Preparation And Properties Of Tetraphenylethlene Based Mechanofluorochromic Materials

It is well known that the different molecular structures of mechanofluorochromic(MFC)materials determined the molecular arrangement and crystal morphology,and then affected their fluorescence characteristics.In order to improve the performance of MFC materials,scientists in related fields have done a lot of research work on the molecular structure design of MFC materials.Tetraphenylethylene(TPE)based aggregation induced emission(AIE)materials with twisted conjugated structure had a high solid-state luminescence efficiency,which is a research hotspot at present.In this paper,two kinds of TPE based MFC materials were designed and synthesized by introducing different types of substituents.The effects of the molecular structures of these TPE derivatives on the properties of AIE and MFC properties were systematically investigated.The first kind of MFC materials synthesized in this paper were the complexes with tetrastyryl group as the end group at the left end,the pentalkyl chain as the end group at the right end and the number of benzene rings(0,1,2,3)as the variable in the middle.The UV-Vis results showed that the maximum absorption peaks of complexes with different number of benzene rings were different.The weak absorption peaks were caused by transition,while the strong absorption peaks were caused by electron transfer.The fluorescence emission spectra in the mixed solvent of H2O/THF showed that with the increase of water content,the fluorescence emission intensity of the complex increased,and the maximum emission wavelength of the complex was found to be red shifted,which was caused by the aggregation of complex molecules with the increase of water content,indicating that this kind of complex had AIE characteristics.The fluorescence emission spectra and CIE spectra of the solid powder before and after grinding showed that the fluorescence emission wavelength of the solid powder after grinding had obvious red shift,and the complexes with benzene ring number of 0 and 1 could be recovered after grinding without solvent dichloromethane fumigation,while the complexes with benzene ring number of 2 and 3 could be recovered after grinding only after solvent dichloromethane fumigation.The maximum fluorescence emission wavelength of complexes with different benzene rings was found to be different,the more planar the molecular structure was,the more obvious the red shift of the maximum fluorescence emission wavelength was.The MFC properties of complex solid powders were caused by the transformation between crystalline and amorphous states.Moreover,it was also found that the polymer films prepared by solution blending of the complex dye and polycaprolactone also had the same MFC properties.The second kind of MFC materials synthesized in this paper were tetrastyryl compound dyes prepared by introducing different types of substituents(methoxy,methyl,ester,cyano and nitro)into the molecular structure of TPE.The UV absorption,AIE and MFC properties of these compound dyes were systematically investigated.The results showed that the maximum UV absorption wavelength of the compounds was found to shift red with the increase of the electronegativity of substituents.All the five compounds were found to be exhibited aggregation induction effect in different proportions of THF/H2 O mixed solvents,and the fluorescence intensity increased with the increase of water content.The five compounds were found to have the properties of friction discoloration,and the red shift could occur after friction.At the same time,with the enhancement of the substituent polarity,the fluorescence emission wavelength of the compounds increased,and the red shift was found to be more and more obvious.Moreover,the results also showed that all the five compounds were found to have self-recovery function at room temperature.