menu

Research

We are developing new chemical reactions by integrating different fields such as chemistry, pharmacology, medicine, and agriculture, using photochemistry as a key. For example, we are investigating chemical reactions to convert dairy-derived biogas into liquid energy such as methanol and formic acid through the photochemistry of chlorine dioxide, and we are researching new therapeutic agents using catalysts that absorb specific light.

Development of chemical reactions using chlorine dioxide

Methanol synthesis from biogas

Ohkubo, K.; Hirose, K. Angew. Chem. Int. Ed. 2018, 57, 2126

Chemical conversion of biogas into useful substances

Carbon-neutral circular dairy farming

Organic photoredox catalysts and chemical reactions

A variety of novel organic synthetic transformations have been made possible by organic photoredox catalysis via photoinduced electron-transfer reactions.
As described above, photocatalytic reactions are made possible by using the electron-transfer state of Acr+–Mes, which can oxidize and reduce external electron donors and acceptors to produce the radical cations and radical anions, respectively. The reactions of radical cations with superoxide anion (O2•–) can efficiently compete with the back electron transfer to yield the oxygenated products. Substrates that cannot react with singlet oxygen can be readily oxygenated by oxygen with Acr+–Mes under visible light irradiation. The oxygenated products become much more difficult to be oxidized by the electron-transfer state of Acr+–Mes, when the selective photocatalytic oxygenation of substrates, which would otherwise be very difficult to achieve, has been made possible with Acr+–Mes. The reactions of radical cations produced by electron transfer from electron donor substrates to the electron-transfer state of Acr+–Mes with nucleophiles such as Br– can also afford the adducts with nucleophiles, when the electron-transfer oxidation of substrates with the electron-transfer state of Acr+–Mes is much faster than that of nucleophiles. In addition, the radical coupling of neutral radicals produced by deprotonation of the produced radical cations can be utilized for the C-C bond formation reactions. Thus, photocatalytic reactions of Acr+–Mes under visible light irradiation provide new ways to design environmentally benign synthesis.
In particular, the use of the excited states of 2,3-dichloro-5,6-dicyano-p-benzoquinone (DDQ) and 3-cyano-1-methylquinolinium ion (QuCN+), which have strong oxidizing ability has made it possible to oxygenate benzene to phenol via formation of benzene radical cation.

Lithium-ion-encapsulated fullerene（Li+@C60）

Lithium-ion-encapsulated fullerene (Li+@C60) exhibits greatly enhanced reactivity in photoinduced electrontransfer reduction with electron donors compared with pristine C60. The enhanced reactivity of Li+@C60 results from the more positive one-electron reduction potential of Li+@C60 (+0.14 V versus a standard calomel electrode (SCE)) than that of C60 ( 0.43 V versus SCE), whereas the reorganization energy of electron transfer of Li+@C60 (1.01 eV) becomes larger than that of C60 (0.73 eV) because of the change in electrostatic interactions of encapsulated Li+ upon electron transfer. Li+@C60 can form strong supramolecular complexes with various anionic electron donors through electrostatic interactions. Li+@C60 can also form strong supramolecular p complexes with various electron donors, such as cyclic porphyrin dimers, corannulene, and crown ether fused monopyrrolotetrathiafulvalenes. Photoinduced electron transfer from electron donors to Li+@C60 afforded long-lived chargeseparated states of supramolecular complexes between electron donors and Li+@C60. A photoelectrochemical solar cell composed of supramolecular nanoclusters of Li+@C60 and zinc sulfonated meso-tetraphenylporphyrin exhibits significant enhancement in the photoelectrochemical performance than that of the reference system containing only a single component.