Research On The Design, Synthesis And Recognition Properties Of Fluorescence Sensors

In recent years, the development of new fluorescent sensors has receivedincreasing attention owing to their visual simplicity, good selectivity, lower cost andinstantaneous response. Besides, fluorescent sensors are non-destructive andnon-invasive, the quantative analysis for the detected object can be obtained from therelationship between fluorescence intensity and object concentrations, which makesfluorescent sensors more attractive application prospects in biological, environmentaland medical fields. The main work of this thesis was the design and synthesis ofseveral fluorescent sensors, and studied on recognition properties of them for cationsand anions. The potential application value of several fluorescent sensors in abovefields was preliminarily assessed by experiments.The main studies of this thesis were as follows:In chapter1, this chapter introduced the back ground of this thesis, described thedefinition, structure and several recognition principles of fluorescence sensors. Thischapter focused on the research status of fluorescence sensors for Al3+, Cd2+, Hg2+,Cr3+and PO43ions based on anthracene, quinoline and acridine derivatives.In chapter2, two new isomerous anthracene-based fluorescent sensors (L1and L2)for Al3+have been designed and synthesized. The two sensors exhibited fluorescenceenhancement upon binding Al3+in CH3CN by PET inhibition processes from both thesulfur and the nitrogen donors to anthracene because of S2N recognition group.However, L2had better recognition for Al3+than L1. The most likely reason was thatthe steric hindrance of L2was smaller than that of L1, and L2for Al3+recognitionhad a more efficient PET mechanism than L1. Besides, both the sensors L1and L2displayed good recognition toward Al3+in CH3CN-H2O (9/1, V/V) solution, whichhad potential applications in environmental detection.In chapter3, a new fluorescence sensor (L3) based on8-hydroxy-2-methylquinol-ine and S2N group has been designed and synthesized. This sensor can selectivelyrecognize Cd2+in aqueous buffer solution based on chelation enhanced fluorescence(CHEF) and exhibit an almost30-fold fluorescence increase. Besides, Hg2+ionsstrongly quenched the fluorescence of L3-Cd2+in the competition experiments ofCd2+mixed with other metal ions. Further spectrum experiments were found thatL3-Hg2+had the different coordination mode from L3-Cd2+because the special S2Ngroup could be used as the chelating unit for Hg2+. Upon addition of Hg2+, Cd2+couldbe replaced from L3-Cd2+to recognize Hg2+. Moreover, the sensor L3for Cd2+and L3-Cd2+for Hg2+could be applied for fluorescence microscopic imaging, which hadpotential applications in environmental detection and biological system.In chapter4, a new C3-symmetric Schiff-base fluorescent sensor (L4) has beendesigned and synthesized based on8-hydroxy-2-methylquinoline. This sensordisplayed good recognition for Cd2+with a large red shift over other metal ions inethanol-H2O (1:1, V/V) neutral aqueous media. The detection mechanism was that theexcited-state intra/intermolecular proton transfer (ESPT) and C=N isomerization wereinhibited to enhance the fluorescent intensity of L4-Cd2+. Moreover, the compositionof the complex L4-Cd2+has been found to be1:3based on the fluorescence titration,Job's plot,1H NMR-titration experiments and further confirmed by X-raycrystallography. More importantly, L4was cell-permeable and could be used toimage Cd2+within living cells.In chapter5, a novel Schiff-base fluorescent sensor (L5) based on acridine hasbeen rationally designed and synthesized. The fluorescent sensor exhibited goodrecognition for Cr3+in methanol. Meanwhile, the L5-Cr3+complex solution alsodisplayed good recognition for PO43by displacement approach. Moreover, L5playeda role of INHIBIT logic gate for Cr3+and PO43. Besides, the sensor could be used inneutral methanol aqueous medium. More importantly, the sensor and its resultantcomplex were successfully used to recognize Cr3+and PO43in living MGC-803cells,which had potential applications in environmental detection and biological system.