Photoacid Spiropyran Fluorescence Switch With Aggregation Induced Luminescent Property:Synthesis And Characterization

Fluorescent molecular switches have been extensively explored recently because of their stimulus-responsive emissions and a broad range of applications in optical data recording,chemical sensors,displays and bio-imaging.As a typical fluorescent molecular switch,spiropyran has good fatigue resistance and photoresponsiveness.However,its own fluorescence characteristics are not very obvious.At present,the method of modifying the fluorophore on the spiropyran is mostly used to fill in the defect that the ring-close form is not fluorescent.On the other hand,fluorescent groups with very good planarity undergo fluorescence quenching(ACQ)at high concentrations or in solid phases,which limited the applications of spiropyrans.For this purpose,we hope to improve the performance of spiropyran molecules in the solid state by introducing tetraphenylethylene with aggregation induced light emission(AIE)properties as a modification group.Traditional spiropyran molecules can achieve switching under the irradiation of ultraviolet light.However,due to the photobleaching of UV light,the fatigue resistance of spiropyrans is greatly reduced.In recent years,negative photochromic spiropyran molecules have been reported to be capable of undergoing transformation under visible light.The photoacid spiropyran molecule is one of them.Herein,we creatively used tetraphenylethylene with AIE properties as a chromophore to modify the photoacid spiropyran molecule,and carried out a detailed investigation of the nature of the molecule.The main contents were as follows:1.We designed and synthesized a novel tetraphenylethylene-modified photoacid fluorescent molecular switch(SPPATPE).It had a multi-stimulus response property and could interconvert between ring-open form and ring-closed form in solution under visible/dark and acid/base stimulation,respectively.The introduction of tetraphenylvinyl groups give the molecule an AIE effect.Both ring-open form and ring-closed form have no fluorescence in solution but strong fluorescence emission in the aggregated state.In addition,non-invasive stimulation(light/heat)in the PVP polymer matrix can initiate reversible tautomerization under solid phase.The addition of another polymer PDMS could greatly improve the water resistance of SPPATPE/PVP.Besides,SPPATPE/PVP/PDMS nanofibers were also prepared by electrospinning to demonstrate the processability of the composite.2.We mainly discussed the mechanochromism behavior of SPPATPE by analyzing the photophysical properties,crystal structure,and in-situ spectroscopy of the single crystal under hydrostatic pressure,the enhancement of the intermolecular π-π interaction and ultimately stronger than the AIE effect is the cause of the change of the fluorescence intensity.