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Ken-ichi Shinohara Associate Professor
School of Materials Science”ŹDepartment of Materials Science”¦New Materials Design and Synthesis”Ė
B.S. from Niigata University (1992), M.S. from Niigata University (1994), Ph.D. from Niigata University (1997)
Research Fellow of Japan Society for the Promotion of Science (JSPS) at Niigata University (1996-1997), Research Associate at Tohoku University (1997-2002), Associate Professor at Japan Advanced Institute of Science and Technology (2002-- ), Visiting Associate Professor at Tohoku University (2003-2004).
Functional Polymer Synthesis, Single-Molecule Imaging, Macromolecular Machines
Spectral Fluctuation of Single-Molecules of a Conjugated Polymer in a Solution
Polymer considered in this study is an extremely complicated example due to its generally varied and dynamic structure, so we have had difficulty in clearly defining the correlation between structure and function at the molecular level. In other words, questions such as "What kind of polymer structures indicate the molecular functions?" have been very difficult to clearly answer at the molecular level. This introduces uncertainty as to whether a proposed molecular design is beneficial or not when we are trying to synthesize novel conjugated polymers with improved functions at the molecular level. Therefore, we thought that if we could directly observe an individual molecular structure and its functionality for a single conjugated polymer, it might then become possible to keep this speculation to a minimum, thus enabling a very clear discussion of the relationship between the molecular structure and function at the molecular level. Their observation of a single molecular spectrum for a conjugated substituted poly(phenylenevinylene) in a polystyrene matrix have been reported, but this was not a in solvo system. If the direct measurement of single molecules of a conjugated polymer in solution can be achieved, the observation of unique phenomena can be expected, e.g., the host-guest interaction of single molecules, leading towards the development of novel systems consisting of molecular devices in solution. We have already reported the results of fluorescence imaging experiments conducted on single molecules of the conjugated poly(9,10-anthracenediyl-ethynylene-1,4-phenylene-ethynylene) [poly(AEPE)], which has a rigid-rod main chain, in a tetrahydrofuran (THF) solution at room temperature using a total internal reflection microscope (TIRFM). In the present study, we conducted single molecule fluorescence imaging and single molecule spectroscopy for conjugated poly(AEPE) having a rigid-rod main chain in methanol at room temperature, and we could successfully detect a unique light-emitting phenomenon which fluctuated dynamically with in the time-scale of several seconds.
The creation of the flexible molecular machine
What function does a synthetic polymer have in the single-molecular-level? Does it have such a dynamic multi-functions as protein which a kind of biopolymer? Mankind does not understand the fundamental properties of synthetic polymers yet and still cannot bring the maximum of capabilities out of them. Polymer is highly capable, useful and indispensable material. Especially, conjugated polymers investigated as advanced materials for photonic and electronic applications have made progress, and has caused an ever-increasing interest from both academic research and industrial development. The conjugated polymers are used as laser dyes, organic light-emitting diodes, and so on. In addition recently, there are some applications as an optical resolution membrane materials. Although conjugated polymers are very interesting and important materials, the mechanism in single-molecular-level of these photonic and electronic function are still not clear owing to the various and complicated structure of the conjugated system in the polymer molecules. Thus, the polymers are the complex system of molecules. Therefore, we thought that if direct observation of single molecule of conjugated polymer were achieved, the polymer function would be clear in molecular level toward the polymer functioning at single molecule unit, that is the single-molecule device. In the other, recently, imaging of single protein molecules using fluorescence microscopy has made remarkable progress after development of single fluorophore imaging methods which were used for specimen on an air-dried surface. Single fluorophores in aqueous solution have been imaged using a total internal reflection fluorescence microscope (TIRFM), in which the background fluorescence is greatly reduced, when a laser beam is totally reflected in the interface between the glass surface and solution, illumination is limited to only the vicinity near the glass surface. In our previous study, this single molecules imaging method was expanded to the organic polymer solution system for the direct observation of single molecules of photofunctional rigid-rod conjugated polymer that is a poly(aryleneethynylene) having anthracene units in the main chain. In this study, we report that single molecule imaging of a stereo-regular ¦Š-conjugated polymer and detection of single molecule slow-twinkling of the photoluminescence in tetrahydrofuran solution at room temperature for the first time.
Single-Molecule Imaging of Synthetic Polymer
¦Š-Conjugated polymers have been developed as advanced materials for photonic or electronic applications. If the ¦Š-conjugated polymer chain can be controlled in the higher order structure, novel functions at the molecular level will become available due to the unique ¦Š-electron system. Many studies confirming the fact that a ¦Š-conjugated polymer has a helical structure have already been completed. Most of these studies have provided us with data on molecular aggregates or data on the average of many molecules. Although we now understand that the main chain of the polymer takes the form of a helix, does one chain have both right- and left-handed helices? What is the ratio of the right-handed helices to the left-handed ones? What about the regions where the helix is reversed and how does it dynamically change? The answers already provided to all these fundamental questions have been based only on conjecture. Therefore, it is necessary to establish a technique that can determine the structure at the single-molecule level in order to achieve the above-mentioned objective. Here we show that a scanning tunneling microscope (STM) allows us to see the ¦Š-electron orbital of a chiral quaternary structure, where it was directly observed and its size was even measured with high resolution.
- Applied Scanning Probe Methods X - Biomimetics and Industrial Applications -, Chapter 31: Scanning Probe Microscope Application for Single Molecules in a ¦Š-Conjugated Polymer toward the Molecular Devices based on Polymer Chemistry,”¤Ken-ichi Shinohara”¤Springer (Berlin), ISBN: 978-3-540-74084-1”¤2008”¤pp 153-182
- Direct Observation of the Chiral Quaternary Structure in a ¦Š-Conjugated Polymer at Room Temperature”¤Ken-ichi Shinohara, Satoshi Yasuda, Gen Kato, Machiko Fujita, and Hidemi Shigekawa”¤J. Am. Chem. Soc. 123, 3619-3620 (2001), Editors' Choice, Science 292, 15 (2001).”¤2001
- Specific and reversible photochemical labeling of plasmid DNA using photoresponsive oligonucleotides containing 3-cyanovinylcarbazole”¤Kenzo Fujimoto, Kaoru Hiratsuka-Konishi, Takashi Sakamoto, Tomoko Ohtake, Ken-ichi Shinohara, and Yoshinaga Yoshimura”¤Mol. Biosyst.”¤8”¤491-494”¤2012
- Substitution Position Effect on Photoluminescence Emission and Chain Conformation of Poly(diphenylacetylene) Derivatives”¤Wang-Eun Lee, Chang-Jin Oh, Geun-Tae Park, Jin-Woo Kim, Heung-Jin Choi, Toshikazu Sakaguchi, Michiya Fujiki, Ayako Nakao, Ken-ichi Shinohara, Giseop Kwak”¤Chem. Commun.”¤46”¤6491-6493”¤2010
”žLectures and Presentations
- Direct Observation of Single-Molecular Macromolecule”¤Ken-ichi Shinohara”¤The Meeting at the Macromolecular Science and Engineering Center, University of Michigan (INVITED)”¤Ann Arbor, USA”¤March 9, 2011
- Single-Molecule Imaging and Synthetic Macromolecular Machines”¤Ken-ichi Shinohara”¤The 14th Asia Chemical Congress (ACC), INV-G1-24 (INVITED)”¤Bangkok, Thailand”¤Sep. 5-8, 2011
- Single-Molecule Imaging of Structure, Property, Reaction and Motion in a ¦Š-Conjugated Polymer Chain”¤Ken-ichi Shinohara”¤KEYNOTE LECTURE, 6th ISAMAP (International Symposium on Advanced Materialsin Asia-Pacific Rim)”¤Chulalongkorn University, Bangkok, Thailand”¤21-23 November, 2009
”žAcademic Society Affiliations
- Biophysics Society of Japan”¤Member”¤1998-
- American Chemical Society”¤Member”¤1994-
- The Society of Polymer Science, Japan”¤Member”¤1994-
- Member: The American Chemical Society (1992- )
- Committee: Colloquium of Tohoku Branch of the Society of Polymer Science, Japan (2001)
- Member: The Society of Polymer Science, Japan (1992- )
¢£Academic Awards Received
- Marquis Who”Ēs Who in the World, 2010 Edition”¤Marquis Who”Ēs Who LLC (New Providence, NJ, USA)
- Marquis Who's Who in Science and Engineering, 2008-2009, 10th Edition”¤Marquis Who”Ēs Who LLC (New Providence, NJ, USA)”¤2009
- Marquis Who's Who in Science and Engineering, 2008-2009, 10th Edition”¤Marquis Who's Who LLC (New Providence, NJ, USA)”¤2008