Regulating the electronic structure of covalent organic frameworks via heterocyclic isomers for highly efficient photocatalytic H2O2 generation

Covalent organic frameworks (COFs) are promising materials for photocatalytic hydrogen peroxide (H₂O₂) production. However, optimizing their electronic structures to enhance charge separation, oxygen adsorption, and reaction efficiency remains a challenge. Here we show that incorporating thiophene and furan isomeric units into the side chains of COFs enables precise tuning of their electronic structures and photocatalytic activity. Thiophene-containing frameworks exhibit superior charge separation and photocatalytic performance compared to those with furan, owing to stronger donor–acceptor interactions. A 2-substituted thiophene-based COF (DT₂TA-TAPB), synthesized from 1,3,5-tris(4-aminophenyl)benzene and 2,5-di(thiophen-2-yl)terephthalaldehyde, exhibits reduced exciton binding energy, extended electron lifetime, and improved spatial charge separation. Mechanistic analysis reveals that the sulfur and adjacent carbon atoms within the thiophene of DT₂TA-TAPB stabilize the endoperoxide intermediate, promoting a one-step, two-electron pathway for H₂O₂ generation. Consequently, DT₂TA-TAPB achieves H₂O₂ yields of 10972 and 8587 μmol g^-1 h^-1 in 10% ethanol and pure water, respectively, outperforming most reported COF-based photocatalysts.