Imine-Linked Covalent Organic Framework with a Naphthalene Moiety as a Sensitive Phosphate Ion Sensing

[Image: see text] Due to the excellent ion-sensing potential of covalent organic frameworks (COFs), the new imine-linked conjugated COF (IC-COF) is synthesized through a water-based synthesis reaction between 1,5-diaminonaphthalene and 2,4,6-tris(4-formylphenoxy)-1,3,5-triazine to create a luminescence sensor. It is noteworthy that the green synthesized IC-COF shows excellent selectivity to phosphate ions (PO(4)(3–)) with a detection limit of 0.61 μM. The recyclability performance of IC-COF is high, indicating that it can be reused without a significant reduction in performance (5.2% decline after 5 cycles). Theoretical calculations using the density functional theory are performed on the IC-COF–PO(4)(3–) and IC-COF–Cu(+) complexes to explore the sensing mechanism. The fluorescence quenching in the presence of PO(4)(3–) ions is attributed to the difference between PO(4)(3–) binding sites to the IC-COF compared to Cu(+), which leads to the considerable change in the IC-COF absorption spectrum from 400 to 600 nm.