Fused Ring Engineering Induced Topology Control in Covalent Organic Frameworks: Unlocking Promoted Photocatalytic H2O2 Production and Selective Methane Oxidation.

Efficient solar-to-chemical energy conversion and the selective activation of methane remain grand challenges in artificial photosynthesis. Here, we report the rational design of two covalent organic frameworks (COFs), Phen-TTA and O-TTA, in which framework topology and π-conjugation are regulated by pairing a triazine-based acceptor with either a rigid 1,10-phenanthroline or a twisted 2,2'-bipyridine donor. The results show that the Phen-TTA, bearing a rigid kgd-v topology, features a narrowed bandgap, reduced exciton binding energy, and accelerated charge-carrier kinetics relative to O-TTA with an hcb topology. Consequently, Phen-TTA delivers a high photocatalytic H2O2 production behavior (21.5 mmol h-1 g-1 and an apparent quantum yield of 5.45% at 450 nm), placing it among the most active COF-based photocatalysts ever reported. Notably, Phen-TTA further enables selective photocatalytic methane oxidation to ethanol (30.1 µmol h-1 g-1, 365 nm irradiation) in the absence of noble-metal cocatalysts. Mechanistic investigations indicate that the enhanced framework rigidity promotes sequential one-electron oxygen reduction to H2O2, while the sustained H2O2 supply undergoes photolysis to yield •OH that drive C─H activation. This work establishes topology engineering as an effective strategy to overcome excitonic and charge-transport limitations in polymeric photocatalysts and demonstrates a rare single-component organic framework for tandem solar-driven methane valorization.