Coordination Self-Assembly And Sensing Applications Of Stimulus Responsive Metal-Organic Gels

Supramolecular gel is one of the hotspot materials that has attracted much attention in recent years,and has been widely used in various fields of life.Since the supramolecular gel is formed by the self-assembly of small accounts of low molecular weight gelators（LMWGs）into larger structures by non-covalent forces,the supramolecular gel can produce responses when it is got external stimuli（optical stimuli,mechanical force stimuli,environmental change,etc.）,which is an ideal stimuli-responsive material.Metal-organic gels（MOGs）are emerging supramolecular gel materials,which are constructed by the induction of coordination of metal ions with LMWG.The redox,optical,and electromagnetic properties of metal ions provide additional latitude for tuning the gel properties,which allows MOGs to have unique and tunable responsiveness when exposed to external stimuli.Therefore,the coordination of metal ions with LMWG is crucial for the construction of MOG and the regulation of stimulus correspondence,and the properties of MOG will depend on the properties of metal ions,the rationally designed LMWG structure and the non-covalent interaction involved in formation of MOG.In this thesis,based on the research of our group,we realize the construction of a series of MOG materials through coordination-directed self-assembly,then study and discuss the phenomena and mechanisms of their stimuli-response properties,and finally expand the application of this series of MOG materials in sensing.The specific content is as follows:1.Research background:The development history of supramolecular gel is briefly reviewed,and the basic concept,different types,physical and chemical properties of supramolecular gel are described and summarized.The concept and rise of metal-organic gels（MOGs）were expounded.Combined with the advantages and limitations of current MOG materials,the application scope and development trend were briefly analyzed.Then the development status and market demand of the two fields of stimuli-responsive sensing and wearable flexible devices are briefly described,and the application potential of MOG materials in the two fields is analyzed.Finally,based on the above arguments,we propose our research plan.2.Lanthanide supramolecular hydrogels for luminescent multi-stimulus response:Luminescent supramolecular hydrogels based on lanthanide metals have extensive application potential due to their unique optical properties and biocompatibility.In this work,we reported the design,synthesis and optical versatility of a series of supramolecular hydrogels based on lanthanide ion.The hydrogel HG-Ln_2nL_3n^1/2 was prepared through the deprotonation self-assembly of curved bitridentate tetrazole-based ligands H₄L^1/2with lanthanide ions.Benefiting from the larger bending angle of the ligands（∠B≈150°）,aggregated cross-linked networks rather than discrete polyhedra form in water.At the same time,the formation mechanism of the hydrogel HG-Ln_2nL_3n^1/2is also proposed.The two hydrogels,HG-Eu_2nL_3n¹ and HG-Ln_2nL_3n²,achieved red light emission and near-infrared emission,respectively.When stimulated by different metal ions,the emission of HG-Eu_2nL_3n¹ hydrogel would be enhanced or quenched.It was confirmed that the intersystem channelization（ISC）efficiency of the assembly from singlet state（S1）to triplet state（T1）would be changed due to the substitution of the coordination lanthanide metal by external metal ions.As a result,the intensity of lanthanide metal sensitized luminescence changes.3.Self-healing metal organic gel-polyvinyl alcohol mixed gel electrolyte for flexible capacitor sensors:Supramolecular gels based on noncovalent interaction are attractive self-healable polymeric electrolytes due to their repeatable spontaneous recovery of mechanical and electrochemical performance.We achieved the transformation of the assembly from discrete metal-organic macrocycles to metal-organic gels by regulating the conformational changes of the ligands during the self-assembly process of coordination with the metal,and constructed the metal-organic gel(Pd_2nl_3n³).We believe that the transition of the ligand from the cis-conformation of the V-shaped rigid ligand to the freely rotatable linear conformation is the main reason for the gelation of the induced assembly.A metal-organic hybrid gel electrolyte system was prepared by the coordination of a novel palladium to metal-organic gel doped with polyvinyl alcohol（PVA）.The reversible coordination and hydrogen bonding interactions endow the PVA-MOG hybrid gels with ultrafast self-healable ability in both mechanical and electrochemical timescales of 180 sec and 60 sec,respectively.The polyaniline（PANI）-based printed interdigital capacitor（IDC）sensor with the hybrid gel electrolyte exhibits a wide voltage window of0-2.75 V,stable charge-discharge cycle at a high scan rate of 500 m V/s.When printed on a glove as a sensor device,it can effectively capture the fisting and stretching movements of the hand,and sensitively output it as an electrical signal through the change of capacitance.4.Summary and outlook:The working system of this paper is summarized by regulating the structure of organic ligands and the application of sensing,and the advantages and limitations of the current system are pointed out.Based on the research progress of the thesis and the understanding of the topic direction,the author puts forward some opinions and prospects.