Photochemical reaction fields with strong coupling between a photon and a molecule

To achieve a future low-carbon society, the effective utilization of photons is essential for the development of technologies based on photochemistry, such as photocatalysis and dye-sensitized solar cells, which have the potential to produce clean energy as well as preserve the environment. Here, we propose that gold nanostructures exhibiting localized surface plasmon (LSP) resonance are promising sites for photochemical reaction fields that increase the interaction between a photon and molecule. These interactions are based on electromagnetic field enhancement effects that are induced by LSP excitations and their localization. In this review, recent studies on the strong coupling field between a photon and molecule for photochemical reactions are discussed. As an outstanding example, this concept was applied to the plasmonic, photoelectric conversion of visible to near-infrared wavelengths using electrodes in which gold nanoblocks were elaborately arrayed on the surface of a single TiO2 crystal. The most important characteristic of this photoelectric conversion is that the photocurrent was stable for more than 200 h without adding the donors, which suggests the possibility that water molecules can act as donors that provide electrons to the d-band holes assisted by the LSP excitation. Therefore, this system has the potential for use in artificial photosynthesis systems with irradiation from near-infrared light.