Emergent Molecular Function Research Team

Principal Investigator

PI Name Kazuo Takimiya
Degree D.Eng.
Title Team Leader
Brief Resume
1994 Ph.D., Hiroshima University
1994 Research Associate, Hiroshima University
1997 Visiting Researcher, Odense University, Denmark
2003 Associate Professor, Hiroshima University
2007 Professor, Hiroshima University
2012 Team Leader, Emergent Molecular Function Research Team, RIKEN
2013 Group Director, Emergent Molecular Function Research Group, Supramolecular Chemistry Division, RIKEN Center for Emergent Matter Science
2017 Professor, Tohoku University (-present)
2018 Team Leader, Emergent Molecular Function Research Team, Supramolecular Chemistry Division, RIKEN Center for Emergent Matter Science (-present)

Outline

Our research activity is based upon organic synthesis that can afford new organic materials utilized in optoelectronic devices, such as organic field-effect transistors (OFETs), organic solar cells (organic photovoltaics, OPVs), and organic thermoelectric devices (OTE). To this end, our team develops new organic materials, which can be designed and synthesized in order to have appropriate molecular and electronic structures for target functionalities. Our recent achievements are: 1) high-performance molecular semiconductors applicable to OFETs with the high mobilities, 2) new non-fullerene acceptors and their OPVs showing high power conversion efficiencies, and 3) new molecular design strategies to control packing structures of organic semiconductors.

Research Fields

Chemistry, Engineering, Materials Science

Keywords

Organic semiconductor
Pi-conjugated compound
Organic Synthesis
Organic field-effect transistor
Organic solar cells
Organic thermoelectric materials

Results

Development of high-mobility organic semiconductors by controlling molecular arrangement

Solid-state properties of organic semiconductors, e.g., carrier mobility, are largely dependent not only on the molecular structure but also packing structure and molecular orientation in the solid state. However, it is very difficult to predict and control the crystal structure at the stage of molecular design, and the development of methodologies for controlling the crystal structure of organic semiconductors is an important issue. We have found that it is possible to lead to a crystal structure suitable for high mobility by introducing a simple substituent such as a methylthio group at an appropriate position in the organic semiconductor skeleton. For example, When four methylthio groups were regio-selectively introduced into pyrene that crystalizes into a sandwich herringbone structure, the crystal structure changes dramatically into a brickwork structure, which enables two-dimensional conduction. The carrier mobility evaluated by using single-crystal field-effect transistors was higher than 30 cm2 V-1 s-1, which was among the highest for organic semiconductors.

Figure

Development of high-mobility organic semiconductors by controlling molecular arrangement

 

Control of packing structures of thienoacene-based organic semiconductors

Solid-state properties of organic semiconductors, e.g., carrier mobility, are largely dependent not only on the molecular structure but also packing structure and molecular orientation in the solid state. The packing structures of representative organic semiconductors, e.g. acenes and thienoacenes, are classified into a herringbone packing, which is characterized with a “T-shaped” edge-to-face structural motif. On the other hand, one of the most promising materials in the organic field-effect transistor realizing the highest mobility is rubrene, which affords another characteristic packing motif, so-called “pitched π-stack”, where the long-molecular axis are inclined so as to form partial π-stacking with end-to-face intermolecular interaction. Although control and prediction of the solid state structures from the molecular level are regarded as formidable task, we recently found that simple methylthionation on a series of thienoacenes selectively induces the rubrene-like “pitched π-stack” in the solid state. These results suggest that a proper molecular modification can pave the way to “artificial rubrene”, i.e., packing structure control of thienoacenes for high-performance organic semiconductors.

Figure

Control of packing structures of thienoacene-based organic semiconductors

Members

Kazuo Takimiya

Team Leader takimiya[at]riken.jp R

Masanori Sawamoto

Postdoctoral Researcher

Kirill Bulgarevich

Postdoctoral Researcher

Kohsuke Kawabata

Visiting Scientist

Daichi Watanabe

Technical Staff I

Shingo Horiuchi

Student Trainee

Publications

  1. K. Sumitomo, Y. Sudo, K. Kanazawa, K. Kawabata, and K. Takimiya

    Enantiopure 2-(2-ethylhexyl)dinaphtho 23-b:2’3′-f thieno 32-b thiophenes: synthesis single-crystal structure and a surprising lack of influence of stereoisomerism on thin-film structure and electronic properties

    Mater. Horiz. 9, 444-451 (2022)
  2. K. Kawabata, and K. Takimiya

    Quinoid-Aromatic Resonance for Very Small Optical Energy Gaps in Small-Molecule Organic Semiconductors: A Naphthodithiophenedione-oligothiophene Triad System

    Chem. Eur. J. 27, 15660-15670 (2021)
  3. K. Takimiya, K. Bulgarevich, M. Abbas, S. Horiuchi, T. Ogaki, K. Kawabata and A. Ablat

    Manipulation of Crystal Structure by Methylthiolation Enabling Ultrahigh Mobility in a Pyrene-Based Molecular Semiconductor

    Adv. Mater. 33, 2102914 (2021)
  4. Y. Wang, and K. Takimiya

    Naphthodithiophenediimide-Bithiopheneimide Copolymers for High-Performance n-Type Organic Thermoelectrics: Significant Impact of Backbone Orientation on Conductivity and Thermoelectric Performance

    Adv. Mater. 32, 2002060 (2020)
  5. C. Wang, D. Hashizume, M. Nakano, T. Ogaki, H. Takenaka, K. Kawabata, and K. Takimiya

    “Disrupt and Induce” Intermolecular Interactions to Rationally Design Organic Semiconductor Crystals: from Herringbone to Rubrene-like Pitched π-Stack

    Chem. Sci. 11, 1573 (2020)

Articles

お問い合わせ

2-1 Hirosawa, Wako, Saitama 351-0198 Japan

E-mail:
takimiya[at]riken.jp

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