Fully Conjugated Two-Dimensional sp2-Carbon Covalent Organic Frameworks as Artificial Photosystem I with High Efficiency

The synthesis of fully conjugated sp²-carbon covalent organic frameworks (COF) is extremely challenging given the difficulty of the formation of very stable carbon-carbon double bonds (-C=C-). Here, we report the successful preparation of a 2D COF (TP-COF) based on triazine as central planar units bridged by sp²-carbon linkers through the -C=C- condensation reaction. High-resolution-transmission electron microscopy (HRTEM) clearly confirmed the tessellated hexagonal pore structure with a pore center-to-center distance of 2 nm. Powder X-ray diffraction (PXRD) together with structural simulations revealed an AA stacking mode of the obtained layered structure. TP-COF turned out to be an excellent semiconductor material with a LUMO energy of −3.23 eV and a band gap of 2.36 eV. Excitingly, this novel sp²-carbon conjugated TP-COF exhibited unprecedented coenzyme regeneration efficiency and can significantly boost the coenzyme-assisted synthesis of l-glutamate to a record-breaking 97 % yield within 12 minutes.