The University of Osaka · Chemistry
Professor Kei Ohkubo's research lab specializes in photocatalysis and photoinduced electron transfer processes, focusing on the development of efficient, selective, and sustainable photocatalytic systems for the functionalization of hydrocarbons and small molecules under ambient conditions. The lab explores the mechanistic pathways of charge separation and radical intermediates using advanced spectroscopic techniques such as laser flash photolysis, with applications in the selective oxidation of arenes and alkanes to valuable oxygenated products. A key focus is on designing organic photocatalysts—particularly acridinium and quinone-based systems—that enable visible-light-driven transformations with high turnover numbers and quantum yields.
Figures are computed from collected data and may differ slightly.
Photocatalytic oxygenation of benzene to phenol occurs under visible-light irradiation of 2,3-dichloro-5,6-dicyano-p-benzoquinone (DDQ) in an oxygen-saturated acetonitrile solution of benzene and tert-butyl nitrite. The photocatalytic reaction is initiated by photoinduced electron transfer from benzene to the triplet excited state of DDQ.
Photooxygenation of p-xylene by oxygen occurs efficiently under photoirradiation of 9-mesityl-2,7,10-trimethylacridinium ion (Me(2)Acr(+)-Mes) to yield p-tolualdehyde and hydrogen peroxide, which is initiated via photoinduced electron transfer of Me(2)Acr(+)-Mes to produce the electron-transfer state.
Long live the state! Photoexcitation of a zinc chlorin–fullerene dyad with a short linkage results in the formation of the ultra-long-lived charge-separated (CS) state by a one-step photoinduced electron transfer without loss of energy, which is inevitable for charge separation by multistep electron-transfer processes. The lifetime of the charge-separated state was 120 s in frozen PhCN at −150 °C (see picture).
Photocatalytic bromination of aromatic hydrocarbons by molecular oxygen with hydrogen bromide occurs efficiently to produce monobrominated products selectively using 9-mesityl-10-methylacridinium ion (Acr+–Mes) as a photocatalyst under visible light irradiation. Both the product yield and selectivity for the bromination of 1,3,5-trimethoxybenzene were 100% with a quantum yield of 4.8%. The photocatalytic turnover number is 900 based on the initial concentration of Acr+–Mes. The reactive radical
Photocatalytic oxygenation of benzene with oxygen and water to phenol has been achieved under ambient conditions by using the 3-cyano-1-methylquinolinium ion as a photocatalyst (see picture). The mechanism was clarified by detecting the π-dimer benzene radical cation produced by photoinduced electron transfer from benzene to the photocatalyst, and by monitoring the reaction of the radical cations with water molecules. Detailed facts of importance to specialist readers are published as ”Supportin
Photooxygenation of cyclohexane by O(2) occurs efficiently under visible-light irradiation of an O(2)-saturated acetonitrile solution containing 9-mesityl-10-methylacridinium ions (Acr(+)-Mes) and HCl to yield cyclohexanone, cyclohexanol and hydrogen peroxide. The photocatalytic reaction is initiated by electron transfer from Cl(-) to the mesitylene radical cation moiety.
A ring-substituted toluene with an electron-withdrawing substituent, p-tolunitrile, is oxygenated by molecular oxygen to yield the corresponding aldehyde with tetrafluoro-p-dicyanobenzene as a photocatalyst under photoirradiation with an Hg lamp (lambda > 300 nm). The oxygenation of a ring-substituted toluene with an electron-donating substituent, p-xylene, by molecular oxygen is also achieved with 10-methyl-9-phenylacridinium ion as a photocatalyst under visible light irradiation, yielding p-to
Abstract The natural photosynthetic reaction center utilizes sequential multi-step electron transfer from the excited chromophore to the terminal electron acceptor via electron mediators to attain a long lifetime of the final charge-separated (CS) state. Contrary to natural systems, simple electron donor–acceptor dyads have been developed to attain a long-lived CS state, where the donor and acceptor molecules are linked with a short spacer. In the case of a directly linked zinc chlorin–fullerene
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