Linkage chemistry-regulated excited-state behavior and reactive oxygen species pathways in donor-acceptor covalent organic polymers.

Covalent organic polymers (COPs) are promising photocatalysts for reactive oxygen species (ROS) generation due to their tunable electronic structures and interfacial properties. However, the role of linkage chemistry in regulating excited-state behavior and ROS generation pathways remains insufficiently understood. Herein, two donor-acceptor COPs differing only in linkage chemistry were constructed using 5,10,15,20-tetra(4-aminophenyl)porphyrin (H₂TAPP) as the electron donor and 2,4,6-tri(4-formylphenyl)-1,3,5-triazine (TFPT) as the electron acceptor, yielding an amide-linked TFPT-Por-COP and an imine-linked TFPT-TAPP-COP. Both COPs exhibit amorphous structures and comparable visible-light absorption, yet display distinctly different photocatalytic behaviors. Spectroscopic characterizations combined with charge density difference (CDD) calculations reveal that the amide linkage induces localized charge redistribution and restrained excited states, whereas the imine linkage promotes electronic delocalization and charge-transfer (CT) characteristics. As a result, TFPT-Por-COP predominantly generates singlet oxygen (1O2), while TFPT-TAPP-COP favors superoxide radical (•O2-) formation, as confirmed by electron spin resonance (ESR) and probe-based experiments. Benefiting from efficient 1O2 generation and superior chemical stability, TFPT-Por-COP was further applied to the fluorescence detection of vitamin B1 (VB1), achieving a low detection limit of 6.5 nmol/L. This work highlights linkage chemistry as a key parameter for modulating excited-state evolution and ROS selectivity in COP-based photocatalytic systems.