Synthesis And Characterization Of Cyanostilbene-Based Organic Solid State Luminescent Materials Exhibiting Stimuli-Responsive Luminescent Switching

Organic solid state luminescent materials have attracted more and more attentions due to excellent photoelectric properties and extensive application prospect.In addition,earlier studies suggested that there were important relationships between molecular packing modes and luminous properties.For example,morst Organic solid state luminescent materials with H-aggregate dramatically decreased the luminescence quantum yield in the solid state(films and crystal).Because the inter dipole interaction along their long axis induced the nonradiative decay of exciton.Recently,knowledge of the role of molecular packing in controlling luminous properties of Organic solid state luminescent materials have been utilized for exploring stimuli-responsive material,where the fine-tune molecular packing modes were achieved by an external stimulus including pressure,heat and solvent vapor.At present,however,the number of organic dyes exhibiting piezofluorochromism was still limited,due to lack of full understanding of the piezochromic mechanisms at the molecular-level.Thus,It was of great significance and challenge to investgate the molecular packing modes and intermolecular interactions for obtaining the practical stimuli-responsive material.A series of novel organic Organic solid state luminescent materials containing aromatic amine were desighed and synthesized.Then the relationship among external factor(heating,pressure and solvent vapor),molecular packing modes and luminescent properties was systematically investigated.In Chapter 2,a rod-like molecules,4,4'-bis(a-cyano-4-phenproalkoxylstryl)biphenyl(Ben-DCSB)has been designed and synthesized.Ben-DCSB presents excellent mechanochromism behaviors.Recrystallized blue-green Ben-DCSB powder are changed into relatively yellow-green with the fluorescence quantum efficiency(?F)obviously converting from original 52.7%to 38.7%after being ground.Photoluminescence(PL)spectra of the samples obtained under different conditions(ungrind and grind)show the maximum emission wavelength(?em)has a significant red-shit as high as 23 nm,after grinding.Observing the morphological structure of Ben-DCSB under different aggregative state by using scanning electron microscopy(SEM),the results indicate that the damage on surface morphology which is caused by external stimuli can be restored by exposing ethanol vapor or heat treatment.The X-ray diffractometry(XRD)measurements,the ungrind dye displays indicative of well-defined microcrystalline-like structures,and grinding dye is amorphous feature in this state.These observations further indicate the mechanochromism originates from the altering mode of molecular packing from the high-order to disorder by grinding.time-resolved fluorescence spectrofluorometer analysis of ungrind ande grind dye show the attenuation exponential increases from single exponential of ungrinding to double-exponential of grinding.The result further demonstrate order degree of the grind sample decreases.The ground powder return to original colour by fuming with solvent(ethanol?dichloromethane?tetrahydrofuran or acetone)or heating at about 100? for 2 min.And the PL spectra show these samples can return original ?cm(485 nm).Moreover,dye Ben-DCSB indicates good reversibility of fluorescence conversion upon grinding-fuming and grinding-heating processes.XRD measurements indicate that the amorphous sample obtained by grinding can revert to crystalline state by fuming with ethanol and heating.Furthermore,the thermal analysis results show Ben-DCSB exists liquid crystalline phase of nematic(schlieren texture)between 194? and 212?,and thermal decomposition temperature of Ben-DCSB is 362 ?,indicating that the compound has better thermal stability.In Chapter 3,three triphenylacrylonitrile derivatives Ph-TPCN,DPA-TPCN and 2DPA-TPCN with substituent of phenyl or different number of diphenylamine are desighed and synthesized.triphenylacrylonitrile derivatives introduced diphenylamine(DPA-TPCN and 2DPA-TPCN)simultaneously exhibit aggregation-induced emission(AIE)activity and mechanochromism behaviors,however,Ph-TPCN introduced phenyl have't these properties,these results indicate that the shrongly twisted group introducted is the primary reason that DPA-TPCN and 2DPA-TPCN exhibiting propertiese of AIE and mechanochromism.Mechanochromism of the DPA-TPCN and 2DPA-TPCN can be understood as a phase transition and reversible fluorescent switching of the gound samples is the result that it has thermodynamical metastable,which is confirmed by SEM,X-ray diffractometry(XRD),time-resolved fluorescence spectrofluorometer and DSC analysis.The thermogravimetric analysis results indicating that the compound has better thermal stability(DPA-TPCN,Td ?349.6?;2DPA-TPCN,Td = 416.5?).Finally,exhibiting abundant colours switching,the triphenylacrylonitrile-based are desighed and synthesized by Suzuki reaction.The blue-green crystal(TPCN-BG)and orange-yellow crystal(TPCN-O)were obtained by two different crystallization methods for the compound TPCN-OCH3.PL spectrum,SEM and XRD analysis results indicate that the phenomenon which a single compound exhites polycrystalline state is due to molecular of TPCN-OCH3 aggregating forms different intermolecular packing.The crystal TPCN-BG both have mechanochromism and vapochromism properties,but the crystal TPCN-O have't these.Although the results formed these two reversible fluorescent switching is due to the molecular stacking changes in aggregation state,mechanochromism is between crystalline and amorphous and vapochromism is between the amorphous-crystalline or two different crystalline.The TPCN-BG and TPCN-O stimulated by thermal all show thermochromism properties,and the fluorescent colour can be recovered blue-green when the n-hexane vapor the sample after themal stimulation,XRD analysis results indicate that the original two different crystalline are destructed amorphous by thermal stimulus.the original two different crystalline are destructed amorphousness by thermal stimulus,and this amorphous after solvent steam or heat treatment can be transformed back into molecular stacking of TPCN-BG.the DSC analysis results show that TPCN-BG and TPCN-O after thermal stimulus became a thermodynamical metastable,the existence of the metastable is to make the root cause of its reversibility.In addition,this amorphous stimulated by different temperature can be converted into two kinds of crystalline state,namely,restore the molecular stacking of TPCN-BG and TPCN-O,respectively.