Engineering N-site isomerism in donor-acceptor covalent organic frameworks for efficient Fenton-like water...

Covalent organic frameworks (COFs) have emerged as promising candidates for singlet oxygen (¹O₂) generation via peroxymonosulfate (PMS) activation, yet their structure-property-activity relationships remain poorly understood. Herein, three constitutionally isomeric donor-acceptor COFs (TF-22Bpy, TA-22Bpy and TA-33Bpy) were constructed via N-site isomeric engineering, which involved precisely modulation of the imine and pyridine nitrogen positions within the skeleton. This systematically structural engineering was undertaken to unravel the fundamental effects of regioisomerism on both the electronic structure and subsequent Fenton-like catalytic activity. Among the isomers, TA-33Bpy showed the best catalytic activity for PMS activation, exhibiting an observed rate constant (k_obs) of 0.165 min^-1. This value is substantially higher than those of TF-22Bpy (0.013 min^-1) and TA-22Bpy (0.052 min^-1) by factors of 12.7 and 3.2, respectively. Mechanistic investigations indicate that direct PMS-COF interaction induces charge polarization within the donor-acceptor framework, generating localized electron-deficient and electron-enriched domains that promote the coupled redox steps required for selective ¹O₂ generation. This work identifies PMS-triggered charge polarization as a key determinant of PMS activation and offers a design principle for high-performance COF catalysts for water purification.