Decoding Photoelectrochemical Systems: Molecular Design and Charge Dynamics in Energy Conversion and Storage

Conspectus Photoelectrochemical (PEC) systems are among the most promising solar-to-electrochemical energy conversion and storage technologies and are uniquely positioned to address global energy demand and environmental sustainability. Mimicking the essential functions of natural photosynthesis, including light harvesting, catalytic water oxidation, CO 2 reduction, and energy storage, requires materials that integrate efficient photon capture with rapid charge transport and robust catalytic activity. However, conventional photoelectrochemical materials are limited by the incomplete utilization of the solar spectrum and rapid charge recombination, leading to a narrowed redox potential window and compromised overall conversion efficiency. In this context, organic molecular PEC materials offer distinct advantages through their tunable, well-defined structures, enabling precise control over their electronic properties, redox behavior, and broad-spectrum light utilization. Integrating electron donor–acceptor (D–A) frameworks with redox-active or catalytic units into porous assemblies establishes spatially organized pathways for charge separation and catalytic transformation, although such a molecular-level design remains in its early stages. The central challenge lies in translating these structure–function insights into design principles that deliver multifunctional materials capable of controlled charge modulation, long-range electron transfer, and adaptive catalysis, thereby advancing the realization of complete artificial photosynthesis. In this Account, we begin with decoding PEC systems through the design principles of molecular materials, emphasizing how molecular-level modifications influence key performance metrics. The main concept of developing molecular materials through molecular engineering for artificial photosynthesis, centered on PEC energy conversion and storage, is presented in this Account. It focuses on the state-of-the-art construction of efficient D–A structures by tuning functional groups and incorporating single and dual metals, with charge dynamics regulated by thermodynamic and kinetic processes. Advances and challenges in molecular engineering are highlighted, emphasizing that designing efficient D–A architectures requires the appropriate selection of molecular functional groups, tailored structures, and optimized properties, which are crucial for regulating long-lived charge separation states and driving diverse redox reactions in PEC systems. We outline best practices for designing and assembling coupled D–A architectures, highlighting our research contributions and the broader progress in solar-to-electrochemical energy conversion and storage during the past decade. The discussion further explores coupled/decoupled strategies, which offer solutions to challenges associated with solar-driven CO 2 splitting (for CO and O 2 generation), N 2 reduction (for NH 3 synthesis), and organic molecular-level energy storage devices (solar batteries), and is extended to perspectives on sustainable development. Taken together, we anticipate that this Account will outline emerging strategies for integrating multifunctionality into PEC molecular assemblies, providing valuable design insights for adaptable materials that enhance solar-to-electrochemical energy conversion and storage efficiency.