Researcher Database

（Last updated : 2022-05-19 11:23:44）

NAGASAWA YUTAKA

Department / Course College of Life Sciences Department of Applied Chemistry

Title / Position Professor

Other Affiliations
1.	Graduate School of Life Sciences

Academic background
1.		Ph.D. (Science)

Subject of research
1.	Real time observation of chemical reactions by femtosecond time-resolved spectroscopy.

Research summary
Real time observation of chemical reactions by femtosecond time-resolved spectroscopy. As discussed below, I have developed the techniques of ultrafast time-resolved spectroscopy, and have conducted a study based on real time measurement of photochemical reaction dynamics in the condensed matters. 1. Ultrafast electron movement I developed a femtosecond fluorescence sum frequency generation method containing high time resolution, and directly measured electron movement reaction between solute and solvent in electron-donating solvent. While Marcus theory concerning electron movement suggested that the upper limit of ET reaction speed in the polar solvent was determined by solvent sum time, I identified that electron movement reaction can occur even in the ultrashort - hundreds of femtoseconds - time area, faster than solvent sum time, and found intramolecular reorientations faster than solvent sum as the driving force. 2. Imbalance between solvent sum dynamics and glass state I have developed various ultrafast time resolution measurement method such as peak shift measurement method of Three-pulse Photon Echo, and have identified solvent responses of various organic solvents with from subpicosecond to femtosecond high time resolution. For example, I conducted a study of electron movement in ion liquid, and found the solvent sum processes that occur continuously and hierarchically from subpicosecond to tens of nanoseconds. And I compared spectrum spread between in solution and in polymer glass, and found that solvent sum dynamics spreading in solution turns into static imbalance in the glass. 3. Electron and energy movements in biomolecules 　Also for energy and electron movements that occur in conjugated protein of photosynthesis system, I have conducted a study to apply ultrafast time resolution measurement techniques. With 3PEPS measurement, I identified imbalance between speed constant and system of excited energy movement in photosynthesis bacteria's antenna complex LH1 and its B820 subunit protein. Furthermore, for electron transport blue copper protein's plastocyanin, and for ligand from cysteine's atoms of sulfur to copper ion - ligand-to-metal charge transfer (LMCT) absorption band, I identified that its charge recombination occurs within 40 femtoseconds. I have detected a vibration mode as uniquely low as approximately 30 cm-1 that is considered skeletal vibration of protein being involved in the function. 4. Developing a new spectroscopy with Degenerated Four-Wave Mixing In order to identify the above elementary process of reaction, I have been also developing a new spectroscopy. Three-pulse Photon Echo (3PE) and Transient Grating (TG) are kinds of Degenerated Four-Wave Mixing (DFWM) method, and are the techniques that measure phase relaxation at electronic state and provide you with findings about linewidth enhancement of electronic spectrum in the condensed matters. In addition, when pulse as ultrashort as tens of femtoseconds is used, it can coherently induce molecule vibration as well. In 3PE method, I found that changing time lag between two pump lights can increase or decrease the amplitude of coherent vibration. 5. Developing and manufacturing femtosecond lasers and microspectroscopic systems Femtosecond Chromium with Cavity-dumper implemented: We manufactured forsterite (Cr:F) laser (oscillation wavelength: 1260 nm). With the second harmonic (630 nm), we achieved the world's highest performance of pulse width 25 fs, energy6 nJ. Furthermore, we implemented the near-infrared fundamental into microscopes to create high-order multiphoton microscopes that utilize three or four photon fluorescence. We also achieved single wavelength reversible reaction control that utilizes non-resonance 3- and 2-photon absorption of photochromic molecular system under the microscope.

Present specialized field
Physical chemistry (Keyword：Ultrafast spectroscopy, time-resolved spectroscopy, energy transfer, electron transfer, solvation, reaction dynamics, nuclear wavepacket dynamics)

Books
1.	2020	Ultrafast Energy Transfer of Biohybrid Photosynthetic Antenna Complexes in Molecular Assembly Systems │ Photosynergetic Responses in Molecules and Molecular Aggregates │ (Co-authored)

Papers
1.	2020	Enhanced light harvesting and photocurrent generation activities of biohybrid light–harvesting 1–Reaction center core complexes (LH1-RCs) from Rhodopseudomonas palustris │ J. Photochem. Photobio. A: Chem. │ ,pp.112790 (Co-authored)
2.	2020	Excited State dynamics of charge transfer complexes of fullerenes in an electron donating solvent │ (Co-authored)
3.	2020	Excited State dynamics of charge transfer complexes of fullerenes in an electron donating solvent │ J. Photochem. Photobio. A: Chem. │ 403,pp.112861 (Co-authored)
4.	2020	Reconstitution of 3-Acetyl Chlorophyll a into Light-Harvesting Complex 2 from the Purple Photosynthetic Bacterium Phaeospirillum molischianum │ ACS Omega │ 5 (12),pp.6817–6825 (Co-authored)
5.	2020	Sequential energy transfer driven by monoexponential dynamics in a biohybrid light-harvesting complex 2 (LH2) │ Photosynth. Res. │ 143,pp.115–128 (Co-authored)
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Academic conference presentation
1.	2019/11/21	Charge Separation and Photocurrent Generation of Biohybrid Light-Harvesting 1-Reaction Center Core Complex (LH1-RC) (3rd International Solar Fuels Conference (ISF-3)\nInternational Conference on Artificial Photosynthesis-2019 (ICARP2019))
2.	2019/11/21	Excitation Energy Transfer Mechanism of Chlorophyll Reconstituted LH2 Biohybrid (3rd International Solar Fuels Conference (ISF-3)\nInternational Conference on Artificial Photosynthesis-2019 (ICARP2019))
3.	2019/11/21	Excited State Dynamics of Charge Transfer Complexes of Fullurenes in Electron Donating Solvent (3rd International Solar Fuels Conference (ISF-3)\nInternational Conference on Artificial Photosynthesis-2019 (ICARP2019))
4.	2019/11/21	Femtosecond Time-Resolved Transient Absorption Spectroscopy of Reaction Center of Green Sulfur Bacteria: Elucidation of Primary Dynamics of Photosynthesis (3rd International Solar Fuels Conference (ISF-3)\nInternational Conference on Artificial Photosynthesis-2019 (ICARP2019))
5.	2019/11/21	Oxidation of B800 Bacteriochlorophyll a in LH2 Proteins from Purple Photosynthetic Bacteria Rhodoblastus acidophilus and Phaeospirillum molischianum (3rd International Solar Fuels Conference (ISF-3)\nInternational Conference on Artificial Photosynthesis-2019 (ICARP2019))
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Grants-in-Aid for Scientific Research -KAKENHI-
1.	1998/04 ～ 2001/03	MOLECULAR ASPECTS OF DYNAMICS IN REACTION PROCESSES AND MOLECULAR INTERACTIONS IN SOLUTION