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[Display omitted] • New fluorene based sensors 4 and 5 were synthesized and characterized. • Ultrasensitive sensing of picric acid (PA) was detected selectively with low limit of detection (LOD) of 22 ppt for sensor 4. • Sensor 5 exhibited PA detection with very low LOD of 0.23 ppt through FRET, IFE and PET based fluorescence quenching mechanisms. • Both sensors were used for rapid detection of picric acid in real samples. • Sensors displayed ultra-selective colorimetric detection of picric acid. • Plausible interaction of sensors with PA was supported by 1HNMR, UV Vis., DLS, and computational studies. New butterfly-shaped π-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. , 1H 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. [ABSTRACT FROM AUTHOR]

[Display omitted] • Fluorene based chemodosimeters 1 and 2 showed excellent selectivity towards cyanide ions. LOD of 1 and 2 was found 0.2 and 0.4 ppb, respectively based on fluorescence emission enhancement. • Both chemosensors were used for rapid detection of cyanide in industrial and food samples. UV–Visible changes in chemosensor due to cyanide were successfully applied to design logic gate. • Chemosensors displayed selective colorimetric detection of cyanide ions. • Sensors' coated test strips were also fabricated for rapid on-site detection of cyanide ions. Rising detrimental effects of cyanide due to its frequent large-scale utilization demand rapid and sensitive detection of cyanide ions. Herein, two new fluorene based chemosensors 1 and 2 have been developed through the Suzuki–Miyaura coupling reaction for fluorescence enhancement based selective detection of cyanide with sensitivity levels down to 0.2 ppb and 0.4 ppb, respectively. The plausible sensing mechanism is based on Michael type adduct formation due to the reaction of cyanide with chemosensors and was confirmed by 1H NMR titration, Job's plot, dynamic light scattering (DLS), and density functional theory (DFT) calculations. Chemosensors 1 and 2 showed excellent linear response towards CN¯ ions (0–100 nM) in the Benesi–Hildebrand plot with association constants (K a) 1.61 × 106 and 7.1 × 105 M¯1, respectively that corresponds to their favorable chemical reaction. Excellent selectivity of chemosensors for cyanide in the presence of other interferences was investigated through fluorescence emission, UV–Visible, and DFT analysis. Surprisingly, an immediate reversible colorimetric change upon alternate shaking and steadiness of chemosensor − CN¯ solution was noticed indicating that chemosensors can act as promising recyclable sensors for colorimetric on-site detection of CN¯. Meanwhile, chemosensors 1 and 2 displayed highly selective colorimetric detection of CN¯ under daylight and UV radiations (365 nm). Further, cyanide responsive test kits were fabricated that provided a low-cost and portable method for on-site detection of CN¯ ions in an aqueous medium. Finally, chemosensors were successfully applied for designing logic gates, and detection of cyanide in industrial waste and food samples. [ABSTRACT FROM AUTHOR]