π-Electronic Effects Dictate Interlayer Charge Transfer in Covalent Organic Frameworks With Boosted Photocatalytic Activity

Understanding interlayer charge transfer is central to the rational design of two-dimensional (2D) covalent organic frameworks (COFs) for high-performance photocatalysis. Herein, we successfully modulate the interlayer charge transfer in donor-imine-donor type COFs by regulating the π-electronic character of knots and linkers. We demonstrate that the rigid pyrene-based knot with profound π-electronic effect promotes efficient interlayer charge transfer, whereas the twisted biphenyl-based counterpart effectively inhibits it combining with experimental and theoretical calculations. Specifically, the pyrene-based units endow enhanced conjugation, improved planarity, and strengthened π-π stacking, giving rise to a substantially larger interlayer charge transfer amount for the fully rigid R-R-COF compared with the twisted T-T-COF. Consequently, R-R-COF achieves a superior H₂ evolution rate of 80.6 mmol g^-1 h^-1, 89.6 times that of T-T-COF (0.9 mmol g^-1 h^-1) under identical conditions. Additionally, we reveal that topological selectivity correlates closely with the electronic nature of the knot. This work establishes π-electronic effect as a key determinant of both interlayer charge transfer efficiency and photocatalytic activity, and provides a rational design strategy for advanced COF-based photocatalysts.