Molecular insights into multi-channel detection of nitrophenol explosives and acids in covalent organic frameworks with diverse hydrazone moieties

Hydrazone-linked covalent organic frameworks are emerging candidates for sensing applications due to their sufficient binding sites and structural concise interfaces. The influence of structural motifs about the hydrazone group on visualization sensing performance and key technology of applications still needs to be illuminated. Herein, two stable crystalline hydrazone-linked COFs (Pythz-COF and Pyaph-COF) with different hydrazone bond content in their skeleton are synthesized by using terephthalic dihydrazide (Thz) and 4-aminobenzohydrazide (APH) as linker, respectively. Both of the COFs presented multi-channel fluorescence sensing ability to nitrophenol explosives and various acids. In particular, Pythz-COF showed a good fluorescence quenching response to 2,4,6-trinitrophenol (TNP), and the KSV value was 7.9 × 104 M−1. At the same time, they also exhibited specific recognition of multiple inorganic and organic acids with remarkable luminescence quenching, and the detection limit of Pythz-COF can be down to 0.02 nmol/L for hydrochloric acid and 5.38 nmol/L for trichloroacetic acid. Furthermore, the COF-based handy test paper was prepared and exhibited a good fluorescence quenching response toward nitrophenol and acid. Pythz-COF presents better sensing ability with a lower detection limit and faster response speed compared with Pyaph-COF, revealing that the introduction of hydrazone moieties is of great significance to multi-channel sensing and will provide references for the design of COF-type fluorescence sensors. [Display omitted] •Two stable crystalline hydrazone-linked COFs (Pythz-COF and Pyaph-COF) with different hydrazone bond content was synthesized.•Remarkable fluorescence sensing ability of two COFs and correspondingly prepared fluorescent test paper for nitrophenol explosives and various acids.•It was proved that the introduction of hydrazone moieties is of great significance to multi-channel sensing.