Challenges in Photoinduced Electron Transfer Systems of Metal Complexes

This review aims to clarify the molecular design principles and operational challenges of photoinduced electron transfer (PET) and photoredox processes in metal complexes. The manuscript is structured to include a survey of established conventional systems, such as Ru complexes, followed by our own research on cost-effective photosensitizers for dye-sensitized solar cells (DSSCs) and carbon dioxide (CO2) reduction. Crucially, our main conclusion emphasizes that achieving high optoelectronic efficiency requires the balanced optimization of excited-state lifetimes, orbital distributions, and matrix environments, rather than a simplistic “one-size-fits-all” approach. Finally, based on the fundamental principles of metal complexes and photocatalytic materials, we offer a critical analysis of the practical challenges and reasons behind our unsuccessful experimental outcomes. Thus, this study provides a perspective on unsuccessful molecular design, comparing typical examples.