Rational Regulation of Dipole Polarization in Donor–Acceptor Covalent Organic Frameworks for Enhanced Photocatalytic Efficiency

The energy difference between the donor and acceptor, along with the energy loss during the charge transfer state, are two critical factors influencing the photocatalytic efficiency of donor–acceptor covalent organic frameworks (D–A COFs). However, there are no reports that systematically clarify the effects of these two aspects based on precise structural models. Herein, three D–A COFs are synthesized using benzene-cored triamines with varying numbers of phenyl groups (n = 1, 2, 3) as electron donors. In particular, the well-designed COFs (named as Tp-Tapb COF), with optimal dipole polarization and planarity, exhibit the highest activity for photocatalytic oxidation of amines in air under visible light illumination and ambient conditions. Furthermore, the experimental results and theoretical calculations revealed that increasing the number of phenyl groups, from 1 (4.18 D) to 2 (4.76 D), contributes to a larger dipole moment, facilitating effective charge transfer and separation. In contrast, a significant reduction in the planarity of COFs inhibits π conjugation, leading to increased energy loss during the charge transfer state, as the number of phenyl groups increases from 2 to 3 (4.96 D). This work provides valuable insight for constructing high-performance linear-linked COFs photocatalysts through rational modulation of dipole polarization.