Manipulating Spin-Orbit Coupling in Conjugated Microporous Polymers Through Torsion Engineering to Generate Efficient Triplet Excitons for High-Performance Photocatalysis.

Maximizing photon utilization in organic photocatalysis requires harnessing both singlet and triplet excitons, however, the strategies to populate the spin-forbidden triplet state in metal-free polymers are rare. To address this issue, we report a new strategy, namely employing a spin-orbit charge transfer intersystem crossing (SOCT-ISC), to unlock the triplet manifold in conjugated microporous polymers (CMPs). Using a postsynthetic [2 + 2] cycloaddition-retroelectrocyclization (CA-RE) reaction, we precisely control the cyano number in the polymer backbone. This chemical modification induces a critical orthogonal molecular torsion, which maximizes spin-orbit coupling (SOC) and minimizes the singlet-triplet energy gap (ΔEST). Femtosecond transient absorption spectroscopy confirms the efficient triplet generation by torsion engineering. Consequently, the optimized photocatalyst achieves a hydrogen peroxide (H2O2) production rate of 5.01 mmol g-1 h-1 in pure water and a rate of 101.26 mmol g-1 h-1 in a benzyl alcohol-coupled system, with a solar-to-chemical conversion (SCC) efficiency of 0.62%, and an outdoor production reaches 5 mmol L-1 daily. This work leverages torsion engineering to harness triplet excitons, demonstrating the successful overcoming of thermodynamic barriers in artificial photosynthesis.