Preparation And Properties Of Metal Ions Sensors Based On Alkoxy Chain Modified Fluorene And Terpyridine

Metal elements were widely used in alloy manufacturing,medical treatment,food additives,military industry,etc.Metal elements were also very important for living organisms,and moderate concentrations of metal ions were beneficial,while excess and deficiency can cause harm.Rapid and accurate detection of metal ion concentration was particularly important.The optical detection method was a non-contact nondestructive detection method with the advantages of high selectivity,high sensitivity,and low cost,which had important application prospects in environmental monitoring and bioscience.Numerous fluorescent probes for the detection of metal ions were often applied only in organic media systems,while for the environment,especially biological media,in situ,rapid and quantitative detection of metal ions in aqueous systems was of greater importance.In this thesis,the alkoxy chains were used to modify the luminescent group fluorene as well as the terpyridine ligand to construct novel functional monomers,and they were radically copolymerized with water-soluble acrylic acid（AA）or acrylamide（AM）to prepare a series of hydrophilic copolymers with different structures.Using its multiple coordination and conjugated fluorescence function,we obtained a fluorescent sensor with highly sensitive detection performance for a variety of metal ions.1.Transition metal ion sensor based on alkoxy chain modified fluorene.The fluorescent monomer 2-vinyl-9,9-bis（2-（2-（2-methoxy ethoxy）ethoxy）ethyl）-fluorene was synthesized.A series of polymers with different components（PTpy AA,PTpy AM,PTpy FAM）were obtained by free radical copolymerization of the modified terpyridine with acrylic acid or acrylamide.The structures of monomers and copolymers were characterized by ¹H NMR,¹³C NMR,and FT-IR.Measuring the molecular weight of polymers by means of a Ubbelohde viscometer.The molecular weights of the polymers with different structures obtained by copolymerization with acrylic acid（PAAF2,PAAF1,PAAF0.5）range from 1.7×10⁵-2.8×10⁵g/mol,and of the polymers copolymerized with acrylamide（PAMF1,PAMF2）range from 1.5×10⁵-2.1×10⁵g/mol.The strong absorption peak at 273 nm in the UV absorption spectrum of the polymers can be attributed toπ-π*transition in the conjugated structure of the polymers,and the absorption peak from 300 nm to 314 nm was attributed to intramolecular charge transfer.Polymer solutions（0.25 mg/m L）were interacts with metal ions(Zn²⁺,Sn²⁺,Cs⁺,Ni²⁺,Cu²⁺,Fe³⁺,Mg²⁺,Co²⁺,Fe²⁺,Cd²⁺,Al³⁺)(10^-6 mol/L)and their sensing properties were studied by color and changes in absorption and emission spectra.The solution changed from colorless to yellow after coordination of Fe³⁺with PAMF,with enhanced absorption peaks at 273 nm and 300 nm and significantly lower fluorescence emission intensity at 320 nm,which was caused by chelation-enhanced quenching（CHEQ）of ligand-metal charge transfer（LMCT）.The solution changed from colorless to yellow after coordination of Fe³⁺with PAAF,from colorless to blue after coordination of Cu²⁺with PAAF,and from colorless to orange after the coordination of Fe²⁺with PAAF.The fluorescence of the solutions also appeared to be quenched to different degrees after coordination.The fluorescence of the PAAF solution was completely quenched when the Fe³⁺concentration was only 4.9×10^-7 mol/L because Fe³⁺can coordinate with both the ether-bonded oxygen atom on the alkoxy chain and the oxygen atom on the carboxylate.The concentrations of Cu²⁺and Fe²⁺were 4.8×10^-7 mol/L and 1.3×10^-6 mol/L,respectively,to completely quench the fluorescence of the PAAF solution,because Cu²⁺and Fe²⁺could only be coordinated with the carboxylate.These fluorescent sensors can be used to detect Fe³⁺,Cu²⁺and Fe²⁺in the aqueous environment because of their good water solubility,high sensitivity and easy observation.2.Transition metal ion sensor based on alkoxy chain modified terpyridine 4-[2-[2-[2-[2-（4-allyloxyethoxy]ethoxy]ethoxy]ethoxy]-ethoxy）-phenylmethyl]-2,2’:6’,2’’-terpyridine was synthesized by introducing hydrophilic alkoxy chains.A series of polymers with different components（PTpy AA,PTpy AM,PTpy FAM）were obtained by free radical copolymerization of the modified terpyridine with acrylic acid or acrylamide.The intermediates and polymer structures were characterized by ¹H NMR,¹³C NMR,and FT-IR.The molecular weight of the polymer was determined by the viscosity method,and the range of molecular weight was 2.75×10⁵-3.71×10⁵ g/mol.The properties of PTpy AA series polymers in different solvents were investigated by UV absorption and fluorescence emission spectroscopy.The absorption peak at 280nm was due to theπ-π*transition of the conjugated structure,and the absorption peak at 335 nm was due to intramolecular charge transfer（ICT）between the powered alkoxy and phenyl groups and the electrically absorbing triple pyridine group.The PTpy AA solution exhibited weak fluorescence emission in DMSO solvent due to more energy loss in photoinduced electron transfer（PET）nonradiative transition.There was a significant fluorescence enhancement with the addition of water to the PTpy AA solution of DMSO,and the interaction of the polymer with water inhibited the PET process.Three polymers（0.5 mg/m L）were coordinated with metal ions(Cd²⁺,Co²⁺,Cs⁺,Cu²⁺,Zn²⁺,Fe³⁺,Fe²⁺,Mg²⁺,Sn²⁺,Ni²⁺)(10^-5 mol/L)and their sensing properties were studied by color and changes in absorption and emission spectra.The solutions changed from colorless to purple after the coordination of Fe³⁺and Fe²⁺with the polymers and from colorless to blue after coordination with Cu²⁺,and the fluorescence of the three polymers was quenched by coordination with Fe³⁺and Fe²⁺.The fluorescence emission intensity of the PTpy AA solution was enhanced by 80%,76%,and 20%after coordination with Zn²⁺,Mg²⁺,and Cs⁺,respectively.PTpy FAM and PTpy FAA contain fluorescent monomers,so their fluorescence intensity is higher compared to PTpy AA and PTpy AM.The coordination of the metal ion and the tripyridine increases the electrophobicity of the pyridine group and enhances the intramolecular charge transfer（ICT）process,which in turn leads to a significant enhancement of the absorption peak at 335 nm.The coordination of alkoxy,terpyridine,and carboxyl groups with metal ions in the polymer molecule and their synergistic effects endow this water-soluble polymer with highly sensitive sensing properties for a variety of metal ions,providing a new strategy for chemical sensor design.