The construction of a light-energy conversion system that employs sunlight for renewable energy is required for the realization of a low-carbon society. Artificial photosynthesis, which stores solar energy as a stable chemical and enables energy use when required, is an important subject. Recently, studies on artificial photosynthesis systems utilizing localized surface plasmon such as hydrogen evolution and ammonia synthesis have received considerable attention. Especially, it is known that ammonia is useful as an energy carrier to realize the hydrogen society. In this review, we introduce the plasmon-induced artificial photosynthesis that generates hydrogen from water and ammonia from protons and atmospheric nitrogen by visible light under normal temperature and pressure.

Multinary metal chalcogenide semiconductor nanoparticles, such as AgInS₂, CuInS₂, and their solid solution with ZnS, have been recently reported to show strong photoluminescence, the wavelength of which was tunable in the range from visible to near IR lights by controlling their chemical composition and size. Many efforts have been made to develop the high-quality nanoparticles for the application to photoluminescent devices, photocatalysts, quantum dot solar cells, and materials for bio-imaging, because of their low toxicity and tunable optical properties. The present review shows that nanoparticles based on I-III-VI₂ group semiconductors are taking an important place in the search for Cd- and Pb-free materials. Chemical synthesis methods of multinary nanoparticles in solution phases are outlined and then we discuss their size- and composition-dependent photochemical properties which are useful for the application to photofunctional materials.

Photochemistry has a very strong interaction in the clinical base of the fluorescent operative diagnosis and the photodynamic treatment (PDT) of cancer. I had been applied for these actual clinical processes, especially, as the spectroscopic tools for 35 years after the getting Ph. D. It is reviewing of the medical application how did our photochemical technologies apply for the clinical cancer using the photosensitizer molecules and laser instruments.

The mechanism that determines the difference in photocatalytic activities between anatase and rutile TiO₂ powders have been studied by femtosecond to millisecond time-resolved visible to mid-IR absorption spectroscopy. The principal difference is the depth of the electron traps that are associated to oxygen vacancies. In anatase TiO₂, the depth of the electron trap is shallower than 0.1 eV and considerable number of free electrons survives longer than 1 ms. However, in the case of rutile TiO₂, the depth is deeper than 0.9 eV and most of the electrons are trapped within a few picoseconds. The longer lifetime of free electrons causes the higher activity for reduction on anatase TiO₂. However, deep electron-trapping in rutile TiO₂ elongates the lifetime of holes, and enhances the multi-hole processes such as water oxidation. These peculiar behaviors of photogenerated electrons and holes induced by defects, which are absent in defect-free single crystals, determine the photocatalytic activities of anatase and rutile TiO₂ powders.

Photodynamic therapy has been accepted as a promising treatment for cancer, and improvements of photosensitizers of reactive oxygen species are important to develop photodynamic therapy. We have developed silyl-substituted porphyrin derivatives to improve the activity of photosensitizer. We found that silylation of porphyrins improved the quantum yield of singlet oxygen sensitization, cellular uptake efficiency, and accumulation efficiency to tumor tissue. Based on these improvements, silylation enhanced the in vivo photodynamic activity. We have also tried to develop the activatable photosensitizers to suppress the photo-induced side effect. We demonstrated that the aggregate of the silylated porphyrin derivative can be applicable to a sono-activatable photosensitizer.

In order to achieve ultralow detection limit, one strategy would be to focus on a detection method that relies on the properties of molecules that become highlighted when we look at molecules at the single-molecule level. On the single-molecule level, fluorescent molecules often exhibit fluctuating emissions between bright ‘‘on’’ and dark “off” states, so-called “blinking.” During the repetitive cycles of excitation and emission, fluorescent molecules may occasionally enter non-fluorescent off states, such as a triplet state, a radical ion state, and an isomerized state. Reversible formation of such off states causes a blinking of the fluorescence. The changes in the surrounding local microenvironment that modulate the duration of these off state (= τ_OFF) would be detectable at the single-molecule level by monitoring of the fluorescence blinking. In this study, we demonstrate that DNA conformations such as a hairpin, a duplex, and a triplex, and single nucleotide changes in DNA sequences can be monitored by controlling the fluorescence blinking.