Design, Synthesis And Sensor Properties Of Conjugated Polymer With Benzimidazole Derivatives As Recognition Units

Conjugated polymers （CPs） has delocalized π-electronic conjugated ‘‘molecular wires’’ cangreatly amplify the fluorescence signal. As compared in small moleculaes, facile energymigration from polymer backbone upon light excitation and the amplification of fluorescentsignals resulted from the excitation energy transfer to the chromophore. CPs has receivedconsiderable attention as sensing materials used in bioanalysis and chemical sensors. In thesematerials, benzimidazole derivatives have excellent corrdination ability and diversecoordination modes with metal ions. However, few reports on benzimidazole derivativesutilized as congjugated polymer chemosensors. In this thesis, we designed, synthesized anddeveloped the new conjugated polymer sensing platform based on benzimidazole derivativesfor detection of matal ions and amino acids. The influence of connective monities on theonjugated polymer for the recognization performance was investigated in detail. Thisdissertation includes four parts:First, The recognization group ethyl2-（4,7-dibromo-2-（pyridin-2-yl）-1H-benzo[d]imid-azol-1-yl）acetate （PBMA） was synthesized, and caped unit （4,7position） linked with conjugated polymer backone as a fluorescent chemosensor（P1） for the Ag⁺ion sensing.The result indicated that P1showed excellent selectivity toward Ag⁺by avoiding theinterference from other metal ions and the detection limt was down to50nm. The emission intensity of P1rapidly descreased and the fluorescent color also changed fromblue to green after addition of Ag⁺. The sensing mechanism of the polymer was also investigated by applying a similar copolymer （P2, P3） and by measuring1H NMRspectra. This is the first copolymer （P1） containing PBMA units in the backbone structure as metal ion chemosensor, which will help to extend the number and the applications of fluorometric polymer sensors for metal ions detection.Second, for the evaluation of relationship between structure and properties, we changed thelinker position （5,5’ position） between PBMA with polymer backone and synthesizedcopolymer P4and P5. The results showed that no significant spectral change was observed inthe fluorescence spectra except in the case of Ni²⁺. Specifically, Ag⁺can not be recognized atall. We further inverstigated the reasons fot change in recognization behaviors with molecular structure and their electrochemied characteristics. With the increase of Ni²⁺concentration, theonset oxidation potential and the oxidation potential of P4or P5were gradually improved.Plausibly, the linking moniety of PBMA with polymer chain has changed the electron densityof the polymer, so the complexing ability of conjugated polymer with metal ions was alsochanged. It is also indicated that the energy level of conjugated polymer could be adjusted bychanging the linking ways between recognization group and congjugated polymer backon oraddition of different metal ion complex with polymer.Third, based on previous research results, pyridine unit in PBMA further replaced withthiophene unit, and the recognization performance of copolymer P6and P7were alsoinvestigated. The novel conjugated polymer P6and P7showed high selectivity for Ag⁺detection. The results indicated that the introduction of S atoms in copolymer （P6, P7） play akey role for detection of Ag⁺.This phenomen further give insight understanding relationshipbetween structure and their properties.Fourth, on the bases of results from copolymer P2, the recognization group as side chain ofconjugated copolymer （P8）, and binding and recognition behavior toward the metal ions andamino acids were investigated. The fluorescence of copolymer P8can be completelyquenched by Cu²⁺and Ni²⁺through a photoinduced electron transfer process, resulting information of metal complexes of polymer ([P8-Cu²⁺] and [P8-Ni²⁺]). These results indicatethat coplymer P8is expected to be a selective chemosensor for Cu²⁺and Ni²⁺. Moreover, insitu formed [P8-Cu²⁺] complex showed excellent fluorescence “turn on” properties with highselectivity towards Cys, while [P8-Ni²⁺] complex with high selectivity towards His and Tryp.These complexes are expected to be promising chemosensors for amino acids due to highselectivity and high sensitivity （detection limit concentration is0.5ppm for Cys,5.0ppm forHis and0.1ppm for Tryp）. It means that the detection selectivity of conjugated polymericchemosensor can be controlled by metal ions. Thus, this work provides a new type ofpromising polymeric fluorescent chemosensor for amino acids.