Molecular Engineering of Donor–Acceptor Structures in Fullerene‐Indacenodithiophene Photocatalysts for Efficient Hydrogen Evolution

ABSTRACT Organic semiconductor photocatalysts hold promise for solar‐driven hydrogen evolution, yet their efficiency is often constrained by weak intermolecular interactions, limited light‐harvesting ability, and inefficient charge transport. Addressing these challenges requires precise structural modulation of donor–acceptor assemblies to establish robust electronic coupling and broaden absorption profiles. In this study, a molecular engineering strategy is introduced that simultaneously tailors the donor side chains and tunes the size of the fullerene acceptor cage, thereby promoting electron transport and enhancing light absorption, which ultimately leads to improve photocatalytic activity. Three fullerene‐indacenodithiophene (IDT) derivatives—SA‐C 60 ‐DTIDTT (SA‐C1), SA‐C 60 ‐IDTT (SA‐C2), and SA‐C 70 ‐IDTT (SA‐C3)—are synthesized and assembled into supramolecular architectures through a liquid–liquid interfacial deposition method. Replacing the thiophene ring in the donor side chain with a benzene ring strengthens π–π stacking interactions, resulting in more efficient charge transport pathways. Incorporation of C 70 , with its extended π‐system, further facilitates electron delocalization and broadens visible‐light absorption. As a result, the SA‐C 70 ‐IDTT photocatalyst achieves a hydrogen evolution rate of 17.16 mmol g −1 h −1 . This study highlights the effectiveness of donor–acceptor structural modulation for constructing high‐performance, solar‐driven hydrogen evolution photocatalysts.