AIE(or AIEE)and Mechanofluorochromic Properties Of The Cruciform Conjugated Fluorescent Dyes With A Phenyl Linkage Center

Mechanofluorochromic(MFC)materials refer to the substances whose fluorescence emission behavior changes under external stimulation,such materials occupy a very important position in the field of optoelectronic materials.Recent research results show that many compounds with aggregation-induced emission(AIE)or aggregation-induced enhanced emission(AIEE)properties exhibit high solid-state luminescence capabilities while exhibiting MFC behavior.Therefore,this thesis starts from the preparation of AIE(or AIEE)type electroluminescent color-changing materials and synthesizes a series of cruciform solid-state fluorescent molecules containing tetraphenylethene and triphenylamine groups with a benzene ring as the core,focusing on their intramolecular charge transfer(ICT),AIE(or AIEE)and mechanofluorochromic properties.The results obtained so far are as follows:(1)The cruciforms MODCS-TPE and FMDCS-TPE containing tetraphenylethene units were designed,and their ICT phenomena,AIE behavior,and MFC properties were studied.The results reveal that MODCS-TPE and FMDCS-TPE show significant AIE behavior(?AIE = 138 and 51),and the solid-state luminous efficiency is 0.321 and 0.312,respectively.Moreover,both have high-contrast reversible MFC performance.After grinding,the fluorescence of the two compounds changes from the blue(471 nm and 478 nm)of the original powder to green(505 nm)and light yellow green(522 nm),thus the grinding process resulted in a red-shift of the fluorescence spectrum at 34 nm and 44 nm,respectively.The two colors can be switched during grinding-heating(for MODCS-TPE)or grinding-fumigation(for MODCS-TPE and FMDCS-TPE).PXRD and DSC analysis revealed that the behavior of MFC stems from the phase transition between crystalline and amorphous samples under external stimuli.(2)The cruciforms FB-CTPAEB and DFB-CTPAEB containing triphenylamine units were designed.Test results show that these two molecules exhibit typical AIEE behavior,with solid-state luminous efficiency as high as 0.693 and 0.442.The initial samples of FB-CTPAEB and DFB-CTPAEB were ground,and their fluorescence colors changed from yellow and red-orange to red,respectively.The corresponding fluorescence bands were red-shifted by 52 nm and 46 nm,respectively.Moreover,the changes in fluorescence emission caused by grinding can be recovered through the solvent fumigation process,reflecting the reversibility of the MFC behavior of these two compounds.PXRD analysis showed that the MFC behavior of FB-CTPAEB and DFB-CTPAEB comes from the transition between the crystalline and amorphous states of the molecule.The planarization of the molecular conformation and subsequent planar intramolecular charge transfer process caused the red shift of the fluorescence spectrum.(3)The D-A type cruciforms MB-CTPEEB and DFB-CTPEEB based on tetraphenylethene were designed and prepared.These two molecules exhibit unique ICT behavior,obvious AIEE characteristics,and high solid-state fluorescence emission capabilities.Their solid-state luminous efficiency is 0.633 and 0.783,respectively.In particular,MB-CTPEEB and DFB-CTPEEB show reversible MFC behavior that is dependent on substituents.Stimulated by external forces,the fluorescent color of DFB-CTPEEB solid powder changed from the initial yellowish green(517 nm)to the final orange(583 nm).In contrast,MB-CTPEEB does not have MFC behavior.This is because compared to DFB-CTPEEB,MB-CTPEEB has a poorly distorted molecular conformation and a relatively weak degree of ICT.This endows DFB-CTPEEB molecule a strong intermolecular force and a tight ?-? stacking,which makes it has less deformability and relatively weaker in-molecular charge transfer behavior under external force.