Synthesis Of Hyperbranched Conjugated Polymer And Sensing Performance For Nitroaromatics

In recent decades,the demand for credible and efficient materials for the detection of explosives have received considerable attention due to their foremost relevance in global security and environment pollution control.Among the present methods for explosive detection,fluorescence-based chemical sensors have received considerable attention because they are simple to use and very sensitive to explosive materials.Fluorescent conjugated polymers?FCPs?have been widely used as optical probes for the design of sensors with low detection limit,owing to their intrinsic signal amplification capability.Many conjugated polymers have been developed and utilized for detection of explosive using fluorescence quenching method and most of them are linear conjugated polymers.However,most of them usually exhibits high viscosity,limited solubility and complicated synthesis process,which limits the application in sensing materials.The hyperbranched conjugated polymers can decrease the viscosity and improve the solubility of the polymer,meanwhile,possess unique optical properties,which attract the attention of many groups.The polymers utilizing silicon based spacers have several advantages,and the solubility and processability of the polymer can be improved due to the chain flexibility arising from the silicon atom.Compared with carbon atom,silicon atom has more electronic level,therefore,nucleus of silicon atom has weakly attract to outermost electron.Since most explosives are electron-deficient nitroaromatic compounds?NACs?,when the NACs close to the silicon atom,outermost electron of silicon atom can quickly transfer to NACs,due to outermost electron is unstable.The silicon atom displayed electropositivity when closed to TNT,which led to the molecules of containing silicon polymers had higher probability of collision with other TNT molecules.Furthermore,the silicon moiety possesses a particularly lowlying LUMO level.Two conjugated polymers based on poly?carbazole-ethynylene?have been successfully synthesized by Sonogashira cross-coupling polymerization.To explore the solubility,optical property and detection of nitroaromatic of polymers by controlling the numbers of conjugated polymer branches.Compared with hyperbranched conjugated polymer,linear conjugated polymer showed low dissolution rate in some solvents.When they reach quenching equilibrium for TNT,the?_EP values of hyperbranched conjugated polymer is higher than that of linear conjugated polymer,indicatingthathyperbranchedstructureofP₂remarkablyenhancesthe electron-transfer between the polymer and TNT due to its multiple exciton migration channels and diffusion pathways via numerous branches.Moreover,the lifetimes of the P₂ remain almost unchanged when different amounts of TNT are added,suggesting quenching mechanism of hyperbranched conjugated polymer is mainly through a static mechanism.By studying this issue,proved that the hyperbranched structure is more effective quenching ability than linear structure.The introduction of silicon moiety in the hyperbranched conjugated polymer could further increase solubility and thermostability.The regular?-conjugated system of hyperbranched conjugated polymer was effectively interrupted by the silicon atom,making the TNT with fluorescent molecular collide,and enhance synergistic effect dynamic and static quenching.Compared with previously reported P₁ polymer,the P₂ possesses flexible silicon atoms and low weight,which offers more possibilities to collision of P₂ and TNT.By detecting fluorescence lifetime of P₂,we have confirmed chemosensor system for explosive detection operating in a simultaneous dynamic and static quenching mechanism.