Nitrogen‐Site Isomerism Unlocks Exciton Dissociation in Vinylene‐Linked COF‐Based Photocatalysts

ABSTRACT

Although covalent organic frameworks (COFs) have garnered significant attention as versatile scaffolds in photocatalysis, it is constrained by the sluggish charge‐carrier dissociation inherent to organic semiconductors. Moreover, how subtle changes in atomic topology within an otherwise similar framework translate into macroscopic optoelectronic behavior remains insufficiently understood. Herein, we demonstrate that precise nitrogen‐site isomerism within the framework backbone serves as a critical lever to manipulate exciton dynamics. By synthesizing two regioisomeric vinylene‐linked COFs, PzDA‐TMT‐COF (pyrazine‐based, para‐N) and DzDA‐TMT‐COF (pyridazine‐based, ortho‐N), we reveal that a subtle translocation of nitrogen atoms induces a profound divergence in charge‐separation efficiency. Despite identical chemical compositions and porosities, the para‐configured PzDA‐TMT‐COF delivers a significantly enhanced hydrogen evolution rate of 13.2 mmol g ⁻¹  h ⁻¹ , significantly outperforming its ortho‐analogue. It is elucidated that this “atomic editing” fundamentally reshapes the intramolecular potential landscape: the para‐substitution maximizes donor–acceptor polarization and minimizes exciton binding energy, thereby accelerating the transition from bound excitons to free charge carriers. Our findings establish a rigorous structure–activity relationship, highlighting that rational control over heteroatom placement is a paramount design principle for organic photocatalysts.