Computational Study of Linker Polarity Effects on Optical Electron Transfer in Imine- and Acylhydrazone-Linked...

Covalent organic frameworks (COFs) have become a research hotspot in photocatalytic materials in recent years due to their highly ordered structures, tunable topologies, and excellent optoelectronic properties. However, the relationship between linker polarity and the direction of optical electron transfer between adjacent structural units remains poorly understood. This study employs density functional theory (DFT) and time-dependent DFT (TD-DFT) calculations to systematically investigate the effects of polarity reversal in imine and acylhydrazone linkers, as well as different fragment models, on the effective optical net electron transfer. To this end, four representative fragment models (K01-K04) were constructed to simulate linear, multi-connected, and branched environments. The results show that, across all models, the direction of the effective optical net electron transfer from phenyl unit (Ph) to UnitB (QPh→UnitB) is highly consistent with the polarity direction of the linker. In imine-linked systems, when the dipole moment of the linker aligns with the intrinsic dipole moment direction between Ph and UnitB, the absolute value of QPh→UnitB is significantly enhanced; in acylhydrazone-linked systems, only K02 and K03 exhibit similar behavior, while K01 and K04 show no obvious enhancement. These findings provide important guidance for designing efficient photocatalytic COFs: tuning the linker orientation to match the intrinsic polarity of adjacent structural units can significantly improve the efficiency of optical net electron transfer between them.