Synthesis And Characterization Of Benzothiadiazole And Benzoselenadiazole With Mechanochromic Fluorescence Materials

Mechanochromic fluorescence materials are a class of intelligent material that the transformation of molecular arrangements in the solid state is sensitive to mechanical stimulation,and exhibiting reversible switching of fluorescence color and fluorescence quantum yield.It has potential applications in the information storage,photoelectric devices and anti-counterfeiting paper.Also,the development of relevant materials helps to promote the study of the theory of the mechanical mechanism.Investigating the relationship between molecular structure and properties has been a hot topic in this field.At present,most of the reported fluorescence emission peaks of mechanochromic fluorescence materials are located in the visible region.However,whether in theoretical research or in practical application,the development of mechanically induced near-infrared fluorescent discoloration materials with high stability is an urgent problem to be resolved.For example,compared with fluorescent molecules in the visible light region,the advantage of near-infrared fluorescent molecules posses of strong tissue penetration,which is conducive to biological imaging experiments.The low-energy emission wavelength can also reduce the damage to cells and tissues.Therefore,the design and synthesis of near-infrared emission of mechanical induced luminescence materials have important research value.Based on this,a series of vinyl substituted benzothiadiazole and benzoselenadiazole fluorescent materials were constructed in this thesis,and the relationship between the molecular structure of this series of compounds and the property of the mechanochromic fluorescence materials was studied in detail.The main research contents are as follows:Firstly,Mechanochromic fluorescence materials with different substituents at the end group were designed and synthesized.Taking benzothiadiazole as electron Acceptor center and N-dimethyl,methoxy and pyridine groups as donor end group,organic small molecule Ⅱ-1～Ⅱ-4 with D-π-A-π-D skeleton was successfully synthesized by Heck coupling reaction.Crystal analysis shows that the molecules are arranged in a loose form through a variety of weak interaction forces.When stimulated by external grinding,the stacking form is easy to change,so the fluorescence discoloration behavior of the mechanical response is shown.The experimental results showed that except compoundⅡ-4 presented mechanically-induced fluorescence hypochromatic-shift,the other three compounds all showed mechanically-induced fluorescence bathochromic-shift.This study showed that the vinyl-functionalized benzothiazole can be used as an excellent mechanochromic fluorescence materials.Secondly,conjugated organic small molecule Ⅲ-1 with 5,6-difluorobenzothiadiazole as the central group was designed and synthesized,and the effect of enhancing the electron-withdrawing ability of the central group on the mechanochromic fluorescence was studied.Experimental results showed that the maximum emission peak of the compound can be shifted from 695 nm in the red area to 745 nm in the near-infrared region under the stimulation of mechanical force.Through in vivo imaging system,the change of fluorescence intensity in this reversible transformation process can be obviously observed.Combining with the crystal structure,we speculated through theoretical calculation that the reason for the mechanical discoloration behavior was that the two molecules had slippage in opposite directions.Thirdly,several benzothiadiazole and benzoselenadiazole derivatives Ⅳ-1～Ⅳ-4 with twisted structure were designed and synthesized,the experimental results showed that only compounds Ⅳ-1 and Ⅳ-4 showed mechanochromic fluorescence behavior.With tetraphenylethene unit as end groups,the benzothiadiazole derivatives Ⅳ-1 showed that the maximum emission peak can be shifted from 600 nm to 610 nm after grinding.However,with tetraphenylethene unit N-dimethyl as end groups,benzoselenadiazole derivatives Ⅳ-4 showed that the maximum emission peak can be shifted from 696 nm to 738 nm under the mechanical force.When processed by dichloromethane solvents for ground sample,it can restore to the original state.The compound Ⅳ-4 showed reversible mechanochromic fluorescence behavior in near-infrared area.This study shows that the benzoselenadiazole framework can also be used to design multifunctional mechanochromic fluorescence materials.