Details of the Researcher

PHOTO

Kohei Okubo
Section
Institute of Multidisciplinary Research for Advanced Materials
Job title
Assistant Professor
Degree

  • Ph.D (Engineering) (Tohoku University)

e-Rad No.
11025305

Research History 1

  • 2025/04 - Present
    Tohoku University　Institute of Multidisciplinary Research for Advanced Materials　Assistant Professor

Education 1

  • Tohoku University　Graduate School of Engineering　Department of Biomolecular Engineering

    2024/04 - 2025/03

Research Interests 3

  • 機能性有機材料

  • 超分子化学

  • 高分子化学

Research Areas 2

  • Nanotechnology/Materials / Polymer materials /

  • Nanotechnology/Materials / Organic functional materials /

Papers 14

  1. Synthesis of High-Purity Porous Organic Polymers and Exploration of Their Inherent Functionality Invited Peer-reviewed

    Kohei Okubo, Kotaro Omote, Hitoshi Kasai, Kouki Oka

    ACS Applied Materials & Interfaces　2026/03/25

    DOI： 10.1021/acsami.6c00001 　

  2. Anion size-dependent carbon dioxide adsorption capacity in high-purity diallyldimethylammonium-based poly(ionic liquid)s Invited Peer-reviewed

    Kohei Okubo, Showa Kitajima, Hitoshi Kasai, Kiyotaka Maruoka, Yuta Takahashi, Yoko Teruuchi, Minoru Takeuchi, Kazuhiko Igarashi, Kouki Oka

    Reaction Chemistry & Engineering　2026

    DOI： 10.1039/D5RE00535C 　

  3. Exploring the advances in 2D materials as a quest for energy storage electrode materials Invited Peer-reviewed

    Sebin Kariachan, Joshin Shibu, Prajitha Velayudhan, Sisanth Krishnageham Sidharthan, Pravitha Velayudhan, Sanu Mathew Simon, Hitoshi Kasai, Kohei Okubo, Sabu Thomas, Kouki Oka, Jibin Keloth Paduvilan

    RSC Advances　16　10847-10886　2026

    DOI： 10.1039/D5RA07292A 　

  4. Water-resistant redox-active metal–organic framework Peer-reviewed

    Ryota Akai, Showa Kitajima, Kohei Okubo, Nobuyuki Serizawa, Hirotomo Nishihara, Hitoshi Kasai, Kouki Oka

    Nature Communications　2025/12/01

    DOI： 10.1038/s41467-025-65849-y 　

  5. Hydroquinone-substituted polyallylamine: redox capability for aqueous polymer–air secondary batteries and recyclability Peer-reviewed

    Kouki Oka, Showa Kitajima, Kohei Okubo, Kiyotaka Maruoka, Yuta Takahashi, Yoko Teruchi, Minoru Takeuchi, Kazuhiko Igarashi, Hitoshi Kasai

    Polymer Journal　2025/11

    DOI： 10.1038/s41428-025-01085-x 　

  6. Iodine-Based Chemical Polymerization Enables the Development of Neat Amorphous Porous Organic Polymers Peer-reviewed

    Kohei Okubo, Haruka Yoshino, Hitoshi Miyasaka, Hitoshi Kasai, Kouki Oka

    ACS Applied Materials & Interfaces　2025/02/21

    Publisher: American Chemical Society (ACS)

    DOI： 10.1021/acsami.4c22197 　

    ISSN： 1944-8244

    eISSN： 1944-8252

  7. Triphenylamine‐Based Porous Organic Polymers with High Porosity: their High Carbon‐Dioxide Adsorption and Proton‐Conductivity Emergence Peer-reviewed

    Kohei Okubo, Showa Kitajima, Hitoshi Kasai, Kouki Oka

    Small　2025/02/17

    Publisher: Wiley

    DOI： 10.1002/smll.202410794 　

    ISSN： 1613-6810

    eISSN： 1613-6829

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    Abstract Amorphous porous organic polymers (POPs) feature high specific surface area and chemical and thermal stability; therefore, they are applied in various fields. It is previously reported that chemical polymerization using iodine as an oxidant enables the synthesis of amorphous POPs without impurities. In this study, an iodine‐based chemical polymerization method is employed to maximize the specific surface area of polytriphenylamine, a typical amorphous POP. Furthermore, 1,3,5‐tris[4‐(diphenylamino)phenyl]benzene, a monomer with three triphenylamine moieties connected by a benzene core, is used to increase the number of reaction points and construct a rigid structure. The resulting poly[1,3,5‐tris[4‐(diphenylamino)phenyl]benzene] (pTTPA) exhibited a high specific surface area. Using 200 equivalents of iodine resulted in a pTTPA with the largest Brunauer–Emmett–Teller (BET) specific surface area (2134.6 m2 g−1) among previously reported triphenylamine‐based amorphous POPs, and demonstrated a high CO2 adsorption capacity (3.31 mmol g−1 at 25 °C). Furthermore, pTTPA exhibited significant water–vapor adsorption when the BET specific surface area reached 1500 m2 g−1, leading to the emergence of proton conductivity (e.g., 4.33 × 10−6 S cm−1 at 95% RH and 90 °C). The findings demonstrate that iodine‐based chemical polymerization enables the maximization of the porosity of amorphous POPs and the development of proton conductivity within them.

  8. Sustainable hydrogen production & storage cycle with dihydrolevoglucosenone (Cyrene™): Hydrogen fixing and release based on alcoholic fermentation with Baker's yeast and dehydrogenation Peer-reviewed

    Takumi Ichimura, Hiroki Maeda, Takuya Shimbayashi, Kohei Okubo, Masayuki Fukushima, Norimitsu Tohnai, Ken-ichi Fujita, Kouki Oka

    International Journal of Hydrogen Energy　72　815-819　2024/06

    Publisher: Elsevier BV

    DOI： 10.1016/j.ijhydene.2024.05.403 　

    ISSN： 0360-3199

  9. Breathing Metal–Organic Frameworks Supported by an Arsenic-Bridged 4,4′-Bipyridine Ligand Peer-reviewed

    Kazuma Kikuchi, Hiroi Sei, Kohei Okubo, Norimitsu Tohnai, Kouki Oka, Shun Dekura, Takashi Kikuchi, Hiroaki Imoto, Kensuke Naka

    Inorganic Chemistry　63　(9)　4337-4343　2024/02/16

    Publisher: American Chemical Society (ACS)

    DOI： 10.1021/acs.inorgchem.3c04570 　

    ISSN： 0020-1669

    eISSN： 1520-510X

  10. Spirobifluorene‐Based Porous Organic Salts: Their Porous Network Diversification and Construction of Chiral Helical Luminescent Structures Peer-reviewed

    Kohei Okubo, Kouki Oka, Keiho Tsuchiya, Atsunori Tomimoto, Norimitsu Tohnai

    Angewandte Chemie International Edition　63　(15)　2024/02/16

    Publisher: Wiley

    DOI： 10.1002/anie.202400475 　

    ISSN： 1433-7851

    eISSN： 1521-3773

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    Abstract Porous organic salts (POSs) are organic porous materials assembled via charge‐assisted hydrogen bonds between strong acids and bases such as sulfonic acids and amines. To diversify the network topology of POSs and extend its functions, this study focused on using 4,4′,4′′,4′′′‐(9,9′‐spirobi[fluorene]‐2,2′,7,7′‐tetrayl)tetrabenzenesulfonic acid (spiroBPS), which is a tetrasulfonic acid comprising a square planar skeleton. The POS consisting of spiroBPS and triphenylmethylamine (TPMA) (spiroBPS/TPMA) was constructed from the two‐fold interpenetration of an orthogonal network with pts topology, which has not been reported in conventional POSs, owing to the shape of the spirobifluorene backbone. Furthermore, combining tris(4‐chlorophenyl)methylamine (TPMA‐Cl) and tris(4‐bromophenyl)methylamine (TPMA‐Br), which are bulkier than TPMA owing to the introduction of halogens at the p‐position of the phenyl groups with spiroBPS allows us to construct novel POSs (spiroBPS/TPMA‐Cl and spiroBPS/TPMA‐Br). These POSs were constructed from a chiral helical network with pth topology, which was induced by the steric hindrance between the halogens and the curved fluorene skeleton. Moreover, spiroBPS/TPMA‐Cl with pth topology exhibited circularly polarized luminescence (CPL) in the solid state, which has not been reported in hydrogen‐bonded organic frameworks (HOFs).

  11. An expanded hydrogen-bonded organic framework formed by a tetrakis(terphenyl)ethene derivative Peer-reviewed

    Mao Yamaguchi, Mario de la Hoz Tomás, Ayano Fujiwara, Ryusei Oketani, Kohei Okubo, Kouki Oka, Norimitsu Tohnai, Abderrazzak Douhal, Ichiro Hisaki

    Bulletin of the Chemical Society of Japan　97　(1)　2024/01/11

    Publisher: Oxford University Press (OUP)

    DOI： 10.1093/bulcsj/uoae004 　

    ISSN： 0009-2673

    eISSN： 1348-0634

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    Abstract A low-density hydrogen-bonded organic framework (HOF) with channel aperture with dimensions of 33.8 Å × 55.2 Å was constructed from a tetrakis(terphenyl)ethene derivative. The structure was successfully characterized by single crystalline X-ray diffraction analysis. Although solvent molecules are included in the channel, the present framework is one of the HOFs with the largest aperture. The framework is based on H-bonded sql-networks that stack in an eclipse fashion. The interlayer interactions were thoroughly investigated on the basis of the crystal structure. Interestingly, thee analogues of tetraarylethene-based tetracarboxylic acids, including the title compounds, formed the same H-bonded sql-network as a lower-dimensional supramolecular motif. However, the motifs are assembled in completely different ways to give the corresponding three types of the framework, indicating the importance of precise design of the secondary interactions between the lower dimensional motifs. In solid state, the molecular unit of the constructed HOF shows a largely Stokes-shifted and strong emission due to a fast (< 15 ps) ICT and a relatively slower (90 ps) intermolecular PT reaction, while in DMF it exhibits a strong H-bond with the solvent.

  12. Tunable mechanochromic luminescence of benzofuran-fused pyrazine: effects of alkyl chain length and branching pattern Peer-reviewed

    Shotaro Nakamura, Kohei Okubo, Yuji Nishii, Koji Hirano, Norimitsu Tohnai, Masahiro Miura

    Journal of Materials Chemistry C　12　(7)　2370-2378　2024/01

    Publisher: Royal Society of Chemistry (RSC)

    DOI： 10.1039/d3tc04748b 　

    ISSN： 2050-7526

    eISSN： 2050-7534

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    Tuning the alkyl chains of bisbenzofuropyrazines allowed control over the on/off switching of mechanochromic luminescence and self-recovery rates.

  13. Stimuli‐Responsive Properties on a Bisbenzofuropyrazine Core: Mechanochromism and Concentration‐Controlled Vapochromism Peer-reviewed

    Shotaro Nakamura, Kohei Okubo, Yuji Nishii, Koji Hirano, Norimitsu Tohnai, Masahiro Miura

    Chemistry – A European Journal　29　(68)　2023/10/20

    Publisher: Wiley

    DOI： 10.1002/chem.202302605 　

    ISSN： 0947-6539

    eISSN： 1521-3765

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    Abstract Stimulus‐responsive organic materials with luminescence switching properties have attracted considerable attention for their practical applications in sensing, security, and display devices. In this paper, bent‐type bisbenzofuropyrazine derivatives, Bent‐H and Bent‐sBu, with good solubilities were synthesized, and their physical and optical properties were investigated in detail. Bent‐H gave three crystalline polymorphs, and they showed different luminescence properties depending on their crystal packing structures. In addition, Bent‐H exhibited mechanochromic luminescence in spite of its rigid skeleton. Bent‐sBu exhibited unique concentration‐dependent vapochromic luminescence. Ground Bent‐sBu was converted to blue‐emissive, green‐emissive, and green‐emissive high‐viscosity solution states at low, moderate, and high concentrations of CHCl3 vapor, respectively. This finding represents a concentration‐dependent multi‐phase transition with an organic solvent, which is of potent interest for application in sensing systems.

  14. Statically and dynamically flexible hydrogen-bonded frameworks based on 4,5,9,10-tetrakis(4-carboxyphenyl)pyrene Peer-reviewed

    Taito Hashimoto, Ryusei Oketani, Asato Inoue, Kohei Okubo, Kouki Oka, Norimitsu Tohnai, Kazuhide Kamiya, Shuji Nakanishi, Ichiro Hisaki

    Chemical Communications　59　(47)　7224-7227　2023/05

    Publisher: Royal Society of Chemistry (RSC)

    DOI： 10.1039/d3cc01877f 　

    ISSN： 1359-7345

    eISSN： 1364-548X

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    Pore shape of a pyrene-based HOF was statically and dynamically modulated by desorption and adsorption of the solvent molecules.

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Misc. 1

  1. 革新的なヨウ素化学重合法による高純度なπ共役高分子の合成とその潜在機能の開拓

    岡 弘樹, 大窪 航平

    アロマティックス　77　44-51　2025/04