Fluorescence detection of 2,4-dinitrophenol and 2,4,6-trinitrophenol using the 2D benzimidazole-linked covalent...

Due to their electron-rich nature, benzimidazole-linked COFs should exhibit excellent fluorescence sensing properties for nitroaromatic compounds (NACs). However, there has been no report on the application of benzimidazole-linked COFs for fluorescence sensing NACs. This study reports two 2D benzimidazole-linked COFs, which were prepared via Schiff base polymerization and cyclicization reaction of 3,3'-diaminobenzidine (DAB) or 1,2,4,5-benzenetetramine tetrahydrochloride (TAB) with ether-linked knot, TPT-3-CHO (TDAB and TTAB). TDAB and TTAB exhibit large specific areas of 2087 and 1912 m² g^-1, excellent crystallinity, and high thermal and chemical stability. The porous 2D benzimidazole-linked COFs can serve as fluorescent sensors for the selective and sensitive detection of 2,4-dinitrophenol (DNP) and 2,4,6-trinitrophenol (TNP), exhibiting high quenching constants (K_SV) and low limits of detection (LODs). The K_SV values and LODs of TDAB for DNP are 2.66 × 10⁴ L mol^-1and 3.24 × 10^-6 mol L^-1, and these of TDAB for TNP are 2.55 × 10⁴ L mol^-1 and 3.79 × 10^-6 mol L^-1. The K_SV values and LODs of TTAB for TNP are 1.06 × 10⁴ L mol^-1and 4.65 × 10^-6 mol L^-1. The fluorescence quenching arises from both photoinduced electron transfer mechanism and absorption competition quenching mechanism. This study authenticates that benzimidazole-linked COFs are promising candidates as fluorescent chemosensors, and opens new avenue for exploring their potential applications to detect NACs for pollution control and prevention.