2D sp2 Carbon-Conjugated Covalent Organic Frameworks for Photocatalytic Hydrogen Production from Water

Photo-to-chemical energy conversion requires a systematic and complex molecular design to manage consecutive photochemical processes, including energy harvesting, exciton migration, electron transfer, charge separation, and charge transport. However, such an integrated design remains a substantial challenge. Here, we report a seamless system in managing these photochemical events on the basis of two-dimensional sp(2) carbon-conjugated covalent organic frameworks. The frameworks are designed to be fully pi conjugated for harvesting a wide range of visible to near-infrared light and to constitute built-in donor-acceptor heterojunction interfaces for splitting excitons. The frameworks create dense yet ordered columnar pi arrays that offer pathways to facilitate exciton migration and charge transport. Loading reaction centers in pores or on surface shortens the electron-transfer distance and promotes the accumulation of electrons at the reaction centers. These three molecular mechanisms are seamlessly integrated in the frameworks and render the system able to efficiently produce hydrogen that is driven by low-energy photons.