Tuning solvent-solute interactions enable visual colorimetric detection of nitro-aromatic explosives.

The Janowski reaction is a critical reaction for visual colorimetric detection of nitro-aromatic explosives. However, the solvent effect is still not well explored. Herein, we report the solvent-dependent activity of the Janowski reaction between 2,4-dinitrotoluene (DNT)/2,4,6-trinitrotoluene (TNT) and NaOH. Four common solvents are studied. It is found that acetone with high donor number and low polarity is able to readily dissolve the product of Janowski reaction (Meisenheimer complexes) via Lewis acid-base interactions and solvation rules, facilitating the Janowski reactions between DNT/TNT and NaOH. Based on the color change of the Janowski reactions within acetone, a visual colorimetric assay is established. The present assay can detect DNT and TNT with a detection limit of 1.4 μM and 1.2 μM, which allows for naked-eye detection. In addition, this assay is highly selective and applicable to DNT/TNT detection in soil samples. Our work reveals the solvent effect on the Janowski reaction, providing a simple and rapid method for detection of nitro-aromatic explosives.