Mixed p–π Resonance in Pyrene‐Based Covalent Organic Frameworks: Shallow Trap Charge Dynamics for Efficient Photocatalysis in Reduction of U(VI)

ABSTRACT Covalent organic frameworks (COFs) represent a versatile platform of photocatalysis for environmental remediation. Nevertheless, their efficiency is often constrained by the presence of deep trap states that lead to rapid charge carrier recombination. Here, we fine‐tune the p–π resonance of pyrene‐based COFs by functionalizing the 5,6 positions of benzo[ c ][1,2,5]thiadiazole‐4,7‐diyl)dibenzaldehyde (BT) with electron‐withdrawing (–F), mixed (–F/–OCH 3 ), and electron‐donating (–OCH 3 ) groups followed by condensation with 4,4′,4″,4‴‐(pyrene‐1,3,6,8‐tetrayl)tetraaniline to afford BTCOF‐2F, BTCOF‐Mix, and BTCOF‐2OCH 3 , respectively. The mixed p–π resonance strengthens the internal electric field, reduces the exciton binding energy to 62.06 meV, and generates long‐lived shallow trap states with a lifetime up to 1574.6 ps for BTCOF‐Mix. As a result, BTCOF‐Mix photocatalysis realizes a U(VI) uptake of 1600.1 mg g −1 and a rate constant of 0.084 min −1 , outperforming those of BTCOF‐2F (1090.2 mg g −1 ) and BTCOF‐2OCH 3 (1245.2 mg g −1 ). Notably, BTCOF‐Mix achieves over 90% selectivity in the presence of competing ions and more than 99% reduction of U(VI) and ensuing recovery by visible‐light photocatalysis from real mining wastewater. This work demonstrates that balancing p–π resonance constitutes a viable approach for modulation of the trap state energetics of COF photocatalysis toward solar‐driven reduction and recovery of radioactive ions in aquatic environments.