Utilization of light energy, especially visible-light energy, which can be gained inevitably from sunlight, has now attracted emerging attention due to the recent serious environmental issues. In the field of homogeneous catalysis, various efficient photoredox reactions have been developed, in which mainly ruthenium and iridium visible-light sensitizers play the key roles in the catalysis to promote single electron transfer to generate reactive radical species under mild conditions. Apart from these reactions, utilization of the excited-state of the catalyst itself may lead to the new type light-controlled reactions. In order to realize such reactions, precise design of the photocatalysts is inevitable for the efficient formation of the desired excited-state. Here, we will introduce our intensive studies on developing the visible-light driven catalysts.
