Regulating π-Conjugation in sp 2 -Carbon-Linked Covalent Organic Frameworks for Efficient Metal-Free CO 2 Photoreduction with H 2 O.

The development of sp 2 -carbon-linked covalent organic frameworks (sp 2 c-COFs) as artificial photocatalysts for solar-driven conversion of CO 2 into chemical feedstock has captured growing attention, but catalytic performance has been significantly limited by their intrinsic organic linkages. Here, a simple, yet efficient approach is reported to improve the CO 2 photoreduction on metal-free sp 2 c-COFs by rationally regulating their intrinsic π-conjugation. The incorporation of ethynyl groups into conjugated skeletons affords a significant improvement in π-conjugation and facilitates the photogenerated charge separation and transfer, thereby boosting the CO 2 photoreduction in a solid-gas mode with only water vapor and CO 2 . The resultant CO production rate reaches as high as 382.0 µmol g -1  h -1 , ranking at the top among all additive-free CO 2 photoreduction catalysts. The simple modulation approach not only enables to achieve enhanced CO 2 reduction performance but also simultaneously gives a rise to extend the understanding of structure-property relationship and offer new possibilities for the development of new π-conjugated COF-based artificial photocatalysts.