Triplet Exciton‐Enhanced Photosynthesis of Hydrogen Peroxide Enabled by Topologically Tuned Covalent Organic Frameworks

Abstract Artificial photosynthesis technology can utilize water, oxygen, and solar energy to produce hydrogen peroxide (H 2 O 2 ), an environmentally friendly oxidant and a clean fuel. However, H 2 O 2 photosynthesis mainly follows photogenerated electrons/holes pathway, which suffers from high thermodynamic barriers and competing reactions. Triplet excitons can spontaneously convert O 2 into singlet oxygen ( 1 O 2 ) intermediate and bypass these challenges, but demonstrating its effects on photocatalysis is still scarce. Here, this study designs twist pyrimidine‐based covalent organic frameworks with excellent triplet exciton production using a topological tuning strategy. The twist configuration modulates the molecular orbital overlap between singlet and triplet states and achieves a 1.8 × 10 7 enhancement in the intersystem crossing rate, obtaining excitation of triplet excitons and the generation of 1 O 2 , rather than exciting photogenerated electrons and holes. A novel triplet exciton‐ 1 O 2 H 2 O 2 photosynthesis pathway is achieved and demonstrates a 38.6% reduction in the generation barrier compared to typical redox pathway, obtaining record activity with rates of 10.80 mmol g −1 h −1 in an O 2 atmosphere and 7.82 mmol g −1 h −1 in air, without the need for a sacrificial agent. The solar‐to‐chemical conversion efficiency is 1.25%.