Donor–Acceptor Pairs in Covalent Organic Frameworks Promoting Electron Transfer for Metal-Free Photocatalytic Organic Synthesis

Abstract

The donor−acceptor-type covalent organic frameworks (COFs) have recently gained increasing interest in photocatalysis, but the photoinduced electron-transfer regimes in the COFs are underexplored. Herein, we demonstrate a designed porphyrinic COF possessing a donor− acceptor structure together with its photocatalytic performance in aerobic coupling of primary amines. The COF could be photoexcited by the full range of visible light to generate electron−hole pairs that could be separated by donor−acceptor pairs. Electron transfer as the mechanism of the reaction from anthracene unit to porphyrin unit was revealed by natural transition orbitals analyses. The electrons migrate to the adsorbed O 2 to generate reactive oxidative species. The COF displays remarkable photocatalytic activities in the coupling of amines to imines, which can be explained mainly by the sufficient charge separation and mobility, benefiting from the donor−acceptor pairs in the COF and their interactions to the reactants and intermediates.

Fabrication of a Covalent Organic Framework-Based Heterojunction via Coupling with ZnAgInS Nanosphere with High Photocatalytic Activity

“…The result (Figure 7a, ZnAgInS/COF(5) + Always dark) showed that there was no obvious dye degradation under the dark condition. As shown in Figure 7a, the absorption efficiencies of the samples for RhB after 30 min of dark reaction were 3.6, 3.8, 3.2, 4.6, 4, and 3.6% for ZnAgInS, COF, ZnAgInS/ COF(2.5), ZnAgInS/COF(5), ZnAgInS/COF (15), and ZnA-gInS/COF (25), respectively. This indicates that the absorption capacities of the prepared samples are close and without obvious differences.…”

“…As shown in Scheme 1, the ZnAgInS/COF was prepared with a facile oil bath heating method that was similar to the preparation of ZnAgInS, except for the addition of TpPa-1 COF at the first step. The prepared ZnAgInS/COF composites with different amounts of TpPa-1 COF (2.5, 5, 15, and 25 wt %) were denoted as ZnAgInS/COF(2.5), ZnAgInS/COF(5), ZnAgInS/COF (15), and ZnAgInS/COF (25), respectively.…”

“…To this point, many photocatalysts have been developed for the degradation of organic pollutants. However, most of them suffer from low photocatalytic activities due to the high recombination rate of the photogenerated charge carriers and low sunlight utilization and quantum yield. , Recently, as a new type of porous crystal materials, covalent organic frameworks (COFs) constructed from organic molecules with covalent bond have attracted a lot of attention. − …”

“…Figure 2. SEM images of (a) ZnAgInS, (b) TpPa-1 COF, (c) ZnAgInS/COF(2.5), (d) ZnAgInS/COF(5), and (e) ZnAgInS/COF(25). TEM images of (f) ZnAgInS, (g) TpPa-1 COF, and (h) ZnAgInS/COF(5).…”

Local charge transfer within a covalent organic framework and Pt nanoparticles promoting interfacial catalysis

“…26 Their tailorable chemical structure allows for tuning of the electronic state of encapsulated metal NPs by tuning the interactions between the pore wall atoms and metal atoms. 27 Importantly, each atom in the framework can be precisely determined, 28–30 which is key to studying the detailed catalytic mechanism and structure–activity relationships. All these factors make COFs promising candidates to encapsulate metal NPs, 31 particularly small metal NPs.…”