A Switch-On fluorescent probe for detection of mesotrione based on the straightforward cleavage of carbon-nitrogen double bond of Schiff base

Schiff bases are generally utilized to detect and quantitatively analyze metallic cations and anions. However, pesticide detection based on Schiff base structure has not been reported so far. Mesotrione is a kind of triketone 4-hydroxy-phenyl-pyruvate-dioxygenase (HPPD) inhibitor whereas excessive use of mesotrione produces residues causing a negative impact on the environment. Herein, we report a Schiff base type probe 6-(2-hydroxybenzylidene)-N-n-butyl-naphthalimide (HNA) which can switch on in a fluorescence mode in response to mesotrione efficiently, enabling the quantification of testing sample. It is worth mentioning that the simple and direct cleavage of the targeted carbon–nitrogen double bond of Schiff base in probe is proved to be triggered by acetophenyl unit in mesotrione which may be ascribed from the competition equilibrium between the intramolecular and intermolecular hydrogen bonds. As a result, the non-fluorescent probe with photo-induced electron transfer process is converted to the precursor of the probe with strong fluorescence. Further results reveal that the strong electronegativity of carbonyl carbon atom in acetophenone group is capable of improving the detection capability of probe. Aided by the switch-on change of fluorescence, the quantitative determination of mesotrione is realized with the limit of detection (LOD) of 0.16 μM with potentials of quantitative sensing in real water samples. Moreover, two other probes bearing pyrene and Schiff base structure are synthesized and exhibit the feasibility of mesotrione detection with LODs of 0.43 μM and 3.20 μM, respectively. The present work provides a novel and convenient method for the detection of mesotrione with high sensitivity and easy operation based on the probe with general C = N of Schiff base structure, which greatly benefit for the future research regarding to the acetophenone-type herbicide sensing.