Preparation And Properties Of Transition Matal Sensors And Fluorescent Dual-network Hydrogels Based On Terpyridine

In recent years,there have been lots of research results in the field of supramolecular chemistry.In the non-covalent bond interactions used in the construction of supramolecular compounds,metal-ligand coordination has attracted wide attention owing to its strong bonding force,ability to respond to multiple external stimuli and reversibility.This coordination has gained widely application in the field of supramolecular sensors and gels.However,most of those series of polymers are generally highly hydrophobic,which limits their further applications in the environment and living systems.In this dissertation,4-（2,2’:6’,2’’-terpyridine-4’-yl）styrene（TPY）was used as ligand,and fluorene and its oligomers were introduced as functional fluorescent groups.The above monomers and hydrophilic acrylic acid（AA）/acrylamide（AM）were subjected to free radical polymerization to obtain a series of copolymers.Different metal ions were added to the polymer aqeous to study their absorption/emission spectra properties.In addition,a chemical crosslinking agent was added during the copolymerization process,and the resulting gels were coordinated with rare earth ions to obtain dual-network hydrogels,which were studied in depth to measure their performances.1.Transition metal ion sensor based on terpyridine.Two fluorescent groups7-vinyl-9,9,9’,9’-dioctyl-[2,2’]-bifluorene（VOF₂）/2-vinyl-9,9-dioctylfluorene（VOF₁）were synthesized.Polymers with different ratio of TPY,VOF₁/VOF₂and acrylic acid（AA）were obtained via free radical polymerization.The structure and molecular weight of the obtained intermediate products,target monomers and polymers were characterized via ¹H NMR,¹³C NMR,ESI-MS,FT-IR and viscosity methods.The polymers were dissolved in water to prepare dilute solutions,to which different concentrations of transition metal ions(Fe²⁺,Cu²⁺,Co²⁺,Sn²⁺,Ni²⁺,Zn²⁺,Cd²⁺)were added.Under natural light and ultraviolet light,the solutions exhibit different color/fluorescence changes.Ultraviolet-visible absorption spectroscopy tested on metal-polymer solutions have found that the intensity of the absorption peak at 284nm caused by theπ-π*transition of the conjugated group decreases with the increase of the metal ion concentration.At the same time,the intensity of the absorption peak at 335 nm caused by the intramolecular charge transfer process（ICT）increases,and the solutions with Fe²⁺exhibit unique absorption peak at 570 nm due to the metal ligand charge transfer（MLCT）process.The fluorescence spectra shows that in the polymer solutions,Zn²⁺and Cd²⁺exhibit fluorescence enhancement effects while other transition metal ions lead to fluorescence quenching,and the quenching degree is related to the metal ion species and the conjugation degree of fluorescent groups.This type of transition metal ion sensor shows good prospects for metal ion detection in water environment and living systems due to high sensitivity and high selectivity.2.Fluorescent doua-network hydrogel.A fluorescent coordinating monomer4’-phenyl-2,2’:6’,2’’-terpyridine-2-methyl-9,9-dioctyl-7-vinylfluorene（VOF-TPY）containing fluorene and terpyridine was synthesized.The polymers（P0,P1,P2,P3）with different ratio of TPY,VOF₁/VOF₂,VOF-TPY and acrylamide（AM）were obtained via free radical copolymerization.The structure and molecular weight of the obtained intermediate products,target monomers and polymers were characterized via¹H NMR,¹³C NMR,ESI-MS,FT-IR and viscosity methods.The polymers were dissolved in water to prepare dilute solutions,and the photophysical properties were tested by ultraviolet-visible absorption and fluorescence pectroscopy,the solutions exhibit absorption peaks at 284 nm and 335 nm due to theπ-π*transition of conjugated group and intramolecular charge transfer process（ICT）,respectively,and the intensity of those absorption peaks differs depending on the type of polymers.The emission peaks of the polymer solutions are located near 360 nm,which are red-shifted with the increase of the degree of molecular conjugation.After being interacted with Eu³⁺,the absorption peaks of polymer solutions at 284 nm are red-shifted to varying degrees.After absorbing light energy,the intramolecular energy is transferred from the fluorescent group to Eu³⁺,so the intensity of the emission peak at 360 nm continues to decrease.At the same time,the characteristic emission peak of Eu³⁺appears at 612 nm and its intensity increases with the increase of the concentration of Eu³⁺.As the macroscopic distance between the fluorescent group and Eu³⁺on the film state decreases,the energy transfer efficiency is higher,and the red light emission of Eu³⁺is more obvious.A chemical cross-linking agent is used to form a basic gel and Eu³⁺is added to coordinate with TPY to form dual-network hydrogels.There is also an intramolecular energy transfer process（IET）in the obtained hydrogels,and the transfer efficiency increases as the volume of the gel decreases.The cross-linking density of dual-network hydrogel formed by Eu³⁺-TPY coordination and chemical cross-linking,increases,which results in a significant decrease in the diameter of the onlooker mesh.Compared with a single chemically cross-linked hydrogel,the deformation of the coordinated hydrogel is increased from 150%to250%when the storage modulus（G’）stars to decrease which also confirms the successful preparation of dual-network hydrogel from the side.