The Design,Synthesis And Properties Of Fluorescence Probes Based On Fluorescein Skeleton

As a kind of dye,fluorescein has attracted the attention of scientists owing to their excellent properties,such as higher fluorescence quantum yield in water,larger molar extinction coefficient,and the long excitation and emission in visible region.In this thesis,fluorescein was selected as a fluorophore,we designed and synthesized a series of new fluorescein derivatives,and studied their fluorescence properties in detail.The main works are as follows:?1?We designed a series of fluorescent probes L¹,L² and L³,which is based on fluorescein modified by glycine,phenylalanine and asparagine,respectively.These probes are developed for relay recognition of copper?II?ions and biothiols via a fluorescence “on-off-on” cascade in 100% HEPES buffer?pH=7.0?.All experiment results showed that probe combined with Cu²⁺ and resulting in the fluorescence quenching first,then fluorescence recovered after the addition of Cys,Hcy and GSH.Finally,this relay recognition was applied in molecular logic gate with IMPLICATION function by using the above fluorescence changes.Moreover,this relay recognition was also applied to HepG2 cell imaging successfully.?2?We designed a new kind of dual mode fluorescent probe L⁴ and L⁵,which is based on an integration of fluorescein and coumarin fluorophores,it can be developed for the discrimination of Cys from Hcy and GSH.This probe shows the advantage of quick reaction with Cys in 5 min,resulting in a strong fluorescence turn-on response when excited at 450 nm.Notably,it also demonstrates the ratiometric fluorescence recognition while excited by a shorter wavelength at 332 nm.All of experiment results suggested probe L⁴ has a high selectivity toward Cys even in the presence of other amino acids,cations and anions.The detection limit of Cys was calculated as 0.084 ?M,which was much lower than the intracellular concentration.1H NMR,MS and DFT calculation were used to reveal the detection mechanism further.Finally,this low cytotoxic probe was successfully applied in bioimaging within HepG2 cells.To our best of knowledge,there is no report about such kind of probe based of fluorescein skeleton.?3?Fluorescence probes L⁶ and L⁷ were synthesized based on monoaldehyde and dualaldehyde functionalized fluorescein.Their UV-vis and fluorescence spectral responses toward TNP were investigated in ethanol and HEPES buffer?pH=7.0?,respectively.All of results suggested TNP could quench the fluorescence by electron transfer from the fluorescein skeleton due to its strong ability of electron-withdrawing.In addition,visual detection of trace amounts of TNP in solution by using test strips was successfully performed.