A Review on Organic Photosensitizers for Hydrogen Evolution by Water Splitting

Hydrogen is increasingly recognized as a key energy vector for future low-carbon energy technologies. Solar-driven water splitting offers a direct and sustainable route to its production, with organic photosensitizers (OPS) emerging as a tunable and synthetically accessible alternative to traditional semiconductors. This review summarizes recent progress in OPS for photocatalytic hydrogen evolution, encompassing diverse molecular architectures ranging from noble-metal-based complexes to noble-metal-free analogues and fully metal-free organic dyes. Particular emphasis is placed on sustainable materials design, including the use of earth-abundant elements and modular synthetic strategies. We further examine the integration of OPS into polymeric and hybrid material systemssuch as metal–organic frameworks (MOFs), conjugated polymers (CPs), and polydopamine (PDA)that enhance structural stability and light-harvesting performance. Key design principles, charge transfer dynamics, and the influence of cocatalysts and sacrificial reagents are discussed. The review concludes by outlining challenges and future directions for developing efficient, stable, and scalable OPS-based platforms for solar hydrogen production.