A covalent organic framework containing bipyridine groups as a fluorescent chemical probe for the ultrasensitive detection of arsenic (III)

• The bipyridine sites of Dpy-TFPB COF acted as selective As 3+ receptors. • The COF is convenient to synthesize and shows good usability. • The COF shows ultralow detection limit, excellent pH stability, and good selectivity. • The study demonstrates the application potential of COFs for As 3+ detection. As a major pollutant, inorganic As(III) is highly toxic, commonly found in the environment, and causes serious public health problems. We created a novel fluorescent switch based on covalent organic frameworks (COF) for detecting arsenic (As 3+ ). The switch was formed by using a bipyridine-based functional COF called Dpy-TFPB. Dpy-TFPB’s nitrogen-based sites are highly selective receptors for As 3+ , and its π bonds act as the signal responder. After adding As 3+ to Dpy-TFPB, we prevent the photoinduced electron transfer (PET) process, and a distinct fluorescent switch-on occurred immediately in the form of a clear, fluorescent color change. As a sensing tool, Dpy-TFPB demonstrated a readily observable response, a high degree of sensitivity, and detected As 3+ in real-time. An ultralow detection limit of 8.86 nmol/L As 3+ was confirmed. X-ray photoelectron spectroscopy and frontier molecular orbital distribution analysis confirmed the selective interactions between As 3+ and the bipyridine sites of Dpy-TFPB that affected the PET process of the COF. We not only demonstrate the potential of COFs to be used as a fluorescent switch-on probe for As 3+ , but also propose the easy framing of novel COFs through the introduction of chelating sites for toxic metals.