Molecular Photosensitizers in Energy Research and Catalysis: Design Principles and Recent Developments

Molecular photosensitizers play a key role in many areas of renewable-energy chemistry and technology, including dye-sensitized solar cells and photocatalysis reactions that generate small-molecule fuels. Although there is much research effort that uses existing "off-the-shelf" photosensitizers to optimize these processes, it is also important to continue to develop new and improved photosensitizers, which can also lead to advances in photovoltaic and photocatalysis applications. Moving beyond the ubiquitous ruthenium polypyridyl class of photosensitizers, recent research has shown that complexes of other transition metals can have improved attributes, in particular, with regard to photostability and excited-state redox properties. In this Perspective, we highlight recent advances in photosensitizer design. We begin with a tutorial on the important criteria for photosensitizer design, following which we describe recent advances and expected future directions that demonstrate the ability to use synthetic chemistry to optimize the excited-state attributes of photosensitizer molecules.