Message(24)From Sendai to Taiwan remembering late Professor Tetsuo Nozoe

From Sendai to Taiwan remembering late Professor Tetsuo Nozoe:
“Exploratory research on time- and space-resolved spectroscopy and chemistry”

In 1966 I finished my undergraduate course in Department of Chemistry at Tohoku University in Sendai where I was so lucky to attend the classroom of organic chemistry by Prof. Tetsuo Nozoe. He retired from Tohoku University in 1966, so I can say we graduated simultaneously. I chose physical chemistry as a major and I started photochemistry research in the laboratory of Prof. Masao Koizumi and studied electronic structure of ?-radicals which are important as transient intermediates of dye photo-oxygenation/reduction by developing a computer program of quantum mechanical calculation besides their spectroscopic measurement. I thought a more photophysics-oriented topic should be fit to me and decided to shift to the laboratory of Prof. Noboru Mataga at Osaka University as a PhD student in 1968.

Laser was invented in 1960, and soon was introduced to chemistry. Prof. Mataga told me that all light sources would be replaced by lasers and new chemistry research would be opened by lasers. His prediction extremely stimulated me and now I believe that my scientific life for exploring new molecular phenomena induced by lasers was started at that time. In Osaka we succeeded in directly measuring the electronic absorption spectra of a weak charge-transfer (CT) complex in the excited singlet state by developing nanosecond electronic absorption spectroscopy system based on a Q-switched Ruby laser[1]. The excited singlet absorption spectra were very similar to absorption spectra of electron acceptor anion and donor cation of the CT complex, indicating that the excited state of weak CT complex is deemed to be an ion-pair. This was the first direct experimental confirmation on CT character in the excited state which was predicted by R. S. Mulliken[2], and received much attention from the relevant research fields. This small but early success convinced me the high potential of lasers in chemistry research, on which I decided to be a scientist.

In Prof. Mataga’s lab systematic studies on energy transfer, electron transfer, hydrogen atom/proton transfer, and exciplex formation of molecules in solution were carried out by developing nanosecond, picosecond, and femtosecond laser spectroscopy systems. I myself shifted from the studies to soft matters like polymer solution, polymer film, micro-particles, micro-crystals, colloid solution, then to nanoparticles and nanocrystals. Time-resolution of total internal reflection, specular reflection, and diffuse reflection were improved by us and applied to clarify their photophysical and photochemical processes. These soft matter systems are in principle inhomogeneous, which pushed us strongly to think of space-resolved spectroscopy and chemistry.

In 1988, JRDC (Research Development Corporation of Japan), later reorganized as JST (Japan Science and Technology Agency), provided me a biggest fund of ERATO (Exploratory Research for Advanced Science and Technology) Project, on which I started Masuhara ERATO “Microphotoconversion” Project. We considered what is the next advantage of lasers in chemistry after time-resolved spectroscopy and came to the conclusion that both time- and space-resolutions should be satisfied simultaneously to understand chemical dynamics at individual positions. During the Project term of 1988 October?1994 March, many researchers and engineers including Drs. Noboru Kitamura, Hirosaki Misawa, Keiji Sasaki, Naoto Tamai, Hiroyuki Sugimura, Kiyoharu Nakatani, Kenji Kamada, Tsuyoshi Asahi et al. (now they are professors or PI as established scientists) developed various time- and space-resolved spectroscopy and explored new chemical phenomena. We were the first group systematically combining pulsed lasers and microscopes for chemistry research and the conclusion of our discussion was always “We are studying on how to study”, which may be our ANECDOTE. Our accomplishments were summarized as 1) optical manipulation and creation, 2) microfabrication and functionalization, 3) dynamic microspectroscopy, 4) microphotochemistry, and 5) microelectrochemisty and microphotoconversion. These results were summarized at the Proceedings of the JRDC-KUL (Katholiche Universiteit Leuven) Joint International Symposium and Published as a book on “Microchemistry: Spectroscopy and Chemistry in Small Domains” from North Holland in 1944. The similar content was published also in Japanese as “Microchemistry: Manipulating reactions in small volume” from Kagaku Dojin Publisher in Kyoto. We still are proud that the Project and these books were the first ahead of the world of chemistry on micrometer-sized volume.

Through these studies we found and analyzed various new molecular phenomena in micrometer-sized domain, which led us to study spectroscopy and chemistry in nanometer-sized volumes. Although I am a chemist, I was offered a laboratory in Department of Applied Physics of Osaka University in 1991, where our research subjects on molecular systems were summarized as 1) nano-spectroscopy and nano-photochemistry, 2) dynamics and application of nano-ablation, and 3) nano-manipulation. Among these studies on laser nano chemistry, we consider that laser-induced crystallization of proteins and amino acids have given highest impact. We proposed that photomechanical mechanism of femtosecond laser ablation involving cavitation is responsible to protein crystal nucleation[3]. On the other hand, high intensity CW laser irradiation under a microscope exerted a force oriented to the focal point upon micro- and nano-objects without photon absorption. This optical trapping are widely recognized as a tool of cell manipulation and of cooling atoms in biology and physics, respectively, while no chemist has utilized it fully. By systematic studies extended for long term, however, we succeeded in laser trapping crystallization in 2007[4].

We consider that laser trapping crystallization of molecular systems is very unique and most promising as a research on time- and space- resolved spectroscopy and chemistry. By systematic studies on molecular aggregates, polymers, micelles, polystyrene and gold nanoparticles dyes, amino acids, and proteins with Drs. Keiji Sasaki, Hiroyuki Yoshikawa, Teruki Sugiyama, and Kenichi Yuyama, we have come to the understanding that the laser trapping phenomena can be classified into Just Trapping, Extended Trapping, and Nucleation and Growth. The concentration increase and anisotropic orientation realized at the focus expand to the outside sometimes up to millimeter range under certain conditions, giving one single crystal at the focus upon laser irradiation. Thus time- and space-resolved controllability enables us to understand dynamics and mechanism of crystallization and to control crystal polymorph including optical chirality. Recently this study is being extended to amyloid fibril formation. Our chemistry is completely different from non-benzenoid chemistry developed by Prof. Tetsuo Nozoe in Taipei, Taiwan for 1922-1948[5], but we try to demonstrate the originality and uniqueness in our work similarly in Hsinchu, Taiwan.

[1] H. Masuhara, N. Mataga, Chem. Phys. Lett., 1970, 6, 608
[2] R. S. Mulliken, W. B. Person, “Molecular Complexes”, Wiley-Interscience, New York-London, 1969
[3] H. Adachi, K. Takano, Y. Hosokawa, T. Inoue, Y. Mori, H. Matsumura, M. Yoshimura, Y. Tsunaka, M. Morikawa, S. Kanaya, H. Masuhara, Y. Kai, T. Sasaki, Jpn. J. Appl. Phys., 2003, 42, L798
[4] T. Sugiyama, T.Adachi, H. Masuhara, Chem. Lett., 2007, 36, 1480
[5] T. Nozoe, “Seventy Years in Organic Chemistry” (Ed.: J. I. Seeman), American Chemical Society, Washington, D.C., 1991

(The Chemical Record NOZOE Commentary for Autograph Books)

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