Molecular Assembly of Functional Motifs for Artificial Photosynthesis

Natural photosynthesis has produced most of the energy that fuels human society and sustains life on earth. However, with an ever-growing demand for energy, urgent efforts are required to develop artificial systems that mimic the essential processes of natural photosynthesis, including light harvesting/charge separation, photocatalytic water oxidation, energy storage, and catalytic CO₂ reduction. Recent advancements have seen the development of nanoscale photoelectrochemical materials that integrate light absorbers with cocatalysts or redox units for artificial photosynthetic systems. However, the potential of molecular photoelectrochemical materials, which couple electron donor–acceptor (D-A) structures with catalytic or redox-active moieties into a periodic porous aggregate, remains largely underexplored. By combining D–A structures with redox moieties, these materials can enable solar-to-electrochemical energy storage process, while the further incorporation of catalytic sites can extend their application to photo(electro)catalytic water oxidation or CO₂ reduction, thus enabling customized artificial systems. On the other hand, they can enhance energy efficiency by molecular-scale in situ photogenerated charge separation coupled with redox reactions─an exciton-involved redox mechanism─to circumvent the energy losses typically associated with charge carrier transport in nanoscale counterparts. Despite these merits, critical challenges remain with a limited understanding of the structure–functional motif relationship at the molecular level and a shortage of molecular assemblies to enable multifunctional motifs necessary for overall natural photosynthesis mimicry.

In this Account, we introduce the general concept of molecular photoelectrochemical materials for artificial photosynthesis, emphasizing their structural advantages in enabling diverse functional motifs. We also outline fundamental design principles and operational mechanisms of these motifs at the molecular level. Furthermore, we present three specific cases of molecular assembly targeting different functional motifs: (1) a donor (photocatalytic water oxidation)–acceptor (reduction) functional motif for solar-to-chemical conversion; (2) a donor (oxidation)–acceptor (reduction) motif for solar-to-electrochemical energy storage; and (3) a donor (oxidation)–acceptor (photocatalytic CO₂ reduction) motif for solar-to-electrochemical energy storage and conversion. The essential role of intramolecular photoinduced PCET during the operation of each functional motif is also discussed. Finally, we conclude with an overview of major challenges and future prospects for modulating molecular assemblies to achieve high energy conversion efficiency, along with a perspective on the design of versatile molecular materials and the implementation of photoinduced PCET to couple multifunctional motifs for overall natural photosynthesis mimicry. We hope that this Account will provide molecular level insight into the rational design of molecular photoelectrochemical materials and inspire advancements in efficient and flexible artificial photosynthesis technologies.