A thiadiazole-based covalent triazine framework nanosheet for highly selective and sensitive primary aromatic amine detection among various amines

Abstract

Primary aromatic amines (PAAs), as a class of persistent and highly toxic organic pollutants, have been posing a great threat to human health and the environment. Therefore, the design and preparation of a highly sensitive and selective luminescent probe to detect PAAs among various amines are important but challenging. In this work, by introducing electron-deficient monomer 4,4′-(benzo[c][1,2,5]thiadiazole-4,7-diyl)dibenzaldehyde (BTDD) with an aggregation-caused quenching behavior into the 2D framework, fluorescent ultrathin covalent triazine framework (F-CTF) nanosheets were constructed. Compared with the aggregated BTDD monomer, the obtained F-CTF-3 nanosheet shows much higher fluorescence quantum yield due to the BTDD fragment being well dispersed in the 2D framework. The F-CTF-3 nanosheet exhibits high stability, high porosity, and high fluorescence performance and has a rich electron-deficient unit in the pore channel, making it an ideal platform for sensing electron-rich PAA molecules. In fact, the F-CTF-3 nanosheet shows high sensitivity and selectivity for PAA detection by fluorescence quenching, among various amines, covering some classic aliphatic amines, heterocyclic amines, secondary aromatic amines and tertiary aromatic amines. To the best of our knowledge, it is the first reported fluorescent sensor for selective sensing of PAAs among various amines. Moreover, F-CTF-3 exhibits unprecedented low detection limits of 11.7 and 1.47 nM toward phenylamine (PA) and p-phenylenediamine (PDA), respectively, surpassing all the reported fluorescent sensors. The combination of experimental analysis and density functional theory (DFT) calculations demonstrates that the unique PAA detection performance of F-CTF-3 can be attributed to the static quenching process, which is confirmed by the formation of a ground-state fluorescence-quenched complex on account of the hydrogen bonding interactions between F-CTF-3 and PAAs. This work not only provides a thiadiazole-based 2D fluorescent organic framework nanosheet, but also an excellent fluorescent sensor with unexpected sensitivity and selectivity for PAA detection.