Research Progress in Donor−Acceptor Type Covalent Organic Frameworks

Abstract

Covalent organic frameworks (COFs) are new organic porous materials constructed by covalent bonds, with the advantages of pre‐designable topology, adjustable pore size and abundant active sites. Many research studies have shown that COFs exhibit great potential in gas adsorption, molecular separation, catalysis, drug delivery, energy storage, etc. However, the electrons and holes of intrinsic COF are prone to compounding in transport, and the carrier lifetime is short. The donor‐acceptor (D−A) type COFs, which are synthesized by introducing D and A units into the COFs backbone, combine separated electron and hole migration pathway, tunable band gap and optoelectronic properties of D‐A type polymers with the unique advantages of COFs and have made great progress in related research in recent years. Here, the synthetic strategies of D−A type COFs are firstly outlined, including the rational design of linkages and D−A units as well as functionalization approaches. Then the applications of D−A type COFs in catalytic reactions, photothermal therapy and electronic materials are systematically summarized. In the final section, the current challenges, and new directions for the development of D−A type COFs are presented.This article is protected by copyright. All rights reserved

Molecular engineering of donor–acceptor sp2-carbon-linked covalent organic frameworks for enhancing photocatalytic hydrogen production

“…Therefore, adjusting the band gap by intensifying the electron-donating ability of the donor was one of the strategies to build an efficient D–A COF platform. 36 The optical band gap ( E g ) was calculated using the Kubelka–Munk function and Tauc plots, and for TTh-COF (2.06 eV), it was narrower than that of Th-COF ( E g = 2.13 eV) and Ph-COF ( E g = 2.53 eV) (Fig. 3b and c).…”

“…31–35 Additionally, D and A structural engineering has been established as an effective method for modulating band gaps to optimize the photocatalytic activity from theoretical studies. 34–36 In D–A type polymers, the lowest unoccupied molecular orbital (LUMO) energy level and the highest occupied molecular orbital (HOMO) energy level are generally determined by the acceptor unit and the donor unit, respectively. Therefore, we can adjust and predict the band gap of D–A COFs at the molecular level by selecting different D and A units according to the requirements of practical application.…”

“…Therefore, we can adjust and predict the band gap of D–A COFs at the molecular level by selecting different D and A units according to the requirements of practical application. 36,37 In addition, π conjugation of bonds also affects electron transfer and light absorption behavior. Fully conjugated sp 2 –carbon bonds effectively enhance the conjugation of COFs, which not only broadens the absorption range of visible light and promotes charge transfer, but also improves the photo-thermal stability of materials.…”

Graphitic Carbon Nitride Modified with 2-Aminothiophene-3-Carbonitrile to Boost Molecular Dipole and n → π* Electronic Transition for Photoreduction of Carbon Dioxide

“…The high symmetry structure of g-CN shows a uniform ESP distribution, which also indicates the absence of additional driving force for charge separation in the triazine unit. In this situation, charge in the entire molecular surface moved disorderly, and the electrons and holes are easy to recombine . It is worth noting that in g-CN-ACT0.05, the region around the ACT molecule showed a negative charge (red part), the triazine unit connected to the ACT is also reshaped due to the IEF resulted from the electron-rich ACT group.…”

“…Moreover, the dipole-induced interactions of symmetrical structures in the conjugated supramolecular network neutralize each other, resulting in the restoration of the excitonic state of electrons. This restoration process transforms the ordered transfer of electron–hole pairs into a disordered and chaotic state, which hampers the separation and transfer of electron–hole pairs …”