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

Abstract

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 (As3+). 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 As3+, and its π bonds act as the signal responder. After adding As3+ 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 As3+ in real-time. An ultralow detection limit of 8.86 nmol/L As3+ was confirmed. X-ray photoelectron spectroscopy and frontier molecular orbital distribution analysis confirmed the selective interactions between As3+ 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 As3+, but also propose the easy framing of novel COFs through the introduction of chelating sites for toxic metals.