32 | December 2021 www.facs.website Manabu Abe Manabu Abe was born in Osaka, Japan. He received his Ph.D. from the Kyoto Institute of Technology with Professor Akira Oku, in 1995. In 1995, he became a faculty staff at Osaka University (Prof. Masatomo Nojima’s group). From 199 to 1998, he was an Alexandervon-Humboldt fellow with Professor Dr. Waldemar Adam at the Universität Würzburg. He was also a visiting researcher at the LMU München (Professor Dr. Herbert Mayr) in 2007. He moved to Hiroshima and became a full-time professor of Organic Chemistry at the Department of Chemistry, Hiroshima University in 2007. His research focuses on reactive intermediates chemistry, especially on diradicals. Zhe Wang Zhe Wang was born in Qingdao, P.R.China. He received his bachelor’s degree (B.Eng.) in chemical engineering from China University of Petroleum (East China) in 2017. He then joined the research group of Prof. Abe at Hiroshima University. He received his master’s degree (M.Sc.) in chemistry from Hiroshima University in 2019 under the supervision of Prof. Dr. Manabu Abe. He is currently a Ph.D. student at Hiroshima University. His research focuses on the kinetic stabilization of singlet 2,2-dimethoxycyclopentane1,3-diyl diradicals using stretch effect induced by macrocyclic structures. In recent years, low-valent chemical species such as radicals and carbenes, which have been recognized as short-lived intermediates, have been isolated by appropriate molecular design, and their chemical properties have been investigated in detail experimentally. In particular, the discovery of isolable carbenes, which are now widely used as indispensable ligands in coordination chemistry and synthetic organic chemistry, has enabled the development of novel highly active catalysts. IN OUR RESEARCH, we have focused on the singlet state of radical pairs that are always involved in the homolysis of bonds but are difficult to observe directly because of their extremely short lifetimes (Scheme 1); moreover, we have been working to elucidate their chemical properties and develop their functions by increasing their lifetimes. In this article, we first review the chemistry of localized singlet 1,3-diradicals intervening in the bond homolysis process of carbon-carbon bonds. Further, we discuss our recent findings on (1) controlling the ground state spin multiplicity (singlet versus triplet); (2) a novel bonding mode (C–π–C); (3) effects of substituents, macrocycles, and solvent viscosity; (4) the nitrogen-atom effect; and (5) the third intermediate in the bond homolysis process. C C C C homolysis singlet radical pair C C transition state Scheme 1 Bond homolysis. Rikuo Akisaka Rikuo Akisaka was born in Kashiwa city, Japan. He received his bachelor’s degree in chemistry from University of Tsukuba in 2016. He received his master’s and Ph.D. degree in chemistry from Hiroshima University under supervision of Professor Manabu Abe in 2018 and 2021, respectively. He currently works with Professor Petr Klan at Masaryk University in Czech Republic as postdoctoral researcher. His current research focuses on the photo-reactivity of a dipyrrinone.
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