Light‐Induced Dynamic Burstein‐Moss‐Type Modulation in Polar Hydrazone‐Linked COFs for H 2 O 2 Photosynthesis

ABSTRACT Efficient photocatalytic H 2 O 2 synthesis in covalent organic frameworks (COFs) requires photogenerated electrons that retain sufficient reducing power after exciton dissociation for O 2 activation and proton‐coupled *OOH formation. However, separated electrons may undergo low‐energy relaxation, localization, trapping, or recombination before reaching reactive sites, thereby weakening their effective reactivity. In photoexcited semiconductors, bandgap renormalization (BGR) commonly favors optical‐gap narrowing and lower‐energy transitions. Herein, we report BTH‐BTDA‐COF, a polar thienyl‐regulated hydrazone‐linked COF that exhibits light‐induced dynamic Burstein–Moss‐type modulation enabled by local charge inhomogeneity. Thienyl incorporation amplifies asymmetric charge polarization, promoting exciton dissociation and photoinduced electron enrichment. Excitation‐density‐dependent PL spectral redistribution, illumination‐dependent transient absorption evolution, light‐induced surface‐potential changes, and prolonged charge‐separated‐state dynamics collectively support carrier‐density‐dependent state filling, which suppresses low‐energy relaxation and helps preserve photogenerated electrons with sufficient reducing power for O 2 activation. Meanwhile, the hydrazone‐linked microenvironment provides proton‐accessible hydrogen‐bonding sites that stabilize oxygenated intermediates and facilitate proton‐assisted *OOH formation. Consequently, BTH‐BTDA‐COF achieves an H 2 O 2 production rate of 7.5 mmol g ‒1 h ‒1 , an apparent quantum yield (AQY) of 11.4% at 420 nm, and a solar‐to‐chemical conversion (SCC) efficiency of 1.04%. This work establishes dynamic Burstein–Moss‐type modulation as a molecular strategy for regulating post‐dissociation electron reactivity and promoting efficient H 2 O 2 photosynthesis in COFs.