Pyrene-Functionalized Nanoporous Covalent Organic Frameworks with a Donor–Acceptor Property for 2,4,6-Trinitrophenol Detection

Achieving a balance between luminescence and stability poses challenges for covalent organic frameworks (COF). Herein, two types of COF materials, namely, C═N-COF and C═C-COF, are synthesized using Schiff-base and Knoevenagel condensation reactions, respectively. FTIR, solid-state 13 C NMR, PXRD, HRXPS, SEM, and TEM techniques are used to characterize the structure and micromorphology of COF materials. The microporous structure of C═N-COF exhibits a well-defined cube-shaped with an average length of ∼100 nm. C═C-COF has good dispersion and uniform morphology, which is very similar to nanorods, with an average length of ∼450 nm and an average width of ∼80 nm. Density functional theory calculations are employed to gain further insights into the relationship between the composition, linkage, and fluorescent properties. 1,4-Phenyldiacetonitrile and 1,3,6,8-tetrakis(4-formylphenyl)pyrene serve as the precursors of the donor (D)–acceptor (A) type C═C-COF framework, thereby enhancing the luminescent performance of COF materials. The results indicate that the D–A-type C═C-COF in tetrahydrofuran exhibits higher luminescent intensity compared to C═N-COF. It is noteworthy that the fluorescence signal of the D–A-type C═C-COF is quenched upon the gradual addition of 2,4,6-trinitrophenol to the suspension. The findings of this study offer valuable insights for the rational design of linkages to develop stable, porous, and highly luminescent COF materials.