Impact of π-conjugation and fluorination on the sensing performance of 1,6-pyrene covalent triazine frameworks

Abstract

In this work, we describe the synthesis of a series covalent triazine frameworks (CTFs) based on 1,6-substituted-pyrene-derivatives, in which triazine units (electron acceptor groups) are either directly bonded to the pyrene core (1,6-Pyr-CTF) or connected via aryl or fluoroaryl-π-linkers (1,6-DPhPyr-CTF and 1,6-2FDPhPyr-CTF). These CTFs were readily synthesized through cyclotrimerization of the corresponding dinitriles, yielding thermally stable products with favorable photophysical properties and fluorescence emission maxima at 401 nm (1,6-Pyr-CTF), 428 nm (1,6-DPhPyr-CTF) and 433 nm (1,6-2FDPhPyr-CTF). These characteristics make them promising candidates for fluorescent sensing of nitroaromatic compounds. Among the synthesized frameworks, the fluorinated diphenylpyrene-triazine (1,6-2FDPhPyr-CTF) exhibits the highest selectivity and sensitivity toward nitro compounds, in EtOH/H₂O dispersions, with K_SV = 4.35 × 10⁴ M⁻¹ (LOD = 0.15 ppm) for picric acid (TNP) or 3.39 × 10⁴ M⁻¹ (LOD = 0.11 ppm) for (p-nitroaniline, 4-NA). These results demonstrate the beneficial effect of extended π-conjugation and fluorine incorporation on the sensing performance of CTFs.