Electrosynthesis,Characterization And Fluorescent Sensing Application Of Amino Acid Grafted Polyfluorene

Conjugated polymers?CPs?possess unique optical and electrochemical properties that make them particularly suitable for a broad variety of sensing tasks.Compared with small molecules,a prominent advantage of using fluorescent CPs is that the signal amplification along the polymer backbone through the?molecular wire?effect,as the molecule wire polymer greatly magnify the change of fluorescence responsive by the facile energy migration along the polymer backbone.Recently,water/alcohol?environmentally friendly solvents?soluble fluorescent CPs have been widely used as optical sensing platforms for highly selective and sensitive detection of different species,especially biologically active species such as organism,tissue,cell,and biomacromolecules?DNA,RNA,protein,and enzyme?and fluorescent imaging in vivo and at the cellular level.The commonly employed reactions for the synthesis of CPs are known as palladium-catalyzed coupling reactions?Suzuki,Heck,and Sonogashira?,Wessling reaction,topopolymerization reaction,and FeCl₃ oxidative polymerization.Electrochemicalpolymerization,a kind of method that has been widely employed for the generation of CPs onto a conductingsurface,as one of fast,reliable and convenient synthetic methods to obtain the target material.As a useful and widely applied technique,electrosynthesis of CPs is still far from mature,and the development of new type of CPs fluorescent sensors and study its application in the actual samples is an important topic andwill provide a promisingplatform for optical sensing applications in business prospects.Polyfluorene?PF?derivatives are a kind of prospective emitting layer fabricated polymer blue light emittingdevices among CPs in that they have a variety of extraordinary properties including a widely energy gap?>2.90 eV?,an excellent thermal stability,a solid-state fluorescence quantum yields?from 0.6 to 0.8?,and could be modified by different groups at C2,C7 and C9 positions.The modification at C9 position by different functional group can not only improve the solubility,electron affinity,and biological compatibility of PFs,but form supramolecular structure which affects the photoelectric performance,and also adjust theaggregation structure of the material.The modification even can were used to improve the oxidation of C9position of which would led to the fluorescencequenching.Three kinds of amino acid functionalized PFs were chosen to study their electrochemical polymerization,optical sensing application,and sensing in real applications.This thesis was carried out with the following three aspects work:1.To obtain the poly[N-?9-fluorenylmethoxycarbonyl?-glycine]?P9FG?by direct anodic oxidation of corresponding monomers,and systematic study its optical properties.Alcohol-solubleP9FG was facilely synthesized by the direct electropolymerizationofcommerciallyavailablemonomer N-?9-fluorenylmethoxycarbonyl?-glycine in a mixture system of boron trifluoride diethyl etherate electrolyte?BFEE?and dichloromethane?DCM?.The structure,properties and optical sensing application of the obtained polymer were described and discussed,and confirmed that the electropolymerization occurred at C2 and C7positions of fluorene units,and amino acid side chain groups were not cleaved from polyfluorene backbone.Fluorescent spectra indicated that P9FG was a good blue light emitting material that could be employed as optical sensors for the detection of Fe³⁺,Cu²⁺and Cr₂O₇^2-.Moreover,P9FG could easily realize fluorescent or ultraviolet detection of Fe³⁺,Cu²⁺and Cr₂O₇^2-.,with a wide concentration range and a low detection limit,respectively.The resulting P9FG will provide a promisingplatform for optical sensing applicaions.2.A simple Schiff based poly?Fmoc-L-histidine??PFLH?sensor that only for Cr³⁺detection.PFLH was facilely synthesized by the direct electropolymerization of commercially available monomer?Fmoc-L-histidine?in boron trifluoride diethyl etherate?BFEE?,and its preliminary application as a fluorescent chemosensor for the highly selective and sensitive detection of Cr³⁺in aqueous solution.Its structure and properties were characterized by ¹H NMR spectra,FT-IR spectra,and quantum chemical calculations.The recognition mechanism of PFLH sensor towards Cr³⁺was that Cr³⁺chelated with the carbonyl oxygen?C=O?and the nitrogen of Schiff base?-C=N-?in the side chain of polymer,which resulted in a great turn-on of the fluorescence,and the carbonyl oxygen synergistically enhanced the recognition of Cr³⁺.The working mechanism was proposed and confirmed by transmission electron microscopy quantum chemical calculations.This PFLH-based?turn-on?fluorescent sensor showed a high sensitivity with a linear response towards Cr³⁺in the concentration range of 5.1 nM-25?M with a low detection limit of 1.7 nM.Satisfactory results indicated that the PFLH-based fluorescent sensor will be a potential tool for the detection and quantification of chromium in edible agro-product and biological samples.3.Poly[N-?9-fluorenylmethoxycarbonyl?-serine]?P9FG?basedfluorescent sensor success achieved changing its ion selectivity by the introduction of phosphate ion in aqueous solution.P9FS was facilely synthesized by the direct electropolymerizationofcommerciallyavailablemonomer?N-?9-fluorenylmethoxycarbonyl?-serine??9FS?in boron trifluoride diethyl etherate?BFEE?,and its preliminary application as a fluorescent chemosensor for the highly selective and sensitive detection of Cr³⁺in aqueous solution,and the structure and properties of PFLH were characterized by ¹H NMR spectra and FT-IR spectra.P9FS could easily realize fluorescent detection of Fe³⁺,Cu²⁺and Cr₂O₇^2-in aqueous solution.In order to obtain a specific selectivity P9FS fluorescent sensor for detection of Cr₂O₇^2-,PO₄3-was used to react with Fe³⁺and Cu²⁺,as the phosphoric can with alkali metal and alkali earth metal and blocked their quenching effect of P9FS.This P9FS-PO₄^3-basedfluorescent sensor showed a high sensitivity with a linear response towards Cr³⁺in the concentration range of 80 nM-795 mM with a low detection limit of 26 nM.TheCr₂O₇^2-in agricultural crops and environment samples was determined facilely and efficiently by usingP9FS-PO₄^3-based fluorescent sensor.