Synthesis And Photophysical Properties Of Fluorescent Polymer Materials Sensing For Fe(Ⅲ)

In recent years,the environmental pollution has been a major concern of the present industrial societies.Fluorescence-based sensors are well known for their high sensitivity,versatility,and fairly good selectivity compared to absorption sensors. Thus the development of new functional fluorescent compounds having responsibility to metal ions is important for expanding the utilization of fluorescent chemosensors. But,any supersaturated concentration of dye is likely to result in migration and phase separation in application.Polymer materials have good stability and high quality of film making.Compared with the detection technique in solution,detecting in film state have showed much more advantages such as the reproductivity,being easy to preserve,the simplified operation and being effective.In the first department of this paper,the latest research progress in supramolecular fluorescence sensors and switches used for metal cation recognition is summarized.Two types of systems were reviewed,photo-induced electron transfer(PET) and intramolecular charge transfer(ICT) systems.And the development of fluorescent polymeric sensor for metal cation recognition was reviewed.Since iron plays an important role in metabolic processes and biological materials,the development of highly selective and sensitive sensors able to detect iron cations in the soil and water sources has become a very important scientific goal. Integrating together the recognition capability of the dyes and the advantages of polymeric materials,the fluorescent polymers having the ability to recognizing metal cation Fe³⁺ were obtained based on norfloxain and 1,8-naphthalimide.The photophysical properties of fluorescent compounds synthesized in this paper were detected,and properties of the fluorescent polymer in the area of reorganization range of metal ions,relationship between fluorescent intensity and concentration of ions and response time were measured in the solution and film state.(1) Novel norfloxacin-containing fluorescent polymers were synthesized via copolymerization of one or two kinds of derivatives of norfloxacin and methylmetacrylate(MMA).Fluorescence characteristics of the polymers as a function of pH and metal cations were investigated in aqueous solution and film state.The presence of metal cations(Mn²⁺,Fe³⁺,Co²⁺,Ni²⁺,Cu²⁺ and Zn²⁺) could quench the fluorescence intensity of the polymers in different levels because the coordination of metal ions and the dyes accelerated the ICT process.Exhibiting powerful oxidizing properties,Fe³⁺ showed the strongest fluorescent quenching on the fluorophores, which was accordance with Stem-Volmer dynamics.The results suggested the possibility that this newly synthesized compound works as a polymeric sensor responding to water polluted by protons and Fe³⁺.(2) Novel naphthalimide-containing green fluorescent polymers were synthesized via two methods.Firstly,we obtained green fluorescent polymers PMMA throught the copolymerization of the monomeric derivative of 1,8-naphthalimide and MMA.The monomeric derivative of 1,8-naphthalimide is a solvatochromic fluorophore exhibiting strong fluorescence in nonpolar solvent.The responses of the polymer in solution and in film state to metal cations were detected in detail.Different linear relationship were received between the relative fluorescent intensity(F₀/F) and the concentration of Fe³⁺[Fe³⁺]in the different range of[Fe³⁺].Then a novel water-soluble green fluorescent polymer PAM was synthesized based on 1,8-naphthalimide through a series of easy reactions with high yields. Fluorescence characteristics of the polymer as a function of pH were investigated, with the pK_a 3.5.The presence of metal cations(Cu²⁺and Fe³⁺) could quench efficiently the fluorescence intensity of aqueous solution of this polymer.(3) The fluorescent polymer containing two dyes having spectra overlap (emission spectrum of the donor partially overlaps the absorption spectrum of the acceptor) were prepared.The photophysical characteristics of the polymer such as the energy transfer phenomenon between the two dyes and the response to metal ions were detected.A new kind of bichromophoric Poly(acrylamide) covalently linked with norfloxacin(NF) and proflavine(PF) molecules were synthesized with different contents of the two dyes.The photophysical properties of the polymer were investigated that energy transfer(ET) from norfloxacin to proflavine occurred in the solid state(containing film and powder) of the polymer but not in aqueous solution because of the high concentration of chromophore groups existing in solid state(film and powder state).The transfer efficiency increased linearly with the content of acceptor either in film or in powder state.Responses of different metal caions on the fluorescence intensity of the polymer solution were investigated.Only Fe³⁺ ions exhibited remarkable fluorescence intensity quenching to the polymer.The linear relationship between[Fe³⁺]and fluorescence intensity can be recorded synchronously at two position,which could enhance the selectivity and precision of the sensor both in aqueous solution and in film state.Fluorescent polyvinyl chloride(PVC) films were prepared thought doping two 1,8-naphthalimide derivates(having spectra overlap) into PVC.The energy transfer efficiency increased linearly with the content of acceptor,pH environments have no influence on the fluorescence of the film.Response of different metal caions on the fluorescence intensity of the film was investigated.Only Fe³⁺ ions exhibited remarkable fluorescence intensity quenching.Different linear relationship were received between the relative fluorescent intensity(F₀/F) at two emission wavelength and the concentration of Fe³⁺ in the different range of[Fe³⁺].All the newly synthesized materials showed selectivity to Fe³⁺,and linear relationship between the fluorescent intensity and the concentration of Fe³⁺ were obtained.They may be as potential efficient and selective sensors for water pollution by Fe³⁺ cations.