Reconstructed covalent organic frameworks

Abstract

Covalent organic frameworks (COFs) are distinguished from other organic polymers by their crystallinity1–3, but it remains challenging to obtain robust, highly crystalline COFs because the framework-forming reactions are poorly reversible4,5. More reversible chemistry can improve crystallinity6–9, but this typically yields COFs with poor physicochemical stability and limited application scope5. Here we report a general and scalable protocol to prepare robust, highly crystalline imine COFs, based on an unexpected framework reconstruction. In contrast to standard approaches in which monomers are initially randomly aligned, our method involves the pre-organization of monomers using a reversible and removable covalent tether, followed by confined polymerization. This reconstruction route produces reconstructed COFs with greatly enhanced crystallinity and much higher porosity by means of a simple vacuum-free synthetic procedure. The increased crystallinity in the reconstructed COFs improves charge carrier transport, leading to sacrificial photocatalytic hydrogen evolution rates of up to 27.98 mmol h−1 g−1. This nanoconfinement-assisted reconstruction strategy is a step towards programming function in organic materials through atomistic structural control.

The effect of enantioselective chiral covalent organic frameworks and cysteine sacrificial donors on photocatalytic hydrogen evolution

“…Meanwhile, 2D COFs have established an unequivocal structure-to-activity correlation based on periodic atomic frameworks and ordered stacking sequences. Especially for photosynthesis, the crystalline 2D COFs exhibit remarkable superiority compared to the other known amorphous organic photocatalysts 28 – 30 . The photocatalytic functionality has been promoted by incorporating photosensitizing groups in building blocks 31 , 32 , constructing donor-acceptor on skeletons 33 – 35 , and extending π-electron conjugation along backbones 36 – 38 .…”

Photo-tailored heterocrystalline covalent organic framework membranes for organics separation

“…NMR spectra reveal that the resonance peaks of PCOM are wider and less resolved than those of DCOM, confirming the poor development of crystalline structure in PCOM (Supplementary Fig. 5 ) 32 . FTIR spectra demonstrate that the C = C stretching band in the keto-enamine linkage of PCOMs was more intense than that of DCOM (Supplementary Fig.…”

Spatial Regulation of Acceptor Units in Olefin‐Linked COFs toward Highly Efficient Photocatalytic H2 Evolution

“…Covalent organic frameworks (COFs), [ 6 ] as a typical class of crystalline porous framework polymers, have attracted increasing attention as photocatalytic candidates due to their highly conjugated, adjustable structures, and anisotropic transport of photogenerated charges. [ 7 ] COFs are usually synthesized by condensation of different monomers, which greatly facilitates the ordered assembly and spatial distance regulation of various acceptor units. Another distinct feature of COFs is their adjustable distance of active centers, which can be controlled by the geometry and size of the monomers.…”

“…In the past decades, many strategies have been developed to boost the photocatalytic performance of COFs, such as active molecular building blocks stack, [ 11 ] donor–acceptor combination, [ 12 ] crystallinity improvement, [ 7a,13 ] heterojunction construction. [ 14 ] Although the photocatalytic efficiency of COFs has been significantly improved, their light conversion efficiency (apparent quantum yield, AQY) of photocatalytic H 2 evolution still has great room for improvement (only ≈10% at present, Table S1, Supporting Information).…”