Synthesis And Photophysical Properties Of Cyanostilbene Functionalized Pyrrolo[3,2-b] Pyrrole Derivatives

Organic luminescent materials have widespread applications in the field of fluorescent liquid crystals,chemosensors,stimuli-responsive,bio-probes,OLEDs and biomedicines.Nowadays,most of organic luminescent materials exhibit aggregation-caused quenching(ACQ)effect and it is hard to apply.aggregation-induced emission(AIE)and aggregation-induced emission enhancement(AIEE)materials show strong fluorescence emission and high fluorescence quantum yield in aggregated state,which could effectively expand the application ranges.Therefore,it is of significant in theory and practice to develop novel aggregation-induced emission materials.According to the previous literature,a series of organic luminescent molecules were synthesized with a good planarity of pyrrolo[3,2-b]pyrrole as the parent by modifying AIE(E)cyanostilbene structure unit and the molecular terminal sites.Correlation between molecular structure and photophysical properties were investigated.1.2,5-substituted pyrrolo[3,2-b]pyrrole parent(2a-2g)with different push-pull electron abilities were constructed by Debus-Radziszewski reaction with aromatic aldehydes(la-1g),4-aminobenzyl cyanide,and 2,3-butanedione,then,cyanostilbene functionalized compounds(3a-3g)were synthesized by Knovenagel condensation reaction with 4-N,N-diethylaminobenzaldehyde and their chemical structures were characterized in detail.The fluorescence emission behavior of the compound 3a-3g were investigated in aggregated state,the results revealed obvious AIE behavior,among them,F substituted compounds 3d and 3e displayed high fluorescence quantum yield,which may be contributed to the change of molecular stacking modes because of the introduction of F atoms.2.Pyrrolo[3,2-b]pyrrole parent(APPP)was synthesized by Debus-Radziszewski reaction with pyridine-4-carboxaldehyde,4-aminobenzyl cyanide and 2,3-diketone,then,compound APPTPEP was further synthesized with 4-(1,2,2-triphenylvinyl)benzaldehyde by Knoevenagel condensation reaction and their chemical structures were full characterized.The incorporation of tetraphenylethylene unit in the backbone endowed the APPTPEP a significant aggregation induced emission(AIE)behavior.The structure of the compound APPTPEP wascharacterized in detail.Compound APPTPEP can effectively recognize PA in the aqueous medium with a detection of 31.5 nm.Pyridyl group was proved as recognition site for PA and their strong interaction was confirmed by IH NMR titration with a molar ratio of 1:2.PA binds to the pyridyl group of APPTPEP to quench fluorescence by photo-induced electron transfer(PET)process was supported by DFT.3.Based on the first chapter of pyrrolo[3,2-b]pyrrole parent 2f,cyanostilbene modified compounds 4a-4o were obtained with introducing different push-pull electron ability groups in by Knovenagel condensation reaction.The results showed that different terminal groups have a obvious regulation effect on the fluorescence emission with emission band in the wide range of 514-574 nm and different terminal groups resulted in significantly different aggregation behavior.Compounds 4f,4g and 4i exhibited obvious spectral shift and they red shifted 34,51 and 9 nm,respectively,which could recovered back after heated ethanol fuming.PXRD,DSC and SEM indicated that the transformation between microcrystalline and amorphous states upon external stimuli should be responsible for the observed reversible mechanofluorochromism(MFC)behaviour.