Donor‐Acceptor Fulvalene‐Analogous Small Molecules for Efficient Photocatalytic Hydrogen Evolution

Abstract Donor–acceptor (D–A) polymers have shown great promise as photocatalysts for hydrogen evolution, benefiting from efficient exciton separation and charge mobility via their push‐pull electronic structure. However, despite advantages like cost‐effectiveness, synthetic accessibility, and well‐defined structures, D–A conjugated small molecules remain underexplored for photocatalytic applications. Herein, three novel D–A‐type fulvalene‐derived small molecules (F‐ID, F‐IC, and BF‐IC) are synthesized through systematic modulation of donor and acceptor units. Spectroscopic and theoretical investigations revealed that both the extended conjugation length of the donor unit and enhanced electron‐withdrawing capability of the acceptor unit can effectively broaden the light absorption range and reduces the optical bandgap. The optimized photocatalyst BF‐IC, exhibiting the most red‐shifted absorption and narrowest bandgap (consistent with DFT calculations), demonstrated superior photocatalytic performance with a hydrogen evolution rate of 13.43 ± 0.62 mmol h −1 g −1 using ascorbic acid as the sacrificial agent. To our knowledge, this work presents the first demonstration of highly efficient hydrogen evolution using a fulvalene‐derived D–A‐type small‐molecule photocatalyst. Our study not only establishes fulvalene‐based D–A systems as a promising new class of photocatalysts for solar‐to‐chemical energy conversion but also offers a rational molecular design strategy for high‐performance photocatalysts through structural modulation.