A Stably Water-Dispersible Cyano-Containing Fully Conjugated Covalent Organic Framework for the Fluorescence Detection of Copper Ions in Aqueous Solution

Excessive and insufficient copper ions in the environmental water bodies will cause various physiological diseases, and thus, the quantitative detection of Cu2+ in water is of vital importance for human health. Covalent organic frameworks (COFs) have shown promising prospects for effective Cu2+ detection due to their robust chemical stability, structural flexibility, and tailorable functionality. However, the majority of COFs, constructed by aryl monomers through π-conjugated frameworks, exhibit high hydrophobicity, which limits their applications in aqueous environments. Here, we address this issue by introducing cyano groups into the skeleton to enhance its hydrophilicity for the synthesis of a fully conjugated COF (TFPT-PDAN) that is capable of dispersing well and stably in water. The resultant TFPT-PDAN aqueous dispersion exhibits a strong and stable fluorescence, and the addition of Cu2+ could cause its fluorescence quenching, which is attributed to the photoinduced electron transfer (PET) process between Cu2+ as the acceptor and TFPT-PDAN as the donor. As expected, TFPT-PDAN exhibits favorable specificity and high sensitivity for detecting Cu2+. This work depicts the possibility of overcoming the dispersion challenge of COFs in water, expanding their sensing applications in aqueous media.