Design And Synthesis Of Multi-functional Fluorescent Chemosensor And Mechanosensor

In the last decades,fluorescent sensors have been widely utilized as popular tools in environmental monitor,biological sciences,and electronic information.Fluorescent chemosensors as most important one among the fluorescent sensors have attracted much attention because of their simplicity,high sensitivity,high selectivity,and real-time detection.There are many types of chemosensors being designed and synthesized for detecting various analytes such as cation,anion,and amino acid.However,most of the sensors possess monofunctional or bifunctional sensing properties,which targets only one or two analytes.In general,preparation of the sensors is time-consuming and costly.Therefore,it is highly desirable to develop new multifunctional sensors for detecting multiple different analytes.Compared with the intensive exploration of fluorescent chomosensors,the studies on fluorescent mechanosensors(also known as mechanochromic materials)remain in the relatively preliminary stage.Due to their potential applications in optical memories,monitoring,and secure communications,fluorescent mechanosensors have invoked much interest recently.However,there are still a great many problems regarding the force sensitivity,reversibility,and color change diversity of these sensors.Therefore,it is essential to develop new kind of fluorescent force sensor with excellent properties.This dissertation includes four parts as follows:1.New linear and branched conjugated polymers containing 2,2'-biimidazole moiety were successfully designed and synthesized through Suzuki coupling reactions,and their fluorescent sensing properties to metal ions,amino acids,and acid gas were investigated.The emission of the two polymers can be efficiently quenched by Co2+through a photo-induced electron transfer process with "turn off ' character without disturbance of Cu2+.The polymers also show ratiometric fluorescence changes toward Ag+.Since cysteine(Cys)can bind Ag+ through the thiol-Ag+ interaction,the resulting polymer-Ag+ complexes exhibit excellent sensing properties for detection of cysteine with high selectivity and fast response(less than I min).The linear detection range of cysteine can be tuned conveniently by changing the amount of Ag+ ions.In addition,we also found that the emission color of the polymer solution can reversibly change from blue to green on exposure to HCl and NH3 gases,which may be utilized to detect strong acidic gas efficiently.It should be noted that the branched polymer possesses a higher sensitivity,compared with the linear polymer.All the results demonstrate that the 2,2'-biimidazole-based conjugated polymers can be used as excellent multifunctional fluorescent sensors.2.A novel conjugated tri-copolymers(P1)containing 2,2'-biimidazole,benzothiadiazole moiety have been successfully designed and synthesized.P1 can form nanoparticals in aqueous solution with regular morphology.Because an obvious fluorescence resonance energy transfer effect exists between carbazole-biimidazole and carbazole-benzothiadiazole units,the nanoparticals showed an orange fluorescence emission(quantum yield is 9%).Based on charge-transfer interaction,these nanoparticals could be used to detect electron deficient nitrocompounds without disturbance of metal ions.The 1,3,5-trinitrophenol showed highest detection sensitivity.We also found that the sensitivity of nanoparticals toward nitroaromatic compounds increased at high water content due to microphase enrichment effect.3.Two pyrene boronic acid cyclic esters,PPB and NPB,were prepared and their solid state fluorescent properties were investigated.Interestingly,the results showed that PPB with 5-membered ring shows reversibly mechanoluminescence and vapochromic behaviour with fast self-recovering ability at room temperature(about five minutes),whereas NPB with 6-membered ring did not.It was demonstrated that the mechanical responsive fluorescent properties of PPB and NPB were highly related to the molecular packing mode and the solid state plasticity.The much softer and more compliant PPB crystal could facilitate the formation of sandwich-like pyrene excimer because the presence of slip planes.Since the recovery process is spontaneous without any external stimulation,the PPB can be used to make a writing board or paper with a spontaneous erasing function.4.We designed and synthesized a novel rhodamine-based mechanochromic elastomer.In order to enhance the sensitivity,the elastomer was prepared by three steps swollen-photopolymerization process to make the chains in the first network highly stretched.The results demonstrated that the elastomer exhibited very promising and unique properties.Three primary-fluorescence colors were presented during continuous uniaxial extension and relaxing process.Broad-spectrum fluorescence color change could be achieved by rational tuning the stretch ratio consequently.The fluorescence quantum yield of the opened zwitterion of this new mechanophore was as high as 0.67 which was almost two orders of magnitude higher than that of the widely employed merocyanine.In addition,the elastomer showed very high sensitivity to stress with a detectable activation strain of about 0.24,which could be used for the finger motion detection.Furthermore,the easy-to-get material,facile preparation and good mechanical property also made it advantageous for practical applications.