Band‐Gap Engineering of Isoreticular Hydrogen‐Bonded Organic Frameworks for Boosting Photocatalytic Hydrogen Evolution

ABSTRACT The rational modulation of band structures in organic semiconductors is central to advancing photocatalytic performance but remains challenging for hydrogen‐bonded organic frameworks (HOFs) due to their structural sensitivity to the modification of organic building units (OBUs). Here, based on the stable mesoporous framework HOF‐102, π‐conjugation‐extended and donor‐acceptor‐tuned OBUs were predesigned by substituting the steric naphthalene units with benzene‐vinyl derivatives bearing ─H, ─CH 3 , or ─CN groups. Through a shape‐fitted π─π stacking strategy, three mesoporous HOFs isoreticular with HOF‐102 were synthesized from the tailored OBUs, namely HOF‐1022, HOF‐1022(CH 3 ), and HOF‐1022(CN). These as‐synthesized HOFs exhibit pronounced variations in visible‐light absorption, with band gaps adjustable from 2.46 to 1.86 eV. Among these HOFs, the D‐A‐optimized HOF‐1022(CN) possesses the narrowest band gap and exhibits significantly enhanced intraframework electron transfer and suppressed charge recombination, yielding an impressive hydrogen evolution activity of 168.2 mmol g −1 h −1 , which is 8.5 times higher than that of HOF‐1022(CH 3 ), and an apparent quantum yield (AQY) of 7.3% at 420 nm. This study represents the first demonstration of band‐gap engineering in HOFs materials and establishes a generalizable molecular‐design principle for developing high‐performance HOFs‐based photocatalysts.