Hiroaki Misawa Festschrift: Frontiers in Photochemistry

Abstract

Published as part of The Journal of Physical Chemistry C special issue “Hiroaki Misawa Festschrift”. This Festschrift is dedicated to Hiroaki Misawa, Extraordinary Professor at the Research Institute for Electronic Science, Hokkaido University, concurrently serving as Professor Emeritus at Hokkaido University, and Specially Appointed Professor at Okayama University, as well as Lifetime Chair Professor at National Yang Ming Chiao Tung University in Taiwan. The collection of articles featured herein is contributed by many of his colleagues, collaborators, friends, and students. It is presented in recognition of Misawa’s numerous outstanding scientific accomplishments, with a special emphasis on his contributions to photochemistry in general and plasmonic chemistry in particular. We honor his significant impact on these fields. Hiroaki Misawa was born and raised in Tokyo, Japan. He earned his B. Eng. degree in Industrial Chemistry from Tokyo Metropolitan University in 1979 under the supervision of Professor Mitsuhiko Hida. During this time, he conducted research on the photochromism of 1-(2-naphthoxy) anthraquinone derivatives under the guidance of Professor Haruo Inoue, who served as a research associate in Professor Hida’s laboratory. After graduating from Tokyo Metropolitan University, he spent five years as a graduate student in the Organic Physical Chemistry Laboratory at the Department of Chemistry, University of Tsukuba, led by the renowned organic photochemist Professor Katsumi Tokumaru. He conducted research on singlet-sensitized decomposition of dibenzoyl peroxide during his Master’s program and on photocatalytic reactions including hydrogen evolution using titanium dioxide (TiO₂) and dye sensitizers such as Eosin Y during both his Ph.D. programs under the supervision of Professor Tokumaru. He received his Ph.D. in Chemistry from the University of Tsukuba in 1984. After obtaining his doctoral degree, he embarked on a postdoctoral research journey under the supervision of Professor Richard A. Caldwell in the Department of Chemistry at the University of Texas at Dallas for almost two years. Here, he delved deep into the photophysical aspects of photoisomerization. His contributions included research that revealed significant isotope effects by combining spectroscopic measurements such as time-resolved absorption spectroscopy in the photoisomerization of trans-1-phenylcyclohexene. His experience in research life in the United States was notably different from that in Japan, bringing him a fresh perspective. At the time, while benzene was still commonly used as a solvent in organic synthesis in Japan, its use required special permits and notifications in the United States. This highlighted his pioneering role in ensuring safety standards within university laboratories. Additionally, his first child was born in the United States, and stories abound of him rushing from the lab to the hospital to witness the event. In 1986, he returned to Japan and served as a Research Associate in the laboratory led by Professor Katsumi Tokumaru at the University of Tsukuba for over two and a half years. During this time, he collaborated with Dr. Hirochika Sakuragi, who was an associate professor in the Tokumaru laboratory, as well as with Dr. Tatsuo Arai, currently an Emeritus Professor at the University of Tsukuba; Dr. Takashi Karatsu, now an Emeritus Professor at Chiba University; Dr. Akihiro Wakisaka, currently an invited researcher at the National Institute of Advanced Industrial Science and Technology; and Dr. Yoshinobu Nishimura, currently an Associate Professor at the University of Tsukuba, among others. Together, they conducted research on the mechanisms of photochemical reactions in dye-sensitized systems and photoisomerization of olefins, as well as studies on solvent effect on charge separation based on photoinduced electron transfer. Additionally, he collaborated with Dr. Yoshiharu Usui from Ibaraki University on research concerning electron transfer mechanisms in dye-sensitized systems. Regarding radical formation, he collaborated with Dr. Bonazzola Lydia from Paris-Sud University on studies related to the ESR of olefin radical cations and conducted time-resolved EPR studies on the photodecomposition of dibenzoyl peroxide with Dr. Seigo Yamauchi, who was a research associate at Kyoto University at that time. These collaborations contributed to a deeper understanding of radical formation in aromatic compounds. In December 1988, he embarked on a different research trajectory by joining the Masuhara Microphotoconversion project (ERATO) as a researcher. The ERATO project, an abbreviation for the Exploratory Research for Advanced Technology, is a research funding initiative from the Japan Science and Technology Agency (JST), aimed at addressing challenges in strategically focused scientific and technological fields. Its goal is to create new technologies contributing to future scientific and technological innovations in response to societal and industrial needs. The project was led by Professor Hiroshi Masuhara, who was then a professor at Kyoto Institute of Technology. During the project period, Professor Masuhara became a professor at Osaka University and currently holds the position of Chair Professor at National Yang Ming Chiao Tung University in Taiwan. The project had a finite duration of five years. It was rare in Japan at the time for university faculty holding permanent positions to resign and participate in short-term project research, indicating his bold decision. The research scope of the project ranged from time-resolved spectroscopy of chemical reactions and photochemical processes, which Professor Masuhara had been advancing, to the development of microspectroscopic techniques for micrometer-sized small domains, as well as the creation of microreactors using techniques such as photolithography and laser processing. This pioneering work laid the foundation for a new research field known as “Integrated Chemistry”, which they called “Microchemistry”. Within this project, he collaborated with Dr. Keiji Sasaki, now an Emeritus Professor at Hokkaido University, to establish laser manipulation techniques and create chemical systems using single particles. As the technical manager of the ERATO project, Dr. Noboru Kitamura, now an Emeritus Professor at Hokkaido University, and Dr. Sasaki often discussed future research directions with him until the last train departure in the streets of Kyoto where the project was based. The laser manipulation technique, developed by Dr. Arthur Ashkin in 1986, won the Nobel Prize in Physics in 2018. Their early investigation and application of this technique to chemical research might have been delayed had they not joined this finite-duration project. An anecdote from that time recounts that when they submitted their first paper on laser manipulation to a chemistry journal in 1990, the editors criticized it, saying it was not chemistry. This incident underscores how techniques now commonplace in molecular biology, cell biology, and analytical chemistry were initially met with skepticism in the field of chemistry. It suggests that their participation in the ERATO project to explore new research fields ultimately led to success. Then, he led the research group as a group leader for two years starting in 1991. In 1993, following the conclusion of the ERATO project, Misawa became an associate professor in the Department of Mechanical Engineering at the University of Tokushima (currently known as Tokushima University). This position was nearly independent, although Dr. Tsutomu Araki had been advancing research as a professor formally in the same laboratory. Two years later, in 1995, he was promoted to full professor at the same university. As a principal investigator (PI), he demonstrated strong leadership and drove numerous large-scale research projects, including those focusing on micromachines, DNA chips, three-dimensional (3D) optical memories, and nanoactuators. Among these projects, the DNA chip research served as a precursor to later plasmonic chemistry studies, utilizing surface plasmon resonance sensors based on propagating surface plasmon polaritons on Au film surfaces. However, his most dedicated research effort at the time was on the development of 3D laser processing techniques using multiphoton absorption in transparent materials induced by femtosecond lasers. He collaborated with Dr. Shigeki Matsuo, currently a professor at Shibaura Institute of Technology, Dr. Hong-Bo Sun, currently a professor at Tsinghua University, Dr. Saulius Juodkazis, currently a professor at Swinburne University, Dr. Vygantas Mizeikis, currently a professor at Shizuoka University, among others, on research related to femtosecond laser nanofabrication. Their work on techniques such as the fabrication of 3D photonic crystals using negative-type photoresists and nanofabrication inside solid substrates such as silica and sapphire was pioneering and garnered international attention. A book detailing the principles and applications of 3D laser microfabrication, including these research endeavors, was coauthored with Dr. Juodkazis and published by Wiley in 2006. Regarding femtosecond laser processing, Dr. Kazuhiko Yamazaki, currently an associate professor at Ibaraki University, obtained a Ph.D. degree in research on 3D optical memory, while Dr. Toshiaki Kondo, currently a professor at Aichi University of Technology, obtained a Ph.D. degree in research on laser interference lithography. The research on laser manipulation, which he had advocated for during the ERATO project, also progressed. His study successfully induced phase transitions in polymer gels using photon pressure, as reported in Nature in 2000, garnering worldwide attention. This research served as a catalyst for further exploration into laser manipulation studies involving proteins, amino acids, and other nanomaterials. Dr. Masafumi Miwa, currently an associate professor at Tokushima University, obtained a Ph.D. degree in research on the fabrication of micromachines using light. In 2003, he proposed quantum lithography technology using entangled photons with Dr. Keiji Sasaki, a professor at Hokkaido University. Their proposal was selected for a large-scale project under JST known as CREST. CREST is a team-type research funding initiative by JST aimed at producing excellent achievements leading to scientific and technological innovation. Following the acceptance of the CREST project, he moved to the Research Institute for Electronic Science at Hokkaido University as a professor in May of the same year. Additionally, Dr. Saulius Juodkazis from the University of Tokushima joined the new Misawa Laboratory as an associate professor. The entangled photons are generated through parametric down-conversion by focusing a 400 nm beam, the second harmonic of a femtosecond laser, onto type-I BBO crystals. However, at that time, the generation yield was weak, insufficient for demonstrating quantum lithography. Dr. Jarutis Vygandas, a CREST postdoctoral researcher, attempted amplification by constructing a resonant circuit. As another approach, the proposal to use the metallic nanostructures that Dr. Kosei Ueno, currently a professor at Hokkaido University, had been researching to demonstrate photochemical reactions induced by weakly entangled photons was put forward by Professors Hiroaki Misawa and Keiji Sasaki. Various sizes and shapes of Au nanostructures, fabricated using electron beam lithography and lift-off techniques by Dr. Ueno, who was a JSPS research fellow in the Misawa laboratory at the time, were demonstrated to function as plasmonic enhancement fields, thereby enhancing the efficiency of two-photon-induced photochemical reactions. Dr. Ueno held positions as both an assistant and associate professor at the Misawa Laboratory until 2019, collaborating with him to advance research in plasmonic chemistry. Due to the enhancement of photochemical reactions by plasmonic fields, he embarked on promoting a Priority Area Research of the Grant-in-Aid for Scientific Research on Strong Photon–Molecule Coupling Fields for Chemical Reactions from the Ministry of Education, Culture, Sports, Science and Technology (MEXT), carrying the catchphrase “Two-photon-induced reactions with a flashlight”. This project, conducted from 2007 to 2011, brought together over 60 researchers from various fields in Japan to advance research in plasmonic chemistry. From this project emerged numerous research achievements that later became vibrant areas of study, including coupled plasmonic systems, forbidden excitations utilizing the breakdown of the long-wavelength approximation, and selective excitation of various optical modes. Particularly, research on nanofabrication using localized optical fields and light energy conversion utilizing hot carriers were deeply explored as two, major, common themes of the project. A significant research outcome was the photocurrent generation driven by the oxidation reaction of water using localized surface plasmons, attracting global attention. As a result of this project, symposia have been held without fail at Pacifichem in Honolulu every five years since 2010, where they are conducted jointly with overseas researchers. In 2009, an international symposium titled “International Symposium on Advances in Nanostructure-Enhanced Photochemical Reactions and Photoenergy Conversion” was organized in collaboration with Professor Johan Hofkens at KU Leuven in Belgium, drawing renowned researchers in the field from around the world. Additionally, as a concluding symposium, the “Conference on The Nanostructure-Enhanced Photo-Energy Conversion” was held in Tokyo in 2012, where 14 globally renowned researchers including Professor Johan Hofkens and Professor Paul Mulvaney at the University of Melbourne, along with members of this project, gathered for fruitful presentations and discussions. During the project, Dr. Yoshiaki Nishijima, currently an associate professor at Yokohama National University, obtained a Ph.D. degree in research on laser oscillation using photonic crystals. Subsequently, as a postdoctoral researcher, he achieved research results on plasmon-induced optoelectronic conversion systems. Dr. Yukie Yokota, currently an assistant professor at Sophia University, obtained a Ph.D. degree in research on the electromagnetic effects of surface-enhanced Raman scattering. To derive design guidelines for the critically important coupled plasmonic nanostructured electrodes, as elucidated by the research findings of this project, efforts were focused on both photoelectric conversion and water splitting systems, as well as on understanding the ultrafast dynamics within coupled plasmonic systems using time-resolved photoemission electron microscopy. By measuring the near-field excitation spectrum with photoemission electron microscopy, a comprehensive understanding of the coupling nature was attained, revealing significant variations in plasmon dephasing dynamics dependent on the plasmonic modes. This accomplishment was facilitated through collaboration between Dr. Quan Sun, a specially appointed assistant professor in the Misawa Laboratory and currently a deputy director at Peking University Yangtze Delta Institute of Optoelectronics, and Dr. Atsushi Kubo, a lecturer at the University of Tsukuba. Concurrently, research on photocurrent generation utilizing water as an electron source was applied to an overall water splitting system, emerging as a significant topic within the realms of photoelectrochemistry and photocatalysis. With the appointment of Dr. Tomoya Oshikiri as an assistant professor in the Misawa Laboratory, currently an associate professor at Tohoku University, progress was made in research concerning ammonia synthesis employing plasmonic hot carriers. Dr. Xu Shi, who earned his doctoral degree in the Misawa Laboratory, and is currently an associate professor at Hokkaido University, contributed to research elucidating the microscopic structure of the Au/TiO₂ interface, shedding light on its impact on water oxidation. These research accomplishments were acknowledged, leading to the receipt of the Minister of Education, Culture, Sports, Science and Technology Award (Research Category) in 2015, followed by the Japan Chemical Society Award in 2016. To coincide with his 60th birthday, a grand celebration was held in Tokyo, inviting related researchers, former staff, as well as graduates and alumni, to commemorate the occasion. Additionally, he has also served as a Chair Professor at National Chiao Tung University in Taiwan since 2015 (currently known as National Yang Ming Chiao Tung University). In Japan’s national universities, formal retirement typically occurs at the age of 65. Three years before reaching this retirement age, a breakthrough was achieved in the development of Au/TiO₂ photoelectrodes in his research group, where most visible light is absorbed by Au nanoparticles. This phenomenon is induced by the strong coupling between the localized surface plasmons of Au nanoparticles and the Fabry-Pérot resonator, designed to ultimately utilize photons impinging on the electrode for Au nanoparticle light absorption (hot carrier generation). This significant discovery provided crucial design guidelines for large-scale photoelectrodes to research groups advancing hot carrier science using plasmonics. Recognizing this research achievement, he was newly selected for the Grant-in-Aid for Specially Promoted Research by MEXT, with the aim of elucidating the origin of hot carriers with high energy resolution and temporal-spatial resolution. This project spans five years, with an additional two years to continue after reaching the regular retirement age. Hence, during the latter two years of the project, he advanced research as a specially appointed professor at Hokkaido University. Collaborative research with Dr. Xu Shi and Prof. Keiji Sasaki revealed that coupled plasmonic structures utilizing strong coupling between plasmon and nanocavity could be employed not only as photoelectrodes for water splitting but also as highly reproducible and sensitive surface-enhanced Raman scattering chips due to their independence from the measurement position under microspectroscopy. This underscores how strong coupling is characterized by spatial and temporal quantum coherence, elucidated through various spatially and temporally resolved spectroscopy and electromagnetic simulations. Leveraging this quantum coherence effectively could further deepen hot carrier science. Even after becoming an emeritus professor at Hokkaido University, Misawa continues to drive research as a Research Promotion Professor at the Research Institute for Electronic Science, Hokkaido University, and as a specially appointed professor at Okayama University, while undertaking new large-scale KAKENHI projects. In 2023, he cochaired the 31st International Conference on Photochemistry with Dr. Yasuyuki Tsuboi, a professor at Osaka Metropolitan University, which was held in Sapporo. Throughout his academic career, he has mentored 31 Ph.D. students (including 3 current students), 64 Master’s students, and 12 postdocs, the majority of whom are now actively engaged as professional scientists/engineers in universities, public institutions, and industry worldwide. He has also welcomed numerous visiting scientists and students from both domestic and foreign institutions to his laboratory, playing a pivotal role in establishing international collaborative relationships with various universities in Taiwan, China, the United States of America, Belgium, Germany, Singapore, and Australia. Additionally, it is important to acknowledge the invaluable support provided by Ms. Yumiko Yamaguchi and numerous other administrative assistants and secretaries in facilitating activities such as visiting professorships and student exchanges with foreign universities, as well as promoting bilateral programs of JST and JSPS. It is a great honor for us to be included among the friends, colleagues, and students of Hiroaki Misawa. With immense pleasure, we dedicate this special issue of The Journal of Physical Chemistry C to him. The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/acs.jpcc.4c05538. 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