The Study On Properties Of Aggregation-induced Emission Of Pyrrolo[3,2-b]pyrrole-based Series Derivatives And Their Applications

Aggregation-induced emission(AIE)is the unique photophysical phenomenon that chromophores with non-emission or weak emission in dilute solutions are induced to emit(or highly emit)in the aggregation states.Compared to the conventional aggregation-caused quenching(ACQ)molecules with planar comformation,chromophores with AIE phenomenon are offen adopted the rotatable propeller-shaped or the vibratile butterfly-shaped molecular comformation.AIE phenomena effectively solve the problem of fluorescence quenching by aggregated ACQ molecules,and enlarge the application ranges of fluorescent materials in organic optoelectronic devices,fluorescence sensing,bioimaging,stimuli-responive and so on.However,with the development of the AIE systems,some difficulties like elaborate synthetic schemes and complex modulating AIE characteristics are emerged.Therefore,developing the novel AIEgens with simple molecular structure and exploring more extensive applications have great significance.Based on our previous research about aryl-substituted pyrrole derivatives,we designed and synthesized a novel AIE system of aryl-substituted pyrrolo[3,2-b]pyrrole derivatives in this thesis,and the AIE performance of this compounds were modified by introducing functional groups with different electronic properties.Compared to aryl-substituted pyrrole derivatives,the molecular core of pyrrolo[3,2-b]pyrrole derivatives with higher nitrogen content and electron-rich ability are realizved to response and detect of common volatile organic compounds.Meanwhile,the coplanarity of molecular core of pyrrolo[3,2-b]pyrrole derivatives are expanded which is favorable to cultivate sigle crystals and further explain the AIE mechanism of this compounds.The rigid coplanar core of pyrrolo[3,2-b]pyrrole derivatives also can be regulated to form the local orderly molecular packing,and then shows the mesomorphic character with introducing additional flexible alkyl chains.The content of this thesis are summarized in chapters:In chapter 2,we synthesized the compound of 1,2,4,5-tetraphenyl-1,4-dihydropyrrolo[3,2-b]pyrrole(DPPTP),exhibiting aggregation-induced enhancement emission(AEE)and crystallization-induced enhancement emission(CEE)properties.In the experiments of detecting tetrahydrofuran,acetone and other organic solvents atmospheres,the DPPTP shows fluorescence quenching response to chloroform which may be ascribed to the effect of the acid/base interaction of DPPTP molecular core with the hydrogen chloride from photodecomposition products of chloroform.So the quantitative detection of chloroform can be achieved in 100?800 ppm by DPPTP with a limit of detection of 95.7 ppm,a rapid process(30 s)and excellent selectivity.In chapter 3,we synthesized seven dropyrrolo[3,2-b]pyrrole derivatives by introducing functional groups with different electronic properties in the phenyl of 1,4-postion of dropyrrolo[3,2-b]pyrrole core.The pyrrolo[3,2-b]pyrrole compounds show AIE(AEE)properties when at least one substituent group acts as pull-electron group,and show ACQ properties when two substituent groups are push-electron groups.Among the seven pyrrolo[3,2-b]pyrrole compounds,DPPHP-2CN with two cyans as substituents manifests the polymorphism-dependent fluorescent emission properties with four different sigle crystal structures,and shows fluorescent response to trifluoroacetic acid(TFA).DPPHP-2CN and DPP-2Py-p with two 4-pyridyls as substituents exhibit mechanochromic behaviors which should be attributed to the change of molecular crystal structure during the grinding process verified by XRD results.In addition,we found out that the aldehyde group can transform anthracene with ACQ properties to AIE characters of 9-anthraldehyde and 9,10-anthracenedicarboxaldehyde,which provide a method of guidance for constructing AIEgens from ACQphores.In chapter 4,based on the synthesis of DPP-2Py-p,we synthesized two dropyrrolo[3,2-b]pyrrole salt derivatives DPP-2Py-5 and DPP-2Py-9 with different alkyl chain length(five-carbon and nine-carbon)bearing p-toluenesulfonate anion as counterion.Both of them show AIE properties,however,only DPP-2Py-9 shows liquid crystal character with semetic A phase observed by polarizing optical microscope(POM)and X-ray diffractometer(XRD).The temperature range of liquid crystal of DPP-2Py-9 is 180?212 ~oC observed by differential scanning calorimetry(DSC).The above results indicate the importance of suitable alkyl length for AIEgens to possess liquid crystallinity.During temperature-dependent fluorescence measurement,the photoluminescence(PL)intensity of DPP-2Py-5 decreases gradually with raising temperature which are ascribed to the thermally activated nonradiative decay process,versus emission wavelength remains unchanged.However,the PL intensity and emission wavelength of DPP-2Py-9 change too drastically over molecular aggregation state in heating process.The intersections between three slopes of PL wavelength in heating process varying three stages with temperature are 190 and 210 ~oC,which demonstrate that the PL emission wavelength of DPP-2Py-9 is swiftly hypochromatic shifted from 630 to 539 nm.The temperature range 190?210 ~oC determined by PL spectrum approximate LC temperature range observed by DSC,so the fluorescence spectrum has great potential to analyse the liquid crystallinity of mesomorphic molecules in the future research.