Fluorene based fluorescent and colorimetric sensors for ultrasensitive detection of nitroaromatics in aqueous medium

New butterfly-shaped pi-extended sensors 4 and 5 were synthesized through the Knoevenagel condensation and the Suzuki-Miyaura coupling reaction. Sensors were employed for sensitive detection of nitroaromatics. Among nitroaromatic compounds (NACs), sensors 4 and 5 exhibited ultrasensitive fluorescence quenching response to picric acid (PA) with quenching efficiency >45 and >260 folds and limit of detection (LOD) 22.0 and 0.23 ppt (parts per trillion), respectively. This ultra-sensitivity was contributed by FRET and IFE processes. Selective interaction of sensors with PA was evaluated by fluorescence, UV-Vis., H-1 NMR titration, dynamic light scattering (DLS), and density functional theory (DFT) calculations. These sensors were successfully employed for detection of picric acid in real water samples. Interestingly, sensors 4 and 5 showed selective colorimetric recognition of picric acid. Moreover, sensors' coated test strips were fabricated for an immediate naked eye detection of PA that demonstrated rapidity, simplicity, and convenience for on-site detection of PA. Robust sensitivity for PA illustrated that these sensors can be employed in the development of new detection tools for PA analysis in real samples.

Automated summary

New butterfly-shaped pi-extended sensors 4 and 5 were synthesized and employed for the sensitive detection of picric acid. These sensors showed ultra-sensitive fluorescence quenching response to picric acid, with a high quenching efficiency and a low limit of detection. Selective interaction of the sensors with picric acid was evaluated through various experiments, and the sensors were successfully applied for detection in real water samples. Furthermore, sensors' colorimetric recognition and coated test strips allowed for immediate naked eye detection of picric acid.