Designing Interactions between Molecular Catalysts and Light Absorbers for Fine-Tuned Performances and Electron-Transfer Mechanisms in CO₂ Photoreduction

ConspectusThe conversion of CO₂ into reduced carbon products by valorizing sunlight as the energy source is a highly attractive strategy to simultaneously mitigate CO₂ emissions and generate renewable fuels. Metal complexes can serve as versatile molecular catalysts for constructing high-performance light-driven systems for CO₂ reduction owing to their well-defined structures for facile mechanism-based synthetic optimization. To drive the CO₂ reduction reaction mediated by molecular catalysts, suitable light absorbers, such as molecular photosensitizers (PSs) or solid-state semiconductors are desirable. Although considerable attention has been dedicated to the synthetic modifications in both molecular catalysts and light absorbers, further improvement using these mature components has reached a plateau. This limitation underscores the need for new design strategies. In this regard, fine-tuning interactions between catalysts and light absorbers holds great promise, as it offers the potential to substantially improve electron transfer kinetics beyond those observed in noninteracting systems, thereby enhancing overall photocatalytic efficiency.We introduce this Account first with an overview comprised of advantages and limitations of molecular systems for photocatalytic CO₂ reduction. We then describe our strategies for modulating charge transfer processes between molecular catalysts and light absorbers by installing additional intermolecular or interfacial interactions, tailored for homogeneous and heterogeneous photocatalytic systems, respectively. For homogeneous systems, we highlight the use of dynamic interactions in supramolecular preassemblies to enhance electron transfer between molecular catalysts and PSs. Representative examples illustrate how such dynamic interactions significantly improve electron transfer efficiency, resulting in state-of-the-art photocatalytic performance. We also describe methods for probing the existence, strength, and functional roles of these interactions in CO₂ photoreduction. For heterogeneous systems, we will discuss the immobilization of molecular catalysts on semiconductor surfaces as molecular hybrid photocatalysts in CO₂ reduction. This section focuses on the correlation among anchoring interactions, interfacial electron transfer dynamics, and overall photocatalytic performance. Finally, we highlight the current challenges and outline future directions for the advancement of interaction-driven molecular systems in CO₂ photoreduction. Overall, this Account is intended to provide strategies on rational design and optimization of CO₂ photoreduction systems, while offering mechanistic insights into interaction-dependent charge transfer pathways.