Construction And Properties Of The Responsive Luminescent Supramolecular Gels Based On Terbium And Europium Ions

The development of luminescent lanthanide materials is an important way to transform China’s lanthanide resource advantages into technological and economic advantages.The responsive luminescent lanthanide supramolecular gel is a new type of luminescent lanthanide materials which are widely used in sensors,fluorescent probes,and anti-counterfeiting materials owing to their unique luminescent properties of lanthanide ions and stimuli responsiveness resulted from supramolecular gels.In order to construct the responsive and luminescent lanthanide supramolecular gels,it is necessary to design and synthesize multifunctional lanthanide ligands with energy match as well as the self-assembly ability.However,the complicated molecular design and tedious synthesis resulted in the time-consuming preparation of lanthanide supramolecular gels.Additionally,due to the unpredictability of the self-assembly of the supramolecular gels,the current lanthanide supramolecular gels still have some problems such as simple function and poor stability,limiting their applications.In this thesis,based on the strong coordination ability of lanthanide ions and the diversity of self-assembly of commercial multifunctional gelators as well as the ligands of lanthanide ions,a variety of multifunctional luminescent lanthanide supramolecular gels with good stability and multifunction were designed and prepared.The relationship between the structure and properties of the luminescent lanthanide supramolecular gels was explored.The application of the prepared lanthanide supramolecular gels in anti-counterfeiting,sensing,bacteriostasis,drug release were also investigated.This thesis is consisted of several sections as the following:（1）A thermally stable lanthanide supramolecular gel was prepared by self-assembly of lanthanide ions(Tb³⁺and Eu³⁺)and Fmoc-phenylalanine（FmocPhe）in methanol/water mixture within several seconds at room temperature.The prepared gels exhibited strong characteristic luminescent behavior of lanthanide ions.The results of the SEM,¹H NMR,FT-IR as well as UV spectroscopy indicated that the formation mechanism of the gels involved the synergistic effect between the lanthanide-ligand coordination,π-πstacking and hydrogen bonding.The coordinating interaction not only accelerated the speed of gelation,but also made the Fmoc-phenylalanine molecules more tightly linked and increased the stability of the gel.The prepared gels showed outstanding thermally stable luminescence.Additionally,the reversible phase transition and“on-off”effect of luminescence could be achieved by alternately titrating NaOH and HCl into the gels.（2）The hybrid lanthanide supramolecular gels were facilely prepared through the self-assembly of the Fmoc-diphenylalanine（Fmoc Phe Phe）,terbium(Tb³⁺),and hydroxybenzoic acid（HA,the isomers are denoted as 2-HA,3-HA,and 4-HA）which was used as a sensitizer to Tb³⁺.By adjusting the positions of hydroxyl groups on hydroxybenzoic acid,the structures and properties of the gels were regulated.2-HA exhibited more effective sensitization to Tb³⁺than 3-HA and 4-HA owing to the more ordered and compact morphology of the gel resulted from the addition of the 2-HA.Due to the effective fluorescence sensitization by 2-HA,the as-prepared gels could be used for salicylic acid sensing with 6.8μM of the detection limit.This strategy had been successfully used for the detection of salicylates in pharmaceuticals and cosmetics.（3）A redox-responsive supramolecular lanthanide gel(DNSA/Eu³⁺)was obtained based on 3,5-dinitrosalicylic acid（DNSA）and europium(Eu³⁺).Upon the addition of TiO₂to the prepared gel,the oxidation process of the gel(DNSA/Eu³⁺/TiO₂)could be achieved by UV irradiation.The DNSA/Eu³⁺/TiO₂gel showed concurrent“on-off”effect of the luminescence and a color change from yellow to red when the gel was stimulated by the reductant and UV irradiation.Importantly,the gels remained stable during the redox process.Based on these properties,the luminescent patterning was achieved.（4）The hydrogel(GA/CCS/DNSA/Eu³⁺)was obtained by mixing phenylboronic acid-modified gelatin（GA-DBA）,catechol-modified carboxymethyl chitosan（CCS-PCA）,3,5-dinitrosalicylic acid（DNSA）,and Eu³⁺ions.The GA/CCS/DNSA/Eu³⁺hydrogel exhibited reversible luminescence,color,and phase changes in response to temperature,acid/base,redox,and salt stimuli.Based on the multiple responsiveness,information encryption and decryption,naked eye sensing of glucose,as well as remarkable shape memory were achieved.Moreover,the self-healing properties were realized due to the dynamic bonds in GA/CCS/DNSA/Eu³⁺hydrogel.Specifically,the GA/CCS/DNSA/Eu³⁺hydrogel possessed antibacterial activity against S.aureus,B.subtilis,P.aeruginosa,and K.Pneumoniae owing to the bacteriostasis of CCS-PCA and DNSA/Eu³⁺complex.（5）A multicolor luminescent lanthanide supramolecular hydrogel（CS/DEX/CP）was constructed by lanthanide coordination polymer（CP）,dextran aldehyde（DEX）,and chitosan（CS）.The CP was formed by self-assembly based on guanosine acid（GMP）,europium ion(Eu³⁺),terbium ion(Tb³⁺),and ciprofloxacin（CIP）.The hydrogel was rapidly formed by the generation of Schiff base bonds of CS and DEX.The luminescence colour of CP varied with pH in the range of 5.5 to 8.0 due to the energy transfer between the ligand and lanthanide ions affected by pH.The luminescence colour of CS/DEX/CP hydrogel showed diverse change at different pH owing to the competitive coordination of CS and DEX.Therefore,when bacteria grew and produced acid,resulting in the visible multicolor luminescence changes as well as the destruction of Schiff base bonds of CS/DEX/CP hydrogels.As a result,the gels could be used to sensing the bacteria by naked eye.In addition,CIP and CS were released from the gels to kill the bacteria according to the amount of bacteria.