| As a novel class of self-assembled materials,?-conjugated low molecular weight organogelators(LMOGs)have recently gained considerable attention for their potential applications in solar cells,field effect transistors,drug delivery,molecular recognition and so on.From the one hand,due to the existence of ?-conjugated molecules,the nanofibers in gels arrange orderly which could amplify fluorescent sensor signals leading to the intermolecular electro-optical signal transportation.From the other hand,the low molecular weight organogelators based on heterocyclic skeleton can enhance both the electron and hole transporting abilities and the chemical stability of materials.Therefore,synthesis of ?-conjugated heterocyclic compounds is an effective way to fabricate nanomaterials.Herein,we intended to design and synthesize benzo-heterocyclic compounds with excellent self-assembling abilities.We discussed their gelation and fluorescence propertities.We synthesized new cyanovinylcarbazole functionalized benzimidazoles CCBM and TCBM.It was found,that they could self-assemble into organogels in some mixed solvents rapidly upon stimulation by ultrasound.Although the emission of CCBM and TCBM in solutions was very weak,the xerogel-based films emitted intense yellow light under UV irradiation on account of AIE(aggregation-induced emission).We found that the emission of CCBM and TCBM in THF/water with high water fraction could be quenched by TFA(trifluoroacetic acid)significantly,so these hydrophobic dyes could be applied to detect acids in water phase.It should be noted that the emission of the nanofibers-based films of CCBM and TCBM could also be quenched rapidly upon exposed to TFA vapor.Particularly,the thinner the film,the higher the performance detected for the sensory properties.For example,the detection limit and the decay time of CCBM towards gaseous TFA in nanofibers-based film with the thickness of 0.21 ?m were 0.33 ppm and 0.38 s,respectively,and those were 8.0 ppm and 2.5 s for the film with the thickness of 1.73 ?m.We provided a strategy for fabricating new fluorescence sensory materials with high performance in probing gaseous acid via organogelation.We have synthesized a series of new ?-iminoenolates and their corresponding difluoroboron complexes without any traditional gelation moieties(for example:long alkyl chain,cholesterol unit and hydrogen bond acceptor etc.),and some of them,were able to gelatinize organic solvents.It was found that the presence of halogen atoms as substituents had a significant effect on gelation ability.In particular,bromo-containing compounds 4A and 4B exhibited excellent gelation abilities compared with other halogen-substituted gelators.By analyses of the single-crystal structure,the PXRD pattern of the xerogel,and electronic spectral changes during gelation,we deemed that 71-?,C-H…F,and C-H…Br interactions were the driving forces for the gelation of 4B.Interestingly,(Z)-1-(4-bromophenyl)-2-(3-methyl-pyrazin-2-yl)ethen-l-ol(8A),prepared in this work,is the lowest-molecular-weight organogelator to have been reported.It should be noted that although ?-iminoenolates 3A-5A are nonemissive in solution,they emit strong yellow light in organogels,which suggests aggregation-induced emissive activity,whereas the difluoroboron complexes 3B-5B show strong fluorescence in solutions,organogels,and xerogel-based films.Moreover,we found that the emission of 4B in a nanofiber-based film could be quenched significantly upon exposure to gaseous trifluoroacetic acid and that the decay time and detection limit were 0.5 s and 0.17 ppm,respectively.In conclusion,the organogelation process of ?-conjugated molecules is an effective way to fabricate 3D network with strong fluorescent properties.The enlarged fluorescent responsive signals originated from efficient exciton migration in 1D nanostructure is benefit to the sensory properties.Thus,through this work we have provided a new strategy for the design of nontraditional ?-gelators. |
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