Thiophene functionalized silicon-containing aggregation-induced emission enhancement materials: applications as fluorescent probes for the detection of nitroaromatic explosives in aqueous-based solutions

Two novel aggregation-induced emission enhancement (AIEE) molecules, namely, 3,4-diphenyl-2,5-di(2-thienyl) phenyltrimethylsilane (DPTB-TMS) and bis[3,4-diphenyl-2,5-di(2-thienyl) phenyl] methylphenylsilane (DPTB-MPS) were designed and synthesized. The optical properties of the two silanes were completely opposite to the traditional luminescent materials. Unlike the aggregation caused quenching, they all emit faint fluorescence in the dispersed state, while emission intensity increased sharply in aggregate states. Fluorescence spectra showed that the two compounds exhibited AIEE properties and that is due to the weak p-p stacking caused by the restriction of intramolecular rotations of dye segments, particularly the -SiMe3 and thienyl groups in the aggregate state. As fluorescent (FL) probes, the fluorescence quenching behavior was further investigated. Thanks to the richer-electron thiophene groups, both compounds showed good performance in detecting nitroaromatics, especially picric acid (PA). The two AIEE FL probes exhibited better quenching efficiency in aqueous-based than in organic-based solutions. For DPTB-MPS, the addition of 80 mM nitrobenzene, 60 mM m-nitrobenzene and 40 mM PA resulted in about 50% quenching in aqueous solutions. The quenching mechanism would be electron transfer from silanes to nitroaromatics. This work provides a basis for designing organic-silanes with "abnormal'' but useful optical properties and FL probes with AIEE properties for the detection of nitroaromatics.