The residue of pesticides in crops, soil, and water continues to be a widespread concern due to the threat to human health and food safety. With the aim to develop highly sensitive sensing materials and portable detection devices, two dicarbazole-based fluorescent micro-/mesoporous polymers (JYs) with a larger specific surface area and pore sizes ranging from 1.1 to 34.2 nm are synthesized. The Stern–Volmer constants of JY fluorescence quenching for imidacloprid (50,063 M–1) exceed 23–51 times those of the reported porous organic polymers (980–2173 M–1). Of particular interest is the observation that JYs show rapid fluorescence response (2 s) and ultralow detection limit (30 ppb) for imidacloprid in water medium. The pronounced chemsensing property is attributed to the synergistic role of the hierarchical pore structure, large π-conjugation of chromophore groups, and strong inner filter effect between the polymer and imidacloprid molecule. Moreover, the pesticide detection of JYs exhibits good interference resistance in complicated service environments such as the extract liquids of the apple peel and field soil as well as aqueous solutions of various cations and anions. Because of the portability, excellent reusability, and sensitive fluorescence response, the prepared JYs and detection devices have promising applications in the on-site monitoring and early warning of the pesticide residues.

The Friedel–Crafts (FC) reaction is a prominent synthetic tool for rapidly constructing complex molecular frameworks, but syntheses of carbazole-based nanoporous organic polymers (CNOPs) via FC hydroxyalkylation are rare. Herein we report the acid-catalyzed FC hydroxyalkylation synthesis of two CNOP networks, prepared (using p-phthalaldehyde) from 1,3,5-tris­(9-carbazolyl)­benzene and tris­[4-(9H-carbazol-9-yl)­phenyl]­amine. The specific surface areas of the CNOPs ranged from 1374 to 1546 m2/g, and the CNOPs had a hierarchical porous structure with pore sizes ranging from 0.87 to 6.60 nm. Furthermore, the high porosity in conjunction with abundant carbazole units in the CNOPs enabled excellent adsorption performance toward C2H6, CO2, and CH4. CNOP-2 derived from 1,3,5-tris­(9-carbazolyl)­benzene and p-phthalaldehyde displayed C2H6, CO2, and CH4 uptakes of up to 98.7, 90.2, and 30.7 cm3/g, respectively, at 1 bar and 273 K. Also, the adsorption selectivities of the CNOPs in conjunction with C2H6/CH4 and CO2/CH4 gas mixtures were 23.4–23.5 and 6.4–7.3, respectively. This work demonstrates a cost-effective FC reaction that can be used to design and construct carbazole-based nanoporous organic polymers.

Aggregation-induced emission (AIE)-active aromatic tetraaldehydes are utilized as starting monomers to create two fluorescent polymers (PAN-TPEs) with hierarchical pores ranging from micropores (1.4−1.9 nm) to mesopores (3.8−26.2 nm). Their chemsensing properties for five pesticides, including imidacloprid, acetamiprid, triflumizole, lambda-cyhalothrin, and indoxacarb, are studied. It is found that the Stern−Volmer quenching coefficient and the limit of detection for imidacloprid in the water medium reach 53 745 M −1 and 28 ppb, respectively, which are much superior to those of the reported porous materials in the literature and exceed 3−10 times of the other four pesticides. Moreover, the polymers exhibit fast fluorescence response for imidacloprid (less than 4 s), and the detection sensitivity is nearly not affected by the common cations and anions. Additionally, the studies reveal that, for the polymer sample with narrower pore channels, the recognition ability for imidacloprid strongly depends on the molecular volumes of pesticides, whereas in the case of the polymer with larger pore sizes, the inner filter effect and the photoinduced electron transfer between the pesticides and the chromophore groups in the polymer skeleton become the major factors. The results are of significance for understanding the effects of porosity parameters and AIE groups in fluorescent porous polymers on the recognizable detection of imidacloprid from other pesticides.