Electron‐Transfer Reactions Triggered by Uncharged or Cationic Photosensitizer: Methodology for Generation of o‐Quinodimethane and Analysis of Back Electron‐Transfer Process

• Published in: Asian journal of organic chemistry 2017-04, Vol.6 (4), p.458-468
• Main Authors: Matsui, Yasunori, Ikeda, Teruyo, Takahashi, Yasutake, Kamata, Masaki, Akagi, Megumi, Ohya, Yukako, Fujino, Ryota, Namai, Hayato, Ohta, Eisuke, Ogaki, Takuya, Miyashi, Tsutomu, Tero‐Kubota, Shozo, Mizuno, Kazuhiko, Ikeda, Hiroshi
• Format: Article
• Language: English
• Subjects: electron transfer; laser chemistry; luminescence; Organic chemistry; quinodimethanes; thermoluminescence
• ISSN: 2193-5807; 2193-5815
• DOI: 10.1002/ajoc.201600570

Photoinduced electron transfer (PET) followed by back electron transfer (BET) reactions of 1,2‐bis(α‐styryl)benzenes 1, generates o‐quinodimethane derivative 2 via the corresponding radical cation 2⋅+. This process serves as a facile method to form o‐quinodimethane intermediates. The intermediacy of 2⋅+ and 2 were confirmed by using various spectroscopic methods and trapping reactions with 3O2 and dienophiles. Kinetic analysis using nanosecond time‐resolved absorption showed that 2⋅+ was transformed to 2 via a BET process, in which the decay of 2⋅+ and rise of 2 have almost the same rate constants of kDECAY=5.6×105 s−1 and kRISE=5.9×105 s−1, respectively. The net BET rate constant evaluated by using Marcus theory is much faster than these experimental values, owing to the reduction based on diffusion. Radically analyzed: Electron‐transfer reactions of 1,2‐bis(α‐styryl)benzene leading to o‐quinodimethane derivatives have been studied. Analysis of photophysical properties and reactivity of o‐quinodimethane revealed its intriguing electronic structure. Kinetic analysis using laser flash photolysis provides valuable insights into reactive intermediates generated upon photoinduced electron‐transfer reactions, including photoredox catalysis.