Two new carbazole-based monomers 6,6'-(9-n-butyl-9H-carbazole-3,6-diyl)bis(1,3,5-triazine-2,4-diamine) and 6,6'-(9H-carbazole-3,6-diyl)bis(1,3,5-triazine-2,4-diamine) are synthesized and employed to polymerize with formamide and N,N-dimethylformamide, respectively, to afford thee fluorescent micro-/mesoporous polyaminals with physicochemical microenvironment modulated by -NH2, -NH-, -N(CH3)2, and n-butyl groups. Their chemosensing properties for five pesticides trifluralin (TFR), triflumizole, imidacloprid, lambda-cyhalothrin, and cyfluthrin are studied. Surprisingly, the polymers exhibit exceptionally high recognition for TFR, and the fluorescent quenching coefficients measured in water reach 4.1 × 106 M-1, being 2 orders of magnitude higher than those of other porous polymers reported in the literature. The limit of detection (0.7 ppb) for TFR can compete with that of the electrochemical method. The fluorescence response at an extremely low concentration of 3 × 10-8 M and selective recognition for TFR are confirmed by the visual observation using the portable polymer plates. Additionally, the different water mediums including varied acid-basic conditions and the presence of heavy metal ions have nearly no effect on the detection sensitivity. The ultrasensitive recognizable response for TFR is explained in terms of the photoinduced electron transfer, inner filter effect, improved hydrophilicity of polymer skeleton and porous trapping effect, and the dimensions and geometric configurations of pesticide molecules.
Keywords: detection; fluorescent polymers; pesticide residues; porous; trifluralin.