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Unveiling the Optimal Conjugation Threshold in Covalent Organic Frameworks for Photocatalytic Hydrogen Peroxide
Mengying Fu1, Zhiqing Lin1, Songyao Dai1
1School of Chemical Engineering and Light Industry, Guangdong University of Technology, Guangzhou, China.
None:
Solar-driven photocatalytic synthesis of hydrogen peroxide (H2O2) offers a sustainable alternative to the energy-intensive anthraquinone process. Donor-acceptor (D-A) covalent organic frameworks (COFs) are highly promising photocatalysts for this transformation; however, the precise correlation between electronic conjugation, D-A pairing, and catalytic efficiency remains poorly understood. Here, we systematically investigate the threshold of conjugation enhancement on photocatalytic H2O2 production by designing D-A COFs with varying degrees of π-conjugation. Using benzotrithiophene (BTT) as the electron donor, we integrated acceptor units featuring alkyne and extended-ring motifs (yielding TATAB-BTT and TATAP-BTT). We reveal a distinct structure-activity relationship: moderate conjugation (TATAB-BTT) optimizes energy-level matching and maximizes charge separation, achieving an outstanding H2O2 production rate of 1610.8 µmol g-1 h-1, outperforming the less-conjugated literature example, TAPB-BTT (557.0 µmol g-1 h-1). Conversely, excessive conjugation (TATAP-BTT) induces a structural mismatch that shifts the electronic configuration from D-A to D-D, severely trapping excitons and diminishing performance (780.0 µmol g-1 h-1. These findings demonstrate that an optimal conjugation threshold is critical for sustaining D-A charge-transfer dynamics, providing a fundamental molecular design principle for next-generation polymeric photocatalysts.
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