Preparation And Evaluation Of Fluorescent Sensing Film Based On Polyfluorenes For Nitroaromatic Explosives Detection

Fluorescent polymer sensing film has important applications in nitroaromatic explosives trace detection. Fluorene based conjugated polymer possessing high light-emitting efficiency, large Stoke’s shift and ease of structural modification, has become one of most popular material to produce a fluorescent polymer sensing film.Herein, polyfluorene was used as the polymer material. Through :he transformation and modification of the substrate, polyfluorene film based on ZnO nanorod arrays and polyfluorene films based on poly dopamine were prepared, respectively, surface topography and fluorescence properties of the two polymer films were evaluated.The first part, ZnO nanorods were prepared on glass substrates by hydrothermal method, and then polyfluorene were coated on. The results showed that ZnO nanorod arrays had good orientation, which could effectively increased the film fluorescence intensity as substrate. Moreover, ZnO nanorod array substrate with longer growth time had greater surface area, which could improve the response rate of film to TNT vapor. The emission intensity of film was quenched by 72% within 20 s, the linearity range could reach to 0.08 ppb-1.5 ppb, and the detection limitation could reach to 0.04 ppb.The second part, with use of dopamine in buffer self-polymerization character, polydopamine layer with different thicknesses were grown on the glass substrate, then the polyfluorene with different concentration from different solvents were coated on. By evaluating the impacts on the surface morphology and fluorescence properties, it was found that when polydopamine layer thickness was 17.3 nm, the polymer concentration was 0.2 mg/mL, and THF was used as solvent, the film was most uniform and possessed outstanding fluorescence properties. Subsequently, polydopamine layer was modified by alkanethiol of different length to alter the hydrophilicity of the substrate surface, the results showed that when alkanethiol carbon atom number was 12, the film would be more uniform. Finally, on the basis above, the polymer molecules capacitive to substrate surface had been changed by altering the length of the side chain of polydopamine molecules. The results showed that when the number of side chain carbon atoms reached to 24, the film possessed outstanding morphology and fluorescence properties.The third part, monolayer film sensing material based on PFPs were prepared by Sonogashira-Hagihara coupling and Click reactions. The SAM film had a satisfactory modified density and fluorescence emission intensity. Meanwhile the SAM film also possessed a high quenching efficiency and fast response rate to nitroaromatic explosives. When the SAM film was placed in DNT and TNT saturated vapor rspectively, the fluorescence emission intensity of the film was quenched by 78% and 76% within 30s. While the SAM film was placed in PA saturated vapor, the fluorescence intensity was quenched by 79% within 2 min.