Sulfur Conversion to Donor-Acceptor Ladder Polymer Networks through Mechanochemical Nucleophilic Aromatic Substitution for Efficient CO₂ Photoreduction

The development of synthetic methods capable of converting elemental sulfur into conjugated porous sulfur-rich polymers remains a great challenge, although direct utilization of this readily available feedstock can significantly enrich its uses and circumvent environmental problems during sulfur storage. We report herein mechanochemical (MC) nucleophilic aromatic substitution (S_NAr) that enables sulfur conversion into thianthrene-bridged porous ladder polymer networks with dense donor-acceptor (D−A) molecular junctions. We demonstrate that the key lies in the generation of bent thianthrene units through a solid-state ball-milling condensation reaction between 1,2-dihaloarenes and elemental sulfur. We also show that the assembling of D−A structural motifs into porous networks affords efficient visible-light-driven photocatalytic reduction of carbon dioxide (CO₂) with water (H₂O) vapor, in the absence of any additional photosensitizer, sacrificial agents or cocatalysts. Exceptional photoinduced charge separation along with boosted exciton dissociation results in a high-performance of carbon monoxide (CO) production rate of 306.1 μmol g⁻¹ h⁻¹ with near 100 % CO selectivity, which is accompanied by H₂O oxidation to O₂, as confirmed by both experimental and theoretical results. We anticipate this novel MC S_NAr approach will advance processing techniques for direct sulfur utilization and facilitate new possibilities for the synthesis of D−A ladder polymer networks with promising potential in photocatalysis.