My Scientific Journey and Colleagues
From Nanosecond Photochemistry to Optical Force Chemistry

July 7, 2021

Hiroshi Masuhara
National Yang Ming Chiao Tung University,
1001 Ta Hsueh Rd., Hsinchu 30010, Taiwan
E-mail: masuhara@masuhara.jp

ABSTRACT
Laser was invented in 1960 and soon introduced to chemistry research. We started time-resolved spectroscopy
and photochemistry and initial trial was focused to nanosecond and then picosecond electronic absorption
spectroscopy for studying molecular electronic excited states, charge separation in molecular complexes, andintermolecular electron transfer in solution. We considered that not only time-resolved but also space-resolved
chemistry would be important for future laser-based chemistry and combined pulsed lasers with optical
microscopes. Further we shifted from micro to nano and opened a new field of laser nanochemistry consisting ofspectroscopy, manipulation, crystallization, and ablation of organic molecules, proteins, nanoparticles, and so on.
Then we have explored many chemical phenomena induced by laser irradiation at solution surfaces, which has
opened a unique seminal study on optical force chemistry.
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１．Starting Chemistry in Sendai, Japan
I entered Tohoku Univ. in 1962 and joined the laboratory of Prof. Masao Koizumi (Late Emeritus Prof. of Tohoku
Univ.) of Physical Chemistry and Photochemistry in the fourth year of undergraduate. I think the reason why I
participated in the Lab of Prof. Koizumi was that I was trying to read “The Nature of the Chemical Bond” written
by Linus Pauling and translated into Japanese by Prof. Koizumi, and his large book “Survey of Photochemistry”(Figure 1). At that time, Profs. Tetsuo Nozoe and Koji Nakanishi were two giants in organic chemistry in Tohoku
Univ. and had a strong presence in the field of Natural Products Chemistry. However, I thought that theintermediate between physics (research on the theory of things) and chemistry (research on the abundance ofthings) was very interesting, and it fitted me. That is the reason I choose physical chemistry and I felt Prof. Koizumi
was a sincere scientist and real gentleman, However, his research life was more than what I, a vague young man,
had thought. Every morning, he walked from his home in Yagiyama to the Faculty of Science in Katahira andworked on a well-defined schedule, while he sometimes rushed to the toilet with his shirt outside on his back. I
remember, like as if it were just yesterday, that I had a strong impression from him about what research is andwhat research life is.
After that, I went on to a doctoral program at the Faculty of Engineering Science, Osaka Univ., and decided to try
to get a Ph.D. degree under the supervision of Prof. Noboru Mataga (Late Emeritus Prof. of Osaka Univ.). That
was in 1968. In front of the nanosecond ruby laser installed in that year, Prof. Mataga told me, “Lasers will replace
all light sources in the future, and photochemical research using lasers will have unlimited possibilities.” I was so
excited with his words. I became the first graduate student at Mataga Lab who obtained a degree in laser-based
research. My first work was to oscillate a nanosecond ruby laser stably. I realized I could be awarded to Ph.D. if
I could write papers unique to nanosecond lasers. So, I was very free to choose a theme. At this time, I think that
I enjoyed the real (true) fun of exploratory research. Since then, I have been studying molecular systems uniqueto lasers and working in the so-called interdisciplinary area, belonging to the departments of chemistry, synthetic
chemistry, polymer science, applied physics, life science, materials science, and applied chemistry. However, myresearch has been consistently laser-based molecular science and photochemistry. I think that there is no otherfield that enables pioneering research and the real thrill of physics and chemistry as much as physical chemistry.

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In 2021 I turned 77 years old. I am still conducting exploratory research using lasers and microscopes at the
National Yang Ming Chiao Tung Univ. (NYCU) in Hsinchu, Taiwan.

Figure 1(Left) L. Pauling, “The Nature of the Chemical Bond”(Translated to Japanese by M. Koizumi), Kyoritsu Shuppan, Tokyo, 1962
(Middle) M. Koizumi, “Survey of Photochemistry” (in Japanese), Asakura Shoten, Tokyo, 1963
(Right upper) N. Mataga, “Introduction to Photochemistry” (in Japanese), Kyoritsu Shuppan, Tokyo, 1975
(Right lower) N. Mataga, T. Kubota, “Molecular Interactions and Electronic Spectra”, Marcel-Dekker, 1970

２． Dye Photochemistry and Flash Photolysis Method at Koizumi Lab, Tohoku University (1965-1968)
Japanese lost many things during the World War II and we started almost from zero. I heard that Prof. Koizumi
considered on critical energy problem of future Japan, as we had and have no natural resource, and decided to
study photo-oxidation and reduction reactions of dye molecules aiming solar energy utilization. In 1965 when I
joined his laboratory, two methods were introduced and utilized to identify photochemical intermediates directly;
one was rigid matrix isolation method and the other was flash photolysis method. The former method was carriedout with ESR spectroscopy by Prof. Michio Okuda (Late Director of the Inst. of Environmental Science,
Environment Agency, Japan) and Dr. Shigeru Niizuma (Emeritus Prof. of Iwate Univ.). Prof. Okuda gave me thetheme of stably capturing and spectroscopy of the pi-radical of the dye intermediate and assigning its electronic
absorption spectrum. At that time all computer programs calculating for molecular electronic structure andelectronic transition must be developed by ourselves. Nobody in the Department of Chemistry in Sendai had any
experience in molecular electronic structure calculation at that time. Learning a lot from the books and reviews
written by Saburo Nagakura, Kenichi Fukui, and Haruo Hosoya groups and being helped by Yuji Mori, Kichisuke
Nishimoto, and Shigeyuki Aono. develop a program for calculating the open-shell electronic structure of thePariser-Parr-Pople method. I truly understood my situation and high potentiality of the Nagakura and the Fukui
Groups in the theoretical chemistry in Japan. Then, while saying that the middle of physics (research on thetheory of things) and chemistry (research on the abundance of things) is interesting, I wanted to shift toward thestudy of abundance of things.
The second method of flash photolysis was made possible by utilizing home-made flash lamp and pulse circuit
using vacuum tubes. In 1959, Drs. Shunji Kato (Late Emeritus Prof. of Osaka Univ.), Kengo Uchida (Emeritus
Prof. of Hirosaki Univ.) and Masao Koizumi reported the first transient absorption spectra of dyes intermediates2

in Nature1) In the flash photolysis where the first flashlight forms excited states of dyes and the second flashlightmonitors the induced photoreaction. It was proposed by Late Dr. Ronald George Wreyford Norrish and Late Dr.
George Porter in England during the Second World War much long before the 1960s when the laser was born
(Figure 2), and they were awarded the Nobel Prize in 1967 together with Late Dr. Manfred Eigen, the developerof the stopped flow method. In late 1960’ Dr. Yoshiharu Usui (Emeritus Prof. of Ibaragi Univ.), Mr. Akira Kira
(Emeritus Researcher of RIKEN, Former Director of Japan Synchrotron Radiation Research Inst. (JASRI)), Mr.
Masaharu Morita (Late Prof. of Matsumoto Dental College), and Mr. Koichi Kikuchi (Emeritus Prof. of Kitasato
Univ.) were engaged in the flash photolysis studies. It was developed to a luminescence-absorption-flash method(named by Prof. Koizumi),2) which was a simultaneous measurement of delayed fluorescence and absorption.
According to Dr. Keitaro Yoshihara (Emeritus Prof. of Inst. for Molecular Science),3) the flash photolysis system
was in operation in the Laboratory of Prof. Saburo Nagakura (Late Emeritus Prof. of the Univ. of Tokyo, Former
director of Inst. for Molecular Science) at the Inst. for Solid State Physics, the Univ. of Tokyo, led by Dr. Hiroshi
Tsubomura (Late Emeritus Prof. of Osaka Univ.) in 1966. In the early days, time-resolved spectroscopy wastechnically possible only for the molecular electronic spectral measurement in the visible wavelength, although it
is now commonplace in all wavelength regions from X-rays to terahertz spectroscopy.

Figure 2(Left) G. Porter, “Chemistry in Microtime: Selected Writings on Flash Photolysis, Free Radicals, and the Excited State”,
Imperial College Press, London, 1977
(Right) D. Phillips, J. Barber, “The Life and Scientific Legacy of George Porter”, Imperial College Press, London, 2006

3． Nano-picosecond Laser Photochemistry at Mataga Laboratory, Osaka University (1968-1984)
Prof. Mataga became a Professor of the newly established Faculty of Engineering Science of Osaka University
when he was already known worldwide as the proposer of the Mataga-Lippert formula6) and the MatagaNishimoto approximation7) at that time. Two reports on these works were later cited in Iwanami’s “50 Years ofJapanese Scientific Papers” (Iwanami Shoten, Publishers.),8) which summarizes typical postwar research
examples. In addition, Prof. Mataga published a famous paper in 1968 that proposed the concept of molecularferromagnetism. 9) I consider these three papers the most notable works by Prof. Mataga before entering thebrilliant laser photochemistry era. A little bit later two books on the state and photochemistry of molecules were
written by Prof. Mataga and published (Figure 1).
In 1968 I started working as a Ph.D. student at the Mataga Lab after obtaining the Master Degree from the3

Koizumi Lab. My work was to operate the laser and enable the nanosecond time-resolved spectroscopy first inJapan. I started experimenting with making and running the equipment from scratch. We managed to operate aruby laser to measure nanosecond transient absorption spectra while learning vacuum tube circuits from Mr.
Tadashi Okada (Emeritus Prof. of Osaka Univ.). After that, a picosecond ruby laser was introduced to the Mataga
Lab. by Mr. Nobuaki Nakashima (Emeritus Prof. of Osaka City Univ.). These ruby lasers could oscillate every 3
min, we adjusted the optical system without a viewer to look at the beam, and we measured absorption spectrausing photographic film and ran into a dark room for developing the film. After that, we could know whether or not
it worked well, and we performed this procedure for more than 10 hours every day.13) However, Windsor, Albrecht,
and Porter et al. had internationally reported the development of the spectroscopy, so that we chose chargetransfer and electron transfer molecular systems as the target, that is, Mataga’s specialty. Their fluorescence iswide covering all the visible wavelength and it was not easy to measure the absorption spectra of the fluorescentstate. Proposing re-absorption method, we successfully measured a S1-Sn absorption of charge-transfer complex
of s-tetracyanobenzene and toluene, and proved that its excited-state absorption is very similar to the anion of
the electron acceptor s-tetracyanobenzene.10) We were surprised to see that Michael Ottolenghi also reported
the similar spectra in the same volume of Chem. Phys. Lett. in 1970. This direct indication that the excited stateof charge transfer complex is an electronic state similar to an ion pair received much attention, and the result
became one of the topics at that time.
Sincere discussion was extended in Japan and abroad, including exciplexes that form a charge-transfer complex
only in an excited state. (At the time, it was called hetero-excimer at the Mataga Lab, while excimers were formed
for the same molecules). Mataga considered that electronic structure of donor-acceptor system is determined byinteraction with solvent and the charge transfer degree gradually changing depending solvent polarity. Albert
Weller proposed that the electron transfer and non-radiative relaxation compete with each other and its ration
depends on solvent polarity. This discussion was developed from initial intermolecular to intramolecular systems,
namely, twisted intramolecular charge transfer dynamics. I remember there were sometimes intense debates
among N. Mataga, S. Nagakura, A. Weller, M. Ottolenghi, Z. Grabowski, K. Zachariasse, Frans C. De Schryver,
J. Verhoeven, W. Rettig, T. Okada, N. Nakashima, S. Iwata, H. Hayashi, T. Kobayashi et al.11.12)
In the early 1980s, we were able to install a Nd3+: YAG laser at Mataga Lab with Kakenhi (JSPS) grants. With thelaser oscillating at 10 Hz, streak cameras and diode array detectors, we were a bit relieved that we had finallyreached some level in front of these modern advanced laser systems. Its optical set up for picosecond transientabsorption spectroscopy,14) was introduced as a representative in the textbook written by Fleming.15) Many
researchers not only in physical chemistry but also in organic chemistry, polymer chemistry, photobiology, andsolid state physics highly evaluated the research of the electron transfer dynamics and the excited state dynamics
of charge transfer complexes. They developed collaborative studies with Mataga Lab. I realized that something
between physics (research on the theory of things) and chemistry (research on the abundance of things) is so
attractive. I think Prof. Mataga has just proved this proverb: the peach and the plum do not speak and try hard to
appeal to people, yet a path is born beneath them because of their flower and fruit.16)
Prof. Mataga did not say anything about my research trial, but when I came to his office with the data, Prof.

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Mataga always discussed them with me for hours. After explaining and discussing the experiment results, I had
more time to talk with Prof. Mataga about what to do next and what might be the future of this research. Prof.
Mataga was often silent for a while. Still, on the other hand, the conversation with Prof. Mataga flourished, and I
was sometimes moved to tears. I think that this discussion-style with the manuscript that was turned red by Prof.
Mataga became the basis for my research life. His seminal work was highly evaluated and he was awarded the
Purple Ribbon Medal in 1995, Porter Medal in 1996 (Figure 3), Japan Academy Prize in 2006, and many others.
Separately from Mataga’s charge transfer and electron transfer studies, I had not found a possible subject enoughconvincing me. I studied photochemistry using a laser of the micellar solution and polymer solution, considering
the development to a higher-order assembly system. However, Prof. Mataga had written about six papers in that
direction in the mid-1950s while working at Koizumi Lab at Osaka City Univ. I felt I was on the palm of a giant. I
thought that studying the excited state dynamics and reactions of solid molecular systems using time-resolved
reflection spectroscopy with a pulsed laser would be a good idea. I tried total internal reflection fluorescence
spectroscopy of organic thin films, and my funding on the application on this method was approved, making myfeeling positive.

Figure 3
Profs. Noboru Mataga and George Porter at IUPAC Symposium on Photochemsitry in Helsinki in 1996.
Prof. Mataga (left) was awarded the Porter Medal directly from Prof. Porter (right). The photo was taken by Prof. Iwao
Yamazaki (Emeritus Prof. of Hokkaido Univ.).

４．Time-resolved Reflection Spectroscopy of Organic Solids at Kyoto Institute of Technology(1984-1991)
I was appointed a Prof. of the Department of Polymer Science, Faculty of Textile Science, Kyoto Inst. of Tech.,which was reorganized in April 1984. I started studying polymer solids by time-resolved solid-state spectroscopy.
Since I could buy a nanosecond excimer laser, I used this laser to come up with many student themes. I asked
Profs. Iwao Yamazaki and Keitaro Yoshihara of the Inst. for Molecular Science to conduct collaborative researchfor single-photon counting fluorescence spectroscopy and picosecond transient absorption spectroscopy,
respectively. I asked them to allow us to use their lasers. As a young Prof. at a local university, I was very gratefulto have collaborated with the Inst. for Molecular Science. Furthermore, Inst. for Molecular Science could afford
to pay for our experiments and travel expenses. It was impossible to follow up with the development of transient5

absorption spectroscopy to picoseconds and femtoseconds with my research funding. Also, I could not competewith the laboratories by Profs. Saburo Nagakura, Noboru Mataga, Ikuzo Tanaka, and Keitaro Yoshihara. So, I
decided to shift more and more towards the study of the abundance of things between physics (research on thetheory of things) and chemistry (research on the abundance of things). In the summer of 1985, Dr. Hiroyuki
Hiraoka of the IBM (IBM Almaden Research Center) in the United States invited me as a Summer Faculty Fellow
for three months, recommended by Prof. Haruo Shizuka (Emeritus Prof. of Gunma Univ.). I thought that I could
study anything freely, so I decided to try a spectroscopic study of polymer laser ablation as new nonlinear
photochemical processes for my future. Ablation itself was famous in Japan for the work of Dr. Susumu Namba(Late Emeritus Researcher of RIKEN and Late Emeritus Professor of Osaka University). R. Srinivasan of the IBM(IBM Thomas J Watson Research Center) wrote a famous paper in 1982. Many researchers have been working
on developing optical lithography techniques, but there had been no fundamental examinations of the molecularor electronic aspects. During my stay at IBM, I studied the ablation of polymer films doped with aromatic
molecules that could lead to spectroscopic research. I posted the results to Prof. Mitsuo Ito (Late Emeritus Prof.
of Tohoku Univ.),17) who was editing Chem. Phys. Lett. I wondered if this was not physical chemistry and would
be refused by Prof. Ito. However, he accepted this as being new physical chemistry. I think that my research
attitude may have been more conservative if Prof. Ito refused at that time. At Kyoto Inst. of Tech., Prof. Akira Itaya(Emeritus Prof. of Kyoto Inst. of Tech.), Dr. Noriaki Ikeda (Emeritus Prof. of Kyoto Inst. of Tech.), and Dr. Hiroshi
Fukumura (Emeritus Prof. Tohoku Univ.) greatly assisted me for developing research on time-resolved reflection
spectroscopy and ablation dynamics.

５． Laser Microchemistry at Masuhara ERATO Project, JST (1988-1994）
In 1984, JST (at that time, Research Development Corporation of Japan (JRDC)) invited me to apply for researchsupervision of the Exploratory Research for Advanced Technology (ERATO) project, which aims to create newscience and technology. Because they are hoping for “picosecond chemistry” and preparing their budget, theysuggested me to write such a proposal. I argued with them that although raising the time resolution frompicosecond to femtoseconds was necessary, already being challenged. I did not think this could be an exploratory
subject for creative science and technology trials. I proposed to pursue the “Microphotoconversion” project aiming
at reaction control. To start from the research of spectroscopy and photochemistry using a microscope, it wascommon knowledge at the time to adopt a micrometer for spatial resolution, and microchemistry using a laser
and a microscope was an issue for the project. The chief coordinator of the council to decide who should be the
ERATO Project leaders and promote the research was Prof. Saburo Nagakura, and later replaced to Prof. Ikuzo
Tanaka (Emeritus Prof. of Tokyo Inst. of Tech., Former president of Tokyo Inst. of Tech.). With the understanding
and support by these two Profs., I significantly advanced my research. I was given two billion JPY research funds
and was able to hire 15 postdocs in five years. It was an exceptional project. Also, I was asked to get a research
place outside the university. Researchers of our project were a full-time researcher and could not concurrently
hold other jobs. At that time, excellent researchers such as Profs. Junichi Nishizawa, Tsuyoshi Masumoto, Osamu
Hayaishi, and Chikara Hayashi were the leaders. On the other hand, I was only 44 years old and had been
studying fundamental research fields until then. It was like walking in the dark. My ERATO research begun withyoung researchers such as Noboru Kitamura (at that time, Assistant Prof. at Tokyo Inst. of Tech., present Emeritus

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Prof. of Hokkaido Univ.), Hiroaki Misawa (at that time, Assistant Prof. of Tsukuba Univ., present Prof. of Hokkaido
Univ.), Keiji Sasaki (at that time, Assistant Prof. of Tokushima Univ. present Prof. of Hokkaido Univ.), Naoto Tamai(at that time, Assistant Prof. of Hokkaido Univ., present Prof. of Kwansei Gakuin Univ.), Nobuyuki Ichinose (Prof.
of Kyoto Inst. of Tech.), and U. Pfeifer-Fukumura (Prof. of Univ. of Applied Sciences Wiesbaden). Drs. Hiroyuki
Sugimura (Prof. of Kyoto Univ.), Kiyoharu Nakatani (Prof. of the Univ. of Tsukuba), Nobuyuki Ichinose (Prof. of
Kyoto Institute of Technology), Atsushi Sekiguchi (Kogakuin Univ.), Tatsuya Uchida (Prof. Tokyo University of
Pharmacy and Life Sciences), Kenji Kamada (Senior Researcher of AIST), Sanyo Hamai (Akita University),
Nobuo Shimo (Idemitsu Kosan Co.,Ltd.), Masatoshi Yanagimachi (Mitsui Chemicals, Inc.), and Seiji Funakura,(DIC Corporation) were also tremendous. They contributed very much to our project.
The results of this Masuhara ERATO Microconversion project include the development of a three-dimensional
spatial and time-resolved spectroscopy system, the development of transient grating diffraction spectroscopy, thespectroscopy and photochemistry of single micrometer microparticle, the solid/solid and solid/liquid interface
layers. Characterization, electrochemistry of single microdroplets, electrochemistry on microarrays, dynamics ofphotoresponsive polymer microgels, optical assembly, and optical drive of microparticle structures were also
topics. To develop a method to create a field that makes these possible, we also worked on surface
micromachining and modification by laser, electrochemical surface micromachining by scanning microscope, andmicropatterning by CVD. The research on space- and time-resolved chemistry, which is now a major trend, using
a combination of laser and microscope began with our ERATO project. A series of achievements was publishedin Japanese in 1993 and English in 1994, respectively, as the world’s first books entitled “Microchemistry” (Figure4). Since then, many researchers around the world have followed us. We pride ourselves on being ahead of
microchemistry flow as a new area of science and technology along with microelectronics, micromachines, andmicrooptics. To confirm this research results, we organized an international conference on microchemistry inBrussels in 1993 with excellent cooperation by Prof. Frans C. De Schryver. Profs. G. Whiteside (Harvard), M. S.
Wrighton (MIT), A. J. Bard (Texas Austin), J. Klafter (Tel Aviv), R. Srinivasan (IBM), D. D. Dlott (Illinois), Ikuzo
Tanaka, Kenichi Honda (Late Professor of Univ. of Tokyo), et al. presented their advanced progress andsupported this organization. We could launch a new research stream of time- and space-resolved chemistry to
the world.

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Figure 4(Left) H. Masuhara, N. Kitamura, H. Misawa, N. Tamai, K. Sasaki, “Microchemistry” (in Japanese), Kagaku Dojin, Kyoto, 1993
(Middle left) H. Masuhara, F. C. De Schryver, N. Kitamura, N. Tamai (Eds.), “Microchemistry: Spectroscopy and Chemistry in
Small Domains”, North Holland, 1944
(Middle right) H. Masuhara, F.C. De Schryver (Eds.), “Organic Mesoscopic Chemistry (IUPAC 21st century chemistry
monograph)”, Blackwell Science, 1999
(Right) H. Masuhara, H. Nakanishi, K. Sasaki (Eds.), “Single Organic Nanoparticles”, Springer, 2003

６． Laser Nanochemistry at Osaka University (1991－2007)
During the development of ERATO research, Prof. Shigeo Minami of the Department of Applied Physics, Osaka
Univ., invited me to have a laboratory there. I again thought that between physics (research on the theory ofthings) and chemistry (research on the abundance of things) was interesting. Still, I was hesitant about whether
I could live in the Department of Applied Physics. When I looked at departments at major universities acrossJapan, there were some instances where physicists moved to the chemistry department. I could not find any
cases where chemists became Professors in the physics department. The Department of Applied Physics ofOsaka Univ. was known to be strong in optics and microscopy. Profs. Yoshiki Ichioka and Shinichiro Nakajima(both Emeritus Prof. of Osaka Univ.) were there in addition to Prof. Minami (Emeritus Prof. of Osaka Univ.). If I
moved to Osaka University, my lab would be the fourth lab related to light. Prof. Satoshi Kawata (Emeritus Prof.
of Osaka Univ.) was an Assistant Prof. of Prof. Minami’s laboratory at that time, while he was already prominent.
If I participated, the laboratory's name in charge was Applied Physics 2nd Laboratory “Applied Optics/Applied
Spectroscopy.” The lecture in charge was “Analytical Instruments and Applied Spectroscopy”. Prof. Hiroshi
Yoshinaga, who started this course during the 2nd World War, was an authority on far-infrared spectroscopy andhad been collaborating on amino acids with Profs. Sanichiro Mizushima and Akiko Hirakawa of the Univ. ofTokyo.18) His research results had been known around the world. Also, Prof. Minami said, “Applied physics ischanging rapidly. Many people are now studying physics and spectroscopy of semiconductors, but in the future,research on the organic matter using lasers will become the mainstream.” Before that, I remembered many
research stories by Profs. Koichi Shimoda, Shigeo Shionoya, Susumu Namba, Chiyoe Yamanaka, Tatsuo Yajima,
et al. through the laser conferences and workshops. There were in principle physicists but show their deep
understanding on chemistry and materials. The spirit of exploration and research had since revived within me,
and I decided to move to the Department of Applied Physics. I thought it was an opportunity to explore newresearch by putting myself in a different environment from others.
In the ERATO project, we studied microchemistry. On the other hand, we developed laser-based spectroscopy
and reaction in the small domains from micro to meso, and meso to nano at Osaka Univ. I wanted to open up a
new research area in laser nanochemistry, which would significantly change the conventional framework of lightand chemistry. Regarding the development of nanospectroscopy and the study of reaction dynamics, I continued
my work focusing on time-resolved reflection spectroscopy, which had been the theme since my research at
Kyoto Inst. of Tech. I have also developed femtosecond specular/regular reflection spectroscopy for solid nanosurfaces and interface layers and femtosecond diffuse reflection spectroscopy for nanoparticle powders. We have8

paved the way to analyze the photoreaction of a heterogeneous molecular solid system at exactly the same level
as the solution. With the leadership of Assistant Prof. Hiroshi Fukumura (Emeritus Prof. of Tohoku Univ.), Mr.
Musubu Ichikawa (Prof. of Shinshu Univ.), Kazuya Watanabe (Prof. of Kyoto Univ.), Akihiro Furube (Prof. ofTokushima Univ.), and Mototsugu Suzuki (the Metropolitan Police Agency) had grown up as researchers. Prof.
Shuichi Hashimoto (Emeritus Professor of Tokushima Univ.) Regarding subsequent nanospectroscopy, Prof.
Asahi launched a single nanoparticle spectrometer combining a microscope and AFM and clarified the correlation
between the shape of the nanoparticles and fluorescence and light scattering spectroscopic data to which Dr.
Victor Volkov (Prof. of Nottingham Trent Univ.) and Hideki Matsune (Prof. of Miyazaki Univ.) contributed.19) These
data were valuable, indicating the size effect of the electronic spectrum of organic solids. At that time, graduate
student Mr. Tamitake Itoh (Senior Researcher of Advanced Inst. of Science and Technology) developed thefemtosecond single nanoparticle spectroscopy and clarified the relaxation dynamics of single gold nanoparticles.
In the field of nanomanipulation and photon pressure chemistry, we have systematically clarified the dynamics inwhich various molecular aggregates, polymers, and nanoparticles in a solution at room temperature were
captured at the focal position by the optical pressure of a focused laser beam under a microscope. In the earlyyears, Prof. Keiji Sasaki constructed a new system and started new research. Then, Mr. Hiroyuki Yoshikawa (Prof.
of Hiroshima Institute of Tech.) continued Prof. Sasaki's research and presented unique results one after another
under top-notch ideas and guidance. From this trend, Mr. Junichi Hotta (Prof. of Yamagata Univ.), Mr. Syoji Ito(Prof. of Osaka Univ.), Mr. Sadahiro Masuo (Prof. of Kwansei Gakuin Univ.), Mr. Yu Nabetani (Prof. of Miyazaki
Univ.), Ms. Chie Hosokawa (Prof. of Osaka City Univ.), Mr. Yoshito Tanaka (Prof. of the Univ. of Tokyo) and Ms.
Yuriko Matsumura from Nara Women’s University (Prof. of Tokyo Healthcare University) have grown up as
professors. The seminal work of optical trapping in chemistry received much attention and Drs. Johan Hofkens(Prof. of Katholieke Universiteit Leuven (KUL)), Trevor Smith (Prof. of Univ. of Melbourne), and Dr. Pawel
Borowicz (former Polish Academy of Science) joined us as postdocs, and Ms. Rachel Miallet-Renault (Prof. Univ.
Paris-Saclay Univ.) and Mr. Michel Sliwa (CNRS Lille) also joined us as graduate exchange students of Ecole
Normale Supérieure Cachan. Some results are included in the books in Figure 4.
Prof. Hiroshi Fukumura initially studied the dynamics and mechanism of nano laser ablation. Mr. Yasuyuki Tsuboi(Prof. of Osaka City Univ.), Mr. Hisashi Fujiwara (Prof. of Hiroshima City Univ.), Mr. Hiroshi Furutani (Prof. of
Osaka Univ.), and Koji Hatanaka (Researcher, Academia Sinica, Taiwan) were the students of this group. One ofnonlinear optical absorptions we proposed is cyclic multiphotonic absorption of the excited singlet state during its
lifetime,20) which can now explain laser ablation, single molecule photoacoustic behavior, and optical resonanceeffect in optical trapping. After he moved to Tohoku Univ. with a student, Mr. Hiroshi Uji-I (Prof. of Hokkaido Univ.
& KUL), Prof. Tsuyoshi Asahi proceeded as a leader in research on laser ablation dynamics and mechanism. Mr.
Yoichiroh Hosokawa (Prof. of Nara Inst. of Science and Tech. (NAIST)) extended their research as graduate
students. As a fundamental study, we proved that abrupt temperature rise in nanosecond excitation and local
transient pressure in femtosecond excitation are the keys to understanding the ablation mechanism anddynamics of organic materials.21.22) In particular, we succeeded in clarifying the process in which the electronic
excitation of molecules evolves into the ablation of solids using a femtosecond laser. I like this work very muchas a bridge between physics (research on the theory of things) and chemistry (research on the abundance of9things). This result, led by Yoichiroh Hosokawa, resulted in a method that attracted widespread attention, suchas non-invasive and non-destructive manipulation of living cells. Dr. Yuqiang Jiang (Chinese Academy of Science,
China), Dr. Tsuyoshi Ohmoto (Private Sector), Dr. Atsushi Yamaguchi, Mr. Takahiro Kaji (Researcher of NICT),and Mr. Ryohei Yasukuni (Prof. of NAIST) have worked along this line. These achievements were also drawing
attention from the bioscience field. For example. Mr. Hiroshi Yoshikawa (Prof. of Osaka Univ.) was playing anactive role in femtosecond application to protein crystallization.
Laser ablation of organic crystals results in formation of fragmented crystals which are usually dispersed in
vacuum chamber in air. However, we carried out nanosecond laser ablation in solution, then the ejected particles
were dispersed homogeneously as they are charged more or less. We confirmed their size distribution from a
few tens to a few hundreds of nanometer, namely, solution ablation is a best laboratory scale fabrication methodof organic nano crystals.19) Dr. Teruki Sugiyama (Prof. of NYCU) and Mr. Yoshiaki Tamaki (Prof. of Univ. of the
Ryukyus), intensively studied the fundamental mechanism and explored the application. Based on this activity, aventure business (AB Size Co. Ltd.) was started by Dr. Isamu Oh and Mr. Sen-ichi Ryu in 2007. The applicationof solution laser ablation to molecular electronics was also started by Prof. Asahi and Mr. Hyeon-Gu Jeon (Prof.
of Ehime Univ.) This experimental study convinces us a high potential of laser ablation in solution.
The stream of my research is often regarded as one of nanoscience and nanotechnology research. Still,
nanotechnology began to gain social attention because the US President Clinton issued a textbook in 200023)
and invested in research. Because I was heading toward nano by focusing on high potential of lasers and theresearch of molecular nanos with light earlier than the 2000s, I could create a unique stream as laser
nanochemistry. At Osaka Univ., Profs. Satoshi Kawata, Toshio Yanagida, and Tomoji Kawai were playing leadingroles in the world of nanoscience and nanotechnology. On the other hand, I could demonstrate my uniquenessby focusing on lasers and molecular systems. Prof. Kawata and I organized a series of Meetings on
Nanophotonics, demonstrated high activity of Department of Applied Physics, Osaka University in 2004-2006,
and published their proceedings (Figure 5). Also based on these achievements, I organized a JSPS research
project named "Molecular Nano Dynamics" with Profs. Hiroyasu Iwasawa, Masahiro Irie, Kohei Uosaki, andHiroshi Fukumura, and worked with many researchers. Fortunately, I was able to summarize those three years'
activities as "Molecular Nano Dynamics" (Figure 5). For celebrating my activity, a special issue for my 60 years
birthday was edited by Profs. Frank Wilkinson and Hiroshi Fukumura, and published in Photochem. and Photobiol.
Sci. in 2005.These research developments had been evaluated, and Prof. G. Schatz, P. Kamat, Editor-in-Chiefof J. Phys. Chem. invited Profs. P. F. Barbara, J. Hofkens, Kei Murakoshi, Tsuyoshi Asahi, Hiroshi Miyasaka, andHiroaki Misawa as Guest Editors, and published my Festschrift in December 2009 (Figure 6). I read J. Phys.
Chem. at Chemistry Department of Tohoku Univ. in Sendai Katahira campus during my master's degree in 1960’s.
At that time, I wondered if I could submit a paper to this journal in the future. I clearly remembered that time.

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Figure 5(Upper) H. Masuhara, S. Kawata (Eds.), “Nanophotonics”, Elsevier, 2004
S. Kawata, H. Masuhara (Eds.), “Nanoplasmonics: From Fundamentals to Applications”, Elsevier, 2006
H. Masuhara, S. Kawata, F. Tokunaga (Eds.), “Nano Biophotonic: Science and Technology”, Elsevier, 2007
(Lower) H. Fukumura, M. Irie, Y. Iwasawa, H. Masuhara, K. Uosaki (Eds.), “Molecular Nano Dynamics Vol. 1 & 2”, VCH-Wiley,
Berlin, 2009

Figure 6(Left) H. Fukumura, F. Wilkinson, “Special Issue of Life and Research of Prof. Hiroshi Masuhara”, Photochemical andPhotobiological Sciences, Royal Society of Chemistry, 2005, 4, 1-164.
(Right) P. F. Barbara, J. Hofkens, H. Misawa, K.Murakoshi, T. Asahi, and H. Miyasaka, “the Hiroshi Masuhara Festschrift:
Exploration with Lasers into New Areas of Molecular Photoscience”, J. Phys. Chem. C, American Chemical Society, 2009,
113 (27), 11425-11974

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7. Optical Force Chemistry at National Yang Ming Chiao Tung University, Taiwan (2008-present)
Fortunately, even after retirement, I have been developing my research activities by holding a laboratory. In 2007,
I established the Laser Bio-Nano Science Laboratory in the 21 Life Science Research Inst. of the Hamano Life
Science Research Foundation in Kobe, together with Drs. Yoichiroh Hosokawa, Teruki Sugiyama, Takayuki
Uwada (Prof. of Josai Univ.), Kazunori Okano (NAIST) and others. Since the foundation set up a three-year
donation course at the Graduate School of Material Science of NAIST in 2008, we all moved to Nara. Although it
was relatively a short term, we succeeded in demonstrating laser trapping-induced crystallization in 2007. In Nara,
Drs. Ken-ichi Yuyama (Osaka City Univ.), Yasuyo Maezawa (private sector), and Takanori Iino (private sector)
graduated the Ph D. course of NAIST. At the same time, Prof. Y.-P. Lee of NCTU offered me a laboratory with
two staffs. I accepted his offer and was assigned with Drs. Atsushi Miura (Prof. of Hokkaido Univ.) and Takayuki
Uwada. Regarding these assignments, I am very grateful to Prof. Soji Tsuchiya (Emeritus Prof. of the Univ. ofTokyo). At the School of Science of NCTU, famous Japanese Profs. Takayoshi Kobayashi and Hiro-o Hamaguchi
had their labs. Also, Profs. M.-C. Lin and S.-H. Lin had shifted from the USA, participated in research activities,
and cooperated to globalize NCTU. Following them, Profs. Hiroki Nakamura (the Inst. for Molecular Sciences),
Koichi Narasaka (the Univ. of Tokyo), Hiroyuki Matsui (the Univ. of Tokyo), Nobuhiro Ohta (Hokkaido Univ.),
Ilhyong Ryu (Osaka Prefecture Univ.), Yoshito Tobe (Osaka Univ.), Yasuki Endo (the Univ. of Tokyo), andTakayuki Ebata (Hiroshima Univ.) joined there.
NCTU and Prof. Lee have been allowing me do my research freely without placing any orders for my researchsubjects. Furthermore, like the Japanese course system, one laboratory was started to create a research teamconsisting of one Professor, one Associate Professor, and one Assistant Professor. Under that condition, thesuccessive presidents of NCTU also allocated me special budgets to buy new instruments and devices. I think
my laboratory is now one of the most cohesive laboratories globally, with a theme focused on optical force
chemistry. In addition to numerous CW lasers and femtosecond lasers, seven microscopes and their associatedoptics are located on five vibration isolation tables. When I arrived in 2008, it had already been decided that the
donation course at NAIST would end after 2011. Therefore, I developed my original research in Taiwan while
proceeding research of the same theme at the same time both in Japan and Taiwan, which was extremely
efficient to start bridging Japanese and Taiwanese collaboration.
The first theme is related to "bio-application of lasers", especially with a femtosecond laser. This research topic
was initially developed in my laboratory in Osaka University, developed in NAIST, and partly shifted to NCTU.
Prof. Fu-Jen Kao of National Yang-Ming Univ. strongly supported us in Taiwan. Femtosecond laser irradiation
produces bubbles and causes the local convection flow and shock waves due to the multiphoton absorption,
which was successfully applied to amyloid fibril formation of insulin, which was demonstrated by Mr. Tsung-Han
Liu (Prof. of Kwansei Gakuin Univ., Japan). More extensively this bubbling phenomenon is utilized to manipulate
the single cell in solution. Since the cells are not illuminated directly by light, they do not undergo photo
decomposition, which is extremely useful for manipulating bio-samples. First, proteins and macromolecules arepatterned on a glass substrate. Then heterologous cells are arranged with a femtosecond laser one by one while
manipulating them in a non-contact and non-destructive manner. Dr. Okano joining us in Taiwan from NAIST

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demonstrated a research approach to measure various functions of cells using the spatial arrangement. Basedon this, we finally set the goal of producing biosensors and biodevices in which living cells are placed. Based onthese results, we were able to summarize a review on our progress in NCTU in J. Photochem. Photobiol. C.24)
The second theme is the study of “molecular crystallization by trapping at the solution surface”. In 2007, Prof.
Sugiyama and Prof. Takuji Adachi (currently Prof. of Univ. of Geneva) succeeded in molecular crystallization withtrapping for the first time in the world. This crystallization is commonly observed when amino acids are optically
captured at the solution surfaces. More interestingly, we found that even unsaturated solutions crystallize.25) The
optical force acts in the space where the light is focused and irradiated, and the molecules gather and crystallize
even under unsaturated solution conditions. We have proposed a mechanism in which focused trapping light isscattered by the crystals. The scattered light causes the molecules to assemble and grow at the crystal edge
even though it is an unsaturated solution. Ms. Jing-Ru Tu, Mr. Chi-Shiun Wu, and Mr. Gino George (Indian
Institute of Science Education and Research, Mohali, India) joined this study. It was in 2013 that Dr. Kenichi
Yuyama was able to demonstrate that idea directly. Recently, Prof. Sugiyama has been developing this molecular
crystallization research for introducing plasmons to lower the threshold of laser power required for crystallization,
arranging gold nanostructures in a chiral manner for chiral crystallization, controlling crystal morphologies.26) In
particular, this chiral crystallization is a significant chemical problem. This was carried out by Ms. An-Chieh Cheng(Prof. Hokkaido Univ.). I think it is an excellent opportunity to demonstrate that optical trapping can be a new
methodology for opening new chemistry. Chiral crystallization is one of the projects that Prof. Sugiyama iscurrently focusing on most.
The third theme is the “optically evolving assembling and swarming of nanoparticles at the solution interfaces”.
We investigated polystyrene nanoparticles of 200 nanometers at the same solution surface. Dr. Wang Shun-Fa(NYCU) succeeded in proving that the aggregate spreads out of focus and has an array using the Bragg reflection.
In addition, although the focal point of 1 micrometer is irradiated, a structure corresponding to it can be formed
even outside the 8 micrometers. To prove this in a more visible form, Dr. Tetsuhiro Kudo (Currently Lecturer of
Toyota Technological Inst.) experimented to capture light using polystyrene particles of 500 nanometers at thesolid-liquid interface that highlights the excellent points of the interface. It was actually observed that thepolystyrene particles were arranged on the glass substrate reflecting the deflection direction of the laser, andfurther arranged in a horn shape to propagate the light to the outside. After that, Dr. Kudo found that when gold
nanoparticles are used, the scattering is very strong, so the gold nanoparticles interact with each other to form a
periodic structure, which works like the Yagi-Uda antenna and scatters light far away, and then many gold
nanoparticles gathered and moved like a group of bees. We named this "optically evolved swarming”, and wehave been researching its dynamics and mechanism.27) Now optically evolved assembling studies are being
extended to proteins and related systems at their solution surface by Drs. Shuich Toyouchi and Roger BresoliObach.
The fourth theme is "femtosecond laser trapping of nanoparticles in solution ". Dr. Anwar Usman (Prof. ofUniversiti Brunei Darussalam) explored a new and unique optical tweezers phenomenon. He worked with Mr.
Wei-Yi Chiang (Rice Univ.) to study the femtosecond trapping phenomenon in solution, a phenomenon in liquids.

13

Nanoparticles gather only in the irradiated space, but gradually form an assembly. When they exceed a specificsize, they are released in one direction. Dr. Masayasu Muramatsu participated from Osaka Univ. to thisfemtosecond trapping and ejection research. We characterized a femtosecond repeating pulse, in which trappingand de-trapping are repeated. Early papers stated that femtosecond laser light and CW laser light trapping had
the same result. But that is the case when the subject is a microparticle. The nanoparticles are captured by lightand form an assembly by optical force. The assembly grows asymmetrically and is finally pushed out by the force
of femtoseconds. The femtosecond pulse exerted optical force on nanoparticles, leading to assembling and thefollowing dynamics completely different way from CW laser irradiation.28) Trapping and assembling of quantum
dots were also tried by Drs. Tetsuhiro Kudo, Wei-Yi Chiang, and Morihiko Hamada.
The study of optical trapping at NYCU in Taiwan is still very unique in the world, while our laboratory would be
the one of the largest in the world as a group studying chemistry utilizing optical manipulation (Figure 7). We
have reached the point where we have discovered a new phenomenon of optical trapping from the material
research side. I have gone back and forth between physics (research on the theory of things) and chemistry(research on the abundance of things). Our present research on optical force chemistry is exactly the researchof exploration and elucidation of new molecular phenomena between them. Many excellent researchers inmolecular science, photochemistry, and boundary areas have come from this field, and we expect many more in
the future.

Figure 7
Group photo of Masuhara - Sugiyama joint laboratory in August 2020. The author and Prof. Sugiyama are the 1st and the
2nd from the left on the top row, respectively. Dr. Kudo is the 4th from the left on the middle row. Dr. Shun-Fa Wang is the far
right on the back row.

Acknowledgement
In the past a few decades, my work has been supported by JSPS, JRDC, JST, and NEDO in Japan and by MOST
and MOE in Taiwan. Recently my activity is due to MOST (MOST 110-2113-M-A49-016) and the Center for
Emergent Functional Matters Science of NYCU from the Future Core Research Center Program within the frame
work of the Higher Education SPROUT Project by MOE in Taiwan.

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References[1] S. Kato, K. Uchida, M. Koizumi, “Reductive Photo-Bleaching of Eosine”, Nature 1959, 184, 1620-1621.
[2] K. Kikuchi, H. Kokubun, M. Koizumi, “Measurement of the delayed fluorescence by a flash technique as anadditional tool for the study of excited states”, Photochem. Photobiol. 1968, 7, 499-501.
[3] K. Yoshihara, “Reminiscences of the Early Days of Ultrafast Spectroscopy”, Molecular Science 2011, 5, A0037.
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Acta 1966, 4, 236-249.
[5] H. Masuhara, M. Okuda, M. Koizumi, “Studies on the Electronic Spectra of the Semiquinones of Anthracene
and its Related Heterocycles. II”, Bull. Chem. Soc. Jan. 1971, 44, 38.
[6] N. Mataga, Y. Kaifu, M. Koizumi, “Solvent Effects upon Fluorescence Spectra and the Dipolemoments ofExcited Molecules”, Bull. Chem. Soc. Jpn. 1955, 29, 465-470.
[7] N. Mataga, K. Nishimoto, “Electronic Structure and Spectra of Nitrogen Heterocycles”, Z. Physik. Chem. 1957,
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[8] “50 Years of Japanese Scientific Papers”, Iwanami Shoten Publishers, Tokyo, 1980.
[9] N. Mataga, “Possible “ferromagnetic states” of some hypothetical hydrocarbons”, Theoret. chim. Acta 1968,
10, 372-376.
[10] H. Masuhara, N. Mataga, “Fluorescence spectra and excited singlet-singlet absorption spectra of stetracyanobenzene EDA complexes by laser excitation”, Chem. Phys. Lett. 1970, 6, 608-610.
[11] “開研究室 15 周年記念”, 阪⼤基礎⼯⼜賀研究室; ⼤阪, 1979. “The fifteenth anniversary of Mataga
Laboratory of Faculty of Engineering Science”, Osaka University, Osaka, 1979.
[12] “⼜賀曻教授退官記念誌 回顧と展望”, ⼤阪, 1991, “The memorial issue for Prof. Mataga upon his retirement:
Reminiscence and Perspective”, Osaka, 1991.
[13] N. Nakashima, M. Murakawa, N. Mataga, “Picosecond flash spectroscopy of solvent-induced intramolecularelectron transfer in the excited 9,9'-bianthryl”, Bull. Chem. Soc. Jpn. 1976, 49, 854-858.
[14] H. Miyasaka, H. Masuhara, N. Mataga, “Picosecond Absorption Spectra and Relaxation Processes of the
Excited Singlet State of Pyrene in Solution”, Laser Chem. 1983, 1, 357-386.
[15] G. R. Fleming, “Chemical Applications of Ultrafast Spectroscopy”, Oxford University Press, New York, 1996.
[16] For the more profound meaning, this idiom represents that if someone has high merit, honest, andstraightforward, he/she doesn't need to advocate or tell people around. Everyone respects and thinks highlyof him/her.
[17] H. Masuhara, H. Hiraoka, E. E. Martinero,” Non-linear photochemistry of polymer films: laser ablation of poly(N-vinylcarbazole)”, Chem. Phys. Lett. 1986, 135, 103-108.
[18] H. Baba, M. Tsuboi, M. Tasumi (Eds.), ”Reminescence of Mizushima Laboratory”, Kyoritsu Shuppan, Tokyo,
1990.
[19] T. Asahi, T. Sugiyama, H. Masuhara, "Laser fabrication and spectroscopy of organic nanoparticles", Acc.
Chem. Res., 2008, 41, 1790.
[20] H. Fukumura, H. Masuhara, "The Mechanism of Dopant-induced Laser Ablation. Possibility of Cyclic
Multiphotonic Absorption in Excited States", Chem. Phys. Lett. 1994, 221, 373-378.

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[21] Y. Hosokawa, M. Yashiro, T. Asahi, H. Masuhara, “Photothermal Conversion Dynamics in Femtosecond andPicosecond Discrete Laser Etching of Cu-phthalocyanine Amorphous Film Analyzed by Ultrafast UV-VIS
Absorption Spectroscopy”, J. Photochem. Photobiol. A 2001, 142, 197-207.
[22] H. Masuhara, "Time-Resolved Spectroscopic and Imaging Studies on Laser Ablation of Molecular Systems:
From Mechanistic Study to Bio/Nano Applications", Bull. Chem. Soc. Jpn. 2013, 86, 755-783.
[23] National Nanotechnology Initiative, USA 2000.
[24] K. Okano, H.-Y. Hsu, Y.-K. Li, H. Masuhara, "In situ patterning and controlling living cells by utilizing
femtosecond laser", J. Photochem. Photobiol. C, 2016, 28, 1-28.
[25] T. Sugiyama, K. Yuyama, H. Masuhara, "Laser Trapping Chemistry: From Polymer Assembly to Amino Acid
Crystallization", Acc. Chem. Res. 2012, 45, 1946-1954.
[26] A.-C. Cheng, H. Masuhara, T. Sugiyama, “Evolving Crystal Morphology of Potassium Chloride Controlled by
Optical Trapping”, J. Phys. Chem. C 2020, 124, 6913-6921.
[27] H. Masuhara, K. Yuyama, “Optical Force-Induced Chemistry at Solution Surface”, Annu. Rev. Phys. Chem.
2021, 72, 565-589.
[28] J. J.-K. Chen, W.-Y. Chiang, T. Kudo, A. Usman, Masuhara, “Nanoparticle Assembling Dynamics Induced
by Pulsed Optical Force”, The. Chem. Record 2021, 21, 1473-1488.

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Chair Professor Hiroshi MASUHARA
Department of Applied ChemistryCenter for Emergent Functional Matter Science
National Yang Ming Chiao Tung University
Ta Shueh Road 1001, Hsinchu City 30010, Taiwan
増原 宏
講座教授、工学博士
国立陽明交通大學 理学院応用化学系
国立陽明交通大學 新世代功能性物質研究中心〒30010 台湾新竹市大學路 1001
masuhara@masuhara.jp
https://masuhara.lab.nycu.edu.tw/
http://www.masuhara.jp/+886-(0)983-811-798