Fluorescent organic–inorganic hybrid polyphosphazene microspheres for the trace detection of nitroaromatic explosives

Highly cross-linked, intrinsically fluorescent organic–inorganic hybrid polymer microspheres bearing primary amine groups on the surface have been successfully prepared through a one-pot polycondensation of hexachlorocyclotriphosphazene with benzidine. Just by the single-step introduction of plentiful π-conjugated benzidine units in the structure, the resulting microspheres easily obtain both the luminescence and abundant active amino groups, with no need for more modification. Thus further using the microspheres as fluorescence-based nitroaromatic sensor, 2,4,6-trinitrotoluene, 2,4-dinitrotoluene, and picric acid can be effectively and sensitively detected. Because the nitroaromatic analytes can be effectively enriched on the surface of the microspheres by the charge-transfer complexing interaction between electron-deficient aromatic rings and electron-rich amino groups, which facilitates the electron transfer and energy transfer from microspheres to nitroaromatics, and finally leads to a significant and sensitive fluorescence quenching response. Moreover, the microspheres also exhibit remarkable thermal stability, photobleaching stability, and solvent resistance and dispersion ability in various solvents including both aqueous and organic media, owing to the highly cross-linked and organic–inorganic hybrid structure.