Highly cross-linked fluorescent poly(cyclotriphosphazene-co-curcumin) microspheres for the selective detection of picric acid in solution phase

Highly cross-linked and organic-inorganic hybrid poly(cyclotriphosphazene-co-curcumin) microspheres (PCPC-MS) were facilely prepared by a one-step precipitation copolymerization method, and served as a fluorescent chemical sensor for the detection of picric acid (PA) in solution phase. The photochemically inert cyclotriphosphazene moieties intentionally introduced into the structure of the sensor could play a role not only in connecting curcumin fluorophores to construct a highly cross-linked fluorescent architecture with excellent thermal stability and photobleaching stability, but also in effectively enriching PA from bulk solution to the surface of the sensor by the acid-base interaction between the acidic phenolic hydroxyl groups of PA molecules and the electron-rich nitrogen atoms of the cyclotriphosphazene units, which might facilitate the formation of a ground-state non-fluorescent complex of the microspheres and PA as well as the excited-state energy transfer from the microspheres to PA. Therefore, PCPC-MS exhibited a fluorescence quenching response towards PA with high sensitivity, efficiency, and selectivity over a number of other analytes such as 2,4,6-trinitrotoluene, 2,4-dinitrotoluene, 1,3-dinitrobenzene, 4-nitrotoluene, nitrobenzene, 4-benzoquinone, chlorobenzene, and nitromethane in methanol. In addition, PCPC-MS could also effectively detect PA in the presence of the other analytes, indicating their remarkable ability for resisting interferences and specific recognition of PA. This study provides new insights into the design and preparation of a polymer-based fluorescence chemical sensor for PA with low toxicity, a simple preparation process, and high selectivity.