Crown ether-bridging tetra-cyanostilbene macrocycle: an effective "turn-on" fluorescent sensor for the pesticide carbendazim.

Carbendazim is widely used as a fungicide in various crops, but its residues might pose a threat to human health and environmental safety. It is significantly expected to develop a simple, sensitive, stable, and on-site method for detecting carbendazim. In this work, the first organic fluorescent sensor for carbendazim was designed and synthesized based on a crown ether-bridging tetra-cyanostilbene macrocycle. This macrocycle exhibited dark-blue fluorescence in THF-H₂O (5:95) solution, which was transformed into bright-blue fluorescence after sensing carbendazim. High sensing selectivity for carbendazim was observed among 24 kinds of pesticides and ions. The detection limit was as low as 4.22 × 10^-8 M. The sensing mechanism was deduced as two carbendazim molecules being encapsulated in the macrocyclic cavity based on multiple hydrogen bonds, π-π stacking, and hydrophobic action, resulting in stronger rotation restriction of aromatic groups and then higher fluorescence emission. The sensing application on test paper, real samples, and simulated water samples indicated excellent qualitative and quantitative detecting capabilities for sensing carbendazim, implying a good application prospect for simple, sensitive, stable, and on-site detection of carbendazim in daily life.