Design Of Fluorescence Sensors And Properties On Their Enantioselective Recognition

Chirality is one of the most fundamental and crucial properties of various natural systems. Recently, research of novel sensor for enantioselective recognition of chiral molecules attracted much interest. Among these sensors, chiral fluorescent sensors attract much attention due to its merits of rapid screening, high sensitivity and selectivity, and many researchers were devoted to the designing, synthesis and application in this field.Optically active 2,2’-binaphthol （BINOL） has been actively used in the design and synthesis of fluorescent sensor for the enantioselective recognition of chiral molecules due to its special C₂ axial symmetry, rigid structure, high chemical stability and relatively good emission efficiency. In addition, much attention have been paid to polymer fluorescent sensor, because of the advantage of polymer-based fluorescence sensors over small molecules which lies in its signal amplification effect due to their rigid configuration and repeating unit in the backbone. In this dissertation, the studies focused on the designing, synthesis and properties of chiral fluorescent sensing and recognition based on （S）-BINOL for enantioselective recognition of chiral molecules.Charpter 2, A chiral host L1 incorporating （S）-BINOL and substituted coumarin moieties was synthesized via a nucleophilic addition-elimination reaction, and ligand L2 could be obtained by the reduction reaction of the imine-based L1 with NaBH4. Chiral fluorescent sensor L1 can form 1:1 complexes with L-and D-phenylalaninol, exhibiting high fluorescence enhancement for L-phenylalaninol and relatively less enhancement for D-phenylalaninol. The value of the enantiomeric fluorescence difference ratio （ef） is 3.07, which can be directly observed by naked eyes under UV-lamp. On the contrary, no obvious fluorescence response and enantioselective recognition effect can be detected for L2 towards chiral amino alcohol compounds.Chapter 3, two chiral fluorescent sensors L1 and L2 were designed and synthesized, and their fluorescent response behavior towards chiral amines, chiral amino alcohols and chiral hydroxyl carboxylic acid were investigated. L1 appears obvious fluorescence quenching "turn-off" response towards enantiomers of both a-phenyl ethylamine and phenylglycinol, and L2 can exhibit greatly fluorescent enhancement "turn-on" response behavior towards （S）-phenyl ethylamine, the value of enantiomeric fluorescence difference ratio （ef） reaches to 4.6 for a-phenyl ethylamine. L2 could be used as fluorescence sensors for simple and direct visual discrimination of organic molecule enatimers under commercially available UV-lamp. On the contrary, no fluorescence enantioselective recognition response could be observed by using （S）-BINOL-based boronic ester sensors L3 and L4 incorporating larger naphthyl or 8-methoxyquinolinyl substituent groups.Chapter 4, a novel chiral fluorescence polymer sensor incorporating （S）-BINOL and oligomeric aniline was designed and synthesized, and its recognition behavior towards various metal ions and chiral amino alcohols were investigated. Polymer sensor exhibits "turn-off" fluorescence quenching response upon addition of Hg²⁺, and moderate "turn-on" fluorescence enhancement behavior towards phenylalaninol enantiomers, the value of ef is 2.06. Meanwhile, this kind （S）-BINOL-based polymer sensor could exhibit highly selective enantioselective recognition response towards L-phenylalaninol upon addition of Hg²⁺ and the value of ef can reach as high as 5.4. This can be attributed to the formation of in situ generated radical cation arisen from oligomeric aniline moiety by Hg²⁺-induction, which is evidenced by further experiments and tests.