Linker‐Engineered Dimeric Acceptors Afford Efficient Organic Photocatalytic Hydrogen Evolution via Tailored Nanomorphology for Long‐Lived Charge Accumulation

ABSTRACT Organic bulk‐heterojunction (BHJ) nanoparticles are promising candidates for solar‐to‐hydrogen conversion. While the development of organic photocatalysts (OPCs) has leveraged advances in organic photovoltaics (OPVs), molecular design rules tailored to photocatalysis remain underdeveloped. Here we introduce linker‐engineered dimeric acceptors that tune self‐assembly and thereby control BHJ nanoparticle morphology, enabling high‐performance OPCs. Two dimer acceptors, DY1 (unfused linker) and DY2 (fused linker), are synthesised from a monomer analogue (MY), establishing a self‐assembly trend of MY > DY2 > DY1. The stronger intermolecular assembly of MY is consistent with a quasi‐core–shell morphology that reduces catalytically accessible donor–acceptor interfaces, whereas the weaker intermolecular assembly of DY1 is associated with a more intermixed morphology and increased recombination losses. In contrast, DY2 exhibits a morphology consistent with improved pathway continuity and sufficient donor/acceptor exposure at the particle surface, supporting enhanced accumulation of long‐lived, surface‐stabilised charges. Consequently, PM6:DY2 OPCs deliver a hydrogen evolution rate of 25.3 µmol h −1 cm −2 , outperforming PM6:MY (1.9 µmol h −1 cm −2 ) and PM6:DY1 (11.9 µmol h −1 cm −2 ). Notably, this performance trend contrasts with that of the corresponding OPVs, suggesting that photovoltaic design principles do not necessarily translate directly to photocatalysts.