Diphenyl imidazole-based supramolecular self-assembly system for an efficient fluorometric detection of picric acid

Selective detection of nitroaromatics is still a major security concern in national security and environmental protection. In this endeavor, a new low molecular weight gelator based on the diphenyl imidazole group had been designed and characterized. This gelator could form stable organogels in DMSO and n-butanol solvents. Both π-π* absorption and fluorescence emission peaks of the gelator in DMSO showed different shifts compared with it in n-butanol during gelation, indicating different self-assembly modes in the two solvents. In addition, the gelation behavior of the gelator were investigated thoroughly by 1H NMR spectroscopy, SEM and XRD techniques. Further, this gelator worked as a selective chemosensor for picric acid in solution and gel states with a fluorescence quenching mechanism, and the limit of detection was 1.75 × 10−7 M and 3.76 × 10−7 M, respectively. The details of the sensing mechanism were elucidated using 1H NMR, Job's and Bensi-Hildebrand methods, which revealed a 1:1 binding ratio via the H-bond interactions between picric acid and gelator. Furthermore, the gelator was successfully practiced for the picric acid quantitative analysis in real water samples. The on-site detection technique using paper strips of the gelator could detect PA with the naked eye up to 10−7 M under UV 365 nm light. This work demonstrated that diphenyl imidazole-based gelator could be a potential soft material for explosive detection.