Design,Synthesis And Properties Of Multiple Stimulus-Responsive Molecules Based On Pyran Skeleton

Stimulus-responsive fluorescent materials are a class of functional materials whose fluorescent properties change under external stimuli.How to design stimulus-responsive materials with significant luminescence changes(??_em>100 nm)under external stimuli is a great challenge.Since polymorphic molecules usually exhibit reversible mechanical force-induced color changes,this thesis takes D-?-A structure pyran derivatives as the matrix and uses crystal structure prediction to guide the design and synthesis of high-contrast mechanical force-induced color materials.The main contents are as follows:Chapter 1:The mechanism of fluorescence generation,the common stimulus response behavior of fluorescent dyes and the research progress of organogel materials are reviewed,with emphasis on fluorescent materials whose physical structure changes under stimulation.Chapter 2:In this chapter,we designed and synthesized six pyran derivatives-based high-contrast mechanochromic materials based on polymorphic prediction.All the six compounds exhibited aggregation induced luminescence(AIE)properties.The polymorph prediction indicated that 4-dicyanomethylene-2,6-distyryl-4H-pyran and 4H-pyran-4-one derivatives(1-Ph,3-Ph,3-Ph F,3-Ph Cl and 3-Np)had the potential to crystallize in both monomer and?dimer aggregates,while barbituric acid-based compound(2-Ph)tended to pack tightly in all aggregated states.The experimental results agreed well with the prediction that the derivatives potentially possessing both monomer and?dimer aggregate structures exhibit excellent mechanochromic behavior,whereas the fluorescence difference for the barbituric acid-based compounds is minimal.We cultivated the single crystals of 3-Ph and 3-Ph Cl by solvent evaporation method,and the crystal structure was consistent with the predicted crystal structure.The formation of aggregates in acetonitrile/water mixed solvent was also confirmed by UV-vis,Tyndall effect and SEM.This compound with an excellent fluorescence difference of three colors during reversible mechanochromism(3-Ph Cl)was chosen as the candidate for an optical recording material and security ink.In addition,we have also conducted preliminary studies on the mechanochromic or photophysical properties of the synthesized 3-Ph Br and other eight compounds.Chapter 3:In this chapter,we found that the three compounds of 3-Ph,3-Ph Cl and 3-Ph Br can form a gel in acetonitrile,and could be converted between heating and cooling,but cannot be formed in other solvents.In order to further study the driving force of compound gelling solvents,we conducted temperature(time)dependent fluorescence spectroscopy,SEM,and XRD tests on them.The experimental results show that the intermolecular?-?interaction may be the main driving force for gel formation.As the temperature decreases,the emission peak becomes stronger and has a tendency of red shift during the transition from hot sol to gel,which is similar to the mechanochromic properties and AIE properties of the dye in the previous chapter.The emission at the short wave can be attributed to the monomer emission,and the emission at the long wave can be attributed to the?-dimer emission.Among them,the morphology of the 3-Ph Cl xerogel is a three-dimensional network structure intertwined,and no obvious diffraction peaks are observed in the XRD pattern which indicate good gelation performance.Combining temperature-variable nuclear magnetic and infrared spectroscopy tests,the mechanism by which halogen atoms coordinate intermolecular forces to promote the formation of gels has been explored.Chapter 4:Herein,we summarize the previous work.The mechanochromic properties of most of the compounds we designed and synthesized are consistent with the polymorphic prediction results.This provides a new idea for the design of high-contrast mechanochromic molecules.However,we still need to learn other crystal structure prediction methods to explore the relationship between structure and properties.Meanwhile,the influence of substitution of different halogen atoms on the gel properties of pyran derivatives was also studied.