Three fluorescent porous aromatic framework materials donated as LNU-9, LNU-10, and LNU-11 were prepared via Suzuki coupling reactions of 1,3,6,8-tetrabromofluorene(TBrPy) with boric acid monomers. The structures and properties of the LNUs were characterized by Fourier transform infrared spectro-scopy(FTIR), thermogravimetric analysis(TGA), nitrogen adsorption-desorption, solid ultraviolet spectroscopy and fluorescence spectroscopy. The disappearance of vibration peaks at 1349, 1144, 495 cm -1 in FTIR spectrum is attributed to the breakage of C—Br and C—B(OH)2 bonds, respectively, indicating the complete polymerization of building monomers into porous skeletons. Powder X-ray diffraction(PXRD) and transmission electron microscopy(TEM) images reveal all the LNUs have amorphous structure. The thermogravimetric ana-lysis results demonstrate the excellent thermal stability of LNUs. In addition, these materials exhibit high chemical stability, as verified by no dissolution or decomposition in various organic solvents such as methanol, ethanol, tetrahydrofuran, acetone, dichloromethane, chloroform, N,N'-dimethylformamide, dimethylsulfoxide, etc. Besides, their large specific surface areas in the range of 800—1500 m 2/g and excellent fluorescence properties make them suitable for the detection of specific nitro explosives. After benzene, bromobenzene, aniline, toluene, chlorobenzene and phenol were added into the methanol solution of LNUs respectively, the luminescence intensity had little change, demonstrating there is no specific interaction between porous skeleton and organic substances. On the contrast, fluorescence of LNUs was almost completely quenched in the respective solution of nitrobenzene, p-nitrophenol, and p-nitrochlorobenzene, indicating the selective detection capability for nitro compounds of the LNUs. Based on these results, we prepared a novel portable paper sensor which realized the facile and rapid real-time detection of nitro explosives, demonstrating an impressive pro-spect in trace detection.
