Synthesis And Properties Of Water Soluble Anionic Fluorescent Probe Based On Electrostatic Interaction

Anions widely exist in the natural environment and play an important role in ecological environment.Fluorescent probe has advantages of convenient operation,and high sensitivity for target analytes and has attracted increasing attention.However,because of hydrogen-bonding interaction of anions with water molecules seriously hinders the development of anion chemosensors in aqueous solution.In this thesis,three water-soluble pyridinium fluorescent anion probes were designed and synthesized.Along with the hydrophobic effect of the cationic probe in water,and the different binding strength between the negatively charged anions and the positively charged probe,which enable the target anions to suitably trigger the aggregation of the probe via the combination of electrostatic ionic bonding,van der Waals forces between the alkyl chains,andπ-stacking of aromatic moieties.In addition,it was found that increasing fatty chain length significantly improved the sensitivity of the cationic probes for the target anions,while the selectivity of the probes seemed to be decreased.Detail studies as following:1.“OFF-ON”type fluorescent probe molecules(TBPD²⁺probes)with alkyl chains in different lengths（10C to 12C）have been synthesized from1,4-dibromo-2,3,5,6-vinylpyridine and 4-vinylpyridine.Studies showing that probes emit weak fluorescence（505 nm）in aqueous solution,and an enhanced yellow fluorescence（535 nm）is generated after the interaction with HSO₃^-.The detection limit of the TBPD²⁺-10C probe for HSO₃^-was determined to be 4.20μM.In addition,the detection sensitivity of the probe for the target was improved by growing the length of the alkyl chain moiety of the probe molecule,which increased the detection limit to 0.5μM.2.SBPD²⁺ probes with different alkyl chain lengths（6C to 9C）were synthesized by Suzki coupling reaction between 4,4’-dibromo-trans-stilbene and 4-pyridine boronic acids.Studies showing that the red-shift fluorescent emission was triggered attributed to the hydrophobicity of probe molecules and the electrostatic effect between anions and probes,which induceπ-πstacking between aromatic rings to produce fluorescence red shift phenomenon,and then trigger the probe to undergo aggregation phenomenon to realize the recognition of target anions（such as SCN^-）.SEM images suggest that different morphologies were formed in the anion-recognition-triggered self-assemblies of the probes,which can be attributed to the different anion molecular geometries.Interestingly,SCN^-could easily form precipitate with the probe and remove this ion from aqueous solution,which provided a new idea for the removal of SCN^-in aqueous environment.3.DBPD²⁺ probes molecules with different alkyl chains lengths（7C to 9C）were synthesized by the Suzuki coupling reaction between 4,4’-dibromobiphenyl and4-pyridine boronic acid.Studies showing that:A water-soluble cationic fluorescent probe with AIE features exhibited unique sensing of charge-diffuse anions,namely,PF₆^-,BF₄^-and SCN^-via ionic interactions and the subtle cooperation of the tunable hydrophobicity.The effect of the fatty chain length on the cationic probes indicated that the sensitivity and selectivity of the probes can be rationally improved by switching their aggregation tendency（hydrophobic effect）in water or by integrating them in the form of a fluorescence chemosensor array.SEM images suggest that different morphologies were formed in the anion-recognition-triggered self-assemblies of the probes,which can be attributed to the different anion molecular geometries.