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.