Mar. 2022, 応用物理学会フォトニクス奨励賞　　　　　　　　　　　　　　　

Sep. 2021, 第3 回 物質・デバイス共同研究賞　　　　　　　　　　　　　　　

Oct. 2020, 新化学技術研究奨励賞　　　　　　　　　　　　　　　

Jun. 2013, Reaxys Ph.D. Prize 2013 Finalist　　　　　　　　　　　　　　　

Mar. 2012, The 4th HOPE Meeting Unique Presentation Award　　　　　　　　　　　　　　　

Mar. 2012, The 4th HOPE Meeting Best Poster Award　　　　　　　　　　　　　　　

Aug. 2010, 錯体化学若手の会夏の学校2010 学生講演賞　　　　　　　　　　　　　　　

Sep. 2009, 第59回錯体化学討論会 ポスター賞　　　　　　　　　　　　　　　

Sep. 2009, 第62回コロイドおよび界面化学討論会 ポスター賞　　　　　　　　　　　　　　　

Jun. 2009, 第2 回京都大学融合ナノ基盤工学研究者交流会 奨励賞　　　　　　　　　　　　　　　

Molecular Assembly in Optical Cavities
Kenji Hirai, Hiroshi Uji-i
Chemistry - An Asian Journal, Oct. 2024, [Peer-reviewed], [Invited], [Lead author, Corresponding author], [International Magazine]
English, Scientific journal

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, 29 May 2024, [Peer-reviewed], [Invited], ［Internationally co-authored］, [International Magazine]
English, Scientific journal

Mechanical Properties of Modulative Undulating Layers in Two-Dimensional Metal–Organic Frameworks
Yuudai Iwai, Sotaro Kusumoto, Ryo Suzuki, Masaru Tachibana, Kazuki Komatsu, Takashi Kikuchi, Saori I. Kawaguchi, Hirokazu Kadobayashi, Yuji Masubuchi, Yuzuki Yamamoto, Yoshiki Ozawa, Masaaki Abe, Kenji Hirai, Benjamin Le Ouay, Masaaki Ohba, Ryo Ohtani
Chemistry of Materials, 36, 11, 5446, 5455, American Chemical Society (ACS), 21 May 2024, [International Magazine]
Scientific journal

Optical Cavity Design and Functionality for Molecular Strong Coupling
Kenji Hirai, James Andell Hutchison, Hiroshi Uji-i
Chemistry – A European Journal, Wiley, 08 Nov. 2023, [Peer-reviewed], [Invited], [Lead author, Corresponding author], ［Internationally co-authored］, [International Magazine]
English, Scientific journal, 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, Wiley, 30 Aug. 2023, [Peer-reviewed], ［Internationally co-authored］, [International Magazine]
English, Scientific journal, 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, Royal Society of Chemistry (RSC), Aug. 2023, [Peer-reviewed], ［Internationally co-authored］, [International Magazine]
English, Scientific journal, 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, American Chemical Society (ACS), 22 Jul. 2023, [Peer-reviewed], [International Magazine]
English, Scientific journal

Molecular Chemistry in Cavity Strong Coupling
Kenji Hirai, James A. Hutchison, Hiroshi Uji-i
Chemical Reviews, 123, 13, 8099, 8126, American Chemical Society (ACS), 30 Jun. 2023, [Peer-reviewed], [Invited], [Lead author, Corresponding author], ［Internationally co-authored］, [International Magazine]
Scientific journal

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, American Chemical Society (ACS), 23 May 2023, [Peer-reviewed], ［Internationally co-authored］, [International Magazine]
Scientific journal

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, Wiley, 21 May 2023, [Peer-reviewed], [Corresponding author], ［Internationally co-authored］, [International Magazine]
English, Scientific journal

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, Royal Society of Chemistry (RSC), 2023, [Peer-reviewed], [Corresponding author], ［Internationally co-authored］, [International Magazine]
English, Scientific journal, 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, American Chemical Society ({ACS}), 09 Dec. 2022, [Peer-reviewed], ［Internationally co-authored］, [International Magazine]
English, Scientific journal

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, Jun. 2022, [Peer-reviewed], [Lead author, Corresponding author], ［Internationally co-authored］, [International Magazine]
English, Scientific journal, 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, American Chemical Society (ACS), 05 May 2022, [Peer-reviewed], ［Internationally co-authored］, [International Magazine]
Scientific journal

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, Royal Society of Chemistry ({RSC}), 2022, [Peer-reviewed], [Corresponding author], ［Internationally co-authored］, [International Magazine]
English, Scientific journal, 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, Royal Society of Chemistry (RSC), 2022, [Peer-reviewed], ［Internationally co-authored］, [International Magazine]
English, Scientific journal, 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, Royal Society of Chemistry (RSC), 2022, [Peer-reviewed], ［Internationally co-authored］, [International Magazine]
English, Scientific journal, 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, Springer Science and Business Media LLC, Dec. 2021, [Peer-reviewed], [International Magazine]
English, Scientific journal, 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, American Chemical Society (ACS), 07 Sep. 2021, [Peer-reviewed], ［Internationally co-authored］, [International Magazine]
English, Scientific journal, 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, Royal Society of Chemistry (RSC), 10 Aug. 2021, [Peer-reviewed], [Lead author, Corresponding author], ［Internationally co-authored］, [International Magazine]
English, Scientific journal,

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, SPIE, 01 Aug. 2021, [Peer-reviewed], [Invited], [Lead author, Corresponding author], ［Internationally co-authored］, [International Magazine]
International conference proceedings

Polariton Chemistry in Cavity Vacuum Fields
Kenji Hirai, Hiroshi Uji-i
Chemistry Letters, 50, 4, 727, 732, The Chemical Society of Japan, 05 Apr. 2021, [Peer-reviewed], [Invited], [Lead author, Corresponding author], ［Internationally co-authored］, [International Magazine]
English, Scientific journal, 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, American Chemical Society (ACS), 30 Nov. 2020, [Peer-reviewed], ［Internationally co-authored］, [International Magazine]
Scientific journal

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, Wiley, 05 Oct. 2020, [Peer-reviewed], ［Internationally co-authored］, [International Magazine]
English, Scientific journal, 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, American Chemical Society (ACS), 28 Aug. 2020, [Peer-reviewed], ［Internationally co-authored］, [International Magazine]
English, Scientific journal, 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, Wiley, Aug. 2020, [Peer-reviewed], [Invited], [Lead author, Corresponding author], ［Internationally co-authored］, [International Magazine]
English, Scientific journal, 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, 10 Mar. 2020, [Peer-reviewed], ［Internationally co-authored］, [International Magazine]
English, Scientific journal

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, 22 Jan. 2020, [Peer-reviewed], [Lead author, Corresponding author], ［Internationally co-authored］, [International Magazine]
English, 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, Springer Singapore, 2020, [Peer-reviewed], [Invited], ［Internationally co-authored］, [International Magazine]
In book

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, Royal Society of Chemistry (RSC), 2020, [Peer-reviewed], [Corresponding author], ［Internationally co-authored］, [International Magazine]
English, Scientific journal,

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, Royal Society of Chemistry (RSC), 2020, [Peer-reviewed], [Lead author, Corresponding author], ［Internationally co-authored］, [International Magazine]
English, Scientific journal,

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, ROYAL SOC CHEMISTRY, Sep. 2019, [Peer-reviewed], ［Internationally co-authored］, [International Magazine]
English, Scientific journal, 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, [Peer-reviewed], [International Magazine]
Scientific journal

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, AMER CHEMICAL SOC, Jun. 2017, [Peer-reviewed], [Lead author, Corresponding author], ［Internationally co-authored］, [International Magazine]
English, Scientific journal, 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, WILEY-V C H VERLAG GMBH, May 2017, [Peer-reviewed], [Last author, Corresponding author], [International Magazine]
English, Scientific journal, 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, ROYAL SOC CHEMISTRY, May 2017, [Peer-reviewed], [Lead author, Corresponding author], [International Magazine]
English, Scientific journal, 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, AMER CHEMICAL SOC, Nov. 2016, [Peer-reviewed], ［Internationally co-authored］, [International Magazine]
English, Scientific journal, 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, NATURE PUBLISHING GROUP, Dec. 2015, [Peer-reviewed], [Lead author, Corresponding author], [International Magazine]
English, Scientific journal, 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, WILEY-V C H VERLAG GMBH, Jul. 2015, [Peer-reviewed], [Lead author], ［Internationally co-authored］, [International Magazine]
English, Scientific journal, 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, AMER CHEMICAL SOC, Oct. 2014, [Peer-reviewed], [Lead author], [International Magazine]
English, Scientific journal, 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
Takuo Wakaoka, Kenji Hirai, Koji Murayama, Yoshihiko Takano, Hiroshi Takagi, Shuhei Furukawa, Susumu Kitagawa
JOURNAL OF MATERIALS CHEMISTRY C, 2, 35, 7173, 7175, ROYAL SOC CHEMISTRY, Sep. 2014, [Peer-reviewed]
English, Scientific journal, 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, AMER CHEMICAL SOC, Apr. 2014, [Peer-reviewed]
English, Scientific journal, 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
Kenji Hirai, Paolo Falcaro, Susumu Kitagawa, Shuhei Furukawa
METAL-ORGANIC FRAMEWORKS FOR PHOTONICS APPLICATIONS, 157, 167, 186, SPRINGER, 2014, [Peer-reviewed], [Invited], [Lead author], ［Internationally co-authored］, [International Magazine]
English, In book, 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, ROYAL SOC CHEMISTRY, 2014, [Peer-reviewed], [Lead author], [International Magazine]
English, Scientific journal, 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, WILEY-V C H VERLAG GMBH, 2013, [Peer-reviewed]
English, Scientific journal

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, AMER ASSOC ADVANCEMENT SCIENCE, Jan. 2013, [Peer-reviewed]
English, Scientific journal, 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, ROYAL SOC CHEMISTRY, 2013, [Peer-reviewed], [Lead author], [International Magazine]
English, Scientific journal, 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, NATURE PUBLISHING GROUP, Aug. 2012, [Peer-reviewed]
English, Scientific journal, 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, ROYAL SOC CHEMISTRY, 2012, [Peer-reviewed], [Lead author], [International Magazine]
English, Scientific journal, 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, ROYAL SOC CHEMISTRY, 2012, [Peer-reviewed], [Lead author], [International Magazine]
English, Scientific journal, 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, AMER CHEMICAL SOC, Aug. 2011, [Peer-reviewed], ［Internationally co-authored］, [International Magazine]
English, Scientific journal, 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, AMER CHEMICAL SOC, Aug. 2011, [Peer-reviewed], [International Magazine]
English, Scientific journal, 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, ROYAL SOC CHEMISTRY, 2011, [Peer-reviewed], ［Internationally co-authored］, [International Magazine]
English, Scientific journal, 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, WILEY-BLACKWELL, 2011, [Peer-reviewed], [Lead author], [International Magazine]
English, Scientific journal

Coordinatively Immobilized Monolayers on Porous Coordination Polymer Crystals
Mio Kondo, Shuhei Furukawa, Kenji Hirai, Susumu Kitagawa
ANGEWANDTE CHEMIE-INTERNATIONAL EDITION, 49, 31, 5327, 5330, WILEY-V C H VERLAG GMBH, 2010, [Peer-reviewed], [International Magazine]
English, Scientific journal

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, WILEY-V C H VERLAG GMBH, 2009, [Peer-reviewed], [International Magazine]
English, Scientific journal

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, ROYAL SOC CHEMISTRY, 2009, [Peer-reviewed], [International Magazine]
English, Scientific journal, 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.

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, Jun. 2023, [Invited], [Lead author, Last author], [Domestic magazines]
Japanese, Introduction scientific journal

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, May 2022, [Invited], [Lead author, Last author, Corresponding author], [Domestic magazines]

光共振器の中の化学反応　　　　　　　　　　　　　　　
平井健二, 光学, 51, 28, 33, Jan. 2022, [Peer-reviewed], [Invited], [Lead author, Last author, Corresponding author], [Domestic magazines]

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, Nov. 2021, [Peer-reviewed], [Invited], [Lead author, Last author, Corresponding author], [Domestic magazines]
Japanese

Modulation of Chemical Reactions in an Optical Cavity　　　　　　　　　　　　　　　
Kenji Hirai, 化学 2020年6月号, 12, 15, May 2020, [Lead author, Last author, Corresponding author]
Japanese

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

Creation and Application of Coordination Nano Space
平井 健二, 北川 進, 科学と工業, 86, 5, 151, 155, May 2012, [Lead author]
大阪工研協会, Japanese

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
日本表面科学会, Japanese

Multifunctional Porous Crystals by Hybridizing Coordination Polymers　　　　　　　　　　　　　　　
Kenji Hirai, Osami Sakata, Susumu Kitagawa, Shuhei Furukawa, SPring-8 Research Frontiers 2011, 84, 85, 2011

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

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

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, 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, Oct. 2019, 9784861047695, 639p, Japanese, Scholarly book

配位空間の化学 : 最新技術と応用
シーエムシー出版, Oct. 2009, 9784781301358, viii, 345p, Japanese

情報エレクトロニクス（電気回路）演習　　　　　　　　　　　　　　　
北海道大学工学部情報エレクトロニクス学科
2021 - Present

応用物性工学　　　　　　　　　　　　　　　
北海道大学工学部情報エレクトロニクス学科
2018 - Present

生体情報工学演習II　　　　　　　　　　　　　　　
北海道大学工学部情報エレクトロニクス学科
2018 - Present

ナノマテリアル特論　　　　　　　　　　　　　　　
北海道大学大学院情報科学院
2018 - Present

生体情報工学実験I　　　　　　　　　　　　　　　
北海道大学工学部情報エレクトロニクス学科
2021 - 2022

生体情報工学実験II　　　　　　　　　　　　　　　
北海道大学工学部情報エレクトロニクス学科
2020 - 2022

物理学I　　　　　　　　　　　　　　　
北海道大学全学共通科目
2019 - 2022

Strong Coupling at Meso-Hierarchy
Grants-in-Aid for Scientific Research
Apr. 2023 - Mar. 2028
雲林院 宏, 平井 健二, 五月女 光
Japan Society for the Promotion of Science, Grant-in-Aid for Transformative Research Areas (A), Hokkaido University, 23H04877

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
科学研究費助成事業
Apr. 2024 - Mar. 2027
平井 健二
日本学術振興会, 基盤研究(B), 北海道大学, 24K01447

光共振器を用いた結晶化を誘導する方法の開発　　　　　　　　　　　　　　　
科学研究費助成事業
May 2024 - Mar. 2026
平井健二
日本学術振興会, 挑戦的研究（萌芽）, Principal investigator, 24K21750

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
Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (B)
Apr. 2021 - Mar. 2024
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。
Japan Society for the Promotion of Science, Grant-in-Aid for Scientific Research (B), Hokkaido University, 21H01899

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
Nov. 2022 - Nov. 2023
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
Grants-in-Aid for Scientific Research Challenging Research (Exploratory)
Jul. 2020 - Mar. 2023
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。
Japan Society for the Promotion of Science, Challenging Research (Exploratory), Hokkaido University, 20K21200

ラビ分裂による化学反応操作法の確立
Precursory Research for Embryonic Science and Technology
Oct. 2018 - Mar. 2022
平井 健二
Japan Society for the Promotion of Science, Principal investigator, Competitive research funding

Laser Heating for Three-Dimensional Material Synthesis
Grants-in-Aid for Scientific Research
Apr. 2018 - Mar. 2021
Hirai Kenji
The methodology to synthesize functional materials at the desired positions is essential to fully utilize their functionality. In this project, we prepared silver nanowire (AgNW) where a gold nanoparticle (AuNP) is deposited. By manipulating AgNW and laser irradiation on AuNP, the heating from AuNP is spatially controllable. This methodology enables to synthesize ZnO and metal-organic frameworks (MOFs) at desired positions.
Japan Society for the Promotion of Science, Grant-in-Aid for Scientific Research (B), Hokkaido University, 18H01948

Manipulation of Self-Assembly by Vibrational Excitation
Grants-in-Aid for Scientific Research Challenging Research (Exploratory)
Jun. 2018 - Mar. 2020
Hirai Kenji
Vibrational strong coupling (VSC) has recently emerged as a novel method for modulating molecular and material properties. It was recently reported that VSC of solvent molecules influences the kinetics of chemical reactions. This suggests that VSC can be used to control other solution-based processes such as crystallization from solution, though they have not been explored yet. As a model system, we investigate the effect of VSC of solvent molecules in crystallization of metal-organic frameworks, namely pseudopolymorphism between ZIF-8 and ZIF-L. ZIF-8 was selectively obtained under VSC of the OH stretching vibration in water, whereas mixtures of ZIF-8 and ZIF-L were obtained without VSC. This work demonstrates that tuning the quantum electromagnetic environment of solutions can bias molecular self-assembly leading to macroscopic material outcomes.
Japan Society for the Promotion of Science, Challenging Research (Exploratory), Hokkaido University, 18K19085

Coordination Polymers as Sacrificial Precursors for Nano- and Micro-structured Inorganic Solids
Grants-in-Aid for Scientific Research Grant-in-Aid for Young Scientists (B)
Apr. 2016 - Mar. 2018
Hirai Kenji
We have demonstrated that nano- micro-structured coordination polymers can be used as precursors for inorganic nano- and microstructures.
We synthesized chiroptical Ag2S-based nanohelices derived from helical coordination polymers (CPs). Right- and left-handed coordination helices used as precursors were prepared from l- and d-glutathione with Ag+ and Cu2+. Pyrolysis of the coordination helices gave right- and left-handed helices of Cu0.12Ag1.94S/C, which exhibit chiroptical activity spanning the entire visible light region.
In the second project, we have demonstrated that CPs can be used as precursors for photocatalysts without stabilizers. The pyrolysis of CP nanowires of [Cd(l‐cysteinate)]n gave CdS/C nanowires that exhibit photocatalytic activity for hydrogen generation superior to CdS nanowires with organic stabilizers.
Japan Society for the Promotion of Science, Grant-in-Aid for Young Scientists (B), Hokkaido University, 16K17875

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
Jun. 2016 - May 2017
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
Jun. 2016 - Mar. 2017
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
Aug. 2015 - Mar. 2016
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
Jul. 2015 - Mar. 2016
平井 健二

配位空間を用いたナノ粒子配列の自在制御　　　　　　　　　　　　　　　
海外特別研究員
Apr. 2013 - Oct. 2014
平井 健二
日本学術振興会

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
特別研究員（DC1）
Apr. 2010 - Mar. 2013
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。
日本学術振興会, 特別研究員奨励費, 京都大学, 10J02257

リアクタ
Patent right, 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
特願2021-007115, 20 Jan. 2021
特開2021-178311, 18 Nov. 2021
Domestic, Domestic
29479358

Bachelor's degree program, School of Engineering

Master's degree program, Graduate School of Information Science and Technology

Doctoral (PhD) degree program, Graduate School of Information Science and Technology