Force-induced Blue-shifted Emission Materials Constructed By Flexible Twisted Conjugated Luminogens

In recent years,mechanochromic luminescent materials have attracted much attention because of their special photophysical properties and broad application prospects.In the reported literature,most of compounds possess red-shifted emission when stimulated by an external mechanical force,while the compounds that are blue-shifted emission are rarely reported.Therefore,how to design molecules to achieve blue-shifted emission of photoluminescence is particularly important for the research of new materials.In this thesis,we synthesized dimethyl succinyl succinate derivatives,studied the changes of their luminescent color under action of external force,and based on these above,discussed their luminescent mechanism.The main contents are as follows:1)Compounds 1,2 and 3 were obtained by reaction of aniline compounds with different substituent with dimethyl succinyl succinate.It was found that fluorescence emission spectra of compounds 1,2 and 3 showed red-shifted emission phenomenon with the increases of electron-donating ability of substituent.The fluorescence emission intensity of compounds1-3 in n-hexane/tetrahydrofuran mixed solvent was significantly enhanced with the increase of n-hexane content,showing AIE(aggregation-induced emission)effect.After grinding,the intramolecular force was destroyed,conjugation degree of flexible twisted conjugated compound was reduced,and result in blue-shifted fluorescence emission.For example,the emission wavelength of compound 1 shifted from 626 nm in crystalline state to 595 nm in amorphous state,and the wavelength changed up to 31 nm,showing a rare force-induced luminescence blue shift.Emission wavelength of compound after fumigation by solvent is red shifted and close to crystal emission wavelength.2)On the basis of the research in previous chapter,compounds 4,5 and 6 were synthesized by introducing short aliphatic chains into para position of aniline compounds in order to increase molecular vibration and rotational freedom.The substituent of compounds4-6 are isopropyl,ethyl and tert-butyl,respectively.Due to introduction of rotatable saturated alkyl groups,the vibration and rotational freedom of molecule are increased,and emission wavelength is red-shifted emission.Their fluorescence emission intensity in mixed solvent of water/tetrahydrofuran increased significantly with increase of water content.After grinding by external force,the twisted configuration structure of three compound crystals was destroyed,and emission peak wavelengths were blue shifted by 22 nm,15 nm and 13 nm,respectively.After fumigating grinding samples with solvent,molecules returned to arrangement structure similar to crystal state,and emission wavelength shifted to long wave direction and was relatively close to fluorescence emission wavelength of crystal.It shows a reversible force luminescent color blue-shifted emission.