A Luminescent Benzimidazole‐Linked Porphyrin Covalent Organic Polymer for Sensitive and Reversible Sensing of Roxarsone in Aqueous Media

The selective detection of toxic organoarsenic compounds in aqueous media presents a significant environmental and analytical challenge. In this study, we report a luminescent benzimidazole‐linked porphyrin covalent organic polymer ( Por‐BPI‐COP ) designed for the fluorescence‐based detection of roxarsone (ROX) in aqueous media. Por‐BPI‐COP is readily synthesized using a one‐pot, metal‐free polycondensation reaction and characterized using standard spectroscopic and microscopic techniques. It demonstrates excellent thermal and chemical stability and strong intrinsic luminescence. Upon titration with ROX, Por‐BPI‐COP exhibits efficient fluorescence “turn‐off” sensing behavior, achieving a Stern‐Volmer quenching constant ( K _SV ) of 9.0 × 10 ³  M ⁻¹ , a limit of detection of 6.8 nM, and a fluorescence quenching efficiency of approximately 46%. Steady‐state and time‐resolved spectroscopic studies indicate that static quenching primarily underlies the sensing response. This mechanism arises from ground‐state donor–acceptor interactions between the π ‐conjugated polymer framework and the electron‐deficient ROX, further supported by specific hydrogen‐bonding interactions. The sensor also displays high selectivity for ROX, reversible fluorescence recovery across multiple sensing cycles, and reliable performance in real water samples. Furthermore, DFT calculations provided molecular‐level insight into the interaction between ROX and Por‐BPI‐COP . This work establishes benzimidazole‐linked porphyrin COPs as a promising new class of luminescent materials for detecting organoarsenic compounds in aqueous environments.