-2(bdc)(1.5)(ndc)(0.5)(bpy)](n)) were organized into a mesoscopic box superstructure. Furthermore, we demonstrated that the box superstructures enhanced the mass transfer kinetics for the separation of hydrocarbons.
• Confined synthesis of CdSe quantum dots in the pores of metal–organic frameworks

  Wakaoka T, Hirai K, Murayama K, Takano Y, Takagi H, Furukawa S, Kitagawa S

  Journal of Materials Chemistry C 2 35 7173 - 7175 2014年09月 [査読有り][通常論文]
   

  Ultra-small CdSe nanoparticles (similar to 2 nm) were synthesised in the pores of a metal-organic framework, MIL-101(Al)-NH2, using a stepwise injection-reaction protocol. Electron microscopy measurements showed that the nanoparticles were densely packed due to the highly ordered pores of the MOF.
• Trapping of a Spatial Transient State During the Framework Transformation of a Porous Coordination Polymer

  Mio Kondo, Shuhei Furukawa, Kenji Hirai, Takaaki Tsuruoka, Julien Reboul, Hiromitsu Uehara, Stephane Diring, Yoko Sakata, Osami Sakata, Susumu Kitagawa

  JOURNAL OF THE AMERICAN CHEMICAL SOCIETY 136 13 4938 - 4944 2014年04月 [査読有り][通常論文]
   

  Structural transformability accompanied by molecular accommodation is a distinguished feature of porous coordination polymers (PCPs) among porous materials. Conventional X-ray crystallography allows for the determination of each structural phase emerged during transformation. However, the propagation mechanism of transformation through an entire crystal still remains in question. Here we elucidate the structural nature of the spatial transient state, in which two different but correlated framework structures, an original phase and a deformed phase, simultaneously exist in one crystal. The deformed phase is distinctively generated only at the crystal surface region by introducing large guest molecules, while the remaining part of crystal containing small molecules maintains the original phase. By means of grazing incidence diffraction techniques we determine that the framework is sheared with sharing one edge of the original primitive cubic structure, leading to the formation of crystal domains with four mirror image relationships.
• Host–Guest Metal-Organic Frameworks for Photonics

  Hirai K, Falcaro P, Kitagawa S, Furukawa S

  Structure and Bonding 157 167 - 186 2014年 [査読有り][招待有り]
   

  The assembly of metal ions and organic linkers gives the highly regulated framework scaffolds, the so-called metal-organic framework (MOFs) or porous coordination polymers (PCPs). MOFs offer fascinating platforms in which light emitting components can be rationally incorporated. A variety of metal ions and organic linkers can be used to fabricate the MOF materials with a wide range of emissive properties. Besides their inherent luminescent properties, the permanent porosity of MOFs enables to accommodate guest species therein. The accommodation of guests in the pores results in the shift of emission wavelength, the change of emission intensity or even the generation of new emission bands. Therefore, the luminescent MOFs can be potentially exploited as a chemical sensor for small molecules or ions. In this chapter, we present a variety of luminescent properties derived from the guest accommodation in MOFs, and we discuss potential applications of luminescent MOFs as sensing materials.
• Impact of crystal orientation on the adsorption kinetics of a porous coordination polymer-quartz crystal microbalance hybrid sensor

  Kenji Hirai, Kenji Sumida, Mikhail Meilikhov, Nicolas Louvain, Masashi Nakahama, Hiromitsu Uehara, Susumu Kitagawa, Shuhei Furukawa

  JOURNAL OF MATERIALS CHEMISTRY C 2 17 3336 - 3344 2014年 [査読有り][通常論文]
   

  The hybridization of porous coordination polymers (PCPs) with electronic devices is a powerful strategy for developing systems that are suitable for advanced applications, such as chemical sensing. The quartz crystal microbalance (QCM) technique is one that allows minute mass changes to be resolved with a high temporal resolution, and the growth of PCP crystals that provide selective adsorption properties on a QCM substrate can facilitate the rapid detection of certain molecules from a gas or vapour mixture. Herein, we demonstrate the immobilization of the flexible PCP Zn(NO2- ip)(bpy) (Zn-CID-5; NO2- ip(2-) = 5- nitroisophthalate, bpy= 4,4' bipyridine) on QCM substrates and investigate the adsorptive properties of the fabricated systems. Notably, the crystal orientation could be controlled by the anchoring of chemical functionalities on the substrate surface, or by the addition of coordination modulators (e. g. 4-phenylpyridine) at the time of growth of the PCP crystals on the substrates. Here, the crystal orientation plays a significant role in determining the detection kinetics of organic vapours (e. g. methanol), and the [010]-oriented case which displays the fastest adsorption kinetics among the samples tested is studied under mixed component (methanol-hexane) conditions to demonstrate its response profile. In all, the results demonstrate the potential utility of PCP/QCM hybrid systems in sensor applications, and also serve to highlight the importance of optimizing the physical orientation of crystal growth in such systems to maximize the overall performance of the system.
• Binary Janus Porous Coordination Polymer Coating for Sensor Devices with Tunable Analyte Affinity

  Mikhail Meilikhov, Shuhei Furukawa, Kenji Hirai, Roland A. Fischer, Susumu Kitagawa

  ANGEWANDTE CHEMIE-INTERNATIONAL EDITION 52 1 341 - 345 2013年 [査読有り][通常論文]
  
• Shape-Memory Nanopores Induced in Coordination Frameworks by Crystal Downsizing

  Yoko Sakata, Shuhei Furukawa, Mio Kondo, Kenji Hirai, Nao Horike, Yohei Takashima, Hiromitsu Uehara, Nicolas Louvain, Mikhail Meilikhov, Takaaki Tsuruoka, Seiji Isoda, Wataru Kosaka, Osami Sakata, Susumu Kitagawa

  SCIENCE 339 6116 193 - 196 2013年01月 [査読有り][通常論文]
   

  Flexible porous coordination polymers change their structure in response to molecular incorporation but recover their original configuration after the guest has been removed. We demonstrated that the crystal downsizing of twofold interpenetrated frameworks of [Cu-2(dicarboxylate)(2)(amine)](n) regulates the structural flexibility and induces a shape-memory effect in the coordination frameworks. In addition to the two structures that contribute to the sorption process (that is, a nonporous closed phase and a guest-included open phase), we isolated an unusual, metastable open dried phase when downsizing the crystals to the mesoscale, and the closed phase was recovered by thermal treatment. Crystal downsizing suppressed the structural mobility and stabilized the open dried phase. The successful isolation of two interconvertible empty phases, the closed phase and the open dried phase, provided switchable sorption properties with or without gate-opening behavior.
• Programmed crystallization via epitaxial growth and ligand replacement towards hybridizing porous coordination polymer crystals

  Kenji Hirai, Kebi Chen, Tomohiro Fukushima, Satoshi Horike, Mio Kondo, Nicolas Louvain, Chiwon Kim, Yoko Sakata, Mikhail Meilikhov, Osami Sakata, Susumu Kitagawa, Shuhei Furukawa

  DALTON TRANSACTIONS 42 45 15868 - 15872 2013年 [査読有り][通常論文]
   

  Hybridized porous coordination polymers (PCPs) are synthesized through epitaxial growth or ligand replacement. Whereas epitaxial growth on the core crystal leads to a sandwich type PCP, ligand replacement near the surface of core crystal results in a core-shell type PCP.
• Mesoscopic architectures of porous coordination polymers fabricated by pseudomorphic replication

  Julien Reboul, Shuhei Furukawa, Nao Horike, Manuel Tsotsalas, Kenji Hirai, Hiromitsu Uehara, Mio Kondo, Nicolas Louvain, Osami Sakata, Susumu Kitagawa

  NATURE MATERIALS 11 8 717 - 723 2012年08月 [査読有り][通常論文]
   

  The spatial organization of porous coordination polymer (PCP) crystals into higher-order structures is critical for their integration into separation systems, heterogeneous catalysts, ion/electron transport and photonic devices. Here, we demonstrate a rapid method to spatially control the nucleation site, leading to the formation of mesoscopic architecture made of PCPs, in both two and three dimensions. Inspired by geological processes, this method relies on the morphological replacement of a shaped sacrificial metal oxide used both as a metal source and as an 'architecture-directing agent' by an analogous PCP architecture. Spatiotemporal harmonization of the metal oxide dissolution and the PCP crystallization allowed the preservation of very fine mineral morphological details of periodic alumina inverse opal structures. The replication of randomly structured alumina aerogels resulted in a PCP architecture with hierarchical porosity in which the hydrophobic micropores of the PCP and the mesopores/macropores inherited from the parent aerogels synergistically enhanced the material's selectivity and mass transfer for water/ethanol separation.
• Redox reaction in two-dimensional porous coordination polymers based on ferrocenedicarboxylates

  Kenji Hirai, Hiromitsu Uehara, Susumu Kitagawa, Shuhei Furukawa

  DALTON TRANSACTIONS 41 14 3924 - 3927 2012年 [査読有り][通常論文]
   

  A series of 1,1'-ferrocenedicarboxylate-based two-dimensional porous coordination polymers were synthesized by incorporating different diamine co-ligands. These compounds immobilized on electrodes, exhibited reversible redox reactions, arising from ferrocenyl moiety.
• Targeted functionalisation of a hierarchically-structured porous coordination polymer crystal enhances its entire function

  Kenji Hirai, Shuhei Furukawa, Mio Kondo, Mikhail Meilikhov, Yoko Sakata, Osami Sakata, Susumu Kitagawa

  CHEMICAL COMMUNICATIONS 48 52 6472 - 6474 2012年 [査読有り][通常論文]
   

  Spatiospecific functionalisation of a shell crystal was performed in a core-shell crystal of a porous coordination polymer (PCP) via post-synthetic modification (PSM). The shell crystal allowed the core crystal to selectively accumulate N,N-dimethylaniline (DMA) and afford the intense exciplex fluorescence.
• Liquid Phase Separation of Polyaromatics on [Cu-2(BDC)(2)(dabco)]

  Michael Maes, Stijn Schouteden, Kenji Hirai, Shuhei Furukawa, Susumu Kitagawa, Dirk E. De Vos

  LANGMUIR 27 15 9083 - 9087 2011年08月 [査読有り][通常論文]
   

  The porous coordination polymer (PCP) [Cu-2(BDC)(2)(dabco)] is capable of selectively adsorbing up to 25 wt % of either 1-methylnaphthalene or 2-methylnaphthalene. Uptakes of unsubstituted naphthalene and 1,4-dimethyl-naphthalene are significantly lower (7-13 wt %), suggesting that monomethyl substituted polyaromatics can be separated from the other fractions. Furthermore, this PCP can perform the difficult separation of 1-methylnaphthalene from 2-methylnaphthalene with separation factors as high as 2.6, proving that specific interactions of the methyl group with the lattice play an important role in determining the adsorption selectivity.
• Porous Coordination Polymer Hybrid Device with Quartz Oscillator: Effect of Crystal Size on Sorption Kinetics

  Hiromitsu Uehara, Stephane Diring, Shuhei Furukawa, Ziya Kalay, Manuel Tsotsalas, Masashi Nakahama, Kenji Hirai, Mio Kondo, Osami Sakata, Susumu Kitagawa

  JOURNAL OF THE AMERICAN CHEMICAL SOCIETY 133 31 11932 - 11935 2011年08月 [査読有り][通常論文]
   

  A new strategy to synthesize mono dispersed porous coordination polymer (PCP) nanocrystals at room temperature was developed and utilized for the formation of PCP thin films on gold substrates with fine control over the crystal sizes using the coordination modulation method. Hybridization of these PCP thin films with an environment-controlled quartz crystal microbalance system allowed determining the adsorption properties for organic vapors (methanol and hexane). In the case of high sensitivity (at the low-concentration dosing of analytes), the sensor response depended on the crystal size but not on the type of analyte. In contrast, at the high-concentration dosing, a clear dependence of the sorption kinetics on the analyte was observed due to significant sorbate-sorbate interaction.
• MOF-on-MOF heteroepitaxy: perfectly oriented [Zn-2(ndc)(2)(dabco)](n) grown on [Cu-2(ndc)(2)(dabco)](n) thin films

  O. Shekhah, K. Hirai, H. Wang, H. Uehara, M. Kondo, S. Diring, D. Zacher, R. A. Fischer, O. Sakata, S. Kitagawa, S. Furukawa, C. Woell

  DALTON TRANSACTIONS 40 18 4954 - 4958 2011年 [査読有り][通常論文]
   

  We report the successful heteroepitaxial growth of perfectly oriented hybrid MOF thin films. By employing step-by-step liquid-phase epitaxy (LPE), [Zn-2(ndc)(2)(dabco)](n) was grown on [Cu-2(ndc)(2)(dabco)](n), thus demonstrating that the MOF-on-MOF deposition scheme developed for powdered microcrystalline MOF materials can also be applied in connection with LPE for MOF thin films or multilayers. The deposition was monitored by surface plasmon resonance (SPR) spectroscopy, the resulting MOF heterostructures were characterized using IR spectroscopy and different types of X-ray diffraction (XRD)-based techniques. The results suggest that the LPE method is a promising way to fabricate and grow MOF heterostructures, and also demonstrates the potential of [Cu-2(ndc)(2)(dabco)](n) MOF thin films as substrates for the LPE-based growth of different MOFs on top.
• Sequential Functionalization of Porous Coordination Polymer Crystals

  Kenji Hirai, Shuhei Furukawa, Mio Kondo, Hiromitsu Uehara, Osami Sakata, Susumu Kitagawa

  ANGEWANDTE CHEMIE-INTERNATIONAL EDITION 50 35 8057 - 8061 2011年 [査読有り][通常論文]
  
• Coordinatively Immobilized Monolayers on Porous Coordination Polymer Crystals

  Mio Kondo, Shuhei Furukawa, Kenji Hirai, Susumu Kitagawa

  ANGEWANDTE CHEMIE-INTERNATIONAL EDITION 49 31 5327 - 5330 2010年 [査読有り][通常論文]
  
• Heterogeneously Hybridized Porous Coordination Polymer Crystals: Fabrication of Heterometallic Core-Shell Single Crystals with an In-Plane Rotational Epitaxial Relationship

  Shuhei Furukawa, Kenji Hirai, Keiji Nakagawa, Yohei Takashima, Ryotaro Matsuda, Takaaki Tsuruoka, Mio Kondo, Rie Haruki, Daisuke Tanaka, Hirotoshi Sakamoto, Satoru Shimomura, Osami Sakata, Susumu Kitagawa

  ANGEWANDTE CHEMIE-INTERNATIONAL EDITION 48 10 1766 - 1770 2009年 [査読有り][通常論文]
  
• A block PCP crystal: anisotropic hybridization of porous coordination polymers by face-selective epitaxial growth

  Shuhei Furukawa, Kenji Hirai, Yohei Takashima, Keiji Nakagawa, Mio Kondo, Takaaki Tsuruoka, Osami Sakata, Susumu Kitagawa

  CHEMICAL COMMUNICATIONS 34 5097 - 5099 2009年 [査読有り][通常論文]
   

  Two porous coordination polymers (PCPs) with different pore surface functionality were integrated into one single crystal by face-selective epitaxial growth, leading to BAB-type block PCP crystals with the core crystal A between the second crystals B.

書籍

• PCP/MOFおよび各種多孔質材料の作り方、使い方、評価解析

  技術情報協会 (範囲:MOFの技術を用いたマイクロパターニングの開発とその応用)
  技術情報協会 2019年10月 (ISBN: 9784861047695) 639p
• 配位空間の化学 : 最新技術と応用

  シーエムシー出版 2009年10月 (ISBN: 9784781301358) viii, 345p

その他活動・業績

• 光共振器を使った機能物性化学

  平井健二 応用物理学会有機分子・バイオエレクトロニクス分科会会誌 34 (2) 58 -61 2023年06月 [査読無し][招待有り]
  
• 振動強結合による化学反応の制御と機能性材料の合成

  平井健二 応用物理学会フォトニクスニュース 8 (1) 52 2022年05月 [査読無し][招待有り]
  
• 光共振器の中の化学反応

  平井健二 光学 51 28 -33 2022年01月 [査読有り][招待有り]
  
• 振動強結合と分子化学の交差

  平井健二 理論化学会誌フロンティア 3 (4) 225 -230 2021年11月 [査読有り][招待有り]
  
• 光共振器で化学反応を制御─量子ゆらぎと有機反応の接点

  平井健二 化学 2020年6月号 12 -15 2020年05月 [査読無し][通常論文]
  
• プラズモン導波路を用いた単一細胞解析と操作

  豊内秀一, 猪瀬朋子, 平井健二, 雲林院宏 月刊「細胞」2020年 2月号 51 -54 2020年 [査読無し][通常論文]
  
• 金属錯体ナノスペースの創製と応用 (ナノ構造の創製と応用)

  平井 健二, 北川 進 科学と工業 86 (5) 151 -155 2012年05月 [査読無し][通常論文]
  
• 多孔性金属錯体（PCP/MOF）の表面化学

  平井健二, 古川修平 表面科学会誌 33 (9) 519 -523 2012年 [査読無し][通常論文]
  
• Multifunctional Porous Crystals by Hybridizing Coordination Polymers

  Kenji Hirai, Osami sakata, Susumu Kitagawa, Shuhei Furukawa SPring-8 Research Frontiers 2011 84 -85 2011年 [査読無し][通常論文]
  
• Evaluation of Structural Relationship in Hybridized Porous Coordination Polymer Crystals

  Kenji Hirai, Shuhei Furukawa, Osami Sakata, Susumu Kitagawa SPring-8 Research Frontiers 2009 98 -99 2010年 [査読無し][通常論文]
  
• エピタキシャル成長によるハイブリッド型多孔性錯体結晶の創製

  平井健二 Bulletin of Japan Society of Coordination Chemistry 55 121 -122 2010年 [査読無し][通常論文]
  

特許

• 特開2021-178311:リアクタ  2021年11月18日

  平井 健二, 高橋 康史  国立大学法人北海道大学, 国立大学法人金沢大学

受賞

• 2022年03月 応用物理学会フォトニクス奨励賞
  
• 2021年09月 第3 回 物質・デバイス共同研究賞
  
• 2020年10月 新化学技術研究奨励賞
  
• 2013年06月 Reaxys Ph.D. Prize 2013 Finalist
  
• 2012年03月 The 4th HOPE Meeting Unique Presentation Award
  
• 2012年03月 The 4th HOPE Meeting Best Poster Award
  
• 2010年08月 錯体化学若手の会夏の学校2010 学生講演賞
  
• 2009年09月 第59回錯体化学討論会 ポスター賞
  
• 2009年09月 第62回コロイドおよび界面化学討論会 ポスター賞
  
• 2009年06月 第2 回京都大学融合ナノ基盤工学研究者交流会 奨励賞
  

共同研究・競争的資金等の研究課題

• メゾ強結合

  日本学術振興会：科学研究費助成事業

  研究期間 : 2023年04月 -2028年03月 

  代表者 : 雲林院 宏, 平井 健二, 五月女 光
• 自己集合による規則配列を利用した高輝度ポラリトン発光

  日本学術振興会：科学研究費助成事業

  研究期間 : 2024年04月 -2027年03月 

  代表者 : 平井 健二
• 光共振器による量子光学現象を利用したイオン伝導度の向上

  日本学術振興会：科学研究費助成事業 基盤研究(B)

  研究期間 : 2021年04月 -2024年03月 

  代表者 : 平井 健二

   

  ２枚の光反射ミラーが向かい合った光共振器の中では、定在波として存在可能な光が限定され、共振器モードとして規定される。この光共振器に分子を導入すると、共分子振動と共振器モードが光を介して可逆にエネルギーを交換するようになる。この可逆なエネルギー交換が、緩和を含む散逸過程や光共振器内での光の損失よりも速くなると、振動強結合と呼ばれる状態になる。振動強結合では、分子振動と光の量子的な重ね合わせ状態、ポラリトンが形成される。このポラリトンの形成に伴い、振動基底状態のエネルギー準位が変化することが理論的にも予測されている。実際、振動強結合の状態では分子の反応性が変化することが観測されており、光共振器の中では分子の物性が変化することが明らかとなっている。 本研究では、有機分子を振動強結合の状態にすることでイオン伝導にかかる物性の制御を試みた。具体的には、カルボニル基を有する分子を光共振器の中に導入し、カルボニル伸縮振動を強結合の状態にした。この状態では、カルボニル基のプロトン解離平衡が変化していることが示唆された。光反射ミラーの距離を変更し、共振器モードのエネルギー準位を変化させることで振動強結合ではない状態にすると、解離平衡は通常の状態に戻った。この結果は、振動強結合によってプロトン解離の平衡が変化していることが示唆している。カルボニル基のプロトン解離平衡の変化は伝導度にも影響することが予測される。
• 多孔性錯体を用いたポラリトンレーザーの開発

  住友財団 基礎科学研究助成

  研究期間 : 2022年11月 -2023年11月 

  代表者 : 平井健二
• 配位自己集合を用いた量子ドットレーザーの開発

  日本学術振興会：科学研究費助成事業 挑戦的研究(萌芽)

  研究期間 : 2020年07月 -2023年03月 

  代表者 : 平井 健二

   

  金属イオンと有機配位子が自己集合することによって、結晶性の多孔性材料である有機金属構造体（MOF:metal-organic framework）が得られる。MOFは規則的な細孔を有しており、細孔の中に内包された分子・粒子は規則的に配列する。本研究では、MOFの細孔内に分子・粒子を配列させる技術を基盤としたレーザー技術の開拓を試みた。 令和3年度は、レーザーの波長変換を可能とする非線形光学応答材料の開発を行った。MOFを用いた非線形光学材料の開発は、対称心を持たないMOFを設計する、または非線形光学応答を示す分子を細孔内に内包させる方法が採られる。本研究では、MOFと細孔内のゲスト分子の相互作用を利用した非線形光学応答材料の開発を試みた。 MOF-177の細孔の中にリチウム内包フラーレン（Li@C60）をゲストとして導入した。MOF-177は対称性の高い構造であるが、Li@C60を内包することでMOF-177の対称性が崩れ、非線形光学応答を示すことがわかった。また、Li@C60も非線形光学応答を示す分子である。このLi@C60を内包したMOF-177から第二次高調波発生を観測した。Li@C60を内包したMOF-177はLi@C60と比較して、第二次高調波発生の効率が40%向上していることを確認した。また、MOF-177の細孔にLi@C60を導入することで、不安定なLi@C60が安定化することが明らかとなった。
• ラビ分裂による化学反応操作法の確立

  科学技術振興機構：さきがけ研究

  研究期間 : 2018年10月 -2022年03月 

  代表者 : 平井 健二
• レーザー加熱による機能性材料の３次元合成

  日本学術振興会：科学研究費助成事業

  研究期間 : 2018年04月 -2021年03月 

  代表者 : 平井 健二, 雲林院 宏, 猪瀬 朋子

   

  機能性材料を目的の場所に配置することが出来れば、電子素子、光学素子、マイクロデバイスの開発が可能となる。本研究では、様々な機能性材料を望みの場所で合成する方法を開発した。具体的には、プローブとしての利用が可能な銀ナノワイヤ（AgNW）上で金ナノ粒子（AuNP）を合成し、プラズモン加熱を利用した機能性材料の合成を行った。AuNPにレーザーを照射することで、AuNP近傍を加熱することが可能である。この加熱方法を利用して酸化亜鉛や有機金属構造体を局所的に合成することに成功した。
• 振動励起による自己集合マニュピレーション

  日本学術振興会：科学研究費助成事業 挑戦的研究(萌芽)

  研究期間 : 2018年06月 -2020年03月 

  代表者 : 平井 健二

   

  亜鉛イオンと2-メチルイミダゾールを含む水溶液を、光共振器の中に導入した状態で、溶液を静置すると、自己集合が進みZIF-8の結晶が得られた。一方、光共振器を用いずに同様の水溶液を静置すると、ZIF-LとZIF-8の混合物が得られる。光共振器中で結晶化を行うことで、ZIF-8が選択的に生成することが明らかとなった。ZIF-LとZIF-8は同一の構成要素から組み上がる多孔性配位高分子（MOF）であるが、配位構造が異なる結晶疑似多形である。振動強結合により、MOFの選択的な結晶化が可能であることが示唆された。
• 配位高分子の犠牲鋳型法による無機酸化物のマルチスケール構造制御

  日本学術振興会：科学研究費助成事業 若手研究(B)

  研究期間 : 2016年04月 -2018年03月 

  代表者 : 平井 健二

   

  本研究では、配位高分子の加熱分解によってナノ・マイクロスケールの無機構造体の合成法を開発した。(i)右巻きと左巻きの螺旋状配位高分子から螺旋状の金属硫化物の合成に成功した。このらせん状の金属硫化物は円偏光二色性を示し、ナノスケールの形状に依存した光学特性を示した。(ii)配位高分子ナノワイヤから光触媒能を有する金属硫化物ナノワイヤの合成に成功した。得られた金属硫化物ナノワイヤは表面が有機保護剤で被覆されていないため、基質がアクセスしやすく、可視光水素発生の触媒能において、従来法のナノワイヤよりも高い活性を示した。これらの結果より、配位高分子を前駆体とした合成法の優位性を示すことが出来た。
• 量子ドットの異方的架橋による２次元規則配列の創出

  村田学術振興財団 研究助成

  研究期間 : 2016年06月 -2017年05月 

  代表者 : 平井 健二
• CdS/Grapheneコンポジットナノワイヤによる可視光CO2還元

  一樹工業技術奨励会 研究助成金

  研究期間 : 2016年06月 -2017年03月 

  代表者 : 平井 健二
• 錯体結晶を前駆体とした酸化チタンのアニオンドーピング

  総合工学振興財団 研究奨励金

  研究期間 : 2015年08月 -2016年03月 

  代表者 : 平井 健二
• チタン錯体を前駆体とした酸化チタンへのアニオンドープ法の確立

  北海道科学技術振興センター 若手研究人材・ネットワーク育成補助金

  研究期間 : 2015年07月 -2016年03月 

  代表者 : 平井 健二
• 配位空間を用いたナノ粒子配列の自在制御

  日本学術振興会：海外特別研究員

  研究期間 : 2013年04月 -2014年10月 

  代表者 : 平井 健二
• 多孔性金属錯体を用いた応答性錯体インターフェイスの構築

  日本学術振興会：特別研究員（DC1）

  研究期間 : 2010年04月 -2013年03月 

  代表者 : 平井 健二

   

  金属イオンと有機配位子が自己集合的に組み上がることで構築される多孔性配位高分子(PCP)は、吸蔵材、分離材、触媒材料として高い特性を示すことが明らかになってきており、近年精力的に研究が行われている。本研究課題では電極基板上でPCPを結晶化させ、その規則的なナノ細孔を利用した機能性デバイスの創出を目指している。 最終年度は以下の3項目において成果が得られた。 1.多孔性配位高分子を用いた複合粒子の作成 PCPでは金属イオンや有機配位子を様々に代えることで、細孔特性を自在に設計することが可能である。同形の骨格構造を有するPCPをエピタキシャル成長によって複合化することで、コアシェル型の構造体の作成を行った。コア結晶には蛍光発光を有するPCPを、シェル結晶にはゲスト選択性を有するPCPを用いた。この組み合わせによって得られたコアシェル型PCPは、選択的にゲスト分子を取り込み、蛍光発光を示すことが明らかとなった。センサー粒子としての応用が期待できる。 2.基板上への多孔性配位高分子の固定化 一般に金属酸化物は成型が容易であるため、薄膜化やパターニングが非常に容易である。本課題では酸化アルミニウムと有機配位子を反応させることによって、基板表面でのPCP合成を行った。得られたPCPは酸化アルミニウムの形状を維持しており、電極表面に固定化する方法として非常に有望であることが明らかとなった。 3.多孔性配位高分子を用いたPCPデバイス 重量変化を振動数の変化として検出することが可能な水晶振動子マイクロバランス(QCM)の電極表面上でPCPを薄膜化し、PCP/QCMハイブリッドセンサーを作成した。PCPは蒸気を吸着し、重量が増加するため、PCP/QCMハイブリッドセンサーによって有機分子の存在を検出することが出来る。QCM上のPCP薄膜を複合膜にすると上記選択性が向上する結果も得られており、1の結果と組み合わせることで、高度なセンサーデバイスの作成が可能となった。

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